CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to United States Patent Application No. 63/358,784, filed July 6, 2022, which is incorporated herein by reference.

BACKGROUND

[0002] Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.

[0003] Robots, vehicles, or other mechanical systems may include clutches to selectively couple and/or decouple sources of rotation, translation, torque, and/or force from actuators, effectors, or other elements that may receive such inputs. For example, a clutch can selectively couple an engine to a transmission of a vehicle, thereby allowing the transmission to change gears while not ‘under load’ from the engine, allowing the engine to continue running while the vehicle is stopped, or allowing some other operation of the vehicle. A clutch may include a variety of elements and may be actuated in a variety of ways. For example, a friction clutch may include a pad or other friction surface that is selectively brought into contact with another friction surface, thereby allowing for graded transmission of torque between the friction surfaces while also allowing for some degree of slip (e.g., during an initial phase of clutching the friction surfaces together, at which point the relative speeds of the friction surfaces differ). Hydraulics, pneumatics, electromagnetics, or other means may be employed to actuate a pad, wrap spring, drum, pressure plate, or other element of a clutch.

[0004] A wrap spring clutch is a variety of clutch wherein the wrapping action of a spring disposed around and in contact with a shaft (or other mechanical member) results in engagement of the wrap spring with the shaft, thereby mechanically coupling the wrap spring to the shaft. Where the wrap spring is in contact with two (or more) shafts, the wrap spring may be configured to engage with both of the two (or more) members, thus mechanically coupling them together (or ‘clutching’ them together). Actuation of such a wrap spring clutch thus includes both rotation of the member(s) in a direction that results in engagement of the wrap spring and allowing the wrap spring to exhibit such engagement. Thus, actuation of such a wrap spring clutch can include controlling an end of the wrap spring (e.g., by exerting a force and/or displacement on a ‘tang’ or other terminal element of the spring) such that it is prevented from further wrapping down onto the member(s), thereby preventing engagement of the member(s).

SUMMARY

[0005] Some embodiments of the present disclosure provide a device including: (i) an input member having a first contact surface; (ii) a wrap spring having a first end and a second end, wherein the wrap spring is wrapped around the input member and in contact with the first contact surface; (iii) a first tang block coupled to the first end of the wrap spring and a second tang block coupled to the second end of the wrap spring; (iv) an output member that is coaxial with the input member; (v) a frame that is rigidly coupled to the output member and that includes a first tang seat and a second tang seat; and (vi) an actuator that is operable for preventing an engaged mode of the wrap spring and for permitting the engaged mode of the w rap spring, wherein preventing the engaged mode of the wrap spring comprises exerting forces on the first tang block and second tang block to maintain the wrap spring in an expanded state, and wherein permitting the engaged mode of the wrap spring comprises at least one of (a) allowing motion of the first tang block relative to the frame such that rotation of the input member in a first direction relative to the output member results in the wrap spring engaging with the first contact surface and transmitting torque between the input member and the output member via the second tang block contacting the second tang seat, or (b) allowing motion of the second tang block relative to the frame such that rotation of the input member in a second direction relative to the output member results in the wrap spring engaging with the first contact surface and transmitting torque betw een the input member and the output member via contact between the first tang block and the first tang seat, wherein the first direction is opposite the second direction.

[0006] Some embodiments of the present disclosure provide a device including: (i) an input member having a first contact surface; (ii) a wrap spring having a first end and a second end, wherein the wrap spring is wrapped around the input member and in contact with the first contact surface; (iii) a first tang block coupled to the first end of the wrap spring and a second tang block coupled to the second end of the wrap spring; (iv) an output member that is coaxial with the input member; (v) a frame that is rigidly coupled to the output member and that includes a first tang seat and a second tang seat; (vi) a first actuator that is operable for preventing a first engaged mode of the wrap spring and for permitting the first engaged mode of the wrap spring, wherein preventing the first engaged mode of the wrap spring comprises exerting forces on the first tang block to maintain the first tang block in contact with the first tang seat, and wherein permitting the first engaged mode of the wrap spring comprises allowing motion of the first tang block relative to the frame such that rotation of the input member in a first direction relative to the output member results in the wrap spring engaging with the first contact surface and transmitting torque between the input member and the output member via the second tang block contacting the second tang seat; and (vii) a second actuator that is operable for preventing a second engaged mode of the wrap spring and for permitting the second engaged mode of the wrap spring, wherein preventing the second engaged mode of the wap spring comprises exerting forces on the second tang block to maintain the second tang block in contact with the second tang seat, and wherein permitting the second engaged mode of the wrap spring comprises allowing motion of the second tang block relative to the frame such that rotation of the input member in a second direction relative to the output member results in the wrap spring engaging with the first contact surface and transmitting torque between the input member and the output member via the first tang block contacting the first tang seat, wherein the first direction is opposite the second direction.

[0007] These as well as other aspects, advantages, and alternatives, will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1A illustrates elements of a wrap spring clutch, in accordance with an example implementation.

[0009] Figure IB illustrates elements of a wrap spring clutch, in accordance with an example implementation.

[0010] Figure 2A illustrates, in a isometric cut-away view, elements of a clutch mechanism, in accordance with an example implementation.

[0011] Figure 2B illustrates elements of the clutch mechanism of Figure 2A, in accordance with an example implementation.

[0012] Figure 2C illustrates elements of the clutch mechanism of Figure 2A, in accordance with an example implementation.

[0013] Figure 3A illustrates, in an isometric cut-away view, elements of a clutch mechanism, in accordance with an example implementation.

[0014] Figure 3B illustrates elements of the clutch mechanism of Figure 3A, in accordance with an example implementation. [0015] Figure 4A illustrates elements of a clutch mechanism, in accordance with an example implementation.

[0016] Figure 4B illustrates elements of a clutch mechanism, in accordance with an example implementation.

[0017] Figure 5A illustrates elements of a clutch mechanism, in accordance with an example implementation.

[0018] Figure 5B illustrates elements of a clutch mechanism, in accordance with an example implementation.

[0019] Figure 5C illustrates elements of a clutch mechanism, in accordance with an example implementation.

[0020] Figure 6A illustrates, in an isometric view, elements of a clutch mechanism, in accordance with an example implementation.

[0021] Figure 6B illustrates, in an isometric cut-away view, elements of the clutch mechanism of Figure 6 A, in accordance with an example implementation.

[0022] Figure 6C illustrates, in a side view, elements of the clutch mechanism of Figure 6A, in accordance with an example implementation.

[0023] Figure 6D illustrates, in cross-sectional view, elements of the clutch mechanism of Figure 6A, in accordance with an example implementation.

[0024] Figure 7A illustrates, in isometric cut-away view, elements of a brake mechanism, in accordance with an example implementation.

[0025] Figure 7B illustrates, in cross-sectional view, elements of the brake mechanism of Figure 7A, in accordance with an example implementation.

DETAILED DESCRIPTION

[0026] In the following detailed description, reference is made to the accompanying figures, which form a part hereof. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, figures, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the scope of the subj ect matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted. combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein.

I. Overview

[0027] Conventional wrap spring clutches use two wrap springs (e.g., as part of two separate unidirectional wrap spring clutches) to effect bidirectional clutching between two rotating members (e.g., an input shaft and an output shaft, an input shaft and a brake rotor). This results in increased complexity, cost, weight, and length, due to both of the two wrap springs of such a clutch being in contact with the same rotating member in order to clutch torques from the rotating member in respective opposite directions.

[0028] The embodiments described herein provide improvements relative to prior wrap spring clutches by allowing a single wrap spring to effect clutching in both directions. Such single-wrap spring bidirectional wrap spring clutches by exerting forces (e.g., opposite forces) on the two ends of the single wrap spring while allowing the wrap spring to rotate. Such forces can be generated by non-rotating actuators (e.g., motors, hydraulic or pneumatic cylinders, solenoids) that then transmit forces or other energies (e.g., magnetic fluxes) to the wrap spring and associated elements of the bidirectional wrap spring clutch in a manner that permits the wrap spring and associated elements to rotate. This can include exerting forces on both ends of the wrap spring to prevent the wrap spring from engaging with an input member (e.g., to expand the wrap spring), allowing the input member to “overrun” in one or both directions of rotation. Permitting an engaged, ‘clutching’ mode of the wrap spring can include removing or reducing such force(s) exerted on one or both ends of the wrap spring. Such a reduction in the force applied to the end(s) of the wrap spring can allow' the end(s) to move, thereby permitting one of the ends of the wrap spring to “wrap down” onto the input member. The opposite end can then transmit forces from the input member, via the wrapped-down wrap spring, into an output member (e.g., a brake rotor, an output shaft).

[0029] Such forces can be exerted on the ends of the wrap spring in a variety of ways. For example, the ends (or “tangs”) of the wrap spring could be coupled to respective tang blocks that are made of a magnetically permeable material or that are otherwise able to be influenced by applied magnetic fields. Magnetic fields could be generated by an actuator (e.g., by a solenoid) to exert magnetic forces on the tang blocks, expanding the wrap spring and allowing an input member to overrun relative to the wrap spring in both directions. Such magnetic fields can be transmitted from non-rotating elements (e.g., solenoids, magnetically permeable plates or other elements) across narrow air gaps into the tang blocks or other associated rotating magnetic elements, thereby permitting forces to be efficiently exerted onto the rotating tang blocks by the non-rotating actuators.

[0030] Alternatively, mechanical forces can be transmitted from a non-rotating actuator to the rotating wrap spring and associated rotating elements to actuate the engagement and disengagement of the wrap spring with an input member. This can include exerting axial forces, along the axis of an input member, through a bearing to a mechanism that is associated with the wrap spring and that is able to rotate with the wrap spring. Such a mechanism could then translate the axial forces and/or translations into forces and/or translations applied to the ends of the wrap spring. These applied forces could act to expand the wrap spring (e.g., by forcing tang blocks coupled to the ends of the wrap spring into respective tang seats of a frame that is rigidly coupled to a brake rotor or other output member) to prevent the wrap spring from engaging with the input member. Removal or reduction of the applied axial force allows the ends of the wrap spring to move, thereby permitting the wrap spring to “wrap down” onto the input member such that it can transmit forces from the input member to a brake rotor or other output member.

[0031] Bidirectional wrap spring clutches as described herein exhibit significant improvements with respect to size, weight, cost, complexity, power rating, torque rating, and power cost to operate (e.g., to maintain a clutch of a brake mechanism in a disengaged state). For example, a single-wrap spring bidirectional wrap spring clutch as described herein can exhibit a one-third reduction in weight and in length (along the axis of a drive shaft being clutched/braked by the device) relative to a two-spring bidirectional wrap spring clutch device. Additionally, bidirectional wrap spring clutches as described herein use reduced power to disengage their wrap spring clutches from an input member when engaged therewith. This power reduction can result from the ability to unwrap the spring from “both ends,” since both ends of such bidirectional wrap spring clutch are actuated. Cost and weight can also be reduced, as the amount of copper (or other materials) used to generate such a reduced disengagement force is also reduced (relative, e.g., to an electromagnetic brake where the magnetic forces are used to actuate a brake disk directly).

[0032] In some examples, a bidirectional wrap spring clutch as described herein could include multiple actuators that are operable to engage or disengage the clutch in respective opposite directions of rotation. For example, a clutch could include first and second solenoids configured to generate respective magnetic fluxes that act, via respective magnetic circuits, to exert respective magnetic forces first and second tang blocks. Such a clutch could then deactivate one of the actuators to selectively permit the wrap spring to wrap down onto an input member in a corresponding direction, while the continued activity of the other actuator allows the input member to overrun the wrap spring in the opposite direction.

[0033] As noted above, bidirectional wrap spring clutch as described herein could be used to selectively couple a drive shaft (e.g., an output shaft of a motor, an input or output shaft of a transmission, a drive shaft of a wheel or robot j oint) to a brake rotor. A pad or other means can be maintained in contact with the brake rotor such that rotation of the brake rotor is continuously resisted. Braking of the drive shaft is thus accomplished by allowing the wrap spring to engage with the drive shaft, thereby coupling the drive shaft to the brake rotor such that the brake pad can apply a large braking force to the drive shaft via the wrap spring and brake rotor. Such a braking mechanism can provide a large braking force (related to the size or other properties of the brake rotor and brake pad) while allowing the braking force to be engaged by the relatively low force and/or torque actuation characteristics provided by the bidirectional wrap spring clutch. The size, weight, complexity, and/or cost of an actuator sufficient to prevent or permit the wrap spring from engaging with the drive member can be relatively much smaller than the size, weight, complexity, and/or cost of an actuator sufficient to “directly” actuate the brake pad and rotor by, e.g., controlling an amount of force applied by the brake pad onto the brake rotor. Leaving the brake rotor mechanically decoupled from the drive shaft can also permit such a brake mechanism to exhibit reduced rotational inertia relative to alternative brake mechanisms. This can be a significant advantage, especially in applications where a robot or other mechanism makes rapid moves repeatedly, thus permitting reduced cycle times and greater productivity and efficiency.

[0034] Note that reference is made throughout this disclosure to input members, output members, drive members, drive shafts, brake members, and ground members, with brake and/or clutch mechanisms incorporating such features generally being described as receiving rotational input via the input members, providing rotational output via the output members, and mechanically grounding the ground members. However, these embodiments are intended as non-limiting examples for illustrative purposes. One of skill in the art will appreciate that the function of input, output, and ground may be assigned to the various elements of the brakes, clutches, or other mechanisms described herein in a variety of ways according to an application. [0035] Further, the term “member” (e g , as in “input member”) is intended to have a broad meaning unless otherwise indicated. While such members may be illustrated by way of example herein as singular cast, machined, or otherwise formed plates or otherwise-shaped elements, it is intended that a “member” may include multiple elements bolted, welded, screwed, clipped, press-fitted, or otherwise fastened together. The multiple elements of a “member” may be bolted, press-fitted, or otherwise fastened together such that they are in intimate contact (e.g., such that large surfaces of such multiple elements of a single “member” are in contact) or may be fastened together via intermediate additional elements of the member (e.g., via a set of rods, pins, cylinders, or screws that may pass through corresponding holes in some intervening member or other element of a device). For example, a “brake member” may include (i) a hub having one or more contact surfaces via which wrap spring(s) may engage with the brake member and (ii) a rotor having a brake surface via which a brake pad can exert braking forces onto the brake member. Such a hub and rotor of an overall “brake member” may be rigidly or non-rigidly coupled together. For example, the rotor and hub could include teeth, cogs, or other features configured to permit the hub and rotor to engage in a limited degree of rotation relative to each other.

[0036] Yet further, embodiments herein are generally described such that activated state of an actuator (e.g., a solenoid generating magnetic flux, an actuator transmitting an axial force through a bearing) prevents the engagement of a wrap spring with an input member, while the non-activated state of the actuator permits the engagement of the wrap spring with the input member. However, the opposite is also possible. For example, a mechanism associated with a wrap spring could include springs or other elements to bias the mechanism toward expanding the wrap spring, thus permitting an input member to overrun the wrap spring in both directions. Such a mechanism could be configured such that axial forces applied thereto cancel such biasing forces, allowing the wrap spring to wrap down onto the input member and thus to clutch the input member to a brake rotor or other output member.

II. Example Unidirectional Wrap Spring Clutch Mechanisms

[0037] A unidirectional wrap spring clutch is a clutching mechanism that includes at least one wrap spring. The wrap spring of such a unidirectional wrap spring clutch is wrapped around and in sliding contact with a contact surface of a drive shaft, input member, output member, or other mechanical member of interest. Rotation of such a drive shaft in a particular direction results in the wTap spring “wrapping down” onto the drive shaft, engaging with the contact surface of the drive shaft and thereby strongly mechanically coupling the wrap spring to the drive shaft. The drive shaft can thus be mechanically coupled to other mechanical elements (e g., an output shaft or other mechanical member) that are coupled to the wrap spring. The wrap spring may be coupled to such other elements directly (e.g., by being welded, bolted, press-fit, or otherwise directly coupled to the other element(s)) or via the “wrapping” process whereby a portion of the wrap spring engages with a contact surface of the other element(s). [0038] This “wrapping down” to engage with the drive shaft can be reversed (or the wrap spring “disengaged” from the contact surface) by rotating the drive shaft opposite the particular direction that resulted in engagement of the wrap spring. Additionally or alternatively, the wrap spring can be directly disengaged from the drive shaft by exerting sufficient force on the wrap spring (e g., on a tang or other feature formed on or affixed to an end of the wrap spring) to disengage it from the drive shaft and/or to prevent it from rotating while the drive shaft rotates to disengage the wrap spring from the drive shaft.

[0039] Figures lAand IB illustrate elements of an example unidirectional wrap spring clutch 100, with Figure 1A showing the elements in an expanded or disassembled view. An input member 110 is able to be clutched to an output member 120 by a wrap spring 130. Referring to Figure IB, when assembled, a first portion 135a of the wTap spring 130 is in contact with a cylindrical contact surface 115 of the input member 110 and a second portion 135b of the wrap spring 130 is in contact with a cylindrical contact surface 125 of the output member 120.

[0040] The “contact” of a wrap spring with its underlying contact surface when the w ap spring is not engaged (e.g., when an end of the wrap spring is prevented from moving with the underlying contact surface and thus “wrapping down” to engage with that contact surface) permits rotation of the contact surface relative to the warp spring. However, it is a direct mechanical contact and is characterized by some degree of sliding friction. Thus, some nonzero degree of torque will be transmitted between the wrap spring and the underlying contact surface via sliding friction between the wrap spring and the contact surface of the input member 110 when the contact surface moves relative to the wrap spring.

[0041] Rotation of the input member 110 in the direction indicated by the curved arrow 101 can result in the wrap spring 130 “wrapping down” to engage with both the input member 110 and the output member 120, thereby mechanically coupling the input member 110 to the output member 120 such that rotation and/or torque in the indicated direction is transmitted, via the wrap spring 130, to the output member 120. Such “engagement” of a wrap spring with an underlying contact surface is characterized by a significantly greater mechanical coupling between the wrap spring and the contact surface due, e g., to an increased normal force exerted by the wrap spring onto the contact surface. This increased normal force may be due in part to the capstan effect and/or other effects related to the enhanced mechanical coupling between the wrap spring and the contact surface. Accordingly, a w rap spring that is “engaged” with its underlying contact surface may exhibit a significantly increased torque exerted on the contact surface when subjected to further relative motion in the ‘engagement’ direction in comparison to when the wrap spring is disengaged from (and thus merely “in contact” with) the contact surface. This increased torque is due primarily to an effect that is sometimes called the “capstan effect” and that is exploited in devices such as a capstan (for driving a rope and/or for using a rope to drive another member). In practice, these factors, as well as other processes (e.g., compression of the member bearing the contact surface), may result in a wrap spring that is “engaged” with a contact surface being functionally rigidly coupled to the contact surface for purposes of further relative motion in the ‘engagement’ direction.

[0042] Rotating in the opposite direction will result in disengagement of the wrap spring 130 from the contact surfaces 115, 125 and substantially no transmission of torque from the input member 110 to the output member 120 (though some small amount of torque transmission, due to friction between the wrap spring 130 and the contact surfaces 115, 125, may occur).

[0043] A wrap spring clutch configured in this manner, absent additional elements, may be referred to as a “one way” or “overrunning” clutch, as the input member 110 is able to drive the output member 120 in one direction while “over-running” relative to the output member 120 when rotating in the opposite direction. Additional elements or features may be added to provide control of this clutching behavior, e.g., to allowthe input member 110 to also over-run in the ‘forward’ direction by preventing the wrap spring from “wrapping down” and engaging with the contact surface 115 of the input member 110. This can be done by preventing the end 137 of the wrap spring 130 from rotating ‘with’ the contact surface 115 of the input member 110. Preventing such a motion of the end 137 of the wrap spring 130 can include preventing all motion of the end 137 of the wrap spring 130, e g., by using an actuator to couple the end 137 to a mechanical ground. In another example, a slip clutch mechanism or other system could be employed to maintain the rate of rotation of end 137 of the wrap spring 130 at a level that is greater than a specified amount (e.g., a specified RPM) and less than the rate of rotation of the input member 110 in the direction of the arrow. In such an example, the output member 120 would rotate at the specified RPM, but only a lower torque would be exerted on the input member 110.

[0044] Such a configuration permitting control of the clutching behavior of the clutch, which may be referred to as a “start-stop clutch” configuration, may include an actuator or other component to control the motion of the end 137 of the wrap spring 130. This can include exerting forces on a “tang” formed on the end 137 of the wrap spring 130, as shown in Figures 1A and IB, or on a “tang block” rigidly coupled to the end 137 of the wrap spring 130 (not shown). If the control tang 137 is free to rotate, this configuration acts similarly to the overrunning configuration - the input can drive the output in only one direction (shown by the arrow 101) via engagement of the wrap spring 130 with the contact surfaces 115, 125. However, if a “stop” of some kind prevents the tang 137 from rotating, the input member 110 may rotate, but the output member 120 is not driven by the input member.

[0045] Such actuation of the end 137 of the wrap spring 130 can also result in a decrease of the amount of torque transmitted by sliding friction between the wrap spring and the underlying contact surface of the input member 110 when the contact surface moves relative to the wrap spring in the “overrunning” direction. This reduction can be due to the actuation of the end 137 of the wrap spring 130 causing expansion of the wap spring 130, reducing or even eliminating its contact with the input member 110 when actuated in this manner, thereby increasing the efficiency of such a clutch when “overrunning.”

[0046] Such a stopped tang 137 prevents the wrap spring 130 from rotating with the input member 110 and “wrapping down" on the contact surface 115 of the input member 110, thereby allowing the input member 110 to rotate without also causing rotation of the spring 130 or output member 120. To effect stoppage of the tang 137, a “finger” or “pawl” (which may be actuated by an electrical solenoid or other means) may be used to stop the control tang directly. In some embodiments, an annular “stop collar” with a recess adapted to surround the control tang 137 of the spring 130 is provided. An additional “finger” or “pawl” can then engage with a cog-like feature on the periphery of the stop collar in order to stop the collar from rotating. This, in turn, prevents the rotation of the control tang 137, which prevents the wrap spring 130 from “engaging” with the input member 110.

[0047] The coil(s) of the wrap spring of such a unidirectional wrap spring clutch may be “right-handed” or “left-handed,” analogous to right-hand and left-hand threads. The “handedness” of the wrap spring 130 in Figures 1A and IB determines which direction of rotation will result in engagement of the wrap spring (the direction indicated by the arrow 101), and which will result in over-running and/or disengagement of the wrap spring. Thus, a unidirectional wrap spring clutch may be configured to drive an output member in either a clockwise or counterclockwise direction, depending on the handedness of the spring used. Composite clutches may include multiple wrap springs so as to permit clutching in both directions.

III. Example Bidirectional Wrap Spring Clutch Mechanisms [0048] Previous wrap spring clutch devices have been unidirectional. That is, a device that includes a single wrap spring can function as a clutch for one rotational direction of an input member (e.g., clockwise) relative to an output member, while such devices are unable to act as a clutch for the opposite direction (e.g., counterclockwise). Clutching for both directions can be achieved by using two such wrap spring clutches (or a ‘single’ clutch mechanism that includes two wrap springs) connected together. However, in such cases bidirectional operation is only achieved by duplicating hardware. Thus, the size (e.g., length) and cost of a bidirectional device (employing two wrap springs) will be inherently larger than for a unidirectional, single wrap spring device.

[0049] The improved wrap spring clutch embodiments described herein are able to achieve bidirectional clutching in a single device using a single wrap spring. Accordingly, the improved bidirectional wrap spring clutch devices described herein exhibit smaller size (e.g., smaller length), reduced cost and complexity, and/or reduced weight relative to a two-spring clutch. In a bidirectional wrap spring clutch as described herein, a single wrap spring is used to control both directions of shaft rotation. The ends (or “tangs”) of the single wrap spring operate “symmetrically,” in that each end plays both the role of a control tang and a fixed tang, depending on the direction of rotation. To actuate the wrap spring, the ends are coupled to tang blocks that can be actuated by an actuator that is external to the wrap spring, input member, output member, and/or other rotating elements of the clutch (and thus may be non-rotating).

[0050] Such an actuator can include an electromagnet, in which case the tang blocks may be composed of magnetic materials (e g , ferromagnetic materials, paramagnetic materials, high-permeability materials) in order to have magnetic forces exerted thereon to actuate the wap spring to engage or disengage with an input member. To focus magnetic fields on the tang blocks and/or adjust the direction of the magnetic force exerted thereon, the tang blocks may sit close to magnetic pole pieces (e.g., ferromagnetic or high-permeability pole pieces) disposed in a rotating frame to complete a magnetic circuit with the electromagnet. When current passes through the coil of the electromagnet, it pulls both tang blocks apart (e.g., against their respective pole pieces into respective tang seats of the frame), expanding the wrap spring and reversing the spring interference of the wrap spring on an input member and disengaging the clutch. When current is turned off, the tang blocks are free to move relative to the frame (and/or tang seats thereof). The tang block on the leading side of an input member rotation will thus seat into contact with the pole pieces as a result of the input member rotation while the opposite tang block will be moved by the rotation of the input member and wrap dow n onto it. This allows torque from the input member to be transmitted into the wrap spring and then into the frame via the leading tang block, effectively coupling the frame and elements coupled thereto (e.g., a friction brake or other brake rotor, some other type of output member) to the input member. Alternate actuator types and methods of coupling the effects of such actuators into forces on the ends of a wrap spring are also possible, as described elsewhere herein.

[0051] Figure 2A is a perspective view of an example bidirectional clutch device 200 with part of a housing 201, coil 210, and plate 215 cut away. Figures 2B and 2C show's subsets of the elements of the bidirectional clutch device 200.

[0052] The bidirectional clutch device 200 includes an input member 220 and an output member 230. The coil 210 is disposed around an axis of rotation of the input member 220. A w ap spring 240 is wrapped around the input member 220 and in contact with a contact surface thereof. There is also a frame 235 that is coupled to (e.g., welded to, bolted to, formed as an intrinsic part of) and capable of rotating with the output member 230. A plate 215 composed of magnetic material directs magnetic flux generated by the coil 210, as does the housing 201.

[0053] The wrap spring 240 has first 241a and second 241b ends (or “tangs”). These tangs 241a, 241b are tangential, rather than radial as in prior wrap spring clutch devices. Each end 241a, 241b of the wrap spring 240 has coupled thereto a respective tang block 245a, 245b. Magnetic (e.g., ferromagnetic, paramagnetic) pole pieces 247 are disposed in the frame 235. The magnetic pole pieces 247 define first 249a and second 249b tang seats, which are contact surfaces for the tang blocks 245a, 245b that extend across end surfaces of the pole pieces 247. When the device 200 is assembled, each tang block 245a, 245b is located near an associated pair of magnetic pole pieces 247 near its associated tang seat 249a, 249b.

[0054] In operation, the operation of the coil 210 can cause the tang blocks 245a, 245b to move toward respective pairs of pole pieces 247 to expand the wrap spring 240, preventing it from engaging with the input member 220. This expanding force can result in the tang blocks 245a, 245b coming into contact with their respective tang seats 249a, 249b. When the coil is not operating to produce magnetic flux (or is producing less than a sufficient amount of magnetic flux), the magnetic forces on the tang blocks 245a, 245b become negligible and the tang blocks 245a, 245b are free to move under forces exerted on them by their respective tangs 241a, 241b. This can allow' the wrap spring 240 to engage with the input member 220, leading to an engaged mode of the clutch 200 whereby torques are transmitted from the input member 220 to the output member 230 (or vice versa).

[0055] Such an engaged mode of the clutch 200 can occur as a result of rotation of the input member 220, causing the wrap spring 240 to rotate with it. For purposes of illustration, this will be described in relation to a clockwise rotation of the input member 220; however, such processes can occur, with the identities of tang blocks, tang seats, etc. reversed as appropriate, for counter-clockwise rotations. Such a clockwise rotation will cause the second tang block 245b to move into contact with (or remain in contact with) its associated second tang seat 249b. When the second tang block 245b contacts the second tang seat 249b, it will prevent the wrap spring 240 from continuing to rotate relative to the frame 235. This will result in the first tang block 245 a moving relative to the frame 235, away from the first tang seat 249a. This movement will result in the first end 241a of the wrap spring 240 wrapping down onto the contact surface of the input member 220, engaging the wrap spring 240 with the input member 220 and allowing torque to be transmitted from the input member 220 to the output member 230 via forces exerted from the input member 220 into the wrap spring 240, from the wrap spring 240 to the second tang block 245b, from the second tang block 245b into the frame 235 via forces exerted contacting the second tang seat 249b, and from the frame 235 to the output member 230. In such an engaged state, the output member 230 is forced to rotate with the input member 220. This is the desired behavior of an engaged clutch.

[0056] When the clutch 200 is to be disengaged, a current of sufficient magnitude is applied to the coil 210. This current creates what is known as a “magnetomotive force” (MMF) in various magnetic circuits of the clutch 200 that include the tang blocks 245a, 245b and that can thus exert magnetic forces on the tang blocks 245a, 245b sufficient to disengage the wrap spring 240 from the input member 220 (potentially in combination with a reverse rotation of the input member 220, in order to reduce the amount of MMF that is sufficient for disengagement of the wrap spring 240). The first 245a and second 245b tang blocks are part of respective first and second magnetic circuits that can be driven by the coil to prevent engagement of the wrap spring 240 with the input member 220 or to disengage the wrap spring 240 from the input member 220.

[0057] The first magnetic circuit is a loop that includes the plate 215, a first magnetic pole piece 247, the first tang block 245 a, a second magnetic pole piece 247 associated with the first tang block 245a, the housing 201, and certain air gaps therebetween. The second magnetic circuit is a loop that includes the plate 215, a third magnetic pole piece 247, the second tang block 245b, a fourth magnetic pole piece 247 associated with the second tang block 245b, the housing 201, and certain air gaps therebetween. Figures 3 A and 3B illustrate aspects of the second magnetic circuit, with the paths followed by magnetic flux through the circuit (as a result of current flowing through the coil 210) being illustrated by arrows.

[0058] Figures 3 A and 3B depict the clutch 200 in a state wherein the second tang block

245b has moved, relative to the frame 235, away from the second tang seat 249b. Such a movement can result in the engagement of the wrap spring 240 with the input member 220 as a result of a counter-clockwise rotation of the input member 210 relative to the output member 220 (or as a result of a clockwise rotation of the output member 230 relative to the input member 220). In such a state, a current passing through the coil 210 will result in the passage, as part of the second magnetic circuit, of magnetic flux through an air gap a short distance between the second tang block 245b and its two associated magnetic pole pieces 247. This results in a force on second tang block 245b toward the pole pieces 247, tending to pull it into contact with the second tang seat 249b (this also results in a force on the first tang block 245a toward its associated pole pieces 247, tending to pull it into contact with the first tang seat 249a). If the current though the coil 210 and resulting MMF are sufficient, this force will result in the tang blocks 245a, 245b being pulled into contact with respective tang seats 249a, 249b, disengaging the wrap spring 240 from the input member 220 and/or preventing the wrap spring 240 from engaging with the input member 220 as a result of rotation of the input member 220 relative to the output member 230.

[0059] The geometry of the device 200 is such that when both tang blocks 245a, 245b are in contact with their associated tang seats 249a, 249b, the wrap spring 240 will be deformed in a manner similar to a helical torsion spring. This deformation expands the spring 240, resulting in the diameter of the spring 240 coils increasing. The amount of the diameter increase may be small (perhaps on the order of 0.001 inch) but it is sufficient to cause the spring 240 to release its grip on the input member 220 and/or to prevent the spring 240 from engaging with the input member 220. Such a release of the input member 220 allows the input and output members to rotate independently, which is the desired behavior for a disengaged clutch.

[0060] Note that the disengaged mode of the clutch 200 including the tang blocks 245a, 245b being in contact with their respective tang seats 249a, 249b is intended as a non-limiting example embodiment of a clutch as described herein in a bi-directionally disengaged mode. It is possible that a bi-directionally disengaged clutch may exhibit only one, or neither tang block in contact with respective tang seats, so long as the tang blocks have moved relative to each other sufficiently to expand the wrap spring, thereby preventing engagement of the wrap spring with an input member.

[0061] Figure 3B depicts a close-up view of a section of the second magnetic circuit, showing in detail the flow of magnetic flux path in the vicinity of the second tang block 245b and associated magnetic pole pieces 247. As described above, an MMF generated by coil 210 causes magnetic fluxes to be generated in the “magnetic circuits” of the device. These circuits include the second circuit, through which magnetic flux flows in a loop as follows: [0062] -the plate 215;

[0063] -an air gap 251a between the plate 215 and an end of one of the magnetic pole pieces 247 associated with the second tang block 245b (a typical value for this gap is in the range of 0.002 to 0.005 inch, though other gap widths are possible);

[0064] -the first of the magnetic pole pieces 247 associated with the second tang block 245b;

[0065] -an air gap 251b between the first magnetic pole piece 247 and the second tang block 245 a (the maximum size of this gap during operation of the device may be in the range of 0.030 to 0.100 inch, for a device with a nominal torque rating of 2 Nt-m, though other maximum gap widths are possible);

[0066] -the second tang block 245 a;

[0067] -an air gap 251c between the second tang block 245 a and a second of the magnetic pole pieces 247 associated with the second tang block 245b;

[0068] -the second of the magnetic pole pieces 247 associated with the second tang block 245b;

[0069] -an air gap 25 Id between the second magnetic pole piece 247 and the housing 201;

[0070] -the housing 201 ;

[0071] -and finally, completing the loop in the plate 215.

[0072] Note that there is no physical connection or contact between the stationary components (housing 201 , plate 215, coil 210) and the other parts of the flux path that are listed above. These listed parts all rotate with the rotating frame 235. Also note that attraction of both tang blocks 245 a, 245b to their respective tang seats 249a, 249b is used to expand the coils of the wrap spring 240. A feature of this example design is that MMF generated by a single coil 210 causes magnetic flux to exist in both of the two magnetic circuits associated respectively with the two tang blocks 245a, 245b. Thus, a single coil 210 does the work of two, decreasing the complexity and cost of the device. Yet further note that part of the housing 201 also functions as part of the magnetic circuits described above; accordingly, the size, weight, complexity, and cost of the device are reduced.

[0073] To reduce an amount of flux leakage at the air gaps 251a, 25 Id between the magnetic pole pieces 247 and the plate 215 and housing 201, those air gaps can be reduced in width. Accordingly, the plate 215 and housing 201 have circular inner edges via which the flux passes to the magnetic pole pieces 247. Such a circular inner edge also reduces ripple in the amount of magnetic force that can be exerted on the tang blocks 245a, 245b as a function of the angle of the frame 235 relative to the plate 215 and housing 201.

[0074] Also, note that the two air gaps 251b, 251c associated with spaces between the second tang block 245b and the two magnetic pole pieces 247 associated therewith are oriented substantially parallel to the associated end 241b of the wrap spring 240. This orientation is substantially tangential, relative to the periphery of input member 220. This is also, roughly, the orientation of the vector representing the magnetic force acting on the second tang block 245b. Accordingly, the magnetic force on the second tang block 245b is substantially tangential. This is beneficial because a tangential motion/force (as compared to a radial motion/force) is more effective in inducing expansion of the coils of the wrap spring 240. This reduction was observed to approximately halve the force that effects the same degree of expansion of the wrap spring 240. Accordingly, it is beneficial that the forces (magnetic or otherwise) exerted on the tang blocks of a clutch as described herein be exerted a direction that is substantially tangential with respect to the wrap spring thereof, e.g., within 15 degrees of a direction of the respective ends of such a wrap spring.

[0075] Indeed, the magnetic pole pieces 247 of the clutch 200 provide the benefit of shaping the magnetic flux that is available from the non-rotating coil 210 (and thus is likely to be substantially radial in direction as it passes from non-rotating elements like the housing 201 and plate 215 to rotating elements associated with the wrap spring 240 and tang blocks 245a, 245b) such that the magnetic forces exerted on the tang blocks 245a, 245b include significant tangential components with respect to the wrap spring 240.

[0076] Alternatively, the tang blocks of a magnetically-actuated bidirectional wrap spring clutch may be reconfigured so as to omit additional magnetic pole pieces while still exerting significant (or substantially only) tangential forces on the ends of the wrap spring thereof. Figure 4A depicts in cross-section elements of an example bidirectional wrap spring clutch as described herein. The bidirectional wrap spring clutch includes a wrap spring 440 with tang blocks 445a coupled to the ends thereof. The wrap spring 440 encircles and is in contact with a contact surface of an input member 420 unless, as depicted in Figure 4A, magnetic forces acting on the tang blocks 445a act to expand the wrap spring 440, preventing it from engaging with the input member 420. Such magnetic forces are created by magnetic fluxes generated by a coil or other actuator (not shown) and transmitted to the tang blocks 445 a from a plate 401 across respective air gaps 451. If the wrap spring 440 is permitted to engage with the input member 420 (e.g., due to cutting power to a coil), the wrap spring 440 can wrap down onto the input member 420 and one of the tang blocks 445a (depending on the rotation of the input member relative to a rotating frame 435a that is coupled to a brake rotor or other output member, not shown) can come into contact with a respective tang seat 449a formed on a housing 435a, thereby exerting a torque into an output member coupled thereto.

[0077] Such a configuration allows the tang blocks 445a to exert substantially tangential forces into the ends of the wrap spring 440 (e.g., forces within 15 degrees of the respective directions of the ends of the wrap spring 440) while omitting additional magnetic pole pieces and the weight and complexity thereof and/or omitting the flux losses associated with additional air gaps in the magnetic circuits. To reduce an amount of flux leakage at the air gaps 451 between the tang blocks 445a and plate 401, those air gaps can be reduced in width. Accordingly, the plate 401 has a circular inner edge via which the flux passes to the tang blocks 445a. Such a circular inner edge also reduces ripple in the amount of magnetic force that can be exerted on the tang blocks 445a as a function of the angle of the frame 435a relative to the plate 401.

[0078] Note that the configuration of tang blocks and tang seats depicted in Figure 4A is meant only as a non-limiting example embodiment. For example, Figure 4B depicts an alternative configuration of tang blocks 445b configured to seat into tang seats 449b of an alternatively configured frame 435b. In this alternative configuration, the surfaces of the tang seats 449b are more radially oriented, relative to the circumference of the wrap spring and other elements of the clutch, compared to the surfaces of the tang seats 449a depicted in Figure 4A (which are tangentially oriented, relative to the wrap spring). Such a more radially oriented tang seat surface could be desirable to, e.g., reduce slippage and wear when the tang block comes into contact with the tang seat in order to transmit clutched forces from the input member to and output member.

[0079] Indeed, the tang blocks have two semi-independent functions: to receive magnetic forces to expand the wrap spring and to transmit clutching forces, which may be many orders of magnitude greater than the spring-expanding magnetic forces, from the wrap spring to the frame when the spring is engaged with the input member. Accordingly, the tang block could include a first portion that is mechanically stiffer or otherwise stronger and that is configured to come into contact with the tang seat but that is not necessarily sensitive to applied magnetic forces. Such a tang block could also include a second portion made of mechanically less strong material that is more sensitive to magnetic forces.

[0080] When the wrap spring of a bidirectional wrap spring clutch as described herein has engaged with the contact surface of an input member, at least one of the tang blocks is at the maximum distance from its associated tang seat. Under this condition, due to the relatively large “air gap” associated with that tang block, a relatively large current must flow in an actuating coil in order to generate sufficient magnetic flux to create a force large enough to disengage the wrap spring from the input member and thus to move the tang block into contact with its tang seat. As an example, a current of more than 4 Amps may be used. The amount of current may be reduced, e.g., by operating a motor or other element to drive the input member in a direction appropriate to assist in disengaging the wrap spring therefrom (i.e., a direction opposite the direction of rotation of the input member that caused the original engagement of the wrap spring).

[0081] After less than (typically) 50 to 200 milliseconds of such a current, both tang blocks will be in firm contact with their associated tang seats. From this point forward, a much low er current is sufficient to maintain the tang blocks in contact with their tang seats and thus to prevent the engaged mode of the wrap spring clutch. For example, if the current used to disengage the wrap spring is 4 Amps, the lower current may be 1 Amp. Reduction of the applied current following disengagement of the wrap spring provides a variety of benefits, including: avoiding overheating and failure of the coil, and reduced power consumption. Such a “two- step” coil drive can include, whenever the coil is to be energized to disengage the wrap spring from the input member, a driver circuit generates a drive current for the coil that consists of a high (e.g., greater than 4 Amps) current for a specified period of time (e.g., at least 50 mSec) followed by a low current (e.g., less than 1 Amp).

[0082] During the initial engagement of a bidirectional wrap spring clutch as described herein (e.g., the initiation of braking for a brake device that includes such a clutch), very high forces are generated in one of the tangs of the wrap spring and in the tang block coupled thereto. For example, in a device rated at 2 Nt-m, it is estimated that the maximum tang force may be approximately 200 pounds. It is practical and cost-effective in many applications to make wrap springs-with-tangs and tang blocks separately, and then to attach one block to each tang of the w ap spring, rather than to fabricate the spnng/block assembly from a single piece of steel or other material. Attaching these parts together is challenging for a variety of reasons:

[0083] -the attachment method must withstand extremely high forces in a very small space; and

[0084] -the size of the parts is so small that the use of threaded fasteners (screws or bolts) — while not impossible — could lead to increased cost for parts and for assembly.

[0085] Typically, the wrap spring and its ends (or tangs) are composed of a heat-treated steel alloy. Attachment methods involving welding or other applications of heat could be deleterious to such heat treatment, perhaps annealing the tang material. Annealed material is significantly less strong than heat-treated material. Accordingly, a w elded tang would, in many circumstances, be too weak to withstand the large forces that it would experience in operation. Instead, a variety of methods described below may be employed to couple tang blocks to the ends of a wrap spring. Note that these methods may be employed to couple tang blocks to the end of the wrap spring of a bidirectional wrap spring clutch as described herein regardless of the method of actuation of the clutch (e.g., magnetic actuation as described above, mechanical actuation as described below, or some other actuation method).

[0086] In a first embodiment, depicted in Figure 5 A, tang block 510a is has formed therein a rectangular hole 511a. The hole 511a is large enough for a tang 525 of a wrap spring 520 and two wedges 513a, 515a to be therein. The right part of Figure 5A shows the isolated tang block 510a while the left part shows a section view through the tang block 510a with tang 525 and wedges 513a, 515a in place. After tang 525 and wedges 513a, 515a have been inserted into the rectangular hole 511a of the tang block 510a, the two wedges 513a, 515a are forced toward each other by great forces (e.g., by a clamp-like device or fixture). This forcing of the wedges 513a, 515a causes them to become locked in place, together with the tang 525, in the rectangular hole 511a of the tang block 510a, thereby rigidly coupling the first end 525 of the wrap spring 520 to the tang block 510a.

[0087] In a second embodiment, depicted in Figure 5B, tang block 510b is has formed therein a tapered rectangular hole 511b. The hole 511b is large enough for the tang 525 of the wrap spring 520 and a single wedge 513b to be therein. The right part of Figure 5B shows a section view of the isolated tang block 510b while the left part shows a section view through the tang block 510b with tang 525 and wedge 513b in place. After the tang 525 and wedge 513b have been inserted into the tapered rectangular hole 511b of the tang block 510b, the wedge 513b is forced down into the tapered hole 511a by great forces (e.g., by a clamp-like device or fixture). This forcing of the wedge 513b causes it to become locked in place, together with the tang 525, in the tapered rectangular hole 511b of the tang block 510b, thereby rigidly coupling the first end 525 of the wrap spring 520 to the tang block 510b. This embodiment has the benefit of using a single wedge, which may be easier to assemble (e.g., when compared to assembling a two-wedge tang block), at the cost of a tapered rectangular hole being formed in the tang block.

[0088] In a third embodiment, depicted in Figure 5C, a rectangular cut or groove 511c is created in one part 510c of a two-part tang block. A small screw or other fastener (not shown) can be used to fasten an end plate 512c of the two-part tang block onto the first part 510c of the tang block in order to create the complete tang block, securing the end of a warp spring (not shown) therein. An advantage of this variation is the relative ease of making a part with a rectangular groove, relative to creating a part with a tapered or non-tapered rectangular hole formed therethrough (e.g., by a drilling operation followed by a broaching operation). A disadvantage of this embodiment is the complexity of assembling the two-part tang block.

[0089] In a fourth embodiment, a rectangular hole can be formed through a tang block that is slightly larger that the wrap spring tang to be inserted therein. After insertion of the tang into the tang block, the tang can be brazed to the tang block. It is beneficial that an oven brazing process be used. An oven with a reducing atmosphere can be used in order to reduce surface oxidation of the parts. Many variations of the process are possible without departing from the teachings of this disclosure. A general description of one possible brazing process follows: [0090] Clean tang and tang block thoroughly to remove all debris and surface oxides.

[0091] Apply a suitable flux to these two parts (flux may be omitted in some embodiments where a reducing atmosphere is used.)

[0092] Place tang block/spring assemblies in holders provided in a suitable jig. Each assembly includes one spring and two tang blocks. The jig is sized to fit within the oven that has been selected for the process. A typical jig may hold roughly 50 to 200 assemblies or more. [0093] Place a brazing material “preform” on each tang of each assembly in the jig.

[0094] Place the fully-loaded jig in the oven, and increase the oven temperature to one suitable for the brazing material being used. (When the preform reaches the melting temperature of the brazing alloy, it will liquify and flow into the gap between the hole and the tang by capillary action.)

[0095] After a suitable time at the brazing temperature, quickly move the jig to the cooling zone of the oven. If the spring material is an “air hardening” alloy, then exposure to the cool atmosphere in the cooling zone will “quench” the parts and thereby heat treat each tang in order to achieve good strength. In the case of, for example, “water hardening” alloys, the entire jig-with-spring/tang assemblies would be plunged into a water bath immediately upon removal from the oven in order to complete heat treatment of tangs.

[0096] By way of this process, tangs will all be securely brazed to an associated tang block, and the parts will be heat-treated as part of the process of removal from the oven.

[0097] In another embodiment, tang blocks are attached to tangs of a wrap spring by way of a swaging operation. After each tang block has been slid onto a corresponding tang, a pair of dies converges on the tang block, compressing it around the tang and forming a strong bond there. The tang can also be roughened by way of an abrasive operation prior to swaging in order to increase the strength of the bond.

[0098] A bidirectional wrap spring clutch as described herein can be actuated in a variety of ways. For example, a coil or other flux-generating actuator can be used to exert magnetic forces on tang blocks coupled to the ends of the wrap spring, e.g., the clutch 200 system depicted in Figures 2A-C and 3A-B. Alternatively, mechanical forces can be transmitted from a non-rotating actuator (e.g., one or more solenoids, motors, linear actuators, hydraulic or pneumatic cylinders, manual levers or other manually-operated elements) to a rotating linkage or other mechanism associated with the wrap spring and the tang blocks coupled thereto. This could include exerting, through a bearing or other means, an axially-oriented force along an axis of rotation of an input member with which the warp spring can engage. This axially- oriented force could be exerted onto a mechanism that converts the axial force into forces (e.g., tangential forces, relative to a circumference of the wrap spring) to maintain the tang blocks in contact with respective tang seats, thereby expanding the wrap spring and preventing its engagement with the input member.

[0099] Figures 6A-D depict aspects of an example of a bidirectional wrap spring clutch 600. A number of solenoids 603 provide actuating forces that eventually, via other elements of the clutch 600, result in actuation of the tangs of the wrap spring (not shown). A mechanical linkage transfers the output of the solenoids 603 (which are attached to the non-rotating housing of the device 600) to the tangs, which may rotate with a rotating frame 632.

[00100] As shown in Figures 6A-D, two solenoids 603 are used, but one or a multiplicity greater than two could be used, or some alternative force-generating actuator(s), without departing from the embodiments disclosed herein. The solenoids 603 have output shafts 604 that are attached via a pivot to a lever 605. Lever 605 is also supported by a stationary pivot 606. Note that the lever 605 has a central hoop that surrounds a central shaft 602 (which may be an input and/or output member of the clutch device 600), and three radial arms. A nonrotating disk 608 of a bearing can be seen below lever 605. This bearing is not exactly a pure thrust bearing (though it provides some functions similar to a thrust bearing, like the transmission of axial or nearly axial forces through a bearing), and accordingly may be referred to as a “thrust plate device” herein. The illustrated thrust plate device and a ‘true’ thrust bearing is that, in a ‘true’ thrust bearing, the two sides of the bearing are coaxial, and they remain so despite external forces that might tend to move them into an eccentric arrangement. In the “thrust plate device” depicted herein, small eccentric movements of the two sides of the bearing are permitted. A housing 601 and a lever return spring 607 are also included. The spring 607 is a form a leaf spring anchored to the housing 601 by two fasteners at its base 609.

[00101] Figure 6B is an oblique side view of the bidirectional clutch device 600 with part of the housing 601 and other elements cut away. Housing 601, shaft 602, and a stationary pivot 606 can be seen. Lever 605, return spring 607, and non-rotating disk 608 can also be seen in this view. Note that non-rotating disk 608 is attached to the lever 605 by way of a gimbal mechanism that permits non-rotating disk 608 to “rock” relative to lever 605. Finally, a rotating disk 610 can also be seen. It is beneficial that the friction coefficient between non-rotating disk 608 and rotating disk 610 be very low, e.g., by selecting appropriate materials chosen. For example, the non-rotating disk 608 may be Teflon and rotating disk 610 may be polished steel (or vice versa) as these two materials exhibit very low friction when in contact. The linkage piece 611 has two circular holes suitable for fitting over two cylindrical pivots 640. Linkage piece 611 is rigidly attached to the rotating disk 610. This linkage piece has two arms extending toward the pivots 640, with one being longer. At the end of each arm, there is a pivot 640. By means of these pivots 640, the two arms actuate two roller arms 635, 638 as described below. [00102] Note that additional or alternative mechanisms could be employed to transmit an axial (or nearly axial) force from a non-rotating actuator to rotating mechanisms configured to translate such axial forces into forces on the tangs of a wrap spring so as to engage, disengage, and/or permit the engagement of a wrap spring of a bidirectional clutch as described herein.

[00103] Figure 6C depicts, in side view, elements of the clutch 600 that are disposed on or within the rotating frame 632. A roller arm 635 rotates about a pivot 636 that is coupled to the rotating frame 632. A circlip (not shown) around the pivot 636 prevents the roller arm 635 from falling off of the pivot 636. A roller 637 is mounted on another pivot (not numbered) at one end of roller arm 635 and is secured there by a circlip (not shown). Finally, a return spring 641 biases the roller arm 635 to rotate clockwise. That rotation tends to move roller 637 to the right. A stop (not shown) allows roller arm 635 to move only several degrees from the position shown in Figure 6C. When the roller arm is against its stop, roller 637 may, for a device with a nominal torque rating of about 2 to 10 Nt-m, be about 0.02 to 0.10 inch to the right of the location depicted in Figure 6B. This dimension will depend on various considerations of the design and is not intended to be limiting.

[00104] There is also a second roller arm 638, pivot 640, spring, and, and associated elements on the opposite side of the frame 632 from the first roller arm 635. One end of this roller arm can be seen protruding past the right edge of the frame 632 in Figure 6C and is denoted 638.

[00105] Figure 6D illustrates a cross-sectional view through elements of the device 600 through the plane 660 depicted in Figure 6C. Figure 6D illustrates a first disengaged configuration of the device 600 in solid lines, and an engaged configuration in dashed lines. Components of the device 600 related to only one of the two tangs (and the single tang block associated therewith) of the wrap spring are seen in this view. Components for actuation of the other tang are on the opposite side of the rotating frame 632, which is hidden in the view of Figure 6D.

[00106] Actuation components similar to those seen in the foreground of Figure 6C are located on the opposite side of the rotating frame 632. The end of the additional roller arm on the opposite side of the rotating frame 632 can be seen to the right side of the rotating frame 632 and is denoted as roller arm 638. The projected location of the pivot for roller arm 638 is denoted as 639 in Figure 6C. There is a cylindrical pivot 640 extending perpendicularly to each roller arm 635, 638. These pivots fit into matching holes in the linkage piece 611 as described above. After the pivots and linkage piece 611 have been assembled, a circlip (not shown) on each pivot prevents the parts from coming apart during operation.

[00107] A wrap spring 652 is wrapped around the input member 602. A first end 655 (or tang) of the spring 652 is coupled to a first tang block 654. The first tang block 654 pivots around the input member 602 by way of, e.g., a journal bearing formed by its inner diameter running against the shaft. In some designs, there may be a brass or “oilite” journal bearing pressed into the bore of the tang block 654 to form this bearing. Tang block 654 includes an active lobe 657a and a counterweight lobe 657b.

[00108] The first wrap spring end 655 fits into a slot, groove, or hole in the active lobe 657a of the first tang block 654. It may be attached using one of the methods discussed above or another method without departing from the teachings of this disclosure. The active lobe 657a has two functionally relevant contact surfaces. The first is where the active lobe 657a contacts a tang seat 656. This will be called the “posterior” contact face. The second is designed to contact the roller 637, which can provide a tangential force on the tang block 654 as the result of an axial force being exerted into the linkage piece 611. This will be called the “actuation” face.

[00109] The “actuated” position of the components depicted in Figures 6A-D can be defined as that position corresponding to a significant axial force exerted into the linkage piece 611, e.g., due to an electrical current being applied to the coils of the solenoids 603. The “unactuated” position oppositely corresponds to no or insignificant application of axial force, e.g., due to insignificant current being applied to the solenoids 603. The unactuated position of the actuation face is shown with dashed lines at 658 (with some exaggeration of the displacement for clarity). The direction of motion for the roller 637 when significant axial force is applied is shown by arrow 670.

[00110] For the unactuated configuration, the wrap spring 652 will firmly grip the input member 602, which will cause tangs 655 and tang blocks 654 to rotate with the input member 602. One of the tangs and tang blocks (depending on the direction of rotation) will be urged into forceful contact with the associated tang seat 656. For example, the posterior seat of the active lobe 657a of the first tang block 654 will be forced into contact with the first tang seat 656 for counterclockwise rotation of the input member 602 from the perspective depicted in Figure 6D. The force of the first tang block 654 upon the first tang seat 656 will exert a torque on the rotating frame 632 causing it to rotate with the input member 602. Where the device is configured as a clutch device, with the rotating frame 632 coupled to an output member, the output member will be forced to turn at the speed of the input member. Where the device 600 is configured as a brake, a braking torque will be applied to the input member 602. Note that return springs 641 will urge the rollers 637 away from the actuation face of the active lobe 657a of each tang block 634, permitting the wrap spring 652 to wrap tightly on the input member 602.

[00111] For actuated configuration, a significant axial force is applied, e.g., by current being passed through the coils of the solenoids 603. This causes the solenoid output shafts 604 and lever 605 to move downward, as depicted in 6Aand 6B. This then causes non-rotating disk 608 and rotating disk 610 of the thrust plate device to move downward. When the rotating disk 610 moves downward, that will cause linkage piece 611 to move downward. Holes of the linkage piece are attached to cylindrical pivots 640 of two roller arms 635 and 638. Thus, downward motion of holes will cause downward motion of cylindrical pivots 640. The downward motion of cylindrical pivots 640 will cause counterclockwise rotation of the roller arm 635. This motion will force roller 637 into contact with the actuation face of active lobe 657a of the first tang block 654. The same will happen for the second tang block, with its active lobe located on the opposite side of rotating frame 632. So, by this action, the posterior face of both tang blocks 654 will be forced into close contact with the associated tang seats 656. Forcing both tang blocks 654 into contact with the associated tang seats will cause wrap spring 652 to deform as a helical torsion spring, expanding the coil diameter. This will cause the spring inside diameter to become larger that the outside diameter of the contact surface of input member 602, causing the spring 652 to disengage from the input member 602. The result is that, for a clutch device the input and output members may turn independently, and for a brake device, negligible braking torque is applied to the input member.

[00112] Clutch and brake devices described above have generally included a single actuation mechanism configured such that the actuation mechanism affected both tang blocks simultaneously. These devices all provided bidirectional clutching (or braking in the case of brake devices) as described above. In an alternative embodiment, a device may include two actuation mechanisms, one for each of the tang blocks. This embodiment is able to both provide bidirectional clutching (or braking) and also provide an overrunning clutch action in either direction of rotation.

[00113] In an overrunning clutch, rotation of an input member in a first direction acts like an engaged conventional clutch (i.e., the wrap spring engages with the input member and the output member turns at the same speed — and direction — as the input shaft). But for the second (opposite) direction of rotation, the wrap spring is disengaged form the input member and so the output member not coupled to the input member. A one-spring, unidirectional wrap spring clutch will act as an overrunning clutch when the single tang of the wrap spring is free to rotate.

[00114] The two actuators of a two-actuator single-wrap spring bidirectional clutch as described herein may be energized by separate driver circuits. The two driver circuits may be separately operated to enable or disable each driver circuit based on the type of operation that is desired at a particular time. If bidirectional operation is desired, the two driver circuits are both enabled, and they each energize their associated actuation mechanisms at the same time, based on some input signal or command. This results in forces being exerted on both tangs of the wrap spring to expand the wrap spring, thus preventing the engaged mode of the wrap spring clutch for either direction of rotation of the input member.

[00115] If overrunning clutching in a first direction is desired, just one of the driver circuits is enabled. Then, the device will act as an overrunning clutch in the first direction, and the wrap spring will engage with the input member if it rotates in the opposite second direction. [00116] If overrunning clutching in the second direction is desired, then the other driver circuit is enabled. Then, the device will act as an overrunning clutch in the second direction, and the wrap spring will engage with the input member if it rotates in the first direction.

IV. Example Brake Mechanisms

[00117] As briefly described above, a brake mechanism can be provided that is superior with respect to size, weight, complexity, cost, and other factors relative to alternative brake mechanisms. This can be achieved by actuating a bidirectional wrap spring clutch as described herein that can quickly and with a high power rating mechanically couple a drive shaft to a brake rotor that is maintained in contact with a brake pad. The force/power used to actuate the wrap spring (e.g., by selectively preventing or permitting motion of control tangs or other end portions of the wrap spring) can be substantially less than the power/force used to actuate the brake by controlling the amount of force exerted by the brake pad onto the brake rotor. Thus, the size, weight, cost, complexity, or other factors of the brake related to an actuator for effecting the control of such forces may be improved.

[00118] Such braking devices have several applications, one of which is that of a “safety brake” in robots. For example, an instance of such bidirectional wrap spring clutched-braking device may be included as an emergency brake for each “degree of freedom” (DOF) of the robot. Each DOF can be driven by a combination of a motor, a “safety brake,” and a transmission. The brake device may be located between the motor and the transmission input shaft. However, note that a brake as described herein may be installed in various locations of a system without departing from the teachings of this disclosure, such as on the “rear” end of or otherwise incorporated into a motor, or at an intermediate stage of a transmission.

[00119] Figures 7A and 7B depict a brake device 700 that clutches an input member 701 to a brake using a bidirectional wrap spring clutch as described herein. Figure 7Ais an oblique view of the device 700 with certain components cut away for ease of illustration and Figure 7B is a side view with certain components viewed in cross-section. The input member 701 extends through the center of the device 700. Depending on the application, one end of this input member 701 may be driven by a motor or transmission and the other end may be used to drive other components or may not be used (in which case it may have bearing disposed thereon to cancel lateral forces exerted on the input member 701 by the device 700 or by other factors).

[00120] The device 700 also includes a variety of components of similar function to device 200. Device 700 include a wrap spring 706 in contact with a contact surface of the input member 701. The wrap spring 706 includes first and second ends coupled to respective first 720a and second 720b tang blocks. Forces can be exerted on these tang blocks, as described elsewhere herein, to expand the wrap spring 706, thus preventing the wrap spring 706 from engaging with the contact surface of the input member 701. Such forces can be reduced, omitted, or reversed to permit engaged modes of the wrap spring 706 wherein one or both of the tang blocks 720a, 720b are permitted, as a result of rotation of the input member 701, to move relative to a rotating frame 707. Such relative motion allows the wrap spring 706 to engage with the input member 701, wrapping down onto the input member 701 and thus allowing the input member 701 to couple forces into the wrap spring 706 and from there (via contact between one of the tang blocks 720a, 720b and a respective tang seat (not numbered) of the rotating frame 707.

[00121] The rotating frame 707 includes (or is rigidly welded, bolted, or otherwise coupled to) square interlock section 715. This interlocks with a mating square hole in the center of a brake disk 716 (which may also be referred to as a “brake rotor”). The brake disk has brake pads 717a and 717b composed of friction material and in braking contact with both sides of the periphery of the brake disk 716. Brake disk 716 forms part of a disk brake device, as will now be described. Brake pads 717a and 717b bear against two non-rotating steel disks, which include stationary disk 718 and pressure disk 719. Stationary disk 718 is stationary. It is part of (or attached to) ahousing 703 so that it does not rotate or translate. Pressure disk 719 is free to move in the axial direction but splines (not shown) prevent it from rotating relative to the housing 703. There are also a number of pressure springs 720 such that the friction materials 717a, 717b exert braking forces onto the brake disk 716.

[00122] The brake disk 716 is free to move in an axial direction due to a small clearance between its square hole and square interlock section 715 of the rotating frame 707. Thus, the force of pressure disk 719 against brake disk 716 will push the brake disk 716 until the friction material 717b contacts the stationary disk 718. Accordingly, a large contact force (sometimes called the “normal force”) is created between pressure disk 719 and friction material 717a, and also between stationary' disk 718 and friction material 717b. This force exists at all times during operation of the device 700.

[00123] The combination of brake disk 716, friction materials 717a, 717b, stationary disk 718, pressure disk 719, and springs 720 constitute a disk brake device. If the normal force is N, the average radius of the friction material is r, and the friction coefficient is p; then this device will exert a torque, T, on square interlock section 715 that is given roughly by

[00124] T = 2prN,

[00125] whenever brake disk 716 rotates.

[00126] As depicted, the clutch aspects of the device 700 incorporate a coil as an actuator and function similarly to the clutch device 200 depicted in Figures 2A-C. However, alternative configurations of a magnetically actuated bidirectional wrap spring clutch, or a bidirectional wrap spring clutch actuated in some other manner (e.g., mechanically, as in device 600), can be used in combination with a brake disk and pads, as described elsewhere herein. The clutch of device 700 may have similar operational states and operations as the other bidirectional wrap spring clutches described herein. When the clutch is disengaged, input member 701 may rotate in either direction with negligible effects from the rest of the device 700. This is because the clutch is disengaged, and the wrap spring 706 is disengaged from the input member 701. Thus, square interlock section 715 does not rotate with the input member 701, and accordingly brake disk 716 does not rotate. As a result, no torque is exerted by brake disk 716 on the square interlock section 715, and accordingly no torque is exerted on input member 701, leaving it free to rotate. In contrast, when the clutch is engaged rotating frame 707 and attached square interlock section 715 must rotate with the input member 701, as the wrap spring 706 in such an engaged state is engaged with the contact surface of the input member 701 and thus couples the input member 701 to the rotating frame 707. Because the square interlock section 715 is rigidly coupled to the rotating frame 707, it must also rotate with the input member 701. This also results in the brake disk being coupled to the input member 701. Accordingly, when the clutch is engaged, the device 700 acts like a friction brake, tending to resist rotation of the input member 701.

[00127] When the input member 701 is mechanically coupled in this way to the brake disk 716 via the engagement of the wrap spring 706, the input member 701 will thus experience a braking torque. The magnitude of this braking torque may be related to a spring force of the springs 720, an average radius of the contact surfaces of the brake disk 716 that are in contact with the friction materials 717a, 717b, and a friction coefficient between the contact surfaces of the brake disk 716 and the friction materials 717a, 717b. By appropriate choice of these spring and rotor parameters, this braking torque can be chosen to meet the particular requirements of an application. Thus, when the brake is engaged, the robot DOF or other mechanism will decelerate very quickly, but not so quickly that it is damaged.

[00128] One application of such a device 700 is as a safety brake for robots and other machines. For such an application, it is beneficial that if there is a power failure, the device will immediately apply braking torque to the input member 701. As explained, the device 700 can exhibit this desired behavior so long as such a power failure results in engagement of the clutch, e.g., if loss of current in a coil-based magnetic actuator of the device 700 results in engagement of the wrap spring 706 with the input member 701, thus clutching the input member 701 to the brake disk 716 as a result of that loss of current.

[00129] The particular arrangements shown in the Figures should not be viewed as limiting. It should be understood that other embodiments may include more or less of each element shown in a given Figure. Further, some of the illustrated elements may be combined or omitted. Yet further, an exemplary embodiment may include elements that are not illustrated in the Figures.

[00130] Additionally, while various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are contemplated herein.