MECHANICALLY AMPLIFIED POSITIONING LIMBS

FIELD

[0001] The present disclosure relates to a positionable platform system with positioning limbs, and more particularly to a positionable platform system with mechanically amplified positioning limbs.

BACKGROUND

[0002] Positionable platforms for certain applications are known in the prior art. One example of a positionable platform is a hexapod platform comprising a parallel robot with a fixed base, six linear actuator members in a generally hexagonal configuration, and a moveable upper platform. The hexapod platform can be moved in six degrees of freedom by the coordinated parallel activation of the six linear actuator members. This type of platform has been in use for some time, as early as the mid 1950's, and is also known commonly as Gough-Stewart platforms.

[0003] These positionable platforms have many uses in positioning an object, such as the positioning of a tire on a moving test bed, tilting flight simulator modules to simulate roll, pitch and yaw, positioning optics, positioning directional manipulators, or alternatively for testing how equipment behaves in a particular pose, motion or vibration. An illustrative example of a hexapod for a very early motion simulator is shown by way of example in US Pat. No. 3,295,224 issued to Cappel.

[0004] These hexapod platforms tend to have large, heavy payloads and the linear actuators in turn are very large, usually with their drive components built into the actuator. One disadvantage of these large actuators is that the dynamic range of motion is very small. Typically, the linear actuating limbs do not even contract down to 50% from maximum displacement to minimum displacement. For some linear actuators, the amount of contraction possible may be much less, such as only 80 to 90% of full length, comparing the distance from full extension of the moveable platform compared to the distance of the fully contracted moveable platform. The bulky construction of the linear actuator members in these prior art designs can cause internal collisions between sections of the linear actuating limb, even further reducing the effective working envelope of the movable platform. Indeed, to try to increase the range of dynamic motion in the working envelope, a significantly larger apparatus is required, which in turn increases size, cost and the overall inertia of the positioning system. [0005] Systems such as taught by Namoun et al, (US Pat. No. 8,495,927) may improve the performance of a hexapod platform by making the linear actuator portion a part of the fixed base and attaching the six members to the actuators with universal ball joints. Although this system has minimal inertia and can move very fast, it nevertheless still suffers from the limited dynamic range of the actuators relative to their full extension.

[0006] Also, current systems measure actuator lengths to determine relatively crude positions of the platform for repositioning to a specific desired location, while sub- millimeter accuracy is required for certain types of applications.

[0007] Thus, what is needed is an improved positionable platform system which overcomes at least some of the limitations of the prior art discussed above.

SUMMARY

[0008] The present disclosure relates to a positionable platform system with mechanically amplified extended length positioning limbs.

[0009] In an aspect, the extended length positioning limbs are configured to provide a significantly improved range of motion for the positionable platform by mechanically amplifying the length of each positioning limb. The result is a positionable platform with a significantly increased working envelope than can be achieved with any prior art platform of similar size and strength. Advantageously, this allows for a much smaller and lighter linear actuator, which in turn decreases the cost and weight of the entire hexapod platform. The platform is well suited to cost sensitive and physically smaller payload applications, such as applications in medical equipment where the positionable platform is used for positioning directional diagnostic devices or directional interventional devices.

[0010] In an embodiment, the positionable platform of the present invention uses a plurality of telescoping sections for the linear actuator members, preferably more than two sections.

[0011] In an embodiment, a first moveable section of the linear actuator member is moved linearly by cables that apply a tensile force for both extension and contraction operations. Additional sets of cables and pulleys may be used to extend and contract a plurality of inner telescoping sections to move in a like manner to the first moveable section, thus mechanically amplifying the translation and significantly increasing the dynamic range of motion. This configuration results in a telescoping limb capable of contracting more than 50 % from maximum to minimum displacement. [0012] In another embodiment, a first moveable section can also be translated by other means, such as a threaded rod and nut assembly, pneumatic cylinder, hydraulic cylinder, linear motor or the like. The separate cable connection to the plurality of inner telescoping sections still provides for the mechanical amplification of the translation thus increasing the dynamic range of motion.

[0013] In another embodiment, linear translation mechanical amplification is proportional to the number of additional telescoping sections being used.

[0014] In another embodiment, the use of cables facilitate the placement of a motion control and cable drive mechanism to be placed on the linear actuator member.

[0015] In another embodiment, the motion control and cable drive mechanism can be placed on a fixed base.

[0016] In another embodiment, control and cable drive mechanism can be located remotely from the hexapod platform.

[0017] In an alternative embodiment, the positioning limbs are made from a scissor-lift mechanism providing mechanical amplification the two or more sections of the scissor- lift mechanism.

[0018] In another alternative embodiment, positioning of the platform, within sub- millimeter accuracy, is achieved by integrating an optical tracker that measures a 3 dimensional positioning error between the current placement of the platform to the desired position, and sends positioning adjustment commands to the individual arms until the overall desired position is reached.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The invention will now be described in detail, with reference to the accompanying drawings of preferred and exemplary embodiments, in which:

[0020] FIG. 1 is a schematic illustration of the full hexapod platform system depicting the telescoping linear actuator members;

[0021] FIG. 2 is a schematic diagram of a single linear actuator member on the fixed base with the cable drive mechanism located on the base;

[0022] FIG. 3 is a schematic diagram of the cable drive mechanism;

[0023] FIG. 4A is a schematic diagram of the internal details of single example of the telescoping linear actuator member and the cable configuration;

[0024] FIGS. 4B and 4C are schematic diagrams depicting an inline cable tensioning method; [0025] FIG. 5 is a schematic diagram of a single linear actuator member and the fixed base with the cable drive mechanism located on the actuator member;

[0026] FIG. 6 is a schematic diagram of a single linear actuator member with the cable drive mechanism located remotely.

[0027] FIG. 7 is a schematic diagram of a single linear actuator in which the first telescoping section is moved by a threaded rod.

[0028] FIG. 8 is a schematic diagram depicting another form of mechanical amplification of the linear actuator member, that being a scissor-lift method.

[0029] FIG. 9 is a schematic diagram depicting a different embodiment of mechanical amplification using cables and different diameter pulleys.

[0030] FIG. 10 is a schematic diagram depicting a positioning error feedback system for making positioning corrections.

[0031] FIG. 1 1 is a schematic block diagram of a generic computing device.

[0032] The same elements will be given the same reference on the various figures for clarity.

DETAILED DESCRIPTION

[0033] As noted above, the present disclosure relates to a positionable platform system with mechanically amplified extended length positioning limbs.

[0034] In an aspect, the extended length positioning limbs are configured to provide a significantly improved range of motion for the positionable platform by mechanically amplifying the length of each positioning limb.

[0035] Turning to FIG. 1 , this illustration depicts a first embodiment of a positionable platform, comprising base 20; a moveable platform 30; six telescoping linear actuator members 40; twelve universal joints 60 connecting the members 40 to base 20 and the moveable platform 30; and a plurality of cable drive mechanisms 70, of which two are shown by way of illustration.

[0036] In the following description, the terms downward and upward will be used with a frame of reference relative to the system 10 as shown in FIG. 1. Here, downward is in the direction of base 20 and upward is in the direction of the moveable platform 30. This does not imply that the hexapod 10 need be used in the orientation shown, relative to the force of gravity, but rather denotes a direction relative to the base 20 and the movable platform 30 as shown in FIG. 1.

[0037] In this illustrative example, the drive mechanism 70 is a cable winch system. However, in other embodiments, the drive mechanism may be implemented in other ways, such as with hydraulic or pneumatic cylinders, electric motors and threaded rods, or other forms of linear motion.

[0038] FIG. 2 depicts an illustrative example of a linear actuator member 40 mounted to base 20 by a universal joint 60. The cable drive mechanism 70 is mounted to the underside of base 20. The drive cables 46 and 47 traverse through base 20 connecting to the linear actuator member 40. The actuator 40 has several sections. In this illustrative embodiment, section 43 is fixed in position and does not move. It holds the other sections and represents the minimum length that the actuator 40 can achieve. Center sections 44a, 44b,... etc. contract into or extend out of the stationary base section 43 and each other center section 44. The final section 45 is similar to center sections 44 as it also contracts into the previous center section 44 but section 45 also has a fixed end connected to the universal joint 60. Pulling on cable 46 causes the telescoping sections 43, 44a, 44b, 45 to extend and pulling on cable 47 causes the same sections 43, 44a, 44b, 45 to contract.

[0039] The universal joint 60 is only shown diagrammatically as a circle. As is well known in the art, the universal joint can be a ball joint or a compound pivot device such that, at a minimum it facilitates two orthogonal axes of rotation. These axes do not need to intersect. As long as these minimum requirements are met, the actual type of universal joint used is not important.

[0040] Now referring to FIG. 3, shown is an illustrative example of a cable drive mechanism 70. A single motor 41 is connected to a winch 42. The motor 41 is able to rotate clockwise and counter clockwise at a velocity and total rotational displacement responding to signals from a computer control, such as from a generic computer as illustrated in FIG. 1 1. For simplicity, the computer and control circuitry are not shown in FIG. 3, as many such devices are known in the art. The cables 46 and 47 are wound about the winch 42 in relative counter-rotation and are anchored to the anchor points 52. If looking towards the shaft of the motor 41 and the rotation is clockwise, the winch 42 will wind cable 47 and release cable 46. In turn, if the motor rotates counter-clockwise the winch 42 will release cable 47 and wind cable 46.

[0041] Now referring to FIG. 4A, shown is an illustrative example of how mechanical amplification may be obtained by the use of cable coupling and pulleys. Here, the outer most telescoping section 43 is fixed into position and has a pulley 48a. The extension cable 46 is fed through this pulley 48a and is then anchored to the next inner telescoping section 44a at anchor point 49a. In FIG. 4A, there are two inner telescoping sections 44a and 44b but this number can be a minimum of one and a maximum of N, where N is limited by the physical attributes of the embodiment. The contracting cable 47 is anchored to the same point 49a on the next inner telescoping section 44a. When the cable drive mechanism 70 winds cable 46 onto the winch 42, the downward force will be redirected up by the pulley 48a causing section 44a to move upwards relative to the outermost and fixed telescoping section 43. Cable 47 is being unwound at the same rate and will be pulled upward at anchor point 49a.

[0042] The mechanical amplification will now be described in more detail. As described in the last paragraph, inner telescoping section 44a is being moved upward by cable 46. An additional cable loop 51 a is anchored to the top of the fixed section 43 at anchor point 49b. The lower portion of cable 51 a loop is fed down through pulley 48b that is attached to section 44a and is directed upward terminating at anchor point 49c on telescoping section 44b. The upper portion of cable loop 51 a is fed upwards through pulley 48c that is attached to section 44a and is directed downward terminating at anchor point 49c on telescoping section 44b. As section 44a is moving upwards away from section 43, pulley 48c will exert a force on cable 51 a. In the frame of reference of 44a the anchor point 49b is moving downward. This will pull the upper loop of cable 51 a downward through pulley 48c, redirected to an upward force at anchor point 49c; thus the next inner telescoping section 44b will move upward relative to section 44a and section 43.

[0043] Likewise this relative motion will also occur for the inner most final telescoping section 45 moving upward relative to section 44b in a similar manner by the upper cable sections 51 b, pulley 48e and anchor points 49d and 49e.

[0044] If a sufficient external force were placed downward on section 45, then contracting cables 47, (lower loop cable 51 a and 51 b) would not be needed. This may occur when there is a weight on the moveable platform 30 and the hexapod 10 is oriented such that the force of gravity is in the direction of base 20. It is desired to operate the hexapod 10 in various orientations such that the force of gravity cannot be used for the restoring counter force. Thus, cable 47 anchored at point 49a will be used to pull the inner section 44a downward contracting into section 43. In the frame of reference of section 44a, anchor point 49b is moving upward. This will apply upward force to the lower loop of cable 51 a that is directed downward by pulley 48b pulling telescoping section 44b at anchor point 49c downward contracting into section 44a. [0045] Likewise this relative motion will also occur for the inner most final telescoping section 45 moving downward relative to section 44b in a similar manner by the lower cable loop 51 b, pulley 48d and anchor points 49d and 49e.

[0046] The diagram shows the cables 46, 47, 51 a and 51 b being different lengths from anchor point to anchor point for improved readability. It should be noted that these cable paths are implemented to be the same length from winch 42 to anchor point 49a, and on inner sections from anchor points 49b to 49c on cable section 51 a, from anchor points 49d to 49e on cable section 51 b. Equal path lengths are needed as a method to maintain equal tension on the cables. Of course, cable-tensioning methods may be deployed to eliminate this constraint. An example of cable tensioning is described next.

[0047] An example of cable tension is illustrated in FIGS. 4B and 4C. The cable 100 is attached to a spring 102. In FIG. 4B the spring 102 is contracting and placing tension on cable 100 linearly in the direction towards the center of the spring 102. The limiting cable 01 is loose. When sufficient force is applied to cable 100 the spring 102 extends as shown in FIG. 4B. The limiting cable 101 is fully stretched and prevents the spring 102 from extending any further. The tensioning system therefore has a hard limit. The springs may be mounted very close to the anchor points on the moveable sections of the actuators (e.g. FIG. 4A anchor point 49a).

[0048] Now referring to FIG. 5, shown is another illustrative embodiment of a single linear actuator member 40 in which the cable drive mechanism 70 is part of the actuator with a universal joint 60 attached to the cable drive mechanism 70. This placement of the cable drive mechanism 70 may allow the universal joint 60 to move more freely as there is no potential interference from cables (e.g. cables 46, 47 in the embodiment shown in FIG. 2).

[0049] FIG. 6 shows another embodiment of a single linear actuator member 40 in which the cable drive mechanism 70 is remotely located relative to the actuator. The remote placement of the cable drive mechanism 70 provides additional configuration options for placement of multiple cable drive mechanisms 70 in a given setup.

[0050] FIG. 7 shows yet another embodiment in which the first telescoping section 44a of the linear actuator member 40 undergoes linear motion via a rotating threaded rod shaft 55. The inner telescoping section 44a is translated relative to the fixed and outermost telescoping section 43 by the use of a motor 41 , the threaded rod shaft 55, and a nut 56. The motor 41 is rigidly attached to section 43 and the nut is attached to section 44a. When the motor 41 rotates the threaded rod 55 displaces the nut 56 upward or downward depending on the direction of rotation. This will in turn displace section 44a upward or downward. The remaining sections are displaced in a manner analogous to the manner previously described for FIG. 2.

[0051] Another form of mechanical amplification is depicted in FIG 8. In this embodiment, a scissor-lift mechanism is used instead of telescoping sections. In this embodiment, a linear actuator member 80 replaces the linear actuator member 40 shown in FIG. 1. In an embodiment, linear actuator member 80 is actuated by an electric motor 81 that has a threaded rod shaft 83. The motor is mounted rigidly to first scissor section 84 near pivot location 85c. The shaft 83 passes through nut 82 attached to first scissor section 84 and is mounted in a way allowing for the nut to pivot. Scissor section 84 consists of two lower arms 84a, 84b, and two double length upper arms 84c, and 84d. Arm 84a is attached to Arm 84b at pivot point 85a. Arm 84a is attached to Arm 84c at pivot point 85b. Arm 84b is attached to Arm 84d at pivot point 85c. Lastly arms 84c and 84d are joined at their midpoints at pivot point 85d. Rotating the motor 81 causes the nut 82 to be pulled along the threaded rod 83, either towards the motor 81 or away from the motor 81 depending on the direction of rotation. The nut 82 will cause pivot point 85b to come towards pivot point 85c, thus contracting section 84 horizontally and extending vertically.

[0052] Mechanical amplification is provided by adding additional scissor sections, for example, scissor sections 86a, 86b and 86c. The minimum number of sections 86 is one and the maximum number of sections 86 is only limited to that which will still allow for a practical design.

[0053] In the illustrative embodiment shown in FIG. 8, the translational motion contracting the scissor horizontally is done by a motor, threaded rod shaft and nut. However, in alternative embodiments, the motion can also be obtained by cables and pulleys, pneumatic or hydraulic cylinders or other forms of linear motion actuation.

[0054] Yet another illustrative embodiment is shown in FIG. 9. In this embodiment, telescoping sections (91a, 91 b and 92) are connected by cables (95a, 95b; 96a, 96b; 97a, 97b respectively) directly to a pulley 90. The pulley 90 has three sections with the radius changing arithmetically by a factor of 1. Radius 90a is distance r; radius 90b is distance 2r and radius 90c is radius 3r. Thus cable 97a will travel twice the distance of cable 95a and cable 96a will travel three times the distance of cable 95a. Rotating the pulley will then cause section 92 to travel 3 times the distance of section 91 a and section 91 b will travel 2 times the distance of section 91a. This will cause the section to extend evenly while telescoping. The downward motion of cables 95a, 96a, and 97a are translated to upward motion through pulleys 93a, 93b and 93c and are attached to movable section 91 a, 91 b, and 92 at attachment points 94a, 94b and 94c. Likewise the extended telescoping sections can be retracted by rotating the pulley 90 in the opposite direction. Cables 95b, 96b and 97b will pull the telescoping section downward. This embodiment allows direct application of an actuation force to each section using cables driven by pulley 90, allowing tension on the cables to be distributed more evenly.

[0055] Now referring to FIG. 10, shown is another embodiment in which the position and orientation of the movable platform 30 may be measured after it is moved into an initial position based on operation of the positioning limbs. In an embodiment, this may be done by the use of a fixed camera 1 10 which may be used to determine the position of various markers as may be provided on the movable platform 30 itself at both ends of the assembly, as identified by optical targets 120 for example).

[0056] By capturing the position and orientation of the movable platform 30 after an initial positioning operation (by determining the location of the markers), and determining any error present between the initial position and a desired position, a computing device (such as generic computer device 1000 of FIG. 1 1 , for example) may be used to calculate a required correction to reposition the movable platform 30 closer to the desired location. If necessary, this process may be repeated until any error between the desired position and the actual position of the movable platform 30 is within an acceptable error range.

[0057] Advantageously, a positioning feedback system may be used to compensate for any positioning error that may accumulate over time, as cables may stretch and other movable parts and joints may become worn.

[0058] Now referencing FIG 1 1 , shown is generic computer device, and associated communications networks, devices, software and firmware may provide a platform for enabling one or more embodiments as described above. By way of example, FIG. 1 1 shows a generic computer device 1000 that may include a central processing unit ("CPU") 1002 connected to a storage unit 1004 and to a random access memory 1006. The CPU 1002 may process an operating system 1001 , application program 1003, and data 1023. The operating system 1001 , application program 1003, and data 1023 may be stored in storage unit 1004 and loaded into memory 1006, as may be required. Computer device 1000 may further include a graphics processing unit (GPU) 1022 which is operatively connected to CPU 1002 and to memory 1006 to offload intensive image processing calculations from CPU 1002 and run these calculations in parallel with CPU 1002. An operator 1007 may interact with the computer device 1000 using a video display 1008 connected by a video interface 1005, and various input/output devices such as a keyboard 1010, mouse 1012, and disk drive or solid state drive 1014 connected by an I/O interface 1009. In known manner, the mouse 1012 may be configured to control movement of a cursor in the video display 1008, and to operate various graphical user interface (GUI) controls appearing in the video display 1008 with a mouse button. The disk drive or solid state drive 1014 may be configured to accept computer readable media 1016. The computer device 1000 may form part of a network via a network interface 101 1 , allowing the computer device 1000 to communicate through wired or wireless communications with other suitably configured data processing systems (not shown). A sensing device or module, such as a digital camera, may comprise an image processor unit 1030 operatively connected to optical device driver 1032, and an optical sensing device 1034 (e.g. a CCD or CMOS sensor) receiving light through an optical lens 1036.

[0059] It will be appreciated that various amendments and modifications may be made to the illustrative embodiments described herein without departing from the scope of the invention, and that the examples provided in the present disclosure are not limiting. Rather, the scope of the invention is defined by the following claims which should be given their broadest interpretation consistent with the scope of the present disclosure.