Technical Field

[0001] The present disclosure relates, generally, to actuator assemblies and, particularly, to sealed actuator assemblies for a robotic manipulator.

Background

[0002] An actuator assembly includes an actuator which is driven by a drive source, such as an electric motor, to cause movement of a mechanism. For example, in robotics, a manipulator typically includes at least one pair of elongate sections which are pivotally connected to each other by an actuator assembly. Operating such an assembly controls relative movement of the sections.

[0003] Some robotic manipulators are hermetically sealed to prevent ingress of fluid from an operating environment. This allows the manipulator to be operated in environments where fluid, such as water or flammable gas, penetrating the manipulator would cause damage to the manipulator and/or present a fire/explosion hazard. Configuring a manipulator to be sealed allows operating the manipulator in physically challenging environments such as underwater, in space, and/or inside a nuclear reactor.

[0004] Sealed manipulators typically include a plurality of sealed actuator assemblies, for example, to enable rotational movement at joints between sections. Configuring such actuator assemblies to remain sealed throughout a defined service cycle often proves challenging. For example, these assemblies typically require a plurality of seals, any of which can degrade due to wear and tear, and fail consequently unsealing the manipulator. Also such assemblies typically include components which are mechanically interlocked, each interconnection being prone to corrosion which, if left untreated, can cause mechanical failure and unseal the manipulator. As such manipulators usually include multiple sealed actuator assemblies the likelihood of seal failure is proportionally increased by the number of assemblies in the manipulator. [0005] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims.

Summary

[0006] According to at least one disclosed embodiment there is provided a sealed actuator assembly for a robotic manipulator. The assembly includes: a drive stack including an electric motor; an output member configured to be drivingly coupled to the motor; a body defining a tub dimensioned to receive the drive stack; a cap configured to be releasably secured to the body to cover the tub, the cap defining an aperture dimensioned to allow the output member to extend through the cap to couple with the motor; a static seal configured to seal between the cap and the body; and a dynamic seal configured to seal between the output member and the cap.

[0007] The drive stack may define opposed ends, and the tub may define a first face arranged to support one end of the drive stack, and the cap may define a second face arranged to support the other end of the drive stack, and securing the cap to the body allows urging the first and second faces against the drive stack.

[0008] The cap may have a flange dimensioned to fit within the tub and the static seal be arranged about the flange such that securing the cap to the body compresses the static seal between the cap and the body.

[0009] The flange may define a first annular groove dimensioned to at least partially receive the static seal.

[0010] The flange and the tub each may define complementary threads configured to allow threadingly engaging the cap with the tub. [0011] The cap may define a second annular groove arranged about the aperture, the second annular groove dimensioned to at least partially receive the dynamic seal.

[0012] The drive stack may also include a gearbox, a PCB and at least one encoder.

[0013] The body may be configured as a first joint housing of the robotic manipulator, and the output member may be configured as a second joint housing of the robotic manipulator, and operating the motor causes relative rotation of the first and second joint housings.

[0014] According to at least one other disclosed embodiment there is provided a robotic manipulator including: a drive stack including an electric motor; an output member configured to be drivingly coupled to the motor; a body defining a tub dimensioned to receive the drive stack; a cap configured to be releasably secured to the body to cover the tub, the cap defining an aperture arranged, in use, to allow the output member to extend through the cap; a static seal configured to seal between the cap and the body; and a dynamic seal configured to seal between the output member and the cap.

[0015] In this embodiment the body may be configured as a first joint housing, and the output member may be configured as a second joint housing, and wherein the motor is operable to cause relative rotation of the first and second joint housings.

[0016] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0017] It will be appreciated that embodiments may comprise steps, features and/or integers disclosed herein or indicated in the specification of this application individually or collectively, and any and all combinations of two or more of said steps or features. Brief Description of Drawings

[0018] Embodiments will now be described by way of example only with reference to the accompany drawings in which:

[0019] Figure 1 is a perspective view of an actuator assembly configured as a joint of a robotic manipulator;

[0020] Figure 2 is an exploded perspective view of the actuator assembly shown in Fig. 1;

[0021] Figure 3 is an exploded perspective view of actuator assembly shown in the previous figures with one of the joint housings removed;

[0022] Figure 4 is an exploded section view of the actuator assembly shown in Fig. 3;

[0023] Figure 5 is a section view of the actuator assembly shown in Fig. 1; and

[0024] Figure 6 is a perspective view of a robotic manipulator embodying a plurality of the actuator assemblies shown in Figure 1

Description of Embodiments

[0025] In the drawings, reference numeral 10 generally designates a sealed actuator assembly 10 for a robotic manipulator 100 (Fig. 6). The assembly 10 includes a drive stack 12 including an electric motor 14, an output member 16 configured to be drivingly coupled to the motor 14, a body 18 defining a tub 20 dimensioned to receive the drive stack 12, a cap 22 configured to be releasably secured to the body 18 to cover the tub 20, the cap 22 defining an aperture 24 dimensioned to allow the output member 16 to extend through the cap 22 to couple with the motor 14, a static seal 26 configured to seal between the cap 22 and the body 18, and a dynamic seal 28 configured to seal between the output member 16 and the cap 22. [0026] Figures 1 to 5 illustrate the actuator assembly 10 configured as a joint for the robotic manipulator 100 and Figure 6 illustrates a plurality of the assemblies 10 assembled as component parts of the manipulator 100. In this embodiment the body 18 is configured as a first joint housing 30 and the output member 16 is configured as a second joint housing 32. The joint housings 30, 32 are configured to be rotatable relative to each other about an axis defined by the drive stack 12. Each joint housing 30, 32 is further configured to be securable to another component of the manipulator 100 such as a base 102, a limb section housing 104, a further joint housing 30, 32, or an end effector 106. In the illustrate embodiment each housing 30, 32 defines an opening 33 surrounded by a bayonet fitting 35 to allow engaging another component.

[0027] Best shown in Figs. 4 and 5, the drive stack 12 includes a plurality of components arranged layer-wise, one on top of another, to form a stack. Typically the drive stack 12 includes the motor 14, a printed circuit board (PCB), a gearbox 38 and at least one positional encoder.

[0028] In the embodiment illustrated in Figs. 1 to 5, the drive stack 12 includes the motor 14, the PCB (not shown) and a motor encoder 36 arranged within a stack shell 42. The motor encoder 36 is arranged adjacent the motor 14 rotor to allow measuring rotation of the motor 14. The shell 42 is fixed to the gearbox 38, in this embodiment in the form of a strain wave gear (also known as a Harmonic Drive). An output encoder (not shown) is secured relative to the gearbox 38 to allow measuring rotation of the first housing 30 with respect to the second housing 32.

[0029] The gearbox 38 surrounds a shaft cross bearing 44 which extends through the drive stack 12. The second joint housing 32 is securable to the shaft cross bearing 44, typically by one or more fasteners, such as bolts (not illustrated). Operation of the motor 14 causes the shaft cross bearing 44 to rotate consequently rotating the second joint housing 32.

[0030] Best shown in Fig. 5, the drive stack 12 defines opposed ends 50, 52. The tub 20 and the cap 22 are shaped to support each end 50, 52 and dimensioned such that securing the cap 22 to the first housing 30 clamps the drive stack 12 between the first housing 30 and the cap 22.

[0031] In the illustrated embodiment, the tub 20 defines a first face 54 on a first shoulder 56 arranged to support one end 52 of the drive stack 12, and the cap 22 defines a second face 58 on a second shoulder 60 arranged to support the other end 50 of the drive stack 12. The first face 54 and second face 58 substantially surround the axis of the drive stack 12 to support a substantial portion of a periphery of each end 50, 52. In other embodiments (not shown), the first face 54 and/or second face 58 is discontinuous, defined by a plurality of ribs or other projections within the tub 20 or cap 22.

[0032] The tub 20 is a blind-end recess defined by the first joint housing 30. The tub 20 defines an end wall 62 joined to a side-wall 64. The side-wall 64 terminates at a rim 66 to define an open end 68. A wiring conduit 69 extends through the side-wall 64 towards the opening 33. The conduit 69 allows cables (not illustrated) to be passed into the tub 20 to supply power and communicate data to/from the drive stack 12.

[0033] The cap 22 is shaped to cover the open end 68 of the tub 20 to inhibit fluid entering the tub 20. The cap 22 includes a flange 70 dimensioned to fit within the side- wall 64 of the tub 20. In the illustrated embodiment, each of the side-wall 64 and the flange 70 define complementary threads 75 to allow threadingly engaging the cap 22 with the tub 20. This arrangement allows the cap 22 to be progressively urged against the drive stack 12 to securely retain the drive stack 12 in the tub 20. In other embodiments (not shown), the cap 22 is releasably securable to the first joint housing 30 with an alternatively configured mechanism, such as a bayonet fitting or a lever closure.

[0034] A peripheral region 71 of the cap 22 is shaped to engage with a tool (not illustrated) to allow rotating the cap 22 relative to the first housing 30. In the illustrated embodiment the peripheral region 71 defines a plurality of notches 73 shaped to engage with a tool head specifically configured for the assembly 10. In other embodiments (not shown), the cap 22 is shaped to engage with a conventional tool fitting, such as a hex socket.

[0035] The static seal 26 is arranged about the flange 70 of the cap 22 to allow compressing the static seal 26 between the cap 22 and the first joint housing 30. In the illustrated embodiment the static seal 26 is in the form of an O-ring and the flange 70 defines a first annular groove 72 dimensioned to at least partially receive the seal 26 to allow arranging the seal 26 against the side-wall 64 of the tub 20 to inhibit fluid ingress.

[0036] The dynamic seal 28 is arranged about the aperture 28 of the cap 22 to allow compressing the dynamic seal 28 between the cap 22 and the second joint housing 32.

In the illustrated embodiment the dynamic seal 28 is in the form of an X-ring and the cap 22 defines a second annular groove 74 surrounding the aperture 28 and dimensioned to at least partially receive the seal 28 to allow arranging the seal 28 against the second joint housing 32 to inhibit fluid ingress whilst the second joint housing 32 moves relative to the first joint housing 30 and the cap 22.

[0037] Assembling the assembly 10 involves: arranging the second joint housing 32 to extend through the aperture 24 of the cap 22 to compress the dynamic seal 28; fixing the second joint housing 32 to the drive stack 12, typically with a plurality of fasteners (not illustrated); releasably securing the first joint housing 30 to a fixed position, such as in a jig (not illustrated), so that the open end 68 of the tub 20 is accessible; placing the drive stack 12 in the tub 20 so that the end 52 of the stack 12 abuts the first shoulder 56; and rotating the peripheral region 71 of the cap 22 so that the threads 75 engage to draw the cap 22 and first joint housing 20 together and compress the static seal 26. The assembly 10 is then sealed.

[0038] Maintaining the assembly 10 involves the above steps in reverse. This readily allows access to both seals 26, 28 for inspection and replacement. [0039] The arrangement of the drive stack 12 in a closed-end tub 20 means that the assembly 10 includes only two seals - the static seal 26 and the dynamic seal 28. This advantageously minimises the number of seals required to provide a rotatable actuator assembly which is fluid-impervious. This enhances reliability of the assembly 10 as leak-points are minimised. Furthermore, this arrangement consequently minimises the number of seal grooves required. As each seal groove is a high tolerance feature this enhances ease of manufacturing and further enhances reliability.

[0040] The assembly 10 includes a single mechanical interface - being between the cap 22 and the tub 20. This advantageously minimises corrosion prone regions. This further enhances reliability of the assembly 10.

[0041] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.