CN113286959A

CN113286959A - Compact actuator arrangement

Info

Publication number: CN113286959A
Application number: CN202080008557.3A
Authority: CN
Inventors: 詹姆斯·B·克拉森; 纳森·阿姆斯特朗
Original assignee: Genesis Advanced Technology Inc; Janice Robot Mobile Technology Co ltd
Current assignee: 1478021 British Columbia Co; Genesis Advanced Technology Inc
Priority date: 2019-01-16
Filing date: 2020-01-16
Publication date: 2021-08-20
Anticipated expiration: 2040-01-16
Also published as: KR20210113341A; WO2020148706A1; CA3122857A1; CN113286959B; EP3911876A1

Abstract

An actuator, comprising: a motor comprising a housing and a drive shaft, the motor being arranged to rotate the drive shaft relative to the housing about a drive shaft axis; a first torque transfer device comprising a first drive member on the drive shaft and a first driven member on the second shaft, the first drive member being arranged to transfer torque to the first driven member such that the first torque transfer device is arranged to transfer torque from the drive shaft to the second shaft, the second shaft being rotatable about a second shaft axis spaced from the drive shaft axis; and an output torque transfer device comprising an output drive member on the second shaft and an output driven member, the output drive member being arranged to transfer torque to the output driven member such that the output driven member rotates about an output axis; wherein the torque ratio of the output torque transmitting device is less than or equal to the torque ratio of the first torque transmitting device.

Description

Compact actuator arrangement

Technical Field

The present invention relates to an actuator and a robot arm comprising such an actuator.

Background

Many machines, particularly robots, rely on compact, lightweight actuators to move arms and other components. The movements often require a high level of precision and high torque, which is difficult to achieve without significantly increasing the size or weight of the actuator.

Known actuators typically comprise an electric motor and a gearbox arrangement for increasing the amount of torque transmitted from the electric motor to make it available and decreasing the output rotational speed of the drive shaft relative to the motor. Usually, the gearbox is designed and manufactured separately from the electric motor, which may have the disadvantageous disadvantage that the axial length of the overall arrangement of the actuator is too large.

Known actuators may also suffer from low efficiency or high levels of inertia, which may reduce the accuracy of the movement.

The present disclosure seeks to address at least some of the above problems.

Disclosure of Invention

According to a first aspect of the present invention, there is provided an actuator comprising: a motor comprising a housing and a drive shaft, the motor being arranged to rotate the drive shaft relative to the housing about a drive shaft axis; a first torque transfer device comprising a first drive member on the drive shaft and a first driven member on the second shaft, the first drive member being arranged to transfer torque to the first driven member such that the first torque transfer device is arranged to transfer torque from the drive shaft to the second shaft, the second shaft being rotatable about a second shaft axis spaced from the drive shaft axis; and an output torque transfer device comprising an output drive member on the second shaft and an output driven member, the output drive member being arranged to transfer torque to the output driven member such that the output driven member rotates about an output axis; wherein the torque ratio of the output torque transmitting device is less than or equal to the torque ratio of the first torque transmitting device.

By such an arrangement, a compact actuator arrangement is provided, given design constraints such as a minimum shaft diameter.

Depending on which components of the actuator are considered to be stationary, the actuator may be considered to operate by the motor housing being arranged to rotate about the drive shaft axis, or by the second shaft being arranged to rotate about the drive shaft axis. These two concepts are substantially similar, but may have an alternative portion that is fixed relative to the outer assembly and an alternative portion that serves as an output member. Thus, whether the second shaft axis and, correspondingly, the second shaft runs around the electric motor or whether the motor housing can rotate may be a matter of frame of reference. In either case, rotation of the motor housing relative to the position of the second shaft axis may be produced.

The torque transmitting devices described herein may be, but are not limited to, pulleys and gears, and the torque transmitting devices may include two gears on different shafts with teeth that interlock with each other or with an intermediate gear, or two pulleys on different shafts connected by at least one cable or belt. By using gears with different numbers of teeth or pulleys with different radii, the transmission of torque can keep the rotational speed and torque level constant or involve a certain degree of mechanical advantage. In some embodiments, non-toothed rollers may be used in a similar manner to toothed gears, where rollers of different radii or different diameters are used to produce the desired ratio of input torque and speed to output torque and speed.

The torque ratios of the torque transmitting devices or combinations of torque transmitting devices may alternatively be referred to as speed ratios, reduction ratios, or mechanical advantages. The torque ratio of a torque converter device is the ratio of the torque output by the device to the torque input by the device.

The torque ratio between the output of the motor and the output at the output member may be at least 12: 1. In other words, the output member may be arranged to rotate at a speed of one twelfth or less of the drive shaft of the motor.

It will be appreciated that a motor with a larger volume can be expected to have higher power. However, this must be balanced by the available space of the torque conversion device inside the actuator and outside the motor. The present inventors have recognized the following design constraints to provide a compact actuator with sufficient output torque and accuracy.

The first and second torque transmitting devices and the motor may be arranged within a cylindrical space having a diameter less than three times a diameter of the motor housing. The motor housing has a diameter of at least 40 mm. The cylindrical space has a diameter of 100mm or less. The axial length of the cylindrical space may be less than three times the axial length of the motor housing.

The actuator may include: a housing defining a cylindrical space; and an electric motor, the first torque transmitting device and the output torque transmitting device being positionable within the housing. By such an arrangement, the frangible portion of the arrangement may be protected by the housing. The housing may be substantially cylindrical.

The first driven member may overlap the output driven member in a direction viewed along the drive shaft axis and/or the second shaft axis. The sum of the radii of the output driven member and the first driven member may exceed the distance between the drive shaft axis and the second shaft axis. This may provide a more compact actuator with a high torque conversion ratio.

The second shaft may extend in a first direction from the first driven member to the output drive member, and the drive shaft may extend in a second direction opposite the first direction from the motor housing to the first drive member. This can be considered as a "fold" of the torque conversion device itself, thereby reducing the axial length of the actuator.

At least one of the first torque conversion device and the output torque conversion device may be a pulley-based system. Alternatively, both may be pulley-based. In the present context, the inventors have recognized that a pulley and cable and pulley and belt torque conversion system provides advantages over a gear system. Specifically, unlike a geared system, two pulleys of a pulley-based system do not need to be in contact. This allows the smaller of the two pulleys in such a system to be smaller than a gear system with some special restrictions on the position of the axis of rotation. Thus, a more compact arrangement with improved torque conversion may be provided.

The motor housing may be at least partially disposed within the output driven member. This may allow for a more compact arrangement.

The output drive member may be arranged within a cylindrical sector space defined by a cylindrical sector subtending the drive shaft axis and having an internal angle at the drive shaft axis of less than 100 °, optionally less than 60 °. This may allow the second shaft and the member fixed to the second shaft to be located within the member the actuator is arranged to move. Thus, the actuator can be integrated compactly in the robot arm.

The cylindrical sectors may be considered as sectors that are extruded along the drive shaft axis. The radius of the sector may not be taken into account as the internal angle at the drive shaft axis determines how the second shaft and the output drive member fit within the robotic arm member near the joint.

According to a second aspect of the present invention, there is provided an actuator comprising: a motor comprising a housing and a drive shaft, the motor being arranged to rotate the drive shaft relative to the housing about a drive shaft axis; a first torque transfer device comprising a first drive member on the drive shaft and a first driven member on the second shaft, the first drive member being arranged to transfer torque to the first driven member such that the first torque transfer device is arranged to transfer torque from the drive shaft to the second shaft, the second shaft being rotatable about a second shaft axis spaced from the drive shaft axis; an output torque transmitting device including an output drive member on a second shaft and an output driven member, the output drive member being arranged to transfer torque to the output driven member such that the output driven member rotates about an output axis; a first connecting flange fixed to the motor housing at an axial end portion of the motor housing opposite to an end portion of the motor housing from which the drive shaft extends; and a second connecting flange arranged such that the drive shaft is located between the second connecting flange and the motor housing, the second connecting flange being fixed to the motor housing via a cross member.

The cross member may be shaped as an extruded arc. It can also be considered as a curved sheet. This may provide good stiffness to the actuator while avoiding contact between the cross member and other components.

The arcuate extent of the cross member may be less than 180 °. This may allow the orbital movement of the second shaft without the cross member obstructing the first torque transmitting device.

According to a third aspect of the present invention, there is provided a robot joint comprising: a first member; a second member pivotably coupled to the first member; and an actuator according to the first or second aspect; wherein the actuator is arranged to rotate the second member relative to the first member.

According to a fourth aspect of the present invention, there is provided a robot joint comprising: a first member; a second member pivotably coupled to the first member; and an actuator, the actuator comprising: a motor comprising a housing and a drive shaft, the motor being arranged to rotate the drive shaft relative to the housing about a drive shaft axis; a first torque transfer device comprising a first drive member on the drive shaft and a first driven member on the second shaft, the first drive member being arranged to transfer torque to the first driven member such that the first torque transfer device is arranged to transfer torque from the drive shaft to the second shaft, the second shaft being rotatable about a second shaft axis spaced from the drive shaft axis; and an output torque transfer device comprising an output drive member on the second shaft and an output driven member, the output drive member being arranged to transfer torque to the output driven member such that the output driven member rotates about an output axis; wherein the actuator is arranged to rotate the first member relative to the second member, and wherein the second shaft is supported by the first member.

By using the first member to support the second shaft, the distance between the second shaft and the drive shaft may be increased, allowing for a larger motor and a larger torque ratio to be provided.

The robot joint may further comprise a third member arranged to rotate with the first member relative to the second member, the first and third members being arranged to support the second shaft.

The robotic joint may further comprise a second cross member arranged to couple the first and third members to each other to provide further support to a second axis. The second cross member may be arranged to prevent separation of the first and second members in a direction parallel to the drive axis.

The actuator within the robot joint of the fourth aspect may be an actuator according to the first or second aspect.

In the third or fourth aspect, the first member may be arranged to pivot relative to the second member about the drive shaft axis.

Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic view of an actuator according to the present disclosure;

FIG. 2 illustrates a perspective view of two torque transmitting devices used in an actuator according to the present disclosure;

FIG. 3 illustrates a cross-section of an actuator according to the present disclosure;

FIG. 4 illustrates a cross-section of an actuator according to the present disclosure;

FIG. 5 illustrates a perspective view of an actuator according to the present disclosure;

FIG. 6 illustrates a cable used in an actuator according to the present disclosure;

FIG. 7 illustrates a schematic diagram of a torque transmitting device used in an alternative actuator according to the present disclosure;

FIG. 8 illustrates a robotic arm according to the present disclosure;

FIG. 9 illustrates a general view of selected parts of an alternative actuator assembly;

FIG. 10 shows a general view of a robotic joint incorporating an alternative actuator assembly;

FIG. 11 shows a robotic arm including an alternative actuator assembly;

FIG. 12 shows a pulley connected to a cable arrangement;

FIG. 13 shows a pulley and cable arrangement with one cable and connector removed;

FIG. 14 shows a cross-sectional view of the connector; and figure 15 shows a top view of the connector.

Detailed Description

Fig. 1 shows a schematic view of an actuator 10 according to the present disclosure. The actuator has an electric motor 100, the electric motor 100 having a stator 104 and a rotor 106, the stator 104 and the rotor 106 being arranged to generate a torque therebetween. The stator 104 is fixed to a motor housing 102, and the motor housing 102 surrounds the motor 100. The rotor 106 is fixed to a drive shaft 108, the drive shaft 108 extending from the housing 102, and the rotor 106 and the drive shaft 108 are arranged to rotate relative to the stator 104 and the motor housing 102 about a drive shaft axis a1 due to the torque generated within the motor 100.

The drive shaft 108 is coupled to a first torque transmitting device 200, specifically to a first pulley 202 of the torque transmitting device 200, which first pulley 202 may also be referred to as a first drive member. The first pulley 202 is coupled to the second pulley 204 via at least one cable 206, the second pulley 204 may be referred to as a first driven member, and the cable 206 may be fixed to the first pulley 202 and/or the second pulley 204, and/or radially pass through at least one of the

pulleys

202, 204. The second pulley 204 is fixed to a second shaft 208, the second shaft 208 being rotatable about a second shaft axis a2 and being supported by a second shaft mount 210. The second shaft mount 210 is rotatably mounted to the motor housing 102 and/or the drive shaft 108 for rotation relative to the motor housing 102 about a drive shaft axis a1 and thereby supports the second shaft 208 such that the second shaft 208 can encircle the motor 100, the second shaft axis a2 encircling the motor 100 with the second shaft 208.

The actuator 10 further includes a second output torque transfer device 300, the second torque transfer device 300 having a third pulley 302 (which may be referred to as an output drive member) and a fourth pulley 304 (which may be referred to as an output driven member), the third pulley 302 being fixed to the second shaft, the fourth pulley 304 being fixed to the motor housing 102 and being an integral part of the motor housing 102. The fourth pulley 304 may thus surround the motor housing 102 and the stator 104. Third pulley 302 and fourth pulley 304 are coupled via cable 306, where cable 306 may also be two or four cables.

With this arrangement, the torque generated by the motor 100 is arranged to rotate the second shaft mount 210 while the motor housing 102 remains stationary such that the second shaft axis a2 and the second shaft 208 encircle the motor 100. Alternatively, with the second shaft mount 210 held stationary, the motor housing 102 and the fourth pulley 304 may rotate.

To secure a portion of the actuator 10 in a stationary state and/or to obtain an output torque from the actuator 10, a fixing plate 218 is provided, the fixing plate 218 being fixed to the second shaft mount 210, and a motor output member 110 is provided, the motor output member 110 being fixed to the motor housing 102. Both the fixed plate 218 and the motor output member 110 may be fixed to external components, and the relative rotation of the motor housing 102 or the second shaft mount 210 may be a simple frame of reference issue, and is determined by which external components are considered fixed and which are considered movable. It will be appreciated that the actuator 10 as a whole may be fixed to, or form part of, a movable member or vehicle and therefore may not be fixed in an absolute sense.

In addition, fig. 1 also shows optional components. These components include bearings. The bearings shown are exemplary and some of the bearings may be omitted or moved. There may be a motor housing bearing 112 around the motor housing 102 and between the motor housing 102 and the second shaft mount 210. There may also be a first drive shaft bearing 114 and a second drive shaft bearing 118 between the drive shaft and the second shaft mount 210. Second shaft 208 may be supported on second shaft mount 210 by first bearing 212, second bearing 214, and third bearing 216. The bearings may be arranged such that second bearing 214 and third bearing 216 are disposed on either side of third pulley 302, such that second shaft 208 is supported on both sides of third pulley 302.

The actuator 10 may also comprise a plurality of encoders arranged to determine the relative rotational position of the components. The first encoder 402 may measure the relative angular position of the drive shaft 108 with respect to the second shaft mount 210, the second encoder 404 may measure the relative position of the second pulley 204, and thus the second shaft 208 with respect to the second shaft mount 210 (or may directly measure the position of the second shaft 208 with respect to the second shaft mount 210), and the third encoder 406 may measure the position of the motor housing 102 with respect to the second shaft mount 210.

By measuring the relative rotational positions of the drive shaft, the motor housing and the

second shaft

108, 208, 102, the strain in the torque transfer device can be determined. In particular, the strain in the

cable

206, 306 between the pulleys of the torque-transmitting

devices

200, 300 can be determined (it can be assumed that the strain in the solid stationary parts of the torque-transmitting devices, i.e. the pulleys and the shaft, is negligible), so that the torque in the actuator 10 can be determined. Over time, observation of the encoder readings may also indicate creep in the cable and may indicate wear.

In some arrangements, only two encoders, such as the first encoder 402 and the second encoder 404, may be used, as only the strain in the first cable 206 may be sufficient to determine the torque transmitted by the actuator 10.

The cable used may be formed of Kevlar (Kevlar) since Kevlar may have a tensile stress that is particularly easy to determine for a given strain and may have sufficient strength to provide the required torque from the actuator. The cables 206a, 206b in the first torque-transmitting device 200 may carry less tension than the cables 306a, 306b of the second torque-transmitting device 300. Thus, the cables 206a, 206b of the first torque-transmitting device 200 may be thinner, or have a smaller diameter or cross-section, than the cables 306a, 306b of the second torque-transmitting device 300.

Fig. 2 shows a first torque transmitting device 200 and a second torque transmitting device 300 of the actuator 10, with other components removed for clarity. It is understood that the motor 100 may be located within the fourth pulley 304, with the drive shaft 108 extending from the motor 100. It can also be seen that the first pulley 208 may be formed internally with the drive shaft 108 and may include a helical groove formed on an outer surface of the drive shaft 108. Two cables 206a, 206b are wound on the first pulley 202 and within the helical groove, and may be wound as follows: as the first pulley 202 rotates about the drive shaft axis a1, the first cable 206a is further wound around the first pulley 202 and the second cable 206b is wound out of the first pulley 202. The two cables 206a, 206b may be wound as follows: terminating at opposite ends of first pulley 202, or extending radially through first pulley 202 and meeting within first pulley 202. The cables 206a, 206b are also wound around the second pulley 204 and may be located in helical grooves of the second pulley 204. The two cables 206a, 206b may be separate portions of a single cable engaged at or within the first pulley 202 or the second pulley 204.

The two cables 206a, 206b may be parallel in the region where they extend between the first pulley 202 and the second pulley 204. This may reduce the likelihood of the two cables 206a, 206b contacting or interfering with each other during operation of the actuator 10. With this arrangement, the first pulley 202 and the second pulley 204 will be arranged to rotate in the same direction.

The second pulley 204 is connected to a second shaft 208, which second shaft 208 is also connected to a third pulley 302, which third pulley 302 forms part of a second torque-transmitting mechanism 300. The diameters of the second pulley 204 and the third pulley 302 may be substantially different, and their diameters may have ratios consistent with the mechanical advantage of each individual

torque transmitting device

200, 300. Specifically, the radius of second pulley 204 may be about five times that of first pulley 202, and the radius of fourth pulley 304 may be about five times that of third pulley 302. Thus, to achieve a compact arrangement, the radius of the second pulley 204 is about five times that of the third pulley 302. Numbers other than five may be used, with the principle that the ratio of radii between first pulley 202 to second pulley 204 and third pulley 302 to fourth pulley 304 remains substantially the same.

Third pulley 302 may be coupled to fourth pulley 304 via four cables, of which only two 306a, 306b are shown. Two parallel cables may be wound on the third pulley 302 in a staggered helix, since one cable is much larger in diameter, requiring more bending stress to be applied to the cable.

The four cables between third pulley 302 and fourth pulley 304 may be parallel in the area where they extend between third pulley 302 and fourth pulley 304. This may reduce the likelihood of the cables contacting or interfering with each other during operation of the actuator 10. With this arrangement, third pulley 302 and fourth pulley 304 will be arranged to rotate in the same direction.

Fig. 3 shows a detailed cross-section of the actuator 10, illustrating the shape of the second shaft mount 210. The second shaft mount 210 may be substantially annular or semi-annular and may include a cross-member disposed generally parallel to the drive shaft axis a1 and the second shaft axis a2, and generally diametrically opposite the second shaft axis a2 such that the drive shaft axis a1 is located between the cross-member and the second shaft axis a 2.

Also visible in fig. 3 is a cable 500 extending through the actuator 10. A first end 502 of the cable 500 is located at an axial end of the actuator 10 near the motor 100, and a second end 506 of the cable 500 is adjacent the fixed plate 218. The intermediate end 504 of the cable 500 may be the end of the cable 500 within the actuator 10, and the intermediate end 504 may convey power to the motor 100 and/or information from the encoder to the outside of the actuator 10. The cable 500 may also have a loop portion 508, the loop portion 508 may extend around the motor housing 102, and the loop (shown in full in fig. 6) may move as the actuator rotates and move the first end 502 relative to the second end 506. Also visible in fig. 3 is a thin cross-section of the cable 500, wherein the cross-section is elongated in a direction along the drive shaft axis a 1. This helps to form the loop portion 508. Thus, the cross-section of cable 500 is elongated in a direction along actuator axis a1, and has a thinner cross-section in a direction perpendicular to actuator axis a1 (i.e., a radial direction).

Fig. 4 shows an actuator 10 comprising an outer housing 600. As can be seen, the outer housing 600 is coupled to the motor housing 102 via the motor housing output member 110. The outer housing 600 also has a central aperture at the opposite end of the motor 100 through which the fixed plate 218 coupled to the second shaft mount is accessible. It can also be seen that the cable 500 extends from the outer housing 600 in both axial directions.

The outer housing 600 is substantially cylindrical with curved side surfaces and two axial end surfaces, thereby substantially enclosing all other components of the actuator 10, including the drive shaft 108, the motor 100, the first and second

torque transmitting devices

200, 300 and all components thereof.

As can be seen from fig. 5, the outer housing 600 is formed by a first part 600a and a second part 600b, both the first part 600a and the second part 600b being substantially cylindrical and both being axially separable. By forming the outer housing 600 from two such components, the housing can be more easily built around the actuator 10.

The outer housing 600 may have a length of 100mm and a diameter of 100 mm. Preferably, the longest dimension of the outer housing 600 is less than 150 mm. An outer housing 600 surrounds the motor and torque transmitting devices. By providing a compact cylindrical outer housing 600, the actuator may provide an enclosure as a whole suitable for use within a humanoid robot.

There may be sufficient space within the outer housing 600 near the motor 100 to provide a brake (not shown). The brake may be arranged to provide a braking force to the drive shaft 108 so as to be positioned around the drive shaft 108 on the opposite side of the motor 100 to the first pulley 202. Accordingly, the drive shaft 108 may extend through the motor 100 and may protrude from the motor 100 in two opposite directions.

The following are disclosed dimensions of three specific examples of actuator arrangements, each having a housing with a diameter of 100 mm. The smaller pulley diameter in each torque transmitting device was 10 mm.

In a first example, the motor is 40mm in diameter and the torque ratios of the two torque transmitting devices are both 4: 1.

In a second example, the motor is 50mm in diameter and the torque ratio of the first torque transmitting device is 3:1 and the torque ratio of the output torque transmitting device is 5: 1.

In a third example, the motor is 60mm in diameter and the torque ratio of the first torque transmitting device is 2:1 and the torque ratio of the output torque transmitting device is 6: 1.

Fig. 6 shows the entire extent of the cable 500 arranged to extend through the actuator 10, including a 180 degree loop portion 508, which loop portion 508 may move with rotation of the actuator 10 to avoid stretching and potential cable damage.

Fig. 7 shows an alternative pulley arrangement 700. The arrangement is powered by an electric motor 702, only an end view of the motor 702 is visible, and the motor 702 is arranged to rotate a drive shaft and pulley 704. The drive shaft and first pulley 704 are coupled to a second pulley 708 via a first cable or belt 706, the second pulley 708 being on a shaft having a third pulley 710, the third pulley 710 being coupled to a fourth pulley 714 via a second cable or belt 712. The fourth pulley 714 is coupled to a fifth pulley 716 via a shaft, the fifth pulley 716 is coupled to a sixth pulley 720 via a cable or belt 718, the sixth pulley 720 is coupled to a seventh pulley 722 via a shaft, the seventh pulley 722 is coupled to a motor housing comprising a final pulley 726 by an additional cable or belt 724.

The arrangement shown in figure 7 may be combined with a substantially similar actuator as described above, but with the need to incorporate additional pulleys and shafts to increase the mechanical advantage obtainable.

It should be understood that although an arrangement having one second shaft and three second shafts is shown, an arrangement having two shafts arranged remote from the motor or four shafts arranged remote from the motor may be used.

Fig. 8 shows a robotic arm 800. The robotic arm 800 has a vertical axis actuator 802, which vertical axis actuator 802 is fixed to the horizontal base B, and a shoulder joint 804, which shoulder joint 804 is coupled to the vertical axis actuator 802 and arranged to move a first member 806 (which may also be referred to as an upper arm 806). The upper arm 806 is coupled to a second member 810, which second member 810 may also be referred to as a lower arm 810 or forearm 810. The upper arm 806 is coupled to a forearm 810 at an elbow joint 808, and there is an end effector 812 at an end of the forearm 810 opposite the elbow joint 808.

The actuators described above may be placed at the elbow joint 808 or shoulder joint 804, and the second shaft mount 210 and fixation plate 218 may be suitably fixed to any of the vertical actuator 802, the upper arm 806, or the lower arm 810.

Fig. 9 shows an alternative actuator 850. The actuator 850 includes a motor 852 having a housing 853 and a drive shaft 854 extending from the housing 853. The motor 852 is arranged to rotate the drive shaft 854 relative to the housing 853 about a drive shaft axis a 3. The drive shaft 854 may also function as a pulley or be fixed to a pulley to drive a cable or belt to rotate the second pulley 856.

The second pulley 856 is supported on a second shaft 853, which second shaft 853 is arranged to rotate about a second shaft axis a4 spaced from the drive shaft axis A3. The second shaft 853 also has a third pulley 857, which third pulley 857 is arranged to drive a belt or cable that is fixed to or otherwise coupled to a fourth pulley 860. Motor housing 853 is located within fourth pulley 860, or is fixed to fourth pulley 860, or is integrated with fourth pulley 860.

It should be appreciated that the above-described aspects of the alternative actuator 850 are substantially similar to the corresponding aspects of the previously described actuator 10. Accordingly, the alternative actuator 850 may also share other features of the actuator 10 that are not explicitly described in connection with the alternative actuator 850.

Fig. 10 shows how an alternative actuator 850 is incorporated into a robotic joint 880. The robotic joint 880 is arranged to pivot the two members relative to each other about the drive shaft axis a 3.

As shown in fig. 10, the second shaft 853 is arranged to be supported by the

outer members

884a, 884 b. Thus, the second shaft 853 has rounded

ends

872a, 872b, which rounded ends 872a, 872b may further comprise bearings arranged to be received in respective bores of the

outer members

884a, 884 b.

The

outer members

884a, 884b are coupled to face

flanges

868a, 868b, which may also be referred to as connection flanges, and each face flange has a

bearing surface

867a, 867b, which bearing

surfaces

867a, 867b are centered on a drive shaft axis A3, and the

outer members

884a, 884b are thereby arranged to rotate about a drive shaft axis A3.

The

face flanges

868a, 868b have bolt holes to allow them to be coupled to additional external parts. The

face flanges

868a, 868b also serve to provide resilient support for the

respective bearing surfaces

867a, 867 b.

The first face flange 868a is coupled to the motor housing 853 via a cross member 870. The cross member 870 has the shape of an annular sector or extruded arc and extends partially around the drive shaft 854. By having this shape, the cross member 870 may provide good strength to the actuator 850. The portion of the actuator coupled to the cross member 870 at the end opposite the motor housing 853 may also support the drive shaft 854, thereby increasing the stiffness of the drive shaft 854.

The second bearing surface 867b is coupled to the motor housing 853 at an end opposite the drive shaft 854. The second bearing surface 867b may be directly secured to the motor housing 853.

The

outer members

884a, 884b are connected via a second cross member 886, which may increase the structural rigidity of the joint arrangement 880. The cross member 886 may also prevent the

outer members

884a, 884b from separating. The outer member may be part of, or affixed to, or integrated with the robotic arm member, such as the robotic arm 800 shown in fig. 8.

Adjacent members of the robotic arm may be fixed to or integrated with two further

outer members

882a, 882 b. A first of the additional outer members 882a is secured between cross member 870 or cross member 870 and first face flange 868 a. A second of the additional outer members 882b is secured to the motor housing 853.

As shown in fig. 10, the second shaft 853 may be supported within a member of the robotic arm within which the actuator 850 is located. By increasing the separation distance between the drive shaft axis A3 and the second shaft axis a4, larger pulleys and/or larger motors may be used, and thus an increase in the torque provided by the actuator 850 may be achieved without increasing the size of the joint.

In a first example of an alternative actuator, the motor is 60mm in diameter and the torque ratio of the first torque transmitting device is 4:1 and the torque ratio of the output torque transmitting device is 6: 1. The smaller pulley diameter in each torque transmitting device was 10 mm.

In a second example of an alternative actuator, the motor is 90mm in diameter and the torque ratio of the first torque transmitting device is 4:1 and the torque ratio of the output torque transmitting device is 9: 1. The smaller pulley diameter in each torque transmitting device was 10 mm.

Improved torque conversion and motor size may be achieved because the spacing between the drive shaft axis and the second shaft axis allows the second shaft axis to be supported by the outer member.

Fig. 11 shows a robotic arm 890 including an alternative actuator 850 and mechanical joint 880. The robotic arm has a first member 892 (lower arm) and a second member 894 (upper arm). As can be seen in fig. 11, the envelope within which the actuator 850 resides is comfortably positioned within the elbow joint, and the

outer members

882, 884 can be placed along the first member 892 and the second member 894.

Fig. 12 shows an inverted view of the fourth pulley 304, showing how the cable portion is connected to the second pulley 304 via the connection 900.

As can be seen in fig. 12, the connector 900 is substantially curved, has a similar curvature to the outer surface of the fourth pulley 304, and has

cable portions

912, 914 extending therefrom, the

cable portions

912, 914 being located between the body of the connector 900 and the second pulley 304, and the

cable portions

912, 914 being connected to the connector 900 at fixing

points

902, 906, which fixing points 902, 906 are located opposite the end of the connector 500 from which the

cable portions

912, 914 extend from the connector 500.

It should be understood that the cable portion 912 may be the same cable portion as the first and second cable portions 306A, 306B shown in fig. 2.

Figure 13 shows fourth pulley 304 with one connector 900 removed, exposing a receiving portion 1000 for receiving connector 900. The receiving portion 1000 has two

helical grooves

1004, 1006 for receiving a first cable portion 912 and a second cable portion 914, and a receiving tooth 1002 for engaging with a corresponding tooth of the connector 900.

Fig. 14 shows a cross-sectional view of the connector 900 with a portion removed. Thus, it can be seen that the cable portion 912 extends from the first fixing point 902 along the length of the connector. The connector 900 also includes a main body 920, the main body 922 being a substantially flat curved portion radially outward of the cable portion 912 and having a toothed portion 522 proximate a radially inward side of the cable portion 912.

The toothed portion 922 includes teeth 924 each having an engagement surface 926, the engagement surface 526 facing in a first direction away from the first fixed point 902 and substantially perpendicular to the body portion 920 and facing the second fixed point 904. Each tooth also has an inclined surface 928. the structure of the inclined surface 926 supports the engagement surface 930 and makes an angle of 20 to 60 degrees with the body portion 920 and the curved surface 930 joining the engagement surface 926 and the inclined surface 928. Each tooth 924 may be solid and defined by an engagement surface 926, an inclined surface 928, and a curved surface 930, and may extend away from the body portion 920.

Fig. 15 gives a top view of the connector 900 showing two

parallel cable portions

912, 914 and a toothed portion 922 between the cables. A second cable portion 914 is also secured to the connection 900 at two securing

points

906, 908, and a toothed portion 922 is located between the securing

points

902, 904, 906, 908. By providing such a symmetrical arrangement, the stresses on the connection can be more equalized and the bending forces on the teeth can be reduced.

The connector 900 may be formed by a molding process (optionally an injection molding process) and may be molded around the

cable portions

912, 914. The

cable portions

912, 914 may be placed in a mold and maintained in tension as the plastic is introduced into the mold, the plastic may diffuse through the fibers of the cable. By molding the connector in this manner, a more consistent tension can be created along the cable. As a result, the connector 900 may develop a degree of residual stress that manifests as tensile stress in each of the

cable portions

912, 914 and compressive stress in the body portion 920.

Excess cable portions may protrude from the mold in two directions (i.e., from the securing points 902, 906), and these cable portions may be used to secure the connector 900 to the second pulley 304 and subsequently removed. Portions of excess cable (not shown) may extend away from the anchor points 902, 906 and may be held in tension to resiliently couple the connector 900 to the pulley 304.

The following clauses provide further disclosure:

A. a connector for connecting a cable to a pulley, comprising:

a toothed portion having a body and a plurality of teeth extending from the body, each of the teeth having an engagement surface facing in a first direction; and

a cable portion extending along the toothed portion and secured thereto at a first securing point, the cable portion extending away from the first securing point and in a first direction along the toothed portion.

B. The connector of clause a, wherein the cable portion is secured to the toothed portion at a second fixed point, a plurality of the teeth being located between the first fixed point and the second fixed point.

C. The connector of clause a or B, wherein the cable portion is a first cable portion, and

wherein the connector further comprises a second cable portion secured to the toothed portion at a third securing point, the cable portion being remote from the third securing point and extending along the toothed portion in a first direction substantially parallel to the first cable portion.

D. The connector according to clause C, wherein the second cable portion is fixed to a toothed portion at a fourth fixed point, a plurality of the teeth being located between the third fixed point and the fourth fixed point.

E. The connecting member according to clause C or D, wherein a plurality of the teeth are located between the first cable part and the second cable part.

F. The connection piece according to any of the preceding clauses, wherein the first cable part and/or the second cable part terminates at a first fixing point and/or a third fixing point, respectively.

G. The joint of any of the preceding clauses wherein the toothed portion is curved.

H. The connection according to any of the preceding clauses wherein the toothed portion is less flexible than the cable portion.

I. The connector of any of the preceding clauses wherein each engagement surface is substantially perpendicular to the body.

J. A connection piece according to any of the preceding clauses, wherein the engagement surfaces of the teeth are perpendicular to and arranged along an arc.

K. A connection piece as claimed in any of the preceding clauses, wherein the teeth are substantially triangular, each tooth having an inclined face extending between the engagement surface and the body.

L. the connector of any of the preceding clauses wherein the inclined face intersects the body at an angle between 10 ° and 60 °.

M. the coupling according to clause K or L, wherein each of the teeth has a curved surface where the inclined surface intersects the engagement surface.

N. a pulley having a cylindrical surface with a receiving portion having a toothed recess arranged to receive a connecting element according to any of the preceding clauses.

O. the pulley of clause N, further comprising a helical groove arranged to receive a cable portion.

P. a pulley and cable system comprising the pulley of clause N or O and the connecting member of any of clauses a to M.

A method of making a connection, said method comprising:

providing a mold for forming the connector portion;

inserting a cable portion through at least one wall of the mold; and

the connector part is moulded around the cable part while the cable part is kept under tension in the mould, so that the connector part creates tensile residual stresses in the cable around the cable.

R. the method of clause Q, wherein the cable portion extends through the connector portion such that the cable portion extends away from the connector portion in two directions.

S. the method according to clause Q or R, wherein the material for forming the connector part is diffused through the fibers of the cable part.

T. the method according to clause Q, R or S, wherein the method forms a connector according to any one of clauses a to M.

U. a method of constructing the pulley and cable system of clause P, comprising:

holding an excess cable portion extending from the first or third fixation point away from the connector portion;

moving the connector into engagement with the receiving portion while applying tension to the excess cable portion; and

the excess cable portion is removed after the connector is engaged with the receiving portion.

Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. An actuator, comprising:

a motor comprising a housing and a drive shaft, the motor being arranged to rotate the drive shaft relative to the housing about a drive shaft axis; a first torque transfer device including a first drive member on the drive shaft and a first driven member on a second shaft, the first drive member being arranged to transfer torque to the first driven member such that the first torque transfer device is arranged to transfer torque from the drive shaft to the second shaft, the second shaft being rotatable about a second shaft axis spaced from the drive shaft axis; and

an output torque transmitting device including an output drive member on the second shaft and an output driven member, the output drive member being arranged to transfer torque to the output driven member such that the output driven member rotates about an output axis;

wherein the torque ratio of the output torque transmitting device is less than or equal to the torque ratio of the first torque transmitting device.

2. The torque converter as recited in claim 1 wherein a torque ratio between an output of said motor and an output of said output member is at least 12: 1.

3. Torque converter according to claim 1 or 2, characterized in that the housing of the electric motor has a diameter of at least 40 mm.

4. The torque converter according to any of the preceding claims, wherein the first and second torque transmitting devices and the motor are arranged within a cylindrical space having a diameter less than three times a diameter of a housing of the motor, optionally wherein the cylindrical space has a diameter of 100mm or less.

5. The actuator of claim 4, wherein the cylindrical space has an axial length less than three times an axial length of a housing of the motor.

6. An actuator according to claim 4 or 5, wherein the actuator comprises a housing defining the cylindrical space, and wherein the electric motor, the first torque transmitting means and the second torque transmitting means are located within the housing of the actuator.

7. An actuator according to any preceding claim, wherein the first driven member overlaps the output driven member as viewed along the drive shaft axis and/or the second shaft axis.

8. An actuator according to any preceding claim, wherein the second shaft extends in a first direction from the first driven member to the output drive member, and wherein the drive shaft extends in a second direction opposite the first direction from a housing of the motor to the first drive member.

9. An actuator according to any preceding claim, wherein the housing of the motor is at least partially disposed within the output driven member.

10. An actuator according to any preceding claim, wherein the output drive member is arranged within a cylindrical sector space defined by a cylindrical sector subtending the drive shaft axis and having an internal angle at the drive shaft axis of less than 100 °, optionally less than 60 °.

11. An actuator according to any preceding claim, wherein at least one of the first torque conversion means and the output torque conversion means is a pulley based system.

12. An actuator according to any preceding claim, wherein the output driven member is fixed to a housing of the motor.

13. An actuator, comprising:

a motor comprising a housing and a drive shaft, the motor being arranged to rotate the drive shaft relative to the housing about a drive shaft axis;

a first torque transfer device including a first drive member on the drive shaft and a first driven member on a second shaft, the first drive member being arranged to transfer torque to the first driven member such that the first torque transfer device is arranged to transfer torque from the drive shaft to a second shaft rotatable about a second shaft axis spaced from the drive shaft axis;

a first connecting flange fixed to a housing of the motor at an axial end portion of the housing of the motor, the axial end portion being opposite to an end portion of the motor housing from which the drive shaft extends; and

a second connecting flange arranged such that the drive shaft is located between the second connecting flange and a housing of the motor, the second connecting flange being fixed to the housing of the motor via a cross member.

14. The actuator of claim 13, wherein the cross member is shaped as an extruded arc.

15. The actuator of claim 14 wherein said arc has an arc extent of less than 180 °.

16. A robotic joint, comprising: a first member;

a second member pivotably coupled to the first member; and

an actuator according to any of the preceding claims;

wherein the actuator is arranged to rotate the second member relative to the first member.

17. A robotic joint, comprising:

a first member;

a second member pivotably coupled to the first member; and

an actuator, the actuator comprising:

a first torque transfer device including a first drive member on the drive shaft and a first driven member on a second shaft, the first drive member being arranged to transfer torque to the first driven member such that the first torque transfer device is arranged to transfer torque from the drive shaft to the second shaft, the second shaft being rotatable about a second shaft axis spaced from the drive shaft axis; and

wherein the actuator is arranged to rotate the first member relative to the second member, and wherein the second shaft is supported by the first member.

18. The robotic joint of claim 17, further comprising a third member arranged to rotate with the first member relative to the second member, the first and third members arranged to support the second shaft.

19. A robotic joint as claimed in claim 17 or 18, further comprising a second cross member arranged to couple the first and third members to each other to provide further support to the second shaft.

20. A robot joint according to claim 17, 18 or 19, wherein the actuator is an actuator according to any of claims 1-15.

21. A robot joint according to any of claims 16-20, wherein the first member is arranged to pivot relative to the second member about the drive shaft axis.