Actuator arrangement

1. An actuator comprising:

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

a first torque transfer device arranged to transfer torque from the drive shaft to a second shaft, the second shaft being rotatable about a second shaft axis parallel to and radially spaced from the drive shaft axis; and

an output torque transfer device arranged to transfer torque from the second shaft to the motor housing,

wherein:

when the motor housing is maintained in a fixed position, rotation of the drive shaft relative to the motor housing causes rotation of the position of the second shaft axis about the motor housing, or

when the position of the second shaft axis is maintained in a fixed position, rotation of the drive shaft relative to the motor housing causes rotation of the motor housing about the position of the second shaft axis.

2. The actuator of claim 1 , wherein:

when the motor housing is maintained in a fixed position, rotation of the drive shaft relative to the motor housing causes rotation of the position of the second shaft axis about the motor housing.

3. The actuator of claim 1 , wherein:

when the position of the second shaft axis is maintained in a fixed position, rotation of the drive shaft relative to the motor housing causes rotation of the motor housing relative to about the position of the second shaft axis.

4. The actuator of claim 1 , further comprising a second shaft mount, the second shaft mount being rotatably coupled to the motor housing, and arranged to support the second shaft.

5. The actuator of claim 1 , wherein at least one of the first torque transfer device and the output torque transfer device comprises a pulley system.

6. The actuator of claim 1 , wherein the first torque transfer device is arranged such that the torque provided to the second shaft is greater than the torque provided to the drive shaft.

7. The actuator of claim 1 , wherein the output torque transfer device is arranged such that the torque provided to the motor housing by the output torque transfer device is greater than the torque provided to the second shaft.

8. The actuator of claim 1 , further comprising an outer housing fixed to the motor housing, the outer housing enclosing at least one of the second shaft, the motor and the first torque transfer device and the output torque transfer device.

9. The actuator of claim 1 , wherein a torque ratio of the first and final torque transfer devices is substantially the same.

10. The actuator of claim 1 , wherein the second shaft and the motor housing have a relative rotational or orbital range of less than 180°.

11. The actuator of claim 1 , wherein an output of the actuator is provided at a member arranged to rotate about the drive shaft axis.

12. The actuator of claim 1 , wherein the second shaft overlaps the motor in a direction along the drive shaft axis.

13. The actuator of claim 1 , wherein a component of the first torque transfer device fixed to the second shaft overlaps the motor housing in a radial direction.

14. The actuator of claim 1 , wherein the output torque transfer device comprises a third shaft, a second torque transfer device arranged to transfer torque from the second shaft to the third shaft, and a third torque transfer device arranged to transfer torque from the third shaft to the motor housing.

15. The actuator of claim 1 , further comprising a plurality of encoders, each encoder arranged to measure a rotational position of the drive shaft, second shaft or motor housing relative to another of the motor housing or the second shaft mount.

16. The actuator of claim 1 , further comprising an electrical cable arranged to provide power to the motor from a location outside the actuator, the electrical cable extending at least partially around the drive shaft and/or the motor housing.

17. A robotic arm comprising a first member, a second member and a joint where the first and second members join,

wherein an actuator according to claim 1 is situated at the joint and configured to actuate the joint to move the first member relative to the second member.

18. An actuator comprising:

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

a first torque transfer device arranged to transfer torque from the drive shaft to a second shaft, the second shaft being rotatable about a second shaft axis spaced from the drive shaft axis; and

an output torque transfer device arranged to transfer torque from the second shaft to an output member, the output member being arranged to rotate about an output axis;

wherein the output axis is coaxial with the drive shaft axis, and

wherein the output member is fixedly attached relative to the stator of the motor.

19. The actuator of claim 18 , wherein the motor is arranged at least partially within the output member.

20. An actuator comprising:

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

a first torque transfer device arranged to transfer torque from the drive shaft to a second shaft, the second shaft being rotatable about a second shaft axis spaced from the drive shaft axis; and

an output torque transfer device arranged to transfer torque from the second shaft to an output member, the output member being arranged to rotate about an output axis;

wherein the motor is arranged at least partially within the output member, and

wherein:

(i) the output member is substantially annular,

(ii) the output member is a pulley, or

(iii) the stator of the motor is fixedly attached with respect to the output member.

21. The actuator of claim 20 , wherein the output member is substantially annular.

22. The actuator of claim 20 , wherein the output member is a pulley.

23. The actuator of claim 20 , wherein the stator of the motor is fixedly attached with respect to the output member.

24. An actuator comprising:

a motor having a housing, a stator, a rotor, and a drive shaft, the motor arranged to rotate the drive shaft relative to the housing about a drive shaft axis;

a first torque transfer device arranged to transfer torque from the drive shaft to a second shaft, the second shaft being rotatable about a second shaft axis spaced from the drive shaft axis; and

an output torque transfer device arranged to transfer torque from the second shaft to an output member, the output member being arranged to rotate about an output axis;

wherein the output member is fixedly attached relative to the stator of the motor.