Joint assembly
A joint assembly for a robot, comprising a housing connected with an output part. The housing comprising a housing wall and a strain wave gearing system. The strain wave gearing system comprising a wave generator, a flexspline, and a circular spline connected to the output part. The wave generator is rotated by a rotor shaft. The rotor shaft is driven by an electric motor comprising a rotor magnet and a stator. The rotor magnet being affixed to the rotor shaft. The joint assembly further comprises one or more sensors comprising one or more magnetic field sensors and one or more pole rings arranged to measure a position of the output part in relation to the housing.
1. A joint assembly for a robot, comprising:
a housing connected with an output part, the housing comprising a housing wall,
a strain wave gearing system comprising:
a wave generator,
a flexspline, and
a circular spline connected to the output part;
a rotor shaft configured to rotate the wave generator;
an electric motor configured to drive the rotor shaft and comprising a rotor magnet and a stator, the rotor magnet being affixed to the rotor shaft; and
sensors arranged to, in combination, determine a position of the output part in relation to the housing, each of said sensors having a magnetic field sensor and a pole ring, wherein one of said sensors is a first sensor configured to measure rotation of the output part in relation to the housing, and one of said sensors is a rotor sensor configured to measure rotation of the rotor shaft;
wherein the pole ring of the first sensor is divided into a number of sections, and wherein a gear ratio of the strain wave gearing system is not divisible to an integer by the number of sections.
2. The joint assembly according to claim 1 , wherein the number of sections are of equal size.
3. The joint assembly according to claim 2 , wherein the number of sections are three sections of 120° each.
4. The joint assembly according to claim 1 , wherein one of the sensors is a second sensor configured to measure rotation of the output part in relation to the housing.
5. The joint assembly according to claim 4 , wherein the housing comprises flexible members configured to facilitate an outer perimeter part of the housing angularly rotating in relation to an inner part of the housing.
6. The joint assembly according to claim 5 , wherein the first sensor is configured to measure the rotation of the output part in relation to the housing near the outer perimeter part of the housing, and the second sensor is configured to measure the rotation of the output part in relation to the housing near the inner part of the housing.
7. The joint assembly according to claim 5 , wherein the housing comprises longitudinal holes, and the first sensor and the second sensor are configured to measure the rotation of the output part in relation to the housing at opposite ends of the longitudinal holes.
8. The joint assembly according to claim 1 , wherein at least one of the pole rings comprises between 10 and 400 poles.
9. The joint assembly according to claim 1 , wherein at least one of the pole rings comprises between 30 and 300 poles.
10. The joint assembly according to claim 1 , wherein at least one of the pole rings comprises between 10 and 500 poles.
11. The joint assembly according to claim 1 , wherein at least one of the pole rings is a 50 mm. pole ring.
12. The joint assembly according to claim 1 , wherein at least one of the magnetic field sensors is positioned in the housing in a space different from that of the flexspline.
13. The joint assembly according to claim 1 , wherein the housing comprises one or more blind holes, and wherein at least one of the magnetic field sensors is positioned in one of said one or more blind holes.
14. The joint assembly according to claim 1 , wherein the flexspline is made of a ferromagnetic steel.
15. The joint assembly according to claim 1 , wherein the joint assembly comprises a planetary gear arranged between the rotor shaft and the wave generator.
16. The joint assembly according to claim 1 further comprising a rotor brake configured to stop or prevent relative movement between the rotor shaft and the flexspline.
17. The joint assembly according to claim 16 , wherein the rotor brake comprises a friction clutch or a friction brake for minimising impact on the joint assembly when the rotor brake brakes.
18. The joint assembly according to claim 16 , wherein the rotor brake is spring-loaded.
19. The joint assembly according to claim 16 , wherein a brake spring is made from a non-ferromagnetic material.
20. The joint assembly according to claim 1 further comprising an output brake configured to stop or prevent rotation of the output part.
21. The joint assembly according to claim 20 , wherein the output brake is configured to stop or prevent rotation of the output part even if the flexspline is broken.
22. A robotic arm comprising the joint assembly according to claim 1 .
23. A method for performing rotational movements, the method comprising:
providing the robotic arm of claim 22 ;
driving the electric motor to rotate the output part; and
measuring the position of the output part in relation to the housing.
24. A joint assembly for a robot, comprising:
a housing connected with an output part, the housing comprising a housing wall;
a strain wave gearing system comprising:
a wave generator,
a flexspline, and
a circular spline connected to the output part,
wherein the wave generator is configured to be rotated by a rotor shaft, the rotor shaft being configured to be driven by an electric motor comprising a rotor magnet and a stator, the rotor magnet being affixed to the rotor shaft, and wherein the joint assembly further comprises:
one or more sensors comprising magnetic field sensors and pole rings arranged to determine a position of the output part in relation to the housing; and
an output brake configured to stop or prevent rotation of the output part even if the flexspline is broken.