High performance differential actuator for robotic interaction tasks
The mechanical differential actuator according to the present invention comprises a mechanical differential having three mechanicals ports. A first transducer with a low impedance is coupled to a first port, a second transducer with a high impedance is coupled to a second port, and the mechanical load is coupled to the third port. The mechanical differential actuator enables controlling a force and a speed at a load coupled thereto through a known relation between the force and the speed. Moreover, the mechanical differential actuator presents a compact structure enabling the transfer of a large force relative to its volume.
1. A mechanical differential actuator for interacting with a mechanical load comprising:
a first transducer;
a second transducer; and
a mechanical differential having three interaction ports, including a first interaction port coupled to the first transducer, a second interaction port coupled to the second transducer, and a third interaction port coupled to the load;
wherein:
the mechanical differential actuator is characterized by an equivalent impedance Z eq ;
the first transducer is characterized by a first mechanical impedance Z 1 ;
the second transducer is characterized by a second mechanical impedance Z 2 ; and
the second mechanical impedance Z 2 is sufficiently large compared to the first mechanical impedance Z 1 that the second mechanical impedance Z 2 does not influence significantly the equivalent mechanical impedance Z eq of the mechanical differential actuator.
2. A mechanical differential actuator as recited in claim 1 , wherein:
the mechanical differential is characterized by a force amplification factor K ; and
( K+ 1) 2 Z 2 >>Z 1 .
3. A mechanical differential actuator as recited in claim 2 , wherein:
Z
eq
≅
K
2
(
K
+
1
)
2
Z
1
.
4. A mechanical differential actuator as recited in claim 1 , wherein the first transducer comprise a source of force.
5. A mechanical differential actuator as recited in claim 4 , wherein the first transducer comprises a controller of the source of force.
6. A mechanical differential actuator as recited in claim 4 , wherein the source of force comprises an element selected from the group consisting of a magneto-rheological damper, an electro-rheological damper, a magnetic particle brake, a magnetic brake based on a hysteresis effect, a stack of piezoelectric actuators acting on friction plates, a mechanism acting as a variable stiffness spring and a direct electromechanical transducer controlled with a feedback of movement state variables of the first transducer.
7. A mechanical differential actuator as recited in claim 4 , wherein the source of force comprises an element selected from the group consisting of a force-controlled direct drive electromechanical transducer and a force-controlled pneumatic transducer.
8. A mechanical differential actuator as recited in claim 4 , wherein the first transducer comprises a variable and a controllable impedance element in parallel with the source of force.
9. A mechanical differential actuator as recited in claim 8 , wherein the first transducer is integrated around the stator.
10. A mechanical differential actuator as recited in claim 1 , wherein the second transducer comprises a source of speed.
11. A mechanical differential actuator as recited in claim 10 , wherein the second transducer comprises a controller of the source of speed.
12. A mechanical differential actuator as recited in claim 10 , wherein the source of speed comprises an element selected from the group consisting of a hydraulic transducer, a direct drive electromechanical transducer having a feedback speed controller, and an ultrasonic actuator.
13. A mechanical differential actuator as recited in claim 1 , wherein the mechanical differential comprises a first speed reducer mechanism for implementing a mechanical differential function, the first transducer being coupled to the first speed reducer.
14. A mechanical differential actuator as recited in claim 13 , wherein the speed reducer mechanism comprises an element selected from the group consisting of a standard gearbox, a planetary gearbox, a cycloidal gearbox, a harmonic drive, a bar mechanism and a cable mechanism.
15. A mechanical differential actuator as recited in claim 13 , wherein the mechanical differential comprises a second speed reducer mechanism for implementing a mechanical differential function, the second transducer being coupled to the second speed reducer.
16. A mechanical differential actuator as recited in claim 15 , wherein the second speed reducer mechanism comprises an element selected from the group consisting of a standard gearbox, a planetary gearbox, a cycloidal gearbox, a harmonic drive, a bar mechanism and a cable mechanism.
17. A mechanical differential actuator as recited in claim 1 , wherein the mechanical differential comprises microelectromechanical systems.
18. A mechanical differential actuator as recited in claim 1 , wherein the first impedance is constant.
19. A mechanical differential actuator as recited in claim 18 , wherein the first transducer comprises a passive mechanical element.
20. A mechanical differential actuator as recited in claim 19 , wherein the passive mechanical element is selected from the group consisting of a passive mechanical spring, a passive mechanical damper, and a passive mechanical inertia.
21. A mechanical differential actuator as recited in claim 1 , wherein the second transducer comprises a rotor, the first transducer comprises a moving end and is integrated inside the rotor, and the mechanical differential comprises a harmonic drive itself comprising:
a flexible spline connected to the moving end of the first transducer;
a wave generator connected to the rotor of the second transducer; and
a circular spline acting as the third interaction port.
22. A mechanical differential actuator as recited in claim 1 , wherein the second transducer comprises a rotor and a stator, the first transducer comprises a moving end and is integrated around the stator, and the mechanical differential comprises a harmonic drive itself comprising:
a flexible spline connected to the moving end of the first transducer;
a wave generator connected to the rotor of the second transducer; and
a circular spline acting as the third interaction port.
23. A mechanical differential actuator as recited in claim 1 , wherein the mechanical differential comprises a speed reducer mechanism for implementing a mechanical differential function, the first and second transducers being coupled to the speed reducer.
24. A mechanical differential actuator as recited in claim 23 , wherein the speed reducer mechanism comprises an element selected from the group consisting of a standard gearbox, a planetary gearbox, a cycloidal gearbox, a harmonic drive, a bar mechanism and a cable mechanism.
25. A mechanical differential actuator as recited in claim 1 , wherein the differential comprises a first and second speed reducers, wherein both speed reducers are implemented using similar physical components.
26. A method of actuating a mechanical load comprising:
providing a mechanical differential having three interaction ports;
providing a first transducer;
providing a second transducer;
coupling the first transducer to a first interaction port of the mechanical differential;
coupling the second transducer to a second interaction port of the mechanical differential;
coupling the load to a third interaction port of the mechanical differential;
characterizing the first transducer by a first mechanical impedance Z 1 ;
characterizing the second transducer by a second mechanical impedance Z 2 ;
characterizing the mechanical differential actuator by an equivalent mechanical impedance Z eq ; and
choosing the second mechanical Z 2 impedance sufficiently large compared to the first mechanical impedance Z 1 so that the second mechanical impedance Z 2 does not influence significantly the equivalent mechanical impedance Z eq of the mechanical differential actuator.
27. A method of actuating a mechanical load as recited in claim 26 , wherein:
the mechanical differential is characterized by a force amplification factor K ; and
( K+ 1) 2 Z 2 >>Z 1 .
28. A method of actuating a mechanical load as recited in claim 27 , wherein:
Z
eq
≅
K
2
(
K
+
1
)
2
Z
1
.
29. A method of actuating a mechanical load as recited in claim 26 , wherein the first transducer comprises a source of force.
30. A method of actuating a mechanical load as recited in claim 26 , wherein the second transducer comprises a source of speed.
31. A mechanical differential actuator as recited in claim 26 , wherein the differential comprises a first and second speed reducers, and wherein said method further comprises:
coupling the first transducer to the first speed reducer;
coupling the second transducer to both the first and second speed reducers; and
coupling the load to one of the second speed reducer.
32. A mechanical differential actuator as recited in claim 26 , comprising:
maintaining the first impedance constant.
33. A method of actuating a mechanical load as recited in claim 32 , further comprising:
integrating the first transducer inside the rotor.
34. A method of actuating a mechanical load as recited in claim 32 , comprising:
integrating the first transducer around the stator.
35. A method of actuating a mechanical load as recited in claim 26 , wherein the first transducer comprises a moving end, the second transducer comprises a rotor, the mechanical differential comprises a harmonic drive including a wave generator, a flexible spline and a circular spline, and wherein said method further comprises:
connecting the flexible spline to the moving end of the first transducer;
connecting the rotor to the wave generator; and
using a circular spline as the third interaction port.