Robot manipulator with modular torque controlled links
An example torque controlled actuator includes a frame, and one or more timing belt stages coupled in serial on the frame. The timing belt stages include an input stage for coupling to a motor and an output stage for coupling to a load, and the timing belt stages couple rotation of the motor to rotation of an output of the output stage. The torque controlled actuator also includes one or more belt idlers coupled to the frame that contact a timing belt of the output stage, and a strain gauge coupled to the frame to determine a tension of the timing belt of the output stage based on force applied by the timing belt of the output stage to the one or more belt idlers.
1. A torque controlled actuator comprising:
a frame;
one or more timing belt stages coupled in serial on the frame, wherein the one or more timing belt stages include an input stage for coupling to a motor and an output stage for coupling to a load, wherein the one or more timing belt stages couple rotation of the motor to rotation of an output of the output stage;
one or more belt idlers coupled to the frame, wherein the one or more belt idlers contact a timing belt of the output stage;
a strain gauge coupled to the frame to determine a tension of the timing belt of the output stage based on force applied by the timing belt of the output stage to the one or more belt idlers; and
a control bus and one or more processors, wherein the strain gauge outputs the tension of the timing belt of the output stage to the control bus, and the one or more processors are coupled to the control bus for determining output torque of the torque controlled actuator based on the tension of the timing belt of the output stage.
2. The torque controlled actuator of claim 1 , wherein the one or more timing belt stages include:
a stage input;
an output hub; and
a timing belt wrapped around the stage input and the output hub.
3. The torque controlled actuator of claim 2 , wherein the stage input and the output hub comprise pulleys mounted on rolling bearings.
4. The torque controlled actuator of claim 2 , further comprising an encoder coupled to the frame to determine an angular position of the output hub.
5. The torque controlled actuator of claim 1 , wherein a given timing belt stage provides a reduction of motor input and increases torque output.
6. The torque controlled actuator of claim 1 , wherein the one or more timing belt stages include three timing belt stages coupled serially and provide a reduction of motor input within a range of 4:1 to 50:1.
7. The torque controlled actuator of claim 1 , wherein the one or more belt idlers include an idler wheel that rolls against the timing belt of the output stage, and the torque controlled actuator further comprises:
a load cell coupled to the one or more belt idlers, wherein the load cell is arranged as a compression structure, wherein deflection of the load cell is determined by the strain gauge, and wherein the strain gauge is coupled to the load cell.
8. The torque controlled actuator of claim 7 , further comprising a hardstop coupled to the frame, the hardstop for limiting an amount of deflection of the load cell providing overload protection.
9. The torque controlled actuator of claim 7 , wherein an applied load to the load cell, F id , is based on a function of output torque T q as follows
F id =2 F b cos(Θ)
F b =T q /r
where F id is a normal force applied to the load cell, F B is a working tension on the timing belt, r is an output hub radius, and Θ is an angle of the timing belt to a normal of the load cell.
10. The torque controlled actuator of claim 1 , wherein the one or more belt idlers are provided in a T-shaped configuration so as to contact the timing belt at multiple locations along a length of the timing belt, wherein the T-shaped configuration includes two idlers maintaining a timing belt preload tension and providing output load to the strain gauge.
11. The torque controlled actuator of claim 10 , further comprising a slider for pre-tensioning the timing belt by moving the T-shaped configuration toward an output of the output stage.
12. The torque controlled actuator of claim 1 , further comprising:
a plurality of belt idlers provided at multiple locations along a length of the timing belt;
a first load cell including the strain gauge configured to determine a first tension of the timing belt of the output stage based on force applied by the timing belt of the output stage to one of the plurality of belt idlers; and
a second load cell including a second strain gauge to determine a second tension of the timing belt of the output stage based on force applied by the timing belt of the output stage to another of the plurality of belt idlers,
wherein a torque of the timing belt of the output stage is based on a difference of the first tension and the second tension.
13. The torque controlled actuator of claim 1 , further comprising one or more idlers to contact timing belts of stages to apply adjustable tension to the timing belts;
wherein the one or more idlers comprise a wheel to apply adjustable tension to the timing belts.
14. The torque controlled actuator of claim 1 , further comprising:
the motor coupled to the input stage and to drive the one or more timing belt stages.
15. The torque controlled actuator of claim 14 , further comprising a motor encoder to sense a position of the motor.
16. The torque controlled actuator of claim 14 , further comprising:
a motor amplifier that determines a motor current based on the tension of the timing belt of the output stage,
wherein the motor amplifier determines the motor current based on a servo control loop to control the motor current applied to the motor to achieve a desired output torque.
17. A torque controlled actuator comprising:
a frame;
one or more timing belt stages coupled in serial on the frame, wherein the one or more timing belt stages include an input stage for coupling to a motor and an output stage for coupling to a load, wherein the one or more timing belt stages couple rotation of the motor to rotation of an output of the output stage;
the motor coupled to the input stage and to drive the one or more timing belt stages;
one or more belt idlers coupled to the frame, wherein the one or more belt idlers contact a timing belt of the output stage;
a strain gauge coupled to the frame to determine a tension of the timing belt of the output stage based on force applied by the timing belt of the output stage to the one or more belt idlers; and
a motor amplifier that determines a motor current based on the tension of the timing belt of the output stage,
wherein the motor amplifier determines the motor current based on a servo control loop to control the motor current applied to the motor to achieve a desired output torque.