Biomimetic transfemoral prosthesis

Abstract

In an artificial limb system having an actuator coupled to a joint for applying a torque characteristic thereto, a control bandwidth of a motor controller for a motor included in the actuator can be increased by augmenting a current feedback loop in the motor controller with a feed forward of estimated back electromotive force (emf) voltage associated with, the motor. Alternatively, the current loop is eliminated and replaced with a voltage loop related to joint torque. The voltage loop may also be augmented with the feed forward of estimated back emf, to improve the robustness of the motor controller.

What is claimed is: 
     
         1 - 22 . (canceled) 
     
     
         23 . A method for controlling a motorized, artificial limb having an actuator, the actuator comprising a motor coupled in series with an elastic element, to apply a torque characteristic to a joint, the method comprising the steps of:
 computing target motor current required to achieve substantially a target torque characteristic at the joint;   measuring motor current and motor speed;   computing a current error as a difference between the target motor current and the measured motor current;   estimating voltage corresponding to back electromotive force related to the motor speed; and   controlling voltage applied to motor windings based on, at least in part, (i) the estimated voltage corresponding to the back electromotive force, and (ii) the current error, to reduce the current error.   
     
     
         24 . The method of  claim 23 , wherein the torque characteristic comprises at least one of a joint torque, a joint impedance, and a joint equilibrium. 
     
     
         25 . The method of  claim 23 , wherein the artificial limb comprises at least one of a prosthetic limb and an orthotic limb. 
     
     
         26 . The method of  claim 23 , wherein the joint is at least one of an ankle joint, a knee joint, and a hip joint. 
     
     
         27 . An artificial limb system comprising:
 an actuator coupled to a joint for applying a torque characteristic thereto, the actuator having a motor coupled in series with an elastic element;   a power source for applying a voltage to windings of the motor;   a current sensor for measuring motor current;   a motor encoder for measuring motor speed; and   a controller configured to:
 compute a current error as a difference between a target current and the measured motor current; 
 estimate voltage corresponding to back electromotive force related to the measured motor speed; and 
 control voltage applied to motor windings based on, at least in part, (i) the estimated voltage corresponding to the back electromotive force, and (ii) the current error, to reduce the current error. 
   
     
     
         28 . The system of  claim 27 , wherein the artificial limb system comprises at least one of a prosthetic limb system and an orthotic limb system. 
     
     
         29 . The system of  claim 27 , wherein the joint is at least one of an ankle joint, a knee joint, and a hip joint. 
     
     
         30 . The system of  claim 27 , wherein the controller is adapted for determining the target motor current to achieve the target joint torque characteristic. 
     
     
         31 . The method of  claim 23 , wherein the back electromotive force is estimated using a current-loop controller. 
     
     
         32 . The method of  claim 23 , wherein the back electromotive force is estimated using a direct measurement of joint torque. 
     
     
         33 . The method of  claim 23 , wherein the target torque characteristic is controlled by a joint torque controller comprising a forward path and a feedback path, and a resonant spring dynamic of the artificial limb appears in the forward path and not the feedback path. 
     
     
         34 . The method of  claim 23 , further comprising estimating a speed of the motor, and using the estimated speed to cancel the back electromotive force. 
     
     
         35 . The method of  claim 23 , wherein the target torque characteristic is controlled by a joint torque controller that applies a proportional-integral (PI) algorithm based on the motor current. 
     
     
         36 . The method of  claim 23 , wherein the target torque characteristic is controlled by a joint torque controller that applies a proportional-integral-derivative (PID) algorithm based on a torque of the joint. 
     
     
         37 . The system of  claim 27 , wherein the controller estimates the back electromotive force. 
     
     
         38 . The system of  claim 27 , wherein the back electromotive force is estimated using a direct measurement of joint torque. 
     
     
         39 . The system of  claim 27 , wherein the controller is further configured to control the target torque characteristic using a forward path and a feedback path, and a resonant spring dynamic of the artificial limb appears in the forward path and not the feedback path. 
     
     
         40 . The system of  claim 27 , wherein the controller is further configured to estimate a speed of the motor, and use the estimated speed to cancel the back electromotive force. 
     
     
         41 . The system of  claim 27 , wherein the controller is further configured to control the target torque characteristic by applying a proportional-integral (PI) algorithm based on the motor current. 
     
     
         42 . The system of  claim 27 , wherein the controller is further configured to control the target torque characteristic by applying a proportional-integral-derivative (PID) algorithm based on a torque of the joint.