Controlling torque in a prosthesis or orthosis based on a deflection of series elastic element

Abstract

In some embodiments of a prosthetic or orthotic ankle/foot, a prediction is made of what the walking speed will be during an upcoming step. When the predicted walking speed is slow, the characteristics of the apparatus are then modified so that less net-work that is performed during that step (as compared to when the predicted walking speed is fast). This may be implemented using one sensor from which the walking speed can be predicted, and a second sensor from which ankle torque can be determined. A controller receives inputs from those sensors, and controls a motor's torque so that the torque for slow walking speeds is lower than the torque for fast walking speeds. This reduces the work performed by the actuator over a gait cycle and the peak actuator power delivered during the gait cycle. In some embodiments, a series elastic element is connected in series with a motor that can drive the ankle, and at least one sensor is provided with an output from which a deflection of the series elastic element can be determined. A controller determines a desired torque based on the output, and controls the motor's torque based on the determined desired torque.

1 . An ankle-foot prosthesis or orthosis apparatus comprising:
 a shank member;   a foot member that is operatively configured with respect to the shank member so as to supporting walking and permit the foot member to plantarflex and dorsiflex with respect to the shank member;   a motor configured to plantarflex the foot member with respect to the shank member;   a series elastic element connected between at least one of (a) the motor and the shank member and (b) the motor and the foot member;   at least one sensor having an output from which a deflection of the series elastic element can be determined; and   a controller configured to determine a desired torque based on the output, and to control the motor's torque based on the determined desired torque.   
     
     
         2 . The apparatus of  claim 1 , wherein the motor is also configured to dorsiflex the foot member with respect to the shank member. 
     
     
         3 . The apparatus of  claim 1 , wherein the at least one sensor comprises a sensor that senses a position of the motor and a sensor that senses an angle of the foot member with respect to the shank member, and the controller determines a torque component Γ S  based on the position of the motor and the sensed angle θ and a torque vs. deflection characteristics of the series elastic element. 
     
     
         4 . The apparatus of  claim 1 , wherein the torque component Γ S  is determined by subtracting the sensed angle θ from a reference angle β, wherein the reference angle θ is determined based on the position of the motor. 
     
     
         5 . The apparatus of  claim 4 , further comprising a bumper that is compressed when the foot member is sufficiently dorsiflexed with respect to the shank member,
 wherein the controller determines a torque component Γ B  based on the sensed angle and a torque vs. deflection characteristics of the bumper, and   wherein the controller determines the desired torque based on Γ S  and Γ B .   
     
     
         6 . A method of controlling an ankle-foot prosthesis or orthosis having a foot member and shank member, with a motor configured to plantarflex the foot member with respect to the shank member and a series elastic element in series with the motor, the method comprising the steps of:
 sensing a position of the motor;   determining a deflection of the series elastic element while the motor is at the position sensed in the sensing step; and   controlling the motor's torque based on the motor position sensed in the sensing step and the deflection determined in the determining step.   
     
     
         7 . The method of  claim 6 , wherein the determining step comprises sensing an actual angle of the foot member with respect to the shank member, and wherein the controlling step comprises determining a torque component Γ S  based on (a) a difference between the actual angle and a reference angle corresponding to the motor position sensed in the sensing step and (b) a torque vs. deflection characteristics of the series elastic element. 
     
     
         8 . The method of  claim 6 , wherein the controlling step further comprises determining a torque component Γ B  based on the actual angle and a torque vs. deflection characteristics of a bumper that is compressed when the foot member presses against the shank member, and adding the torque component Γ S  to the torque component Γ B . 
     
     
         9 . An apparatus comprising:
 a proximal member;   a distal member that is operatively configured with respect to the proximal member so that an angle between the distal member and the proximal member can vary;   a motor configured to vary the angle between the distal member and the proximal member;   a series elastic element connected between at least one of (a) the motor and the proximal member and (b) the motor and the distal member;   at least one sensor having an output from which a deflection of the series elastic element can be determined; and   a controller configured to determine a desired torque based on the output, and to control the motor's torque based on the determined desired torque.   
     
     
         10 . The apparatus of  claim 9 , wherein the at least one sensor comprises a sensor that senses a position of the motor and a sensor that senses the angle between the distal member and the proximal member, and the controller determines a torque component Γ S  based on the position of the motor, the sensed angle θ, and a torque vs. deflection characteristics of the series elastic element. 
     
     
         11 . The apparatus of  claim 9 , wherein the torque component Γ S  is determined by subtracting the sensed angle θ from a reference angle β, wherein the reference angle β is determined based on the position of the motor. 
     
     
         12 . The apparatus of  claim 11 , further comprising a bumper that is compressed when the angle between the distal member and the proximal member distal member exceeds a threshold angle,
 wherein the controller determines a torque component Γ B  based on the sensed angle and a torque vs. deflection characteristics of the bumper, and   wherein the controller determines the desired torque based on Γ S  and Γ B .