Controlling power in a prosthesis or orthosis based on predicted walking speed or surrogate for same

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 first sensor having an output from which a walking speed of an upcoming step can be predicted;   at least one second sensor having an output from which ankle torque can be determined; and   a controller configured to control the motor's torque, based on the output of the at least one first sensor and the at least one second sensor, so that the motor's torque for slow walking speeds is lower than the motor's torque for fast walking speeds.   
     
     
         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 first sensor comprises at least one of an angular rate sensor and an IMU. 
     
     
         4 . The apparatus of  claim 1 , wherein the controller controls the motor's torque based on the output of the at least one first sensor immediately before a reflex occurs. 
     
     
         5 . The apparatus of  claim 1 , wherein the controller is configured to (i) determine, based on the output of the at least one first sensor, a control gain that varies with walking speed, wherein the control gain at slow walking speeds is lower than the control gain at fast walking speeds, (ii) determine a desired motor torque based on the control gain and a determined ankle torque, and (iii) drive the motor to achieve the desired motor torque. 
     
     
         6 . The apparatus of  claim 1 , wherein the controller is configured to (i) determine, based on the output of the at least one first sensor, an angular rate ω x  of the shank, (ii) determine a control gain Kv(ω x ) that is a function of the angular rate, wherein the control gain at low angular velocities is lower than the control gain at low angular velocities, (iii) determine a desired motor torque based on the equation Motor torque=Kv(ω x )×pff×(normalized_Torque) n , where pff is a constant and n is between 2 and 7, and (iv) drive the motor to achieve the desired motor torque. 
     
     
         7 . The apparatus of  claim 6 , wherein Kv(ω x )=0 when ω x =0, Kv(ω x )=1 when ω x  exceeds a threshold ω TH , and Kv(ω x ) is a monotonically increasing function between ω x =0 and ω TH . 
     
     
         8 . The apparatus of  claim 7 , wherein the motor is also configured to dorsiflex the foot member with respect to the shank member. 
     
     
         9 . The apparatus of  claim 1 , wherein the at least one second sensor measures ankle torque directly. 
     
     
         10 . The apparatus of  claim 1 , wherein the at least one second sensor has at least one output from which a deflection of series elastic element can be determined, and the controller computes the torque based on the at least one output. 
     
     
         11 . The apparatus of  claim 1 , wherein the at least one second 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 computes the torque based on the sensed position of the motor and the sensed angle. 
     
     
         12 . The apparatus of  claim 1 , wherein the at least one second 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 sensed position of the motor, the sensed angle, and a torque vs. deflection characteristics of the series elastic element. 
     
     
         13 . The apparatus of  claim 12 , 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 a total torque based on Γ S  and Γ B .   
     
     
         14 . A method of modifying characteristics of an ankle-foot prosthesis or orthosis apparatus, the method comprising the steps of:
 predicting what a walking speed will be during an upcoming step; and   modifying a characteristic of the apparatus during the upcoming step in situations when the predicted walking speed is slow, wherein the modification of the characteristic results in a reduction in net non-conservative work that is performed during the upcoming step as compared to the net non-conservative work that is performed when the predicted walking speed is fast.   
     
     
         15 . The method of  claim 14 , wherein the step of modifying a characteristic comprises reducing a power control gain in situations when the predicted walking speed is slow. 
     
     
         16 . The method of  claim 14 , wherein the predicting step comprises predicting what a walking speed will be during an upcoming step based on a shank angular rate measurement during a controlled dorsiflexion phase that directly precedes the upcoming step. 
     
     
         17 . The method of  claim 16 , wherein the shank angular rate measurement is made at foot-flat. 
     
     
         18 . An apparatus comprising:
 a proximal member;   a distal member that is operatively connected with respect to the proximal member by a joint 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 first sensor having an output from which a walking speed of an upcoming step can be predicted;   at least one second sensor having an output from which a joint torque can be determined; and   a controller configured to control the motor's torque, based on the output of the at least one first sensor and the at least one second sensor, so that the motor's torque for slow walking speeds is lower than the motor's torque for fast walking speeds.   
     
     
         19 . The apparatus of  claim 18 , wherein the at least one first sensor comprises at least one of an angular rate sensor and an IMU. 
     
     
         20 . The apparatus of  claim 18 , wherein the controller controls the motor's torque based on the output of the at least one first sensor immediately before a reflex occurs. 
     
     
         21 . The apparatus of  claim 18 , wherein the controller is configured to (i) determine, based on the output of the at least one first sensor, a control gain that varies with walking speed, wherein the control gain at slow walking speeds is lower than the control gain at fast walking speeds, (ii) determine a desired motor torque based on the control gain and a determined joint torque, and (iii) drive the motor to achieve the desired motor torque.