Reactive layer control system for prosthetic and orthotic devices
A variable gain impedance controller for use in a control system for controlling a motorized prosthetic or orthotic apparatus provided with a joint The controller comprises a sensor input for receiving a signal indicative of an interaction between the apparatus and the ground, a torque sensor input for receiving a signal indicative of the torque at the joint and a variable gain scheduler in communication with the sensor input so as to receive data therefrom thereby providing a variable torque gain. The variable gain impedance controller adjusts its control on the apparatus based on the variable torque gain and the indicated torque so as to a) increase the joint resistance to motion when the signal received from the sensor input indicates an interaction between the apparatus and the ground and b) decrease the joint resistance to motion when the signal received from the sensor input indicates an absence of interaction between the apparatus and the ground.
1. An apparatus, comprising:
an actuator coupled to a prosthetic limb member, the actuator forming at least a portion of a joint of the apparatus;
a force sensor configured to output a first signal indicative of an interaction between the apparatus and ground;
a torque sensor configured to output a second signal indicative of torque at the joint;
a position sensor configured to output a third signal indicative of position of the joint; and
a variable gain impedance controller comprising a processor in communication with the force sensor and the torque sensor, the processor configured to:
receive the first signal from the force sensor, the second signal from the torque sensor, and the third signal from the position sensor,
based at least in part on the first signal, determine a torque feedback, wherein during stance phase the torque feedback is determined using the torque and a first gain factor and during swing phase the torque feedback is determined using the torque and a second gain factor that is different from the first gain factor,
determine a variable velocity gain and a variable position gain based at least in part on the first signal indicative of the interaction between the apparatus and the ground, and
output a control signal to the actuator based at least in part on the variable velocity gain, a difference between a velocity set-point and a velocity estimation of the apparatus, the variable position gain, a difference between a position set-point and the third signal indicative of the position of the joint, and the torque feedback, wherein based at least in part on the torque feedback determined using the first gain factor, the control signal causes the actuator to increase joint resistance to motion and based at least in part on the torque feedback determined using the second gain factor, the control signal causes the actuator to decrease joint resistance to motion.
2. The apparatus of claim 1 , wherein the velocity estimation is obtained by an auto-regressive-moving-average process applied to the third signal indicative of the position of the joint.
3. The apparatus of claim 1 , wherein the processor is further configured to:
determine a braking feedback value when the velocity estimation is greater than a first threshold and the position indicated by the third signal is greater than a second threshold, and
output the control signal to the actuator based at least in part on the braking feedback value so as to increase the joint resistance to motion.
4. The apparatus of claim 3 , wherein the braking feedback value is based on a ratio of the velocity estimation to a square of an indicated position offset with a motion stop target of the apparatus.
5. The apparatus of claim 3 , wherein a motion stop target of the apparatus is dynamically adjustable.
6. The apparatus of claim 1 , wherein the first signal is a measure of load at a shank portion of the apparatus, and wherein the interaction between the apparatus and the ground is determined by a single value hysteretic thresholding of the first signal received from the force sensor.
7. The apparatus of claim 1 , wherein the first gain factor is a substantially unitary positive value and the second gain factor is a substantially unitary negative value, and wherein the substantially unitary positive value causes the actuator to increase joint resistance to motion such that an increase in the torque causes the actuator to increase resistance and the substantially unitary negative value causes the actuator to decrease joint resistance to motion such that an increase in the torque causes the actuator to decrease resistance.