Actuator control system and related methods
An actuator control system includes a motorized joint having first and second members rotatable relative to one another. An actuator is coupled with the motorized joint and is configured to rotate the first member relative to the second member in response to an input including a voltage, a current, or any combination thereof. A controller is coupled with the actuator and is configured to control the input using a control algorithm. The control algorithm controls the input based upon a mathematical model of biological muscle actuation that models titin as a filament which winds around actin during muscle actuation. In implementations the mathematical model includes mathematical representations of a contractile element, a viscous damping element in parallel with the contractile element, and a spring in series with the contractile element through a pulley and simultaneously in parallel with the contractile element.
1. An actuator control system, comprising:
a motorized joint comprising a first member and a second member rotatable relative to the first member;
an actuator coupled with the motorized joint and configured to rotate the first member relative to the second member in response to an input comprising one of a voltage, a current, and any combination thereof, and;
a controller coupled with the actuator and configured to control the input using a control algorithm;
wherein the control algorithm controls the input based upon a mathematical model of biological muscle actuation that models titin as a filament which winds around actin during muscle actuation.
2. The actuator control system of claim 1 , wherein the mathematical model models an N2A region of titin binding to actin during muscle actuation.
3. The actuator control system of claim 1 , wherein the mathematical model comprises mathematical representations of a contractile element, a viscous damping element in parallel with the contractile element, and a spring in series with the contractile element through a pulley and simultaneously in parallel with the contractile element.
4. The actuator control system of claim 1 , further comprising a sensor configured to sense a state of the motorized joint from among a plurality of states, and wherein the controller controls the input based upon a sensed state.
5. The actuator control system of claim 4 , wherein the plurality of states comprises a standing state, a controlled plantar flexion state, a controlled dorsiflexion state, a powered plantar flexion state, an early swing state, and a late swing state.
6. An actuator control system, comprising:
a motorized joint comprising a first member and a second member rotatable relative to the first member;
an actuator coupled with the motorized joint and configured to rotate the first member relative to the second member in response to an input comprising one of a voltage, a current, and any combination thereof, and;
a controller coupled with the actuator and comprising a control algorithm comprising a mathematical model of biological muscle actuation that comprises mathematical representations of:
a contractile element;
a viscous damping element in parallel with the contractile element, and;
a spring (titin spring) in series with the contractile element through a pulley and simultaneously in parallel with the contractile element;
wherein the controller is configured to generate the input using the mathematical model and data from one or more sensors coupled with the motorized joint.
7. The actuator control system of claim 6 , wherein the mathematical model defines a muscular force (F m ) of a muscle tendon unit (MTU) as F m =k ss (X m −X p )=k ts X ts +F ce +c ce {dot over (X)} ce , where k ss is a spring rate of a series spring, X m is a change in length of the MTU, X p is a change in length of the viscous damping element, k ts is a spring rate of the titin spring, X ts is a change in length of the titin spring, F ce is a force of the contractile element, c ce is a damping rate of the contractile element, and {dot over (X)} ce is a damper velocity of the viscous damping element.
8. The actuator control system of claim 6 , wherein the titin spring of the mathematical model comprises an exponential spring.
9. The actuator control system of claim 6 , wherein the mathematical model further comprises a mathematical representation of a second spring in series with the viscous damping element and attached to an axle of the pulley.
10. The actuator control system of claim 6 , wherein the mathematical model further comprises a mathematical representation of a clutch configured to selectively prevent rotation, but not translation, of the pulley.
11. The actuator control system of claim 6 , wherein the viscous damping element comprises a damping rate that is related to a muscle activation level.
12. The actuator control system of claim 6 , wherein the viscous damping element comprises a bi-directional damping rate.
13. An actuator control system, comprising:
a foot-ankle prosthesis comprising a joint, the joint rotatably coupling a first member with a second member;
an actuator coupled with the foot-ankle prosthesis and configured to cause dorsiflexion and plantar flexion of the foot-ankle prosthesis by rotating the first member relative to the second member in response to an input comprising one of a voltage, a current, and any combination thereof, and;
a controller coupled with the actuator and configured to generate the input using a control algorithm;
wherein the control algorithm is based upon a mathematical model of biological muscle actuation that models titin as a filament which winds around actin during muscle actuation.
14. The actuator control system of claim 13 , wherein the mathematical model models an N2A region of titin binding to actin during muscle actuation.
15. The actuator control system of claim 13 , wherein the mathematical model comprises a mathematical representation of a virtual anterior muscle for effecting dorsiflexion and a virtual posterior muscle for effecting plantar flexion, the virtual posterior muscle modeled after a combination of a soleus muscle and a gastrocnemius muscle.
16. The actuator control system of claim 15 , wherein the mathematical model is configured to, using a sensed ankle angular position: calculate a length of the virtual anterior muscle, calculate a length of the virtual posterior muscle, calculate a force produced by the virtual anterior muscle, and calculate a force produced by the virtual posterior muscle.
17. The actuator control system of claim 16 , wherein the mathematical model is configured to calculate a net ankle torque using the calculated force produced by the virtual anterior muscle and the calculated force produced by the virtual posterior muscle and, using the calculated net ankle torque, generate the input.
18. The actuator control system of claim 15 , wherein the mathematical model comprises a value representing a muscle activation level of the virtual anterior muscle, a value representing a muscle activation level of the virtual posterior muscle, a value related to an attachment parameter of the virtual anterior muscle, and a value related to an attachment parameter of the virtual posterior muscle.
19. The actuator control system of claim 13 , wherein the mathematical model models a non-linear relationship of muscle force to muscle length during muscle stretch and during muscle shortening.
20. The actuator control system of claim 13 , wherein the mathematical model models powered plantar flexion activation in relation to an angular velocity of the first member relative to the second member during controlled dorsiflexion.