Motor Control Engineering Motor Control Engineering ViewView

Topics:Topics:

1- Muscle and Spinal Cord Models1- Muscle and Spinal Cord Models

2- Classic Control/Control 2- Classic Control/Control VariablesVariables

3- Model Based Strategies3- Model Based Strategies

Stark, Lawrence W. 1968. Neurological Control Systems; Studies in Bioengineering. New York: Plenum Press.

Classic ControlClassic Control(Modeling Eye (Modeling Eye

Movement)Movement)

Control VariablesControl Variables

1- Force !?1- Force !? 2- Position !?2- Position !? 3- Velocity !?3- Velocity !? 4- Stiffness !?4- Stiffness !? 5- Viscosity !?5- Viscosity !? 6- Impedance !?6- Impedance !?

Stein, R.C. (1982)Stein, R.C. (1982) Behavioral and Brain Behavioral and Brain

SciencesSciences

What Muscle Variable(s) Does the What Muscle Variable(s) Does the Nervous System Control in Limb Nervous System Control in Limb Movements? Movements?

Stiffness ControlStiffness Control

F = k ( X – XF = k ( X – X00) :) : رابطه يك فنر رابطه يك فنر(عضله)(عضله)

Muscle StiffnessMuscle Stiffness

K = F/XK = F/X

K >> 1 => Force ControlK >> 1 => Force Control

K << 1 => Position ControlK << 1 => Position Control

Stiffness Control Stiffness Control (cont.)(cont.)

Stiffness Control Stiffness Control (cont.)(cont.)

1- Feldman & Bizzi (EPH), 1- Feldman & Bizzi (EPH), 1966,1979,19861966,1979,1986

2- Houk (Stiffness and Reflex), 19792- Houk (Stiffness and Reflex), 1979

3- Hasan, 19863- Hasan, 1986

How CNS May Changes How CNS May Changes Joint Stiffness?Joint Stiffness?

1- Muscle active characteristic1- Muscle active characteristic

2- Muscle passive characteristic2- Muscle passive characteristic

3- 3- αα--γγ co-activation & spinal reflex loop co-activation & spinal reflex loop (muscle spindle)(muscle spindle)

4- Co-contraction4- Co-contraction

Stiffness Control Stiffness Control DiagramDiagram

Trajectory

Selector

FeedforwardController

SpinalCircuits

andMuscles

Joint-LoadDynamics

Torque

Disturbance

ReceptorsDelay

Brain Model

Joint Movement

Td

d

Torque

Angle1

2

i=1 f=2

v

Td

βv = Θf - Td/σ Load EffectLoad Effect

Stiffness Control Diagram Stiffness Control Diagram (cont.)(cont.)

Optimizer

Program

Inverse Dynamic

Controller

DisturbanceGf (s)Delay

Td

d

G(s)Delay

v

CNS

Impedance Definition:Impedance Definition:

Winters Winters et alet al. (1988):. (1988):

“ “the automatic capability of the the automatic capability of the system to resist an applied load system to resist an applied load before voluntary intervention takes before voluntary intervention takes place” place”

orque)

Angle)(

orque)

Angle)(

Impedance ControlImpedance Control

11- Hoffer (1982). Central Control - Hoffer (1982). Central Control and Reflex Regulation of and Reflex Regulation of Mechanical Impedance: The Basis Mechanical Impedance: The Basis for a Unified Motor-Control for a Unified Motor-Control Scheme. Scheme. Behavioral and Brain Behavioral and Brain SciencesSciences

Impedance Control Impedance Control (cont.)(cont.)

22- Stein, R. C., (1982). What Muscle - Stein, R. C., (1982). What Muscle Variable(s) Does the Nervous Variable(s) Does the Nervous System Control in Limb Movements? System Control in Limb Movements? Behavioral and Brain SciencesBehavioral and Brain Sciences

Impedance Control Impedance Control (cont.)(cont.)

33-Hogan, N., (1984a). Adaptive Control -Hogan, N., (1984a). Adaptive Control of Mechanical Impedance by of Mechanical Impedance by Coactivation of Antagonist MusclesCoactivation of Antagonist Muscles. IEEE . IEEE Trans. on Automatic ControlTrans. on Automatic Control, ,

Hogan, N., (1985a). Impedance Control: Hogan, N., (1985a). Impedance Control: An Approach to Manipulation: Part I-An Approach to Manipulation: Part I-Theory.Theory. Journal of Dynamic Systems, Journal of Dynamic Systems, Measurement, and ControlMeasurement, and Control, ,

Hogan, N., (1985c). The Mechanics of Hogan, N., (1985c). The Mechanics of Multi-Joint Posture and Movement Multi-Joint Posture and Movement Control. Control. Biological CyberneticBiological Cybernetic, 52, 315-, 52, 315-331.331.

Muscle 2-D Muscle 2-D CharacteristicCharacteristic

Joint ImpedanceJoint Impedance

orque)

Angle)(

bTorque

( )

(Angular Velocity )

Is Joint Impedance Is Joint Impedance Short-Term Predictor?Short-Term Predictor?

Joint Impedance Joint Impedance (cont.)(cont.)

PlantPlantPDPDControl SignalControl Signal

OutputReferenceReference

Smith, A. M. (1996) ,Smith, A. M. (1996) ,

Does the Cerebellum Learn Does the Cerebellum Learn Strategies for the Optimal Time-Strategies for the Optimal Time-Varing Control of Joint Stiffness? Varing Control of Joint Stiffness? Behavioral and Brain SciencesBehavioral and Brain Sciences