Principal Investigator: H.F. Machiel Van der Loos, Ph.D.
Co-Investigators: Felix E. Zajac, Ph.D.; Douglas Schwandt, MSME; David A. Brown, Ph.D., P.T.; Charles Burgar, M.D.
A. Objective: The Motor Control Physiology Lab of the Rehabilitation R&D Center uses an instrumented ergometer (TILT-I) to conduct NIH and VA supported studies on how neurological normal and stroke-induced hemiparetic persons pedal. Such studies are hoped to provide clues into why gait, another bipedal motor task, is impaired.
B. Research Plan: The servo-controlled motor will be able to deliver a programmable torque to the crank. Without this enhancement, it is difficult, if not impossible, to ascertain whether it is the paretic or the non-paretic leg, or their interaction that impairs pedaling performance. With the enhancement, it is possible to sort out the effects because the servomotor can deliver the cranking torque that a leg generates during normal two-legged pedaling. Thus, each of the two legs can be studied in isolation.
With the servomotor, the experimenter will be able to define any braking or active torque profile T=f(t). The time-dependent function f(t) may be defined in terms of inertial, damping and spring constant factors, or calculated in real-time during each pedaling cycle from other sources such as pedal force sensors or random event generators. The programmability, coupled with certain changes in drivetrain, will allow the experimenter more precisely controlled crank torque than currently possible. The servomotor will also allow us to apply perturbations during cycling. The analysis of neuromuscular responses to events such as torque pulses will let us explore the roles of impedance control and feedback as factors in human motor control
C. Methodology
Define operating specifications for torque requirements.
Design the motor and drivetrain to include the motor on TILT-I. Integrate the servo control with the data collection functions. Consult with the on-going TILT-II specification and design process to establish the nature and extent of modifications to accommodate the servomotor and drivetrain at a future date.
Specify and procure the motor, drivetrain, safety devices, and electronics.
Perform the detailed design and engineering of the motor mounting for TILT-I.
Perform structural upgrades to TILT-I, and add the motor.
Program and test the procured motor controller to simulate loads equivalent to the brake/flywheel system, to validate the use of the motor.
Work with experimenters to try a variety of workloads needed for experiments.
D. Findings to Date: The data collection environment, motor, drivetrain and servo control components have been specified and procured. Special electronics and wiring for optical encoder interfacing have been completed. Data collection software has been written in LabView (TM), and rudimentary motor control has been demonstrated. Motor mount and drivetrain mechanical design and power/safety electrical design are complete. Structural upgrades to TILT-1 have been done to accommodate the motor mounting.
Testing of control algorithms are underway on a test bench with a hand crank. Installation of the motor on TILT-I needs to await the completion of TILT-II and the transfer of on-going experiments from TILT-I to TILT-II.