Control strategies for functional electrical stimulation induced cycling
Functional Electrical Stimulation cycling ergometers and mobile cycling systems have been developed over a number of years to allow Spinal Cord Injured persons to exercise. Standard able bodied exercise tests are adapted and applied to paraplegic cyclists. A modified recumbent tricycle is instrumentated with an electric motor and sensors to measure cadence and the power produced by the cyclist at the crank. They are then integrated to a stimulator and a laptop computer. The tricycle is mounted on an indoor cycling trainer to provide a novel test bed for the implementation of exercise testing. Controllers are desired to control cadence and power during cycling. Identification of input-output data for the cadence-motor loop and the power-stimulation loop is undertaken. Three muscle groups are stimulated on a paraplegic subject to produce power. Models are identified of the power and cadence systems. Thereafter controllers are designed, via polynomial methods. The results show that the controllers are robust during cadence tracking, power tracking and for disturbance rejection. The controllers can be accurately applied to exercise testing protocols. The concept of VO2 control is induced. VO2 is the rate of oxygen uptake during exercise. VO2-power dynamics are identified and as before a model is fitted to the measured data. Controllers are designed and further modified, as the understanding of the VO2 dynamics is developed. This is through a series of tests to improve the accuracy of the control. The results illustrate that VO2 control is a novel and practical application. These findings develop the field of functional Electrical Stimulation Induced Cycling within the laboratory. However further work is required to develop this application outside laboratory conditions.