Setup and procedure for online identification of electrically stimulated muscle with Matlab Simulink

This paper first describes a laboratory setup for biomechanical experiments that runs within the universal simulation environment Matlab Simulink. The overall system comprises a personal computer, two AMTI (Advanced Mechanical Technology, Inc., Watertown, MA 02472) force plates, Parotec force-sensor shoe insoles, Optotrak system for noncontact 3D position measuring, and a computer-controlled four-channel electrical stimulator. Conceptually, the most important application is implementation of closed-loop electrical stimulation of intact and paralyzed subjects in the laboratory. Second, the system was tested in real-time muscle model identification procedure during a standing experiment. The plantarflexors of three nonimpaired subjects were excited with pseudorandom binary sequences (PRBSs) with small deviations around selected operating points. Electrically stimulated muscles were presented with a linear local dynamic block that was identified with a recursive least-square method (RARX). RARX block was designed with fundamental Matlab Simulink blocks that support real-time operation. Introduced was online estimation of model output, which offers a great manner of instant model validation. Two modes of operation with online validation were tested, In the first mode, the operating point for selected excitation level was identified online. In the second mode, the operating point was measured in preceding experiments. Both procedures resulted in satisfying second-order models that will be used in the adaptive controller design.