Admittance control for an electromechanical rowing machine

The paper considers a conceptual design for an electromechanical rowing machine and its control system. The concept includes a DC motor, a gear transmission, a drum and a pull cable. The force-velocity characteristic of a commercial rowing machine was modeled by a fourth-order mechanical admittance, and its parameters were identified from actual exercise data by a collocation method. The admittance controller is related to, and an extension of the natural admittance control proposed by Newman. The controller of this paper is able to achieve any desired target admittance for the electromechanical system at its mechanical (user) port, as long as the admittance is strictly proper. A fourth-order mechanical admittance was identified by the collocation method, with very good agreement to the data. The identified admittance was subsequently used as the target admittance of the electromechanical control system. A scale-size prototype was used to test the controller in a realtime experiment. Achievement of the target admittance was verified by simulating its response to the force profile of the experiment. The resulting velocity was in close agreement to that recorded from the experiment.