An approach to sliding-mode based control

The paper presents a sliding-mode based implementation of impedance control. The sliding surface is defined as a measure of the impedance error. When the system variables correspond to the sliding surface, then the desired impedance is implemented. The proposed control approach is composed of two parts. First, the system is controlled such that the state variables reach certain values corresponding to a neighborhood of the sliding surface. This part is performed using a control law consisting of a version of the computed torque and an impedance error-based switching function. The paper uses a new formulation of the acceleration signal for the computed torque calculation. The need for such a neighborhood is to avoid chattering which is typical to sliding-ode based control laws. The second part is performed using a PI-controller which ensures that the state variables further converge to some desired values corresponding to the sliding surface, such that the impedance error would tend to zero asymptotically. The proposed method has been verified experimentally. The method is practical and superior to other known methods.<
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