Comments on "A new method of switching surface design for multivariable variable structure system"

This note points out some errors in the above paper (Lee and Zu, ibid., vol. 39, no. 2, p. 414-19, 1994). It is argued that the proof in the main theorem is not mathematically rigorous. The control scheme requires the derivative of the sliding variable to be available, which is equivalent to saying that the uncertainties of the system are measurable. This is highly impractical if not impossible to implement. The theorem also says that the proposed new switching surface and control scheme can guarantee robustness of the system from initial time to final time. This is also incorrect because the theorem only shows that the sliding variable tends to zero approximately, i.e., the sliding motion only occurs approximately at t=/spl infin/. The paper also contains several misprints.<>