Comments on "Sliding-mode motion/force control of constrained robots

In the above paper by Lian and Lin (ibid. vol.43(8) (1998)) the authors claim their control law ensures the motion and force errors are asymptotically driven to zero and that the actual forces will asymptotically approach the desired forces. However, the commenters point out that the authors´ claim is invalid due to an error in the sliding-mode control stability analysis. Specific details of the errors are given.