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This paper proposes a new adaptive law for a sliding mode control (SMC) scheme to achieve the effective switching gain tuning near the sliding surface. The proposed adaptive law makes the switching gains rapidly and effectively decrease near the sliding surface to provide the well-functioning adaptation while avoiding the sign changes caused by excessive adaptation. Such an adaptation mechanism contributes to chattering reduction and fast adaptation of the switching gains without temporary large tracking errors. The proposed adaptive SMC (ASMC) works together with a time-delay controller (TDC) for a more practical implementation based on a model-free controller. Fortunately, the proposed ASMC has an additional benefit of suppressing time-delay estimation errors inherently arising from the TDC. In other words, the proposed ASMC acts in synergy with the TDC. The simulations are performed, and the comparisons are made with the existing control schemes to illustrate the good tracking performance of the proposed ASMC. These simulations have shown that with a 2 degree-of-freedom robot manipulator, the proposed ASMC has a good nominal and robust performance with a very strategic adaptive law. INDEX TERMS Adaptive sliding mode control (ASMC), time-delay controller (TDC), time-delay estimation (TDE), adaptation, robot manipulators.

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