In the article titled “Quadratic Integral Sliding Mode Control for Nonlinear Harmonic Gear Drive Systems with Mismatched Uncertainties” [1], an additional reference should have been cited, which is included in the text below, as reference 19 [2]. Accordingly, the sentence referring to Equation (18) in Section 3, “Quadratic Integral Sliding Mode Design,” should read as follows:

In order to compensate for the effect of mismatched uncertainties, the quadratic integral sliding mode surface is designed as in [19].