The belt and glass have similar brake system structures at wheels (Lee and Jeong, 2017). The friction force (F_f) and normal force (F_N) from the sprag slip phenomenon are described in Equation (10), which was first defined by Spurr (1961). Self-excited vibration due to the sprag slip mechanism generates vibration even if the coefficient of friction λ, i.e., – dμ/dν is negative. This phenomenon is caused by the instability of the geometric structure and boundary conditions. Here, the angle of the lip touching the glass is an important DP. From Equation (10), as the angle increases, the friction and normal force (L) also increase. When the denominator becomes 0, FN and Ff ≈ ∞, and the corresponding sprag slip criterion is shown in Equation (11). (Spurr, 1961; Ghazaly et al., 2014).