【正文】 the lasercutting machine are posed of beltdrives. The elastic servomechanism can be described by a twomass system interconnected by a spring. Owing to the presence of elasticity, friction and disturbances, the closedloop performance using a conventional control approach is limited. Therefore, the motion control algorithm is derived using the variable system structure control theory. It is shown that the proposed control e!ectively suppresses the mechanical vibrations and ensures pensation of the system uncertainties. Thus, accurate position tracking is guaranteed. ( 2020 Elsevier Science 184。td. All rights reserved.) Keywords: Position control。 Variable structure control。 Ueda, 1993). Consequently, beltdrives suffer from lower repeatability and accuracy. Moreover, the beltdrive dynamics include more resonance frequencies, which are a destabilising factor in a feedback control (Moon, 1997). Therefore, a conventional control approach like PI, PD or PID control fails to achieve acceptable performance. Plant parameter variations, uncertain dynamics and load torque disturbances, as well as mechanical vibrations, are factors that have to be addressed to guarantee robust system stability and the high performance of the system. An advanced robust motion control scheme is introduced in this paper, which deals with the issues related to motion control of the drives with timing belts. The control scheme is developed on the basis of the motion control algorithm introduced by Jezernik, Curk and Harnik (1994). It possesses robust properties against the disturbances that are associated with a nominal plant model, as it has been developed with the use of the variable structure system (VSS) theory (Utkin, 1992). The crucial part of the control scheme is the asymptotic disturbance estimator. However, as shown in this paper, it fails to stabilise resonant belt dynamics, since it was developed for a rigid robot mechanism. Therefore, this paper introduces an improved motion control scheme, which suppresses the vibrations that would arise due to the nonrigid, elastic drive. Consequently, a rapid response with low position tracking error is guaranteed. The paper is set out as follows. The lasercutting machine is presented and the control plant model of the machine drives is developed in Section 2. In Section 3, the VSS control regarding the elastic servomechanism is discussed and the derivation of the motion control scheme is described. Section 4 presents the experimental results and a followup discussion. The paper is summarized and concluded in Section 5. 2. The control plant . The machine description The lasercutting machine consists of the XY horizontal table and a laser system (Fig. 1). The fundamental ponents of the laser system are: ● the power supply unit, which is placed off the table and thus is not considered in the motion control design。 each bridgeside is connected to one of the beltdrives. The driving pulleys of the beltdrives are linked to the driving axis, which is driven via the additional beltdrive and the gearbox is used to reduce the speed of the motor. Fig. 2. The drive. . Assumptions The machine drives represent a plex nonlinear distributed parameter system. The highorder system possesses several resonant frequencies that can be observed by the drives39。 ●a rigid link between a motor shaft and a driving pulley of the beltdrive could be adopted。 K the spring stiffness。 τ the motor shaft torque。 the transmission constant. Fig. 4. The block scheme of the mechanical model: symbol are as explained in Fig. 3. Fig. 5. The block scheme of the control plant. 3. The motion control algorithm The erroneous control model with structured and unstructured uncertainties demands a robust control law. VSS control ensures robust stability for the systems with a nonaccurate model, namely, it has been proven in the VSS theory that the closedloop behavior is determined by selection of a sliding manifold. The goal of the VSS control design is to find a control input so that the motion of the system states is restricted to the sliding manifold. If the system states are restricted to the sliding manifold then the sliding mode occurs. The conventional approach utilises discontinuous switching control to guarantee a slidin