Modeling And Synchronized Control Of H-type Gantry Stages Under High Speed

H-type gantry stages, well characterized by the simple structure and high stability, have been widely adopted in precision metrology, NC machining, and semiconductor packaging equipments. The bilateral linear motor driving is superior to the traditional ballscrew driving by conquering its drawbacks which is characterized by lots of transition elements, the sluggish response and nonlinear friction, etc. Thus, higher acceleration/deceleration, accuracy can be easely obtained, which adapts to frequent pick-and-place operations and fast precise point-to-point (PTP) motions in the semiconductor packaging industry. However, with the increase of speeds and accelerations, the dynamic characteristic of the gantry turns out to be the significant impacts on the system positioning accuracy and synchronous performance. Therefore, this paper investigates the dynamic modeling and synchronous control of a bilateral drive gantry stages under the condition of high speed. The major work herein is as follows:(1) Based on the Euler-Lagrange equation, this paper builds up the coupling dynamic model of the H-type gantry stage. Furthermore, two problems are theoretically investigated in detail. First, the effect of the joint rigidity on systematic frequency characteristics; second, the effect of the torsion impact on the synchronous performance of the gantry which is induced by the moving head's rapid acceleration and deceleration motions. Simulations indicate that the systematic bandwidth could be enlarged by enhancing the joint rigidity. When the moving head performs high acceleration motions, torsion impact would be notably present which may induce structural vibration. Therefore, advanced control algorithms should be developed to suppress the aforementioned negative effects.(2) Bilateral drive H-type gantry stages, a kind of typical coupling MIMO system, require to minimize the synchronous error during the trajectory tracking and positioning. Through establishing the linear quadratic performance specifications containing synchronous error and its differential, the synchronous problem of coupling MIMO system can be transferred to a linear quadratic optimal control problem. And control laws satisfying performance specifications are calculated through the Raccati equation and Lyapunov equation. The effects of weight coefficients a andβon the synchronous performance are analyzed, which revise the synchronous error and its differential, respectively. Simulations indicate that higher a andβcan add to the systematic synchronous performance, and the synchronous error is more susceptible to the value ofβ.(3) As the systematic robustness deteriorates in case of disturbance in the linear quadratic optimal synchronous control, a sliding structure optimal synchronous controller is proposed, which integrates the sliding-mode variable structure control and the linear quadratic optimal control. The former is intended for suppressing the surrounding disturbance, while the latter for reshaping the dynamic and static performance of the system. Also, a simple disturbance observer is designed to estimate the upper bound of disturbance through an adaptive law, which implements the systematic robustness under the condition of unknown upper disturbance bounds.(4) A dual-axies synchronous control system is developed. Synchronization controller with the synchronization error compensation is designed, and synchronous error protection and homing of the dual-axies are implemented. It has been applied to the RFID tag assembly of equipment, experiment and application results show that the effectiveness of control method.