To realize high-performance contouring tracking of dual-linear-motor-driven (DLMD) gantry, both motion coordination of multiaxes and synchronization of redundant actuators are indispensable factors. However, earlier contouring methods of multiaxes systems only focus on motion coordination, leading to certain inherent limitations and uncertainties when applied to DLMD gantry. Especially, the usually ignored synchronization issue may directly affect the normal operation of system. To this end, this paper proposes a novel contouring control method by integrating both motion coordination between axes and synchronization of redundant actuators. With the knowledge of the complete system dynamics, corresponding modification and extension have been done within the framework of global task coordinate frame (GTCF). Subsequently, both associated issues are effectively dealt with in the task space to simultaneously obtain efficient motion coordination ability and high-level synchronization, along with more accurate contouring error calculation. The proposed method is compared with the earlier GTCF-based contouring control method without consideration of a synchronization issue. The experimental results fully indicate the effectiveness and superiority of the proposed method to indeed guarantee and further improve the contouring performance.

Integrated Coordinated/Synchronized Contouring Control of a Dual-Linear-Motor-Driven Gantry

Dual-linear-motor-driven gantry systems have been widely used in high-speed or heavy payload precision motion systems. Due to the unique physical properties such as mechanical coupling, the precise synchronization control of such kinds of systems is crucial to achieve good tracking and smooth operation performance. However, the existing synchronization schemes usually focus on the pure motion synchronization only and, thus, have certain inherent performance limitations. In this paper, an accurate multi-input multi-output mathematical model of a dual-driven gantry is presented first, where the complete planar motions of the crossbeam include the traditional linear motion along the guide rails and the previously ignored rotational motion around the mass center. With the better understanding of the mechanical coupling and the internal forces caused by the rotational dynamics, an advanced synchronization control scheme by directly taking into account the additive rotational dynamics is presented, which not only synchronizes the motions of two parallel motors but also regulates the internal forces. In the proposed scheme, the adaptive robust control algorithm is also applied to obtain a guaranteed robust performance in the presence of both parametric uncertainties and uncertain nonlinearities. Comparative experiments with previous control schemes are carried out to show the better synchronization performance and verify the effectiveness of the proposed method.

Advanced Synchronization Control of a Dual-Linear-Motor-Driven Gantry With Rotational Dynamics

This paper proposes a new structure for cross-coupling synchronous controller using an H∞ control scheme to shape position commands for precise tracking in multiaxial motion control, together with its stability analysis. This proposed structure has the advantage that the controller has a simpler design process and more robust performance than conventional ones. The proposed controller is evaluated and compared simulated and experimentally with an unsynchronous controlled system and a conventional system. The simulated and experimental results show that the new structure reduces the position synchronous error remarkably. In addition, this new controller can easily be implemented on most currently used motion systems used by reprogramming the reference position command subroutine.

Robust Cross-Coupling Synchronous Control by Shaping Position Commands in Multiaxes System

Synchronization analysis and control of three eccentric rotors in a vibrating system using adaptive sliding mode control algorithm

Dual drive gantry mechanisms, in which two actuators are physically connected through a crossbeam to provide a joint thrust for higher acceleration, are widely used in high-speed or heavy payload precision motion control applications. Synchronizing motions of the two actuators and avoiding excessive internal forces are both essential to the smooth operation of these systems. This paper presents a novel synchronization control scheme with thrust allocation that achieves not only better motion synchronization of the two actuators but also simultaneous regulation of internal forces. With decreased internal forces, lesser wear in sliding parts, lower energy consumption, and higher performances can be achieved for dual drive gantry stages. In contrast, existing synchronization control approaches mainly focus on pure motion compensation and synchronization of the two actuators only. Due to the near-rigid physical coupling between the two actuators, excessive internal forces or the “pull and drag” phenomena could still exhibit under existing approaches even when their motions are quite well synchronized. Comparative experimental results are also obtained to show the superiority of the proposed synchronization controller over existing ones in practical applications.

Modeling and Synchronization Control of a Dual Drive Industrial Gantry Stage

The present paper deals with the development of synchronizing controller for dual-drive servo system that is often used for SMD (Surface Mount Device) assembly machine. Instead of coordinating the commands to the individual feed drives and implementing closed position loop control for each axis, this work is achieved by the evaluation of an optimal cross-coupled compensator aimed specifically at improving synchronous accuracy in dual feed drives. The optimal control formulation explicitly includes the synchronous error in the performance index to be minimized. In this paper, surface chip mounter is used for experiment. It demands to synchronize the positions of its two primary driving axes. The system is modeled as the first order approximation and cross-coupled optimal synchronizing controller is designed. The synchronizing control is simulated and experimented with actual system for various velocity profiles. The results show that the proposed controller reduces the synchronous error considerably, compared to the conventional uncoupled control for the dual-drive system.

Optimal Cross-Coupled Synchronizing Control of Dual-Drive Gantry System for a SMD Assembly Machine

Gantry mechanisms have been widely used for precision manufacturing and material handling in electronics, nuclear, and automotive industries. Dual-drive servo mechanism is a way to increase control bandwidth, in which two primary axes aligned in parallel are synchronously driven by identical servo motors. With this mechanism, a flexible coupling (compliance mechanism) is often introduced in order to avoid the damage by the servo mismatch between the primary drives located at each side of gantry. This paper describes the design guidelines of the dual-drive servo mechanism with focus on its dynamic characteristics and control ramifications. That is, the effect on the system bandwidth which is critical on the system performance, the errors and torques exerted on guide ways in case of servo mismatch, the vibration characteristics concerned with dynamic error and settling time, and the driving force required at each axis for control are thoroughly investigated.

Heung Keun Park

Papers

Optimal Cross-Coupled Synchronizing Control of Dual-Drive Gantry System for a SMD Assembly Machine

Design of a dual-drive mechanism for precision gantry