Ser Yong Lim

Iterative learning control of permanent magnet linear motor with relay automatic tuning

Abstract In this paper, a feedforward–feedback control structure is proposed for precision motion control of a permanent magnet linear motor (PMLM) for applications which are inherently repetitive in terms of the motion trajectories. The control scheme utilises an efficient marriage of conventional PID feedback control and an intelligent feedforward control using an iterative learning control (ILC) algorithm. The PID feedback control stabilizes the PMLM system, while the ILC feedforward control enhances the trajectories tracking performance by capitalising on the experience gained from the repeated execution of the same operations. A relay automatic tuning method is developed and incorporated, so that an initial set of control settings may be automatically derived from a few cycles of self-induced controlled oscillations. This self-tuning feature enables the PMLM application system to be operated quickly near optimal conditions simply at a push-button efficiency. Extensive experimental results are presented to demonstrate the appeal and effectiveness of the proposed scheme.

Coordinated motion control of moving gantry stages for precision applications based on an observer-augmented composite controller

High-precision operation in gantry systems is required to meet higher demands on positioning accuracy in a wide range of applications such as circuit assembly, precision metrology, and wafer stepping. In this paper, the experimental study of an observer-augmented composite control scheme for coordinated motion control of moving gantry stages for precision applications is presented. The scheme will be implemented and compared to other control schemes currently available for this purpose, including a master-slave and a set-point coordinated scheme. Experimental results will illustrate the enhanced performance of the fully coordinated control scheme with respect to tight trajectory tracking purposes.

A walk‐through programmed robot for welding in shipyards

Automating the welding process for the shipbuilding industry is very challenging and important, as this industry relies heavily on quality welds. Conventional robotic welding systems are seldom used because the welding tasks in shipyards are characterised by non‐standardised workpieces which are large but small in batch sizes. Furthermore, geometries and locations of the workpieces are uncertain. To tackle the problem, a Ship Welding Robot System (SWERS) has been developed for the welding process. The main features of the SWERS include a special teaching procedure that allows the human user to teach the robot welding paths at a much easier and faster pace. In addition, operation of the system is made easier through a custom designed man‐machine interface. Through this interface, only a few buttons need to be pressed to command the robot into different modes. Optimised welding parameters can be selected from a large database through a Graphical User Interface system.

Various developments in mechatronics in Asia

This paper presents various interesting developments in mechatronics within Asia. As a synergy of core technologies, mechatronics is fast becoming an important component of modern products and processes and is poised to become a key technology to employ to gain a competitive edge in the modern manufacturing era wherein products and processes are becoming highly integrated in functionalities. The development of mechatronics will therefore be crucial to the continued competitiveness of a manufacturing intensive economy, typical of many countries in Asia. This paper discusses various developments of mechatronics in Asia from three perspectives: education, research and applications of the technology.

Compliant motion using a mobile manipulator: an operational space formulation approach to aircraft canopy polishing

The operational space formulation provides a framework for the analysis and control of robotic systems with respect to interactions with their environments. In this paper, we discuss its implementation on a mobile manipulator programmed to polish an aircraft canopy with a curved surface of unknown geometry. The polishing task requires the robot to apply a specified normal force on the canopy surface while simultaneously performing a compliant motion keeping the surface of the grinding tool tangentially in contact with the workpiece. A human operator controls the mobile base via a joystick to guide the polishing tool to desired areas on the canopy surface, effectively increasing the mobile manipulators reachable workspace. The results demonstrate the efficacy of compliant motion and force regulation based on the operational space formulation for robots performing tasks in unknown environments with robustness towards base motion disturbances. The mobile manipulator consists of a PUMA 560 arm mounted on top of a Nomad XR4000 mobile base. Implementation issues are discussed and experimental results are shown.

Two-degree-of-freedom controller incorporating RBF adaptation for precision motion control applications

This paper presents a robust servo control method for linear motor systems, based on a composite of two-degree-of-freedom control theory and nonlinear adaptive control using a radial basis function (RBF). This controller consists of a simple feedforward compensator, a PD+D/sup 2/ feedback control, and the RBF adaptive compensator. The proposed method can determine the control parameters for both the feedforward and PD+D/sup 2/ feedback control based on only an estimated dominant second-order model. The RBF compensator is a form of self-tuning control which compensate for remaining uncertainties in the system, residual of the linear model. Rigid proofs are provided guaranteeing the robustness of the proposed controller. Simulation results confirm the much superior performance of the proposed control over a conventional feedforward plus feedback control.

Geometrical Error Modeling and Compensation Using Neural Networks

This paper describes an approach based on neural networks (NNs) for geometrical error modeling and compensation for precision motion systems. A laser interferometer is used to obtain the systematic error measurements of the geometrical errors, based on which an error model may be constructed and, consequently, a model-based compensation may be incorporated in the motion-control system. NNs are used to approximate the components of geometrical errors, thus dispensing with the conventional lookup table. Apart from serving as a more adequate model due to its inherent nonlinear characteristics, the use of NNs also results in less memory requirements to implement the error compensation for a specified precision compared to the use of lookup table. The adequacy and clear benefits of the proposed approach are illustrated via applications to various configurations of precision-positioning stages, including a single-axis, a gantry, and a complete XY stage

Adaptive joint friction compensation using a model-based operational space velocity observer

An operational space controller that employs a velocity observer and a friction adaptation law to achieve higher tracking accuracy is presented. Without velocity measurements, the overall observer-controller system can achieve a semi-global asymptotic stability for the position and velocity tracking errors, and position and velocity estimation errors. The estimated friction coefficients can also approach the actual coefficients asymptotically. Experimental results indicate that the proposed adaptive observer-controller is able to achieve higher tracking accuracy than the observer-controller without friction compensation.

The Operational Space Formulation implementation to aircraft canopy polishing using a mobile manipulator

The Operational Space Formulation provides a framework for the analysis and control of manipulator systems with respect to the behavior of their end-effectors. Its application to aircraft canopy polishing is shown using a mobile manipulator. The mobile manipulator end-effector maintains a desired force normal to the canopy surface of unknown geometry in doing a compliant polishing motion, while, at the same time, its mobile base moves around the shop floor, effectively increasing the mobile manipulators workspace. The mobile manipulator consists of a PUMA 560 mounted on top of a Nomad XR4000. Implementation issues are discussed and simultaneous motion and force regulation results are shown.

High-precision control of linear actuators incorporating acceleration sensing ☆

Abstract This paper presents the application of the acceleration sensor in the enhancement of the performance of high-precision motion tracking linear actuators which are based on permanent magnet linear motors (PMLM). A feedforward–feedback control structure is developed which harness effectively the acceleration measurements made available. It utilises a linear full-state feedback controller and an iterative learning feedforward controller (ILC). Experimental results show the acceleration feedback can improve the tracking performance and learning convergence of the control system.