http://oar.a-star.edu.sg:80/jspui/handle/123456789/115 2017-06-24T09:43:43Z 2017-06-24T09:43:43Z Hey, Jonathan Kiew, Choon Meng Yang, Guilin Ricardo, Martinez-Botas http://oar.a-star.edu.sg:80/jspui/handle/123456789/982 2015-03-26T08:21:31Z 2014-10-01T00:00:00Z

Title: Model-Based Compensation of Thermal Disturbance in a Precision Linear Electromagnetic Actuator Authors: Hey, Jonathan; Kiew, Choon Meng; Yang, Guilin; Ricardo, Martinez-Botas Abstract: Thermal disturbance is a major source of positioning error in precision-positioning systems. The conventional approach of using special materials for construction and sophisticated geometric design based on advanced computer simulation can be costly as well as time consuming to implement. Moreover, dynamic thermal disturbances cannot be effectively compensated for by such methods. The approach presented in this paper uses model estimated position error coupled with sensor measurement as a feedback compensator of the output shaft position. A state-space model is used in a modified Kalman Filter to reduce the total number of temperature sensors needed for estimation of the thermally induced position error. A maximum temperature estimation error of 1.8% of the measurement range is recorded. An online parameter estimation method is implemented to “fine tune” a transfer function model during a calibration stage before compensation. The model-based compensation method resulted in a mean uni- directional positioning deviation of −0.2 µm and repeatability of ±0.7 µm during a 5-h continuous operation.

2014-10-01T00:00:00Z Short, Joel Stephen Poo, Aun Neow Ang, Marcelo H Lai, Chow Yin Tao, Pey Yuen http://oar.a-star.edu.sg:80/jspui/handle/123456789/885 2014-12-11T08:24:52Z 2014-07-08T00:00:00Z

Title: Hamiltonian Exploitation in Underactuated Robot System Inversion Authors: Short, Joel Stephen; Poo, Aun Neow; Ang, Marcelo H; Lai, Chow Yin; Tao, Pey Yuen Abstract: A new stable model inversion method extension is presented with the aim of providing solutions to the feedforward control of underactuated robots performing cyclic tasks. The method uses a boundary value problem framework along with a Hamiltonian formalism, representing the dynamic equations of motion, to find solutions for the control of movement between non-equilibrium points in taskspace. The benefits of the method are demonstrated with a simulated robot system.

2014-07-08T00:00:00Z Lai, Chow Yin http://oar.a-star.edu.sg:80/jspui/handle/123456789/884 2014-12-11T08:23:50Z 2014-07-08T00:00:00Z

Title: Decoupling of macro-mini manipulator using adaptive neural networks Authors: Lai, Chow Yin Abstract: Attaching a small manipulator (mini) with fast dynamic response at the end of a bigger manipulator (macro) with larger workspace leads to the concept of macro-mini manipulator, which is seen as a way to improve the system performance as compared to the macro manipulator acting alone, for example in terms of positioning accuracy. However, cross coupling between the two counterparts could undermine the practicality of the concept. In this paper, an adaptive neural network decoupler is presented to reduce the coupling effect of the macro-mini manipulators, without the need to have a proper dynamic model of the macro, and without alteration to the macro's controller. The stability of the proposed scheme is analyzed through the use of Lyapunov criterion. Simulation results show that by using the proposed neural network decoupler, the positioning accuracy of the macro-mini system can be improved significantly even when the macro manipulator is perturbed by external disturbances.

2014-07-08T00:00:00Z Lai, Chow Yin http://oar.a-star.edu.sg:80/jspui/handle/123456789/883 2014-12-11T08:20:10Z 2014-07-08T00:00:00Z

Title: Improving the transient performance in robotics force control using nonlinear damping Authors: Lai, Chow Yin Abstract: Robotics force control is increasingly being used in the manufacturing industry, to perform surface polishing, deburring, parts mating etc. However, to avoid the high impact force which could damage the workpiece, a common strategy is to command the robot to approach the workpiece slowly, which increases the overall cycle time. In this paper, we propose a nonlinear damping control scheme which reduces the force overshoot without compromising on the dynamic response. The controller design and the parameter tuning are relatively straightforward because of the clear physical meanings of the parameters. Finally, the effectiveness of the proposed controller is verified through simulation studies.

2014-07-08T00:00:00Z