A Predictive Velocity Observer in Wire Bonder’s Control System

Lei Zhou,Wennong Zhang,Zexiang Li,Jiangang Li

doi:10.1155/2014/398205

Abstract

Wire bonder is a typical high speed machine. The motion speed of XY-stage is the key factor of bonding efficiency. However, phase lag elements in the servo system limit the bandwidth and slow down the system’s response. A predictive velocity observer is proposed to compensate for those phase lags. Then, the velocity loop controller can be designed as for a servo system which does not have those phase lags. Loop gains are enlarged and bandwidth is enlarged correspondingly. Then, the motion speed is improved and settling time is decreased. Experiment results verify that the predictive velocity observer provided a significant phase lead and the performance of wire bonder is improved.

Highlights

Wire bonder [1] is typical high speed machine
A typical auto-gold wire bonder consists of several modules such as auto-material handling module, pattern recognition (PR) system, ultrasonic generator (USG) module, electronic fire off (EFO) module, bond head, and XY-stage
Based on the idea of velocity observer and Smith predictor, we propose a predictive velocity observer to provide phase advance

Summary

Introduction

Wire bonder [1] is typical high speed machine. It bonds wires which form a circuit between the pad and the lead. The phase lag elements contain filters and pure time delays. Low-pass filters and pure time delays produce more phase lags at higher frequency range. The bandwidth of the feedback control loop is not enlarged. There are many modified Smith predictors [20, 21] It uses a model of the plant without pure time delay and takes the output of the model as feedback signal. The delay time will lower the control performance in high speed motion control system. Phase lags are modeled as a first order low-pass filter and a pure time delay. The results will show that the performance of wire bonder’s control system is significantly improved and high speed motion is achieved

Servo System Description

The Predictive Observer

Implementation of Predictive Velocity Observer

Experiments

Conclusions