Design and vibration control of a notch-based compliant stage for display panel inspection applications

Abstract

Both fast positioning and eliminating relative vibration between automatic optical inspection devices and the associated workpieces are critical for enhancing the throughput of product inspection. Both goals can be achieved by proper control of the stage where the camera is mounted. In this work, a one-dimensional compliant stage, consist of a notch-based structure and a mechanical amplifier, is designed and controlled for fulfilling the above mentioned goals. Essential finite element simulation and structural testing are performed to further characterize the structure and to obtain the system dynamics for controller design. The fundamental natural frequency of the designed stage is approximately 410 Hz and a displacement amplification ratio of 1.21 is achieved. The stage is actuated by a PI-843.40 piezoelectric actuator and the motion is monitored by an ASP-10-CTR capacitance probe. The entire signal acquisition and control are performed under a NI LabView environment using a NI cRIO-9014 FPGA real time controller, where both PID and sliding motion controllers are implemented. The results indicate that a close loop bandwidth of 12 Hz or 29 Hz and a steady state resolution of 50 nm can be achieved after PID or sliding mode control. With such a response, the motion induced vibration may be suppressed for subsequent automatic optical inspection and other applications such as coordinate measurement systems.