Gain-compensation Methodology for a Sinusoidal Scan of a Galvanometer Mirror in Proportional-Integral-Differential Control Using Pre-emphasis Techniques

Summary

We propose a method to extend the corresponding frequency by using a pre-emphasis technique. This method compensates for the gain reduction of a galvanometer mirror in sine-wave path tracking using proportional-integral-differential control.

Abstract

Galvanometer mirrors are used for optical applications such as target tracking, drawing, and scanning control because of their high speed and accuracy. However, the responsiveness of a galvanometer mirror is limited by its inertia; hence, the gain of a galvanometer mirror is reduced when the control path is steep. In this research, we propose a method to extend the corresponding frequency using a pre-emphasis technique to compensate for the gain reduction of galvanometer mirrors in sine-wave path tracking using proportional-integral-differential (PID) control. The pre-emphasis technique obtains an input value for a desired output value in advance. Applying this method to control the galvanometer mirror, the raw gain of a galvanometer mirror in each frequency and amplitude for sine-wave path tracking using a PID controller was calculated. Where PID control is not effective, maintaining a gain of 0 dB to improve the trajectory tracking accuracy, it is possible to expand the speed range in which a gain of 0 dB can be obtained without tuning the PID control parameters. However, if there is only one frequency, amplification is possible with a single pre-emphasis coefficient. Therefore, a sine wave is suitable for this technique, unlike triangular and sawtooth waves. Hence, we can adopt a pre-emphasis technique to configure the parameters in advance, and we need not prepare additional active control models and hardware. The parameters are updated immediately within the next cycle because of the open loop after the pre-emphasis coefficients are set. In other words, to regard the controller as a black box, we need to know only the input-to-output ratio, and detailed modeling is not required. This simplicity allows our system to be easily embedded in applications. Our method using the pre-emphasis technique for a motion-blur compensation system and the experiment conducted to evaluate the method are explained.

Introduction

Various optical actuators and control methods suitable for various optical applications have been proposed and developed^1,2. These optical actuators are able to control the optical path; galvanometer mirrors especially offer a good balance in terms of accuracy, speed, mobility, and cost^3,4,5. Actually, the advantage offered by the speed and accuracy of galvanometer mirrors has led to the realization of a variety of optical applications, such as target tracking and drawing, scanning control, and motion-blur compensatio....

Protocol

1. Acquisition of Gain Data for a Galvanometer Mirror

1. Fix the galvanometer mirror such that it is stabilized to protect it from damage while oscillating. Not only the galvanometer mirror, but also the body of the galvanometer mirror, moves if not fixed in place using a custom-made metal jig with a circular hole for the galvanometer mirror. Fix the jig onto an optical carrier and an optical bench.
2. Connect BNC cables from the AD/DA board through a terminal block to the input and position sockets in the servo driver of the galvanometer mirror.
3. Program the sine-wave function generator as a graphical user interface (GUI) using the SDK of the....

Results

The results presented here were obtained using an AD/DA board and a camera. Figure 1 shows the procedure of the pre-emphasis technique; therefore, it is the core of this article. It is unnecessary to set the parameters of the PID control after the initialization state; hence, the online process is significantly simple.

Figure 10 shows the results obtained by applying the pre-emphasis technique t.......

Discussion

This article presents a procedure capable of expanding the sine-wave frequency range to achieve high-accuracy trajectory tracking with PID control. Because the responsiveness of a galvanometer mirror is limited by its inertia, it is critical to use a galvanometer mirror when the control path is steep. However, in this research, we propose a method to improve the specification of control and then prove the method by obtaining experimental results.

In our procedure, step 2.5 is the most critical.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Galvanometer mirror	Cambridge Technology	M3s X axis
Custom-made metal jig	ASKK	-	With circular hole for galvanometer mirror
Optical carrier	SIGMAKOKI	CAA-60L
Optical bench	SIGMAKOKI	OBT-1500LH
Oscilloscope	Tektronix	MSO 4054
AD/DA board	Interface	PCI-361216
PC	DELL	Precision T3600
Galvanometer mirror servo controller	Cambridge Technology	Minisax
Lens	Nikon	AF-S NIKKOR 200mm f/2G ED VR II
High-speed camera	Mikrotron	Eosens MC4083	Discontinued, but sold as MC4087. The cable connection is different from MC4083
Conveyor belt	ASUKA	-	With a speed-control motor(BX5120A-A made by Oriental Motor), iron rubber belt(100-F20-800A-J made by NOK), and so on
Printable tape	A-one	F20A4-6
Photographic texture	Shutterstock, Inc.	231357754	Printed computer motherboard with microcircuit, close up
Terminal block	Interface	TNS-6851B
CoaXPress board	AVALDATA	APX-3664
MATLAB	mathworks	MATLAB R2015a