Precision Tool Setting

8/2/2019 Precision Tool Setting

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C. L. CHAO

Dept. of Mechanical EngineeringTam-Kang University

Precision Engineering Group

1

Development of a Sub-pixel Optical Vision

System for Precision Tool Setting

C. L. Chao1, J. Neou2, T.A. Cheng3, C.W.Chao4,

1 Department of Mechanical and Electro-Mechanical Engineering, Tam-Kang University

2. Department of Electrical Engineering, Hsiuping Institute of Technology

3. Department of Mechanical Engineering, Chung Cheng Institute of Technology

4. Department of Information Management, Hsing-Wu College


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Outline

Introduction

Influence of tool-setting error

Optical tool-setting system

Sub-pixel image analysis technique

Results and discussion

Conclusion


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Tool Setting-introduction

Vacuum

Chuck

Spindle

Workpiece

To align thetool tip with therotational axis of

work spindle


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Profile error induced by tool offset

Too high

Too low

Spindle Axis

Spindle Axis

Workpiece


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Tool off too high


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Offset error < 0.5m


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Off to the right

Spindle Axis

CL CL

Resulted Profile

Spindle AxisTargeted Profile

Off to the left

Feeding direction

Profile error induced by tool offset


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Tool setting procedures

Preset tool

by LVDT

Test cutting of

soft metal

stud

Measuring the

tool offset

Adjusting

tool

Optical tool

setting

Start the cutting

processChanging

tool


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Precision positioning stage/machine tool

CCD Camera

Tool-post

Axis

Precision Machine

Tool


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Schematic presentation of the optical tool settingsystem

CCDCamera

To PC andFrame

Grabber

Tool

Tool PostLighting Unit


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CCD

Camera

Digital

Image

Frame

Grabbing

ImageEnhancement

Edge

Detection Refinement

Image analysis procedure for tool setting system


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Edge detection

Roberts

Sobel

Laplacian Zernike

Original Image

After refinement


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Edge Detection


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Original CCD image and the detected edge ofa round-nose tool


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Schematic representation of the step-like nature ofthe tool-edge movement shown by the pixels

Tool EdgeTransition

Zone

Pixel


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The physical dimension represented by a pixel

The resolution of the precision machine tools

available today

Normally > 2m

Normally ~ 1nm


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10

20

30

40

50

5 10 15 20 25 30 35 40

Pixel Coordinate

Pixe

lArea

504

506

508

510

512

0 100 200 300 400 500

Platform Micro Movement(step)

PixelC

oordinate

Fine tool movement against pixel coordinate

Ideal Practical


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Response of pixel counting against fine movement ofprecision positioning stage

617.0

617.5

618.0

618.5

619.0

0 20 40 60 80 100

Platform Micro Movement

PixelCoordinate

504

506

508

510

512

0 100 200 300 400 500

Platform Micro Movement


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Least square technique to average out the noise

504

506

508

510

512

0 100 200 300 400 500

Platform Micro Movement(step)

PixelCoordinate


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Experiments for comparing the movements made bystages and readings detected by the system

XTool Tip

Tool


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Sub-pixel dividing-fixed sampling points

50 100 150 200 250 300 350 400 450 500 550

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

1.83751.85531.87531.9305

1.9971

0.50230.55490.52090.5527

0.7124

0.04360.08580.0862

0.2487

0.3734

0.0978

0.2015

0.33220.3322MeasurementE

rror(um)

Sampling Points

0.1um

0.2um

0.4um0.8um


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Sub-pixel dividing-fixed assessment lengths

20 25 30 35 40 45 50

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

1.96712.0019

1.39571.3957

0.4129

0.60350.76070.7607

0.1169

0.2487

0.37340.3734

0.09780.2015

0.33220.3322

Measurement

Error(um)

Accessment Distance(um)

0.1um

0.2um

0.4um

0.8um


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Conclusion

The corresponding dimension represented by a pixel,

step size of the fine movement made by the precisionstage, number of sampling points, total assessmentlength are the key factors in deciding the achievableaccuracy

An assessment length equals to (or longer than) a full6~8 pixels size is recommended to get better result

An error band within 0.1m was achieved using the

developed optical vision system (with the pixel sizearound 6m) and sub-pixel dividing technique.


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Thank you for your time

Documents

Precision Tool Setting