General Production and QC Software

Axometrics, Inc.

103 Quality Circle, Suite 215

Huntsville, AL 35806

Phone: (256) 704-3332

Fax: (256) 971-2073

E-Mail:

Website: http://www.axometrics.com

Axometrics

General Production and QC Software

AxoStep (APM Turret)

Calculation Library

©2015 Axometrics, Inc. All rights reserved.

AxoScan, AxoView, Axometrics and the Axometrics logo are trademarks of Axometrics, Inc.

1

CONTENTS

1 Introduction 2

2 Multi-Domain LCD Production Measurements 3

2.1 Live Image 4

2.1.1 Focus Controls 5

2.1.2 Stage Controls 5

2.1.3 Pixel Definition 6

2.1.4 Define Pixel 7

2.2 Subdomain Settings 10

2.2.1 Additional LCD Options 13

2.3 Analysis Options 14

2.3.1 Layer count 14

2.3.2 Alignment correction 16

2.3.3 Refractive Index 16

2.4 Compensation and Parameter Limits. 18

1  Introduction

This manual describes configuring a multi-domain LCD measurement with an AxoStep Panel Mapper turret fixture using AxoStep production software.

2  Multi-Domain LCD Production Measurements

If the AxoStep LCD Measurement subroutines have been installed, then the option “AxoStep LCD Measurement” will be available in the Calculation Type pull down menu in the main recipe editor screen (See Section Error! Reference source not found. of the General Production Software Manual).

After selecting “AxoStep LCD Measurement”, pressing the Sample Settings button generates the following screen that is used to configure the sample settings for an multi-domain AxoStep measurement.

2.1  Live Image

The AxoStep APM production recipe editor Uses the pixel finding and centering alg orithms from the AxoStep Viewer.

Live Image: When the Sample Settings window for the APM AxoStep is opened, a connection to the AxoStep Engine configured in the production software is automatically made. The live image from the AxoStep Engine is showin in the Live Image window.

Test Measurement: Press this button to perform a test measurement using the AxoStep Engine.

Reconnect: Press this button to reconnect to AxoStep Engine, when something has caused the connection to the AxoStep engine to close or you have changed the digital zoom of the AxoStep Engine

Reset Camera: Press this button to send a Reset command to the AxoStep engine to reset the camera.

Open Large View: When this button is pressed, a large window showing the live image will be opened. This window can be resized as desired.

Wavelength: Use this control to set the wavelength of the AxoStep Engine.

Image Sampling: This indicator shows the physical size (in mm) of each pixel in the image.

AutoScale Images: When this box is checked, the live image will be autoscaled between the brightest pixel and the dimmest pixel.

Min Intensity and Max Intensity: This is used to manually set the minimum and maximum intensity in the Live Image window. Since the image is 14-bin, the intensity values can range between 0 and 16383. If the AutoScal Images check box is selected, the values in Min Intensity and Max Intensity are ignored.

2.1.1  Focus Controls

These controls operate identically to the controls on the focus Engine.

Current Position (mm): This indicator shows the current position of the focus stage.

Move: When this button is pressed it will bring up a dialog box asking the location

Up and Down Arrows: The Up and Down arrows on the Focus controls will move the stage in discrete steps given by the value in Step_focus(mm).

Step_Focus (mm): This is the distance to move the focus stage for each press of the Up and Down Arrows

Auto: Press this button to initiate an autofocus routine in the Focus Engine.

2.1.2  Stage Controls

Stage Location: This indicator shows the current location of the XY stage. Note that if the XY stage is moved using an external program this indicator does not currently automatically update.

Move: Press this button to move the XY stage to the location specified in the controls labeled x and y

Check: When this button is pressed, the a query command is made to the XY stage, and the Stage Location indicator is updated.

Up, Down, Left, and Right Arrows: These buttons will move the XY stage in discrete steps of distance given in the Step (mm) control.

Step (mm): This is the distance that is moved each time one of the the arrow buttons are pressed.

2.1.3  Pixel Definition

Locate Pixel: Press this button to Locate a Pixel in the live image.

Center Pixel: Press this button to locate the pixel and move it to the center of the live image window

Load Pixel: Press this button to load an image from a file (*.bmp, *.jpeg, *.tiff) to use as the pixel definition.

Define Pixel: When this button is pressed, it will open the Define Pixel window.

Force Algorithm to choose a Result Near the Center of the Image: Check this box when multiple pixels are in the live image window. It will cause the software to choose the pixel that is closest to the center of the image.

Apply Binary Threshold to Pixel and Image Before Search: When this box is checked, a binary threshold is applied to the image and the pixel before the search algorithm is applied (default level=64). See Appendix A for more information about using binary thresholding.

2.1.4  Define Pixel

Live Image: Press this button to capture a Live Image from the AxoStep Engine.

Click and Drag a yellow box around the region in the image that you want to define as a pixel

Note: When defining a pixel it is important that the region contain at a border of the black matrix on the outside of the pixel

Define Pixel. Press this button to define the selected region selected as a pixel.

Save Pixel: Press this button to Save the Pixel definition as a bitmap. Important: The software only stores the file location of the pixel in the recipe, and not the actual pixel in memory. When needed, it loads the pixel image from the file location. Therefore, the user must save the pixel definition.

Test: Once the pixel is defined, press this button to test the pixel search algorithm.

Log Pixel Search: This is a diagnostic tool. Check this box to create a binary log file (*.bog) of the pixel search, for diagnostic purposes.

View Pixel Search: This is a diagnostic tool that when checked, a low level window will appear showing critical information about the pixel search.

Tilt and Rotation: If the AxoStep turret used to define the pixel is not at normal incidence set the Tilt and Rotation coordinates for the turret here before testing.

Pixel: This indicator shows the currently defined pixel.

Test for Rotation: Check this box if the orientation of the test sample is different than what was used to define the pixel. Note: Turret rotations are handled automaticaly. Depending on the Algorithm used the Test for rotation can be very slow.

Algorithm: This is the computational method used for pixel centering. There are 4 methods available.

1. Correlation 1: An Image correlation between the defined pixel and the image based on the Fast Fourier Transform
2. RMS difference 1: and RMS difference between the defined pixel and the image based on the Fast Fourier Transform.
3. Correlation 2: A direct correlation (based on raster scanning) between the defined pixel and the image
4. RMS difference 2 (recommended if not performing Test for Rotation): A direct RMS difference calculation (based on raster scanning) between the defined pixel and the image. This is the slowest algorithm but it is also the most robust.

Display Threshold Image: When this box is checked it will display the image and pixel after a binary threshold operation.

Advanced Settings: From the front window pull-down Menu, click Tools>Advanced Settings

This brings up the following floating dialog (does not lock out the main window)

Algorithm, Test for Rotation, Apply Threshold to Image Before Search and Forced Image to Choose a result near the center of the image. are all described above.

Binary Threshold Value (0-255): This is the threshold value that is used when creating a binary image. The defaullt value is 64. A non-threshold and a threshold image are shown below.

The Threshold image is created as follows:

1. The image intensity is scaled between 0 and 255 (this is because the pixel search is much faster with 8-bit images)

1. Any intensity values that are less than the Binary Threshold Value (default 64) are set to 0.
2. Any intensity values that are greater than the Binary Threshold Value are set to 255.

Threshold images are particularly useful when the intensity between when the pixel is defined and measured are different, or if there are multiple pixels with different intensities in the image (because of wavelength setting)

Invert image Intensity: Will invert the image and pixel intensity before performing the pixel search (Only used on cells with no-black matrix)

Scale Image Intensity using Mode Value: Used in cases where there is little or no black matrix, or the black matrix is partially transparent.

Pixel Definition, shows the file location of the Pixel.

Xsampling and Ysampling show the pixel size in the image in true coordinates.

2.2  Subdomain Settings

After Performing a test measurement, the software will open the resultant *.astp file in the subdomain window.

Important:

1.  Select Transmittance from the Parameter to Plot control

2.  Select the on-axis image (Polar=0, Azimuth-0) from the Current image Control

3.  Press the Find Pixel button

Before you start to define your subdomains make sure that the Pixel is correctly located.

Also it is a good idea to check each image in the list from the Current Image control to make sure all images are properly registered.

Once the Pixel is properly centered, you can click and drag out a region to define as a subdomain

Press the Add Button and the following dialog will appear

You can use any name you like for your region Label, and you can adjust the size of the region if necessary (the region will remain centered if you change the size).

Click on the region to highlight it and you can adjust the LCD parameters using the slider controls below.

Additionally you can press the Launch LCDView button, and the data from the current subdomain will be imported into LCDView.

When LCDView is closed the fitted parameters will be re-loaded into the production software.

2.2.1  Additional LCD Options

The following additional options are available

Force Front Pre-Tilt to be Positive. When this box is checked, if the data fitting results in negative front pre-tilt, the Rubbing direction will be changed by 180 degrees to force the front pre-tilt to be a positive value.

Lock Cell Gap when performing Alternative Scan. When this option is checked, and an alternative scan is being performed (say scanning voltage), the cell gap will only be optimized on the first measurement of the alternative scan.

Force Pre-Tilt Angle to be less than 90 deg: When this box is checked, if the data fitting results in front pre-tilt value greater than 90 degrees, the Rubbing direction will be changed by 180 degrees to force the front pre-tilt to a value of 180-original pre-tilt (thus making it less than 90 degrees).

Perform Second Optimization: If this box is checked, the following additional options are available

The secondary optimization will be performed on all subdomains.

2.3  Analysis Options

Perform AutoFocus: When this box is checked, the recipe will perform an auto-focus for each XY position.

Center Pixel: When this box is checked a pixel centering operation will be performed before each measurement acquisition in the recipe.

Ignore Pattern Matching: When this box is checked, not pattern matching is performed in any of the data acquisition. It is used in cases where there is no pixel structure in the image

Register Images: When this box is checked, the image registration algorithm is performed before any data analysis is performed.

Check Rotation: check this box to perform rotation checking when doing pattern matching, this i the same as Test For Rotation (Section 2.1.4)

2.3.1  Layer count

The user can select the number of layers used in the liquid crystal simulation from the Program Options window (Tools>Program Options...), under the Data-Fitting Section in the tree-menu.

In general, the orientations of the liquid crystal directors vary over the thickness of the cell gap. In reality this variation is a perfectly continuous over this distance. To fit the liquid crystal parameters, this smooth variation is approximated using a stack of discrete homogenous layers. By using a larger number of layers, the simulation accuracy can be improved. However, the number of layers necessary to obtain an accurate result is dependent on the LC cell type. For example, a Super-Twisted-Nematic (STN) cell will require a large number of layers, but a Vertically Aligned (VA) LC cell can be suitably represented using a much smaller number of layers.

LCDView gives the user two options for setting the number of layers, and thereby determine the simulation accuracy.

Adaptive Layer Count: LCDview uses an iterative algorithm to determine the type of LC cell, and adaptively determine the optimum number of layers necessary to accurately represent the inhomogeneous variation of the LC cell.

Manual Layer Count: The user can manually enter the number of layers used for the simulation.

In general, it is recommended that the user use the Adaptive Layer Count option when fitting LC data. However, if unusual results are obtained, the user might want to consider using the manual layer count.

Max Iterations is the maximum number of iterations that the Optimization algorithm will use to fit the data

Tolerance is a parameter used by the algorithm to determine when to stop the optimization procedure. The lower the number, the more stable the solution. The computer stops optimizing when Tolerance reaches a value less than 0.00005. When this happens the algorithm thinks it has found a solution. Although the algorithm has found a solution, it might not be the correct solution. A common pitfall in non-linear optimization methods like the one being used here is that they are susceptible to local minima. See section 6.2 for a description of local-minima. The ultimate determination of how good the fit is rests with the merit function value, not the Tolerance Value.