Open Adaptable Test for Flat-Panel Displays Saves You Time to Market and Cost

Overview

In this millennium, flat panel displays (FPDs) have become a crucial computer and communications technology with ubiquitous applications, from personal digital assistants to mobile phones to personal computers. As new FPD applications and new display technologies such as color and organic light emitting diode (OLED) displays come to market, manufactures need test and inspection approaches that:
1) Can quickly bring the new product to market, and
2) Are easily adaptable to meet future manufacturing and test needs

NI’s Display Test application platform is a configurable test and inspection tool built on modular, open components that uniquely address these needs.

Most test engineers acknowledge that, in addition to low price, defining the funcationality of your system is an important advantage of modular measurement and automation systems. For years, National Instruments customers have used modular products (i.e. IMAQ Vision software and image acquisition hardware) to create user-defined vision systems. As requirement have changed, customers have had the flexibility and scalability to upgrade their systems easily.

With the introduction of NI Display Test, customers now have the advantage of short time to market and low development risk – traits usually associated with turnkey systems. As an application platform built on NI's core hardware and software products, NI Display Test combines the advantage of both user-defined and vendor-defined systems.

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Application Platform

NI Display Test, with its comprehensive suite of built-in display tests, saves the time and energy of having to recreate common vision tests needed for display inspection applications. With each configurable display test, customers can enter test parameters and measurement tolerances. As applications change over time, NI Display Test Application Software can be reconfigured to new hardware test requirements, because it is built on scalable NI products, such as LabVIEW, LabWindows/CVI, TestStand, IMAQ, and PXI.

Types of Display Applications

Communication between machines and people is becoming a more common part of everyday life. Flat-panel displays have become an important medium of choice for consumer electronic and equipment providers. These displays can be found on products such as:

• Cellular and PDA mobile terminals
• Automotive displays
• Medical devices
• Computers
• Household appliances

Drive Toward Integration and New Technology
A cellular phone is as much a part of personal accessory today as a watch, wallet or purse. And the personal digital assistant (PDA) is not limited to the high-tech office setting. As these products continue to mature, pressure increases for technology improvements to gain product differentiation. Expect to see a neatly packaged mobile terminal that integrates the functionality integration of a cellular phone, PDA, digital camera, video, Internet connection, sophisticated mouse, and keyboard.

The transition from monochrome to color displays is the current push on display technology improvements for cellular and PDA mobile terminals. Higher resolution screens and the ability to run video is also an important element in the transition to third-generation Internet services. As integration and new technologies are introduced, the open architecture of NI Display Test makes it well suited to adapt to the changes in measurement requirements.

NI Display Test Product Content

NI Display Test is based on open NI software and hardware products such as TestStand, LabVIEW, LabWindows/CVI, IMAQ Vision, and PXI. It offers easy-to-use inspection software that does not require any programming. Recommended configuration of NI Display Test include:

• PXI-8176; 1.2 GHz Pentium III based controller
• PXI-1000B 8-slot PXI/CompactPCI chassis
• PXI-1411 color image acquisition module
• NI Display Test Application Software

The NI Display Test Application Software, which includes TestStand, IMAQ Vision, and the Display Test Libraries (a set of configurable tests integrated directly into TestStand), is built within TestStand and includes a suite of configurable tests. TestStand provides both a Test Sequence Editor and Operator Interface in which tests can be selected and deployed on a production station. NI Display Test Application Software is compatible with the entire range of National Instruments IMAQ image acquisition devices.

National Instruments offers a wide selection of analog and digital IMAQ acquisition devices available for PCI or PXI/CompactPCI platforms. Because all NI IMAQ acquisition devices offer the RTSI bus or PXI trigger bus, you can easily synchronize image acquisition with motion control, data acquisition, and other I/O functions.


Benefits of NI Display Test

Reliable	Use off-the-shelf components and proven PC technology. (TestStand, IMAQ, and PXI).
Scalable	Create new vision tests; creates other types of functional tests (LabVIEW, Visual Basic, C/C++, LabWindows/CVI).
Configurable	Set test parameters through an interactive menu-driven environment.
Shorter Time to Market	Ready-to-use product with an open architecture – reconfigurable software for hardware changes.
Lower Cost	Scalability (of tools-based products) lowers the cost of ownership.

As with all imaging systems, selecting the correct combination of camera, optics, lighting, and fixturing is essential for accurate inspection. Graftek Imaging (www.graftek.com) provides an imaging accessories kit for use with NI Display Test; this kit contains essential components for starting up your display inspection application. Many applications, though, may require a different combinationof camera, optics, and lighting. The table below shows combinations of camera, optics, and lighting that will give the best results for a given display.

Optical Configurations

Display Size	Camera	Lens	Lighting	Fixturing
2.5 x 2.5 in.	CV-S3200P 758 x 582, color CCD	HF16HA-1 16 mm lens at 8.25 in. WD	SCDI-187-FO	Extended LCD Inspection Stand
4 x 4 in.	CV-S3200P 758 x 582, color CCD	HF12.5HA-1 16mm lens at 10.55 in. WD	SCDI-187-FO	Extended LCD Inspection Stand
7 x 7 in.	DFW-SX900 1280 x 960, color, digital CCD	HF9HA-1 9mm lens at 135 in. WD	Call	Extended LCD Inspection Stand

Suite of Display Tests

NI Display Test consists of a comprehensive suite of built-in display inspection tests. Test engineers can work with either acquired images from a camera or read from a file.

The Display Test Library is a set of configurable steps in the TestStand Sequence Editor, and each display test is within the Display Test Library. Test engineers build a test sequence by selecting and configuring their desired tests. Developers can easily program additional steps using LabVIEW, LabWindows/CVI, Visual Basic, or C/C++ to communicate to the unit under test.

NI Display Test consists of the following built-in tests:

• Alignment – Computes the location, orientation, and skew of the display. It also can compute the location of the housing that surrounds the display as well as the pixel gap between the display and the housing.
• Pixel Defects – Detects defective rows, columns, or individual pixels.
• Contrast – Computes the average intensities of the black regions and the white regions of the display and then returns the difference between the mean black and mean white intensity values as the contrast of the display pixels.
• Icon Presence – Determines the presence of selected icons in regions of interest.
• Gray-scale Illumination – Divides the inspection region into rectangular bins and computes the intensity statistics for each bin. You can specify the number of bins you want to use.
• Color Illumination – Divides the inspection region into rectangular bins and computes the color statistics for each bin. You can specify the number of bins in the inspection region and the color model you want to use to compute the statistics.
• OCR – Reads a string of characters on the display and determines whether the string matches the expected output.
• Segment Distortion – Locates groups, or segments, of display pixels in an image and computes the distortion of the segments.
• Gross Defects – Locates, counts, and measures defects – such as scratches and blemishes – in an inspection region.
• Character Verification – Finds characters in the image similar to a pattern that you specify and determines the similarity between each character and the pattern.
• Housing Color – Compares the color of the display housing to a color template.
• Keypad Inspection – Searches areas in an image to verify that all keys on a keypad are present and of good quality.
• Keypad Backlight – Computes the color statistics of the backlight.

Configuration of Display Tests

Test engineers can interactively set up a display test a through a configuration interface. The setup of a test involves the following:

(1) Setting parameters that govern the behavior of the test
(2) Selecting inspection regions
(3) Setting tolerances to specify the acceptable range of values

The configuration interface guides you through the setup of the test by providing continuous feedback of the measurements made by the test. These measurements are graphically displayed on the inspection image as well as reported in numeric tables.

Parameters
Test engineers must be able to dictate how the vision tools process the image and make measurements. Because a unit under test (UUT) and the conditions of test vary significantly, fixed algorithms cannot meet reliability requirements. Therefore, each inspection test in the NI Display Test software has a set of parameters that can be modified. The following list is a sample of some of the parameters within different tests:

• Alignment – engineers can specify different edge strength, width, slope and subsampling intervals.
• Pixel Defects – engineers can specify the choice of inspection patterns and whether to compensate the image for intensity variations.
• Contrast – engineers can use the "Border Size" parameter to specify how many pixels near the region boundaries the test should omit from the contrast measurement.
• Gray Scale Illumination – engineers can specify the number of regions to divide the display.
• Color Illumination – engineers can choose measurements in the RGB (red, green, blue), HSL (hue, saturation, luminance), or CIE spaces.
• Icon Presence – engineers can choose to use color information when looking for the icon. If using color, one can also specify how much importance is given to the color information in the test.
• Gross Defects – engineers can specify the size of the defects or ignore defects touching the boundary of the inspection region.
• Housing Color – engineers can specify how sensitive the test is to the color information.
• Keypad Inspection – engineers can choose to search for the keys within one inspection region or specify individual regions for each key.

Inspection Regions
Using NI Display Test, engineers can specify the regions within the image from which the measurements are made. Selecting inspection regions in NI Display Test has many benefits:

• Improves the accuracy of the measurements by targeting the specific regions in the image.
• Avoids inaccuracies that may occur due to irrelevant (noisy) information in other parts of the display.
• Maps the display region using a four-sided polygon and accurately locates the centers of the display pixels even under significant perspective errors (i.e., when the camera is viewing the display from an angle).
• Engineers can draw (specify) inspection regions with arbitrary (free-hand) shapes in the Keypad Backlight test, which enables engineers to precisely specify the backlit regions on the keypad.
• Improves the time performance of the test because measurements are made only within the inspection region. The time taken to make measurements is directly proportional to the size of the inspection region.

Tolerance Selection for Measured Values
Prior to running display inspection testing, the test engineer sets the minimum and maximum tolerances around each of the measured values. Typically, a "golden unit" deemed to have good quality characteristics is used to set these values.

During the operation of the test, a "Pass" will be awarded to a test if all of its measured values fall within the set minimum and maximum tolerances. Otherwise a 'Failure" will result and be reported in the appropriate report.

Adding Additional Tests within TestStand

NI Display Test comes with a built-in suite of display tests. Customers may want to add a unique customer-defined machine vision test different than those found within the suite of tests. The ability to add additional tests is a core attribute of TestStand. To add another machine vision, or any other kind of measurement routine to the Display Test Library, you:

• Define a TestStand step type for the custom step
• Write a code module that implements the run time functionality of the test
• Write a code module that implements a GUI for test configuration
• Attach the run-time and configuration code modules to the TestStand step type.

Using Active X, you can write code modules in LabVIEW, LabWindows/CVI, Visual Basic ,or C/C++. For more information on TestStand step types and custom tests, go to the end of this document to "Advanced Users – Building Custom Configurable Tests".

Design Verification Test

NI Display Test has four important benefits as a tool for test engineers involved in research, design, or verification; and it can be used to easily adapt NI Display Test from design and verification applications to production test:

1. Display Test Code is already finished – There is no need to become a machine vision software expert. Because most of the common tests are written and included in the suite of tests within the NI Display Test Library, test engineers can focus on their primary goal. By choosing appropriate parameters, inspection regions, and tolerances, laboratory test engineers are immediately able to conduct experiments.

2. LabVIEW makes it easy to add tests – The goals of design verification tests, which are to qualify the characteristics of materials, components, and systems, require engineers to create flexible tests, specific to particular tasks. This need to deploy flexible measurement software in the laboratory environment has led to the success of products such as LabVIEW, LabWindows/CVI, and Measurement Studio for Visual Basic. The National Instruments integrated software framework makes it easy to incorporate additional measurement tests within NI Display Test.

3. TestStand increases the efficiency of automated laboratory tests – NI Display Test incorporates TestStand in conjunction with a suite of display tests to greatly improve the efficiency of experiments in laboratory tests. Whether conducting a Pixel Defect Test or testing the functionality of a mobile terminal – automated setup and operation could be up to 20 times more efficient with NI Display Test.

4. No need to maintain custom software – The vision engineering group at National Instruments will make maintenance and general improvements to the NI Display Test application software. Additional tests will be added to the future software upgrade versions.

Manufacturing Test

Display inspection is used in many different manufacturing test applications. A UUT could be a display component, or the UUT could be a fully assembled cell phone or an automotive DVD screen. NI Display Test has been developed to scale across a broad set of test requirements.

The following block diagram – an integrated manufacturing test system for a mobile terminal UUT, an integrated cell phone/PDA – represents a wide set of functional test requirements. An integrated manufacturing test platform could include, for example, the following functional tests:

• Mechanical
• Electrical
• Audio
• RF
• Vision
• Serial Communication

There are two dimensions of an integrated manufacturing test system – the deployment and development environments.

Within the deployment environment are the elements of hardware and software that perform the tests in the production line. The development environment encompasses the tools used to create and maintain the test code in a manufacturing test system. The shaded blocks represent National Instrument products for both the deployment and development dimensions.



NI Display Test, as depicted in the figure, is built on the open NI architecture. It is easy to incorporate any of the above test functions, with NI Display Test, into an integrated test platform by creating custom TestStand step types to perform the desired functionality.

Comparative Analysis versus Vendor-Defined Systems

The manufacturing environment has a set of needs different from those found in the laboratory. Because the manufacturing environment is mission critical and involves a high amount of investment, most decisions about production test solutions weigh heavily upon the "time, risk, and cost" assessment of the test manager.

Vendor-defined test solutions are generally viewed as having short time to market and low risk. However, in industries where the rate of change in technology is great, such as consumer electronics and displays, vendor-defined solutions often lead to increased cost, development time, and risk. Production test solutions, in fast-changing applications, require scalability, flexibility, and an open architecture in order to effectively cope with new requirements and without being fundamentally altered or completely replaced.

The chart illustrates the lower "time, risk, and cost" attributes of National Instruments products compared to custom and vendor-defined systems. When reading through the diagram, observe the size of the following symbols to gauge the impact of a new test requirement:

Time
N Risk
$ Cost
P Just do it – already available


Both hardware and software elements of a manufacturing test system need to cope with new test requirements. NI Display Test offers a suite of display inspection tests. If additional measurement tests are required, then the National Instruments open architecture for both software and hardware products, provides a scalable, flexible development framework – LabVIEW, LabWindows/CVI, TestStand, IMAQ Vision, and PXI.

Conclusion

Applications and technical requirements for flat-panel displays are growing. Display inspection solutions need to scale easily to changes in display test requirements without being fundamentally altered or completely replaced.

NI Display Test is for flat-panel display testing by design validation engineers and manufacturing test engineers. Built on NI’s proven software tools, such as LabVIEW and TestStand, and the industry-standard PXI platform, it provides a comprehensive suite of built-in display tests. Unlike vendor-defined solutions, NI Display Test Application Software is inherently scalable to additional hardware and new test requirements

Advanced Users – Building Custom Configurable Tests

NI Display Test includes the open architecture and modular approach of TestStand, which provides the necessary infrastructure to develop additional measurement configurable tests. The foundation of a configurable test is the flexibility and modularity of the TestStand step.

A TestStand step does more than just call a code module. In fact, it performs numerous operations before and after calling the code module. Some of those operations include evaluating a precondition, executing engine callbacks, running prestep and poststep routines, evaluating status expressions, etc.

All the various operations of a step interact with each other to provide the desired functionality. Step properties play a key role. They serve as a repository of data that every step operation can use. You can think of step properties as local variables for a particular step. These properties hold configuration information, as well as test results. A big advantage of having step properties is that every instance of a particular step type will have its own set of step properties. You can thus have two steps of the same type configured to behave differently.

The following diagram represents the interaction of some step operations with the step properties. It shows how you can use step properties to share data between the various step operations.


This diagram shows some of the available step operations. For a complete listing of all the available step operations, please review the section ""Step Execution" in the TestStand User Manual.


A step has two modes of operation – configuration and execution modes. During configuration mode, the properties of the step are set to specific values. The setting of these properties can be through a configuration panel or dynamically through a tool such as the Property Loader. During execution mode, the step calls a test code module. This code module can access parameters that were previously set in the step properties when the test was being configured.


For example, consider the Keypad Inspection test within NI Display Test. During configuration mode, the operator can use the configuration interface to configure parameters such as "Source", "Template Path," or "Minimum Score," among others, as shown here.

When the configuration interface is closed, all parameters currently displayed in the dialog are stored in their corresponding TestStand step properties, i.e. "Camera," "TemplatePath," and "MinMatchScore," as shown below.



When the Keypad Inspection test is executed, it calls the "niKeypadInspectioRuntimeTest" function, included in the NIDisplayConf.dll. This function receives the sequence context as a parameter, which enables the test code to access all the step properties to perform the test according to its configuration.


A configurable test step has the following characteristics:

• Contains a set of defined step properties that hold information specific to the current test.
• Provides a user interface for configuring all test parameters. The user interface must be interactive, so the user can immediately visualize the effects of changing parameters. The modified parameters must be stored in the step properties.
• Calls a code module that performs a specific action based on how the step was configured. Any value returned by the code module must also be stored in step properties.

A configurable test step must be self-contained. The user should be able to easily configure the test parameters without knowing the intricacies of the configurator or the test itself. When creating configurable steps, you should consider the following:

• Defining how the test will be performed is the most important task of creating any step type. This task requires identifying how the test will be executed and how the data will be acquired and stored.
• There are three main aspects to consider when creating a configurable step:
  1. The execution flow of the step
  2. How the step will store configuration and test data
  3. How the user will configure the step parameters

By understanding the flow of your test, you can create a step that is modular and takes advantage of the open features of TestStand found within NI Display Test.

• A Configuration Interface is a program with which the user can interactively configure the parameters of a test via a graphical user interface. Normally this interface runs the test in a loop so the user can visualize how modifying the parameters will affect the test. They generally include a Pass/Fail indicator that helps the user set the tolerances and visualize when the test is out of range. A configuration interface can be implemented using LabVIEW, LabWindows/CVI, Visual Basic, Visual C++, ANSI C, or any other programming language compatible with TestStand.

• When all your configurable steps are completed, it’s a good idea to create a palette to group them together. This open feature of TestStand accessible by users will make your custom steps look native to the TestStand environment for everyone to use.

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