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Quality Control Automation

Discusses the importance of quality control in manufacturing, describing in detail how to easily automate quality control data collection, storage and analysis for all types of measuring tools.

Companies today are under constant pressure to become more efficient in their manufacturing processes, increasing productivity while keeping costs down. In addition to efficiency, accuracy is imperative as companies race to develop and maintain procedural standards to meet ISO 9000 compliance and position themselves for corporate survival in the Twenty-First Century.

It’s All About Quality

The idea behind initiatives like ISO 9000 is to encourage manufacturers to develop their own standards for quality control and then implement procedures that allow them to meet these pre-established standards. The primary reason for developing standards is so that when one manufacturer purchases a product or part from another, there is some guarantee of consistency and quality as well as accountability when there is a problem. Ideally, every manufacturer should want to continually improve the quality of the products they produce. The first step toward achieving this goal of constantly improving quality is to develop methods for measuring everything you manufacture for consistency and compliance with pre-defined standards.

An integral part of most manufacturing quality control procedures is simply to measure every part produced at every stage of the manufacturing process. "Statistical process control" (SPC) is then used to examine the measurements analyzing trends or variations that could cause parts to be "out of spec". A typical scenario could be as follows: you manufacture widgets that are made up of several wire forms and each are cut with a different cutting machine. As the blades wear out on the cutting machines, you eventually produce parts that vary in size. In addition, each of the different cutting machines may have blades that wear out at different rates. By measuring each part after it has been cut, you can determine the optimal number of cuts to make before changing a blade. If you cut your parts in large batches, you can also catch problems, like a defective blade, before you produce thousands of bad parts due to a problem with your cutter. Not only does quality control help you produce products that consistently meet certain standards, it also has the added benefit of making your processes more efficient and more cost effective.

These quality control concepts are nothing new. I will assume you are familiar with Dr. W. Edwards Deming whose preachings on quality control to the Japanese changed the implicit meaning of the words "Made in Japan". Dr. Deming’s methodologies stress working together in a systematic way to continuously improve the way an organization does whatever it does.

Manufacturing a product is a procedure. Quality control is a procedure to monitor a procedure with the goal of making it more efficient. The following discussion is designed to explore ways to make the quality control procedure itself more efficient by automating the measuring and "SPC" process by using computers.

First Steps in Quality Control

Typically, when a manufacturer implements a quality control procedure that involves measuring something, they start by purchasing a measuring instrument (e.g. a caliper, micrometer, height gage, bore gage, force gage, CMM, etc.) from one of the many metrology companies. The manufacturer might then develop a procedure for measuring their parts where someone is given the task of taking measurements and writing them down on a piece of paper. The measurements would then be keyed into either a spreadsheet or a dedicated SPC software program for analysis by an engineer. Obviously this method has some potential pitfalls since people are involved in the manual data collection and data entry part of the process. Manual data entry is slow and tedious and people make mistakes.

Automating Quality Control

Tool Time

A more accurate and more efficient approach to data collection is to enter data from your measuring instruments directly into a spreadsheet or SPC program. Most measuring tools today are available with some form of electronic output making it possible to connect the instrument to dataloggers, printers or to a computer, thereby eliminating the steps of manually writing down measurements and typing them in. Automating data collection removes all possibility of human error and it also allows for real time data analysis. In addition to collecting an accurate computerized record, it is also possible to control an entire process based on the input from the tools that you use to measure the process. From our previous example, when you measure each part that comes out of your cutting machine, the measurement can be fed immediately to a PC that has been programmed to instruct an operator to change the blade when the measurements fall outside a specific tolerance. This type of automation creates an extremely efficient process designed to maintain the manufacturers’ quality control standards.

Interestingly, the metrology industry has never settled on any one standard for the electronic interface between instruments. This is due, in part, to simple rivalries between companies. Each of the different "key players" in the measuring tool industry developed their own electronic interface with the hope of making theirs’ the standard for the entire industry. By protecting their interface standard with patents, they lock the competition out from any large manufacturer that adopts their electronic interface standard.

Most of the electronic interface standards were also developed long before computers were commonly found in the manufacturing environment. Because personal computers are now the dominant tool for data collection and analysis, an entire industry has grown out of the need to convert the different measuring tool interfaces to one that is compatible with PCs.

The PC Connection

If you look on the back of any computer you will find many different connectors or "ports". Most of the connectors are designed to connect to a specific type of device. For example, the keyboard port is designed to connect to a keyboard, and the printer port is designed to connect to a printer.

Fortunately, the original designers of the IBM PC had the foresight to include an additional connector called an RS232 port. The RS232 port was intended to be a general input/output port, thereby allowing data to be sent and received to and from many different types of external devices.

What Exactly is RS232?

RS232 stands for "Recommended Standard #232". It is a standard developed by the Institute of Electrical and Electronic Engineers (IEEE) and was originally designed to allow a computer to be connected to a modem so that data could be transmitted over telephone lines. The standard defines the electrical characteristics (i.e. connector pinouts, voltage levels and electrical signals) for transmitting data from one electronic device to another. The RS232 interface is also called a "serial" interface because digital data is transmitted "serially" one bit at a time. Bytes of data are taken apart by a transmitter with each bit being transmitted in series. The receiving device collects the bits and puts them back together into the original data bytes. The content and structure of any data that is transmitted is not defined by the RS232 standard, however, the most commonly used format for data is text and decimal numbers, i.e. readable data (at least in the measuring instrument industry).

In addition to RS232, RS485 and RS422 data is also serial. RS 485 is also called "multi-drop" as you can address multiple devices over an RS485 cable. Both RS485 and RS422 are easily converted to RS232 or you can purchase special ports for your PC. Converters are available from companies such as B&B Electronics.

An Almost Perfect Standard

There are three factors that make the RS232 standard the ideal interface for instrumentation. Firstly, every PC in the world comes equipped with at least one or two serial ports (RS232 connectors). Even laptops and palmtops come with at least one serial port. Additional serial ports and multiplexers are readily available and are very low in cost (on the order of $40.00 for each additional port). Additional serial ports and multiplexers are available from companies like Digi International, Sealevel Systems and Western Telematic. Secondly, there is an extremely large amount of inexpensive PC software available for transmitting and receiving data through the serial port. This is perhaps the most important aspect for any data communications standard. If there is no software available to support an interface standard, the hardware that uses the standard is practically useless. Finally, the RS232 standard is extremely easy and inexpensive to implement. Although not all of the manufacturers of measuring instruments have adopted RS232 as their standard interface, the writing is on the wall. Those that have not yet adopted RS232 at the instrument level, sell additional hardware that will convert whatever output they have to RS232.

The entire Fowler/Sylvac line of measuring instruments available from the Fred V. Fowler Co. (including calipers, micrometers, height gages, bore gages, etc.) have a built-in RS232 interface. The L.S. Starrett Company also manufactures some measuring instruments with direct RS232 output, as does Chatillon. Although most companies have RS232 output on their "high end" instruments, companies like Mitutoyo, Federal and Brown & Sharp do not have direct RS232 output on their calipers and small measuring instruments. However, there are a number of manufacturers of converters that will convert the output from these instruments to RS232. Companies that specialize in RS232 converters include B&B Electronics, GageTalker Corp, Gage Connections, Micro Ridge and the Fred V. Fowler Corp. Converters can cost anywhere from $159 to $600. In almost all cases a measuring instrument with direct RS232 output will cost roughly the same as one that does not have RS232 output, therefore you sometimes pay a penalty for using instruments that do not have direct RS232 output. In fact, the cost of a caliper with direct RS232 output is less than the cost of a typical converter.

Choosing the Right Software - The Final Step

All of the factors outlined above exemplify how easy and inexpensive it is to connect almost any measuring instrument to a PC. The remaining piece of the puzzle is to choose the right software to run on your PC. Unfortunately, you cannot simply plug a measuring instrument into the serial port on your PC and expect the data from the instrument to magically appear in your favorite spreadsheet or SPC program; at least not without the right software. Fortunately, as mentioned above, there is no shortage of excellent (and inexpensive) software for inputting instrument data through the serial port. The choice of what software to use depends greatly on what you want to do with your data. If you simply want to capture data and save it to a disk file or print it out, then terminal programs are an option. You can also purchase specialized SPC software that supports direct data input from the most common RS232 instruments (or from the devices that convert instrument data to RS232). Another option is to use a software product called the "WinWedge" that allows you to input data from any measuring instrument directly into any PC program that you want, including your favorite spreadsheet or database.

Terminal Programs

A terminal program allows you to send and receive data in and out the serial port on a PC. Most terminal programs are designed for transferring files from one PC to another over phone lines using a modem, however, almost all can be used to capture and display data from measuring instruments. Microsoft Windows, in fact, comes with an excellent terminal program called "Terminal" in Windows 3.1 and "HyperTerminal" in Windows 95. With either of these programs you can input data from a measuring instrument and at a minimum, save the data to a disk file that can be imported into a spreadsheet, database, SPC package, etc. However, terminal programs do not parse or filter your data, and the importing process can be slow and tedious. If all you want to do is capture and save measurements, then a terminal program is an option.

Additionally, commercial terminal programs such as ProComm from DataStorm Technologies and DynaCom from FutureSoft have many advanced features, including script languages, and are available at most software outlets for under $200. They, however, are often more difficult to use since they can require some custom programming to implement a data collection application.

Specialized SPC Software With RS232 Data Input Capabilities

If your goal is to perform statistical analysis of measurement data, there are a number of specialized software packages available that are designed to provide the most common statistical functions, including X-bar and R-chart functions, trend analysis and just plain graphing and reporting of data. Many of the latest programs support data input directly from instruments connected to the serial port on your PC. Programs like SQCpack from PQ Systems, SPC Express from Fred V. Fowler Corp., Minitab from Minitab, Inc., NWA Quality Monitor from Northwest Analytical, Gainseeker SPC from Hertzler Systems Inc. and QI Analyst from SPSS are all good "Stat" packages with built in support for some RS232 data. Most of these products are priced from $400 and up. These programs are all very helpful if you need to perform more sophisticated statistical analysis of your data.

WinWedge

WinWedge, available from TAL Technologies, Inc. is essentially a fully configurable serial device driver that allows you to input data from any instrument with an RS232 interface directly into any Windows, Windows 95, NT or DOS application program. The "Wedge" works by tricking your computer into treating the serial port as a second keyboard. This allows you to input measurements directly into any PC program including your favorite spreadsheet, database or SPC program. The Wedge also parses and filters your data and executes additional keystrokes. This means you collect only the data you want in an appropriate format for your application. The SoftwareWedge also allows you to input data using Dynamic Data Exchange (DDE) for complete data collection in the background. DDE is very powerful and allows the user to collect data from many different serial ports simultaneously. Hence, you can input data from many measuring devices all connected to the same computer.

WinWedge also offers full two-way serial communication. So the Wedge can send commands, for example to prompt your device for a reading, to completely automate your data collection. For example, a Fowler/Sylvac caliper can be prompted for a reading by toggling the DTR (data terminal ready) line. This type of prompting is easily accomplished using the Wedge.

For many applications, a good spreadsheet like Microsoft Excel, Quattro Pro or Lotus 123 may have all the features you need including basic statistical functions and graphing and charting capabilities. The only problem with spreadsheets is that they do not support inputting data from the serial port. The Wedge overcomes this limitation and thus makes it possible to use a standard spreadsheet with serial instruments. The SoftwareWedge ranges in price from $159 to $495. There are several versions of WinWedge for both DOS and Windows 3.x, Windows 95 and NT, and in general, the lower price versions are perfectly capable of interfacing most common measuring instruments. WinWedge is easy to use and flexible, and comes with unlimited technical support for free.

Conclusion

In summary, automating quality control processes improves productivity and ensures accurate and precise product manufacturing. So if you have not already automated your quality control procedures, don’t hesitate. It is a simple and inexpensive solution to improve your products and your company’s reputation.


Categories: Additional Resources

Last Updated: 2011.07.12

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