Don’t Hesitate to Automate! Quality control automation.
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.
TAL Technologies, Inc.
2101 Brandywine Street,
Suite 102
Philadelphia, PA 19130, USA
Tel: 800-722-6004
Tel: 215-496-0222
Fax: 215-496-0322 |
