Editor's CommentaryFrom the monthly column Quality Gauging Tips.
A combination of electronic technology and economics enabled gaging to become digital about 30 years ago. With a digital signal available, it became possible to transfer information via cable directly from a gage or digital indicator to the data collector. This made it much more practical to make process control decisions based on statistical analysis.
Electronic data collection also occasioned a major improvement in data quality. Prior to this leap, data was either handwritten onto a sheet of paper and then logged into a computer, or it was logged into the computer directly at the point of gaging. You can understand how an operator measuring hundreds of parts could easily transpose numbers, skip digits or enter wrong numbers. These problems were virtually eliminated by having data go directly to the data analysis software. When electronic data collection strategies were first implemented, it was not unusual to see collection efficiencies and error reduction increase tenfold over manual collection methods.
These days, checking parts at a gaging station with a hand tool or a dedicated fixture gage connected to a computer for data collection is the norm. Today’s hand tools and digital indicators have data output built in, and collecting data is easy and cost effective. It is also inexpensive, fast and reliable, and it provides a great solution for many process and quality-control applications.
But what happens when the part can’t be brought to the bench? Maybe it’s still in the machine or it is simply too large to bring to the gaging station. Running a long cable from the gage to the computer can be a hazard, and if multiple dimensions need to be checked with different gaging, a collection of long cables can quickly become a snarled mess.
Technology is ready to take another leap. Just as cellphones and wireless computer peripherals have become common, wireless technology is moving out onto the shop floor. Small transmitters are now being built into digital indicators that enable them to transmit data to the gaging computer. Each integrated transmitter in the digital indicator uses slightly different signal coding, enabling many gaging stations to communicate to a single computer simultaneously. Today, these transmitters are not that much more expensive than data cable, making the cost more than justifiable when cabling alone won’t get the job done.
With these transmitters, very large parts can be measured where they sit, and parts can be measured in the machine tool without having cables get caught in the tooling. Plus, many digital indicators provide feedback by generating a signal to the operator that the transmission was received and acknowledged by the computer. This is virtually instantaneous so as not to slow the operator down, and most transmitters can be configured to provide a go or no-go signal to the user depending on whether the part is within tolerance.
Another application might be to have multiple digital indicators on one gaging fixture. Usually each digital indicator has its own cable, and some type of interface box is required to handle multiplexing the signals to the computer. With the integration of the transmitter, both the cabling and the multiplexers are eliminated, resulting in a cleaner-looking gaging station. In addition, the PC running the data collection software can be triggered by the operator to gather the data from the multiple digital indicators.
Eliminating cables is great, but probably the best application for this technology is right at the machine tool. The data can be transmitted wirelessly to the machine tool’s controller and put to use in the calculations for offsetting. Thus, as the operator measures the parts, the data is used to assign the proper offsets, greatly improving the quality and throughput of the machine tool. Out-of-spec parts are virtually eliminated, and the machine’s ability to make parts to the desired dimensions is greatly improved.
Today the triangle is becoming complete, with a combination of digital gaging for accurate shop floor measurement, unrestricted wireless transmission of reliable data, and statistics for process control. These three tools enable truly effective use of measurement data.blog comments powered by Disqus