A major supplier of components to the automobile industry had approached bespoke production equipment specialist, Alphr Technology to design and manufacture two machines. The first would heat metal compression limiters to 380oC within a few seconds by induction, and would then press them into the top of a plastic component. The second machine would inspect and leak test each component to ensure that the limiters protruded by the correct distance above its surface. A measurement accuracy of +/-0.3mm or better was needed.
The inspection process needed to be carried out automatically using a sensor system that would simultaneously check the top and bottom of the component. The design engineers at Alphr Technology initially felt that optical sensors would be unsuitable, because the body of the plastic component is matt black and the compression limiters have a highly reflective surface. Achieving reliable discrimination between the component and the limiter by optical means would have proved difficult.
As an alternative, linear variable differential transformers were considered, but speed of response, the potential for physical damage and the high contact temperature were deemed potential issues. A vision system would have increased costs and would have been difficult to configure for this rather unusual application, so this too was ruled out.
At this point, the Alphr Technology design team turned to its trusted long-term supplier, Omron Electronics for advice and suggestions. Omron proposed the ZS family of laser measurement sensors, complete with a servo drive system that would allow smooth and precise movement of the sensors as they scanned the component under inspection.
The ZS laser sensing system is designed to deal with difficult surfaces and textures. It is capable of delivering dependable results, not only with black plastics, as used in the present application, but also with foils and even with glass. A built-in user interface makes it easy to match the sensor's operating characteristics to the application, while a user-friendly PC-based configuration tool allows the settings to be fine tuned, and the performance of the sensors to be monitored while they are in use. Up to nine ZS sensing heads and controllers can be daisy chained, a factor that also attracted Alphr to the system, since this application involves four of them - two to inspect the bottom of the component, and two to inspect the top.
ZS sensors also make measurements in as little as 110us, thus easily satisfying the need for speed. Moreover, in the configuration used by Alphr Technology, they deliver accurate and repeatable results to within +/-0.01mm, and that's some thirty times better than the design specification. Alphr Technology's Paul Bridgwater takes up the story.
"Even though we'd seen the specifications for these sensors, we were still a little sceptical about whether they would work in our application but Omron certainly wasn't slow in convincing us! Within just a few days of receiving our enquiry, the company sent an engineer to our premises to demonstrate the equipment using samples of the actual components that would inspected by the machine.
"Not only that, having shown us convincingly that the ZS sensors were suitable for the job, the engineer took the product samples back to Omron for further tests. As a result, the Omron application team was able to provide us with details of the optimum settings for the sensors in our application. That made commissioning very easy. In spite of the challenges of the application, the sensors worked first time, and they do exactly what they are supposed to do."
Alphr Technology also found the sensors easy to integrate with its PC-based control system. On this occasion, serial connections were used but, in future applications, the company expects to make use of the USB connectivity provided by the units.
As well as the sensors, Omron Electronics supplied the servo drive system that enables the sensors to scan the component under inspection. Products from the XtraDrive range were chosen on the basis of their compact size, high positional accuracy and near zero settling time. An integral auto-tune function also ensured that they were easy to set up. The machine is now in full service and working dependably, and Mr Bridgwater is very satisfied with the outcome.
"Being able to use the same supplier for the two key items of equipment needed for this project - the sensors and the servo systems - was a major benefit, as was the absolutely superb support we received from Omron throughout the project. In addition, not only are the ZS sensors and the XtraDrive servos doing a great job in this project, their capabilities have opened new doors for us the design of future machines, and we'll certainly be using them again."