A manufacturer of DC actuator motor assemblies needed to develop a production line test system for a new product. Past production testing systems for the actuators had used PCs running DOS based software with PLCs for managing production traffic control. Because testing the motors was time consuming, there were typically several PC test stands on a single production line to keep up with production rate.
When development of a new production line started, the manufacturer decided to break from the DOS based systems they had been using and to also make a number of other modifications to result in more efficient testing. One of the first decisions was to go with a Windows 95 based testing platform. Next it was decided that each tester would now test two actuators simultaneously to decrease testing time per motor. Also, the PLCs used in the previous systems would be eliminated with their functions being replaced by the PC.
The manufacturer contracted SDS to develop the new PC based test system. A DAS-1800HC plug in data acquisition board provided 32 differential A/D channels for acquiring the analog data and two D/A channels to power the DC motors. A PIOSSR-120 DIO board (120 Digital IO points) interfaced into several PB-24 racks which held solid state input and output modules.
Visual Basic was used for the software development. VB provides a good compromise between flexibility and rapid program development. Since the tester was going into a production environment and had a long anticipated lifetime, the fact that VB was a industry standard language and the code could be commented was important. It was important that future engineers could easily read and modify the system code.
The system also interfaced to a servo motor controller card that controlled two servo motors. The servo motors were used to place loads on the actuators during testing. Resolvers on the servo motors were connected to a quadrature encoder circuit that interfaced into the PIOSSR-120 to provide position information.
The system uses the PIOSSR-120 and the solid state relays to perform a number of functions including: monitoring pallet traffic; lifting and clamping motors into position for testing; reading shaft angle; and fault monitoring.
The testing consists of measuring several test parameters as the motors are moved through their clockwise and counter-clockwise directions in both a no-load and loaded condition. Parameters measured include potentiometer feedback, potentiometer bias, motor voltage, motor current, and shaft position (via encoder circuitry). The system also tests for starting voltage (minimum voltage to move motor) and backlash in the gear train. All test parameters are displayed on screen along with a pass/fail result. If a actuator fails the failed parameter is highlighted in red for easy identification.
At the end of the test the system codes the actuator as good or bad and saves the test results to disk. A new data file is created for the test results each day.