Precision Measurement Application

Laser Measurement Station

This station was used to measure a small crystal used in the manufacture of medical CT scanners. A Keyence laser scanner was used to measure the crystal in three different axes, providing both dimensional and “squareness” information to an operator.

The controller used was a Koyo (Automation Direct) PLC and a Keyence precision scanning CCD laser measurement system. The operator unit on the right shows the Keyence unit where setpoints and measurement data is set up. This information is transferred serially to the PLC which logs the data into registers for transfer to a computer with a database. This technique is often used in multiple measurement applications where a PLC is used as a manipulator controller and a data concentrator.

Crystal manipulator and measurement

The crystal (shown to the left of the stainless steel datum – its very small) is placed in the tooling which contains a small vacuum hole. The vacuum pulls the crystal up firmly into a small pocket. An analog vacuum measurement is used to determine whether the top of the crystal is flat, irregularities cause the vacuum to leak. The steel datum point is used as a reference to measure the length of the crystal precisely rather than using the actual position of the actuators, this provides accuracy greater than if the actual position were used due to the slop in the actuator bearing. The distance from the side of the crystal to the datum is also measured at the top and bottom of the crystal fo give the parallel-ness of the top to the sides. The crystal is rotated 90 degrees on axis and the measurement taken again. The entire mechanism then tilts 90 degrees to measure the length.

There is a lot going on in a very small space in this application. The tooling was designed by Agile Engineering in Knoxville, Tennessee for the end user, CTI. My old company ACS designed and built the controls. Another example of several companies working together for a successful project.


Electrical Engineer and business owner from the Nashville, Tennessee area. I also play music, Chess and Go.