Introduction
As part of the normal engineering process, it’s often necessary to measure the reliability of mechanical
assemblies over long periods of time under various stress conditions. This requires that data on the
assembly be recorder and wear out or failure mechanisms be evaluated.
Problem
In the case of flexible joints on shafts, the parts are rotated at high speeds over an extended period of time to
simulate the typical operating life. The failure modes include deformation and cracking of the rubber boots,
for which periodic manual observation is the only way of identifying failure. It’s impractical to continuously
record video and difficult to capture images of a part spinning at up to 10,000 RPM.
Solution
A system incorporating an ADwin-light-16 has been designed that allows unattended monitoring of the
rubber joint boots over extended periods of time. The ADwin is used to measure the rotational speed of the
part via a reflective optical sensor. Next, the ADwin calculates the delay required to achieve an absolute
offset (in degrees) that is used to make the part appear to be motionless using a strobe light. The ADwin can
also calculate a phase delay that when used in conjunction with the strobe, will make the part appear to
rotate at a much slower RPM, typically in the range of 1-10 RPM. Finally, the ADwin is used to trigger a
camera which captures a sequence of images that capture a full 360 degree view of the part being tested. A
program written in Visual Basic is used to set-up the capture parameters, schedule the periodic collection of
the images and store the images in a sequence of files on disk.
Benefits
By using an automated system, the need to have a person manually inspect the boot for failures has been
eliminated. Instead, the history of the complete test is recorded in a sequence of files that can played back
later for analysis. By freezing the motion of the part, the joint boot can be inspected without stopping the test
and individual sites can be inspected for degradation.
Equipment Used
- ADwin-light-16 - Real-time, data acquisition and control system
- Reflective Optical Sensor - Provides TTL pulse for every shaft revolution
- High Speed Machine Vision Strobe - Provides up to 10,000 flashes per minute, externally triggered
- Sony Camera - Provides 30 frames/second at 640 x 480 resolution
- Matrox Frame Grabber - Captures images from the camera for processing
- Vision Processing Software - Compresses images to minimize storage requirements
|
