MC Controller Provides Extreme Solution for Fox Racing Shox

Fox Racing Shox, an industry leader in the design and manufacture of high performance shock absorbers and racing suspension products for mountain bikes, motorcycles, ATV’s, and snowmobiles, turned to Emerson to help push the envelope in racing shock performance.

Mountain bike suspension forks are subjected to high stress forces by today’s extreme riders. After miles of ascents and descents on some of the world’s toughest terrain the forks have a tendency to fatigue.

Typically the stress takes its toll on the critical weld between the top of the fork and the stem that fits into the frame headset. To test various welds for the best possible strength, Fox Racing Shox designed a new Stress Testing machine utilizing a Control Techniques solution.

Fox Racing Shox had the in-house expertise to design the mechanics of the new Stress Test machine. They called on Control Techniques to help in designing a control system to perform the needed motion and data analysis. The solution required a Control Techniques MC-224 Motion Coordinator and five “Motion Made Easy” EN-204 Servo drives with matched NT-330 servomotors coupled to five linear actuators. A force transducer was connected to each actuator and fed back to the MC-224 as a voltage proportional to force. The MC-224 communicated its data to a micro-PLC with touch screen operator interface.

After loading up the machine with five sample forks, the operator enters a variety of test parameters through the touch screen including force, run time, and frequency (speed) of the motion. The PLC transfers this test data to the MC-224, which coordinates the motion of the five axes.

The application required closed-loop control using the force feedback (voltage), while still requiring position feedback monitoring (encoder). The MC-224 was able to close the loop from the force value at 2ms for all axes. This gave the machine very accurate control of the force applied to the forks, since all PID tuning terms were available. The MC-224 tightly controls five axes of motion to apply a push-pull bending force to the bike forks under test. The force transducer coupled to the linear actuator provides accurate force feedback to the MC-224 through an analog input. The MC-224 generates a true sine wave motion profile independent for each axis. Each sine wave is adjustable by the operator for amplitude (peak force) and frequency (move speed), which can be changed “on-the-fly.”

The multi-tasking ability of the MC-224 is used to separate the motion programs and the PLC communications program. As the metal in the fork fatigues over time, the ending stroke position of the push-pull will change. The final stroke position is captured for each axis. This critical data is sent to the PLC for later analysis, which ultimately results better fork designs.

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