Encoder 10-Turn Test

When it comes to electronic length control of roll formed parts, a material encoder is a critical part of the process. That’s because the encoder is the measuring device for the system. Everything the control system knows about the material comes from the encoder – speed, distance, and direction.

If the encoder hardware is defective, it might still work intermittently or partially, yet transmit erroneous data to the control system. A simple test to verify the encoder hardware is working properly can be performed by the user.

This 10-Turn Test essentially checks the internal hardware of the encoder, the cable from the encoder to the control system, and the encoder circuits on the machine controller.

1. This test requires a person to be in physical contact with the length measuring device near material and tooling. The test should only be performed while the machine is in a safe and emergency-stopped condition.
2. Mark the encoder wheel and a fixed point. The fixed point can be on the material, or on the body of the encoder. As long as it’s a simple reference point for the mark made on the wheel. The mark can be a piece of tape, paint marker, grease pen, etc.Encoder Wheel and Body Marked
3. In the machine controller, set the Correction Factor to 100%.
4. Align the marks as closely as possible, and reference the shear to the material (Manual Shear). At this point, the machine controller should display 0.000”.
5. Spin the encoder wheel by hand ten rotations in one direction.
6. After the tenth rotation, line the marks up.
7. Look on the machine controller display. Assuming the encoder wheel has a 12” circumference, the total distance displayed should be equal to 120.000” (10’). If the count is off by a few thousandths of an inch, this is a minor error. It’s most likely due to user error and the difficulty of a human being accurate to 0.001”.
8. Now, spin the encoder wheel by hand ten rotations in the opposite direction.
9. After the tenth rotation, line the marks up.
10. Look on the machine controller display. The total distance displayed should be equal to 0.000” (0’). If the count is off by a few thousandths of an inch, this is a minor error. It’s most likely due to user error and the difficulty of a human being accurate to 0.001”.

In either case, if the distance displayed if off by more than a few thousandths of an inch, the likelihood is that the encoder hardware (internal bearings or electronics) have been damaged, and the unit needs to be rebuilt. It’s also possible the encoder cable is damaged, or that the circuits on the machine controller have been damaged.

It’s always a good idea to test a known, working encoder in the place of the suspect encoder to verify where the exact nature of the problem exists. If the problem follows the encoder, replace/repair the encoder. If not, try exchanging encoder cables next and so on, until the problem is isolated.

If all hardware is tested “good”, yet length variance still persists, check the encoder tracking.