Observed Homing Behavior
The proximity sensors operated correctly, but the ESS did not initially register the index pulse during Mach4 homing. The measured index signal rose to approximately +4 V when active and remained at only a few millivolts otherwise.
| Input setting | Observed result | Diagnostic meaning |
|---|---|---|
| Active when high | Homing completed immediately after backing off the proximity sensor | The index input was not being recognized before the hardware correction. |
| Active when low | The servo continued rotating after proximity-sensor backoff | The selected polarity did not match the index signal. |
Root Cause: MB3 5 V Input Bridge
The MB3 backside bridge that configures the input to accept 5 V signals had not been soldered. Consequently, the measured index pulse was present at the field wiring but was not accepted correctly by the input circuit. Soldering that bridge corrected the hardware configuration.
This distinction is important: measuring a voltage transition at the terminal confirms that the sensor produces a signal, but it does not prove that the MB3 input is configured to recognize that signal level.
Correct the Index Input Configuration
- De-energize the equipment and inspect the backside of the MB3 for the 5 V input-selection bridge.
- Solder the 5 V bridge so the assigned input can accept the index signal.
- Confirm that the index is assigned to the documented X310-X313 and COM input group. In the reported wiring, COM was connected to 0 V.
- Configure the index input as active when high, matching the measured pulse and the polarity that worked in this installation.
- Run the Mach4 homing cycle and observe the transition from proximity-sensor detection and backoff to index detection.
Verification and Remaining Ambiguity
After the 5 V bridge was soldered and the input was tested, index homing operated correctly. The working polarity was active when high. Verify success by confirming that the axis completes homing on the index event after proximity-sensor backoff rather than stopping immediately after backoff or rotating continuously.
The evidence does not identify the exact ESS or Mach4 configuration fields used to enable index homing. It establishes only that the capability was enabled, the signal was assigned within X310-X313 and COM, and the missing MB3 5 V bridge caused the reported failure.
FAQ
Why does ESS MB3 index homing stop after the proximity-sensor backoff?
If the index pulse is not recognized, the cycle can appear to finish at backoff. In this case, the MB3 bridge required for accepting the 5 V input signal had not been soldered.
Should the MB3 index input be active high or active low?
Use the polarity that matches the measured signal. This installation produced an approximately +4 V active pulse and worked with active when high; active when low caused continuous servo rotation after backoff.
How was the Mach4 index input wired for X310-X313?
The index was assigned within the X310-X313 and COM input group, with COM connected to 0 V. The MB3 backside 5 V bridge also had to be soldered for the input to recognize the signal.