Omron FH Vision — STEP Trigger Not Accepted

Omron · intermediate · 20 min

When an Omron FH vision controller ignores its measurement trigger, work the STEP / BUSY / READY handshake and the STEP input filter before suspecting the camera — most 'no measurement' cases are signal timing.

ℹ️ The FH runs on a simple handshake: STEP in, BUSY while it works, READY when it can take the next one. If a trigger seems ignored, one of those three signals explains it.

How the FH trigger handshake works

An Omron FH / FHV vision controller executes a measurement when a measurement trigger — the STEP signal turning ON — is input. The handshake is:

1. The external device (PLC/robot) turns STEP ON.
2. When the Sensor Controller confirms STEP is ON, it outputs the BUSY signal while it processes.
3. The READY signal indicates the controller can accept a trigger. Notably, even while a measurement is executing (READY on), the next STEP can be acknowledged — the FH supports multiple-trigger handling — so 'READY is on but nothing happened' is not automatically a fault.

So if measurements aren't happening, check whether STEP is actually being seen, whether BUSY responds, and whether the flow/scene completes.

Why a STEP trigger gets ignored

1. The STEP pulse is too short or noisy. The FH applies a STEP input filter as a countermeasure against chattering and noise, with a default filter value of 100 μs. A trigger pulse shorter than the filter, or a noisy line, can be rejected. Verify the PLC/robot holds STEP on longer than the filter setting, and check wiring for noise.
2. STEP isn't electrically reaching the controller. Confirm the STEP line polarity/common and that the input actually toggles at the controller — watch the I/O monitor when the trigger fires.
3. Wrong scene / no valid flow. Confirm the intended scene is loaded and its measurement flow is valid; a trigger into an empty or wrong scene produces no useful measurement.
4. Controller not in the run/measurement state. If the controller is sitting in a setup/edit context rather than running measurement, external triggers won't drive production measurements — return it to the measurement (RUN) state.
5. BUSY not being observed. If the PLC fires STEP again before BUSY clears without honoring the handshake, triggers can appear lost — sequence STEP against BUSY/READY correctly.

Step-by-step checks

1. Watch STEP at the controller I/O monitor when the line fires — confirm it toggles ON.
2. Confirm BUSY asserts in response; if STEP toggles but BUSY never asserts, the pulse is being filtered (too short) or wired wrong.
3. Check the STEP filter value vs. the actual pulse width; lengthen the trigger or adjust the filter if legitimately needed.
4. Verify the loaded scene and that measurement (RUN) mode is active.
5. Review the handshake timing in your PLC — respect BUSY/READY before re-triggering.

When it's really the camera

Only once STEP is confirmed reaching the controller, BUSY responds, and the correct scene runs should you look at the camera, cable, or lighting. A manual measurement from the console isolates optics from trigger wiring.