FANUC High-Speed Skip: how does response time affect measurement, and why is continuous skip not a stop function?
Signal paths and delay-distance calculations explain High-Speed Skip, distinguish it from Continuous High-Speed Skip, and provide a layered approach to validating measurement errors.
Contents
High-Speed Skip reduces response time in one part of the measurement chain. Equating a fast response with high overall machine measurement accuracy overlooks the probe, receiver, mechanical repeatability and measurement program.
Identify the two different purposes first
Pages 178 and 185 of the FANUC Plus series catalog explain that High-Speed Skip uses a signal sent directly to the CNC, reducing delay from PMC processing. Continuous High-Speed Skip can repeatedly capture coordinates during motion; a trigger does not stop the axes. The latter is not a faster-stopping version of the former, and their measurement workflows are not interchangeable.
The catalog lists ordinary High-Speed Skip as a basic function of the 30i-B Plus and 0i-F Plus; the configuration for Continuous High-Speed Skip must be checked separately. This article explains functions and validation methods, not probe wiring, parameter activation or motion programs triggered by signals.
Convert delay into a distance estimate
In a simplified constant-speed model, the delay distance is e＝v×t. If feedrate v is in mm/min and delay t in ms, then e＝v×t÷60000, in mm. Assume a delay of 1 ms somewhere in the chain:
| Assumed feedrate | Distance corresponding to 1 ms | Engineering meaning |
|---|---|---|
| 60 mm/min | 0.001 mm, or 1 μm | Delay distance is smaller at lower speeds |
| 600 mm/min | 0.010 mm, or 10 μm | A tenfold speed increase produces a tenfold delay-distance increase |
The 1 ms value is an assumption chosen for calculation, not a FANUC specification or recommended measurement condition. The calculation excludes acceleration/deceleration, compensation and other errors, so it cannot directly establish an upper bound on measurement error.
Response time is not an accuracy specification
The cited catalog specifies a CNC-side High-Speed Skip response of 0.1 ms or less. Substituting that value into the formula would still describe only the distance associated with that time component. Receiver delay, trigger repeatability, stylus calibration and axis motion conditions do not disappear.
Distinguish systematic bias in a fixed direction, the spread of repeated measurements, and changes in results when speed changes. These phenomena require different comparisons; a single reading close to the reference value does not establish acceptance.
Organize meaningful comparisons
- Measure the same reference using an approved procedure, keeping the direction and probe unchanged. Record repeated results to assess repeatability.
- Compare different measurement speeds within permitted conditions, retain the raw values and observe whether the bias changes with speed.
- Separately verify handling of missing triggers, invalid results and equipment-not-ready conditions. Automatic coordinate or compensation updates require a separate acceptance check.
Continuous sampling also requires confirmation of the travel endpoint and the probe's permitted contact method. A trigger signal cannot replace stopping logic. More information is available in the OPTION section.