Planning position-and-measure steps for a surface-profile experiment

A surface-profile experiment asks how a measured surface quantity changes with position. Its credibility depends on knowing both what the probe measured and where that measurement belongs. A list of stage coordinates beside a list of sensor readings is not sufficient unless the relationship between the lists is verified.

The method below is a conceptual planning aid. It does not establish surface-metrology accuracy, sensor compatibility or measurement qualification for catalogue stages.

Define the profile and reference

State which feature is being evaluated: a line across a step, a series of cross-sections or another clearly bounded region. Identify the part datum and explain how the sampling coordinates are referenced to it.

KEYENCE’s profile measurement guide identifies arrangements based on relative movement of a workpiece or sensor, including displacement sensors used with stages. This supports considering the architecture, not assuming a particular sensor-stage pairing is suitable.

Decide which object moves. A moving sample carries its fixture and may require secure retention. A moving probe carries its mounting and service connections. Compare the resulting geometry and loads before treating the two arrangements as interchangeable.

Choose sampling positions deliberately

Build the coordinate list around the feature and intended analysis. State the nominal spacing, end points and any locally denser regions. If the smallest relevant feature has not been defined, the motion team cannot independently choose a meaningful sampling interval.

Sampling pitch is not the same as lateral resolution. The probe’s interaction with the surface and the uncertainty of the coordinate also matter. Have the metrology owner document the limitations of the proposed measurement method and how they affect interpretation.

Separate a position-and-measure sequence from a continuous scan. This article’s approach pauses or otherwise establishes a defined measurement condition at each location. A continuous trajectory needs a different timing analysis and should receive its own requirements review.

Preserve the coordinate-to-reading relationship

Each observation should contain a sample identifier, requested coordinate, available position evidence, probe value, units and validity status. Keep raw observations before applying leveling, filtering or interpolation.

Define what makes the probe ready and what marks completion of an acquisition. A reading returned after a move may still belong to an earlier measurement if the interface buffers data. Ask the integrator to demonstrate the correspondence rather than infer it from similar timestamps.

Plan how to handle a sensor that cannot measure a particular surface region. Invalid data should remain visible. A software-filled profile can be useful for presentation, but must not be mistaken for directly measured shape.

Practical profile-experiment checklist

• Mark the profile path and part reference on a drawing.
• Record the probe’s measurement principle and target-material assumptions.
• List sample positions, ordering and the intended analysis.
• Check probe, holder and surface clearance along the entire path.
• Define readiness and acquisition association for every point.
• Preserve validity flags, original readings and any later processing separately.
• Include a reference artifact or independent check appropriate to the measurement claim.

Specify whether remounting the part is part of the evaluation. Repeat measurements without disturbing the fixture test a different condition from repeat measurements after removal and replacement.

Hypothetical example: a missing observation near an edge

Imagine a proposed profile across a shallow step. The coordinate list contains equally spaced locations, but the selected optical probe returns invalid data near the edge. The plotting software initially connects the points on either side with a smooth line.

The review changes the data record to expose the invalid region and requires the metrology owner to decide whether another measurement method or sampling arrangement is needed. No feature height, probe accuracy or stage capability is predicted. The example demonstrates why a visually complete curve is not necessarily a complete measurement.

Qualify the assembled measurement chain

Evaluate the fixture, coordinate evidence, probe response and analysis together using a reference appropriate to the intended claim. Linear stages and multi-axis assemblies can be compared for mechanical reach and layout. Their catalogue values are inputs to the review, not uncertainty statements for the finished surface-profile experiment.

Document the units and sign convention before plotting results, especially when a sensor reports increasing distance while the desired profile represents increasing height.