How Measurement Anchoring Solves Sources of Positional Error

In factory automation, a common source of measurement error is variation in part location in the measurement station.

Part location varies due to wear or dirt accumulation on part locating surfaces and position variation of transport mechanisms. Providing precise, repeatable part positioning by mechanical methods is often expensive, requires significant maintenance effort and, particularly in high-speed manufacturing, is simply impractical to implement.

Introduction to Measurement Anchoring

The smartest of today’s 3D sensors eliminate errors caused by part position variation with a technique known as measurement anchoring.

Anchoring tracks the movement of parts within the field of view of the sensor, compensating for variations in the translational position of parts in 3D. The movement is calculated as an offset from the position of a measured feature. The offset is then used to correct the positions of measurement regions for other measurement tools.

Measurement AnchoringAnchoring Feature in 3D Smart Sensors

Application Examples

A simple example is measuring the width of a roughly positioned part. Anchoring determines the actual location of one edge of the part and the relative position of the other edge, measuring the difference between the two edge locations to accurately determine part width, independent of part location. Anchoring ensures that the regions used to measure features are correctly positioned for every part.

3D smart sensors can apply anchoring in all 3 dimensions – X, Y and Z. Multiple anchors can be applied to different features simultaneously. For example, you could anchor measurements relative to the left edge of a target at the same time as other measurements are anchored relative to the top edge of a target.

Additional Benefits

Measurement Anchoring simplifies part-positioning requirements for in-line measurement applications, reducing cost and complexity of part location fixturing. Anchoring can also be effective to compensate for the effect of transport vibration or conveyor unevenness through constant monitoring of height variation.