Precision Calibration for Linear Modules: A Step-by-Step Guide | MachineMFG

# Precision Calibration for Linear Modules: A Step-by-Step Guide

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Linear modules are high-precision transmission components, and precision is a critical feature of these modules.

During their use, it is essential to prevent any degradation of the modules’ accuracy to truly harness their stability.

Linear modules, also known as linear units, cartesian robots, or linear slides, represent the automated upgrade from linear rails, linear motion modules, and ball screw linear transmission mechanisms.

By combining various units, they can accomplish linear and curved movements under load, making light-load automation more flexible and positioning more precise.

The precision of a linear module typically refers to both its repeatability and guiding accuracy.

Repeatability is the module’s accuracy as measured by a micrometer or laser interferometer after seven reciprocating motions.

A linear module that achieves an accuracy of plus or minus 0.02 to 0.01 millimeters generally falls within the medium to high precision category.

Guiding accuracy, on the other hand, is the most basic performance indicator of a linear guideway.

Whether loaded or unloaded, the moving components should maintain the linearity of their trajectory and the accuracy of their positioning. This is crucial for ensuring the optimal operation of machine tools.

Generally, various equipment have specific regulations or standards for the planeness, verticality, and equidistance of the guideway itself. The accuracy calibration of the linear module is primarily carried out in the following four areas:

Positioning Accuracy:

Represented by the absolute value of the largest discrepancy between the actual distance moved from the reference position and the instructed value, based on the longer travel distance.

Repeat Positioning Accuracy:

Perform positioning seven times in the same direction for any point, measure the stopping position, and calculate half of the larger difference in dial readings.

As a test principle, tests are performed at roughly the middle and two ends of the moving distance, using the larger value from the test values as the measured value, represented by the larger difference with a plus or minus sign.

Related reading: Positioning Accuracy vs. Repeatability in CNC Machines

Backlash:

Feed is given to the internal slide. The reading of the test indicator when the slide just starts to move is used as the reference.

Starting from this state, without relying on the feed device, a load is applied in the same direction as the movement of the internal slide (the direction of the workbench feed).

The difference between the reference value at the start of the test and the position on return is taken as the measured value.

Tests are conducted at the middle and roughly the ends of the moving parts, taking the larger of the obtained values as the measured value.

Running Parallelism:

Place a standard ruler on the platform where the linear module is installed, test within the range that the internal slide can move using a test indicator. The larger difference in readings within the moving range is the measured value.

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