Increasing Precision of Absolute Position Measurement in NC Machine Tools by Means of Diminishing Inertia Loads in Measurement Unit

摘要

The paper describes the research and its results aimed at increasing precision of absolute position measurement in numerically controlled (NC) machine tools and preventing machining errors. The precision of that measurement unit depends on the inertia of its component parts. When abrupt braking and follow-up stopping occurs, any part of the measurement system could be subjected to torsional vibrations caused mainly by inertia of the encoder disk and transmission gear and leading to significant measurement and machining errors. The increase in precision was achieved by means of diminishing those inertia loads via developing special designs of the position encoder and the transmission between the encoder and the tool leadscrew. To decrease the inertia of the encoder, the mass of its disk was lowered by substituting the multi-track Gray-code scale with a one-track scale of one-variable group. On the other hand, a high-ratio, no-slack and low-weight gear of the wave or planetary type was proposed as such transmission which could lead to lower inertia loads there and a higher precision in general.