On a New Method of Roundness Measurement Based on the Three-point Method
1966 Volume 32 Issue 383 Pages 831-836
Details
1966 Volume 32 Issue 383 Pages 831-836
A new method of roundness measurement of machine elements based on the three-point method is studied. In this method a workpiece is surrounded with three detectors M1, M2 and M3, each of which is different in its detective magnification, and is able to rotate freely in them. The outputs of detectors are summed together and are indicated on a indicator.
The rotational error of a workpiece (eccentric motion or play of rotating centre) does not appear on the indicator if the relative angular positions of the detectors r (between M1 and M2) and φ (between M1 and M3) are adequately arranged. Let the ratios of the detective magnifications of the detectors M1, M2 and M3 be 1 : a : b, then the combinations of (τ, φ) or (a, b) can be selected as follows so as to cancel the rotational error of a workpiece.
1 + a cos τ b cos φ = 0 asinτ-sinbφ=0
These equations correspond to the magnifying power of the Fourier coefficient of first order of workpiece profile Under these conditions the combinations of (τ, φ) and (a, b) are calculated numerically in which the magnifying powers of the Fourier coefficients of the higher order of workpiece profile are as large as possible.
It is proved experimentally, that this method can be used practically for measuring roundness without any high precision turn device.
