Optical Technique for In-Process Measurement of Surface Roughness During A.C.C. Grinding

Abstract

Based upon the principle of Adaptive Computer Control (ACC) of machine tools, the overall problems of ACC Control of the grinding process is initially discussed in general terms. Following this, the paper concentrates on in-process measurement of surface roughness during grinding with view to incorporating it as an integral part of a CNC system for automatically achieving the desired surface finish. On the basis of autocorrelation techniques, general equations of surface topography are derived. It is shown that the surface topography characteristics can be adequately described by the power spectral density (PSD) of the surface roughness. The intensity of reflected beam from a given ground surface is found to be exponentially related to the ‘RMS Surface Finish’ value σz (Rq). The ‘Total Integrated Scatter’ (TIS) of the scattered light caused by surface roughness is found to be related to the zeroth moment of the PSD. From this it is shown that the reflectance Ir and TIS value Is which are measured by using optical sensors, can be used to compare the surface finish of a given component with that of a standard sample — e.g. a Rupert Gauge; hence, normalised values Vrn, Vsn for the variables Ir, Is can be obtained from measurements. Experimental results show that the ratio $R = \frac{{{V_{rn}} - {V_{sn}}}}{{{V_{rn}} + {V_{sn}}}}$ is suitable for surface finish measurement and it is found to be reasonably independent of the material. Therefore, it can be used for in-process measurement of surface roughness in an adaptive computer control loop for obtaining the desired surface finish in grinding.