Real-time compensation of time-variant volumetric error on a machining center.

An error compensation system has been developed to enhance the time-variant volumetric accuracy of a 3-axis machining center by correcting the existing machine errors through sensing, metrology, and computer control techniques. A general methodology has been developed to synthesize both the geometric and thermal errors of machines into a time-variant volumetric error model. Instead of the well-known 21 geometric error components, 32 machine linkage errors are formulated as a 4D error field including the space domain and the time domain. Different types of models are proposed for different kinds of thermal error components. A compen­ sation controller based on an IBM/PC has been linked with a CNC controller to compensate for machine errors in real time. This scheme has been implemented on a horizontal machining center and has been shown, using metrology instruments, to improve the machine accuracy by an order of magnitude. A cut workpiece in­ spected using a coordinate measuring machine (CMM) has also shown that di­ mension errors have been reduced from 92.4 fim to 18.9 \x,m in a dimension of 404 x 310 mm2 and the depth difference of milled surf aces has been reduced from 196 fim to 8 fim.

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