Abstract: A quasi-online roundness measurement and compensation system is proposed for crankshaft pin journals, in which, roundness measurement mechanism based on a wheel-concentric swing arm and a V-block is investigated according to the motion characteristic of constant distance between the wheel central and pin journal’s central during follow grinding. Follow scanning is realized for the wheel-concentric swing arm through both the self-gravity and the driven force from pin journal’s eccentric rotation. The capture and detachment operations of a target pin journal are achieved for the V-block by a flexible dragline. Consequently, quasi-online roundness measurement is fulfilled for crankshaft pin journals. The precise geometric collection between the angle position of leading shaft of the follow grinder and the scanning angle of the probe, which is placed on the centerline of the V-block, is kinematically analyzed. Solving method for roundness error signal based on a micro-variation equivalent mode is carried out for the process of probe signal. Through an implementation test on MQG1000 type CNC crankshaft follow grinder and the roundness analysis data acquired from JL4G15D type crankshaft sample, the presented quasi-online roundness measurement and compensation system emerges good characteristics in precise machining of crankshaft pin journals, such as compact structure, high efficiency, and good roundness compensation performance.

Key words: crankshaft;pin journal;follow grinding;roundness measurement;roundness compensation