Abstract: The crankshaft of marine diesel engine, with the discontinuous axis, the big length to diameter ratio and the poor rigidity, generates the complex elastic deformation under its enormous gravity and clamping force. The deformation causes the poor coaxiality of all the main journals, which has the detrimental effect on the grinding precision. An automatic alignment system integrated into the crankshaft tangential point tracing grinder is studied. An on-machine measuring device of main journals’ central position and the corresponding calculation model of the deviation of main journal’s center are proposed. The influences of geometric error and position error of measuring device on the measured results are analyzed. On the basis of the kinematic analysis of servo steady rest and the deviation of main journal’s center, the calculation model of position of the upper and lower support heads are established. The adjustment amounts of support heads are obtained by comparing their current and desired positons, which are employed to align the workpiece automatically in tangential point tracing grinding. The results of the experiments using a crankshaft of eight throws demonstrate that the automatic alignment system not only works as effectively as the manual alignment but reduces the labor intensity and increases the automation of tangential point tracing grinding as well.

Key words: automatic alignment, deformation measurement, marine crankshaft, servo steady rest