In-situ roundness measurement and correction for pin journals in oscillating grinding machines

• Measuring mechanism emerges characteristics of simple structure, compact size, and high scanning speed.
• The interference introduced by measuring mechanism swing is solved by an equal angle-interval sampling algorithm.
• Roundness error is extracted in frequency domain using a small-signal model of the V-block roundness measurement method.
• Transformation function is derived for the implementation of in-situ roundness measurement data in pin chasing grinding programme.
• Peak-to-peak value of the roundness error is suppressed to 2.689 µm for a crankshaft pin journal in practical investigation.

In the mass production of vehicle-engine crankshafts, pin chasing grinding using oscillating grinding machines is a widely accepted method to achieve flexible and efficient performance. However, the eccentric movement of pin journals makes it difficult to develop an in-process roundness measurement scheme for the improvement of contour precision. Here, a new in-situ roundness measurement strategy is proposed with high scanning speed. The measuring mechanism is composed of a V-block and an adaptive telescopic support. The swing pattern of the telescopic support and the V-block is analysed for an equal angle-interval signal sampling. Hence roundness error signal is extracted in frequency domain using a small-signal model of the V-block roundness measurement method and the Fast Fourier Transformation. To implement the roundness data in the CNC coordinate system of an oscillating grinding machine, a transformation function is derived according to the motion model of pin chasing grinding methodology. Computer simulation reveals the relationship between the rotational position of the crankshaft component and the scanning angle of the displacement probe on the V-block, as well as the influence introduced by the rotation centre drift. Prototype investigation indicates the validity of the theoretical analysis and the feasibility of the new strategy.

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