Demand for precision machining of dies and molds with complex shapes has been increasing. Though high performance CNC machine tools are widely utilized for precision machining, machining error compensation is still necessary to meet accuracy requirements. For precision measurement, a workpiece must usually be unloaded from a CNC machine tool. Then, the workpiece is measured by a precision measurement device, such as 3D CMM. After the machining error is clarified according to the measurements taken, the workpiece must be re-clamped for the necessary error compensation machining. This error compensation machining is costly and time consuming, and it requires a highly skilled machinists. The re-clamping of the workpiece also causes positioning errors. Therefore, demands for on-machinemeasurement have been increasing. In this paper, an on-machine measurement device that consists of a line laser displacement sensor is developed. This measurement device, attached to the spindle head of a machine tool with magnetic clamps, has special features, such as noncontact, multi-point, high-speed measurement capabilities. Additionally, a sequential multi-point method, an extension of the two-point method, is applied for shape measurement accuracy.

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