Study on Negative Pressure Approach for Surface Profile Measurement With Coolant Condition

ABSTRACT The optical sensor used for in‐process measurement would provide measurement results in real time for machining compensation. Meanwhile, the coolant used during the machining process covers the workpiece surface, block optical measurement path. Existing coolant displacement approaches use air/water/coolant to help a single‐point laser sensor conduct measurements on the workpiece surface with coolant condition. This paper proposed a negative pressure approach, which can help a 2D laser sensor conduct in‐process measurement with coolant condition with higher efficiency. Instead of resisting coolant via high‐speed air/liquid, the new approach utilises the negative pressure to draw coolant away from the measurement window. The applicator conducting a negative pressure approach was studied and the applicator's working performance was simulated to guide its design. The proposed negative pressure approach helped a 2D laser beam conduct measurement on a workpiece submerged in coolant with T c = 12 mm. For a workpiece with stepped features of 0.35 mm, when the coolant thickness was T c = 12 mm, the measurement uncertainty was 1.73 µm. Compared with the existing approaches, the negative pressure approach provides 8.8 times the measurement window size and 1000 times the measurement efficiency. This provides a new, efficient and workable solution for 2D laser sensor in‐process measurement with coolant condition.