In-process measurement can provide feedback for control of workpiece precision in terms of size, roughness and, in particular, mid-spatial frequency form error. Optical measurement methods are of the non-contact type and possess high precision, which should be used for in-process form error measurement. In precision machining, coolant is commonly used to reduce heat generation and thermal deformation on workpiece surface. However, the use of coolant will induce an opaque coolant barrier if optical measurement methods are used. In this paper, a new multiple air beam approach is proposed. The new approach permits displacement of coolant from any direction and with a large thickness, which represents a massive amount. The model, the working principle, and the key features of the new approach are presented. Based on the proposed new approach, a new in-process form error optical measurement system is developed. The coolant removal capability and the performance of this new multiple air beam approach were assessed. The experimental results show that workpiece surface y(x, z) can be measured successfully with the standard deviation up to 0.3011μm even under a massive amount of coolant where the coolant thickness is 15mm. This means a relative uncertainty of 2σ up to 4.35% and the workpiece surface is deeply immersed in the opaque coolant. The results also show that, in terms of coolant removal capability, air supply, and air velocity, the proposed new approach is respectively 3.3, 1.3, and 5.3 times better than the previous single air beam approach. The results demonstrate significant improvements by the new multiple air beam method together with the developed measurement system.
(Supervisor: Prof. Yongsheng Gao)