Characteristics of the transparent fluid assisted in-process measurement method
by Tao Zhengsu
Ph.D. Mechanical Engineering
xvii, 114 leaves : ill. (some col.) ; 30 cm
Coolant fluid is often utilized in precision machining processes. The optical measurement method is a highly accurate method. However, the coolant fluid blocks the light beams from this layer and makes optical measurement impossible. This dissertation describes the fluid and optical characteristics of a new in-process measurement method assisted by a transparent fluid. Fluid model of the transparent window and related experiments are provided....[ Read more ]
Coolant fluid is often utilized in precision machining processes. The optical measurement method is a highly accurate method. However, the coolant fluid blocks the light beams from this layer and makes optical measurement impossible. This dissertation describes the fluid and optical characteristics of a new in-process measurement method assisted by a transparent fluid. Fluid model of the transparent window and related experiments are provided.
In modeling the motions of the fluids for the transparent window, the transparent flow is simplified as a line source, when it flows into the narrow gap zone between the bottom of the applicator and the workpiece surface. The coolant flow and the line source are combined to a flow potential field. The complex potential theory is utilized to find the boundary line of the two fluid flows. Furthermore, the equations of the transparent window boundary line are obtained, which are functions of the transparent fluid flow rate, the gap, and the velocity of workpiece movement.
An experimental setup is developed to simulate the movement of the worktable and workpiece, the coolant fluid condition, and to capture images of the transparent window under various conditions. After analysis, the experimental results are found to correspond with the results of the theoretical model in the effective area of the applicator.
There are two assisting layers in the new method, the applicator and fluid layer. These layers are the extra parts for a laser sensor, and change the properties of the sensor, and so as the measurement results. The experimental results show that the laser beam propagation will be changed when it passes through the assisting layers. The effects are governed by the thickness of the applicator and the fluid layer, the refraction indexes of the layers, and the incidence angle of the laser beam. A correction formula has been derived to correct the measurement output. The experiments also indicate that the installation error should be limited to less than 2 degrees for correct measurement.
The Reynolds number of the flow in the transparent window region is in the range from 50 to 6000. This makes the flow either laminar or turbulent. The theoretical analysis and experiments show that the deflection of laser beam through a laminar or turbulent flow fluid layer is small under the conditions of the method. However, in the turbulent flow, air bubbles may exist, which will be a serious problem for laser beam propagation in the transparent window. The experiments and analyses show that the effect of the flowing fluid layer can be controlled to an acceptable level.
The coolant fluid is opaque for a laser beam. The effects on the optical measurement depend on the density of the coolant and the thickness of the fluid layer. When the density is high, the propagation of the laser beam becomes more difficult, and the diffusion of the laser increases. A large number of the experiments were performed. The results show that, if the thickness of the fluid layer is less than 0.5mm and the density of the coolant in the transparent window is lower than 2%, the measurement error is acceptable.
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