The Design Of Visual Inspection Device For The Casting Turbine Blades

Turbine blades are key components of aircraft engines, which work under high temperatures, pressures and stress. Casting blades, casting by titanium and nickel based superalloy, have curved and torsion deformations when they were molded by uneven thermal stress, which made them deviated from the design requirements.So they have to be tested after casted. Model gap and CMM are current methods of blade messurement. Both of them take a lot of time measuring. This paper studied on turbine blade measurement and designed a special measuring device prototype, including:(1) Builded a turbine blade measurement platform and determined that the measurement platform includes two translational and rotational degrees of freedom. Choose the linear structured light vision sensor as a core component of the measuring device based on the measurement process and calibrated the degrees of freedom. Design translation axis, rotation axis and the positioning surface clamping calibration algorithm. Write calibration software module and obtain the calibration parameters through experiments.(2) Designed a linear structured light vision sensor. Studied algorithms of laser plane calibration and camera calibration. Selected the proper sensor hardware by analyzing the demand for turbine blades measurement. Established a sensor measurement model and analysised the internal structure parameter such as the distance and angle between the camera and laser. Selected the optimal configuration parameters to improve the theoretical level sensor measurement accuracy.(3) Proposed an algorithm of improved laser stripe centerline extraction which firstly used median filter denoising with connected domain and edge deburring, and then used the normal direction based on the focus of the two-step method for gray image pre-processing to extract the centerline stripes. This algorithm can well remove the interference caused by the ambient light and adapted to the environment, and use less than 0.05 second in processing single image.(4) Developed a measurement system software and completed calibration experiments of the sensor and measurement system and completed experiments of casting turbine blade surface contour detection. Measured the distance of two ball center to accuracy evaluation of measuring sensors and measurement platform according to the German VDI/VDE standard. Experiments show that sensor measurement accuracyachieves 0.03 mm and measurement system accuracy achieves 0.04 mm. Results show that the measured cross-section blade and blade surface contour section feature extraction accuracy can achieve 0.08 mm.