Study On The Lapping Of Flexible Joint Blades Based On Contact Force Feedback Method

Inertial navigation systems are playing essential roles in aircrafts and strategic weapons. The system is used to detect and then control the space attitude of the aircraft. The guide accuracy largely determines the performance of the whole equipment. Dynamically tuned gyroscopes(DTG) are widely used as such attitude measurement devices because of its compact structure and low cost, without loss of guide accuracy. In DTGs, flexible joints are the only path to transmit the driving torque from the motor to the spinning wheel, and are also the main sources of disturbance torques. Therefore the dimension consistency of the four flexible blades on one joint should be strictly controlled. Another factor to be considered is the thickness of deteriorated layers on the machined blades as they affect its long-term stability of mechanical characteristic. The existing final finishing of the joint blades are often done by hand lapping, without effective measuring techniques. Thus the resulted thickness of the blades cannot be guaranteed.In this paper, one method of dimension measuring and force-controlled lapping is proposed. A multi-axis lapping device is developed based on the force feedback method, where two-dimension coordinate measuring and force-controlled lapping are integrated. Theoretical analysis and experimental examinations are carried out to assess the performance of the motion system and force sensor. Constant force control is achieved by continually changing the position of the work-piece according to the force signals. Later, coordinate measuring method based on constant contact force is studied.The layout of the five-axis lapping system was firstly proposed, considering the complicated structure and stringent dimension requirement of the joint. In this part, the motion systems including one orthogonal XY precision stage are established and tested. One novel two-dimension force sensor based on strain gauges is designed. FEA analysis are carried out to determine the optimum location of sensing elements. After that, calibration of the designed force sensor is performed.Later, constant force control algorithm is developed. Magnitude of the real contact force component along one direction can be quantitatively controlled by fast response of the moving parts. Automatic measuring schemes specially designed for joint neck structure are proposed and then realized on VB.Net platform.Finally, the repeatability of the proposed coordinate measuring method is obtained through a series of measurement trails. The measuring errors of the system, mainly due to the deformation of the probe and sensor, are estimated and successfully compensated. After that, free abrasive lapping experiments are conducted on flexible joints. Dimensions of the neck structure are examined before and after the lapping process to determine the ratio of removed amounts between the part and the lapping tool. The finished surface topography are examined after lapping. Preliminary results show that the lapping system is capable of controlling the dimension of the neck and finished surface quality can be improved.