Wheel Setting Error Modeling and Compensation for Arc Envelope Grinding of Large-Aperture Aspherical Optics

Precision grinding is a key process for realizing the use of large-aperture aspherical optical elements in laser nuclear fusion devices,large-aperture astronomical telescopes,and high-resolution space cameras.In this study,the arc envelope grinding process of large-aperture aspherical optics is investigated using a CM1500 precision grinding machine with a maximum machinable diameter ofΦ1500 mm.The form error of the aspherical workpiece induced by wheel setting errors is analytically modeled for both parallel and cross grinding.Results show that the form error is more sensitive to the wheel setting error along the feed direction than that along the lateral direction.It is a bilinear function of the feed-direction wheel setting error and the distance to the optical axis.Based on the error function above,a method to determine the wheel setting error is proposed.Subsequently,grinding tests are performed with the wheels aligned accurately.Using a newly proposed partial error compensation method with an appropriate compensation factor,a form error of 3.4μm peak-to-valley(PV)for aΦ400 mm elliptical K9 glass surface is achieved.

Abnormal Vertical Dynamic Performance of Subway Vehicles

A serious wheel out-of-round phenomenon exists in a certain subway vehicle in China. More seriously, the vertical vibration of car body of this subway vehicle will go beyond the restriction of the standard criterion when the wheel out-of-round exceeds 0.2 mm in radial direction. And the wheel out-of-round problem could not be solved by polishing the rail or re-profiling wheels. Aimed at this problem, a further analysis is conducted on the structure and the suspension systems of the subway vehicle. It is thought that the additional stiffness function of the traction bar, caused by the short length and the bigger connection stiffness of the traction bar, leads to the problem that the subway vehicle is sensitive to the vertical impact. By taking into account the stiffness of the traction bar, dynamic simulation models of the subway vehicle are set up to study the influence of the additional stiffness function of the traction bar on the vertical dynamic performance of the subway vehicle through the simulation method. The response of the subway vehicle to vertical impact of a triangle pitch is also simulated. Simulation results indicate that the connection between the car body and the bogie will become rigid and the damping function of the secondary suspension will be decreased due to the additional stiffness of the traction bar in braking condition or running on curve track. Then the vertical response of the car body to vertical impact will be strengthened and the vertical ride index decreased. The vertical dynamic performance of the subway vehicle will be improved through the method of decreasing the connection stiffness of the traction bar, which has been validated by the simulation results. This method of improvement can effectively solve the problem of abnormal dynamic performance of this subway vehicle, and provide a foundation for a new theory about the traction bar system design.

A New Set of Wheels

The German auto giant shifts gears to increase its presence and appeal in