Real-time monitoring and control system of an industrial robot with 6 degrees of freedom for grinding and polishing of aspherical mirror
Aspherical mirrors have higher performance and lighter weight than spherical mirrors. However, it is not easy to process, measure, and evaluate their shapes. In particular, large aperture aspherical mirrors used in satellites require high precision and take a long time to process. The conventional process is machined using a computer numerical control with a gantry structure. However, there is a disadvantage that it is difficult to process complex shapes due to lack of degrees of freedom. In order to overcome these problems, we developed a shape processing system using an industrial robot with 6 degrees of freedom. The system consists of toolpath generation program, real-time robot monitoring, and control program. We have verified the performance of the developed system through simulation software provided by the robot manufacturer as well as actual robot operation.
Control Method and Tool Path Interpolation of Aspherical Grinding-Polishing
An interpolation and curve partition method is proposed for the grinding and polishing of aspherical lenses. The aspherical tool path was typically partitioned using the lens coordinate, because the path cannot be written with the tool coordinate. The new partitioning method proposed in this study solved this problem using numerical analysis and made user-based partitioning possible. The interpolation algorithm was derived from the equation of asphericity. The idea for this came from the motion profile of commercial motion controllers. Each section in the separated path has ideal inputs, such as the acceleration and velocity, which are corrected afterwards by position feedback. A nano accuracy machine was constructed to test the proposed algorithm. The position error, the control accuracy, was monitored during the tracking of the tool path of the aspherical lens. The performance of the new partitioning method was compared with that of the conventional partitioning methods. We found that the proposed method was more effective at a higher feed rate, so that the processing time can be reduced simply by improving partitioning. The best accuracy in the test was under 100 nm.
Control of reflective cracking
The first is 'fatigue' cracking of the layer. This type of cracking is the result of the application of loads on the pavement and is controlled by appropriate thickness design which 'ill not be discussed in detail here. Thickness design includes not only the design strength and thickness of the stabilised, but other design elements such as delaying reflection cracking, or limiting stresses in the stabilised layer, by adopting a minimum thickness of overlying material. This may include an unbound layer utilising the 'upside down' pavement approach. The actual thickness required of the overlying material varies but for example PIARC (Ref.1) recently reported when the thickness of coated materials exceeds 20 cm the emergence of shrinkage cracks at the surface is generally uncommon; when it is 15 cm thick, the cracks emerge at the surface, but do not shorten the life of the surface course, especially if they are sealed. This experience has been gained 'with legal axle loads of 130 kN, considerably greater than the Australian legal axle load.