Since the proposal of bonnet polishing technology, it has been widely used in the surface polishing of various high-precision curved components. Because of its unique polishing tools and polishing method, it has the characteristics of high polishing efficiency and high polishing accuracy. Therefore, bonnet polishing technology is particularly important in engineering applications. We mainly review the research progress of bonnet polishing technology in the past 10 years, including the introduction of bonnet polishing technology applied to important engineering projects such as the European Extremely Large Telescope, the main mirror of Japan’s next-generation space telescope, the Shenguang-III mainframe unit, and the artificial skeleton. We summarize the key technologies of bonnet polishing technology such as removal mechanism, removal function, motion control, process control, and software development according to the typical applications of bonnet polishing technology. Finally, the current limitations are summarized according to the characteristics of bonnet polishing technology, and the development trend of bonnet polishing technology is also foreseen, hoping to provide a reference for the subsequent in-depth research of bonnet polishing technology.
A sphere precessions polishing (SPP) method is proposed to perform the precessions polishing function like the bonnet polishing technique. A compliant inflated hollow ball is adopted as the sphere polishing tool, and three motors are used to collaboratively drive the sphere tool rotating around a desired axis tilting with a precessions angle. A prototype is developed to validate the technical feasibility and demonstrate the polishing removal functions. The polishing spots of vertical polishing show a typical W shape-like profile, and tilted polishing results reveal a D shape-like profile. This proposed SPP method can be regarded as a potential candidate technique to realize the precision precessions polishing in the optical precision engineering.
There has been many models for material removal mechanisms of bonnet polishing (BP) based on the well-known Preston model. However, some experimental investigations have demonstrated that the relationship between process parameters and material removal are not linear at all, especially the relative velocity, which cannot be accounted explicitly by the classical model. Accordingly, in this paper, an analytical model is proposed to investigate the nonlinear relationship between relative velocity and material removal in BP based on the mutual interaction of the slurry, pad and workpiece among the BP interfaces with the micro-contact theory and the tribology theory. Good agreement between the predicted results of proposed model and the experimental data is obtained, and the nonlinear material removal with the change of relative velocity is attributed to the variation of the real contact area.
With the aim to conveniently evaluate the abrasive worn states in precision grinding, this paper presents an image detection and evaluation function for grinding wheel’s micro-surface recovering. Any curved object have different focus level in the same image. With a fixed focus detector drived by motor, the information of abrasive height can be extracted from image sequence by focus evaluation. We propose and compared two method and find Gray-Level-Variance (GLV) have a better robustness on wheel’s surface recovering. The arithmetic works better and smoother when LULU operator is cooperated. Finally, we make a comparision between the result of GLV and ultra-depth 3D microscope in comparative section. The information of single abrasive and diamond pellets are concerned to prove the arithmetic’s validity and stability.
The ultra-precision single point diamond flycutting is an effective way for finishing potassium dihydrogen phosphate (KDP) crystals. However, the dynamic performance and motion precision of the machine tool would introduce the errors and have an adverse effect on the surface quality of elements. In this study, a significant method is presented to trace error sources by combining monitoring the rotary errors and analyzing the machined surface. On the one hand, forward recursion method is adopted. Based on the online measuring platform, the radial error, axial error and inclination error of spindle rotation can be obtained. Through the Fourier transform algorithm, the frequency information in each direction is known. Furthermore, the waviness along the feed direction is identified, which is determined by the rotation fluctuation. On the other hand, a novel method for errors tracing is presented by a reverse thinking mode based on the surface topography. The wavelet analysis is carried out along the cutting direction, and the obvious waviness appears in the 4th layer, of which the dominant frequency is 594Hz. Through the knocking test for the spindle system, the waviness error along the cutting direction is determined as the modal vibration of the spindle system.
To obtain high removal rate and low damages in machining of hard and brittle material,an optical fabrication technology based on fixed abrasive diamond pellets(FADPs) elasticity tool(ET) is proposed. In this paper, we focus on improve the removal efficiency and surface quality by optimizing process parameters, which including speed ratios, eccentricity, spindle speed, pressure, diamond granularity and dwell time. Removal function (RF) model of ET is proposed and optimized. Effects of process parameters on the removal efficiency and surface roughness are illustrated by series of simulation and experiments. Experiment results indicate increasing spindle speed can improve removal efficiency and surface roughness. Orthogonal experiment indicates diamond granularity have greatest impact on removal efficiency and surface roughness. In addition, the removal rate 11.26 mm3/min and surface roughness Ra 4.89 nm is obtained by 10 μm and 3 μm of FADPs respectively.
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