Bonnet Polishing Research Articles

Prediction of the material removal rate in bonnet polishing using a Bayesian optimization deep neural network

The material removal mechanism in robotic bonnet polishing is complex and influenced by multiple factors, necessitating an appropriate method to establish a material removal model. This study employs a Bayesian optimized deep neural network (BO-DNN) to model the intricate relationship between polishing parameters and material removal rate (MRR) using removal function spot experimental data. The tree-structured Parzen estimator (TPE) improves model convergence speed and accuracy, while particle swarm optimization (PSO) assists in inverse verification. Results show that the BO-DNN model achieves a root mean square error (RMSE) of 0.0293 and a Pearson correlation coefficient (PCC) of 99.42% for the total sample, representing approximately a 50% improvement in predictive accuracy over the unoptimized DNN model. The inverse verification results closely match the experimental data, confirming the model’s reliability. This study offers theoretical insights and practical references for advancing robotic bonnet polishing technology.

Application and development of bonnet polishing technology

Application and development of bonnet polishing technology

Improved performance of three mirror anastigmat telescope with freeform surface: Optical design, testing and validation aspects

"In this paper, the optical design of a Three Mirror Anastigmat (TMA) Telescope is modified by substitution of a convex freeform secondary and optimization carried out to obtain improved performance. The proposed convex freeform surface is precisely manufactured using the bonnet polishing technique and tested with a sub-aperture stitched algorithm, meeting the specified surface accuracy requirements. Further, to validate the design, the realized secondary freeform optic is tested in conjunction with primary and tertiary optics in the conceived TMA configuration. The telescope system performance is established using a double-pass interferometric test setup. The modified design enhances the telescope system's performance in the extended field of view (FoV) from ±2.5° to ±3.5° across the track and from ±0.4° to ±0.6° along the track. Measured performance results demonstrate an average modulation transfer function (MTF) of 0.56 and an average Strehl ratio of 0.64 at all field points. The effective focal length of the system is computed to be 975 mm. In summary, the proposed freeform surface significantly improves the optical system performance within the available real estate of the envisaged space telescope system."

Simulation model optimization for bonnet polishing considering consistent contact area response

Simulation model optimization for bonnet polishing considering consistent contact area response

Material removal and tool path ripple error of bonnet polishing using pads with different groove patterns

Material removal and tool path ripple error of bonnet polishing using pads with different groove patterns

Active Compliance Smart Control Strategy of Hybrid Mechanism for Bonnet Polishing.

Compliance control strategies have been utilised for the ultraprecision polishing process for many years. Most researchers execute active compliance control strategies by employing impedance control law on a robot development platform. However, these methods are limited by the load capacity, positioning accuracy, and repeatability of polishing mechanisms. Moreover, a sophisticated actuator mounted at the end of the end-effector of robots is difficult to maintain in the polishing scenario. In contrast, a hybrid mechanism for polishing that possesses the advantages of serial and parallel mechanisms can mitigate the above problems, especially when an active compliance control strategy is employed. In this research, a high-frequency-impedance robust force control strategy is proposed. It outputs a position adjustment value directly according to a contact pressure adjustment value. An open architecture control system with customised software is developed to respond to external interrupts during the polishing procedure, implementing the active compliance control strategy on a hybrid mechanism. Through this method, the hybrid mechanism can adapt to the external environment with a given contact pressure automatically instead of relying on estimating the environment stiffness. Experimental results show that the proposed strategy adapts the unknown freeform surface without overshooting and improves the surface quality. The average surface roughness value decreases from 0.057 um to 0.027 um.

Study of Modified Offset Trajectory for Bonnet Polishing Based on Lifting Bonnet Method.

The inability to converge at the edge of a workpiece during polishing affects the edge profile accuracy and surface quality of the workpiece. In this study, a bias trajectory generation method based on the lifting bonnet method that can maintain the morphology of polished edges is presented. Firstly, by establishing the polishing parameters and the decreasing rule in line with the principles of the lifting bonnet method, we obtained the residual height spacing, the radius of the polishing area, the centre offset position, and the pressing depth for each offset trajectory. Subsequently, the modified bias trajectory algorithm correction coefficients were obtained by fitting the edge trajectories using cubic Bessel curves, which were multiplied with the bias amount to obtain the final modified bias trajectory. Finally, an experiment was designed to compare the edge effect of the modified bias trajectory with the traditional grating trajectory. The experimental findings indicate that the reduction in edge collapse following the implementation of the modified offset trajectory was 1.30 μm. In contrast, the edge collapse after polishing with the traditional grating trajectory amounted to 98.67 μm. Moreover, the edge collapse ensuing traditional polishing trajectory was 75.9 times more pronounced than that observed after using the modified offset trajectory. It is shown that the modified bias trajectory method can not only maintain the original edge morphology of the workpiece but can also promote the convergence of the edge effect to a certain extent.

Research on the modification of the tool influence function for robotic bonnet polishing with stiffness modeling

Robotic bonnet polishing (RBP) technology is widely used in the polishing process of optical components, but industrial robots have the characteristics of a wide processing range and low body stiffness. Therefore, in the actual polishing process, there are different polishing forces due to different stiffnesses, which leads to different tool influence functions (TIF) affecting the surface quality of optical components. To achieve a uniform surface quality of the components polished by the RBP, we modeled the stiffness of the robot and modified the TIF in conjunction with the Preston equation, finally verifying the accuracy of the modified model through experiments. The results of the fixed-point polishing experiments show that the maximum relative error before the TIF correction is 12.5% and the maximum relative error after the correction is 2.8% within the robot's 600mm*600mm machining range. The results of the plane polishing experiments show that the maximum relative error before the TIF correction is 13% and the maximum relative error after the correction is 1.7%. Therefore, a method for TIF corrections from RBP based on stiffness modeling has important engineering implications.

Study on the Impact of Positioning Errors on the Process Performance of Robotic Bonnet Polishing

Study on the Impact of Positioning Errors on the Process Performance of Robotic Bonnet Polishing

Effect of dispersion performance of polishing slurry on the polishing quality of glass-ceramics in bonnet polishing

Effect of dispersion performance of polishing slurry on the polishing quality of glass-ceramics in bonnet polishing

Convex optical freeforms using fringe Zernike overlay approach for two-mirror and three-mirror telescopes for space applications

The challenge in manufacturing and testing of convex optical parts is well known in comparison to its concave counterpart and an optimized imaging system invariably features a combination of both. Of late, freeform mirrors find lot of interest in space applications as the optical systems remain compact within the allocated envelope. As is well known, these freeform mirrors are difficult to manufacture and test due to their lack of rotational or translational symmetry and poses additional challenges if it has convex profile. In the current investigations, two new convex freeform optical surfaces are proposed which is based on fringe Zernike overlay technique. The first convex freeform envisaged is for a two-mirror off-axis telescope where the secondary mirror is an off-axis freeform and the second convex freeform for a three-mirror anastigmat telescope where the secondary mirror is an on-axis convex freeform. Substitution of these convex freeform surfaces in the two-mirror and three-mirror telescope systems aid in the correction of asymmetrical aberrations to a wider view field, thereby enhancing the performances of the de-centred and tilted systems in the respective configurations. The procedure adopted for the manufacturing of these convex freeform surfaces using bonnet polishing methods and the interferometric tests using modified-Hindle null corrector and subaperture-stitching techniques for evaluation are described in detail.

Theoretical and experimental investigation of material removal in semi-rigid bonnet polishing of binderless tungsten carbide

Binderless tungsten carbide (B-WC) has become a typical material for mold inserts due to its super mechanical and thermal properties. However, it is a typical hard-brittle material that is difficult to implement precision and high-efficiency polishing. This paper answers this challenge using a semi-rigid bonnet (SRB) tool, together with systematic theoretical and experimental investigation on its material removal. First, both polishing spots generation and uniform polishing experiments were conducted to demonstrate the polishing performance and material removal characteristic of SRB on B-WC substrates. Afterwards, the tool influence function model of SRB was established and verified experimentally, which enables the accurate prediction of surface generation during polishing. Finally, the surface and subsurface integrity of a B-WC substrate before and after SRB polishing was demonstrated. The results indicate that SRB is effective for fast polishing of B-WC with superior surface and sub-surface qualities. This discovery also paves the way for the application of SRB for the polishing of other hard materials. The developed material removal model can be a theoretical basis for the prediction of surface generation during the polishing process.

Modeling and Simulation of Removal Function for Dual-axis Wheel Polishing

Modern optical manufacturing techniques, such as stress disc polishing, bonnet polishing, magnetorheological finishing, and ion beam finishing, suffer from edge effects or low removal efficiency. To solve the above problems, this paper mainly studies dual-axis wheel polishing technology. According to the Preston equation combined with Hertz contact theory and kinematics, a theoretical removal function model of dual-axis wheel polishing is established. Then, the removal function shape and removal efficiency under different revolution-to-rotation speed ratios are simulated. From the simulation results, it can be concluded that the removal function of the dual-axis wheel polishing technology in this paper is Gauss type when the revolution-to-rotation speed ratio is 10:1 or less. With the increase of rotation ratio, the efficiency of the removal function is higher. This paper establishes a theoretical foundation for the design of the dual-axis wheel polishing device.

Study on optimization of the dynamic performance of the robot bonnet polishing system

To solve the problem of processing quality degradation due to vibration in the robot bonnet polishing system (RBPS), the vibration generation mechanism of the polishing system is revealed based on the modal analysis and dynamic modeling of the RBPS. The modal analysis results showed that the operating frequency of the system is near the natural frequency, which makes the system susceptible to resonance. On the other hand, the forced vibration caused by the polishing force leads to high vibration at the end of the robot during the polishing process. In order to suppress the vibration generated by the polishing system and optimize the dynamic characteristics of the polishing system, a vibration suppression method to increase the damping ratio of the system was proposed. The experiments of SiC fixed point polishing were performed using both vibration suppression bonnet and original bonnet. The surfaces RMS and PV of the parts polished by the vibration suppression bonnet were generally better than those of the original bonnet. The vibration suppression bonnet has improved the convergence ratio of RMS and PV by 42.59% and 19.56% respectively over the original bonnet in the whole surface polishing experiments. The PSD analysis illustrated that the vibration suppression bonnet can better suppress the intermediate frequency errors. The effectiveness of the method in suppressing vibration and improving machining quality is demonstrated.

Polishing Approaches at Atomic and Close-to-Atomic Scale

Roughness down to atomic and close-to-atomic scale is receiving an increasing attention in recent studies of manufacturing development, which can be realized by high-precision polishing processes. This review presents polishing approaches at atomic and close-to-atomic scale on planar and curved surfaces, including chemical mechanical polishing, plasma-assisted polishing, catalyst-referred etching, bonnet polishing, elastic emission machining, ion beam figuring, magnetorheological finishing, and fluid jet polishing. These polishing approaches are discussed in detail in terms of removal mechanisms, polishing systems, and industrial applications. The authors also offer perspectives for future studies to address existing and potential challenges and promote technological progress.

An adaptive bonnet polishing approach based on dual-mode contact depth TIF

An adaptive bonnet polishing approach based on dual-mode contact depth TIF

Towards modeling and restraining surface ripples during bonnet polishing based on frequency domain characteristic control

Extensive research has been conducted on Bonnet polishing for its ability to manufacture freeform surfaces with nano-scale precision. However, surface ripples are easy to introduce under regular motion, and the underlying principle to address this problem remains unclear. In this study, a novel methodology based on frequency domain characterization is proposed, connecting the spatial process parameters and frequency domain evaluation index directly. Bessel function and single pulse convolution are introduced for model establishment. Tool radius, tool tilt angle, and contact radius are correlated with surface ripple mitigation. Polishing parameters optimization case study was conducted and verified using self-designed polishing robot.

多工序组合气囊抛光策略智能优化

多工序组合气囊抛光策略智能优化

Effect of the Binder during Ultra-Precision Polishing of Tungsten Carbide Using a Semirigid Bonnet Tool.

Tungsten carbide (WC) has the characteristics of high hardness, high strength, corrosion resistance, wear resistance and excellent fracture toughness. Accordingly, it has been commonly used as the material for cutting tools and molds in glass-forming techniques. To obtain ultra-smooth surfaces, fine polishing of WC is indispensable. However, the efficiency of WC polishing is low using the existing polishing methods, and the mechanism behind the polishing process requires further investigation. Specifically, the effect of the binder in WC polishing is not clear since there are different kinds of WC with various weight percentages of the binder. In this paper, we present the findings of a study on the polishing performance of two kinds of WC material, with and without the binder, using a semi-rigid (SR) bonnet polishing tool. A series of experiments were performed on a 6-DOF robotic polishing instrument to investigate the material-removal characteristics, surface integrity and sub-surface damage after polishing. The results demonstrate that the SR bonnet polishing tool successfully reduced the surface roughness of WC with and without the binder to the nanometric level, though the lowest surface roughness was obtained on binder-less WC. No obvious sub-surface damage was observed under SEM inspection, while the processing efficiency was greatly improved owing to the high material removal rate of the tool. Based on our analysis of key polishing parameters and corresponding surface integrities, the effect of the binder on the polishing performance is explained, which offers excellent guidance for WC polishing.

Towards understanding and restraining the mechanical relaxation effect in polishing silicon carbide with a detachable bonnet tool

Bonnet polishing has shown promising shape adaptability and processing quality in the surface finishing of glass-ceramic optical components with complex surfaces. This study proposed a new robotic bonnet polishing device with a detachable polishing cloth to realize relatively high polishing accuracy on sintered silicon carbide (S-SiC) with low cost and pollution. During polishing, the contact state between the secondary-thermoformed polishing cloth and workpiece was found to follow a complex force curve, including a short-term force drop caused by quasi-stress relaxation and a long-term force rise caused by creep. Therefore, a predictive model was established to modify the removal efficiency error induced by force fluctuation and to estimate the remaining service time. On this basis, a new approach was proposed to accelerate the initial-stage creep and restrain the force drop during polishing via temperature control. The results obtained in tool influence function and form correction experiments proved that the temperature threshold to suppress the stress relaxation effect of the polishing pad is around 45 °C. Meanwhile, the pre-treatment time of the pad can be compressed by more than half at this temperature to maintain the high determinacy and efficiency of the polishing process. After polishing, almost no subsurface damage was detected near the surface of the S-SiC block. However, due to the impact of original micropores and the scratches caused by the abrasive aggregation effect, the roughness is challenging to continue decreasing after Ra reaches 3∼4 nm.