Objective The application of complex surfaces in aerospace, optical engineering, shipbuilding, and other fields is becoming increasingly widespread. The surface roughness of complex surface components directly affects their performance, efficiency, and lifespan. Improving the surface quality of complex surface components has a significant impact on enhancing their operational performance. The substantial demand for high-precision machining imposes higher requirements on the surface accuracy and complexity of related optical elements. To address the challenges in machining difficult optical elements, such as processing deep cavities and high steepness optical components, this paper proposed a robot-assisted wheel abrasive belt grinding method. Additionally, a gravity compensation system for the wheel abrasive belt grinding device was designed, and the constant force loading and smooth control problems in robot-assisted wheel abrasive belt grinding under arbitrary processing orientations were investigated. Methods This paper proposed a robot-assisted wheel abrasive belt grinding method (Fig.1) and analyzed the influence of the end effector's gravity component on the output pressure. A gravity compensation system for the wheel abrasive belt grinding device was designed (Fig.4), and a physical prototype of the device was built (Fig.5). The performance of the gravity compensation system was tested. Based on Hertz contact theory and Preston equation, the removal function of the wheel abrasive belt grinding device was established (Fig.11). The effectiveness of the device was validated through grinding experiments on a sinusoidal silicon carbide (SiC) surface (Fig.16) and a zinc sulfide (ZnS) aspheric surface (Fig.19). Results and Discussions Due to the influence of the gravity from the cantilever structure of the grinding device itself, when the grinding tool undergoes changes in posture, the output pressure at the end of the grinding device's contact wheel will experience noticeable variations. To address this, we established a model for the gravity component of the cantilever and designed a gravity compensation system. During the operation of the gravity compensation control system, real-time communication was established between the upper computer, attitude sensor, and DA conversion module. The system received angle change signals from the attitude sensor and processed the data using the gravity compensation algorithm. Subsequently, the system sent corresponding signals to the DA conversion module, triggering the electrical proportional valve to respond, control the current, and output the compensated air pressure, thus achieving a stable control of the output pressure for the MQQTB10-10D low-friction linear cylinder. The system was capable of achieving constant force control within the range of 0-63 N (Fig.6), with maximum pressure fluctuations less than 0.36 N. The response time of the gravity compensation system was less than 300 ms, enabling constant force loading of the wheel abrasive belt grinding tool under arbitrary postures. Conclusions In this paper, a constant force loading system was established for the public-self-rotation wheel abrasive belt grinding tool of the robot-assisted wheel abrasive belt grinding system. A gravity compensation system based on attitude sensors was designed. The wheel belt grinding process was applied to both atmospheric pressure sintered SiC and ZnS aspheric surfaces. For SiC, the Ra value decreased from 0.168 μm to 9.565 nm after machining, resulting in a sinusoidal surface with a PV value of 1.414 μm. As for ZnS aspheric, the Ra value reduced from 0.492 μm to 10.2 nm, and the PV value converged from 8.4 μm to 2.7 μm after the grinding process. This validated the processing stability of the wheel abrasive belt grinding tool and the rationality of the grinding algorithm. The study can provide theoretical guidance for robot-assisted grinding of complex surface optical elements and hold practical value in this field. © 2023 Chinese Society of Astronautics. All rights reserved.
