Robotic Polishing System Research Articles

Surface Performance of Titanium Alloy Brake Shell Polished by Industrial Robot Based on Digital Twin

The titanium alloy brake shell is an important component used in aviation, but its surface polishing is mostly done manually, making it difficult to ensure surface quality and consistency. As a result, an industrial robot polishing system based on digital twin is proposed, which can realize the interaction between physical and virtual platforms by using digital twin technology, acquire various parameters in real time, and monitor the polishing process. Based on this system, a removal depth model was established, and the polishing parameters to be analyzed were determined by combining the removal depth model. On this basis, the influence law of polishing parameters on surface roughness is analyzed through physical tests, and orthogonal experiments are used to optimize the polishing parameters. The results show that the surface roughness is reduced to 0.171 μm after optimization. Finally, the reliability of the polishing system is verified through the polishing machining test, and the surface quality of titanium alloy brake shell is significantly improved.

Contact Force Control of Robot Polishing System Based on Vision Control Algorithm

Contact Force Control of Robot Polishing System Based on Vision Control Algorithm

Sensor-based force decouple controller design of macro–mini manipulator

A robotic polishing system includes a force-controlled end-effector (mini manipulator) and a position-controlled industrial robot (macro manipulator). This combination mode has a fast response and a large workspace. However, the force-controlled axis component of the macro motions and the geometric of the workpiece surfaces will affect the contact force response rate and tracking accuracy due to the coupling dynamics between the macro and mini, limiting system performance. A new dynamic decoupling method employing dual force sensors (DFSs) is proposed to address these problems. One of the force sensors installed between the endpoint of the macro and the fixed platform of the mini realizes the dynamic decoupling of the macro and mini. The other one is added at the endpoint of the mini to obtain the interaction force in contact with the environment and feed it back to the control loop. When the disturbances produced by the macro trajectories and the uncertainties coming from the workpiece are introduced into the system, the proposed method can improve force response rate and tracking accuracy without knowing the dynamic models and parameters of the macro and the geometric of the workpiece surface. Several experiments are carried out under various conditions. Experimental results indicate that the contact force response rate and tracking error of DFSs are better than those of the conventional force-controlled and impedance matching methods, proving the proposed method’s effectiveness. In addition, the last comparison experiment verifies that the DFSs method applies to different kinds of end-effectors with various dynamics. • This paper proposes a new dynamic decoupling method based on force sensors. • It can obtain the coupling force to realize dynamic decoupling regardless of models. • It can reduce the disturbance effects of the macro and the workpiece on the force. • The proposed method can improve contact force response rate and tracking accuracy.

Movement Modeling and Control for Robotic Bonnet Polishing

With the increasing demand for high-precision optical components, bonnet polishing technology is increasingly being used in the polishing process of optical components owing to its high removal efficiency and high surface accuracy. However, it is expensive and difficult to implement dedicated bonnet polishing machine tools, and their processing range is limited. This research combines bonnet polishing technology with industrial robot-assisted processing technology to propose a robotic bonnet polishing control model for large-diameter axisymmetric aspherical optical components. Using the transformation relations of the spatial coordinate system, the transformation relations of the workpiece coordinate system, local coordinate system of the polishing point, and tool coordinate system of the bonnet sphere center are established to obtain the bonnet precession polishing motion model. The polishing trajectory of large-diameter axisymmetric aspherical components and the variation in the linkage angle difference were simulated by adding an efficiency-optimal control strategy to the motion model. The robot motion was simulated in Robostudio to verify the correctness of the precession motion model and control algorithm. Lastly, the robotic bonnet polishing system was successfully applied to the polishing process of the optical components.

Optimization of static performance for robot polishing system based on work stiffness evaluation

Robot-assisted bonnet polishing system (RABPS) is widely used in the polishing of optical components due to its low cost, high efficiency and rapid polishing. However, due to the insufficient stiffness of the robot, it is easy to produce vibration in the machining process, which not only causes the size of the polishing contact area to deviate from the ideal value, but also affects the removal amount of workpiece. First, this paper analyzes the influence of robot system stiffness on the actual polishing area size and polishing removal. Next, based on the analysis of the technical characteristics of multiple groups of polishing posture corresponding to the same point of robot bonnet polishing, the optimization method of robot static stiffness performance is proposed. Finally, the correctness and efficiency of the optimization method are validated by simulation and experiment. The working stiffness of the robot increases by 26.8% and the roughness of the polished surface is improved by 42.9% after posture optimization.

An Optimized Design of New XYθ Mobile Positioning Microrobotic Platform for Polishing Robot Application Using Artificial Neural Network and Teaching‐Learning Based Optimization

Compliant mechanisms with flexure hinges have been widely applied for positioners, bioengineering, and aerospace. In this study, a new optimized design method for the mobile microrobotic platform was developed for the polishing robot system. A metaheuristic‐based machine learning technique in combination with finite element analysis (FEA) was developed. The designed platform allows three degrees of freedom with two x‐and‐y translations and one z‐axis rotation. A new hybrid displacement amplification mechanism was also developed using Scott‐Russell and two‐lever mechanisms to magnify the workspace of the platform. The leaf hinges were employed due to their large rotation, and the right circular hinges were adopted because of their high accuracy. In modeling the behaviors of the developed platform, the artificial neural network is formulated in combination with the teaching‐learning‐based optimization (TLBO) method. The ANN architecture was optimized through TLBO to a better approximation. And then, three optimized case studies were conducted by the TLBO. The data is collected through FEA simulation. The modeling results from the TLBO‐based ANN were well established with excellent metrics of R, R2, and MSE. The optimized results found that the proposed MPM platform achieves a max‐y stroke of 1568.1 μm, max‐x stroke of 735.55 μm, and max‐θ rotation angle of 2.26 degrees. The proposed MPM platform can operate at a high displacement amplification ratio of over 9.

Development of robotic polishing/fettling system on ceramic pots

Current robot polishing techniques are available for objects with computer-aided design geometric models but not for objects without geometric models such as ceramic or clay pots. In this study, we developed a robotic polishing/fettling system to polish the molding defects of ceramic objects. The polishing force on the object surfaces is required to be constant to obtain better results. Thus, the proposed robotic polishing system was designed with a stepper motor, ball screw, and force sensor. The proposed system acquired a rough robot polishing/fettling trajectory and adopted a fuzzy proportional–integral–derivative controller to regulate the trajectory to maintain the desired contact force response from a ceramic object. We developed the temporary desired value technique to make the polishing force response close to the desired one. We validated the system on a six-degrees-of-freedom Staubli TX 40L robotic arm. Experiments were performed to test the effectiveness of the system. The robot trajectory responses showed that the proposed system performed well in tracking the desired force in the polishing/fettling process. We used a 3D microscope to verify that the molding defect of the ceramic pot was significantly removed to evaluate the polishing/fettling quality.

Contact force controlled robotic polishing for complex PMMA parts with an active end-effector

Due to the advantages in weather resistance, light transmittance and dimension stability, PMMA has been widely used in various fields such as aerospace and optical engineering. However, fully automatic robot systems are seldom used for polishing complex PMMA parts with high surface integrity. Therefore, a robotic polishing system with a new active end-effector is developed in this paper. In the system, a 6-degree-of-freedom industrial robot is utilized to polish the part profile along the preprogrammed paths, and then the system configuration is introduced in detail. For precisely controlling the normal contact force, both a linear voice coil motor and a force sensor are used in the designed end-effector. Meanwhile, a tilt sensor is also used to compensate the gravity component of the polishing tool along the force-controlled direction. Subsequently, a hybrid force controller, which consists of a PID controller and a Fuzzy controller, is designed to maintain the contact force between the polishing tool and the part within an allowable range. Finally, validation experiments are conducted with the designed robotic polishing system on a complex PMMA part. The experimental results show that the proposed robotic polishing system can strictly control the normal contact force and ensure high surface integrity of the PMMA part.

Vision-based initial point alignment control for the wheel hubs in the robotic polishing system

In the robotic polishing system for the wheel hubs, initial point alignment is a very important procedure before the robot starts to polish. Since the surface shapes of the wheel hubs are complex, traditional contact sensors are not suitable for the initial point alignment. Therefore, this paper presents a vision-based initial point alignment control method due to the merits of non-contact and high precision of the vision sensor. The main procedures of the new proposed initial point alignment methods are as follows. Firstly, the center point of the wheel hub is computed based on the growth of sampled points (GSP) method. Secondly, the center lines of the spokes of the wheel hub are extracted based on the edges of the spokes. Based on the center point and the center lines of the spokes, the needed rotation angle of the wheel hub denoting the current and target initial points can be computed. Thirdly, an alignment controller is designed to align the current initial point with the target one. Finally, experiments are well conducted to demonstrate the effectiveness of the proposed initial point alignment control method for the wheel hubs.

An integrated processing energy modeling and optimization of automated robotic polishing system

The automated robotic polishing system (ARPS) consisting of several robotic polishing cells (RPCs) is widely adopted in polishing industry to replace manual labor. Recently, energy-saving becomes a hotspot issue in manufacturing industry because of the increase in energy costs and requirement of environmental protection. Traditionally, robot motion planning and task scheduling are carried out separately and sequentially, which constrain the potential for energy-saving. In this paper, a task energy characteristic model is proposed as a polynomial function of the feedrate override to forecast the energy consumption of the polishing process of RPC, in which the designed parameters of the RPC and the polishing process parameters are encapsulated into the polynomial coefficients based on experimental data. Furthermore, an optimization model is proposed for an ARPS with mass tasks to minimize the energy consumption, in which the robot motion planning and the task scheduling are considered integratedly. An adaptive genetic algorithm with elite retention strategy is adopted to solve the optimization model. A case study is introduced to verify the proposed approach, which demonstrates the forecast error of task energy is less than 7%, and the proposed optimization approach can reduce the energy consumption of ARPS by more than 18% compared with the original processing scheme.

Optimization of the Polishing Efficiency and Torque by Using Taguchi Method and ANOVA in Robotic Polishing

Surface finishing and polishing are important quality assurance processes in many manufacturing industries. A polished surface (low surface roughness) is linked with many useful properties other than providing an appealing gloss to the product, such as surface friction, electrical and chemical resistance, thermal conductivity, reflection, and product life. All these properties require an efficient polishing system working with the best machining parameters. This study analyzed the effects of the different input polishing parameters on the polishing efficiency and torque in the robotic polishing system for the circular-shaped workpieces (such as ring, cylinder, sphere, cone, etc.) by using the Taguchi method and analysis of variance (ANOVA). A customized rotatory passive gripper is designed to hold the watch bezel during polishing. Under the design of experiments (DOE) technique, Taguchi’s L 18 array is selected to find the optimized process parameters for polishing efficiency (based on surface roughness) and torque. Experimental results with the statistical analysis by signal-to-noise ratio and ANOVA (95% confidence level) confirms that the polishing force and tool speed are the most influencing parameter for polishing efficiency in the system. Linear regression equations are modeled for the polishing efficiency and torque. Finally, a confirmation test is conducted for the validation of the experimentation results against actual results.

Fabrication of SiC Off-axis Aspheric Mirror by Using Robot Polishing

Two silicon carbide (SiC) lightweight off-axis aspheric mirrors were fabricated by using robot polishing technology. One is a primary mirror with dimension 380mm×328mm, the other is a tertiary mirror with dimension 294mm×238mm. The robot polishing technology is the combination of CCOS technology and a 6-axises industrial robot. The setup of robot polishing system is discussed, and the mirror aspheric grinding, surface polishing and figuring process are reported in this paper. The final surface shape error of primary mirror is 11.4nm RMS, and the tertiary is 12.1nm RMS. The capability of off-axis aspheric mirror fabricating on robot polishing system is verified.

Fast Fabrication of 1.26-Meter-Long Optic for Elliptic Cylindrical Focusing Bending Mirror

As beamline emittance reaching the diffraction limit, the demand for focusing mirrors over one meter in length is ever increasing. Bending mirrors, are competitive for its adjustable radius and high manufacture precision, whose final surface form is managed by a delicate bending of a high precision plane. A special contour plays an essential role and benefits this final touch, given that the computed torque along the length closely correlates with the corresponding width of the optics. However, it poses main challenges with severe edge effect, deformation and metrology to the fabrication of the precursor plane mirror. This paper reports on a fast processing technology for a 1.26-meter-long plane as a bending mirror with irregular shape. A smooth surface with a slope error of 0.67 urad(RMS) and 0.3nm roughness is achieved through deterministic flexible finishing of robot polishing system and annular polishing, providing a high precision and cost-effective method to meet the growing needs for long X-ray mirrors.

Research and application on force control of industrial robot polishing concave curved surfaces

In order to improve the quality of the industrial robot automatic polishing on curved surfaces and ensure the constant polishing pressure during polishing process, a method for polishing complex concave cavity surfaces with industrial robot is proposed in this article. The method can achieve stable force control and precise position control and is easy to be realized online. In order to ensure the removal rate uniformity of surface material at different normal vectors, a method for adjusting the speed of motorized spindle in real time according to the surface normal vector is proposed. After planning the trajectory and normal vectors, combined with the feedback force signal from the sensor and the proportional–integral controller in the direction of the normal vector, the robot terminal tool corrects the trajectory in the direction of the surface normal vector, indirectly realizing force control between the tool and the surface. The robot polishing system with different polishing tools has different system stiffness. In order to ensure the polishing system with different stiffness to have a better tracking performance of the contact force, an adaptive proportional–integral control algorithm proposed in this article can be used to evaluate the stiffness of polishing system and to adjust proportional–integral parameters. The simulation and experimental results indicate that the method can realize the polishing of concave cavity surface commendably.

A practical approach for automated polishing system of free-form surface path generation based on industrial arm robot

In manufacturing environment where a robot arm is programmed to follow a specified path such as in polishing, the geometric coordinate transformation of an automated polishing system frames is needed for polishing workpiece surface. As the presence of kinematic singularities can extremely affect the robot’s performance, singularity regions in the task space for robot are clearly identified using determinant of the robot’s Jacobian matrix. Based on the free-form surface polishing requirements, programing an industrial robot with Teach Pendant manually is skill dependent and time consuming. Therefore, a scheme of an automatic polishing system is proposed, which includes a 6DOF arm robot. An automatic planning and programming system based on data from a CAD system is described to create robot paths. The robot program which contains the polishing path is generated in certain order using RoboGuide software in virtual environment. A Human Machine Interface has been used to control the entire polishing system online. Finally, the generated path is successfully applied in robotic polishing system. The experimental results prove that the proposed method is effective and feasible. The outcomes of this work contribute to enhancing the use of arm robot for polish free-form workpiece surfaces.

TOWARDS AN AUTOMATED POLISHING SYSTEM - CAPTURING MANUAL POLISHING OPERATIONS

Advancements in robotic and automation industries have influenced many manual manufacturing operations. With a great level of success, robots have taken over from man in many processes such as part manufacturing, transfer and assembly. However, in other traditionally manual operations such as polishing, automation has only partially been successful, typically limited to parts with simple geometry and low accuracy. Automated polishing systems using robots have been attempted already by a number of industrial and research groups; however, there are few examples of deploying such a system as a part of a routine production process in high-technology industries, such as aerospace. This is due to limitations in flexibility, speed of operation, and inspection processes, when compared with manual polishing processes. The need for automated polishing processes is discussed in this article and the problem with the existing system was explained to be a lack of understanding and the disconnect from manual operations. In collaboration with industrial partners, a mechatronic based data capturing device was developed to accurately capture and analyze operational variables such as force, torque, vibration, polishing pattern, and feed rates. Also reported in this article is a set of experiments carried out to identify the polishing parameters that a manual operator controls through tactile and visual sensing. The captured data is interpreted to the operators’ preferences and polishing methods and should then be included in the design of an automated polishing system. The research results reported in this article are fed back to an ongoing research project on developing an integrated robotic polishing system.

Design and Analysis of the End-Effector of the Flexible Polishing Robot

The continuous growth of labor Cost, Study on the flexible robotic polishing systems has important realistic meanings. In this paper, After fully understanding the requirements of designing polishing tool based on polishing technology, a robot end-effector polishing tool held by the arm of robot is designed, and the establishment of a dynamic model and the equations of motion dynamics, which to provide technical support and theoretical basis for further development and optimization of flexible robotic polishing systems.

Automatic robotic polishing on titanium alloy parts with compliant force/position control

In this article, an automatic robotic polishing technique and system is developed for the polishing of titanium alloy curved parts. By means of a designed compliant end-effector with a force sensor, the robotic polishing system with a position-based explicit force control architecture is first built to perform the polishing operation. Then, a specially designed multi-axis robotic post-processor based on computer-aided design/computer-aided manufacturing is developed to generate the basic position and posture of the polishing tool without any complicated teaching processes. Subsequently, an adaptive Anti-Saturation Integral Separated Fuzzy PI controller, which is able to imitate the manual polishing operation and prevent undesirable vibrations and mechanical collisions, is designed to control the normal contact force. The basic trajectory is changed each time after the current polishing cycle has been finished by online self-learning, and a new basic trajectory is generated for the next polishing cycle. Finally, the effectiveness of the proposed automatic polishing technique is evaluated by actual polishing experiments on titanium alloy (TC11) parts, and the experimental results show that the proposed automatic robotic polishing technique has a perfect control effect on the contact force and thus can achieve a good and uniform surface quality of the part.

Robot-Assisted Vibration Polishing of NiCo Retroreflector Moulds

Galvanic retroreflector moulds suffer from fabrication errors and considerable wear due to the manufacturing process and the subsequent use for injection moulding. To remove degradations like flaws and wear marks from the mould’s optical surfaces without tedious manual labour, a partially automated process chain using a 6-axis robot is being developed combining surface metrology and machining technology. The areal limitation of the structured surfaces excludes conventional rotatory polishing processes. Vibration polishing is applied instead to remove critical surface errors and to enhance surface roughness to a near optical value of Sa ≤ 50 nm. The work presented in this paper gives insights into experiments performed on a robot polishing system and illustrates and the suitability for an application in the aforementioned partially automated process chain.

The Study of the Constant Force Polishing by the Multi-Robot

In this paper, the study of the dynamics for the constant force polishing robot system is aimed, through the establishment of the dynamics equations for the end of the robot polishing. By comparing the before and the after installation of terminal buffer actuator force was verified by the experiment, the feasibility and stability constant of the system for the constant force polishing on the multi-robot are obtained.