Position Of Workpiece Research Articles

Optimization of a clamping concept based on machine learning

Fixtures are an important element of the manufacturing system, as they ensure productive and accurate machining of differently shaped workpieces. Regarding the fixture design or the layout of fixture elements, a high static and dynamic stiffness of fixtures is therefore required to ensure the defined position and orientation of workpieces under process loads, e.g. cutting forces. Nowadays, with the increase in computing performance and the development of new algorithms, machine learning (ML) offers an appropriate possibility to use regression methods for creating realistic, rapid and reliable equivalent ML models instead of simulations based on the finite element method (FEM). This research work introduces a novel method that allows an optimization of clamping concepts and fixture design by means of ML, in order to reduce manufacturing errors and to obtain an increased stiffness of fixtures and machining accuracy. This paper describes the preparation of a dataset for training ML models, the systematic selection of the most promising regression algorithm based on relevant criteria, the implementation of the chosen algorithm Extreme Gradient Boosting (XGBoost) and other comparable algorithms, the analysis of their regression results, and the validation of the optimization for a selected clamping concept.

Improvement of stiffness during milling thin-walled workpiece based on mechanical/magnetorheological composite clamping

Because of the weak rigidity and complex structure, aerospace thin-walled parts are prone to deformation under the influence of machine tool vibration, cutting force and heat during milling. Based on the previous magnetorheological fluid (MRF) flexible fixture, this paper proposes a mechanical/magnetorheological composite clamping method to suppress vibration and improve machining accuracy. Firstly, the relationship between shear stress, workpiece position and MRF height is experimentally analyzed, and a mathematical model of composite clamping is established. Through the single-factor test, it is found that the experimental and predicted milling force curves tend to be consistent, and the maximum milling force errors in X, Y and Z directions are 19.9%, 13.4% and 16.2% respectively. When the spindle speed, depth of cut and feeding speed change, the errors between experimental and predicted milling force in three directions are controlled within 10%, which can verify the reliability of the prediction model. Then, the frequency response impact experiments are carried out on single mechanical clamping and composite clamping respectively, which proves that the stability of composite clamping is better than single mechanical clamping. Finally, by comparing the test results of milling thin-walled part, it is found that the surface roughness values Ra, Rq and Rz of composite clamping parts decrease by 49.0%, 56.7% and 43.3% respectively. Therefore, the mechanical/magnetorheological composite clamping method proposed in this paper has remarkable effect on suppressing chatter, which can effectively improve the milling surface quality of parts.

Milling vibration control of semiconical shell workpiece with multiple distribution tuned mass dampers

Considering the complexity geometry and thin wall feature, the semiconical shell workpiece will induce complicated and intense vibration in the milling process leading to poor surface quality and large machining deformation. In order to suppress the vibration, this paper focused on the semiconical shell workpiece and proposed a multiple distribution tuned mass damper (MDTMD) vibration control technique by attaching a series of optimized tuned mass dampers (TMD) to each optimal position of workpiece. The vibration characteristics and modal shapes of workpiece were obtained with the use of spectro-geometric-Ritz method (SGM) and the dynamic model of workpiece with MDTMD was established. A novel design of TMD was proposed. The optimal parameters and positions of each TMD were determined simultaneously using numerical optimization algorithm based on the modal summation method. Theoretical studies and experiment results shown that the proposed MDTMD method can remarkably improve the dynamic stiffness of the workpiece. The performance of vibration suppression is further verified in the impact tests and milling experiments.

Agile robotics for industrial applications: Editorial

While multi-robot cells are being used more often in industry, the problem of work-piece position optimization is still solved using heuristics and the human experience and, in most industrial cases, even a feasible solution takes a considerable amount of trials to be found. Indeed, the optimization of a generic performance index along a path is complex, due to the dimension of the feasible-configuration space. This work faces this challenge by proposing an iterative layered-optimization method that integrates a Whale Optimization and an Ant Colony Optimization algorithm, the method allows the optimization of a user-defined objective function, along a working path, in order to achieve a quasi-optimal, collision free solution in the feasible-configuration space.

Deep reinforcement learning for the control of conjugate heat transfer

This research gauges the ability of deep reinforcement learning (DRL) techniques to assist the control of conjugate heat transfer systems governed by the coupled Navier–Stokes and heat equations. It uses a novel, “degenerate” version of the proximal policy optimization (PPO) algorithm, intended for situations where the optimal policy to be learnt by a neural network does not depend on state, as is notably the case in optimization and open-loop control problems. The numerical reward fed to the neural network is computed with an in-house stabilized finite elements environment combining variational multi-scale (VMS) modeling of the governing equations, immerse volume method, and multi-component anisotropic mesh adaptation. Several test cases of natural and forced convection in two and three dimensions are used as testbed for developing the methodology. The approach successfully alleviates the natural convection induced enhancement of heat transfer in a two-dimensional, differentially heated square cavity controlled by piece-wise constant fluctuations of the sidewall temperature. It also proves capable of improving the homogeneity of temperature across the surface of two and three-dimensional hot workpieces under impingement cooling. Various cases are tackled, in which the position of multiple cold air injectors is optimized relative to a fixed workpiece position. The flexibility of the numerical framework makes it tractable to solve also the inverse problem, i.e., to optimize the workpiece position relative to a fixed injector distribution. The obtained results showcase the potential of the method for black-box optimization of practically meaningful computational fluid dynamics (CFD) conjugate heat transfer systems. More significantly, they stress how DRL can reveal unanticipated solutions or parameter relations (as the optimal workpiece position under symmetrical actuation turns to be offset from the symmetry axis), in addition to being a tool for optimizing searches in large parameter spaces.

Towards optimal task positioning in multi-robot cells, using nested meta-heuristic swarm algorithms

While multi-robot cells are being used more often in industry, the problem of work-piece position optimization is still solved using heuristics and the human experience and, in most industrial cases, even a feasible solution takes a considerable amount of trials to be found. Indeed, the optimization of a generic performance index along a path is complex, due to the dimension of the feasible-configuration space. This work faces this challenge by proposing an iterative layered-optimization method that integrates a Whale Optimization and an Ant Colony Optimization algorithm, the method allows the optimization of a user-defined objective function, along a working path, in order to achieve a quasi-optimal, collision free solution in the feasible-configuration space. • Work-piece position affects the outcome of the processing in a robotic operated cell. • Heuristic algorithms are shown to explore consistently the optimization search space. • Task redundancy exploitation is a key factor in robotic operated cells.

Photoelectric Detection of Hole Shape and Size for Large Plate Parts

The measurement of hole shape and size of large plate parts has always been a technical problem. The article proposes a technology to use non-contact photoelectric detection technology for online detection of the shape and position of large plate-shaped workpieces. The detection principle is: the control system controls the photoelectric detection system to move in a straight line along the guide rail at a uniform speed, and the large plate-shaped workpiece the hole shape and size are measured, and the lighting system moves synchronously with the photoelectric detection system to provide the light source for it. The images collected by the photoelectric detection system are processed through digital image processing and image splicing technology to realize the hole shape and size of large plate workpieces. Non-contact measurement.

Two-dimensional high-precision non-contact automatic measurement method based on image corner coordinates

Aiming at some shortcomings of the existing non-contact two-dimensional high-precision measurement methods, this paper proposes a two-dimensional high-precision non-contact automatic measurement method based on the corner coordinates of the image. Firstly, this paper designs a set of simple image acquisition device and explains the advantages of the Canny operator used in the image contour detection algorithm. Subsequently, this paper proposes a dimension calibration algorithm based on image corner coordinates, which can convert the pixel size to the actual size, and achieves the function of the algorithm by hierarchical, multi-step processing of the image. Finally, in order to realize the intelligent positioning and selection of the standard size workpiece position, an automatic measurement and positioning system is designed, which can convert the actual size signal into the pulse time control signal. The experimental results show that the measurement method proposed in this paper has the advantages of fast measurement speed, high robustness, low cost and high degree of automation. When using a black-and-white checkerboard paper with an accuracy of 0.1 mm, the measurement accuracy can reach the micron level.

Elucidation of Mechanism Underlying Workpiece Jump in Hammer Forging

During the process of drop hammer forging, workpieces sometimes jump after strikes. The present research investigates the mechanism of the workpiece jump by means of experiments and numerical simulations. In the experiments, workpieces were struck by vertical symmetrical flat dies or vertical asymmetrical dies. A high-speed camera was used to measure the workpiece deformation, the position of workpieces during jumping and the position of the dies. Strain of lower dies and structures of the hammer were measured by strain gauges. Vibration of the antirattler under the hammer, elastic vibration of lower dies and structures of the hammer, and contact area between workpieces and dies were analyzed by numerical simulations. The results indicate that workpieces jump by adhesive force between workpieces and dies, and by elastic vibration of lower dies and structures of the hammer.

Stepper Motor Control System for XY Module for IC Production

The presented in the paper control system of the stepper motor of the two-coordinate printing module is developed on the basis of modern elements and allows you to control the stepper motor, providing the required shaft rotation speed and adjusting the number of rotation steps. This system realizes the processing of a moving object in several coordinates simultaneously without kinematic elements that convert rotary motion into linear, which makes it possible to speed up the time and accuracy of the processing tool. A forked optical sensor is used as workpiece position sensors. UART and USB bus are used for communication with the computer.

Accuracy Analysis of Machining Trajectory Contemplating Workpiece Dislocation on a Six Degree of Freedom Machining Bed

Machining is material removal from a workpiece. Current spindle technologies allow the material to be removed very quickly but unfortunately this compromises the accuracy of the desired machined trajectory on the workpiece. Proposed solution to the problem is restricting motion of the tool and giving rotation to the workpiece. This paper presents analysis of the accuracy of trajectory of material removal from a workpiece, such that the workpiece rotates with six degrees of freedom, in the presence of error generated due to an offset of the workpiece from centre of the moving platform of the machining bed. The kinematics of the machining bed is, therefore, modeled using as inverse kinematic formulation applying geometric and vector addition method. The mechanism outputs three rotational and three translational motions. The leg length for each of six legs of the bed is computed individually. Moreover, workpiece position offset error is modelled to find actual leg lengths of the bed. Finally accuracy computation model is proposed to analyse the accuracy of the final trajectory of the motion of the workpiece. The models are verified in simulation for a trajectory and validated experimentally on a six degree of freedom (6DOF) machining bed. The results reveal maximum inaccuracy in machining trajectory to be 1% in experiments while less than 1% in simulation. This verifies quality of the mechanism and efficacy of the proposed 6DOF machining bed in machining accuracy.

Inverse determination of thermal boundary condition and temperature distribution of workpiece during drilling process

For the problem that the moving thermal boundary condition of workpiece is difficult to be measured directly in drilling process, an efficient estimation scheme is developed in this study. The proposed scheme takes into account the heat transfer characteristics of the drilling workpiece. Specifically, according to the moving boundary position of workpiece, the heat transfer system of drilling workpiece is approximated by several linear subspaces. Correspondingly, the estimation results of unknown variable are obtained by comprehensively weighting the estimated results obtained from linear subspaces. Both numerical simulations and experimental tests are utilized to prove the validity of the above scheme. Effects of some important factors such as aperture size and measurement errors on the estimation results are discussed in detail. Comparisons with the traditional scheme are also carried out. The results obtained indicate that the presented approach can effectively estimate the moving thermal boundary condition of workpiece, obviously reduce the calculation cost, and has good adaptive capability. This method can be used for online monitoring of the temperature distribution in drilling area, thereby ensuring the machining quality of the workpiece and the service life of the drilling tool.

Workpiece force and position control for active and flexible fixtures in assembly

With strengthening focus on digitalization and flexibility, active and flexible fixtures can provide the right tools for manufacturing systems. However, fixturing solutions are often too individualized for processes and need a universal approach. Firstly, a system formulation of multiple workpieces interacting with each other is presented. Secondly, strategies for direct and indirect force control along with their characteristics have been developed. The stability of assembly of force-controlled components has been analyzed, and certain key characteristics have been presented. The position control under different signal types, including oscillatory, have been discussed. Finally, a set of experiments have been conducted for performance evaluation.

Управляемые шпиндельные опоры как инструмент обеспечения качества обработки

The purpose of the work is to provide conditions for machined workpiece surface quality control based on the use of gas-magnetic supports in machine-tool systems (on example of the 3K227A internal grinding machine). To model the trajectory of tool and workpiece mutual movement the methods of nonlinear dynamics are used. The literature data on the problem are analyzed and experimental studies are carried out. Based on the considered issues of controlling the dynamic stability of technological systems under machining by means of contactless controlled gas-magnetic supports of spindle units, a scheme for adaptive control of the machine-tool system is proposed. It allows in many respects to eliminate external mechanical effects on the technological system, internal vibrations caused by drives and moving parts, as well as to compensate temperature deformations of the spindle unit frame and body. An adaptive control system based on gas-magnetic supports of the spindle assembly and the workpiece, as well as the control systems of the position of workpiece and tool (on example of 3K227A internal grinding machine) are demonstrated in action. The gas-magnetic support control system developed at Komsomolsk-na-Amure State Technical University makes it possible to set the position of the rotor axis with the accuracy of 0.1 microns. The study results obtained lead to the conclusion that the control of two adaptive links on the gas-magnetic supports, i.e., the spindle assembly of the tool and the spindle assembly of the workpiece, allows to achieve a rotation accuracy of up to 0.2 microns. The methods of nonlinear dynamics make it possible to construct an attractor (trajectory) of the tool tip movement in the real time, which provides a possibility to affect the input parameters of the machining process and thereby to control the output parameters. In addition to this, the control system of machine-tool system dynamic stability is applicable to other processing types as well, including edge cutting machining.

Fundamental investigation of gyro finishing experimental investigation of contact force between cylindrical workpiece and abrasive media under dry condition

Gyro finishing, which is one of the mass finishing, is expected to be an excellent finishing process of a workpiece with a complex shape. However, its fundamental researches are few, and hence the development of techniques to address its issues/problems, such as the decline of shape accuracy and low process controllability, is hindered by a lack of understanding of the process. Thus, a fundamental investigation of gyro finishing is conducted in the present research. The contact force acting on a cylindrical workpiece, which was designated by simplifying a large gear, was measured under different conditions in workpiece position, amount of abrasive media, and rotational speed of the container. In addition, the abrasive media height above the workpiece was measured, and effects of various factors on the contact force were investigated. From the results, the height above the workpiece was confirmed to have a strong correlation with the contact force. This was considered to be caused by increasing of the resistance of the abrasive media motion, and it was considered a major factor of the contact force. On the other hand, the effect of the abrasive media momentum and the distance between the workpiece and the container wall on the contact force was confirmed weak. Moreover, the variation of the surface roughness was investigated under different contact force conditions, and the improving speed of the surface roughness was faster under the higher contact force condition. Thus, contact force was a significant factor affecting the finishing performance, and this investigation featuring the contact force acting on the workpiece was considered significant to understand the gyro finishing process and to increase the contact force and the finishing performance.

Computer Vision Tool-Setting System of Numerical Control Machine Tool.

An automatic tool-setting and workpiece online detecting system was proposed to study the key technologies of next-generation intelligent vision computerized numerical control (CNC) machines. A computer vision automatic tool-setting system for a CNC machine was set up on the basis of the vision tool-setting principle. A rapid vision calibration method based on the position feedback from the CNC machine was proposed on the basis of the theory of traditional vision system calibration. The coordinate mapping relationship of the image and the CNC machine, the tool-setting mark point on the workpiece, and the tool tip were calibrated. The vision system performance testing and system calibration experiments were performed. Experimental results indicated that the time consumption was 128 ms in image processing. The precision of tool setting and measuring was less than 1 μm. The workpiece positioning and processing online detection function of the system can completely meet the requirements of visual CNC machine application, and the system has wide application prospects.

Nonlinearities of hardware-in-the-loop environment affecting turning process emulation

In hardware-in-the-loop (HIL) experimental environment, a local softening character of the emulated cutting force is observed during the emulation of turning, which affects the stability properties of the process. The real workpiece is substituted by a dummy one that is clamped to the real main spindle. It is excited in the lateral direction by an electromagnetic actuator. The position of the dummy workpiece is monitored by contactless laser-based sensors to close the feedback loop. The previous and the present position of the workpiece is stored to attain the effect of surface regeneration. The desired cutting force characteristic is calculated by means of a high performance real-time computer. The experimental results gained for the linear loss of stability of the process and for the spindle speed dependent dynamics leads to the conclusion that the dominant frequency decreases as the virtual depth of cut and thus the emulated cutting force increases. This is identified for a wide range of real spindle speeds and virtual depth of cuts. The measurement results are supported by theoretical stability analysis and the variation of the dominant frequency is tracked by means of the unexpected local softening nonlinearity of the electromagnetic actuator emulating the real cutting forces, which are also confirmed analytically. These results are needed in future development of a portable HIL system, to analyse chatter phenomena in the presence of cutting force nonlinearities and to test specific cutting tools before prototyping.

A novel reverse helical milling process for reducing push-out delamination of CFRP

When drilling Carbon fiber reinforced plastic (CFRP), delamination can be found at hole-exit frequently, which is known as typical machining damage and would weaken the mechanical strength of finished components. The occurrence of delamination is regarded as the consequence of the deformation of uncut material that caused by thrust force. This study aims to propose a new reverse helical milling (RHM) method to restrain the delamination, in which, the principle of reducing the deformation extent of uncut material is via material rigidity enhancement. Firstly, two-dimensional analysis was used to contribute the avoidance of push-out delamination during CFRP drilling. Then, considering both CFRP and metal-CFRP stacks, an idea of reversing feed direction of cutting tool is processed, which enhances the rigidity of uncut material by means of either increasing the uncut thickness or providing an equivalent back-up without employing any extra facility. In order to realize reverse cutting without changing the original position of both workpiece and machine equipment, special cutting tools and detailed operation steps are designed. Finally, confirmatory experiments were carried out and the results demonstrated that RHM will neither deteriorate the existing delamination nor generate new ones and as a result, the push-out delamination was effectively reduced.

A Systematic Model of Machining Error Reduction in Robotic Grinding

Robotic grinding is a promising automatic technique for free-form surface manufacturing. One important problem that restrains the application of robotic grinding is the machining quality. Existing methods considers only individual kinematic errors or joint stiffness. In this article, a systematic method of error compensation, workpiece position optimization and tool pose optimization is proposed to reduce the machining error. First, the mathematical models of machining error with respect to both kinematic errors and joint stiffness are built using speed and force adjoint transformation, respectively. Compared with existing indirect index evaluation models, this model is improved by directly building the quantitative function relationship between the machining error and the corresponding factors. Based on the model, an error compensation strategy is presented by only fine-tuning the workpiece frame position. Then, an objective function based on the compensated machining error is defined to optimize both the workpiece position and the tool pose. Experiments demonstrate the availability of the proposed method for machining error reduction.

Characteristics of shear stress based on magnetorheological fluid flexible fixture during milling of the thin-walled part

With light weight and good overall structure, thin-walled part has been widely used in various fields like aerospace. However, it has low stiffness in the cutting process. Traditional fixture clamping workpiece has a long positioning and adjustment cycle and is likely to deform, making it difficult to control machining efficiency and quality. In this study, a mechanical-magnetorheological fluid (MRF) composite flexible clamping method was proposed, and a theoretical mathematical model of the shear stress of MRF was constructed. The real value and the theoretical value of shear stress show consistent upward and downward trends. Based on the prediction model, the coupling relations between magnetic field intensity and thickness and position of workpiece were studied. Results demonstrate that workpiece thickness has less significant influence on shear stress compared with workpiece position. Combined with the experimental results, the smaller the workpiece thickness and the closer to the magnetic field, the larger the shear stress. The shear stress of the workpiece 1 mm thick is 21.5% higher than that of the workpiece with the thickness of 8 mm at position of 10 mm. Finally, the thin-walled part was used to demonstrate MRF clamping. Compared with the traditional clamping method, the proposed method can decrease the cutting force by 14.3%. Moreover, the residual stress σx and σy decrease by 37.0% and 43.9%, the flatness value decreases by 55.6%, and the roughness Ra, Rz and Rq decrease by 55.6%, 53.2%, and 56.7%. The quality of the thin-walled part was effectively controlled.