Position Of Workpiece Research Articles

Region-Based Approach for Machining Time Improvement in Robot Surface Finishing

Traditionally, in robotic surface finishing, the entire workpiece is processed at a uniform speed, predetermined by the operator, which does not account for variations in the machinability across different regions of the workpiece. This conventional approach often leads to inefficiencies, especially given the diverse geometrical characteristics of workpieces that could potentially allow for different machining speeds. Our study introduces a region-based approach, which improves surface finishing machining time by allowing variable speeds and directions tailored to each region’s specific characteristics. This method leverages a task-oriented strategy integrating robot kinematics and workpiece surface geometry, subdivided by the clustering algorithm. Subsequently, methods for optimization algorithms were developed to calculate each region’s optimal machining speeds and directions. The efficacy of this approach was validated through numerical results on two distinct workpieces, demonstrating significant improvements in machining times. The region-based approach yielded up to a 37% reduction in machining time compared to traditional single-direction machining. Further enhancements were achieved by optimizing the workpiece positioning, which, in our case, added up to an additional 16% improvement from the initial position. Validation processes were conducted to ensure the collaborative robot’s joint velocities remained within safe operational limits while executing the region-based surface finishing strategy.

Effect of different beam distances in laser soldering process: a numerical and experimental study

PurposeThis paper aims to investigate the effect of different beam distance by understanding laser beam influence on solder joint quality. The utilisation numerical-based simulations and experimental validation will help to minimise the formation of micro void in PTH that can lead to cracks and defects on passive devices.Design/methodology/approachThe research uses a combination approach of numerical-based simulation using Finite Volume Method (FVM) and experimental validation to explore the impact of different laser beam distances on solder joint quality in PTH assemblies. The study visualises solder flow and identifies the optimal beam distance for placing a soldering workpiece and a suitable tolerance distance for inserting the solder wire.FindingsThe simulation results show the formation of micro void that occurs in PTH region with low volume fraction and unbalance heat concentration profile observed. The experimental results indicate that the focus point of the laser beam at a 99.0 mm distance yields the smallest beam size. Simulation visualisation demonstrates that the laser beam’s converging area at +4.6 mm from the focus point which provides optimal tolerance distances for placing the solder wire. The high-power laser diode exhibits maximum tolerance distance at 103.6 mm from the focus point where suitable beam distance for positioning of the soldering workpiece with 50% laser power. The simulation results align with the IPC-A-610 standard, ensuring optimal filling height, fillet shape with a 90° contact angle and defect-free.Practical implicationsThis research provides implications for the industry by demonstrating the capability of the simulation approach to produce high-quality solder joints. The parameters, such as beam distance and power levels, offer practical guidelines for improving laser soldering processes in the manufacturing industry.Originality/valueThis study contributes to the field by combining high-power laser diode technology with numerical-based simulations to optimise the beam distance parameters for minimising micro void formation in the PTH region.

Robotical Automation in CNC Machine Tools: A Review

Abstract Robotics and automation have significantly transformed Computer Numerical Control (CNC) machining operations, enhancing productivity, precision, and efficiency. Robots are employed to load and unload raw materials, workpieces, and finished parts onto CNC machines. They can efficiently handle heavy and bulky components, reducing the demand of manual labour and minimizing the risk of injuries. Robots can also be used in CNC machine tools to perform tasks such as automatic tool changing system, part inspection, and workpiece positioning. Automation technologies, including in-line inspection systems and Non-Destructive Testing (NDT) methods, can be integrated into CNC machining cells to enhance accuracy and reduce scrap and rework in machining operations. These systems collect real-time data on process parameters and machine tool performance to predict maintenance, optimize machining parameters, and improve overall efficiency. In the current study, applications of robotics and automation in the modification of CNC machine tools are reviewed and discussed. Different applications of robotics and automation in CNC machine tools, such as automated material handling, automatic tool changing, robotic work cells, adaptive machining, machine tending, quality inspection, data monitoring and analysis, and production line integration, are discussed. Thus, by analysing recent achievements in published papers, new ideas and concepts of future research works are suggested. As a result, accuracy as well as productivity in the process of part production can be enhanced by applying robotics and automation in CNC machining operations.

Influence of Machine Tool Operating Conditions on the Resulting Circularity and Positioning Accuracy

The operating conditions of the production process significantly influence the resulting dimensional and form accuracy of the workpiece. The operating conditions include the position of the workpiece location, with internal and external heat sources influenced not only by the machine location but also by its operation. In addition, there are the cutting conditions and the feed rate requirements of CNC machine tools. These changes, such as workpiece position, feed rates, and machine heat load, are further reflected in the ability of the machine to run at the position required and interpolate within the given tolerances of circularity. For the accuracy and repeatability of positioning, the machine was set up according to ISO 230-2 and for the circular interpolation tests according to ISO 230-4. The obtained results show the importance of attention to the appropriate setting of the operating conditions of the production process, where the knowledge of the geometric accuracy of the CNC machine tool in its working space can systematically increase the manufacturing accuracy itself or be another tool suitable for predicting the dimensional and form accuracy of workpieces.

Geometric Error-Based Multi-Source Error Identification and Compensation Strategy for Five-Axis Side Milling

Based on a multi-source error model, this paper discusses the principle of error element identification and uses the mirror bias method to compensate the geometric errors of a process system. Firstly, a nine-line measurement method to determine the geometric error of the linear feed axes of machine tools is introduced, and the geometric error identification model based on the “nine-line method” is established. Then, using a ballbar mounted in the axial, tangential, and radial directions of the machine, the geometric error elements of the rotation axis are identified by three simple measurements in each direction. Subsequently, for the more common flat vise clamping workpiece in actual production, the workpiece position error is identified by using the traditional process of dimensional chain, and the workpiece attitude error is identified by fitting the angle between the positioning plane and the horizontal plane by the least squares method. Finally, based on the tool position points and tool axis vectors obtained from the multi-source error model, the error compensation value is solved using inverse machine tool kinematics to offset the machining error by mirroring the error value of the same size, and based on the “S-shaped specimen” to compensate the processing experiments, after compensation, the processing error is reduced by 30~45%, verifying the effectiveness of the compensation method.

Enhancing Welding Efficiency and Reliability in Unstructured Environments: A Computational Analysis of Spot-Welded Steel Sheet Connections

High-strength steels play a crucial role in various industries such as shipbuilding, construction, and aerospace due to their unique properties. Welding of these steels in unstructured workspaces presents challenges in terms of variability in workpiece position, shape, and environmental conditions. The research utilizes a portable robotic welding system with a novel seam-tracking method to address the challenges of welding in unstructured workspaces. Additionally, the study involves the analysis of different steel grades, including tool steels, stainless steel 440A, to understand their mechanical properties and applications. Experimental results demonstrate the effectiveness of the portable robotic welding system in accurately tracking welding seams in various positions. The study also provides insights into the mechanical properties and applications of different high-strength steel grades, emphasizing the importance of understanding spot weld behavior for improved structural performance. The findings underscore the significance of welding parameters, base-metal properties, and welding characteristics in determining the quality and durability of spot-welded joints.

Investigation of the Efficiency of Roll Profiles and Technological Schemes of Deformation of Asymmetric Rolling in Relief Rolls of C11000 Copper Alloy by FEM Simulation

In this paper, finite element simulation of asymmetric rolling in relief rolls of C11000 copper alloy in order to analyze the effectiveness of possible roll profiles and technological schemes of deformation was performed. The scientific innovation of this work lies in determining the patterns of development of stress-strain state parameters for various configurations of rolls, as well as determining the effectiveness of metal processing using various technological schemes. It was found that the use of trapezoidal relief makes it possible to increase the level of metal processing by almost 5 times compared with the use of radial relief. Comparison of technological schemes of deformation showed that deformation with 180° workpiece turning between passes significantly reduces the influence of the asymmetry factor. Deformation without changing the workpiece position between the passes has the opposite effect, and such a scheme significantly increases the influence of the asymmetry factor. Deformation with a transverse workpiece shift for the relief period between passes has the effect of a “golden mean.” The conducted laboratory experiment for lead billet showed that the shape change of lead billet during computer simulation has a high level of convergence with real conditions. At each stage of deformation, the difference in the geometric parameters of the workpiece between the model and the experiment did not exceed 3-5%. When deforming a copper billet, the maximum difference level was 8%, which is the result of the low rigidity of the rolling cage with smooth rolls.

A study of the accuracy of industrial robots and laser-tracking for timber machining across the workspace

ABSTRACT The aim of the present study was to investigate the accuracy of an industrial robot when milling glued-laminated timber along a vertical work plane while maximising the advantageous size of the workspace. The authors discovered a research gap in the machining accuracy within the workspace of an industrial robot. Hence, the examination comprises 50 distinct positions allocated in a grid, each with 3 machined specimens resulting in a total of 150 samples. The workpiece positions were referenced using laser-tracking technology to adjust the robot machining code to the actual workpiece position, while simultaneously assessing the machining accuracy using laser scans of the samples. As a result, accuracy maps are presented indicating the nominal-actual deviation including referencing errors and workpiece dimensional deviations (absolute accuracy) and the robot-only nominal-actual deviation (relative accuracy), subsequently proving that both comply with the EN 14080 standard. Furthermore, a calculation of the centre of accuracy defines the point of highest relative accuracy. The objective was achieved and advocated for a more pronounced utilisation of the workspace when machining timber with industrial robots. Applying these insights to the machining of large complex parts, multi-workpiece stacks and mobile robot platforms can enhance the possibilities and efficiency within timber construction.

Multi-View consistency-based point cloud registration method with low overlap rate

Accurate and efficient workpiece measurement is crucial for workpiece processing and quality monitoring. Non-contact optical measurement methods have gained more attention due to their simplicity, efficiency, and flexibility compared to complicated and inefficient contact measurement methods. Multi-view registration of measurement data is a key issue in workpiece measurement, as it relies on the system’s geometric accuracy and motion stability, presenting challenges such as the insufficient overlap of multi-viewpoint cloud data and cumulative error. To address these challenges, this paper proposes a multi-view planning and registration algorithm with a low overlap rate. The multi-view planning algorithm employs a greedy method to plan the scanning viewpoints of the workpiece to obtain complete point cloud data efficiently. The multi-view registration algorithm extracts features using a multi-scale geometric feature extraction network, matches the features based on the Hungarian algorithm, builds a graph, and optimizes workpiece positions based on the G2O algorithm for multi-view registration, effectively reducing cumulative error. Measurement experiments on blade workpieces confirm the feasibility of the proposed algorithms.

Reconfigurable open architecture control system with integrated digital twin for 3-axis woodworking milling machine

ABSTRACT This study proposes a reconfigurable open architecture control system for the Computer Numerical Control (CNC) woodworking educational machine tool called “EMCO F1 CNC”. On this machine physical hardware reconfiguration (spindle position can be vertical and horizontal) is possible. The idea was to develop a control system that would follow the configuration changes of the machine tool. The educational character of the machine and its reconfigurability demand possibilities for machining programme simulations in order to determine optimal workpiece position in the workspace and programme verification. Those are the reasons for developing a virtual machine tool integrated with the control system as a digital twin. The study presents a novel methodology for the development of control systems, merging the concept of “virtual commissioning” with iterative error-driven processes. The objective was to develop a dynamic control system capable of promptly adjusting to kinematics changes in real time. In a wood machining experiment, a test workpiece for machine tools for both machine configurations verified the operation of the developed control system.

Numerical investigation on design parameters of orifice plate for positioning of workpiece in cavitation zone for cavitation machining

ABSTRACT The recent development of non-traditional machining techniques, such as cavitation machining (CM), has been gaining traction amongst researchers due to its sustainable nature. The present research focuses on the use of computational fluid dynamics (CFD) model to predict the location of workpiece in the fluid domain and bubble distribution during CM process. For efficient CM, the correct positioning of a workpiece in cavitation zone is essential, as the implosion of the cavity bubble leads to formation of micro-jet and shock waves for a few milli-to-microseconds generating high temperature and pressure on workpiece. The aim is to harness cavitation phenomena in material processing, particularly by using orifice plates as a common tool to induce hydrodynamic cavitation. To generalise the investigation, the flow simulation through orifice plate with different aspect ratios (l/d) are carried out. For the bubble distribution and their diameters, the Lagrangian discrete phase model (DPM) is used in the downstream side of the flow domain. Using this information, bubble dynamics have also been investigated using the Keller–Miksis (KM) model to compute the implosion time and intensity in the zone. The presented exploration determines the orifice dimensions to optimize implosion intensity, ensuring precise workpiece placement in real-time CM.

Simplifying the monoscopic deflectometric measurement by extra-facility-free workpiece positioning

Monoscopic deflectometry is a powerful and flexible measuring method for optical surfaces. Precise workpiece positioning is of significance because it directly determines the reliability of the measurement results. But unfortunately, the need for additional facilities severely limits the application of the monoscopic deflectometry. In this paper, a self-positioning method is proposed by combining the ray-tracing and Gaussian process regression. The phases retrieved from the captured images are parameterized using the Zernike polynomials. Then a training model is established for describing the relationship between the Zernike coefficients and the workpiece positions. Workpiece positioning is implemented by computing the associated joint Gaussian distribution. Experimental results show that the positioning accuracy of optical surfaces is comparable with that of a coordinate measuring machine, with a deviation less than 8 × 10−4° in tilt and 4 μm in translation. This greatly simplifies the sophisticated operation and improves the practicability and efficiency of deflectometric measurements.

Development and Validation of a Screw Interlock Recognition Method based on Logistic Regression

Conventional robotic screw methods rely on position control and the use of a threshold value, normally a contact force value, to detect the contact between tool and screw, so the nut-runner can be placed correctly on the workpiece. In the case of a dynamic workspace, the variance of the workpiece position will likely cause the nut-runner to be positioned incorrectly and will significantly decrease the success rate of the screw task.This paper proposes a novel method based on a logistic regression model for flexible Human-Robot-Collaboration (HRC) screw assembly operations in highly dynamic workspaces. The proposed method is part of a screwing strategy based on impedance control and developed for HRC applications. The screwing strategy consists of a spiral movement executed by the robot while approaching the workpiece and it is used as a search procedure to find the screw. The proposed method is used to detect when the tool correctly interlocks with the screw head so the robot can proceed with the screwing process. The goal is to stop the spiral movement timely when the nut-runner has correctly interlocked with the screw head to ensure a successful screw task and avoid potential damage to the nut-runner or the workpiece.The proposed screw interlock recognition method utilizes a logistic regression model to observe the contact forces between tool and screw head. The learning model is trained using force data collected from experiments and then its feasibility is validated with further testing.

Estimation and compensation of cutting force induced position error in robot machining system

Recently, industrial robots have been widely used in manufacturing due to their various advantages when compared with other equipment, such as maneuverability in a wide range of workspaces, high degrees of freedom, and flexibility. However, due to the low stiffness, they are difficult to be used for precision metal cutting process those require high position control performance under cutting force. This paper proposes a compensation method that estimates the position error induced by the cutting force and compensates the error by controlling the workpiece position by using additional two-axis servo system. The cutting force model was constructed to estimate the cutting force generated during milling without sensors. The kinematic and stiffness models of the industrial robot were developed to calculate the angular error of each joint and position error of the tool center position caused by cutting force. To verify the performance of the proposed compensation method, series of experiments were conducted under various cutting conditions and compared with traditional on-line compensation method. The position accuracy was increased by 63.68 % after the application of the proposed compensation method.

Machine vision–based automatic planning for microdroplet coating trajectory on irregularly shaped regions of metal surfaces

Metal surface coating technology plays a crucial role in various aspects of metal engineering such as enhancing metal oxidation resistance, corrosion prevention, insulation, decoration, and surface performance. This paper presents a machine vision–based automatic planning algorithm for microdroplet coating trajectory on irregularly shaped regions of metal surfaces, aiming to achieve uniform coating on different surface shapes and sizes. First, the process of microdroplet shape changes on metal surfaces is analyzed, the wetting circle diameter of a fully spread microdroplet is estimated, and the distance between two neighboring microdroplets is confirmed. Then, color pattern image processing (region contour extraction, feature point extraction, deburring, and equidistant offset algorithms) and template matching technology are developed to extract coating trajectory contours and accurately locate the workpieces on the workbench. To ensure a smooth and continuous coating trajectory, rational cubic Bézier curves are employed to interpolate the contour feature points, forming C1 continuous curves. Finally, taking into consideration the distance between two neighboring microdroplets, the continuous curves are equidistant offset and equichord discretized to determine the microdroplet locations. The experimental results demonstrate that the proposed algorithm successfully achieves arbitrary workpiece positioning, automatic planning of coating trajectory and uniform microdroplet coating on different surface shapes and sizes.

An Improved Simulated Annealing Algorithm in Dataset Domain for Optimizing Robust Workpiece Fixture Layout

AbstractThe robust layout of the fixture on the workpiece solves the problem of workpiece fixing well. Aiming at the problem of workpiece position error caused by fixture source error on workpiece surface, an improved simulated annealing algorithm based on dataset domain is adopted to reduce the workpiece position error caused by fixture locator deviation as much as possible. To find a better robust layout way, a point differentiation method is proposed to discretize continuous workpieces to obtain the dataset domain. Meanwhile, two objective functions considering curvature and non‐curvature are used to evaluate the placement scheme of locators. A point differentiation method is proposed to discretize continuous workpieces to obtain the dataset domains. Meanwhile, two objective functions considering curvature and non‐curvature are used to evaluate locator layout schemes. To improve the performance of the algorithm, an AHP‐based multi‐attribute decision‐making method is used to find a set of optimal parameters to configure the algorithm. The benchmark example and practical verification show that the locator obtained by the algorithm proposed is less discrete and denser, which solves the problem of fixture positioning very well, and the position error of the workpiece is effectively reduced.

Hybrid optimization algorithm for thermal displacement compensation of computer numerical control machine tool using regression analysis and fuzzy inference.

During the machining process, the computer numerical control machine is susceptible to variations in ambient temperature, cutting heat, and friction within the transmission parts, which generate different heat sources. These heat sources affect the machine structure in different ways, causing deformation of the machine and displacement of the tooltip and workpiece position, ultimately resulting in deviations in machining accuracy. The amount of thermal drift depends on several factors, including the material of the machine components, the cutting conditions, the duration of the machining process, and the environment. This study proposes a hybrid optimization algorithm to optimize the thermal variables of computer numerical control machine tool spindles. The proposed approach combines regression analysis and fuzzy inference to model the thermal behavior of the spindle. Spindle speed and 16 temperature measurement points distributed on the machine are input factors, while the spindle's axial thermal error is considered an output factor. This study develops a regression equation for each speed to account for the different temperature rise slopes and spindle thermal variations at different speeds. The experimental results show that the hybrid thermal displacement compensation framework proposed in this study effectively reduces the thermal displacement error caused by spindle temperature variation. Furthermore, the study finds that the model can be adapted to significant variations in environmental conditions by limiting the machining speed range, which significantly reduces the amount of data needed for model adaptation and shortens the adaptation time of the thermal displacement compensation model. As a result, this framework can indirectly improve product yield. The effects observed in this study are remarkable.

Improving Etched Flatness by Micro Airflow Array Pressurization in ITO Glass Laser Machining.

In laser etching of ITO glass, the warpage due to workpiece positioning causes breakpoint or deformation of micron-scale etching circuits. Based on traditional laser etching, a micro-airflow array pressurization is proposed by using a micro-flow air bearing through airflow positioning. The objective is to achieve high-precision laser etching by pressurized micro-deformation of ITO glass during positioning. First, the micro-air flow and pressurized micro-deformation were modelled in relation to the airflow pressure and etching gap in order to analyze the flatness variation behavior. Then, the surface flatness was investigated in relation to the airflow parameters and relative bearing location. Finally, the critical value of the pressurization parameter were calculated using a data-twin and were applied to industrial ITO glass etching. It is shown that the uniform flow pressure distribution and surface central micro-deformation were formed by positive airflow pressure in the airflow area. The airflow pressure and etching gap could promote surface flatness, while excessive values could result in excessive deformation. Under the micro flow pressure, the initial flatness of the workpiece was able to be compensated within the critical pressurization parameter. By controlling the micro flow stress, the micro-airflow array pressurization could reduce the flatness to 22 μm with stress of 10.7-12.6 Pa. In industrial production, the surface fine circuits can be laser etched with an optimized micro flow pressure, which solves the problems of local breaks or deformed circuits due to the conventional etching process and the structural layout.

Software-Defined Workpiece Positioning for Resource-Optimized Machine Tool Utilization

4. GÖNNHEIMER P., et. al., 2022, Datenaufnahme und -verarbeitung in der Brownfield-Produktion, Zeitschrift für wirtschaftlichen Fabrikbetrieb, 117/5, 317–320. Google Scholar

Gap and Force Adjustment during Laser Beam Welding by Means of a Closed-Loop Control Utilizing Fixture-Integrated Sensors and Actuators

The development of adaptive and intelligent clamping devices allows for the reduction of rejects and defects based on weld discontinuities in laser-beam welding. The utilization of fixture-integrated sensors and actuators is a new approach, realizing adaptive clamping devices that enable in-process data acquisition and a time-dependent adjustment of process conditions and workpiece position by means of a closed-loop control. The present work focused on sensor and actuator integration for an adaptive clamping device utilized for laser-beam welding in a butt-joint configuration, in which the position and acting forces of the sheets to be welded can be adjusted during the process (studied welding speeds: 1 m/min, 5 m/min). Therefore, a novel clamping system was designed allowing for the integration of inductive probes and force cells for obtaining time-dependent data of the joint gap and resulting forces during welding due to the displacement of the sheets. A novel automation engineering concept allowed the communication between different sensors, actuators and the laser-beam welding setup based on an EtherCAT bus. The subsequent development of a position control and a force control and their combination was operated with a real time PC as master in the bus system and proved the feasibility of the approach based on proportional controllers. Finally, the scalability regarding higher welding speeds was demonstrated.