Tool Position Research Articles

Kinematic Modeling of a Trepanation Surgical Robot System

This paper presents the concept of a parallel medical robotic service system to assist in a surgical procedure involving precise exploratory trepanation holes in a patient’s skull. The target position and orientation of the trepanation tool in the cranial region is determined using a prior intracranial image analysis using an external medical imaging system. A trepanning actuation system is attached to the end-effector of the parallel robot. The end-effector will act as an accurate positioner for the trepanning drill in the medical intervention area. The conceptual design of the mechanical actuation subsystem of a trepanning robot was developed in the SolidWorks 2022 software environment. The virtual model of the kinematic chain of the robot and the assumed design parameters were used to analytically derive the equations describing the inverse kinematics task. An analysis of the forward kinematics task of the parallel manipulator was also carried out using analytical and numerical methods. A workspace analysis was performed using Matlab based on the kinematic model of the parallel robot. This paper significantly advances the field by presenting the conceptual design of the actuation subsystem, deriving the kinematics equations, conducting a thorough workspace analysis, and establishing a foundation for subsequent control-algorithm development.

Assessment of repeatability in newly developed ultra-precision tool setting method using electrical breakdown for ultra-precision machining

Ultra-precision work coordinate system (WCS) setting by measuring the relative distance between the workpiece and the tool is a key element to further improve the accuracy of ultra-precision machine tools. Touch probe is the most widely used WCS method in conventional machining, yet it cannot be used in ultra-precision machining (UPM) applications due to the nature of contact with the workpiece, potentially resulting in surface damage or tool breakage. Furthermore, indirect methods, such as a touch probe, require the sensor to be replaced with a tool after setting the work coordinate. This induces uncertainty. In this paper, the repeatability of the newly proposed non-contact and direct WCS method using electrical breakdown (E.B.) was evaluated for the use in UPM. The standard deviation of the tool positions after performing the method 11 times was under 40 nm. Using a tungsten carbide tool and aluminum workpiece, the proposed method’s repeatability and surface damage were investigated.

Optimizing 5-axis tool positioning and orientation for machining CFRP curved surfaces: considering fibers’ orientation

Optimizing 5-axis tool positioning and orientation for machining CFRP curved surfaces: considering fibers’ orientation

Surface texture topography evaluation and classification by considering the tool posture changes in five-axis milling

Surface texture topography affects the performance of industrial parts, such as precision and service life. Different tool postures may lead to various texture topographies in five-axis milling. In this paper, surface texture topography quality and texture trend evaluation indexes are proposed considering the influence of tool posture in five-axis milling. Based on the evaluation, the ranges of tool posture angles corresponding to surface texture topographies of different characteristic are obtained through surface texture topographies classification. The result can provide reference for singularity avoidance in path planning and machining error compensation in five-axis milling. The influence of tool posture change on the surface texture quality could be avoided while adjusting the tool posture angle in the determined range. Firstly, the general tool cutting edge point expression with the typical structure parameters of the end mills is proposed. The general digital model of surface texture topography is established with the improvement of the unit time calculation and computing vertex judgment in simulation. Secondly, several evaluation indexes are proposed to represent the quality and the overall trend of the surface texture topography with digital extraction of indexes realized on the surface digital model. On this basis, the classification of the surface texture topographies and the determination of the range of tool posture angle for each class of textures are proposed. Thirdly, the evaluation and classification of the ball-end milling plane texture topographies are carried out, which divide the texture topographies into zero-inclination angle textures and non-zero inclination angle textures. The surface textures are further divided to detailed five categories with the tool posture angle range determined. Different tool posture angles of the same class are used to generate a texture topography for the comparison to verify the evaluation indexes and the classification result. Finally, the plane cutting orthogonal experiments are carried out. The general surface digital model is verified by the comparison in surface texture characteristic of different types of mills between digital model and machined surface. Based on the ball-end milling plane classification result, the machined surface textures and extracted indexes are compared to verify the effectiveness of the proposed evaluation indexes and the classification result. The fillet-end milling surface textures are further classified and verified based on the method above. In addition, the spherical surface textures of ball-end milling are carried out for further verification.

Способ профилирования внутренних резьб при фрезеровании

Analysis of the works devoted to thread milling showed that milling of the threads with a special profile differing from the metric profile was not sufficiently studied. Based on data of the existing threads profile analysis, the paper proposes a generalized profiling scheme using the example of a round thread. The theory of envelopes of the cutting tool positions family makes it possible to analyze the shape of the resulting thread profile and the cutting tool profiling in shaping with a kinematic scheme of thread milling with the parallel thread and tool axes. Mathematical expressions are provided that allow calculating geometric error in the round thread using the proposed method and profiling a thread cutter to form the thread of the accepted accuracy degree. The specified method could be extended to a thread with any profile described by a mathematical expression in its axial plane. Study results could be useful to the developers in designing the thread mills and to the technologists to assess the possibility of using thread milling in machining threads with the round profile.

A C3 continuous double circumscribed corner rounding method for five-axis linear tool path with improved kinematics performance

Abstract Corner rounding methods have been widely developed to pursue the smooth motions of machine tools. However, most corner rounding methods, which adopt the double inscribed transitions, still remain an inherent issue of retaining large curvatures of transition curves. Even for those double circumscribed transitions-based methods with relatively small curvatures, they also constrain excessively the transition lengths and are limited to a low-order continuity, deteriorating the feedrate and jerk of machine tools. For addressing these problems, a C3 continuous double circumscribed corner rounding (DCCR) method is proposed for five-axis linear tool path. In this method, the C3 continuous double circumscribed B-splines are specially designed to round the corners of tool position and tool orientation, whose transition lengths are analytically determined by jointly constraining the approximation errors, overlaps elimination, and parameter synchronization. Moreover, the excessive constrains of transition lengths imposed by traditional methods are alleviated by fully considering the effects of overlaps and parameter synchronization, and the jerk of rotary axes is also limited with a high-order continuity. Compared to the existing double inscribed corner rounding (DICR) and DCCR methods, experiment results demonstrate that our method can improve further the feedrate while limiting the jerk of machine tools.

A novel calibration method for angular misalignment in independently controlled fast tool servo-based diamond turning

With significant technological progress in optics fields, such as VR and 3D sensing technologies, the demand for optical components with complex shapes (e.g., freeform surfaces) has expanded significantly in recent years. Ultra-precision diamond turning is one of the common manufacturing methods used for freeform optics. There are two tool-motion mechanisms for freeform diamond turning: slow tool servo (STS), which moves the entire tool rest, and fast tool servo (FTS), which only drives the diamond tool. In particular, high-frequency and long-stroke FTS units driven by a separate control system from the machine tool controller have recently been developed as a new trend in FTS-based diamond turning. However, this type of independent FTS control system causes a time delay between the machine tool instruction and the FTS tool motion. Even a millisecond-scale time delay can cause a considerable angular misalignment owing to the high rotation rate of the spindle, resulting in a micron-scale form error on the workpiece surface. In this paper, a novel method for precisely measuring the time delay from the machined workpiece surface and compensating for the misalignment based on the measured time delay was proposed. To measure the time delay, spherical dimples were machined on the workpiece surface by using STS and FTS. Subsequently, the angular misalignment and time delay were obtained by comparing the measured surface profiles at specific positions of the spherical dimples. Thus, the time delay can be measured with microsecond-scale accuracy. Based on the measured time delay, the shifted tool position along the spindle axis by the time delay was compensated to the ideal tool position by considering the cutting velocity. Consequently, the angular misalignment was completely eliminated, and submicron-level form accuracy was achieved. This calibration method of angular misalignment for an independent FTS unit is expected to significantly improve the accuracy of ultra-precision machining of freeform optics.

Ethical and Legal Considerations behind the Prevalence of ChatGPT: Risks and Regulations

In response to the prevalence of ChatGPT, this paper summarized its technical model, core capabilities, and application scenarios, analyzed the ethical risks such as autonomy, moral misconduct, human alienation, and value reconstruction, as well as legal risks such as legal entity status, copyright ownership, data security, and algorithmic black box. Then proposed the regulating principles of tool positioning, safety, legality, transparency, credibility, fairness, shared responsibility, and the regulating path of encouraging the development of autonomous, safe and controllable technologies, improving artificial intelligence legislation and justice, and establishing a diverse governance system.

Predicting cutting forces in 5-axis milling of sculptured surfaces directly from a CAM tool path

The present work is motivated by the fact that for predicting the cutting forces which arise under various cutting conditions, workpiece-tool pairs, machining depths and tool orientation, numerical methods are slower and less efficient than analytical methods. In addition, recent developments in Computer Assisted Machining (CAM) techniques have enabled analytical methods to be applied even with complex workpiece geometry. The method developed in this paper is both practical and inexpensive. It is based on an analytical method using only few approximations and uses the toolpath file as the main information source for the machined surface. This method takes into account both tool position and orientation in a 5-axis finishing milling process with ball-end cutter, independent of the machining parameters and the couple of tool-workpiece materials. However, this calculation must be supplemented by a mechanistic approach in order to obtain results equivalent to those of the experiment. The result is a model which is implemented in a program allowing the visualization of the cutting forces along a given path. The program is easy to apply in practical cases with the possibility of implementing it in a machining software.

Experimental investigations and error analysis on 3-PRS parallel kinematic machine

Industrial robots play a predominant role in factory automation particularly in the area of machining like grinding, cutting, milling, drilling, polishing etc. In these applications serial manipulators could not provide rigidity and accuracy. This research focuses on the need for precise angular drilling applications. Generally, special fixtures are used to make angular hole in drilling machines. In this research, the 3-PRS (Prismatic – Revolute – Spherical) parallel mechanism is redesigned to execute angular drilling operations. The moving/mobile platform (MP) of the proposed manipulator is utilized as worktable. The experimental model is fabricated with lead screw and nut pair to obtain precise position of drill tool and to maintain high stiffness. By varying the geometric parameters, the positions of parallel kinematic machine (PKM) are analysed. Moreover, the orientation error and parallelism of the developed PKM are studied in detail using laser torch and height gauge. Further, the PKM positions are simulated through ADAMS software package and the same is compared with the real-time accelerometer values. From the experimental study, the deviations in orientation, parallelism and position of the PKM are found to be minimal and satisfactory.

PseudoSegRT: efficient pseudo-labelling for intraoperative OCT segmentation

PurposeRobotic ophthalmic microsurgery has significant potential to help improve the success of challenging procedures and overcome the physical limitations of the surgeon. Intraoperative optical coherence tomography (iOCT) has been reported for the visualisation of ophthalmic surgical manoeuvres, where deep learning methods can be used for real-time tissue segmentation and surgical tool tracking. However, many of these methods rely heavily on labelled datasets, where producing annotated segmentation datasets is a time-consuming and tedious task.MethodsTo address this challenge, we propose a robust and efficient semi-supervised method for boundary segmentation in retinal OCT to guide a robotic surgical system. The proposed method uses U-Net as the base model and implements a pseudo-labelling strategy which combines the labelled data with unlabelled OCT scans during training. After training, the model is optimised and accelerated with the use of TensorRT.ResultsCompared with fully supervised learning, the pseudo-labelling method can improve the generalisability of the model and show better performance for unseen data from a different distribution using only 2% of labelled training samples. The accelerated GPU inference takes less than 1 millisecond per frame with FP16 precision.ConclusionOur approach demonstrates the potential of using pseudo-labelling strategies in real-time OCT segmentation tasks to guide robotic systems. Furthermore, the accelerated GPU inference of our network is highly promising for segmenting OCT images and guiding the position of a surgical tool (e.g. needle) for sub-retinal injections.

An analytical local tool path smoothing method with curvature control

In traditional multi-axis machining, the linear tool path generated by computer-aided manufacturing systems is still in a broad tool path format, resulting in discontinuities at the corners, which slow down tool motion, and also trigger tool vibration, reducing machining accuracy and surface quality. In order to ensure the C3 continuity of the tool during the multi-axis machining process, this paper proposes an analytical B-spline local smoothing method with curvature control. The tool position trajectory and tool orientation are both smoothed by a 5th spline curve with 9 control points. Optimal control points are determined for position and orientation splines to achieve C3 continuity at the junctions between the spline and linear segment while preserving the predefined geometric tolerance limits and minimizing the maximum curvature of the inserted B-spline curve. The smoothed tool path is expected to have less curvature fluctuation, which can significantly improve both the kinematic performance of the machine tool and the machining efficiency. Both computer simulations and physical printing experiments are carried out to demonstrate the improvements of our proposed method in motion smoothness and tracking accuracy in multi-axis machining tasks.

Modified tool radius compensation in the Archimedes' spiral tool path for high speed machining of circular geometry

A key role in HSM (High Speed Machining) is played by the NC program code, which guides the tool along a programmed path without jumps in velocity and acceleration. The commonly used CAM (Computer Aided Manufacturing) software offers many operations for dynamic machining, but the generated code is difficult to edit. An alternative is to use parameterized technology cycles. Unfortunately, the circular pocket cycle available on the Siemens Sinumerik 840D controller was not designed for HSM machining. The purpose of the article is to program an Archimedes' spiral using modified tool radius compensation. The parametric NC code was implemented on the Siemens Sinumerik 840D controller as a technology cycle. The obtained trajectory of the tool meets the curvature continuity condition (C2 continuity). The algorithm uses 3 NC program blocks to define the spiral, regardless of its length. Tool positions are calculated directly by the interpolator during the tool's circular motion (G2/G3). Spiral step is achieved by an additional contour offset (OFFN function), and also by multiple repetitions of circles (TURN function). The change in the effective tool radius value during active tool radius compensation (G41/G42) moves the tool away from the contour along the length of the entire NC block. Several spiral programming variants that are used in cycles were analyzed to identify the feed rate drops at joining points between program blocks. During the process, the trajectory and feed rate were recorded using the Sinumerik Trace function. A problem with the Siemens Sinumerik controller was identified when machine axes exceed the acceleration limit. Synchronized actions were implemented to reduce the feed rate, with the acceleration and jerk limit that are specified in the part program being taken into account. The presented cycle, with the graphical user interface, highlights the potential for HSM milling. The conducted experiment shows the need to supplement the Siemens Sinumerik controller with Archimedes' spiral interpolation. New technology cycles will increase productivity and open up new possibilities, such as tapered threads milling.

Manufacturing Analysis of Face Milling Technology by Tool Setting Using the Same Initial Parameters

Abstract The axis of rotation of the tool is perpendicular for the machined surface in case of face milling technology. This technology is applicable for manufacturing of planar surfaces. It can be feasible by conventional or computer numerical controlled (CNC) machines. The aim of this study is the manufacturing analysis of different tool settings that can cause different arc of contacts. The applied manufacturing parameters are the same except the tool position is changed in comparison with the workpiece. The tool is doing rotation motion while we are moving the table under to tool. The edge geometry of the tool can significantly influence the chip separation conditions, the tool wear and the received surface roughness.

Model of Influence of the Machined Material Properties on Wear of the Polymeric-Abrasive Tool Filaments

Abstract For polymer-abrasive brush tools (PABT) working on CNC machines it is necessary to correct their wear constantly, since it is much higher compared to the wear of metal tools. Based on the dependence of tool wear on machining parameters for various materials, it is necessary to study the influence of the physical and mechanical properties of the material machined. The purpose of the paper is to study the process of finishing the surfaces of parts made of materials of different types with PABT. The analysis of dimensional wear of disc PABTs during the polishing various materials with certain physical and mechanical properties is provided in the article. The polishing was carried out in rational modes that ensure high quality and productivity of surface treatment. The similarity theory and dimensional analysis were used to assess the influence of the properties of the material machined on the intensity of PABT filament wear. To calculate it, dimensionless complexes were established, which take into account the physical and mechanical properties of the machined materials and evaluate their resistance to the penetration of abrasive grains, the ability of the material to absorb mechanical energy in the process of deformation and destruction under the impact of PABT filaments. The developed model was created for the first time. It made it possible to solve the problem of predicting the degree of dimensional wear of the disc PABT when polishing various materials, including difficult-to-machine ones. Prediction of the intensity of PABT filaments wear allows timely correction of the tool position during machining on CNC machines to ensure a constant pressing of the PABT to the surface being machined. The obtained Км material coefficient takes into account the influence of the physical and mechanical properties of the machined material and then estimates the intensity of PABT filaments wear. The KМ material coefficient can also be used to assess the PABT life and calculate the economic efficiency of the parts finishing treatment at the stage of technology development and the selection of polishing tools.

Ball-End Cutting Tool Posture Optimization for Robot Surface Milling Considering Different Joint Load

Robots with openness and flexibility have attracted a large number of researchers to conduct in-depth studies in the field of surface machining. However, there is a redundant degree of freedom (DOF) in 6-DOF robot machining: when a ball end milling cutter is used to process curved parts, the tool point needs to strictly follow the planned milling trajectory, but the tool axis vector only needs to be within a certain range. During the machining process, the rotation of the tool around its axis is not constrained. Therefore, it is necessary to optimize the redundant DOF. Aiming at the redundant DOF of the tool axis vector in ball end milling for surface parts, a Redundancy Optimization strategy for Minimum Joint trajectory (ROMJ) is proposed. It takes the shortest trajectory of robot joints as the optimization objective, and the numerical optimization method is adopted to carry out the optimal design of tool axis vector trajectory in the milling process. Before optimization, to decrease the data volume, the number of track points is sampled and adjusted based on curve characterization errors. In the optimization process, considering the obvious difference in the load quality characteristics of the robot joints, a Redundancy Optimization strategy for Minimum Joint trajectory considering the different Load of joints (ROMJ-L) is proposed. The load difference coefficients of each joint are introduced into the optimization objective of the trajectory of robot joints. By using this method, the optimal design of each joint trajectory of the robot is realized. In order to verify the methods proposed in this paper, a comparison experiment is carried out. The results show that under the same tool point trajectory, the proposed methods can significantly reduce the robot joint trajectory, and the joint trajectory is influenced by the load difference of each joint. Finally, an Eflin-10 robot is used to process the butterfly trajectory tool path by the trajectory planned by the ROMJ-L method, and the results show that the method is practical.

Design and modeling of a passive magnetic vibration absorber for robotic polishing process

Due to the low stiffness of workpieces, chattering easily occurs during robotic polishing operations and leads to poor surface quality and reduced machining accuracy. In this work, in order to reduce vibration during robotic polishing, a passive vibration absorber was designed by the principles of homopolar repulsion and electromagnetic induction. The passive vibration absorber included an upper platform, a damping block, and a lower platform. The flange of the robot was connected to the end polishing effector through the top platform, and its base platform and damping block were movable along the guiding shafts. In addition, permanent magnets were attached to the top and lower platforms and the damping block. During the polishing process, a repulsive force was generated between the homo-polar permanent magnets existing on the upper plate and the damping block. Similarly, a repulsive force was also generated between the bottom platform and the damping block. Due to the magnetic field generated by the eddy current, the magnetic field of the permanent magnets was time-varying and opposite to the external magnetic field of the moving damping block, which generated a repulsive force to compensate for vibration during the polishing process. As the workpiece had multiple modes involved in vibration and its dynamic characteristics varied with the position of the grinding tool, the repulsive force and the damping force effectively reduced vibration and dissipated the energy of the oscillating system. The modeling and dynamic analysis of the proposed vibration absorber were performed to achieve an optimal design. Finally, experimental studies were carried out to evaluate the effects of this vibration absorber. The experimental results demonstrated that the absorber could effectively limit the fluctuation of the polishing force, suppress the vibration of the spindle, and enhance the surface quality of the polished workpiece.

하이브리드 가공기의 FSW를 위한 어드미턴스 힘 제어에 관한 연구

This paper presents force control along the z-axis during friction stir welding (FSW) using a hybrid machine (F1300, Hwacheon Machinery). An admittance force controller is applied to control the position compensation of the tool for force change. During FSW with P-control, the values of the coefficients m, c, and k satisfying the position output of the tool for unit force input are selected as the coefficients for the controller. In the frequency domain analysis of the open loop transfer function, the coefficients are optimized to suppress, low pass, or cut-off of noise of the vibration data. Verification experiments revealed that the sensitivity of the axial force was up to 32.5 kgf, the tool position compensation value in the axial direction was stably controlled within 0.1 mm, and the internal voids of the material could be further reduced.

Three-Dimensional Displacement Measurement of Micro-Milling Tool Based on Fiber Array Encoding

The vibration of the micro-milling tool presents a significant chaotic vibration phenomenon, which has a great influence on the tool life and part machining precision, and is one of the basic problems restricting the improvement of machining efficiency and machining accuracy in micro-milling. To overcome the difficulty of the traditional vibration measurement method with the online measurement of micro-milling tool multi-dimensional vibration, a three-dimensional (3D) measurement method of the micro-milling tool is proposed based on multi-fiber array coding, which converts the tool space motion into a decoding process of the optical coding array employing the tool modulating the multi-fiber array encoding. A 6 × 6 optical fiber array was designed, and a 3D motion platform for micro-milling tools was built to verify the characteristics of the optical fiber measurement system. The measurement results show that the measuring accuracy of the system reached 1 µm, and the maximum linear error in x-, y-, and z-direction are 1.5%, 2.58%, and 2.43%, respectively; the tool space motion position measurement results show that the maximum measurement error of the measuring system was 3.4%. The designed system has unique coding characteristics for the tool position in the space of 100 µm3. It provides a new idea and realization means for the online vibration measurement of micro-milling tools.

The modeling method of machine tool geometry error based on Bryan principle

The error caused by measurement itself directly affects the accuracy of models. The error caused by the failure to follow the Bryan principle in the process of measuring the volumetric error of the machine tool makes the geometric accuracy of the machine tool after compensation less than the ideal effect. In this paper, it is proposed that the measurement error will be caused by the non coincidence of the measurement point and the tool position point in the measurement of linear axis error. According to Bryan principle, the relationship between the center point of the reflective mirror of the laser interferometer and the tool position point is analyzed. The straightness error produced in the measurement process is introduced into the volumetric error of the machine tool, and the geometric model containing the measurement error is established to improve the modeling accuracy of the machine tool. To prove the effectiveness of compensating measurement errors, an experiment has been conducted on a three-axis vertical machining center. The experimental results show that the geometric accuracy of the machine tool is improved by 23% after the measurement error is compensated.