Tool Orientation Research Articles

Advanced teleoperation and control system for industrial robots based on augmented virtuality and haptic feedback

There are some industrial tasks that are still mainly performed manually by human workers due to their complexity, which is the case of surface treatment operations (such as sanding, deburring, finishing, grinding, polishing, etc.) used to repair defects. This work develops an advanced teleoperation and control system for industrial robots in order to assist the human operator to perform the mentioned tasks. On the one hand, the controlled robotic system provides strength and accuracy, holding the tool, keeping the right tool orientation and guaranteeing a smooth approach to the workpiece. On the other hand, the advanced teleoperation provides security and comfort to the user when performing the task. In particular, the proposed teleoperation uses augmented virtuality (i.e., a virtual world that includes non-modeled real-world data) and haptic feedback to provide the user an immersive virtual experience when remotely teleoperating the tool of the robot system to treat arbitrary regions of the workpiece surface. The method is illustrated with a car body surface treatment operation, although it can be easily extended to other surface treatment applications or even to other industrial tasks where the human operator may benefit from robotic assistance. The effectiveness of the proposed approach is shown with several experiments using a 6R robotic arm. Moreover, a comparison of the performance obtained manually by an expert and that obtained with the proposed method has also been conducted in order to show the suitability of the proposed approach.

Asymmetrical pythagorean-hodograph (PH) spline-based C3 continuous corner smoothing algorithm for five-axis tool paths with short segments

• A real-time C 3 continuous corner smoothing algorithm is proposed for five-axis short linear segments. • The proposed method can achieve lower curvature based on asymmetrical PH splines. • Smoothing errors around the corners are bounded under given constraints. • The arc-length can be analytically calculated to achieve real-time interpolation. • Experiments verify that much lower curvature and higher machining efficiency can be realized. Local corner smoothing is widely used for the G01 motion commands to achieve the motion continuity of transition corners. Most splines constructed by the existing local corner smoothing methods oriented for five-axis machining mainly must be connected by linear segments. However, with respect to the five axis machining of the corners with short line segments, these kinds of methods need that both ends of the constructed splines usually must be shrunk with the same proportion to avoid the overlapping of adjacent splines. This will lead to relatively large curvatures of the obtained trajectories together with relatively low machining efficiency. This article proposes a new real-time corner smoothing algorithm for five-axis machine tools by constructing the C 3 continuous asymmetrical PH splines. The typical characteristic lies in that the control points related to the two ends of the PH spline can be independently adjusted through reasonably introducing two more adjustable variables, which are realized by analytically calculating and then adding two additional control points into the corresponding control polygon. As a result, the PH spline poses the property of the asymmetry about the angular bisector. Based on this, the short linear commands of tool tip and tool orientation can be smoothed only through inserting different lengths of asymmetrical PH splines that can be connected directly. The motion variance of the smoothed tool orientation related to the tool tip displacement is analytically proved to be C 3 continuous, and thus, the synchronization between tool tip and tool orientation is guaranteed. The outstanding advantage of the algorithm for short line segments is twofold. The first is that the performance of the drives can be more fully utilized to reduce cycle time since the curvature around corners are reduced by adopting the asymmetrical profile, and the second is that the synchronization procedure is greatly simplified since the algorithm eliminates the requirement to convert the intermediate line segments into a spline between the adjacent connected PH splines. Both simulation and the experimental results demonstrate that the proposed algorithm can realize a higher machining efficiency.

A visual path-following learning approach for industrial robots using DRL

Manufacturing companies are in constant need for improved agility. An adequate combination of speed, responsiveness, and business agility to cope with fluctuating raw material costs is essential for today’s increasingly demanding markets. Agility in robots is key in operations requiring on-demand control of a robot’s tool position and orientation, reducing or eliminating extra programming efforts. Vision-based perception using full-state or partial-state observations and learning techniques are useful to create truly adaptive industrial robots. We propose using a Deep Reinforcement Learning (DRL) approach to solve path-following tasks using a simplified virtual environment with domain randomisation to provide the agent with enough exploration and observation variability during the training to generate useful policies to be transferred to an industrial robot. We validated our approach using a KUKA KR16HW robot equipped with a Fronius GMAW welding machine. The path was manually drawn on two workpieces so the robot was able to perceive, learn and follow it during welding experiments. It was also found that small processing times due to motion prediction (3.5 ms) did not slow down the process, which resulted in smooth robot operations. The novel approach can be implemented onto different industrial robots to carry out different tasks requiring material deposition.

A Novel Method of Blade-Inclined Ultrasonic Cutting Nomex Honeycomb Core With Straight Blade

Abstract Ultrasonic cutting with a straight blade is an advanced method for cutting Nomex honeycomb cores. However, crushing has generally been observed on the machining surface of the honeycomb core during ultrasonic cutting (UC). In this paper, to avoid crushing, a new blade-inclined ultrasonic cutting (BIUC) method is proposed to decrease the geometric interference between the cutting tool and the honeycomb cores. The cutting geometry systems of UC and BIUC with a straight blade are systematically established to study the effect of the cutting geometry on the machining quality. The crushing degrees caused by the major flank under different tool orientations in UC and BIUC are analyzed. The causes of crushing during the machining of the honeycomb core were revealed from the aspects of machining quality, cutting force, and geometric interference between the major flank and the material. Experiments involving the quantitative analysis of the crushing and cutting forces verify that the BIUC method is able to avoid crushing by controlling the cutting angle. This paper provides a new method for solving the crushing problem in machining honeycomb core with a straight blade.

The Opposite Orientation of Product Marketing and Finance Tool Marketing

Product marketing orientates to the increasing appeal of customer goods, while finance tool market – to rising appeal of private saving investment. The authors show that these two forms of marketing hide competition between the growth in consumption and the growth in investment in today’s economy. The growth in consumption reduces relatively the resources of economy for GDP growth, while the growth in investment cut resources providing the rise in population living standard. Ways and methods of marketing available on market do not necessarily promote shaping of reasonable structure and volumes of consumption. No marketing methods of raising finance investment can compete with appeal of private consumption, because of the essence of consumption itself and because of relatively low volume of private savings of the Russian population. This situation, according to the authors, forms an economic basis of maintaining rather low rates of GDP growth in the future.

Development of Tool Orientation Strategy with Alternative Orientation and Non-machinable Area Identification in 5-Axis Peripheral Milling of a Sculptured Surface based on a Faceted Models

The peripheral milling strategy of using a cylinder cutter is an effective strategy commonly used on planar or ruled surfaces because of its high material removal rate (MRR). However, using a peripheral milling strategy on a sculptured surface pre

Feedrate blending method for five-axis linear tool path under geometric and kinematic constraints

To tackle the bottlenecks of the linear interpolation and two-step geometry-based corner smoothing methods in five-axis machining, an analytical one-step corner smoothing method based on feedrate blending is proposed in this paper. In the proposed algorithm, the maximum kinematics adjustments scheme together with the variable acceleration and jerk optimization algorithms are first adopted to determine the dynamic performances along the linear segments. Meanwhile, the smooth feedrate profiles of the tool tip position in the workpiece coordinate system (WCS) and tool orientation in the machine coordinate system (MCS) are generated by the tool tip mastered jerk-limited feedrate scheduling scheme, with which the tool tip feedrate and angular feedrate in the WCS, together with the translational and rotatory feedrate in the MCS are well bounded. Then, the blending time is calculated based on the specified tool tip error and tool orientation error in the WCS, and the feedrate profiles are blended to generate the smooth trajectories under axial kinematic constraints along the whole paths in both the WCS and MCS. Since the proposed method can generate the smooth corner trajectory by directly blending the feedrate profiles, it eliminates the construction and interpolation process of parametric splines in two-step corner smoothing algorithms and shows better tracking and real-time performances. Finally, simulation and experimental results validate the effectiveness and feasibility of the proposed method.

Theoretical approaches for determining machining conditions affecting a machined surface topography in filleted end milling

This study demonstrates theoretical approaches useful for practical determination of machining conditions affecting machined surface topography in filleted end milling. Tool orientation is investigated in particular. There are dominant processing parameters' optimizations from various perspectives, whereas a few comprehensive strategies have been proposed to determine machining conditions in filleted end milling. It is also practically scarce to discover the optimization strategy taking path interval determination as the theoretical fountainhead. In this study, theoretical approaches were described to determine machining conditions affecting machined surface topography in filleted end milling. After geometrical description was arranged to model multi-axis filleted end milling, multi-layer approach and the other computable parameters were proposed to obtain decent surface topography generated in filleted end milling. The analytical example focusing on tool orientation was provided with discussion. As a result, some characteristics of theoretical approaches were revealed with the visual evidences. Finally, optimal tool orientation will be arranged based on the findings.

Bacterial Programming Based Kinematic Chain Estimation of Construction Vehicle

Construction vehicle automation for high accuracy applications require information about the state of the machine, resulting in a fully sensitized system with precise kinematic parameters. Since the measurement of these parameters contains uncertainties, accurate measurement of them is an expensive task. Automatic calibration of link parameters makes the task of kinematic parameter determination easier. This study reports a method for forward kinematic chain estimation of an excavator by bacterial programming (BP) based on randomly placed inertial navigation systems (INS) per segments with microelectromechanical sensors (MEMS) within. MEMS INS with fusion techniques provide increasing accuracy with outstanding resilience against harsh environment in a rigid housing. With known robot kinematic the tool orientation estimation can be made more accurate also the path can be planned. The unknown model structure and parameters are established and identified by BP without any a priori or given information about the device according to Denavit-Hartenberg (DH) transformation conventions. Fundamentals of this approach are described in detail and shown on simulated measurement results.

Determination of the cutting force components while milling cylindrical surfaces with an oriented tool

Purpose. Construction of a general modular mathematical spatial model of the removal allowance process and shaping when milling round surfaces of rotation, such as camshaft necks, cylindrical surfaces of gearbox shafts and others. Determination of the components of the cutting forces when machining with crossed axes of the milling cutter and part in order to use the results when assigning machining modes. Methodology. Theoretical development of a modular mathematical model of the removal allowance process and shaping during milling of cylindrical surfaces was carried out using a matrix apparatus for converting coordinate systems. Unified modules were developed: instrumental, orientation and shaping, which allowed us to describe the processing of the part more clearly. All calculations were performed in the mathematical package Mathcad. Using the functions available in the package, a graphical representation of the mathematical model of the tool and machined surfaces was obtained. Using the logical blocks developed in the program, the characteristics of the treated surface were investigated, such as roughness in the axial and radial planes. The influence of the tool orientation angle and the number of cutter teeth on the roughness of the machined surface was investigated. The known formulas for calculating the cutting forces during milling are specified. Findings. A general modular mathematical spatial model is constructed of the removal process of an allowance and formation at milling by the oriented tool of round surfaces of rotation, such as necks of camshafts, cylindrical surfaces of shafts of transmissions and others. The roughness parameters of the treated surface are determined. The outflow of the tool characteristics and the angle of its orientation on the geometric roughness in the axial and radial sections is investigated. The area of the layer cut off by one tooth of a mill is defined. The calculation formulas are specified for finding the components of cutting forces during milling. Originality. A modular spatial model of the process of milling cylindrical surfaces with an oriented tool is proposed, on the basis of which the components of cutting forces are calculated, which can be used in designing new tools and improving machining conditions by the existing ones. Practical value. Based on the use of modern computer facilities and software, the developed calculation program allows controlling the process of forming cylindrical surfaces during their milling with an oriented tool. It also allows predicting the initial machining accuracy by determining the parameters of geometric roughness in axial and radial sections. This makes it possible to choose the optimal tool orientation angle, milling cutter parameters and cutting modes to achieve high productivity and processing quality.

Partition-based five-axis tool path generation for freeform surface machining using a non-spherical tool

Freeform surfaces are widely used in many industries for various purposes, and multi-axis CNC machining is the most adopted method for machining them due to its high accuracy and flexibility. The prevailing type of cutter used in machining freeform surfaces is the so-called ball-end type, which is simply a hemisphere and thus has a constant curvature on the cutter surface. Naturally, for a complex surface with a large deviation in curvature, a cutter shape with variable curvature will be more desirable, as we can adaptively choose a portion of smaller curvature on the cutting edge to machine those relatively flat portions on the surface so to enlarge the cutting width and hence reduce the machining time. Towards this objective, in this paper, we present an algorithm which, given an arbitrary freeform surface to machine and a general non-spherical cutter, will generate a five-axis tool path that will strive to match every cutting point on the surface with a locally optimal tool posture (i.e., the contact point on the cutter surface together with the tool orientation) as well as the corresponding optimal feed direction, while both the local gouging-free and global collision-free constraints and the cusp height requirement are all satisfied. The experimental results in both computer simulation and physical machining are also reported, which confirm that, when compared to using a simple ball-end cutter, by using a non-spherical cutter and adaptively adjusting the contacting tool posture and the feed direction, a large improvement in machining efficiency could be achieved, e.g., as much as 60 % achieved in our experiments.

A variable-depth multi-layer five-axis trochoidal milling method for machining deep freeform 3D slots

Trochoidal milling is a popular machining method for slotting operation, as it avoids a full tool-workpiece engagement and hence helps, often significantly, slow down the tool wear, which is particularly a concern in the machining of hard-to-cut materials like titanium alloy. However, as the traditional trochoidal milling method assumes a fixed tool orientation, it can only apply to 2D shaped slots, while for many industrial parts the slot to cut is typically a genuine 3D freeform slot such as grooves on a blisk. In this paper, we present a multi-layer five-axis trochoidal milling method for machining an arbitrary 3D deep slot that is defined by two freeform side boundary surfaces. Aiming at minimizing the total cutting time, instead of conservatively dividing the slot into equi-depth layers, we strive to minimize the number of layers with variable layer depths while at the same time satisfying the two most critical physical constraints on the tool – the tool deformation and the tool stress. Both computer simulation and physical cutting experiments of the proposed method have been carried out, and the experimental results confirm the feasibility and advantages of the proposed method.

Congratulations! The Best Paper Award 2020

The 11th Best Paper Award 2020 ceremony was held virtually on September 23, 2020. Due to the COVID-19 pandemic and concerns about the health and safety of the attendees, the winners and IJAT committee members who took part in the selection process attended through Zoom. The Best Paper was carefully selected from among the 84 papers published in Vol.13 (2019). The Best Paper Award winners were given a certificate with a nearly USD 1,000 honorarium. We congratulate the winners and sincerely wish them success in the future. The Best Paper Award 2020 Title: Tool Orientation Angle Optimization for a Multi-Axis Robotic Milling System Authors: Leandro Batista da Silva, Hayato Yoshioka, Hidenori Shinno, and Jiang Zhu Int. J. of Automation Technology, Vol.13 No.5, pp. 574-582, September 2019

Tool orientation adjustment for improving the kinematics performance of 5-axis ball-end machining via CPM method.

• A novel CPM method is proposed to adjust tool orientations for 5-axis ball-end machining. • Linearization strategy developed can simplify greatly the solving of the CPM model. • Kinematics performance is improved while maintaining the expected cutting performance. • Simulation and actual milling testings are conducted to validate the proposed method. For 5-axis ball-end machining, it is desired to maintain the expected cutting performance of tool orientation when adjusting tool orientation for improving the motions of rotary axes of 5-axis machine. For this purpose, a cutting performance maintained (CPM) method is proposed to adjust the tool orientations, the objective of which is to minimize the sum of the absolute deviations between the initial and adjusted coordinates of the rotary axes while improving the kinematics performance of the rotary axes and ensuring no machining interferences. In order to speed up the solving of the optimization objective, the analytical linear representations for the drive limits of rotary axes and especially irregular geometry feasible domains (GFDs) of tool orientations are first discussed in detail. The nonlinearity of the objective function is then eliminated by introducing two new auxiliary variables for further simplifying the computation of optimal tool orientation. After rewriting the drive limits and GFD constraints with the two auxiliary variables, the linear objective function can be efficiently solved by the simple linear programming method. The tool orientations adjusted by the proposed CPM method can not only improve the interference-free motions of the rotary axes, but also can maintain the expected cutting performance. Finally, the computer simulation and real milling were conducted to validate the proposed method.

Minimizing Flute Engagement to Adjust Tool Orientation for Reducing Surface Errors in Five-Axis Ball End Milling Operations

AbstractSurface errors due to force-induced tool and workpiece deflections are one of the major errors in multi-axis machining of parts especially with thin-walled structures. Dominant approaches to reduce these surface errors are re-machining the part, feed scheduling, and tool path modification. These methods are time consuming and computationally costly, and they rely on experimental data which is used in cutting force and deflection predictions. The present paper introduces a pure geometrical approach to reduce surface errors drastically by minimizing the engagement lengths of flutes’ cutting edges when a point on the flute’s cutting edge is in contact with the design surface. The total engagement length of the flutes’ cutting edges when one of them generates a contact point on the workpiece surface is formulated and considered as the minimization objective function of an optimization problem. Tilt and lead angles, which define the tool orientation, are the design variables of the optimization problem subjected to constraints based on the geometrical requirements of the ball end milling process. The optimization problem uses the nominal tool path to generate an optimal tool path with adjusted tool orientations. The presented method is computationally inexpensive and does not need any experimentally calibrated coefficients to predict cutting forces because of the pure geometrical nature of the approach. The method is experimentally validated through five-axis ball end milling experiments in which more than 90% surface error reduction is achieved.

Multi-axis synchronization machining effects on free-form surface with image processing

The high surface quality of free-form machined products is demanded by the industries. There were several different approaches proposed in the literature for improving the roughness/texture of machined surface, from tool path generation, tool orientation identification, tool geometry selection, to tool assembly error investigation on the causes and solutions. However, the traces caused by the asynchronous behavior of multi-axis tools were not widely discussed. This study explores the telltale surface characteristic left behind by a ball-end milling operation, using from the image process of scallops/cusps figure of the workpieces, through the spectrum/FFT (fast Fourier transform) plot to identify the parallel of the tool path and the types of traces. Using the distribution of peak frequency and related bandwidth as an index for the performance of synchronous machining, it will reveal the parameters setting of different motion control and the compliance of the dynamic synchronous motion. The tendency of performance index matched the measured roughness result of the workpieces.

A decoupled five-axis local smoothing interpolation method to achieve continuous acceleration of tool axis

Five-axis machines are widely used in high-speed and high-precision machining of complex sculptured surfaces for the ability to adjust the tool orientation. But, most of the five-axis machining trajectories generated by computer-aided manufacturing (CAM) software are G01 blocks in the form of a large number of linear segments. The G01 blocks for surface machining show inadequacies as their high-order discontinuities. Although there are a lot of researches to deal with the discontinuities, there are still many problems such as smoothing error control, motion synchronization, kinematic constraints limitation. Besides, the kinematic constraints of the tool orientation motion are always neglected. In this paper, a two-step real-time decoupling local smoothing method is proposed for the problem of the five-axis tool path smoothing. The C2 continuity of the tool path is guaranteed within the error limited. Not only the kinematic constraints of tool tip motion but also the kinematic constraints of the tool orientation motion are considered. The continuous acceleration of each axis motion of the machine tool is realized through feed-rate scheduling by finite impulse response (FIR) filtering. Finally, through numerical simulations and experiments, compared with the existing method and G01 linear interpolation, it is verified that the proposed smoothing interpolation method has a higher computation efficiency and can improve the processing efficiency and surface quality of the tool path while satisfying the specified smoothing error constraints and kinematic constraints.

Smoothing method of generating flank milling tool paths for five-axis flat-end machining considering constraints

Gouging and collision avoidances, tool path smoothness, and geometric deviation should be considered concurrently when generating a five-axis flank milling tool path. The tool orientations of the generated tool path, which can achieve smooth rotary axis motions of the machine tool, can improve the machining quality. Tool orientation planning for five-axis ball-end machining does not affect the position of the ball center point. However, different from ball-end cutters, tool orientation adjustments for flat-end machining will affect the cutter reference point position, which may cause local gouging between the bottom circular edge of the flat-end cutter and the constraint surfaces of the workpiece or excess uncut material left. Hence, generating a smooth flank milling tool path for five-axis flat-end machining which meets all the requirements is a challenge. To deal with this problem, a method of smoothness flank milling tool path generation for flat-end cutters considering constraints is developed in this research, which can minimize the angular accelerations of the rotary axes. B-spline curves are used to represent the displacements of the rotary axes so that the rotary axes’ motions along the tool path can be directly smoothed. The sum of the squares of the first, second, and third derivatives of the cutter reference point trajectory and the two rotary axes’ displacement curves are then utilized as the smoothness indicators for the five-axis tool paths. The method of tool orientation and positioning adjustments for flat-end cutters based on the differential rigid body motion is also presented, ensuring the bottom circular edge of a flat-end cutter is tangent to the constraint surfaces of the workpiece along the tool path. Besides, the discrete vector model is utilized to represent the workpiece geometry, and intersection points between the discrete vectors and the tool swept envelope are calculated to determine the geometric deviation for a flank milling tool path. Finally, a multi-objective optimization problem with constraints is established to generate flank milling paths with flat-end cutters. Numerical examples and machining tests are carried out to confirm the validity and effectiveness of the proposed approach.

Tool Orientation Optimization and Path Planning for 5-Axis Machining

Tool path generation is a fundamental problem in 5-axis CNC machining, which consists of tool orientation planning and cutter-contact (CC) point planning. The planning strategy highly depends on the type of tool cutters. For ball-end cutters, the tool orientation and CC point location can be planned separately; while for flat end cutters, the two are highly dependent on each other. This paper generates a smooth tool path of workpiece surfaces for flat end mills from two stages: Computing smooth tool orientations on the surface without gouging and collisions and then designing the CC point path. By solving the tool posture optimization problem the authors achieve both the path smoothness and the machining efficiency. Experimental results are provided to show the effectiveness of the method.

Optimization of the cutter size and tool orientation for reaching the critical state with multi-constraints in deep and narrow channel parts machining

Increasing the cutter size to enhance its stiffness is of great significance for improving the machining efficiency and precision of deep and narrow channel parts. In this paper, the concept of cutter size critical sphere (CSCS) is presented, which is a specified sphere and tangent to several geometric constraints of tool accessible regions. With this concept, the complex multi-constraints of the workpiece can be transformed into several simple but precise geometric conditions to optimize the size and tool orientation of a conical cutter. The conical cutter generated by CSCS can reach a critical state with multi-constraints simultaneously. Firstly, the mathematical principle of the conical cutter generated by a cylindrical cutter is deduced based on the motion envelope theory. Secondly, the concept of CSCS is proposed based on the deduced mathematical principle and the calculation method of the CSCS with the general situation is provided. Thirdly, the CSCS with special situations is discussed and the calculation method is proposed. Fourthly, the mathematical model and solving algorithm for the max-size CSCS is given. The solving algorithm is designed based on the 3D Medial Axis Transformation (3D MAT) theory. Finally, the proposed method is verified by three simulation experiments and a comparison experiment. The results show that the proposed method can efficiently and accurately calculate the max size and tool orientation of the conical cutter simultaneously. The optimized conical cutter can be tangent to the multi-constraints of the workpiece but do no interfer with them.