Linear Axis Research Articles

A cardioid-parametric model for the Magnus effect in baseballs

The Magnus effect is responsible for deflecting the trajectory of a spinning baseball. The deflection at the end of the trajectory can be estimated by simulating some similar trajectories or by clustering real paths; however, previous to this study, there are no reports for a detailed connection between the initial throw conditions and the resulting deflection by using. The only approximation about this is the PITCHf/x algorithm, which uses the kinematics equations. In this work, deflections from simulated spinning throws with random linear and angular velocities and spin axis parallel to the horizontal plane are analyzed in their polar representation. A cardioid function is proposed to express the vertical deflection as response of the angular velocity. This is based on both theoretical arguments from the ball movement equations and from the numerical solution of such equations. We found that the vertical deflection fits a cardioid model as function of the Magnus coefficient and the spin angle, for a set of trajectories with initial linear velocities symmetrically distributed around the direction of motion. A variation of the model can be applied to estimate the radial deflection whereas an extended model should be explored for trajectories with velocities asymmetrically distributed. The model is suitable for many applications: from video games to pitching machines. In addition, the model approaches to the results obatined with the kinematic equations, which serves as validation of the PITCHf/x algorithm.

Design and Development of a Three-Dimensional Printing High-Throughput Melt Electrowriting Technology Platform

Three-dimensionally (3D) printed scaffolds and cell culture lattices with microscale features are increasingly being used in tissue engineering and regenerative medicine. One additive manufacturing technology used to design and fabricate such structures is melt electrowriting (MEW), a process which needs to be scaled in production to effectively translate to industrial applications. In this study, a scale-up printer, designed with eight simultaneously extruding heads, is constructed and validated. Importantly, identical structures could be fabricated using parameters developed from a single-head system, therefore establishing a MEW printer ecosystem that allows for direct upscaling from laboratory research. The successful transfer to vertically mounted collectors produced homogeneous reproducible scaffolds with identical morphologies and fiber diameters. These proof-of-concept experiments also show that MEW is capable of large-scale fabrication, successfully demonstrated by manufacturing 780 × 780-mm sheets of scaffolds/lattices. This study demonstrates that upscaling MEW can be realized by multiplying the number of print heads, while vertical mounting of the collector significantly reduces the MEW footprint. Additionally, economic aspects were considered during the development and costly components, such as the x, y, and z linear axes, were minimized. Herein, a systems engineering approach for the development of a high-throughput MEW technology platform is presented for the first time.

Machine Learning for Tool Wear Classification in Milling Based on Force and Current Sensors

This paper presents how to classify the wear state of an end-mill based on force and current signals of the linear axes. The data is divided in binary classes based on the maximum flank wear. A support vector machine and a random forest are trained on orthogonal cutting experiments, but the validation is performed on arbitrary tool paths. To achieve this unique level of generality the signals are transformed into the rotation tool coordinate system. The features are extracted over five cutter revolutions. Support vector machines outperform random forests achieving 99,8% and 97% accuracy in the two classes on the test data and 98% and 61% accuracy on the validation data.

Volumetric error compensation model for five-axis machine tools considering effects of rotation tool center point

Conventional volumetric error compensation strategies for five-axis machines directly generate compensation values without considering the RTCP (rotation tool center point) effects, which causes additional movements of translational axes with the movement of rotary axes, so the compensation values for three linear axes need to be recalculated. In this paper, a volumetric error compensation model considering RTCP is proposed. In the model, the compensation values for translational axes totally consist of three parts, i.e., position errors caused by the volumetric error, position variations caused by the compensation of rotary axes, and caused by RTCP. Firstly, the compensation values for rotary axes are obtained based on the volumetric error model and the inverse kinematics. Then, the compensation values for three linear axes are calculated in detail based on the compensation values of rotary axes and RTCP effects. Finally, ballbar tests of a cone-frustum toolpath are selected to verify the proposed compensation model.

INCREASING PRODUCTIVITY OF CUTTING PROCESSES BY REAL-TIME COMPENSATION OF TOOL DEFLECTION DUE TO PROCESS FORCES

The Internet of Production (IoP) describes a vision in which a broad range of different production data is available in real-time. Based on this data, for example, new control types can be implemented, which improve individual manufacturing processes directly at the machine. A possible application scenario is a tool deflection compensation. Although the problem of tool deflection is well known in the industrial field, a process-parallel compensation is not common in industrial applications. State-of-the-art solutions require time and cost consuming tests to determine necessary cutting parameters. An NC-integrated compensation that adapts the tool path in real-time will make these tests obsolete and furthermore enables higher chip removal rates. In this paper, a control-internal real-time compensation of tool deflection is described, which is based on a process-parallel measurement of process forces. The compensation software is designed as an extension to the NC kernel and thereby integrated into the position control loop of an in-series NC. The compensation movements are generated by manipulating the reference values of the feed axes. The approach is investigated by experiments with linear axis movements. During these tests, a significantly reduction of geometrical machining errors is possible.

Experimental study of effectiveness of robotic cleaning for fish-processing plants

This paper presents the development and experimental testing of the effectiveness of a robotic cleaning system for fish processing plants. The processing of fish introduces a substantial risk of bacterial contamination, which can cause the spoilage of fish and pose a threat to consumers’ health. Good operational hygiene and precautions, in addition to regular cleaning of the processing plants, are necessary for the reduction of the risk of contamination. The state-of-the art cleaning techniques currently include manual cleaning operations of fish processing plants. The experiments of robotic cleaning presented in this paper were performed in two rounds. First, a test using a conventional low-cost industrial robot mounted on a vertical linear axis was used. As the results from this test seemed promising, a second robotic system was built aiming at a more industrialized version. This system consisted of a serial manipulator, tailored for the task, mounted on a horizontal transportation system, and a comparison was conducted between the cleaning performed by human operators and that performed by the robotic system. An electrical stunner with a connected conveyor belt, which is a typical installation for salmon processing plants, was experimentally inoculated with a cocktail of fish-spoilage bacteria that were allowed to develop a biofilm. Back-to-back cleaning trials with biofilms of Pseudomonas fluorescens, Pseudomonas putida, and Photobacterium phosphoreum confirmed that the industrialized robotic prototype performed equally well or better than the conventional manual cleaning procedure currently used in the industry. The results demonstrate that a robotic system can deliver satisfactory results in the cleaning of fish processing plants, thereby minimizing the potential for the spread of contamination. The proposed robotic concept allows for an automated cleaning system, reduced human labor, increased profitability for the industry, and better stability of the cleaning process.

A Novel 13-step Diagonal/Sequential Measurement Method for Error Measurement and Compensation of Linear Axis Machining Center

CNC machining center is the biggest breakthrough in manufacturing industry. In three axis machining center total 21 geometric errors exist. Different techniques are used to improve machining accuracy thereby different compensation techniques has developed with time. Direct and indirect measurement methods are used to measure errors in machining center. Aim of this study is to analyse13-step diagonal or 13-sequential method to measure the error values in machining center by using interferometer by taking measurements on 13 lines. Measurements on twelve lines are measured by 12- line method but thirteenth line is measured by using step diagonal method along a body diagonal of machining center by moving one axis at a time. Experiment is done on machining center in three ways (1) without giving compensation (2) with lead screw compensation and (3) with 13-step diagonal method compensation. Two verification experiments are conducted (a) by using interferometer and (b) by manufacturing a designed part on machining center. Later manufactured part is measured on CMM before and after giving compensation. It is expected that the accuracy of machining center may improve error considerably. Errors along body diagonal are measured by using direct measurement which is more accurate and can give better results.

Utilization of Multi-Axis Positioning Repeatability Performance in Kinematic Modelling

Detailed description of the multi-axis repeatability performance and the modelling of non-systematic variations in the positioning performance of machine tools can support the understanding of root-causes of capability variations in manufacturing processes. Kinematic characterization is implemented through repeated measurements, which include variations related to the performance of the machine tool. This paper addresses the integration of the positional repeatability in kinematic modelling through the employment of direct measurement results. The findings of this research can be used to develop standardized approaches. The statistical population of random errors along the multi-axis travel first requires the proper management of experimental data. In this paper a methodology and its application are presented for the determination of repeatability under static and unloaded conditions as an inhomogeneous parameter in the work space. The proposed approach is demonstrated in a case study, where the component errors of a linear axis are investigated with repeated laser interferometer measurements to quantify the estimated repeatability and express it in the composed repeatability budget. The conclusions of the proposed methodology outline the sensitivity of kinematic models relying on measurement data, as the repeatability of the system can be in the same magnitude as the systematic errors.

Method to evaluate speed and accuracy performance of CNC machine tools by speed-error 2-D representation

In this research, we propose a method to evaluate both speed and accuracy performance of CNC machine tools at the same time. An important facet of the contouring performance of machine tools with computer numerical control (CNC) is the machining of workpieces within the desired accuracy and within as short a time as possible. For this reason, a method for evaluating speed and accuracy in the two dimensions of speed and error based on the actual trajectory, which is the actual movement trajectory with respect to the linear axes of CNC machine tools, has been proposed. In this research, we explain the method proposed for linear axes and propose a method to evaluate the speed and accuracy of a rotary axis and a linear axis in the two dimensions of speed and error by introducing a cylindrical surface to the combined movement of the rotary and linear axes. With experiments, we quantitatively evaluated the speed and accuracy of multiple CNC machine tools using two-dimensional representation with graphs of the actual speed and maximum error for the combined movement of a rotary axis and a linear axis.

Visual Identification and Extraction of Intrinsic Axes in High-Dimensional Data

Interactive axis extraction for high-dimensional data visualization has been demonstrated to be powerful in high-dimensional data exploring and understanding. The extracted axes help to yield new 2-D arrangements of data points, providing new insights into the data. However, the existing interfaces for extraction only support linear axes or non-linear axes without specific semantics. When the data points lie in a manifold, it is hard to capture intrinsic features of the manifold by either linear axes or non-linear axes without specific semantics. Furthermore, a dataset with complicated topology would contain holes and branches. While a branch often indicates a local trend, it may not make sense to project data points to an axis in a different branch. In this paper, we propose an interactive visual interface to identify and extract intrinsic axes in high-dimensional data. The system contains four major views. The topology view presents the skeleton-based topology of the dataset. The detail view provides a force-directed layout of a high-dimensional data and allows interactive extracting intrinsic axes. The characteristics of extracted axes are visualized in the intrinsic axes view. The projection view layouts data points aligning with extracted intrinsic axes. Case studies and comparative experiments demonstrate the usefulness of our visual analytics system.

A Recognition Methodology for the Key Geometric Errors of a Multi‐Axis Machine Tool Based on Accuracy Retentivity Analysis

This paper proposes a recognition methodology for key geometric errors using the feature extraction method and accuracy retentivity analysis and presents the approach of optimization compensation of the geometric error of a multiaxis machine tool. The universal kinematics relations of the multiaxis machine tool are first modelled mathematically based on screw theory. Then, the retentivity of geometric accuracy with respect to the geometric error is defined based on the mapping between the constitutive geometric errors and the time domain. The results show that the variation in the spatial error vector is nonlinear while considering the operation time of the machine tool and the position of the motion axes. Based on this aspect, key factors are extracted that simultaneously consider the correlation, similarity, and sensitivity of the geometric error terms, and the results reveal that the effect of the position‐independent geometric errors (PIGEs) on the error vectors of the position and orientation is greater than that of the position‐dependent geometric errors (PDGEs) of the linear and rotary axes. Then, the fruit fly optimization algorithm (FOA) is adopted to determine the compensation values through multiobjective tradeoffs between accuracy retentivity and fluctuation in the geometric errors. Finally, an experiment on a four‐axis horizontal boring machine tool is used to validate the effectiveness of the proposed approach. The experimental results show that the variations in the precision of each test piece are lower than 25.0%, and the maximum variance in the detection indexes between the finished test pieces is 0.002 mm when the optimized parameters are used for error compensation. This method not only recognizes the key geometric errors but also compensates for the geometric error of the machine tool based on the accuracy retentivity analysis results. The results show that the proposed methodology can effectively enhance the machining accuracy.

Extended Linearisation Control Approaches for a High-Speed Linear Axis with Pneumatic Muscles

This paper presents nonlinear control approaches based on extended linearisation techniques for a high-speed linear axis driven by pneumatic muscles. Its guided carriage is actuated by a nonlinear drive system consisting of two pulley tackles with pneumatic muscle actuators mounted at both sides. This innovative drive concept allows for an increased workspace as well as higher carriage velocities as compared to a direct actuation. The proposed control scheme has a cascaded structure, where two alternative design methods in the framework of extended linearisation are discussed and investigated: eigenvalue placement (EVP) and an optimal design based on the state-dependent Riccati equation (SDRE). Unmodelled hysteresis in the force characteristic of the pneumatic muscles is counteracted by an additional control loop with proportional-integral (PI) behaviour. Implementations of both control approaches on a test rig are compared to each other and show excellent closed-loop performance.

Fast Laser Cutting of Thin Metal

Abstract Since the emergence of high power single mode fiber lasers cutting velocities of more than 100 m/min can be achieved easily on a straight cut. Results of laser fusion cutting of thin sheet metal with a 2 kW single mode fiber and 4 kW laser will be introduced. Several thicknesses of electrical sheets, aluminium sheets and high strength steel sheets have been cut with maximum speeds of 150 m/min. The cutting quality in terms of cutting edge appearance, burr formation, and kerf width has been analysed. In the case of 2D contour cutting high cutting speeds cannot be accomplished due to steady decelerating and accelerating of the cutting machine. Two alternative concepts will be presented which help to realize high cutting speeds on a contour cut: The first concept shifts the machine movement for filigree structures to high dynamic light weight linear axes whereas the second concept forbears to use cutting gases and allows therefore the usage of galvanometer driven fast mirrors to move the laser beam.

Modelling and characterisation of geometric errors on 5-axis machine-tool

This research work deals with the geometric modelling of 5-axis machine tool based on a standardised parameterisation of geometric errors with the aim to decrease the volumetric error in the workspace. The identification of the model’s parameters is based on the development of a new standard thermo-invariant material namely the Multi-Feature Bar. Thanks to its calibration and a European intercomparison, it now provides a direct metrological traceability to the SI metre for dimensional measurement on machine tool in a hostile environment. The identification of three intrinsic parameters of this standard, coupled with a measurement procedure ensures a complete and traceable identification of motion errors of linear axes. An identification procedure of location and orientation errors of axes is proposed by probing a datum sphere in the workspace and minimising the time drift of the structural loop and the effects of the previously identified motion errors. Finally, the developed model partially identified, allows the characterisation of 95% of the measured volumetric error. Therefore, the mean volumetric error not characterised by the model only amounts to 8 μm.

COMPARISON OF STATIC AND DYNAMIC LASER BASED POSITIONING METHODS FOR CHARACTERIZATION OF CNC MACHINES

In the paper we compare the laser based measurements of linear parameters of numerically controlled machines. A new dynamic method of measuring machine positioning is described and compared with the widely used static method. The algorithms of the dynamic method are presented and the comparison results of both methods are shown. It is proven that with the new method the measurement time of linear errors of the CNC machines can be reduced significantly. Additionally the machine wear-out in the linear axes can also be easily and efficiently monitored.

An identifying method with considering coupling relationship of geometric errors parameters of machine tools

The geometric errors parameters are important for machining accuracy of five-axis machine tool. However, most of the error identification methods only based on the detection instruments to achieve identification of single error parameter, without considering the coupling relationship of these errors between five axes. This paper measures and identifies the position-dependent error parameters and verticality errors of non-orthogonal five-axis machine tools. First, position-dependent error parameters related to the translational axis are measured by the laser interferometer. Next, based on its identification method, the rotary axis is measured in the axial, radial and tangential measurement modes by using a double ball bar. With the measured result, 18 position-dependent errors which related to the motion of linear axis, 6 position-dependent error parameters and 2 verticality errors of axis C and 4 position-dependent error parameters and 1 verticality error of axis B are identified. Finally, the identification results are verified by the compensation of an actual process on the sample of S-shaped piece, whose precise results show that the machining precision increased by 84.2% on average after compensation. Consequently, the measurement and identification method as well as the effectiveness of the compensation method of this paper are verified.

A new method for field dynamic balancing of rigid motorized spindles based on real-time position data of CNC machine tools

In high-speed precision machining, the spindle balance state may be altered by re-clamping of the workpiece or tool changes, as well as a number of other reasons. Therefore, repeating the dynamic balancing process on-site after any changes have been made to the spindle system is of utmost importance. This paper proposes a new method for balancing rigid motorized spindles based on the real-time position data of CNC machine tools with the aim of reducing the costs associated with external balancing instruments and improving the efficiency of the dynamic balancing process. Moreover, the proposed technique can be integrated into CNC controllers and data such as the amplitude and phase angle of spindle can be extracted based on the real-time position of linear axis with the feed direction perpendicular to the spindle axis. The speed of the spindle and the reference position of the correction masses can then be calculated using the index pulse of the spindle measurement system and unbalanced spindle data. The dynamic balancing system was shown to accurately identify sensitive processing speeds of motorized spindles, which is crucial to high-speed high-precision machining. Finally, the feasibility and the stability of the spindle dynamic balancing system were experimentally validated using an LDT500 ultra-precision diamond turning. The roughness of the machined surface was shown to decrease from 25.2 to 5.9 nm and thus, verifies the feasibility of applying spindle dynamic balancing system in practical engineering.

Twenty-year survivorship of tree seedlings in wind-created gaps in an upland hardwood forest in the eastern US

Wind is a common canopy disturbance in the upland oak (Quercus)- and hickory (Carya)-dominated stands of the Central Hardwood Region of the eastern US. Canopy openings range from small gaps, resulting from windthrow of single dominant trees, to occasional large gaps of many hectares formed by straight-line winds associated with severe thunderstorms and rare subtropical hurricanes. Vegetation regeneration response in small gaps and larger artificially created (i.e., timber harvested) gaps has been extensively studied, but little has been reported on naturally formed large gaps (> 6 trees) where a partial canopy typically remains from residual overstory and midstory trees. We investigated advance regeneration survivorship on a landscape scale within and around 12 large wind-felled gaps created by Hurricane Opal (October 1995) in a Southern Appalachian watershed. We hypothesized that survivorship would (1) change along a linear distance gradient from the unaffected forest towards gap center (2) vary in relation to categorical gap locations-within-gaps versus in the adjacent unaffected forest and (3) be affected by vegetation and environmental variables. In early 1996 we tagged tree seedlings in quadrats located along linear axes that extended from gap center into the unaffected forest and measured a variety of vegetation and environmental variables. Overall mean survivorship declined from 1997 (0.96) to 2016 (0.56). We found that survivorship was related to linear distance gradients for species rated intermediate in shade tolerance, such as red oaks, but not for shade intolerant, tolerant, and semi-tolerant species (e.g. white oaks). We found that survivorship increased on a linear distance gradient from gap center into the unaffected forest over the first 9 years of our investigation. By year 20 this relationship had reversed: survivorship increased from the unaffected forest to gap centers. Survivorship was also modeled as a function of categorical location of tagged seedlings within-gaps versus in the unaffected forest. Again, we found that survivorship of only intermediate shade tolerant species was related to categorical locations. Survivorship decreased in relation to time and cohort competition and increased with initial seedling height. Our 20-year investigation revealed changes in dynamics of regeneration that would not have been apparent in a short-term study. These results will enable resource managers to assess regeneration development in large gaps following windstorms in oak-dominated hardwood stands.

Intelligent 4D Mechatronic Microsystem Used in Metrological Measurement and Integrated Control Processes

AbstractThe smart mechatronic microsystem in 4D is designed and built for metrological and indstrial measurements and applications. The intelligent mechatronic system consists of 3 electric linear axes and a rotation system mounted on the linear Z-axis, which increases the capacity of the measuring and positioning system, allowing further expansion of the technical and technological services of the entire mecatronic system by connecting grippers, palpator, stylus module, etc.

The identification method of the relative position relationship between the rotary and linear axis of multi-axis numerical control machine tool by laser tracker

In the multi-axis machining process, the relative position relationship between the linear and rotary axis also has certain influence on the machining accuracy in addition to 6 geometric errors of each axis. How to accurately detect and compensate for this error will have a positive effect on further improving the machining of multi-axis machine tool. The laser tracker is adopted multi-station and time-sharing measurement to identify the relative position relationship between the rotary and linear axis on the basis of global positioning system principle in this paper, which will provide data support for accuracy compensation for multi-axis machine tool. The relative position relationship between the rotary and linear axis is characterized by the homogeneous transformation matrix, and its influence on the motion accuracy of machine tool is also analyzed. Meanwhile, the mathematical model concerning on identifying the relative position relationship between the rotary and linear axis with laser tracker is established, and the corresponding measurement algorithm of machine tool motion and identification algorithm of the relative position relationship are derived respectively. The feasibility and accuracy of the derived algorithms are demonstrated in simulations. Meanwhile, the experiment further validates the feasibility of the proposed method.