Open AccessArticle
Self-Organization and Self-Coordination in Welding Automation with Collaborating Teams of Industrial Robots
Machines 2016, 4(4), 23; doi:10.3390/machines4040023 -
Abstract
In welding automation, growing interest can be recognized in applying teams of industrial robots to perform manufacturing processes through collaboration. Although robot teamwork can increase profitability and cost-effectiveness in production, the programming of the robots is still a problem. It is extremely time
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In welding automation, growing interest can be recognized in applying teams of industrial robots to perform manufacturing processes through collaboration. Although robot teamwork can increase profitability and cost-effectiveness in production, the programming of the robots is still a problem. It is extremely time consuming and requires special expertise in synchronizing the activities of the robots to avoid any collision. Therefore, a research project has been initiated to solve those problems. This paper will present strategies, concepts, and research results in applying robot operating system (ROS) and ROS-based solutions to overcome existing technical deficits through the integration of self-organization capabilities, autonomous path planning, and self-coordination of the robots’ work. The new approach should contribute to improving the application of robot teamwork and collaboration in the manufacturing sector at a higher level of flexibility and reduced need for human intervention. Full article
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Open AccessArticle
Kinematics and Dynamics of a Translational Parallel Robot Based on Planar Mechanisms
Machines 2016, 4(4), 22; doi:10.3390/machines4040022 -
Abstract
In this contribution, a novel translational parallel robot composed of an arrangement of mechanisms with planar motion is presented. Its mobility is analyzed and the position analysis is solved by using equations derived from mechanical constraints. Furthermore, the analysis of velocity and acceleration
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In this contribution, a novel translational parallel robot composed of an arrangement of mechanisms with planar motion is presented. Its mobility is analyzed and the position analysis is solved by using equations derived from mechanical constraints. Furthermore, the analysis of velocity and acceleration are solved by means of the screw theory. For completeness, the inverse dynamics are also presented and solved by means of an interesting combination of the screw theory and the virtual work principle. Finally, a numerical example is included to show the application of the kinematic model, which is verified with the aid of a commercially available software. Full article
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Open AccessArticle
Study on Payload Effects on the Joint Motion Accuracy of Serial Mechanical Mechanisms
Machines 2016, 4(4), 21; doi:10.3390/machines4040021 -
Abstract
Robotic manipulators have been widely used in many arenas, when the robotic arm performs positioning, a traditional controller (e.g., a proportional-integral-derivative, PID controller) has the problem of not being able to compensate the payload variations. When the end-effector of the robotic arm grasps
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Robotic manipulators have been widely used in many arenas, when the robotic arm performs positioning, a traditional controller (e.g., a proportional-integral-derivative, PID controller) has the problem of not being able to compensate the payload variations. When the end-effector of the robotic arm grasps different payload masses as most applications require, the output of joint motion will vary under different payload masses, which will decrease the end-effector positioning accuracy of the robotic arm system. Based on the model reference adaptive control technique, the payload variation effect can be solved, therefore improving the positioning accuracy. This paper studies payload effects on the joint motion accuracy of serial mechanical mechanisms. Full article
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Open AccessArticle
Rotor Unbalance Estimation with Reduced Number of Sensors
Machines 2016, 4(4), 19; doi:10.3390/machines4040019 -
Abstract
The most common cause of the excessive vibration in rotating machines is the rotor mass unbalance. If a machine vibration due to mass unbalance exceeds the alarm limits, then it may lead to machine failure. Therefore, rotating machines should be regularly checked to
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The most common cause of the excessive vibration in rotating machines is the rotor mass unbalance. If a machine vibration due to mass unbalance exceeds the alarm limits, then it may lead to machine failure. Therefore, rotating machines should be regularly checked to ensure that they are properly balanced. Currently, industries use the influence coefficient (IC) balancing technique for in situ machine balancing. The accepted practice is to use the vibration measurements in both vertical and horizontal directions at the machine-bearing pedestals together with the tachometer signal to estimate the machine rotor unbalance (both mass and phase angle). It is generally believed that the use of the machine vibration measurements in the vertical and horizontal directions represents better machine dynamics, and hence the estimated unbalance is likely to be more accurate. However, this paper applies the same concept of the IC method but with a reduced number of vibration sensors (one sensor per bearing pedestal at 45° instead of two sensors at the vertical and horizontal directions). The use of one sensor per bearing pedestal at 45° from both vertical and horizontal directions is likely to have responses from both directions. The reduction in the number of sensors by half will definitely save the instruments and their maintenance cost and reduce the computational effort in the signal processing significantly. The proposed concept is applied on a small-size laboratory rig with two balancing planes. The paper presents the unbalance estimations by using the measured vibration responses in both the vertical and horizontal directions simultaneously and using vibration responses measured at 45°. Full article
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Open AccessArticle
Vibration Isolation and Trajectory Following Control of a Cable Suspended Stewart Platform
Machines 2016, 4(4), 20; doi:10.3390/machines4040020 -
Abstract
To achieve high-quality vibration isolation and trajectory following control of a cable driven parallel robot based Stewart platform in the five hundred meter aperture spherical radio telescope (FAST) design, the integrated dynamic model of the Stewart platform including the electric cylinder is established
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To achieve high-quality vibration isolation and trajectory following control of a cable driven parallel robot based Stewart platform in the five hundred meter aperture spherical radio telescope (FAST) design, the integrated dynamic model of the Stewart platform including the electric cylinder is established in this paper, the globally feedback linearization of the dynamic model is implemented based on the control law partitioning approach. To overcome the disadvantages of the external disturbance on the base and unmodeled flexibility of the mechanism, a PID (Proportional-Derivative-Integral) controller with base acceleration feedforward is designed in the operational space of the Stewart platform. Experiments of the vibration isolation and trajectory following control of the cable suspended Stewart platform with presence of the base disturbance is carried out. The experimental results show that the presented control scheme has the advantage of stable dynamics, high accuracy and strong robustness. Full article
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Open AccessArticle
On the “Zero of Potential of the Electric Field Produced by the Heart Beat”. A Machine Capable of Estimating this Underlying Persistent Error in Electrocardiography
Machines 2016, 4(4), 18; doi:10.3390/machines4040018 -
Abstract
Modern electrocardiography (ECG) uses a constructed reference potential for the majority of leads. This reference potential, named after its inventor as the Wilson central terminal, is assumed to have negligible value and to be stationary during the cardiac cycle. However, the problem of
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Modern electrocardiography (ECG) uses a constructed reference potential for the majority of leads. This reference potential, named after its inventor as the Wilson central terminal, is assumed to have negligible value and to be stationary during the cardiac cycle. However, the problem of its variability during the cardiac cycle has been known almost since the inception of 12-lead electrocardiography. Due to the cumbersomeness of the measurement system required to fully appreciate these variations, this topic has received scant research attention during the last 60 years. Taking advantage of modern electronic amplifiers’ capability to detect small voltages, drawing only femtoamperes from physiological equivalent signal sources and of the right-leg connection availability, we developed a complete electrocardiography device that, aside from the eight independent signals of the standard 12-lead ECG, allows direct recording of the Wilson central terminal components. In this paper, we present details of the circuit together with its initial clinical evaluation. For this trial, we recorded data from 44 volunteer patients at Campbelltown Hospital (Campbelltown, Australia) and we found that the Wilson central terminal amplitude, as foreseen by Frank and others in the 1950s, is not negligible, its amplitude in relation to the lead II is, on average, 51.2%, and thus it may be clinically relevant. Full article
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Open AccessArticle
Aeronautical Magnetic Torque Limiter for Passive Protection against Overloads
Machines 2016, 4(3), 17; doi:10.3390/machines4030017 -
Abstract
Actual aerospace and defense technologies present multiple limitations that need to be overcome in order to evolve to less contaminating and more efficient aircraft solutions. Contactless technologies come with essential advantages such as the absence of wear and friction. This work describes the
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Actual aerospace and defense technologies present multiple limitations that need to be overcome in order to evolve to less contaminating and more efficient aircraft solutions. Contactless technologies come with essential advantages such as the absence of wear and friction. This work describes the design, prototype, and performance test according to RTCA-DO-160 of an aeronautical magnetic torque limiter. The results show correct continuous transmission operation (2250 rpm and 24 Nm) from −50 °C to +90 °C. Moreover, overload protection has been demonstrated for more than 200 jamming events without damage or required maintenance to the device. Full article
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Open AccessArticle
Self-Sensing Electromagnets for Robotic Tooling Systems: Combining Sensor and Actuator
Machines 2016, 4(3), 16; doi:10.3390/machines4030016 -
Abstract
A low-cost method, which integrates distance sensing functionality into a switched electromagnet by using a hybrid switching mode and current ripple measurements, is proposed. The electromagnet is controlled by a micro-controller via a MOSFET H bridge, utilizing a comparator-based current control. Additionally, a
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A low-cost method, which integrates distance sensing functionality into a switched electromagnet by using a hybrid switching mode and current ripple measurements, is proposed. The electromagnet is controlled by a micro-controller via a MOSFET H bridge, utilizing a comparator-based current control. Additionally, a method for calculating the inductance of the electromagnet and approximating the magnetic contact between the electromagnet and its target is also presented. The resulting tool is attached to an industrial robot, and the system performance using this setup is evaluated. Distance sensing in the range of 0 mm to 5.2 mm is demonstrated. It is also shown that the relation between magnetic contact, coil current and calculated inductance can be reduced to a predictive look-up table, enabling the quality of the magnetic contact to be estimated using minimal computational effort. Full article
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Open AccessArticle
Optimization Design and Performance Analysis of a PM Brushless Rotor Claw Pole Motor with FEM
Machines 2016, 4(3), 15; doi:10.3390/machines4030015 -
Abstract
A new type of permanent magnet (PM) brushless claw pole motor (CPM) with soft magnetic composite (SMC) core is designed and analyzed in this paper. The PMs are mounted on the claw pole surface, and the three-phase stator windings are fed by variable-frequency
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A new type of permanent magnet (PM) brushless claw pole motor (CPM) with soft magnetic composite (SMC) core is designed and analyzed in this paper. The PMs are mounted on the claw pole surface, and the three-phase stator windings are fed by variable-frequency three-phase AC currents. The advantages of the proposed CPM are that the slip rings on the rotor are cast off and it can achieve the efficiency improvement and higher power density. The effects of the claw-pole structure parameters, the air-gap length, and the PM thinner parameter of the proposed CPM on the output torque are investigated by using three-dimensional time-stepping finite element method (3D TS-FEM). The optimal rotor structure of the proposed CPM is obtained by using the response surface methodology (RSM) and the particle swarm optimization (PSO) method and the comparison of full-load performances of the proposed CPM with different material cores (SMC and silicon steel) is analyzed. Full article
Open AccessArticle
Open Source Laser Polymer Welding System: Design and Characterization of Linear Low-Density Polyethylene Multilayer Welds
Machines 2016, 4(3), 14; doi:10.3390/machines4030014 -
Abstract
The use of lasers to weld polymer sheets provides a means of highly-adaptive and custom additive manufacturing for a wide array of industrial, medical, and end user/consumer applications. This paper provides an open source design for a laser polymer welding system, which can
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The use of lasers to weld polymer sheets provides a means of highly-adaptive and custom additive manufacturing for a wide array of industrial, medical, and end user/consumer applications. This paper provides an open source design for a laser polymer welding system, which can be fabricated with low-cost fused filament fabrication and off-the-shelf mechanical and electrical parts. The system is controlled with free and open source software and firmware. The operation of the machine is validated and the performance of the system is quantified for the mechanical properties (peak load) and weld width of linear low density polyethylene (LLDPE) lap welds manufactured with the system as a function of linear energy density. The results provide incident laser power and machine parameters that enable both dual (two layers) and multilayer (three layers while welding only two sheets) polymer welded systems. The application of these parameter sets provides users of the open source laser polymer welder with the fundamental requirements to produce mechanically stable LLDPE multi-layer welded products, such as heat exchangers. Full article
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Open AccessArticle
Software Architecture and Framework for Programmable Logic Controllers: A Case Study and Suggestions for Research
Machines 2016, 4(2), 13; doi:10.3390/machines4020013 -
Abstract
Programmable Logic Controllers (PLCs) are widely used for control and automation of machines and processes, so the quality of PLC software has a direct impact on production efficiency. This paper describes a PLC program for a food production line that was completely rewritten
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Programmable Logic Controllers (PLCs) are widely used for control and automation of machines and processes, so the quality of PLC software has a direct impact on production efficiency. This paper describes a PLC program for a food production line that was completely rewritten using a different software architecture and framework. The PLC hardware and the production line equipment were not changed, so this project provides an opportunity to quantify the impact of different PLC software architecture on production efficiency. The average number of cases of products produced per production hour during the first ten months with the new program was 6.1% higher than the average during the previous ten months with the old program. PLC software, unlike most other software, is often used by the end-user for troubleshooting. In this case, a relatively simple architecture and framework that favors the end-user significantly improved production efficiency over a more sophisticated architecture and framework that favors the software developer. Suggestions for further research on software architecture and framework are given. Full article
Open AccessArticle
Z-Damper: A New Paradigm for Attenuation of Vibrations
Machines 2016, 4(2), 12; doi:10.3390/machines4020012 -
Abstract
Magnetic linear gear provides a new and unique opportunity for coupling mechanical impedances and optimizing vibration damping. In the present paper a new magneto-mechanical vibration damper (the so-called Z-damper) is described. Its expected theoretical dynamic behavior shows a particularly high damping capability, a
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Magnetic linear gear provides a new and unique opportunity for coupling mechanical impedances and optimizing vibration damping. In the present paper a new magneto-mechanical vibration damper (the so-called Z-damper) is described. Its expected theoretical dynamic behavior shows a particularly high damping capability, a low frequency, as well as an optimal behavior for high frequencies. Full article
Open AccessArticle
Performance Evaluation of a Prototyped Breadfruit Seed Dehulling Machine
Machines 2016, 4(2), 11; doi:10.3390/machines4020011 -
Abstract
The drudgery involved in dehulling breadfruit seed by traditional methods has been highlighted as one of the major problems hindering the realization of the full potential of breadfruit as a field to food material. This paper describes a development in an African breadfruit
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The drudgery involved in dehulling breadfruit seed by traditional methods has been highlighted as one of the major problems hindering the realization of the full potential of breadfruit as a field to food material. This paper describes a development in an African breadfruit seed dehulling machine with increased throughput of about 70% above reported machines. The machine consists of a 20 mm diameter shaft, carrying a spiral wound around its circumference (feeder). The feeder provides the required rotational motion and turns a circular disk that rotates against a fixed disk. The two disks can be adjusted to maintain a pre-determined gap for dehulling. An inbuilt drying unit reduces the moisture content of the breadfruit for easy separation of the cotyledon from the endosperm immediately after the dehulling process. The sifting unit that separates the shell from the seed is achieved in this design with an electric fan. The machine is design to run at a speed of 250 rpm with an electric motor as the prime mover. The dehulling efficiency up to 86% and breakage of less than 1.3% was obtained at a clearance setting of 12.4 mm between disks. A sifting efficiency of 100% was achieved. Based on the design diameter and clearance between the dehulling disks, the machine throughput was 216 kg/h with an electric power requirement of 1.207 kW. Full article
Open AccessArticle
A Novel Modelling Approach for Condensing Boilers Based on Hybrid Dynamical Systems
Machines 2016, 4(2), 10; doi:10.3390/machines4020010 -
Abstract
Condensing boilers use waste heat from flue gases to pre-heat cold water entering the boiler. Flue gases are condensed into liquid form, thus recovering their latent heat of vaporization, which results in as much as 10%–12% increase in efficiency. Modeling these heat transfer
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Condensing boilers use waste heat from flue gases to pre-heat cold water entering the boiler. Flue gases are condensed into liquid form, thus recovering their latent heat of vaporization, which results in as much as 10%–12% increase in efficiency. Modeling these heat transfer phenomena is crucial to control this equipment. Despite the many approaches to the condensing boiler modeling, the following shortcomings are still not addressed: thermal dynamics are oversimplified with a nonlinear efficiency curve (which is calculated at steady-state); the dry/wet heat exchange is modeled in a fixed proportion. In this work we cover these shortcomings by developing a novel hybrid dynamic model which avoids the static nonlinear efficiency curve and accounts for a time-varying proportion of dry/wet heat exchange. The procedure for deriving the model is described and the efficiency of the resulting condensing boiler is shown. Full article
Open AccessArticle
One-Dimensional Haptic Rendering Using Audio Speaker with Displacement Determined by Inductance
Machines 2016, 4(1), 9; doi:10.3390/machines4010009 -
Abstract
We report overall design considerations and preliminary results for a new haptic rendering device based on an audio loudspeaker. Our application models tissue properties during microsurgery. For example, the device could respond to the tip of a tool by simulating a particular tissue,
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We report overall design considerations and preliminary results for a new haptic rendering device based on an audio loudspeaker. Our application models tissue properties during microsurgery. For example, the device could respond to the tip of a tool by simulating a particular tissue, displaying a desired compressibility and viscosity, giving way as the tissue is disrupted, or exhibiting independent motion, such as that caused by pulsations in blood pressure. Although limited to one degree of freedom and with a relatively small range of displacement compared to other available haptic rendering devices, our design exhibits high bandwidth, low friction, low hysteresis, and low mass. These features are consistent with modeling interactions with delicate tissues during microsurgery. In addition, our haptic rendering device is designed to be simple and inexpensive to manufacture, in part through an innovative method of measuring displacement by existing variations in the speaker’s inductance as the voice coil moves over the permanent magnet. Low latency and jitter are achieved by running the real-time simulation models on a dedicated microprocessor, while maintaining bidirectional communication with a standard laptop computer for user controls and data logging. Full article
Open AccessArticle
Design and Analysis of a Haptic Device Design for Large and Fast Movements
Machines 2016, 4(1), 8; doi:10.3390/machines4010008 -
Abstract
Haptic devices tend to be kept small as it is easier to achieve a large change of stiffness with a low associated apparent mass. If large movements are required there is a usually a reduction in the quality of the haptic sensations which
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Haptic devices tend to be kept small as it is easier to achieve a large change of stiffness with a low associated apparent mass. If large movements are required there is a usually a reduction in the quality of the haptic sensations which can be displayed. The typical measure of haptic device performance is impedance-width (z-width) but this does not account for actuator saturation, usable workspace or the ability to do rapid movements. This paper presents the analysis and evaluation of a haptic device design, utilizing a variant of redundant kinematics, sometimes referred to as a macro-micro configuration, intended to allow large and fast movements without loss of impedance-width. A brief mathematical analysis of the design constraints is given and a prototype system is described where the effects of different elements of the control scheme can be examined to better understand the potential benefits and trade-offs in the design. Finally, the performance of the system is evaluated using a Fitts’ Law test and found to compare favourably with similar evaluations of smaller workspace devices. Full article
Open AccessArticle
Algorithms for Optimal Model Distributions in Adaptive Switching Control Schemes
Machines 2016, 4(1), 7; doi:10.3390/machines4010007 -
Abstract
Several multiple model adaptive control architectures have been proposed in the literature. Despite many advances in theory, the crucial question of how to synthesize the pairs model/controller in a structurally optimal way is to a large extent not addressed. In particular, it is
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Several multiple model adaptive control architectures have been proposed in the literature. Despite many advances in theory, the crucial question of how to synthesize the pairs model/controller in a structurally optimal way is to a large extent not addressed. In particular, it is not clear how to place the pairs model/controller is such a way that the properties of the switching algorithm (e.g., number of switches, learning transient, final performance) are optimal with respect to some criteria. In this work, we focus on the so-called multi-model unfalsified adaptive supervisory switching control (MUASSC) scheme; we define a suitable structural optimality criterion and develop algorithms for synthesizing the pairs model/controller in such a way that they are optimal with respect to the structural optimality criterion we defined. The peculiarity of the proposed optimality criterion and algorithms is that the optimization is carried out so as to optimize the entire behavior of the adaptive algorithm, i.e., both the learning transient and the steady-state response. A comparison is made with respect to the model distribution of the robust multiple model adaptive control (RMMAC), where the optimization considers only the steady-state ideal response and neglects any learning transient. Full article
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Open AccessArticle
Bidirectional Haptic Communication: Application to the Teaching and Improvement of Handwriting Capabilities
Machines 2016, 4(1), 6; doi:10.3390/machines4010006 -
Abstract
The objective of this work is to study the relevance of haptic feedback in remote communication between people. The application is handwriting. A haptic device designed to help people to improve their writing skills is presented. Two experimental sessions are then proposed to
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The objective of this work is to study the relevance of haptic feedback in remote communication between people. The application is handwriting. A haptic device designed to help people to improve their writing skills is presented. Two experimental sessions are then proposed to a group of people. In the first test, two subjects communicate through a bilateral system by means of a haptic feedback to accomplish the task. Secondly, a blank test is performed. The results of the two tests are compared and analyzed in order to evaluate the importance of the haptic feedback in the context of collaboration between two people. Full article
Open AccessArticle
Joint Mechanism That Mimics Elastic Characteristics in Human Running
Machines 2016, 4(1), 5; doi:10.3390/machines4010005 -
Abstract
Analysis of human running has revealed that the motion of the human leg can be modeled by a compression spring because the joints of the leg behave like a torsion spring in the stance phase. In this paper, we describe the development of
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Analysis of human running has revealed that the motion of the human leg can be modeled by a compression spring because the joints of the leg behave like a torsion spring in the stance phase. In this paper, we describe the development of a joint mechanism that mimics the elastic characteristics of the joints of the stance leg. The knee was equipped with a mechanism comprising two laminated leaf springs made of carbon fiber-reinforced plastic for adjusting the joint stiffness and a worm gear in order to achieve active movement. Using this mechanism, we were able to achieve joint stiffness mimicking that of a human knee joint that can be adjusted by varying the effective length of one of the laminated leaf springs. The equation proposed for calculating the joint stiffness considers the difference between the position of the fixed point of the leaf spring and the position of the rotational center of the joint. We evaluated the performance of the laminated leaf spring and the effectiveness of the proposed equation for joint stiffness. We were able to make a bipedal robot run with one leg using pelvic oscillation for storing energy produced by the resonance related to leg elasticity. Full article
Open AccessArticle
Dynamic Contact between a Wire Rope and a Pulley Using Absolute Nodal Coordinate Formulation
Machines 2016, 4(1), 4; doi:10.3390/machines4010004 -
Abstract
Wire rope and pulley devices are used in various machines. To use these machines more safely, it is necessary to analyze the behavior of the contact between them. In this study, we represent a wire rope by a numerical model of a flexible
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Wire rope and pulley devices are used in various machines. To use these machines more safely, it is necessary to analyze the behavior of the contact between them. In this study, we represent a wire rope by a numerical model of a flexible body. This flexible body is expressed in the absolute nodal coordinate formulation (ANCF), and the model includes the normal contact force and the frictional force between the wire rope and the pulley. The normal contact force is expressed by spring-damper elements, and the frictional force is expressed by the Quinn method. The advantage of the Quinn method is that it reduces the numerical problems associated with the discontinuities in Coulomb friction at zero velocity. By using the numerical model, simulations are performed, and the validity of this model is shown by comparing its results with those of an experiment. Through numerical simulations, we confirm the proposed model for the contact between the wire rope and the pulley. We confirmed that the behavior of the wire rope changes when both the bending elastic modulus of the wire rope and the mass added to each end of the wire rope are changed. Full article