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Machines, Volume 9, Issue 3 (March 2021) – 23 articles

Cover Story (view full-size image): A setup is built representing a downscaled active car suspension application based on a widely available theoretical full-car suspension model. This setup mimics the behavior of a car driving on a realistic road surface in which active suspension components can counteract vibrations of a central platform representing a car body to maximize the driver's comfort. The actuators consist of servomotors from which a rotational torque is converted to a linear force through an electromechanical cylinder. The laboratory test setup allows the examination of a wide variety of different hardware and control aspects. Therefore, this setup is an excellent validation case for a novel methodology to simultaneously co-design the hardware architecture and control configuration for interacting systems. View this paper.
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Open AccessArticle
On the Possibility of Generalizing the Results of Studies of Dynamical Systems on the Example of a Vehicle Suspension
Machines 2021, 9(3), 68; https://doi.org/10.3390/machines9030068 - 22 Mar 2021
Viewed by 296
Abstract
The dynamics of mechanical systems, the operation of electromagnetic and electronic devices and devices, the principle of operation of a number of machines and mechanisms, engineering structures from various fields are often described by differential equations and their systems. Differential equations are often [...] Read more.
The dynamics of mechanical systems, the operation of electromagnetic and electronic devices and devices, the principle of operation of a number of machines and mechanisms, engineering structures from various fields are often described by differential equations and their systems. Differential equations are often mathematical models of the movement and operation of various engineering objects. As a rule, such equations are solved by numerical methods for specific parameter values. These methods of solving differential equations are widely used in practice. However, these methods also have significant disadvantages. For example, the solution of differential equations is obtained for a specific object with the specified parameters. In this case, a solution is obtained for a single point in the parameter space of a set of similar objects, points in this space of the considered family of objects. A natural question arises: Is it possible to extend the results of the solution for a single point in space (a specific object) and the identified properties and regularities to other points (other objects) of the considered family? The purpose of this article is to identify conditions under which it is possible to generalize the results of solving differential equations with specific parameter values describing a single construction to the entire family of similar constructions, the entire space of parameters under consideration. The implementation of the identified conditions is illustrated by the example of solving the problem of “analyzing the dynamic properties of a mathematical model of a car with adaptive (adjustable) suspension of a new principle of action (developed by the authors), moving at a variable speed along an indirect profile of the road surface and developing recommendations for their radical improvement”. Full article
(This article belongs to the Section Machine Design and Theory)
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Open AccessArticle
A Variable Parameter Ambient Vibration Control Method Based on Quasi-Zero Stiffness in Robotic Drilling Systems
Machines 2021, 9(3), 67; https://doi.org/10.3390/machines9030067 - 21 Mar 2021
Viewed by 391
Abstract
Vibrations in the aircraft assembly building will affect the precision of the robotic drilling system. A variable stiffness and damping semiactive vibration control mechanism with quasi-zero stiffness characteristics is developed. The quasi-zero stiffness of the mechanism is realized by the parallel connection of [...] Read more.
Vibrations in the aircraft assembly building will affect the precision of the robotic drilling system. A variable stiffness and damping semiactive vibration control mechanism with quasi-zero stiffness characteristics is developed. The quasi-zero stiffness of the mechanism is realized by the parallel connection of four vertically arranged bearing springs and two symmetrical horizontally arranged negative stiffness elements. Firstly, the quasi-zero stiffness parameters of the mechanism at the static equilibrium position are obtained through analysis. Secondly, the harmonic balance method is used to deal with the differential equations of motion. The effects of every parameter on the displacement transmissibility are analyzed, and the variable parameter control strategies are proposed. Finally, the system responses of the passive and semiactive vibration isolation mechanisms to the segmental variable frequency excitations are compared through virtual prototype experiments. The results show that the frequency range of vibration isolation is widened, and the stability of the vibration control system is effectively improved without resonance through the semiactive vibration control method. It is of innovative significance for ambient vibration control in robotic drilling systems. Full article
(This article belongs to the Section Automation Systems)
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Open AccessArticle
A Method of Fast Segmentation for Banana Stalk Exploited Lightweight Multi-Feature Fusion Deep Neural Network
Machines 2021, 9(3), 66; https://doi.org/10.3390/machines9030066 - 18 Mar 2021
Viewed by 270
Abstract
In an orchard environment with a complex background and changing light conditions, the banana stalk, fruit, branches, and leaves are very similar in color. The fast and accurate detection and segmentation of a banana stalk are crucial to realize the automatic picking using [...] Read more.
In an orchard environment with a complex background and changing light conditions, the banana stalk, fruit, branches, and leaves are very similar in color. The fast and accurate detection and segmentation of a banana stalk are crucial to realize the automatic picking using a banana picking robot. In this paper, a banana stalk segmentation method based on a lightweight multi-feature fusion deep neural network (MFN) is proposed. The proposed network is mainly composed of encoding and decoding networks, in which the sandglass bottleneck design is adopted to alleviate the information a loss in high dimension. In the decoding network, a different sized dilated convolution kernel is used for convolution operation to make the extracted banana stalk features denser. The proposed network is verified by experiments. In the experiments, the detection precision, segmentation accuracy, number of parameters, operation efficiency, and average execution time are used as evaluation metrics, and the proposed network is compared with Resnet_Segnet, Mobilenet_Segnet, and a few other networks. The experimental results show that compared to other networks, the number of network parameters of the proposed network is significantly reduced, the running frame rate is improved, and the average execution time is shortened. Full article
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Open AccessArticle
A Two-Stage Filter Split-Optimization Approach for Obtaining Multiple Solutions with Identical Objective Value
Machines 2021, 9(3), 65; https://doi.org/10.3390/machines9030065 - 16 Mar 2021
Viewed by 295
Abstract
A tremendous amount of work has been done in the recent years in the optimization of input parameters, however, current optimization techniques can only provide a single optimal input process parameter combination. Although alternative techniques have been developed to provide multiple solutions with [...] Read more.
A tremendous amount of work has been done in the recent years in the optimization of input parameters, however, current optimization techniques can only provide a single optimal input process parameter combination. Although alternative techniques have been developed to provide multiple solutions with identical objective values, these techniques have low efficiency when searching for multiple solutions. In this paper, a two-stage filter split-optimization approach is proposed to obtain multiple solutions, at a higher efficiency than for a single-objective optimization problem. The aforementioned tasks are accomplished by first performing an initial split-optimization and then performing a second optimization after excluding input parameters from having their range split into sub-ranges based on the results of the initial optimization. The proposed approach enables the algorithm to explore input parameters that have a more significant impact on the objective function, thereby enabling it to find multiple optimal solutions more efficiently. The proposed approach was validated by using it to optimize the input process parameters of an electrochemical machining problem with five input parameters. The results from the case study show that though the proposed approach provided fewer optimal solutions it was able to obtain them at twice the efficiency when compared to the original method. Full article
(This article belongs to the Section Advanced Manufacturing)
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Open AccessArticle
The Simulation of Heat Supply System with a Scale Formation Factor to Enable Automation of Greenhouse Geothermal Heat Supply System
Machines 2021, 9(3), 64; https://doi.org/10.3390/machines9030064 - 14 Mar 2021
Viewed by 406
Abstract
This article presents the results of the simulation of an automatic control system for the heat supply of a greenhouse complex with a geothermal heat source, conducted in order to study the possibility of geothermal heat supply system automation. Scilab version 6.1 was [...] Read more.
This article presents the results of the simulation of an automatic control system for the heat supply of a greenhouse complex with a geothermal heat source, conducted in order to study the possibility of geothermal heat supply system automation. Scilab version 6.1 was used for simulation. Based on the results of the simulation, the optimal mode of the automation system function of the heat exchanger primary circuit was developed and implemented. Reagentless treatment of geothermal water in the heat supply system with an acoustic–magnetic device (designed and patented by the authors of this paper) can significantly reduce the intensity of scale formation in the heat exchanger and geothermal heat supply system equipment. It provides conditions for the automation of geothermal heat supply systems of greenhouses with a surface heat exchanger. Using an automation system allows greater accuracy and reliability in maintaining the required temperature regime (18–20 °C) in the greenhouse, reduces the frequency of system shutdown for unplanned cleaning of the heat exchanger and equipment, reduces the complexity of manual operations of heat exchanger and equipment maintenance (removal of sludge, scale) and reduces the economic costs of transportation and heat consumption. Full article
(This article belongs to the Special Issue Mechatronic System for Automatic Control)
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Open AccessArticle
Simulation Modeling of First Rise Section of Water Supply System with Installed Complex of Automatic Pump Performance Control
Machines 2021, 9(3), 63; https://doi.org/10.3390/machines9030063 - 14 Mar 2021
Viewed by 355
Abstract
The article considers the important problem of technical and economic optimization of the operating modes of the first rise section of water supply systems. At the same time, the task is to minimize the costs associated with the excessive operation of pumps, while [...] Read more.
The article considers the important problem of technical and economic optimization of the operating modes of the first rise section of water supply systems. At the same time, the task is to minimize the costs associated with the excessive operation of pumps, while providing the protection of the pipeline from freezing in harsh natural operating conditions. To solve this problem, a computer simulation model was developed for the first rise section, equipped with a pump performance control system. The main differences of the developed model are: integrated approach to the analysis of parameters of various physical nature, assessment of the object economic indicators, possibility of simulating non-standard control algorithms. Preliminary studies of the model have shown the possibility and feasibility of its application for calculating the optimal parameters and operating modes of the object under consideration. Based on the simulation results, it was revealed that to calculate the control action by level, it is advisable to use the PID law, for temperature—PD law, for flow rate—PI law. To calculate the main control action, it is proposed to simultaneously calculate the actions in terms of level and temperature, followed by bringing the larger of them to the value of the setpoint for the flow rate maintained by the flow controller. The studies of the proposed management concept for the first rise section have shown its high technical and economic efficiency. In particular, the savings in electricity consumption are estimated at about 55.2% while providing pipeline frost protection. Full article
(This article belongs to the Special Issue Mechatronic System for Automatic Control)
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Open AccessArticle
Validation of Complex Control Systems with Heterogeneous Digital Models in Industry 4.0 Framework
Machines 2021, 9(3), 62; https://doi.org/10.3390/machines9030062 - 14 Mar 2021
Viewed by 529
Abstract
The precise evaluation of the system design and characteristics is a challenge for experts and engineers. This paper considers the problem of the development and application of a digital twin to assess cyberphysical systems. We analyze the details of digital twin applications at [...] Read more.
The precise evaluation of the system design and characteristics is a challenge for experts and engineers. This paper considers the problem of the development and application of a digital twin to assess cyberphysical systems. We analyze the details of digital twin applications at different lifecycle stages. The work reviews and summarizes properties of models concerning the digital and physical components of a cyberphysical system (CPS). The other issue of a CPS is increasing cybersecurity threat for objects, so special attention is paid to the heterogeneous digital twin usage scenarios to improve CPS cybersecurity. The article also details the heterogeneous digital twin’s implementation for a real upper-level control system of a nuclear power plant. The presented heterogeneous digital twin combines virtual machines with real equipment, namely hardware-in-the-loop (HiL) components. The achievements and drawbacks of the implemented model, including single timescale maintaining challenges, are discussed. Full article
(This article belongs to the Special Issue Mechatronic System for Automatic Control)
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Open AccessArticle
Aeroelastic Response of Aircraft Wings to External Store Separation Using Flexible Multibody Dynamics
Machines 2021, 9(3), 61; https://doi.org/10.3390/machines9030061 - 13 Mar 2021
Viewed by 315
Abstract
In aviation, using external stores under the wings is a common method of carrying payload or fuel. In some cases, the payload can be rigidly attached to the wing. However, stores must often be ejected during flight for aircraft, such as military type, [...] Read more.
In aviation, using external stores under the wings is a common method of carrying payload or fuel. In some cases, the payload can be rigidly attached to the wing. However, stores must often be ejected during flight for aircraft, such as military type, which carry drop tanks and missiles. This may cause the wing to respond dynamically with increasing amplitudes, due to the impulsive load of ejection and the change of total mass. This is especially critical in aircraft with highly flexible wings, such as those with high aspect ratios. In this case, it is crucial to evaluate the wing response to store separation, which requires a suitable simulation environment that is able to support nonlinear and multidisciplinary analysis. To address such a need, this work presents the use of flexible multibody dynamics in the simulation of wing response to store separation. To demonstrate, a highly compliant wing was selected with a rigid body that was mounted on the wing to represent an external store. The time marching simulation of the wing before and after the store separation was presented to show the features and benefits of the method. Full article
(This article belongs to the Special Issue Dynamic Stability Analysis of Aerospace Structures)
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Open AccessArticle
Design and Optimization of a Centrifugal Pump for Slurry Transport Using the Response Surface Method
Machines 2021, 9(3), 60; https://doi.org/10.3390/machines9030060 - 13 Mar 2021
Viewed by 313
Abstract
Since centrifugal pumps consume a mammoth amount of energy in various industrial applications, their design and optimization are highly relevant to saving maximum energy and increasing the system’s efficiency. In the current investigation, a centrifugal pump has been designed and optimized. The study [...] Read more.
Since centrifugal pumps consume a mammoth amount of energy in various industrial applications, their design and optimization are highly relevant to saving maximum energy and increasing the system’s efficiency. In the current investigation, a centrifugal pump has been designed and optimized. The study has been carried out for the specific application of transportation of slurry at a flow rate of 120 m3/hr to a head of 20 m. For the optimization process, a multi-objective genetic algorithm (MOGA) and response surface methodology (RSM) have been employed. The process is based on the mean line design of the pump. It utilizes six geometric parameters as design variables, i.e., number of vanes, inlet beta shroud, exit beta shroud, hub inlet blade draft, Rake angle, and the impeller’s rotational speed. The objective functions employed are pump power, hydraulic efficiency, volumetric efficiency, and pump efficiency. In this reference, five different software packages, i.e., ANSYS Vista, ANSYS DesignModeler, response surface optimization software, and ANSYS CFX, were coupled to achieve the optimized design of the pump geometry. Characteristic maps were generated using simulations conducted for 45 points. Additionally, erosion rate was predicted using 3-D numerical simulations under various conditions. Finally, the transient behavior of the pump, being the highlight of the study, was evaluated. Results suggest that the maximum fluctuation in the local pressure and stresses on the cases correspond to a phase angle of 0°–30° of the casing that in turn corresponds to the maximum erosion rates in the region. Full article
(This article belongs to the Section Machine Design and Theory)
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Open AccessArticle
Application of the Sequence Planner Control Framework to an Intelligent Automation System with a Focus on Error Handling
Machines 2021, 9(3), 59; https://doi.org/10.3390/machines9030059 - 12 Mar 2021
Viewed by 263
Abstract
Future automation systems are likely to include devices with a varying degree of autonomy, as well as advanced algorithms for perception and control. Human operators will be expected to work side by side with both collaborative robots performing assembly tasks and roaming robots [...] Read more.
Future automation systems are likely to include devices with a varying degree of autonomy, as well as advanced algorithms for perception and control. Human operators will be expected to work side by side with both collaborative robots performing assembly tasks and roaming robots that handle material transport. To maintain the flexibility provided by human operators when introducing such robots, these autonomous robots need to be intelligently coordinated, i.e., they need to be supported by an intelligent automation system. One challenge in developing intelligent automation systems is handling the large amount of possible error situations that can arise due to the volatile and sometimes unpredictable nature of the environment. Sequence Planner is a control framework that supports the development of intelligent automation systems. This paper describes Sequence Planner and tests its ability to handle errors that arise during execution of an intelligent automation system. An automation system, developed using Sequence Planner, is subjected to a number of scenarios where errors occur. The error scenarios and experimental results are presented along with a discussion of the experience gained in trying to achieve robust intelligent automation. Full article
(This article belongs to the Special Issue Mechatronic System for Automatic Control)
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Open AccessArticle
Dual-Motor Planetary Transmission to Improve Efficiency in Electric Vehicles
Machines 2021, 9(3), 58; https://doi.org/10.3390/machines9030058 - 11 Mar 2021
Viewed by 295
Abstract
Electric cars are typically subject to highly variable operational conditions, especially when they drive in urban environments. Consequently, the efficiency of the electric motors may degrade significantly, possibly leading to lower autonomy and higher running costs. Latest advances in power electronics and motion [...] Read more.
Electric cars are typically subject to highly variable operational conditions, especially when they drive in urban environments. Consequently, the efficiency of the electric motors may degrade significantly, possibly leading to lower autonomy and higher running costs. Latest advances in power electronics and motion control have paved the way to the development of novel architectures of full electric power transmissions. In this paper, a dual-motor solution is proposed where two smaller motors are coupled via a planetary gear, in contrast to the standard configuration that uses one larger motor directly connected to the drive wheels with a fixed ratio reducer. The dual-motor architecture guarantees that both motors operate in the vicinity of their optimal working range, resulting in a higher overall energy efficiency. The technical requirements and the control strategy of the dual-motor system are selected through a parametric optimization process. Results included were obtained from extensive simulations performed over different standard driving cycles, showing that the dual-motor power transmission generally outperforms the single-motor counterpart with an average efficiency improvement of about 9% that is reached in both the power delivery and regeneration stage. Full article
(This article belongs to the Special Issue Italian Advances on MMS)
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Open AccessArticle
Valve Deadzone/Backlash Compensation for Lifting Motion Control of Hydraulic Manipulators
Machines 2021, 9(3), 57; https://doi.org/10.3390/machines9030057 - 08 Mar 2021
Viewed by 318
Abstract
In this paper, a novel nonlinear model and high-precision lifting motion control method of a hydraulic manipulator driven by a proportional valve are presented, with consideration of severe system nonlinearities, various uncertainties as well as valve backlash/deadzone input nonlinearities. To accomplish this mission, [...] Read more.
In this paper, a novel nonlinear model and high-precision lifting motion control method of a hydraulic manipulator driven by a proportional valve are presented, with consideration of severe system nonlinearities, various uncertainties as well as valve backlash/deadzone input nonlinearities. To accomplish this mission, based on the independent valve orifice throttling process, a new comprehensive pressure-flow model is proposed to uniformly indicate both the backlash and deadzone effects on the flow characteristics. Furthermore, in the manipulator lifting dynamics, considering mechanism nonlinearity and utilizing a smooth LuGre friction model to describe the friction dynamics, a nonlinear state-space mathematical model of hydraulic manipulation system is then established. To suppress the adverse effects of severe nonlinearities and uncertainties in the system, a high precision adaptive robust control method is proposed via backstepping, in which a projection-type adaptive law in combination with a robust feedback term is conducted to attenuate various uncertainties and disturbances. Lyapunov stability analysis demonstrates that the proposed control scheme can acquire transient and steady-state close-loop stability, and the excellent tracking performance of the designed control law is verified by comparative simulation results. Full article
(This article belongs to the Special Issue Advanced Control of Industrial Electro-Hydraulic Systems)
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Open AccessArticle
Minimum Mapping from EMG Signals at Human Elbow and Shoulder Movements into Two DoF Upper-Limb Robot with Machine Learning
Machines 2021, 9(3), 56; https://doi.org/10.3390/machines9030056 - 05 Mar 2021
Viewed by 382
Abstract
This research focuses on the minimum process of classifying three upper arm movements (elbow extension, shoulder extension, combined shoulder and elbow extension) of humans with three electromyography (EMG) signals, to control a 2-degrees of freedom (DoF) robotic arm. The proposed minimum process consists [...] Read more.
This research focuses on the minimum process of classifying three upper arm movements (elbow extension, shoulder extension, combined shoulder and elbow extension) of humans with three electromyography (EMG) signals, to control a 2-degrees of freedom (DoF) robotic arm. The proposed minimum process consists of four parts: time divisions of data, Teager–Kaiser energy operator (TKEO), the conventional EMG feature extraction (i.e., the mean absolute value (MAV), zero crossings (ZC), slope-sign changes (SSC), and waveform length (WL)), and eight major machine learning models (i.e., decision tree (medium), decision tree (fine), k-Nearest Neighbor (KNN) (weighted KNN, KNN (fine), Support Vector Machine (SVM) (cubic and fine Gaussian SVM), Ensemble (bagged trees and subspace KNN). Then, we compare and investigate 48 classification models (i.e., 47 models are proposed, and 1 model is the conventional) based on five healthy subjects. The results showed that all the classification models achieved accuracies ranging between 74–98%, and the processing speed is below 40 ms and indicated acceptable controller delay for robotic arm control. Moreover, we confirmed that the classification model with no time division, with TKEO, and with ensemble (subspace KNN) had the best performance in accuracy rates at 96.67, recall rates at 99.66, and precision rates at 96.99. In short, the combination of the proposed TKEO and ensemble (subspace KNN) plays an important role to achieve the EMG classification. Full article
(This article belongs to the Section Mechatronic and Intelligent Machines)
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Open AccessArticle
Optimal Hardware and Control Co-Design Applied to an Active Car Suspension Setup
Machines 2021, 9(3), 55; https://doi.org/10.3390/machines9030055 - 04 Mar 2021
Viewed by 303
Abstract
For complex systems, it is not easy to obtain optimal designs for the hardware architecture and control configurations. Every design aspect influences the final performance, and often the interactions of the different components cannot be clearly determined in advance. In this work, a [...] Read more.
For complex systems, it is not easy to obtain optimal designs for the hardware architecture and control configurations. Every design aspect influences the final performance, and often the interactions of the different components cannot be clearly determined in advance. In this work, a novel co-design optimization method was applied that allows the optimal placement and selection of actuators and sensors to be performed simultaneously with the determination of the control architecture and associated controller tuning parameters. This novel co-design method was applied to a state-space model of a downscaled active car suspension laboratory setup. This setup mimics a car driving over a specific road surface while active components in the suspension have to increase the driver’s comfort by counteracting unwanted vibrations. The result of this co-design optimization methodology is a Pareto front that graphically represents the trade-off between the maximum performance and the total implementation cost; the co-design results were validated with measurements of the physical active car suspension setup. The obtained controller tuning parameters are compared herein with existing controller tuning methods to demonstrate that the co-design method is able to determine optimal controller tuning parameters. Full article
(This article belongs to the Section Machine Design and Theory)
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Open AccessArticle
Development of Digital Models of Interconnected Electrical Profiles for Rolling–Drawing Wire Mills
Machines 2021, 9(3), 54; https://doi.org/10.3390/machines9030054 - 04 Mar 2021
Viewed by 334
Abstract
The latest development trend in rolling industry is the combination of various technological operations in continuous production lines. In the production of long products, the combination of rolling and drawing processes looks promising. A wire drawing mill developed by the team of authors [...] Read more.
The latest development trend in rolling industry is the combination of various technological operations in continuous production lines. In the production of long products, the combination of rolling and drawing processes looks promising. A wire drawing mill developed by the team of authors of this work belongs to the conceptually new, integrated lines. The creation of new integrated rolling mills requires a research phase, where relevant concepts are scrutinized using the methods of mathematical modeling. This requires the development of digital (Digital Twin) models that reliably describe the technological processes. It seems efficient to create a Digital Twin for individual units, with their subsequent integration into a complex digital model. This approach was applied in the development of models of electrical systems for the new line. Such models should take into account a wide range of real-life physical relationships. At the same time, a three-high continuous train of stands with an idle inter-stand is the least studied technological unit of the new mill. The absence of an electric drive of the middle stand determines the particulars of deformation processes and the stands’ interconnections through the processed metal. To date, a comprehensive study of such objects has not been carried out. Therefore, the task of studying this technological unit is of immediate interest. The presented publication is devoted to the development of digital models of deformation zones of drive stands and idle stands, as well as of their relationship through the processed metal. The task is solved using the example of an operating pilot production line that implements rolling technology with an idle stand. The authors describe individual Digital Twins and present the structure of the complex model of the studied unit. The most important purpose of the model is to use it in the development of a control method for electric drives of stands to ensure the stability of the rolling process. The developed method should provide a reduction in energy consumption due to the use of friction force reserves present in the idle stand. The authors also substantiate the control principle based on continuous monitoring and alignment of critical angles in the deformation zones of the drive stands. The paper describes a structure of the control system and explains the technical implementation of this principle. The results of mathematical modeling and oscillograms of typical transient processes are presented. The advantages provided by implementing the proposed control method are shown. The work provides an indirect confirmation of the adequacy of the model to the physical object. Recommendations are given on the use of the developed Digital Twin in the study of rolling processes on sheet and sectional mills. Full article
(This article belongs to the Special Issue Mechatronic System for Automatic Control)
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Open AccessArticle
Feeling Machine for Process Monitoring of Components with Stock Allowance
Machines 2021, 9(3), 53; https://doi.org/10.3390/machines9030053 - 04 Mar 2021
Viewed by 244
Abstract
To realize the increasing automation and flexibilization of production, it is necessary to monitor component-specific characteristics under fluctuating production conditions. Signals with a high correlation to the process quality have to be evaluated. In machining, the process force is an important measurand, which [...] Read more.
To realize the increasing automation and flexibilization of production, it is necessary to monitor component-specific characteristics under fluctuating production conditions. Signals with a high correlation to the process quality have to be evaluated. In machining, the process force is an important measurand, which is sensitive to changes in the process. Feeling machines with force-sensitive machine tool components are therefore a promising signal source to monitor the machining. However, the force is also sensitive to non-critical process fluctuations such as stock allowance. Consequently, it is necessary to perform signal pre-processing and generate features that increase the robustness of the monitoring. In this paper, the material-specific cutting force was investigated for the first time concerning its suitability for process monitoring of parts with a stock allowance. The sensitivity of confidence limits was evaluated based on the normed bandgap. For the investigation, face turning processes of 20MnCr5 were carried out. The results show that the use of material-specific cutting force improves the sensitivity of the confidence limits to process errors. In this context, the feeling machine can be used to substitute the dynamometer for process monitoring. Full article
(This article belongs to the Section Advanced Manufacturing)
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Open AccessArticle
On the Suspension Design of Paquitop, a Novel Service Robot for Home Assistance Applications
Machines 2021, 9(3), 52; https://doi.org/10.3390/machines9030052 - 02 Mar 2021
Viewed by 376
Abstract
The general and constant ageing of the world population that has been observed in the last decade has led robotics researchers community to focus its aims to answer the ever-growing demand for health care, housing, care-giving, and social security. Among others, the researchers [...] Read more.
The general and constant ageing of the world population that has been observed in the last decade has led robotics researchers community to focus its aims to answer the ever-growing demand for health care, housing, care-giving, and social security. Among others, the researchers at Politecnico di Torino are developing a novel platform to enhance the performance offered by present-day issues, and to assess many others which were not even taken into consideration before they have been highlighted by the pandemic emergency currently in progress. This situation, in fact, made dramatically clear how important it is to have reliable non-human operators whom one can trust when the life of elderly or weak patients is endangered by the simple presence of other people. The platform, named Paquitop, features an innovative architecture conceived for omni-directional planar motion. The machine is designed for domestic, unstructured, and variously populated environments. Therefore, the mobile robot should be able to avoid or pass over small obstacles, passing through the capability to achieve specific person tracking tasks, and arriving to the need of operating with an high dynamic performance. Given its purpose, this work addresses the design of the suspension system which enables the platform to ensure a steady floor contact and adequate stability in every using condition. Different configurations of such system are then presented and compared through use-case simulations. Full article
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Open AccessArticle
Developing New Thermal Protection Method for AC Electric Motors
Machines 2021, 9(3), 51; https://doi.org/10.3390/machines9030051 - 01 Mar 2021
Viewed by 336
Abstract
Monitoring the thermal state of windings of electrical machines is a backbone for protection from unacceptable overheating. A large number of different methods and systems aim to solve this problem. This article discusses the main known methods of thermal protection of electric motors [...] Read more.
Monitoring the thermal state of windings of electrical machines is a backbone for protection from unacceptable overheating. A large number of different methods and systems aim to solve this problem. This article discusses the main known methods of thermal protection of electric motors and provides their comparative analysis. This paper shows that the most promising methods are those based on control of the current active resistance of the stator winding, as its value uniquely depends on temperature. It is demonstrated that the known methods have a number of disadvantages. A new phase method for thermal protection of AC motors is proposed. The method is based on the fact that a temperature-induced change in the active and reactive components of the winding impedance causes a corresponding change in the angle between the vectors of phase voltages and currents. This allows for thermal protection by controlling the change in this angle. This article provides tabular analytical substantiation of the proposed method, which is based on the direct measurements of voltage and current and the subsequent algorithmic calculation of physical values functionally related to the sought angle. The authors develop a structural block diagram of a device that implements the proposed thermal protection method. All relevant experimental studies were carried out. In this case, a small-sized electronic thermometer with a remote digital temperature sensor connected to the USB port of a personal computer was used as a temperature meter. The results obtained confirm the functional capability and efficiency of the proposed technical solution. Full article
(This article belongs to the Special Issue Mechatronic System for Automatic Control)
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Open AccessArticle
Geometric Design and Prototyping of a (2-RRU)-URR Parallel Mechanism for Thumb Rehabilitation Therapy
Machines 2021, 9(3), 50; https://doi.org/10.3390/machines9030050 - 26 Feb 2021
Viewed by 384
Abstract
In this paper, the geometrical design of a (2-RRU)-URR (where R and U stand for the revolute and universal joints, respectively) parallel mechanism was demonstrated for thumb rehabilitation therapy. This paper consists of two parts: the design procedure for the development of a [...] Read more.
In this paper, the geometrical design of a (2-RRU)-URR (where R and U stand for the revolute and universal joints, respectively) parallel mechanism was demonstrated for thumb rehabilitation therapy. This paper consists of two parts: the design procedure for the development of a thumb rehabilitation device and the user experiment with the prototype. Because the hand generally has a limited working area, the design of the hand attachment parts and the placement of the actuators requires careful consideration of the various factors. Along with the kinematic requirements of the device, the interaction between the mechanism and the fingers must be considered. The proposed mechanism has three actuators placed in the hand attachment. When the mechanism is attached to the hand, there is the possibility of collisions between the fingers of the user and the mechanism. Two design candidates were devised while considering the limited working area of the hand and the need to avoid collisions. Due to the dependency of the workspace on the placement of the actuators, a comparison of the workspace of the two candidate designs and the target workspace was carried out. The target workspace was determined through the use of thumb trajectory measurement data. A prototype was manufactured using 3D printed plastic and aluminum materials. To confirm the practical performance of the prototype, user experiments were conducted in which a comparison between the thumb measurement data and the controlled trajectory of each person was done. Motion in two directions, specifically, adduction–abduction and flexion–extension were performed. The results showed that the controlled trajectory of flexion–extension were closely matched to the thumb measurement trajectory. Finally, the experimental results are discussed. Full article
(This article belongs to the Special Issue Italian Advances on MMS)
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Open AccessArticle
Design of Nonlinear Control of Gas Turbine Engine Based on Constant Eigenvectors
Machines 2021, 9(3), 49; https://doi.org/10.3390/machines9030049 - 25 Feb 2021
Viewed by 453
Abstract
A gas turbine engine represents a complex dynamic control object. Its characteristics change depending on the state of the environment and the regimes of its operation. This paper discusses an algorithmic approach to the design of a nonlinear controller, based on the concept [...] Read more.
A gas turbine engine represents a complex dynamic control object. Its characteristics change depending on the state of the environment and the regimes of its operation. This paper discusses an algorithmic approach to the design of a nonlinear controller, based on the concept of constant eigenvectors and analytical design of the control system. The proposed design method makes it possible to ensure the stability and the required quality of transient processes at different acceleration modes. In this case, the constancy of the matrix of the canonical basis of the closed-loop control system is assumed, which guarantees stability. The design of a neural network dynamic model of a gas turbine engine based on a neural network approximator with one input and multiple outputs is considered. An example of the design of a nonlinear controller for a gas turbine engine is considered, the neural network model of which is given in the state space. The application of neural network approximation of controller coefficients is presented. Full article
(This article belongs to the Special Issue Mechatronic System for Automatic Control)
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Open AccessCommunication
Numerical Simulation and Experimental Validation of Surface Roughness by the Smoothing Small Ball-Burnishing Process
Machines 2021, 9(3), 48; https://doi.org/10.3390/machines9030048 - 25 Feb 2021
Viewed by 328
Abstract
The smoothing ball-burnishing process has commonly been used as a post-processing method to reduce the irregularities of machined surfaces. However, the mechanism of this process has rarely been examined. In this study, a simulation procedure is proposed to predict the surface roughness of [...] Read more.
The smoothing ball-burnishing process has commonly been used as a post-processing method to reduce the irregularities of machined surfaces. However, the mechanism of this process has rarely been examined. In this study, a simulation procedure is proposed to predict the surface roughness of a burnished workpiece under varying burnishing forces. The roughness of the workpiece surface was firstly approximated by parabolic functions. The burnishing process was then numerically simulated through two steps, namely the elastic–plastic indentation of the burnishing ball on the workpiece’s surface, and the sliding movement of the burnishing tool. The results of the simulation were verified by conducting small ball-burnishing experiments on oxygen-free copper (OFC) and Polmax materials using a load cell-embedded small ball-burnishing tool. For the OFC material, the optimal burnishing force was 3 N. The obtained experimental surface roughness was 0.18 μm, and the simulated roughness value was 0.14 μm. For the Polmax material, when the burnishing force was set at its optimal value—12 N, the best experimental and simulated surface roughness were 0.12 μm and 0.10 μm, respectively. Full article
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Open AccessArticle
Consideration of Distinguishing Design Features of Gas-Turbine and Gas-Reciprocating Units in Design of Emergency Control Systems
Machines 2021, 9(3), 47; https://doi.org/10.3390/machines9030047 - 24 Feb 2021
Viewed by 345
Abstract
Modern gas-turbine units (GTUs) and gas-reciprocating units (GRUs) have found a wide use at power plants, including distributed generation facilities, running on gaseous fuel. The design features of these generating units have a considerable effect on the nature and parameters of transient processes [...] Read more.
Modern gas-turbine units (GTUs) and gas-reciprocating units (GRUs) have found a wide use at power plants, including distributed generation facilities, running on gaseous fuel. The design features of these generating units have a considerable effect on the nature and parameters of transient processes due to emergency disturbances in the adjacent network. The study shows that single-shaft gas-turbine and gas-reciprocating units do not allow even short-term considerable frequency drops. These schemes and operating conditions arise due to emergency active power shortages when the connection between the power plant and the power system weakens due to repair conditions or islanded operation. The paper presents the results of transient process calculations for operating power plants (distributed generation facilities), which make it possible to identify the unfavorable properties of GTUs and GRUs. The results show that two-shaft (three-shaft) GTUs and GRUs can switch to out-of-step conditions even when short-circuits in the adjacent network are cleared with high-speed relay protection devices. The features of out-of-step conditions and the admissibility of their short-term duration for the spontaneous restoration of generators’ synchronization are considered. The findings suggest that considering the fundamental design features of generating units provides informed technical decisions on equipping power plants (distributed generation (DG) facilities) and the adjacent network with efficient emergency control systems. Full article
(This article belongs to the Special Issue Mechatronic System for Automatic Control)
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Open AccessArticle
Adaptive Cutting Control for Roadheaders Based on Performance Optimization
Machines 2021, 9(3), 46; https://doi.org/10.3390/machines9030046 - 24 Feb 2021
Viewed by 313
Abstract
Aiming at addressing the problems of high specific energy consumption for cutting and slow response to the change of hardness in the control of existing mining roadheaders, an adaptive variable speed cutting control method based on cutting performance optimization is proposed by analyzing [...] Read more.
Aiming at addressing the problems of high specific energy consumption for cutting and slow response to the change of hardness in the control of existing mining roadheaders, an adaptive variable speed cutting control method based on cutting performance optimization is proposed by analyzing the working principle of roadheaders. Firstly, cylinder pressure and motor current are invoked as the criteria to judge load changes. Particle swarm optimization is utilized to optimize the cutting parameters under different impedance. Then, the relation between cutting speed, motor current and cylinder pressure is established by using fuzzy neural network to train cutting parameters and identification parameters under different conditions. Finally, the vector control of motor and electro-hydraulic servo valve is used to control the cutting speed. The results show that the cutting unit can adapt to different load signals and always keep the roadheader in the optimal working state. The rotation speed regulation of the cutting head reaches the stable state after 0.05 s, with the overshoot of 1.42%. The swing speed regulation of the cutting head reaches the stable state after 1 s, with the overshoot of 5.3%. Conclusions provide a basis for improving the cutting efficiency and prolonging the working life of the roadheader. Full article
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