Machines — Open Access Engineering Journal

This paper presents an application of multivariate state estimation technique (MSET), sequential probability ratio test (SPRT) and kernel regression for low speed slew bearing condition monitoring and prognosis. The method is applied in two steps. Step (1) is the detection of the incipient slew bearing defect. In this step, combined MSET and SPRT is used with circular-domain kurtosis, time-domain kurtosis, wavelet decomposition (WD) kurtosis, empirical mode decomposition (EMD) kurtosis and the largest Lyapunov exponent (LLE) feature. Step (2) is the prediction of the selected features’ trends and the estimation of the remaining useful life (RUL) of the slew bearing. In this step, kernel regression is used with time-domain kurtosis, WD kurtosis and the LLE feature. The application of the method is demonstrated with laboratory slew bearing acceleration data. Full article

A system for automatic mounting of high tolerance wedges inside a wave power linear generator is proposed. As for any renewable energy concept utilising numerous smaller generation units, minimising the production cost per unit is vital for commercialization. The linear generator in question uses self-locking wedges, which are challenging to mount using industrial robots due to the high tolerances used, and because of the fact that any angular error remaining after calibration risks damaging the equipment. Using two types of probes, mechanical touch probes and inductive proximity sensors, combined with a flexible robot tool and iterative calibration routines, an automatic mounting system that overcomes the challenges of high tolerance wedge mounting is presented. The system is experimentally verified to work at mounting speeds of up to 50$\mathrm{m}\mathrm{m}/\mathrm{s}$, and calibration accuracies of 0.25$\mathrm{m}\mathrm{m}$and 0.1 ∘ are achieved. The use of a flexible robot tool, able to move freely in one Cartesian plane, was found to be essential for making the system work. Full article

Inthispaper, adirectuncertaintyminimizationframeworkisdevelopedanddemonstrated for model reference adaptive control laws. The proposed framework consists of a novel architecture involvingmodificationtermsintheadaptivecontrollawandtheupdatelaw. Inparticular,theseterms areconstructedthroughagradientminimizationprocedureinordertoachieveimprovedclosed-loop system performance with adaptive control laws. The proposed framework is first developed for adaptive control laws with linear reference models and then generalized to adaptive control laws with nonlinear reference models. Two illustrative numerical examples are included to demonstrate the efficacy of the proposed framework. Full article

This study includes a life cycle assessment of double-arm type robotic tools made with three different materials. The robotic arms are used for Liquid Crystal Display (LCD) panel handling. The environmental impacts generated during all the life stages of the robots have been investigated. The study shows that composite materials have less environmental impact compared with metallic materials. It is also found that the most significant impact category generated by the robotic tools is carcinogen, while the use stage of the robotic tool’s life cycle has the greatest environmental impact. Full article

The windings insulation of electrical machines will remain a topic that is updated frequently. The criteria severity requested by the electrical machine applications increases continuously. Manufacturers and designers are always confronted with new requirements or new criteria with enhanced performances. The most problematic requirements that will be investigated here are the extremely long lifespan coupled to critical operating conditions (overload, supply grid instabilities, and critical operating environments). Increasing lifespan does not have a considerable benefit because the purchasing price of usual machines has to be compared to the purchasing price and maintenance price of long lifespan machines. A machine having a 40-year lifespan will cost more than twice the usual price of a 20-year lifetime machine. Systems which need a long lifetime are systems which are crucial for a country, and those for which outage costs are exorbitant. Nuclear power stations are such systems. It is certain that the used technologies have evolved since the first nuclear power plant, but they cannot evolve as quickly as in other sectors of activities. No-one wants to use an immature technology in such power plants. Even if the electrical machines have exceeded 100 years of age, their improvements are linked to a patient and continuous work. Nowadays, the windings insulation systems have a well-established structure, especially high voltage windings. Unfortunately, a high life span is not only linked to this result. Several manufacturers’ improvements induced by many years of experiment have led to the writing of standards that help the customers and the manufacturers to regularly enhance the insulation specifications or qualifications. Hence, in this publication, the authors will give a step by step exhaustive review of one insulation layout and will take time to give a detailed report on the standards that are linked to insulation systems. No standard can provide insurance about lifespan, nor do any insulation tests incorporate all of the operating conditions: thermal, mechanical, moisture and chemical. Even if one manufacturer uses the standards compliance to demonstrate the quality of its realization; in the end, the successful use in operation remains an objective test. Thereafter, both customer and manufacturers will use the standards while knowing that such documents cannot fully satisfy their wishes. In one 20-year historical review, the authors will highlight the duration in insulation improvements and small breakthroughs in standards writing. High lifespan machines are not the main interest of standards. A large part of this publication is dedicated to the improvements of the insulation wall to achieve the lifespan. Even if the choice of raw materials is fundamental, the understanding of ageing phenomena also leads to improvements. Full article

Autonomous vehicles are expected to play a key role in the future of urban transportation systems, as they offer potential for additional safety, increased productivity, greater accessibility, better road efficiency, and positive impact on the environment. Research in autonomous systems has seen dramatic advances in recent years, due to the increases in available computing power and reduced cost in sensing and computing technologies, resulting in maturing technological readiness level of fully autonomous vehicles. The objective of this paper is to provide a general overview of the recent developments in the realm of autonomous vehicle software systems. Fundamental components of autonomous vehicle software are reviewed, and recent developments in each area are discussed. Full article

Presented in this paper is a method for the design of modular reconfigurable machine tools (MRMTs). An MRMT is capable of using a minimal number of modules through reconfiguration to perform the required machining tasks for a family of parts. The proposed method consists of three steps: module identification, module determination, and layout synthesis. In the first step, the module components are collected from a family of general-purpose machines to establish a module library. In the second step, for a given family of parts to be machined, a set of needed modules are selected from the module library to construct a desired reconfigurable machine tool. In the third step, a final machine layout is decided though evaluation by considering a number of performance indices. Based on this method, a software package has been developed that can design an MRMT for a given part family. Full article

Optimal and intuitive robotic machining is still a challenge. One of the main reasons for this is the lack of robot stiffness, which is also dependent on the robot positioning in the Cartesian space. To make up for this deficiency and with the aim of increasing robot machining accuracy, this contribution describes a solution approach for optimizing the stiffness over a desired milling path using the free degree of freedom of the machining process. The optimal motion is computed based on the semantic and mathematical interpretation of the manufacturing process modeled on its components: product, process and resource; and by configuring automatically a sample-based motion problem and the transition-based rapid-random tree algorithm for computing an optimal motion. The approach is simulated on a CAM software for a machining path revealing its functionality and outlining future potentials for the optimal motion generation for robotic machining processes. Full article

Although intelligent machine learning techniques have been used for input-output modeling of many different manufacturing processes, these techniques map directly from the input process parameters to the outputs and do not take into consideration any partial knowledge available about the mechanisms and physics of the process. In this paper, a new approach is presented for taking advantage of the partial knowledge available about the mechanisms of the process and embedding it into the neural network structure. To validate the proposed approach, it is used to create a forward prediction model for the process of electrochemical micro-machining (μ-ECM). The prediction accuracy of the proposed approach is compared to the prediction accuracy of pure neural structure models with different structures and the results show that the Neural Network (NN) models with embedded knowledge have better prediction accuracy over pure NN models. Full article

This paper addresses the identification and correction of amplitude and offset errors in the sinusoidal outputs from incremental position encoders. Precise angular position measurement is of high importance in many position control applications. Manufacturing tolerances and noise from thermal and electromagnetic interference sources introduce systematic and random errors in the orthogonal sine cosine output line signals. Evaluation of these signals reproduces deviations in the measured angular position. This paper proposes two methods to identify and compensate for the influence of the systematic errors online without the necessity of a reference measurement during identification. The key component of the methods is a nonlinear estimator that exploits the orthogonality property of harmonic functions. The first method explains the basic idea with a scalar error model and operates continuously but exhibits an angular shift in direction of rotation during transients of the parameters, whereas the second method assumes an error model with error parameters as a function over one full revolution of the encoder. The latter updates the error function iteratively in subsequent revolutions. Full article

The modelling, optimization issues and stiffness for several types of three degrees-of-freedom parallel robotic manipulators, i.e., 3-DOF pure translational, 3-DOF pure rotational and 3-DOF mixed motion types, are studied in this paper. First of all, the kinematics and Jacobian for the robotic manipulators are determined through different approaches; secondly, objective functions modelling are presented, and the associated optimization issues and the geometric parameters’ effect on the objective functions for the robotic mechanisms are illustrated and analyzed in detail. Through employing several multi-objective optimization approaches, we manifest an overall process and approach for multi-objective optimization of robotic systems. The correlation among different stiffness models is finally presented. The results indicate that the kinetostatic compliance model is the closest one to the traditional stiffness model. Full article

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

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

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

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

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

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

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

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