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Abstract

This article introduces the design and the experimental validation of the Trackhold, a novel mechanical motion-tracker for upper limb physical rehabilitation. The Trackhold is based on a passively balanced mechanism that can approximately relieve the weight of the patient's arm regardless of the position. The system features a novel kinematic architecture with large workspace and custom developed joint sensors providing accurate real-time measure of the upper limb posture. The design approach of the device, which went through kinetostatic and dynamic analyses, is presented and details on the employed mechatronic solutions are provided. A prototype of the Trackhold has been fabricated and functionally validated.
https://www.iris.sssup.it/retrieve/handle/11382/503444/12089/Trackhold_final_small.pdf
... For example, the computation of the magnetic field plays an important role in solving the governing equation of the magnetic energy harvester to analyse the output power of the device [4]. Taking advantage of the sinusoidal distribution of the diametrically magnetised permanent magnets, Fontana et al. [6] design and derive fastcomputed expressions of the magnetic field of these magnets to optimise the permanent magnet-based Hall effect sensors, that are utilised in a Trackholda passive arm support device [11]. The traditional and well-established Finite Element Method (FEM) [1,12] to compute the three-dimensional (3D) magnetic field is reliable, but can be very time-consuming for fast iterations during the design phase [13], although 2D simulations can be fast enough to enable topology optimization and parameter studies. ...
... Fig. 5. = |̂− | (5,95) . 100%, (11) where i denotes the axial, azimuthal and radial components. ...
Article
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Permanent magnets are essential components in a range of applications from robotics to energy harvesting devices. Computing the field distribution of permanent magnets is crucial for designing and optimising these devices, but currently existing techniques, such as the Finite Element Method (FEM), are very time-consuming. Deep learning (DL) has been widely utilised to solve regression and classification problems and could enable an efficient computation of permanent magnet field distributions. However, deep learning requires large amounts of training data, which is difficult to obtain with current methods. In this work we represented the axial, azimuthal and radial components of the magnetic field created by permanent magnets and uniform magnetisations in semi-analytical expressions (SAE). These forms can be further simplified, and we validated these against the FEM for individual geometries such as an elliptical cylinder and a cone. The computational efficiency of the semi-analytical forms enables the generation of training datasets. Finally, we built a machine learning model using the training data generated by the SAEs and demonstrate that the machine learning model can predict the field distributions of permanent magnets in various configurations. The predicted magnetic field using the machine learning model is in good agreement with the ground-truth, with r² for the axial, azimuthal and radial components being 0.999, 0.997 and 0.998, respectively for the magnetised elliptical cylinders, and 0.999, 0.999, 0.998 for the magnetised cones. Furthermore, the computational times of the machine learning models when executed on a CPU are more than 28 and 12 times faster than the SAEs of the elliptical cylinders and cones, respectively; the models are very fast to execute on a GPU with 22.7 s for the elliptical cylinders and 36.8 s for the cones. This work shows that it is possible to train a machine learning model to predict permanent magnet field distributions based on a training with semi-analytical expressions of various magnet geometries. The code for generating the training data, constructing the machine learning model and applying the model to new data is made openly available (github link here after acceptance).
... In electrical machines, permanent magnets have been widely used for many years. Recently, they have been implemented extensively in non-contact sensing applications [1][2][3], permanent magnetic gears [4][5][6], permanent magnetic couplings [7,8], permanent magnet-bearings [9], non-contact cam mechanisms [10], energy harvesters [11,12] and magnetic guns [13]. In practical applications, the computation of the magnetic field, interaction forces and torques between permanent magnets is of great importance [14][15][16][17][18]. ...
... Based on the magnetic charge or Coulombian approach [17], the magnetic field intensity at any point K (r, α, z) in a cylindrical coordinate system, which lies on plane O′X′Y′ (Fig. 1), can be calculated using Eq. (2) (2) where is the permeability of the vacuum, P is a point on the surface of the cylinder (Fig. 1), is the surface charge density, and is the volume charge density. ...
Article
This research presents semi-analytical and closed-form models to calculate the magnetic field distribution of elliptical cylinder permanent magnets with uniform diametrical magnetization at any point in three dimensional (3D) space. Using the magnetic charge approach, an accurate and fast-computed model is derived. The semi-analytical model yields results in excellent agreement with those of Finite Element Analysis. Moreover, it took less than 0.65 ms to compute each component of the magnetic field of the cylinder on a modern personal computer, which demonstrates its efficiency over the well-known Finite Element Analysis method, in terms of computation time. The accuracy and efficiency of the closed-form expressions are analysed and compared with the semi-analytical model. Two and three dimensional analyses of the magnetic field distribution of diametrically magnetised cylinders with different elliptical profiles are also conducted in this study, using the derived model. The analytical model can be used to calculate the magnetic field of an annular elliptical cylinder using the principle of superposition. In cases where the major and minor semi-axes of the elliptical cylinder are equal, it becomes a circular cylinder; therefore, the derived model can be used to compute the magnetic field of a circular cylinder with diametrical magnetization, which can be shown to outperform the existing analytical model in terms of computational cost.
... Using nonlinear energy storage and release properties, GC mechanisms can generate torque that partially or fully compensates for the gravitational torque. Therefore, the resultant torque at the joint could theoretically reach zero and successfully reduce the required torques at the joints and energy consumption in various applications [5][6][7]. Since the GC mechanism exploits a conversion between the gravitational potential energy and elastic potential energy, it could even be applied to robots with quasi-static motion. In this context, our research goal is to develop a new type of energy-efficient actuator based on the principle of the GC mechanism. ...
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This paper proposes a new type of energy-efficient actuator called variable gravity compensation module integrated actuator (VGCA). VGCA improves the energy efficiency by compensating the gravitational torque at the target joint. Additionally, the variability of compensation torque can further improve the energy efficiency by dealing with the variation of payload, which is required in many robotic applications. As a core part of the VGCA, a compact variable gravity compensation module, called CVGCm, is a cylindrical compact modular unit based on the cam and variable pivot of the lever mechanism. By the theoretically designed cam and lever profiles, the CVGCm can generate a non-linear compensation torque and energy-free variability. First, the functional principles of CVGCm and VGCA are explained. Next, implementation detail and manufacturing of VGCA are introduced. Subsequently, the power estimation model of the actuator is explained based on the Lagrangian method. The experimental results showed that the CVGCm achieved a rapid change of the compensation torque in the compact module. Furthermore, compared to the actuator without CVGCm, VGCA showed a 63.1% reduction of current in static motion and a 64.0% reduction of power in dynamic motion.
... OR more than a century, gravity compensation mechanisms have been developed to reduce actuators' load capacity and improve systems' energy efficiency by compensating for gravitational torque [1]. Recently, they have been actively applied in various robotic applications such as mobile manipulation robots (mobile manipulator and exoskeleton) and surgical robots in which actuator size reduction and energy efficiency are essential [2][3][4][5][6][7][8][9][10]. ...
Article
In this paper, we propose a compact variable gravity compensation (CVGC) mechanism with a geometrically optimized lever shape. The CVGC mechanism can be used to generate gravity compensation torque by employing a cam and lever mechanism and can also amplify the gravity compensation torque by varying the pivot point of the lever. Among these advantages, we aimed to maximize the variable ratio of torque generation with an optimized lever. First, the mechanism concept and details of the CVGC mechanism are explained. Next, the conceptual benefit of using a curved lever instead of the original lever is explained. Afterward, the modeling and mechanics of the testbed using a curved lever are presented for force analysis. Based on these mechanics and B-spline curve representation, the methodology for optimizing the curved lever and cam profile design is presented. Finally, the performance of variable gravity compensation using the optimized lever is verified through experiments that compare the designed and measured gravity compensation torque. As we had hoped, the verification test shows that using the optimized curved lever improves the variable ratio from 5.27 to 14.43.
... The mechanism has been applied to industrial manipulator robots for decades to reduce the maintenance cost of electrical power consumption. In recent years, the applications have been expanded to the mobile platform (e.g., exoskeleton robots, mobile robots) to reduce the system weight and size by improving the energy efficiency of the actuators [2][3][4][5][6][7][8][9][10]. ...
... Następnie stopniowo rozbudowywano/dopracowywano konstrukcję, układ napędowy i sterowania, umożliwiając jednoczesne ćwiczenie kilku stawów. Końcowym celem tego podejścia było uzyskanie rozwiązań pełniących rolę mniej lub bardziej rozbudowanych egzoszkieletów do kompleksowej rehabilitacji [214,215]. Jednocześnie okazało się, że rynek oczekuje nie tylko drogich, skomplikowanych i stacjonarnych rozwiązań w postaci egzoszkieletów, lecz również istnieje ogromne zapotrzebowanie na rozwiązania mniej skomplikowane, a posiadające rozbudowane moduły zapewniające różnego rodzaju biofeedback. Pojawiły się również próby przygotowywania opracowań dotyczących nowych sposobów rehabilitacji, m.in. ...
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The monograph presents modern mechatronic solutions supporting rehabilitation, in particular convalescence of the upper limb of people with neurological dysfunctions. This was accomplished on the example of 12 proprietary solutions for which patent applications were filed or patents and industrial designs were obtained. The developed mechatronic solutions were equipped with, i.a. diagnostic systems of rehabilitation progress, proposing a comprehensive set of exercises, which is supported by feedback from the patient. In addition, there were used modules dedicated to individual rehabilitation, which are characterized by „the innovation” allowing patenting proprietary solutions. On the basis of the knowledge obtained in this way, there was proposed a methodology for developing innovative solutions in rehabilitation devices supporting the implementation of future projects in this field. The innovative solutions described in the monograph to support the recovery of patients after various types of injuries and diseases, in particular after passive and spastic paralysis resulting from a stroke, do not focus on the development of an exoskeleton, but rather compact solutions for specific elements, i.a. requiring the rehabilitation of the upper limb. The presented constructional solutions focus directly on selected parts of the upper limb (including finger rehabilitation – different types of hand grip, rehabilitation of the wrist, upper limb), as well as indirectly on the whole limb (including a device for wrist rehabilitation and its ability to move on the platform, a device to change position from sitting to straight). In these studies, there are visible direct analogies to the activities of everyday life, the possibilities of their simplification and self-fulfillment by the patients, taking into account their current health condition. The monograph proposes examples of paths that innovation development can take. An algorithm that facilitates the preparation of this type of innovation is presented. Moreover, an important issue is also the opportunity to evaluate the proposed solutions and their real needs in terms of future recipients. The convalescence process based on neurorehabilitation presented in the monograph is very complex. An attempt to propose this type of mechatronic innovation is therefore a very interesting, but also a difficult challenge. This subject is very important both in purely technical and utilitarian terms.
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