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 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.
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 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.
Abstract: The release of the open source 3-D printer known as the RepRap (a self-Replicating Rapid prototyper) resulted in the potential for distributed manufacturing of products for significantly lower costs than conventional manufacturing. This development, coupled with open source-appropriate technology (OSAT), has enabled the opportunity for 3-D printers to be used for sustainable development. In this context, OSAT provides the opportunity to modify and improve the physical designs of their printers and desired digitally-shared objects. However, these 3-D printers require electricity while more than a billion people still lack electricity. To enable the utilization of RepRaps in off-grid communities, solar photovoltaic (PV)-powered mobile systems have been developed, but recent improvements in novel delta-style 3-D printer designs allows for reduced costs and improved performance. This study builds on these innovations to develop and experimentally validate a mobile solar-PV-powered delta 3-D printer system. It is designed to run the RepRap 3-D printer regardless of solar flux. The electrical system design is tested outdoors for operating conditions: (1) PV charging battery and running 3-D printer; (2) printing under low insolation; (3) battery powering the 3-D printer alone; (4) PV charging the battery only; and (5) battery fully charged with PV-powered 3-D printing. The results show the system performed as required under all conditions providing feasibility for adoption in off-grid rural communities. 3-D printers powered by affordable mobile PV solar systems have a great potential to reduce poverty through employment creation, as well as ensuring a constant supply of scarce products for isolated communities.
Abstract: In electric power generation, customers want generators with high efficiency. Nowadays, modern turbo-generators have efficiencies greater than 98%. Although this amount should not be obtained for all kind of machines, efficiency will remain one of the main parameters for customer choice. Efficiency is also linked to the life of the machine: the higher the efficiency is, the longer the machine’s lifetime. During the past decade, new forms of energy production have appeared and generators have been developed to fit well into this market. For example, wind generators evolved towards permanent magnet generators having high polarity and running at low speed. Nevertheless, their structure is not fixed. An industrial company has built a prototype of such a generator which uses fractional-slot concentrated-windings (FSCW). This kind of winding is not the structure used by default in such electrical machines. Another field of interest is in autonomous generators which can be used on boats. Even if everyone has in mind large merchant ships, we must not forget smaller ships, such as fishing boats and short-range cruise ships, which spend the most of their time near the coast. This kind of ship does nothave large areas for installing the electric generation or the electric propulsion. It is the reason why, in this article, we focus on the efficiency of machines using fractional-slot concentrated-windings. In many publications which compare performances between distributed and concentrated windings, the result is almost the same. The efficiency of FSCW is not as high as the efficiency associated to the machines which are using distributed windings. Design methods have to be redrawn to integrate, as soon as possible, the loss mitigation in order to provide the best efficiency in power conversion. The following discussion, step by step, introduces the loss mitigation in every part of a machine using FSCW. To close the discussion, a design is produced and it appears that efficiency can be enhanced with suitable design methods.
Abstract: Bipedal humanoid robots are expected to play a major role in the future. Performing bipedal locomotion requires high energy due to the high torque that needs to be provided by its legs’ joints. Taking the WABIAN-2R as an example, it uses harmonic gears in its joint to increase the torque. However, using such a mechanism increases the weight of the legs and therefore increases energy consumption. Therefore, the idea of developing a mechanism with adjustable stiffness to be connected to the leg joint is introduced here. The proposed mechanism would have the ability to provide passive and active motion. The mechanism would be attached to the ankle pitch joint as an artificial tendon. Using computer simulations, the dynamical performance of the mechanism is analytically evaluated.
Abstract: Combine harvesters used today can achieve throughput rates of over 70 tons of grain per hour; however, their technical performance potential is currently not being exhausted by any means. The global market for combine harvesters, its stocks and recent production is described. According to farm size distribution and regional field sizes, Germany was divided into three combine-harvesting regions. The simulation results show that in Germany about 45,000 units of combine harvesters in three performance categories are necessary. However, the calculations also show that future domestic sales of combine harvesters will depend greatly on the service life of the units currently in use.