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Made available in DSpace on 2022-04-28T19:48:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-01-01 In this paper, a compact Series Elastic Actuator is designed and evaluated. The proposed actuator will be used to drive the joints of the modular exoskeleton for lower limbs ExoTAO (Transparent Active Orthosis), available at the Robotic Rehabilitation Laboratory of EESC/USP. This equipment is being developed to assist in the rehabilitation of people with motor disabilities resulting from injuries to the central nervous system or to the spinal cord. The differential of the proposed actuator is the use of a customized and compact torsion spring, providing the necessary levels of torque and velocity to drive the exoskeleton. Such performance levels were evaluated considering the characteristics of the selected components and the gait patterns available in the literature. In addition to the theoretical analysis, experimental tests were also conducted with the actuator in order to evaluate its performance in achieving a satisfactory torque control. Time and frequency responses show the proposed actuator is able to reproduce the necessary torque to drive the exoskeleton ExoTAO, achieving high bandwidth values. Department of Mechanical Engineering Engineering School of São Carlos University of São Paulo, 400, Trabalhador São-Carlense Avenue, SP São Paulo State University (UNESP), 505, Profa. Isette Corrêa Fontão Avenue, SP Universidade Estadual Paulista Júlio de Mesquita Filho Câmpus São João da Boa Vista Av. Profa. Isette Correa Fontão, 505 – Jardim das Flores, SP Av. Trabalhador São-Carlense, 400. Parque Arnold Schmidt, SP São Paulo State University (UNESP), 505, Profa. Isette Corrêa Fontão Avenue, SP Universidade Estadual Paulista Júlio de Mesquita Filho Câmpus São João da Boa Vista Av. Profa. Isette Correa Fontão, 505 – Jardim das Flores, SP

Modal identification is a key step in modal analysis. It enables the researcher to extract modal parameters, such as natural frequency, amplitude, and damping from a given structure. There are a considerable number of techniques in the state of the art aiming to address this problem, where multi-mode approaches arise as an appealing choice due to their ability to deal with mode coupling. This tutorial paper focuses on the complex-curve fitting technique, originally conceived for an application distinct from modal analysis. It aims at guiding other researchers by providing a tutorial-like and in-depth analysis of this important method, associated with a nonlinear weighting procedure for improved precision. Additionally, this paper fills a gap on the original technique, which is limited to the ratio of two polynomials, by proposing an automatic parameter extraction technique. The original and improved methods are applied on both simulated and experimental data, highlighting the effectiveness of the proposed changes. The proposed procedure is also compared with the rational fraction polynomial method.

Este documento versa sobre a dinâmica de engrenagens.

Este documento inclui os aspetos gerais sobre engrenagens.

Este documento versa sobre engrenagens cilíndricas de dentes inclinados.

Este documento versa sobre as engrenagens de parafuso sem-fim.

Este documento versa sobre a temática das rodas de atrito.

Este documento versa sobre as transmissões por correntes.

Este documento versa sobre engrenagens cilíndricas de dentes retos.

Este documento versa sobre as engrenagens cónicas.

This paper presents a low-cost/high-precision smart power supply for application on data loggers. The microprocessor unit is the brain of the system and manages the events and was optimized to provide electrical energy to the electronic devices under normal operation and under the presence of disruptive events. The measurements showed that when switching either from battery to AC or from AC to battery, neither caused the shutdown of the power supply nor affected the behavior of the power supply. The power supply was able to charge 80% of the battery on a fast recharge of 1 h and the remaining 20% on a slow recharge of 2 h. The current allocated to the battery did not affect the operation of the power supply. The tests also showed that the power supply was able to transmit relevant information about its operation to external computers through a serial connection. This information includes the voltages at the battery and at the output of the voltage regulators, the voltage level of the AC network, the level of the battery charge and if it was being recharged, the current being drained, the internal temperatures at two locations (one measured on the resistor that limits battery charge and another measured on the output diode of the regulators), and whether the cooling system is being used. The total cost of this smart power supply is less than $150, demonstrating good potential for its popularization., This work was partially supported by FCT national funds, under the national support to R&D units grant, through the reference project UIDB/04436/2020 and UIDP/04436/2020. This research was also partially supported by the FAPESP agency (Fundação de Amparo à Pesquisa do Estado de São Paulo) through the project with the reference 2019/05248-7. Professor João Paulo Carmo was support by a PQ scholarship with the reference CNPq 304312/2020-7.

Nowadays, the automotive industries seek to consider increasingly higher standards of competitiveness. This sector is looking for a proper management methodology to solve a given problem in its kind of organization. In this sense, continuous improvement is essential for any business environment, due to provide conditions for getting excellence levels. Based on this strategy, the Lean Six Sigma (LSS) appears as an option to be applied. Although Lean was originated in the automotive industry, systematic review about Lean Six Sigma in this industry has a lack of research, considering tools and aspects within metrics. For that, the objective of this work is to carry out a literature review on the implementation of Lean Six Sigma in the automotive industry. The databases adopted for this research were Web of Science and Google Scholar, resulting in 69 selected articles. The results indicated that the implementation of this methodology contributes to the continuous improvement process and problem-solving in the automotive branch.

This work reports on a numerical and experimental study of the transient behavior of a dual-skin chest-freezer refrigeration system, operating with R290. A simpler dynamic mathematical model, called thermal, and a more sophisticated one, called capacitive, which models the mass distribution in the systems components, were evaluated. The experiments provided measured data for the characterization of the transient operation of the appliance, supply of models’ input data, and validation of the models. Comparisons between simulation and experimental results showed a very good agreement for both transient and time-averaged systems behavior and performance. The maximum relative error for temperatures at pull-down and on/off operations was 5.5 % . The capacitive model simulated the transient experimental behavior of the refrigeration system well when goods were inserted in the freezer’s cabinet, showing a 2.7 % maximum relative error for the systems performance parameters. Moreover, it yielded a parametric analysis of the refrigerant charge, determining a 200g mass of R290 for the optimum performance. The thermal model is an excellent feature for a first design, simulating 100 min of a real operation in few seconds. The capacitive model provides more complex results, and is a very good tool for a detailed systems design. The experimental data can be used by other researchers for validating their simulations and experimental studies. The paper provides new findings for a system operating with R290, a fluid that has been widely used in small scale refrigeration systems for household applications.

This paper presents the application of digital image correlation to uniaxial and diametral compression tests to identify the Drucker-Prager/cap shear failure and the elastic parameters of a lead zirconate titanate powder (PZT). The calibrated parameters were validated through finite element simulation of the cold isostatic pressing of a hollow hemisphere used in piezoelectric transducers. The results showed that the dilatancy stresses were 50–65% lower than the fracture stresses, demonstrating that adopting the fracture stress may overestimate material cohesion. The simulation using the calibrated model achieved an excellent agreement with the measured geometry, with a difference of only 1.1% in the dimension and 2.0% in the average density. The results highlight how digital image correlation can obtain more accurate parameters with fewer tests. The proposed methodology can be used to calibrate other powder materials, especially those in which dilatancy plays a key role.

Mullite, one of the main refractory materials, has several applications that may demand tiny structures with complex geometries, and digital light processing (DLP) can produce such parts with outstanding dimensional precision and surface quality. In this work, electrofused mullite powder was used as a raw material for additive manufacturing by DLP. Photosensitive mullite suspensions were developed and their rheological behavior, stability, and thermal decomposition were investigated. Mullite parts were printed from suspensions with different ceramic loadings, debound, and sintered at different temperatures (from 1500 to 1650 °C). Density and strength increased with an increase in both solid loading and sintering temperature. Printed parts from slurry with 50 vol% of solid loading sintered at 1650 °C reached a relative density of 97.7 ± 0.3 % and flexural strength of 95.2 ± 5.0 MPa.

This paper presents the experimental results of saturated two-phase flow ammonia in a vertical shell and tube heat exchanger comprising of seven dimpled enhanced tubes. The tests were conducted for a wide range of parameters. The heat load was provided by hot ethylene glycol/water solution flowing on the shell side. Saturation temperature of ammonia was -20°C ≤ T sat ≤ 2°C, heat flux range 5 kW m−2 ≤ q ˙ ≤ 45 kW m−2, exit vapor quality range 0.1 ≤ x ≤ 0.9 and a mass flux range of 34.99 kg m−2 s−1 ≤ G ≤ 66.32 kg m−2 s−1. For each saturation temperature, the effects of heat flux and mass flux were studied for the saturated temperature range while the exit vapor quality at each mass flux was varied between 0.2 and 0.9. Two phase heat transfer coefficient increased with saturation temperature and heat flux. For all experimental conditions, performance showed initial increase and then a classic drop at the onset of dry out. The dimple tube showed better heat transfer coefficient compared to the previous studies performed on plain tubes with ammonia.

The present paper concerns an experimental investigation about the heat transfer coefficient during convective condensation of hydrocarbons and their zeotropic mixtures. Experiments were performed in a horizontal smooth channel, with internal diameter of 9.43 mm for R600a, R290, R1270, R600a/R290 (70/30 molar fraction) and R600a/R1270 (75/25 molar fraction), for mass velocities ranging from 50 to 250 kg m−2 s−1, vapor qualities from unity to zero, heat fluxes from 5 to 60 kW m−2 and a saturation temperature of 35°C. Experiments were also performed for R134a. In general, higher heat transfer coefficients were obtained for the hydrocarbons compared to R134a. The heat transfer process was dominated by shear effects for the hydrocarbons regardless of the mass velocity. At low mass velocities (below 100 kg m−2 s−1), both mixtures provided lower heat transfer coefficients than the pure fluids. At high mass velocities a reduction of the heat transfer coefficient compared to the pure fluid was noticed only for R600a/R1270 at high qualities. The experimental data is compared against prediction methods from literature and based on the pure fluids database, a new strictly empirical prediction method is proposed, which performs better for both pure fluids and mixtures database. For the mixtures, the performance of the methods was improved when considering a correction for the mass transfer effects associated to the concentration gradients near the liquid/vapor interface.

One alternative to overcome the presence of singularities within Parallel Manipulators’ workspace is kinematic redundancy. This design alternative can be realized by adding an extra active joint to a kinematic chain. Due to this addition, the IKM presents an infinite number of solutions requiring a redundancy resolution scheme. Moreover, Parallel Manipulators’ control may require complex strategies due to their coupled and complex dynamic and kinematic relations. In this work, a model-free, a joint space computed torque, and a hybrid joint-task-space computed torque control strategies are experimentally compared for a kinematically redundant parallel manipulator. The latter is a novel strategy that requires the measurement of the end-effector’s pose, which is performed by an eye-to-hand limited frame rate camera. The impact of up to three kinematic redundancy levels is also experimentally evaluated using prepositioning and ongoing positioning redundancy resolution schemes. The data are assessed by evaluating a prescribed trajectory executed using a planar kinematically redundant parallel manipulator. These results indicate that kinematic redundancy can not only be used as an alternative design for reducing the presence of singular regions, as claimed in the literature, but also be used along with model-based control strategies for improving dynamic performance and accuracy of parallel manipulators.