The phenomenon of non-linearity is the main problem of a DC motor and optimum performance cannot be obtained by the calculation of the controller's parameters using conventional methods. However, a DC motor is considered an extremely common device by the low-cost and effective dynamic response in various applications. Thus, it has been a subject for research studies to take advantage of its maximum performance. This manuscript proposes an experimental methodology that consists of the following: The DC motor's characterization method for finding the ideal frequency. The design of the Firmware-based Pulse Width Modulation (PWM) generating module and the P, PD, PID controller's implementation in an own FPGA-based programmable microprocessor to obtain almost the same performance as a servo-amplifier commercial of direct-drive. The PWM is a technique widely used to regulate the speed of rotation of a DC motor, in this case, the duty cycle of the PWM is used to provide the torque necessary to the mechanics of the system in order to look for a linear relationship but using the right frequency of the characterized DC motor. Finally, based on a built prototype of a micro-positioning system using the characterized motors, and the mathematical model, in both cases the three controllers were applied in order to establish the comparison between the responses, seeking to observe if the experimental results show a great difference with respect to the simulation results. The main aim of this study is to show that the proposed methodology works. However, since there was no significant difference in both results, motors used in the closed-loop control present approximately the same linear response as that of the motor model used in the simulation.

BackgroundGait analysis and research have been developed to obtain characteristics of movement patterns of people while walking. However, traditional measuring systems present different drawbacks that reduce their use and application. Among those drawbacks one can find: high price, low sampling frequency and limiting number of steps to be analyzed. Traditional measuring gait systems carry out their measurement at frequencies oscillating between 60 to 100 Hz. It can be argued about the need of higher sampling rates for gait measurements. However small displacements of the knee or hip for example, cannot be seen with low frequencies required a more detailed sampling and higher frequency sampling. Bearing this in mind, in this paper is presented a 250 Hz system based on accelerometers for gait measurement, and the particularities of knee and hip angles during gait are highlighted.MethodsThe system was designed with a PCI data acquisition card instrumented with an FPGA to achieve a rate sample of 250 Hz. The accelerometers were placed in thighs and legs to calculate the joint angles of hip and knee in the sagittal plane. The angles were estimated using the acceleration polygon method without integrating the acceleration and without filters.ResultsThe gait of thirty healthy people of Mexican phenotype was analyzed over a flat floor free of obstacles. The results showed the gait phases and particularities associated with the walking style and people's laterality; the movement patterns were similar in the thirty persons. Based on the results, the particularities as the maximum amplitude in the angles and the shape in the movement patterns were related to the anthropometry and people phenotype.ConclusionsThe sampling frequency was essential to record 340 samples in single gait cycle and so registering the gait cycle with its particularities. In this work were recorded an average of 8 to 10 gait cycles, and the results showed variation regarding works carried out in biomechanics laboratories; this variation was related to the method and reference frame used to obtain the joint angles and the accuracy of measurement system.

En este trabajo se propone un controlador de velocidad para motores de Corriente Directa (CD) sin dependencia de sensores mecánicos (encoders). El controlador se basa en estrategias de estimación en tiempo real y medición indirecta. Para esto, la corriente de inducido es utilizada como única variable eléctrica disponible por medición. Por lo cual, la correcta instrumentación del proceso de adquisición de datos es de vital importancia para garantizar que las mediciones correspondan con el valor real. El proceso de estimación se realiza en dos etapas principales, en una primera etapa se utiliza la técnica de diseño de observadores de modos deslizantes para estimar el par eléctrico del motor. En la segunda etapa se utiliza la técnica de diseño de observadores por ubicación de polos. La ley de control proporcional integral clásica PI en combinación con la retroalimentación de los estados se utiliza para establecer las acciones del sistema de control. La validación del controlador se realiza por medio de simulación digital y con pruebas experimentales de laboratorio sobre un motor en derivación con excitación separada. La implementación del banco de trabajo consiste en una tarjeta de adquisición y control DSP, un convertidor electrónico de CD-CD, una tarjeta de instrumentación para medir la corriente y una computadora PC. La tarjeta DSP es programada mediante diagramas de bloques. El manejo de la potencia entregada al motor se realiza a través del convertidor CD-CD con base en la técnica PWM. La velocidad del motor muestra un comportamiento asintóticamente estable ante cambios en el par de la carga y en los valores de velocidad de referencia. Los resultados de las pruebas demuestran la robustez, la precisión y la rapidez de convergencia del control propuesto. Descriptores: Control de velocidad, motor de CD, observador de estados, sensor de corriente, proporcional integral.

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In this article, we present a system to measure current in the range of 0 to 10 μA with high-voltage isolation up to 5 kV. This current monitor consists of three ammeters connected in series, to improve the resolution in the measurement. The design features several innovative elements such as using low voltage to provide power to the devices to measure the current and digitize it with a sampling frequency of 1 KHz, it is generated based on a DC-DC converter that produces three voltages, +12 V, −12 V, and 5 V, from a conventional 10 V source. The three voltages are referenced to the same floating ground. The DC-DC converter has a high voltage insulation up to 5 kV and four optocouplers with an insulation up to 20 kV are used to read the digitized data. The introduction of a DC-DC converter contributed to reduce the noise level in the analog part of the circuit which has been resolved implementing shields inside the board. In particle physics, several systems are used to detect particles in high-energy physics experiments such as Gas Electron Multiplier (GEM), micromegas, etc. GEMs suffer small deteriorations due to discharges in constant operation and require monitoring the current consumption at high frequency (1 kHz). In this work, we present the design and operation of a 0 to 10 μA auto scale ammeter. The results obtained by monitoring the current in a 10 × 10 cm2 GEM are shown.

This paper presents an algorithm to estimate the knee angle from hip angle and gait parameters. This algorithm uses a single sensor on the thigh to achieve the estimation. Hip-knee natural correlations were employed in order to analyze the gait flexion-extension movements in two stages: 1) when the foot is not in full contact with the floor (swing phase and heel contact); 2) when the whole sole makes contact with the ground (stance phase). The estimation is developed in real-time for gait movements and speed fluctuations do not distort the angle estimated. In addition, the simple linear regression was used to approximate the estimated angle to actual knee angle. The experimental results obtained from the gait studies, showed an acceptable knee angle approximation; the mean error estimation was 8.25∘. The major goal of this work was the development of an algorithm that can solve the problem of human body-intelligent transfemoral prosthesis coordination, even if there are gait speed fluctuations.

ABSTRACT. Current research reports on the development of a portable electronic system to assess the kinematics of the lower limb joints at the sagittal plane. The electronic device characteristics and the different communication protocols to transfer data are also reported. Research obtained the hip and knee angles to analyze the lower limb kinematics during multiple gait cycles. Results showed that the movement patterns, found in the analysis made on people from central Mexico, were cyclical and alternating. The knee described a one third curve in flexion-extension movements just before the start of the flexionextension curve in the swing phase. Moreover data obtained showed a correlation of movement between hip and knee during walking.Keywords: electronic system, joints, lower limb, gait, movement pattern.Projeto de um sistema de medição de baixo custo baseado em acelerômetros para análise de marcha RESUMO. Este trabalho descreve o desenvolvimento de um sistema electrônico portátil para avaliar a cinemática das articulações dos membros inferiores no plano sagital. Além disso, as características dos dispositivos eletrônicos e os diferentes protocolos de comunicação para transferência de dados são relatados. O objetivo deste trabalho é obter os ângulos de quadril e joelho para análise cinemática dos membros inferiores durante os múltiplos ciclos de marcha. Os resultados mostraram que os padrões de movimento são cíclicos e alternados. Esses padrões foram encontrados na análise feita em pessoas do México central: o joelho descreve um terço de curva em movimentos de flexão-extensão pouco antes de iniciar a curva de flexão-extensão na fase de balanço. Além disso, os dados obtidos mostraram uma correlação de movimento entre quadril e joelho durante a caminhada.Palavras-chave: sistema eletrônico, juntas, membros inferiores, marcha, padrão de movimento.

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