Shaft Encoder Research Articles

System for measuring the size of high-current density solid electron beams

A measurement system is described for determining the size of a high-current density solid electron beam from a Pierce-type electron gun. The apparatus incorporates ten graphite apertures and two graphite tubes mounted at 30/spl deg/ intervals on an off-axis drum that is rotated by a stepper motor. The graphite apertures are used to make localized beam-edge current-interception measurements at ten discrete locations at 1-cm intervals along the length of the beam. The graphite tubes can be used either to produce an integrated edge-current profile over an 11.4-cm length of the beam, or to measure the net current outside of two specific diameters centered on the beam axis. The active aperture or tube and its position with respect to the beam axis are determined by the orientation of the drum, which is read out using an absolute shaft encoder. This permits the position of each aperture or tube to be determined to an accuracy of 60 /spl mu/m.

Shaft encoder characterization via theoretical model of differentiator with both differential and integral nonlinearities

A model of an incremental shaft encoder is developed to facilitate sensor characterization. The model is obtained through derivation of a new mathematical formula for the spectral characteristics of the error which accrues when a sampled, nominally constant-rate signal is uniformly quantized, having been subject to both differential and integral nonlinearities. The spectrum of the error in the rate estimate generated when a digital differentiator is applied to such a signal is shown to be of particular importance. Subsequent sensor characterization involves some basic signal processing of a set of sampled sensor outputs, obtained when the encoder rotates at an almost uniform rate, followed by a simple curve-fitting procedure using the formula for estimated rate error. Both computer-generated, finite-length data sets and experimental data derived from encoder-based shaft velocity measurements are utilized to verify the theoretical model. The methodology of the mathematical analysis is applicable to other digital sensors and to a more general class of systems; such as data converters, which involve the digital differentiation of quantized, noise-affected signals. The paper illustrates how the combined influence of quantization error and of additional sources of noise can be described in an analytical, but applicable, manner.

NFO speed control of induction motor without using shaft encoder

This article focuses on the design and analysis of a speed-sensorless vector control of induction motor based upon a Natural Field Orientation (NFO). This method allows high-dynamic vector control of PWM VSI fed induction motor. The main merit of NFO is given by no requirement on any speed or position sensor. The presence of a tacho-generator or optical shaft encoder is commonly undesirable. These transducers significantly increase the costs and reduce the reliability and robustness of the overall system. The NFO method doesn't employ computationally extensive algorithms such as Model Reference Adaptive System or methods based on Kalman filter. Simulation results from a model-based computer-aided design approach using MATLAB/SIMULINK software will be presented.

High-performance speed control of electric machine using low-precision shaft encoder

For a high-performance servo drive system, it is important to estimate and control the motor speed precisely over a wide-speed range. Therefore, the disturbance-rejection ability and the robustness to variations of the mechanical parameters such as inertia should be considered. This paper shows that the adaptive state estimator and self-tuning regulator based on the recursive extended least squares (RELS) parameter identification method can achieve high-performance speed control over a wide-speed range. The RELS method identifies the variations of mechanical parameters, and the estimated mechanical parameters are used to replace the role of manual tuning by adjusting the gain of the speed controller automatically for good dynamic response. Also, these estimated parameters are used to adapt the Kalman filter, which is an optimal state estimator, to provide good estimation performance for the rotor speed, rotor position and disturbance torque even in a noisy environment. Simulation and experimental results show an improved speed control performance in the wide-speed range.

A new system for the measurement of displacements of the human body with widespread applications in human movement studies

This paper reports the development, construction and use of a new system for the measurement of linear kinematics in one, two or three dimensions. The system uses a series of rotary shaft encoders and inelastic tensioned strings to measure the linear displacement of key anatomical points in space. The system is simple, inexpensive, portable, accurate and flexible. It is therefore suitable for inclusion in a variety of motion analysis studies. Details of the construction, calibration and interfacing of the device to an IBM PC computer are given as is a full mathematical description of the appropriate measurement theory for one, two and three dimensions. Examples of the results obtained from the device during gait, running, rising to stand, sitting down and pointing with the upper limb are given. Finally it is proposed that, provided the constraints of the system are considered, this method has the potential to measure a variety of functional human movements simply and inexpensively and may therefore be a valuable addition to the methods available to the motion scientist.

A periodic burst injection method for deriving rotor position in saturated cage-salient induction motors without a shaft encoder

This paper describes a new method for estimating the incremental rotor position for an induction machine without using a shaft sensor. The method assumes a saturated induction motor having an engineered cage saliency spanning one pole pitch. The voltage-source inverter driving the machine is also used to inject a high-frequency signal which is needed to detect position. The paper discusses two ways in which this can be achieved. This method has been proven successful with a loaded machine at low speeds and overcomes problems associated with saturation.

Rotor resistance adaptation for sensorless vector-controlled induction machines

The vector control method is widely used for induction motor drives. In these applications, a rotational transducer such as a shaft encoder is used. A rotational transducer, however, cannot be mounted in some cases, such as motor drives in a hostile environment or high-speed motor drives. Several sensorless vector-controlled induction machine drive methods have been proposed. These methods have the disadvantage that rotor resistance variation causes errors in the estimation of the motor speed. It is difficult to estimate the motor speed and the rotor resistance simultaneously, because the equivalent rotor resistance is the ratio of the rotor resistance to the slip at steady state. Therefore, we have proposed a method of simultaneously estimating the motor speed and the rotor resistance of an induction motor by superimposing ac components on the field current command. This paper presents a modified method of the rotor resistance adaptation. The validity of the proposed method is verified by experiments. © 1998 Scripta Technica, Electr Eng Jpn, 125(2): 65–72, 1998

High resolution optical shaft encoder for motor speed control based on an optical disk pick-up

Using a three-beam optical pick-up from a compact disk player and a flexible, shaft-mounted diffraction grating, we obtain information about the rotation speed and angular position of the motor’s spindle. This information may be used for feedback to the motor for smooth operation. Due to the small size of the focused spot and the built-in auto-focus mechanism of the optical head, the proposed encoder can achieve submicrometer resolution. With high resolution, reliable operation, and low-cost elements, the proposed method is suitable for rotary and linear motion control where accurate positioning of an object is required.

Laser Velocimeter Measurements in the Pump of an Automotive Torque Converter Part I – Effect of Speed Ratio

A torque converter was tested at four turbine/pump rotational speed ratios (0.200, 0.400, 0.600, and 0.800) all with a constant pump rotational speed in order to determine the effect of speed ratio on the torque converter pump flow field. Laser velocimetry was used to measure three components of velocity within the pump and a shaft encoder was employed to record the instantaneous pump angular position. Shaft encoder information was correlated with measured velocities to develop flow field blade‐to‐blade profiles and vector plots. Measurements were obtained in both the pump mid‐ and exit planes for all four speed ratios. Results showed large separation regions and jet/wake flows throughout the pump. The midplane flow was found to have strong counter‐clockwise secondary components and the exit plane flow had strong clockwise secondary components. Mass flows were calculated from the velocity data and were found to decrease as the speed ratio was increased. Also, the vorticity and slip factors were calculated from the experimental data and are included. The mid‐plane slip factors compare favorably to those for conventional centrifugal pumps but less slip was present in the exit plane than the mid‐plane. Neither the slip factor nor the vorticity were seen to be strongly affected by the speed ratio. Finally, the torque core‐to‐shell and blade‐to‐blade torque distributions are presented for both planes.

Thermodynamics in a turbocharged direct injection diesel engine

Software has been developed for the calculation of the thermodynamic cycle and the entropy changes in a turbocharged, direct injection, diesel engine based upon the measured cylinder pressure and a shaft encoder output. Assumptions of homogeneous mixture and equilibrium thermodynamic properties are made for the products of combustion and the temporal variation in the fluid thermodynamic state is followed in a quasi-steady manner through a series of adjacent equilibrium states, each separated by finite intervals of one degree crank angle (1°CA). The thermodynamic properties are calculated by either of two equivalent formulations — equilibrium constants or minimization of Gibbs free energy, and are expressed in algebraic equations for the partial derivative of internal energy and gas constant with respect to temperature, pressure and equivalence ratio. The effect of the engine operating conditions on the thermodynamic cycle is studied. Results show that the dynamic fuel injection timing and hence the ignition delay are strongly influenced by the operating conditions, and this explains the reasons for incorporating a fuel injection control system in modern vehicular engines for the optimization of the engine combustion cycle.

Estimation of the section thickness and optical disector height with a simple calibration method

The distance between the upper and lower surfaces of a section (i.e. the section thickness) can be measured with a microcator or a shaft encoder. In the present report, an alternative simple method is described for estimating the section thickness where such equipment is not available. The basic principle of the method is based on a calibration method already described in the literature. The main difference is that it enables one to make more precise measurements. Provided that the calibration and measurements are made properly, this method can be used in estimating the section thickness, optical disector heights, and in particular in the determination of the thickness sampling fraction for the optical fractionator.

Laser Velocimeter Measurements in the Turbine of an Automotive Torque Converter: Part II—Unsteady Measurements

The unsteady velocity field found in the turbine of an automotive torque converter was measured using laser velocimetry. Velocities in the inlet, quarter, mild, and exit planes of the turbine were investigated at two significantly different turbine/pump rotational speed ratios: 0.065 and 0.800. A data organization method was developed to visualize the three-dimensional, periodic unsteady velocity field in the rotating frame. For this method, the acquired data are assumed to be periodic at synchronous and blade interaction frequencies. Two shaft encoders were employed to obtain the instantaneous angular position of the torque converter pump and turbine at the instant of laser velocimeter data acquisition. By proper “registration” of the velocity data, visualizing the transient interaction effects between the turbine, pump, and stator was possible. Results showed strong cyclic velocity fluctuations in the turbine inlet plane as a function of the relative turbine-pump position. These fluctuations are due to the passing of upstream pump blades by the slower rotating turbine blades. Typical fluctuations in the through flow velocity were 3.6 m/s. Quarter and midplane velocity fluctuations were seen to be lower; typical values were 1.5 m/s and 0.8 m/s, respectively. The flow field in the turbine exit plane was seen to be relatively steady with negligible fluctuations of less than 0.03 m/s. From the velocity data, the fluctuations of turbine performance parameters such as flow inlet angles, root-mean-square unsteadiness, and output torque per blade passage were calculated. Incidence angles were seen to vary by 3 and 6 deg for the 0.800 and 0.065 speed ratios, respectively, while the exit angles remained steady. The turbine output torque per blade passage fluctuated by 0.05 Nm for the 0.800 speed ratio and 0.13 Nm for the 0.065 speed ratio.

Laser Velocimeter Measurements in the Turbine of an Automotive Torque Converter: Part I—Average Measurements

The three-dimensional average velocity field in an automotive torque converter turbine was examined. Two significantly different operating conditions of the torque converter were tested: the 0.065 and 0.800 turbine/pump speed ratio. Velocities were measured using a one-directional, frequency-shifted laser velocimeter. The instantaneous angular positions of the torque converter turbine and pump were recorded using digital shaft encoders. Shaft encoder information and velocities were correlated to generate average velocity blade-to-blade profiles and velocity vector plots. Measurements were taken in the inlet, quarter, mid, and exit planes of the turbine. From the experimental velocity measurements, mass flows, turbine output torque, average vorticities, viscous dissipation, inlet incidence flow angles, and exit flow angles were calculated. Average mass flows were 23.4 kg/s and 14.7 kg/s for the 0.065 and 0.800 speed ratios, respectively. Velocity vector plots for both turbine/pump speed ratios showed the flow field in the turbine quarter and midplanes to be highly nonuniform with separation regions and reversed flows at the core-suction corner. For the conditions tested, the turbine inlet flow was seen to have a high relative incidence angle, while the relative turbine exit flow angle was close to the blade angle.

Nonlinear dynamics of a sinusoidally driven pendulum in a repulsive magnetic field

The dynamics of a sinusoidally driven pendulum in a repulsive magnetic field is investigated theoretically and experimentally. The experimental data are acquired using a shaft encoder interfaced to a PC which measures the angular displacement of the pendulum as a function of time. Both the theoretical simulations and the experimental measurements exhibit regions of periodic and chaotic behavior, depending on the system parameters. Amplitude jumps, hysteresis, and bistable states are also observed. The simplicity of the apparatus makes this experiment suitable for an advanced undergraduate laboratory.

Hydro-resistive measurement of dynamic lifting strength

A device is described for measuring strength and power outputs of dynamic vertical lifts between heights of 0.4 and 2.2 m. The device is safe, robust, and easily transportable. It consists of a water-filled tube 2 m high and 200 mm internal diameter. The subject pulls vertically on a handle which is connected with flexible wire rope via a series of pulleys to a piston suspended inside the tube. The piston has holes which can be closed with bungs. The drag force is proportional to the square of the velocity. The constant of proportionality can be chosen over a more than 100-fold range and is independent of temperature. Manual force is measured using a strain gauged cantilever over which the rope passes. Rope movement is monitored with a shaft encoder. These devices are sampled synchronously by an interfaced computer. Velocity and power are derived from the measurements of displacement, time and force. Teh device is highly accurate. Power measurements are not significantly different on two separate days although repetitions on one day show a warming-up effect. This device allows the study of dynamic lifts ranging from slow, high force, quasi-isokinetic lifts to lifts where high velocities and accelerations occur.

Use of a `look-up' table improves the accuracy of a low-cost resolver-based absolute shaft encoder

The accuracy of a low-cost, resolver-based 14-bit absolute encoder has been improved significantly from about 10 to about 2 arcmin (the resolution limit) by the use of a `look-up' table. The methodology adopted for generating this table and incorporating it into the drive-system software of our four-element -ray telescope array is described.

Rotor Resistance Adaptation for Sensorless Vector Controlled Induction Machines

The vector control method is widely used for induction motor drives. In these applications, a rotational transducer such as a shaft encoder is used. A rotational transducer, however, cannot be mounted in some cases such as motor drives in a hostile environment, high speed motor drives, etc. Several sensorless vector controlled induction machine drive methods have been proposed. These methods have a disadvantage that the rotor resistance variation causes the estimation error of the motor speed. It is difficult to estimate the motor speed and the rotor resistance simultaneously, because the equivalent rotor resistance is the ratio between the rotor resistance and the slip under steady states. Therefore, we have proposed a method of estimating simultaneously the motor speed and the rotor resistance of an induction motor by superimposing AC components on the field current command. This paper presents a modified method of the rotor resistance adptation. The validity of the proposed method is verified by the experimentation.

Effect of Engine Operating Condition on Thermodynamic Cycle.

A sophisticated software is developed for the calculation of thermodynamic cycle and entropy change in a turbocharged, direct-injection, diesel engine based upon the measured cylinder pressure and shaft encoder output. Assumptions of homogeneous mixture and equilibrium thermodynamic properties for the products of combustion are made and the temporal variation in fluid thermodynamic state is effectively progress in a pseudo quasi-steady manner through a series of adjacent equilibrium states, each separated by a relatively small but finite interval of one-degree crank angle. The thermodynamic properties are calculated by either of two equivalent formulations-equilibrium constants or minimisation of Gibbs free energy, and are expressed in algebraic equations for the partial derivative of internal energy and gas constant with respect to temperature, pressure and equivalence ratio. The effect of engine operating conditions on the thermodynamic cycle is studied. Results show that the dynamic fuel injection timing and hence the ignition delay are strongly dependent on the operating conditions, which explains the reason for incorporating a fuel injection control system in modern vehicular engines for the oprimisation of engine combustion cylcle.

ASIC implementation of a digital tachometer with high precision in a wide speed range

A common method in adjustable speed drives uses an incremental shaft encoder and an electronic circuit for velocity estimation. The usual method of counting pulses coming from the encoder in a fixed period of time produces a high-precision velocity estimate in the high-speed range. High precision in the low-speed range can be achieved measuring the elapsed time between two successive pulses coming from the encoder. In this paper, a mixed method that combines the best of the two previously mentioned approaches has been implemented using a simple electronic circuit based on one field-programmable gate array (FPGA) and one read-only memory (ROM).

96/05341 The study of thermodynamic cycle and entropy change in a turbocharged DI diesel engine

A software program has been developed for calculating the thermodynamic cycle, in particular the entropy changes, in a turbocharged direct-injection diesel engine, based on the measured cylinder pressure and the output of a shaft encoder. Assumptions of homogeneous mixture and equilibrium thermodynamic properties are made for the products of combustion, and the temporal variation in the fluid thermodynamic state is followed in a quasi-steady manner through a series of adjacent equilibrium states, separated by finite intervals of 1° crank angle. Calculations of the thermodynamic properties and equilibrium chemical products of fuel-air reaction are based on the method of minimising Gibbs free energy with a flexibly defined number of product species. The effect of the engine operating conditions on the thermodynamic cycle is studied. Results show that the dynamic fuel-injection timing, and hence ignition delay, are strongly influenced by the operating conditions, and this explains the reasons for incorporating a fuel-injection control system in modern vehicular engines for optimising the engine combustion cycle. The effect of fuel-injection timing on the thermodynamic cycle is also studied with 8 °CA retard and advance reference to the base-line fuel-injection setting.