Showing papers on "Angular velocity published in 1995"

Attitude control without angular velocity measurement: a passivity approach

Abstract: It is well known that the linear feedback of the quarternion of the attitude error and angular velocity globally stabilizes the attitude of a rigid body. In this note, we show that the angular velocity feedback can be replaced by a nonlinear filter of the quarternion, thus removing the need of direct angular velocity measurement. In contrast to other approaches, this design exploits the inherent passivity of the system; a dynamic observer reconstructing the velocity is not needed. An application of the proposed scheme is illustrated for the robot control problem. Simulation results are included to illustrate the theoretical results.

Slow rotation of the Sun's interior

Abstract: THE rotation of the Sun is not that of a rigid body; at its surface, the gas near the poles has a lower angular velocity than that near the equator(1). This latitudinal variation persists to the base of the convection zone, below which the angular velocity becomes approximately uniform(2,3). Any variations of angular velocity at much greater depths are, however, poorly constrained(4-10). Observations of solar oscillation modes have been used to probe density variations in the Sun; rotational splitting of degenerate modes, although difficult to resolve, provides important constraints on the dynamical structure(11). Here we report observations of rotationally split: modes made over a three-year period with the Birmingham Solar Oscillations Network. Our results indicate that there is a substantial region inside the Sun that is rotating more slowly than the surface. This situation seems likely to be transient-the minimum-energy state would have all the deeper regions rotating with the same angular velocity-and is at variance with our current ideas about the rotational evolution of main-sequence stars(12). We have no solution to the dynamical problem this poses.

General local stability criteria for stratified, weakly magnetized rotating systems

Abstract: We consider the local stability of laminar differential rotation in a weakly magnetized plasma to adiabatic axisymmetric disturbances. Our assumptions are considerably less restrictive than those of previous analyses. The angular velocity need not have cylindrical isorotational surfaces, and {ital a} {ital priori} convective stability is not assumed. In an unmagnetized gas, stability under these circumstances would be governed by the Ho/iland criteria. These criteria change qualitatively when even a weak magnetic field is present. In a magnetized plasma, the new criteria for stability have the same general form exhibited by the purely hydrodynamical case, but with all angular momentum gradients replaced by angular velocity gradients. Our findings are in accord with those of Papaloizou & Szuszkiewicz, who, using very different methods, considered the stability of iso-rotational field configurations. The results presented here thus point very generally to angular velocity gradients, not angular momentum gradients, as the fundamental stability discriminants in rotating astrophysical plasmas. {copyright} {ital 1995 The American Astronomical Society.}

Deformation of a graphic object to emphasize effects of motion

Abstract: A three-dimensional graphic object appearing in an animation is deformed to simulate the effects of motion on the object. A user can selectively apply a stretch, yield, or flex deformation effect to the control vertices of the object, to change the shape of the object as a function of any of a linear velocity, angular velocity, linear acceleration, or angular acceleration of the object. Various other parameters for each of these deformation effects can also be selected and set by the user, including a sensitivity to the motion in generating the deformation and a maximum deformation. The flex deformation can selectively be set to either a linear or curved profile, simulating the effect of friction applied by the environment on one or more surfaces of the object. The stretch deformation can selectively be set to either a constant or a free volume to simulate the effect of inertia, causing a body to elongate or shrink in the direction of the movement. The yield deformation can be set either a linear or curved profile, simulating the displacement of an object's internal matter toward one end that occurs, relative to the direction of the object's motion, i.e., causing one end to bulge. For each control vertex on the object, an effect offset is determined for each motion component and for each selected deformation effect. The sum of the effect offsets for the control vertex represents a total offset that is added to the original control vertex to determine a deformed control vertex. This step is repeated for all control vertices to produce the deformed object.

Micromechanical resonator of a vibration gyrometer

Abstract: For a micromechanical resonator of a vibration gyrometer, the two resonating masses, which vibrate in phase opposition and are joined across a coupling region, are suspended by at least one suspension spring. The suspension springs are thereby designed to be soft in the direction of vibration and substantially harder in all other degrees of freedom. This allows the moment of rotation of the rate of rotation (absolute angular velocity) to be transferred to the resonating masses. Interference signals when measuring Coriolis forces are suppressed by means of subtraction. The resonator is patterned out of a semiconductor material and can be excited to vibrate in the electrostatic or electromagnetic field by means of suitable current supply leads.

Image blur suppression device for an optical camera

Abstract: A motion compensation device for suppressing image blur in an imaging optical system corrects for both vertical and horizontal blur using an angular velocity sensor. The angular velocity sensors detect the rotary motion in the imaging optical system, such as for a camera. An actuator generates drive power to drive the compensation optical system, electromagnetically, approximately perpendicular to the optical axis of the imaging optical system, based on the output from the angular velocity sensor, and a location detector that monitors the location of the compensation optical system. A signal monitor monitors the driving signal that drives the actuator. An optimal driving signal convertor converts the output from the angular velocity sensor to an optimal driving signal for the actuator. The driving signal of actuator is corrected based on the difference between the optimal driving signal and driving signal as monitored by signal monitor.

The pattern speed of the bar in NGC 4596

Abstract: We have used the Tremaine-Weinberg method to measure the angular speed of rotation for the bar in the SBO galaxy NGC 936. With this technique, the bar's pattern speed, Omega(p), can be derived from the luminosity and stellar-kinematic information in long-slit spectral observations taken parallel to the major axis of the galaxy. The kinematic measurement required is the mean line-of-sight velocity of all stellar light entering the slit. This quantity can only be calculated reliably if any asymmetry in the shape of the broadening function of the spectral lines is also measured, and so we present a method which allows for such asymmetry. The technique also returns a true measure of the rms uncertainty in the estimate. Application of the analysis to a set of long-slit spectra of NGC 936 returns four separate measures of Omega(p) which are mutually consistent. Combination of these data produces a best estimate for the bar pattern speed of Omega(p), = 60 +/- 14 km s(-1) kpc(-1) (assuming a distance of 16.6 Mpc). This result refines the only previous attempt to make this measurement, which yielded an estimate for Omega(p), in NGC 936 of 104 +/- 37 km s(-1) kpc(-1) The new measurement places the co-rotation radius just beyond the end of the bar, in agreement with theoretical calculations.

Nonlinear speed observer for high-performance induction motor control

Abstract: In this paper, we consider the problem of estimating the angular velocity of an induction motor using encoder measurements. Two methods are compared. In the first method, the speed is found by calculating the backward difference of the position measurement and low-pass filtering the result. In the second method, the velocity is estimated using a nonlinear observer constructed using the known dynamic model of the induction motor. The performance of the two methods is evaluated in the context of their use for velocity feedback in a high-performance field-oriented control law. Experimental results demonstrate that the speed observer leads to a smoother operation of the motor in closed-loop. With the estimator based on differentiation, either the delay imposed by the low-pass filter is too large to maintain high bandwidth feedback, or the fluctuations in the estimated speed are so large that much more energy ends up being dissipated to achieve the same control task. >

Finite element simulation of the inertia welding of two similar parts

Abstract: A complete thermo‐mechanical model for the simulation of the inertia welding process of two similar parts is described. The material behaviour is represented by an incompressible viscoplastic Norton—Hoff law in which the rheological parameters are dependent on temperature. The friction law was determined experimentally and depends on the prescribed pressure and the relative rotating velocity between the two parts. The mechanical problem is solved considering the virtual work principle including inertia terms. The computation of the three components of the velocity field such as radial, longitudinal and rotational velocity, in an axisymmetric approximation allows to take into account the torsional effects. The domain is updated based on a Lagrangian formulation. The non‐linear heat transfer equation with boundary conditions (convection, radiation and friction flux) is solved separately for each time step. Error estimators on mechanical and thermal computation are devised to adapt the mesh in an automatic w...

Nonlinear feedback control with global stabilization

Abstract: Hamilton-Jacobi-Bellman theory is shown to provide a unified framework for nonlinear feedback control laws for special classes of nonlinear systems. These classes include Jurdjevic-Quinn type systems, as well as minimum phase systems with relative degree {1, 1, ..., 1}. Several examples are given to illustrate these results. For the controlled Lorenz equation, results obtained by Vincent and Yu are extended. Next, for spacecraft angular velocity stabilization with two torque inputs, a family of nonlinear feedback control laws that globally asymptotically stabilize angular velocity is established. Special cases of this family of control laws include generalizations of the locally stabilizing control laws of Brockett and Aeyels to global stabilization as well as the globally stabilizing control laws of Irving and Crouch and Byrnes and Isidori. Finally, the results are applied to spacecraft angular velocity stabilization with only one torque input. These last results extend control laws given by Outbib and Sallet.

Dynamic behavior control apparatus of automotive vehicle

Abstract: A dynamic behavior control apparatus of an automotive vehicle wherein a side slip angle and its angular velocity are detected to determine whether a dynamic state of the vehicle defined by the detected side slip angle and its angular velocity is in a stable region or an unstable region, and wherein an unstable degree of the dynamic state of the vehicle is calculated. As a result of the detection and calculation, each target braking force of front and rear road wheels of the vehicle is calculated for correction of unstable behavior of the vehicle. A boundary line of the stable and unstable regions is varied in accordance with a driving condition amount of the vehicle such as a vehicle speed, a steering angle and a steering angle velocity and a travel circumstance amount such as a road surface frictional coefficient.

Peristaltic pulse pumping systems and methods

Abstract: A peristaltic pumping apparatus and associated method control power to the pump rotor to establish, during a preestablished first time period, a selected first angular velocity and sequentially establishing during a preestablished second time period immediately following the first time period a second angular velocity different than the first angular velocity. In this fashion, the apparatus and method achieve flow rates well below the minimum continuous flow rate of the rotor.

Long-time tails in angular momentum correlations

Abstract: We compare computer simulation results for the angular velocity autocorrelation function (AVACF) of a colloidal particle with theoretical predictions. We consider both spherical and nonspherical particles in two and three dimensions. The theoretical prediction for the long‐time decay of the AVACF in three dimensions is well known, here we also give the two‐dimensional result, along with a sketch of how it was derived. For spherical particles we find excellent agreement between the simulations results and theoretical predictions in both two and three dimensions. We also find that the same expressions apply to the nonspherical particles when the particles have had time to undergo a significant angular displacement. This observation is again in agreement with theory.

Absolute stress determination in orthotropic materials from angular dependences of ultrasonic velocities

Abstract: In this paper we describe a method to determine absolute plane stresses in orthotropic materials from the angular dependence of ultrasonic velocities. No prior information on material anisotropy (texture) is required since the stress dependent elastic constants and stresses are found simultaneously from velocity data using least‐squares optimization. In the optimization algorithm no relation between the stress dependent elastic constants and stresses is assumed and therefore they are considered as uncoupled variables, but it is shown that the iteration process converges to the correct (coupled) values. The method is applicable for stress measurements in materials which have undergone a complicated (possibly plastic) history of loading and unloading; thus it can be used to determine both applied and residual stresses. To check the proposed technique we use synthetic sets of experimental data for different degrees of anisotropy and stress levels. Calculations using these synthetic data show that when the principal stress directions coincide with the symmetry axes the angular velocity data in the plane perpendicular to the stress plane may be used for reconstruction of both stress components. When the stress is off the symmetry axis, the shear and the difference of the normal stress components may be determined from the angular dependence of the velocities in the plane of stresses. In both cases the stress determination accuracy depends only on the accuracy of velocity measurements and is independent of stress level and material anisotropy.

Suboptimal command generation for control moment gyroscopes and feedback control of spacecraft

Abstract: This paper presents a suboptimal gimbal-angle command generation technique and a Lyapunov-based tracking control law for control moment gyroscopes. The formulation of the open-loop maneuver problem exploits the principle of conservation of angular momentum. This allows for a reduction in the dimensionality of the problem— only the kinematics need be considered. The gimbal rates are parametrized as polynomial functions of time, and the parameters are optimized. The objective function of the optimization is the singularity measure. The optimal null motion used is determined after computing the open-loop gimbal-rate profiles. A feedback strategy is used to track the open-loop reference attitude and angular velocity profiles. Null motion is also used to allow the closedloop gimbal angles to follow the open-loop gimbal-angle histories. This procedure avoids neighboring singularities and also provides repeatability. Simulation results are presented for rest-to-rest maneuvers using a model of a ground-based test article. The results show that a wide domain of singularity-free operation around the reference solution can be provided with this approach.

Method for coordinating motion control of a multiple axis machine

Abstract: A multiple axis machine includes a plurality of servo-motors that produce movement of a member in at least two axes. The servo-motors are controlled by a computer which runs a simulation of a line shaft power train for producing movement of the member. Specifically, characteristics of a line shaft for powering the machine are defined along with characteristics of a pair of mechanical linkages with dynamically variable kinematics that are driven by the line shaft to produce movement along the two axes. The computer simulates a virtual line shaft using the line shaft characteristics and produces an angular acceleration, an angular velocity and an angular position of the virtual line shaft. The computer also simulates a pair of virtual mechanical linkages with dynamically variable kinematics based upon the linkage characteristics, and based on the angular acceleration, angular velocity and angular position of the virtual line shaft. The simulations produce control signals that operate actuators for each axis of the machine, and produce dynamically variable kinematic feedback force signals which are applied to the simulation of the virtual line shaft to simulate dynamically variable kinematic forces exerted by the mechanical linkages on the virtual line shaft.

Method for determining a wheel brake pressure

Abstract: A method for controlling the brakes in an automotive vehicle. The vehicle has a velocity and a plurality of wheels, each wheel having an angular velocity and a brake which is operable by applying a pressure agent to the brake. An amount of the pressure agent to be applied to, or released from, each brake, individually, to implement a desired braking operation is determined. Switching times corresponding to the amounts of the pressure agent are calculated for opening and closing the inlet valve or outlet valve of each respective brake, individually. An estimated vehicle velocity and an estimated wheel angular velocity which result from applying the pressure agent to the brakes are determined. The actual velocity of the vehicle and the actual angular velocity of the wheels are determined by measuring the angular velocity, and determining the velocity based on the measurement. A comparison is performed, either between (1) the actual velocity and the estimated vehicle velocity, or (2) the actual angular velocity and the estimated wheel angular velocity. The amounts of the pressure agent to be applied to, or released from, each respective brake are adjusted, based on the comparison.

Electric power steering apparatus with enhanced road feel

Abstract: An electrically-operated steering apparatus in which in addition to avoiding an increase in cost caused by installing a new sensor or using a high process speed CPU, steering feels, such as steering wheel return, viscous feeling, inertial feeling and frictional feeling, are improved. In addition to assisting a static steering torque on the basis of a torque sensor, with a motor-applied voltage detection circuit capable of removing the square wave component attendant on the PWM drive of a motor, a motor angular velocity ω is estimated from the output data of the relevant circuit. A motor angular acceleration dω/dt is estimated from the motor angular velocity ω by using a differential calculator. The steering friction and the moment of inertia are compensated on the basis of the motor angular velocity ω and motor angular acceleration dω/dt, respectively.

On the spatial propagation of transient magnetic fields in AC machines

Abstract: AC motors have proliferated as the most important machine type used in speed variable drive systems. The dynamic analysis and description of revolving field machines is supported by well-established theories: Park's transformation (1929), and the space vector theory by Kovacs and Racz (1959). Yet some inconsistencies with the theory of dynamic systems exist; the machine eigenvalues suggest the existence of two damped oscillators. A transient condition is described by time-dependent oscillations of terminal quantities. It appears unsatisfactory that the respective eigenfrequencies change with the velocity of the reference frame. This contradicts the common understanding according to which the eigenfrequency is an inherent system property. A clarification is reached using a novel approach for the dynamic analysis. The approach is based on complex state variables. These characterize a transient condition by the spatial propagation of distributed magnetic fields. The formal analysis is an extension to the space vector theory and the theory of dynamic systems.

Offset-drift correcting device for gyro-sensor

Abstract: An offset-drift correcting device is designed for a gyro-sensor mounted on an object and outputting a signal representing an angular speed of the object. The device includes a first section for detecting whether or not the object is rotating. A second section connected to the gyro-sensor is operative for smoothing the angular speed represented by the output signal of the gyro-sensor, and deriving an average angular speed of the object from the angular speed represented by the output signal of the gyro-sensor. A third section connected to the first section and the second section is operative for estimating an offset level of the output signal of the gyro-sensor in response to the average angular speed derived by the second section in cases where the first section detects that the object is not rotating. The third section includes an adaptive filter processing an output signal of the second section which represents the derived average angular speed. A fourth section connected to the gyro-sensor and the third section is operative for subtracting the offset level estimated by the third section from the output signal of the gyro-sensor to convert the output signal of the gyro-sensor into an offset-free signal.

Steering controller for vehicle

Abstract: PURPOSE: To enable a driver to easily execute obstacle evading operation by providing this steering control device with a steering control means for compensating the addition quantity of steering torque at the time of detecting a steering angular velocity more than a prescribed value by a steering angular velocity detecting means and preventing the generation of a deviation from a road. CONSTITUTION: A steering control part SC is provided with a reference yaw rate calculating means 11 for setting up a yaw rate generated at the time of traveling on a road as a reference, a steering control means 13 and a steering angular velocity sensor 17 connected to the means 13. When a steering wheel is suddenly turned right in order to evade a forward obstacle detected by a driver at the time of traveling on a road curved right, an actual large right yaw rate is generated and left operation torque is applied to a steering means 15 so as to restore the vehicle to a correct route. When the steering angular velocity detected by a steering angular velocity sensor 17 exceeds a reference value, steering assist torque is compensated so as to assist the evading operation and steering torque is canceled.

Driving force control system for vehicle and the method thereof

Abstract: In a driving force control system for a vehicle, an angular velocity of the course direction of the vehicle body is calculated On the other hand, a target angular velocity of the course direction is determined based on a steering angle and a vehicle speed Then, based on the degree of the deviation of the calculated angular velocity from the target angular velocity, a correction coefficient for reducing an engine power is generated When the vehicle traces off the course in the marginal condition on the low friction coefficient road, the correction coefficient reduces the engine power to prevent the vehicle from going out of the course

Analysis and processing of shaft angular velocity signals in rotating machinery for diagnostic applications

Abstract: The paper presents the application of some modern signal processing methods to the analysis of angular velocity signals in a rotating machine for diagnostic purposes. The signal processing techniques considered in this paper include: classical non-parametric spectral analysis; principal component analysis; joint time-frequency analysis; the discrete wavelet transform; and change detection algorithm based on residual generation. These algorithms are employed to process shaft angular velocity data measured from an internal combustion engine, with the intent of detecting engine misfire. The results of these analyses show that these algorithms have potential for on-board diagnostic application in passenger and commercial vehicles, and more generally for failure detection of other classes of rotating machines.