Showing papers on "Angular velocity published in 1991"

A globally convergent angular velocity observer for rigid body motion

Abstract: The problem of obtaining the angular velocity of a rigid body from orientation and torque measurements only, without noisy numerical differentiation, is considered. A novel angular velocity/angular momentum observer for rigid body motion is presented. Using Euler quaternions and a mechanical energy function approach, it is shown that the observer estimates converge globally and that the convergence is eventually exponential. It is hoped that a mechanical energy function approach to rigid body control can be combined with the observer presented to lead to a globally stable, nonlinear, observer-based, rigid-body controller in which the observer and controller errors can be separated, in much the same way as one can separate controller and observer poles in the output feedback controllers of linear system theory. >

Declining rotation curves - the end of a conspiracy

Abstract: New observations of H I rotation curves at the Very Large Array have uncovered two galaxies with rotation curves declining between 1 and 3 optical radii The velocity decrease is large, more than 50 km s-1 (approximately 25% of the maximum rotation velocity), and is present on both sides of the galaxies; projection effects can be ruled out We interpret the decrease in rotation velocity as an indication of a large ratio of luminous to dark mass in the luminous regions of these systems An analysis of the current observations combined with rotation curves from the literature shows a clear correlation between peak circular velocity of a galaxy, its central surface brightness and the slope of the rotation curve in the outer parts This correlation indicates a weakening of the well-known conspiracy between luminous and dark matter, and may provide evidence in favor of the idea that dark matter is baryonic Although we do not sample the full morphological Hubble sequence, a strong correlation between slope of the rotation curve and morphological type is found This result seems to support earlier suggestions that the ratio between the mass in dark and luminous matter might be the critical parameter that controls the Hubble sequence

Static and dynamic assessment of the Biodex dynamometer.

Abstract: The validity and accuracy of the Biodex dynamometer was investigated under static and dynamic conditions. Static torque and angular position output correlated well with externally derived data (r = 0.998 and r greater than 0.999, respectively). Three subjects performed maximal voluntary knee extensions and flexions at angular velocities from 60 to 450 degrees.s-1. Using linear accelerometry, high speed filming and Biodex software, data were collected for lever arm angular velocity and linear accelerations, and subject generated torque. Analysis of synchronized angular position and velocity changes revealed the dynamometer controlled angular velocity of the lever arm to within 3.5% of the preset value. Small transient velocity overshoots were apparent on reaching the set velocity. High frequency torque artefacts were observed at all test velocities, but most noticeably at the faster speeds, and were associated with lever arm accelerations accompanying directional changes, application of resistive torques by the dynamometer, and limb instability. Isokinematic torques collected from ten subjects (240, 300 and 400 degrees.s-1) identified possible errors associated with reporting knee extension torques at 30 degrees of flexion. As a result of tissue and padding compliance, leg extension angular velocity exceeded lever arm angular velocity over most of the range of motion, while during flexion this compliance meant that knee and lever arm angles were not always identical, particularly at the start of motion. Nevertheless, the Biodex dynamometer was found to be both a valid and an accurate research tool; however, caution must be exercised when interpreting and ascribing torques and angular velocities to the limb producing motion.

Method and system for detecting the misfire of an internal combustion engine utilizing engine torque nonuniformity

Abstract: An improved method and system are provided for the detection of internal combustion engine misfires utilizing optimum signal processing. The method and system exploit a measurement of engine crankshaft angular velocity in conjunction with hybrid electronic signal processing. Once the angular velocity signal is conditioned to minimize the effects of random error and external disturbances, four alternate computationally efficient methods may be used to extract information pertaining to individual cylinder torque productions. Two of the methods employ extremal samples of the estimated torque or velocity waveform to obtain a random torque nonuniformity index or metric. The other two methods utilize a transformation into the frequency domain after the input data is first sampled and windowed to substantially lower probability of error. All of the methods provide an M-dimensional torque non-uniformity vector of individual cylinder performance for each individual engine cycle. A reference level for the nonuniformity index is derived for any given cylinder in any given cycle. This yields misfire detection at a relatively early time and is particularly suitable for transient engine operation.

Development of the Wake behind a Circular Cylinder Impulsively Started into Rotatory and Rectilinear Motion: Intermediate Rotation Rates

Abstract: The temporal development of two-dimensional viscous incompressible flow generated by a circular cylinder started impulsively into steady rotatory and rectilinear motion is studied by integration of a velocity/vorticity formulation of the governing equations, using an explicit finite-difference/pseudo-spectral technique and an implementation of the Biot-Savart law. Results are presented for a Reynolds number of 200 (based on the cylinder diameter 2a and the magnitude U of the rectilinear velocity) for several values of the angular/rectilinear speed ratio alpha = (omega x a)/U (where omega is the angular speed) up to 3.25. Several aspects of the kinematics and dynamics of the flow not considered earlier are discussed. For higher values of alpha, the results indicate that for Re = 200, vortex shedding does indeed occur for alpha = 3.25. The shedding process is; however, very different from that which gives rise to the usual Karman vortex street for alpha = 0. In particular, consecutive vortices shed by the body can be shed from the same side and be of the same sense, in contrast to the nonrotating case, in which mirror-image vortices of opposite sense are shed alternately on opposite sides of the body. The implications of the results are discussed in relation to the possibility of suppressing vortex shedding by open or closed-loop control of the rotation rate.

Estimation of 3D angular motion using gyroscopes and linear accelerometers

Abstract: The authors present a novel, real-time angular motion estimation technique using a linear Gaussian estimator, and the outputs of linear accelerometers and gyroscopes, to assess the actual angular velocity of a rigid body in three-dimensional (3D) space. The method obtains the covariances of the random actual 3D angular velocity, the angular velocity measurement, and the measurement noise from the time averages of the outputs of an array of nine linear accelerometers and the outputs of three orthogonal gyroscopes. These statistics are used by the estimator to calculate the angular velocity of the rigid body in 3D space. The multisensor technique performance is evaluated through a computer simulation. Results indicate that the method leads to more accurate angular velocity values than are obtained conventionally. >

A fast subspace algorithm for recovering rigid motion

Abstract: The image motion field for an observer moving through a static environment depends on the observer's translational and rotational velocities along with the distances to surface points. Given such a motion field as input the authors present a new algorithm for computing the observer's motion and the depth structure of the scene. The approach is a further development of sub-space methods. This class of methods involve splitting the equations describing the motion field into separate equations for the observer's translational direction, the rotational velocity and the relative depths. The resulting equations can then be solved successively, beginning with the equations for the translational direction. The authors show how this first step can be simplified considerably. The consequence is that the observer's velocity and the relative depths to points in the scene can all be recovered by successively solving three linear problems. >

Piezoelectric beams and vibrating angular rate sensors

Abstract: A tuning fork angular rate sensor made out of a single piece of quartz has been studied. The piezoelectric effect is used both to excite a reference vibration in the plane of the tuning fork and to detect a vibration normal to this plane. The amplitude of the second vibration is directly proportional to the applied angular velocity. The structure is made rigid in order for it to survive in a harsh environment. This implies that the only vibrationally active areas are the tines of the tuning fork. The performance of the sensor is predicted with the help of a phenomenological piezoelectric beam theory. This theory shows that it suffices to study the two-dimensional (2-D) dielectric field in the cross-sections of the beams in order to obtain the values of the piezoelectric equivalent components. Estimates of these values can be obtained without the use of special computer programs. The predictions are shown to be in agreement with measurements. >

Image blur correcting apparatus

Abstract: An image blur correcting apparatus includes a lens-barrel part having a lens and an imaging device, an image signal processing device for forming a video signal from an electrical signal obtained at the imaging device, a supporting body for supporting the lens-barrel part in a freely pivoting manner around a rotation axis crossing a beam axis incident to the lens-barrel part at approximately right angles, and an actuator device attached between the lens-barrel part and the supporting body for rotating the lens-barrel part. The apparatus further includes a relative angle detecting device for detecting a relative angle between the lens-barrel part and the supporting body and a device for detecting a moving vector indicating an amount of blur of the image from correlation between two frames of image information from the image signal processing means, which are continuous in view of time. Finally, the device includes an angular velocity accumulating device for calculating rotating angular velocity using a zoom multiplying factor or the like from the detected result of the moving vector.

Improving the velocity sensing resolution of pulse encoders by FIR prediction

Abstract: An FIR (finite impulse response) predictor based approach is presented to increase the highest possible velocity sampling rate of a cycle-length measuring based velocity feedback system. The proposed method improves the slow-speed characteristics of optical pulse encoders in applications where the angular velocities down to about 0.5 RPM are of interest. The proposed principle works well in elevator control applications where the approximate shape of the low-speed curve is a second order polynomial. However, the same principle with an appropriate set of predictor coefficients can be applied to more general velocity sensing applications, as well. >

Stabilizing and destabilizing effects of a solid‐body rotation on quasi‐two‐dimensional shear layers

Abstract: The effect of a solid‐body rotation, characterized by an angular velocity Ω, on a two‐dimensional mixing layer (in a plane perpendicular to Ω) of relative vorticity ω2D, upon which is superposed a small three‐dimensional turbulent perturbation, is considered. Using the Kelvin theorem in the frame rotating with Ω, and with the aid of arguments based on the straining of absolute vortex filaments by the basic velocity, it is shown that the rotation is always stabilizing (with respect to the nonrotating case) in the cyclonic case. In the anticyclonic case, a slight rotation is destabilizing. At a local Rossby number R0=‖ω2D‖/2‖Ω‖ of the order of 1, the anticyclonic rotation disrupts catastrophically the coherent structures of the mixing layer. Anticyclonic rotation becomes stabilizing again for R0<0.5. Also presented are three‐dimensional numerical simulations which support the theory, and agree qualitatively with experimental results. The consequences for oceanic and atmospheric vortices are briefly discussed.

Apparatus for estimating current heading using magnetic and angular velocity sensors

Abstract: A heading detecting apparatus for estimating a current heading of a moving body is described that individually analyzes and evaluates error factors that are respectively included in the heading data of a magnetic sensor and in the angular velocity data of a turning angular velocity sensor (e.g., optical fiber gyro, mechanical gyro, vibration gyro, gas rate gyro) and determines the rate of use of the output data of the turning angular velocity and magnetic sensors.

Offset correction apparatus of turning angular velocity sensor

Abstract: An offset correction apparatus comprising a turning angular velocity sensor, a vehicle speed sensor for outputting a pulsed signal every constant distance traveled by a vehicle, a stop determining unit for determining that the vehicle is at a stop, an offset calculation unit for integrating an output of the turning angular velocity sensor during a period of time that the stop of the vehicle is determined by the stop determining unit and then calculating an offset value of the output of the turning angular velocity sensor, a storage unit to store the offset value calculated by the offset calculation unit, and a heading correction unit for correcting heading data obtained from the output of the turning angular velocity sensor, with the offset value, wherein when the pulsed signal from the vehicle speed sensor disappears and the output from the turning angular velocity sensor is less than a threshold, the stop determining unit determines that the vehicle is at a stop.

On the rotation vector differential equation

Abstract: A direct and simple derivation of the differential equation of the rotation vector is provided. The property that the time derivative of the rotation vector and the angular velocity have equal magnitude along the direction of the rotation vector is also derived. >

Visual processing of rotary motion.

Abstract: Local descriptions of velocity fields (e.g., rotation, divergence, and deformation) contain a wealth of information for form perception and ego motion. In spite of this, human psychophysical performance in estimating these entities has not yet been thoroughly examined. In this paper, we report on the visual discrimination of rotary motion. A sequence of image frames is used to elicit an apparent rotation of an annulus, composed of dots in the frontoparallel plane, around a fixation spot at the center of the annulus. Differential angular velocity thresholds are measured as a function of the angular velocity, the diameter of the annulus, the number of dots, the display time per frame, and the number of frames. The results show a U-shaped dependence of angular velocity discrimination on spatial scale, with minimal Weber fractions of 7%. Experiments with a scatter in the distance of the individual dots to the center of rotation demonstrate th-at angular velocity cannot be assessed directly; perceived angular velocity depends strongly on the distance of the dots relative to the center of rotation. We suggest that the estimation of rotary motion is mediated by local estimations of linear velocity.

Solar differential rotation determined by polar crown filaments

Abstract: The rotation rates obtained by tracing 124 polar crown filaments are presented in comparison with previous results. Higher filament rotation rate in polar regions was detected and discussed in terms of the various phenomena such as: the projection effect due to the height of measured tracers, the connection of polar filaments with the magnetic field patterns which show an increase of the rotation rate at high latitudes, rigid rotation of polar filaments which form pivot points, and eventual change of the differential rotation law during the cycle. However, when the height correction for an average height of 1% of the solar radius is applied, the filament rotation rate in polar regions decreases. Then the rotation law becomes: Ω(φ) = 14.45 − 0.11 sin2 φ − 3.69 sin4 φ (° day−1, sidereal).

Rocking response of rectangular rigid blocks under random noise base excitations

Abstract: The response of a rigid rectangular block resting on a rigid foundation and acted upon simultaneously by a horizontal and a vertical random white-noise excitation is considered. In the equation of motion, the energy dissipation is modeled through a viscous damping term. Under the assumption that the body does not topple, the steady-state joint probability density function of the rotation and the rotational velocity is obtained using the Fokker-Planck equation approach. Closed form solution is obtained for a specific combination of system parameters. A more general but approximate solution to the joint probability density function based on the method of equivalent non-linearization is also presented. Further, the problem of overturning of the block is approached in the framework of the diffusion methods for first passage failure studies. The overturning of the block is deemed incipient when the response trajectories in the phase plane cross the separatrix of the conservative unforced system. Expressions for the moments of first passage time are obtained via a series solution to the governing generalized Pontriagin-Vitt equations. Numerical results illustra- tive of the theoretical solutions are presented and their validity is examined through limited amount of digital simulations.

Spatial orientation of VOR to combined vestibular stimuli in squirrel monkeys.

Abstract: The interaction of angular and linear stimuli produces a complex alignment of spatial orientation and the VOR. This phenomenon was studied by measuring three dimensional eye movements in 6 squirrel monkeys during centrifugation in the dark. The axis of eye rotation was always aligned with gravity and with the spinal axis of the upright monkeys. The erect monkeys were oriented such that they were either facing toward the direction of motion or were facing away from the motion. Angular velocity trapezoids were utilized as the motion stimuli with a ramp acceleration of 10°/s2 to a constant velocity of 200°/s. This yields a final centripetal acceleration of 1 g. The orientation of centripetal acceleration dramatically altered the VOR by changing the axis of eye rotation, the peak value of slow phase eye velocity, and the time constant of per-rotary decay. The axis of eye rotation always tended to align with gravito-inertial force, the peak value of slow phase eye velocity was greater when the monkey faced the...

Rotation of ultrasonically levitated glycerol drops

Abstract: Ultrasonic levitation is used to suspend single millimeter‐size glycerol drops in a rectangular chamber. Audio‐frequency laterally standing waves set up in the chamber are used to torque the suspended drops. The shape evolution of the drop under the combined effect of centrifugal forces and the acoustic radiation stress, along with its angular velocity are monitored, using video imaging and light scattering techniques. The results show good qualitative agreement with the theoretically predicted shape evolution as a function of angular velocity.

Vehicle control apparatus

Abstract: The invention relates to a vehicle control apparatus for controlling the posture of the vehicle by changing the damping force of the shock absorbers so as to obtain improved driving stability and riding comfort, and/or by changing the steering ratio of the rear wheels of the vehicle in relation to the front wheels in response to the driving condition of the vehicle. The vehicle behaviour during driving is correctly analyzed by computation and map-retrieval from the output signal of an angular velocity sensor. The vehicle control apparatus can correctly compensate the output signal, which has errors caused by secular change, temperature change, etc., by using a zero-point calculation means for calculating a zero-point signal and an angular velocity correction means for correcting the output signal of the angular velocity sensor.

Egomotion from global flow field data

Abstract: The author presents two independent, global algorithms to compute the motion parameters. The flow circulation algorithm fits a linear surface to the curl of the flow field. The parameters of this linear surface are proportional to the angular velocity components. The author shows that instead of the curl values one can use circulation values that are simply contour integrals of the flow field on the image plane. The FOE (focus of expansion) location algorithm computes a certain circular components of the flow field that is a quadratic polynomial only when the correct FOE is used in the computation of the circular component. The author uses this observation to provide a method to determine the location of the FOE. Experimental results are presented. >

Dynamic behavior of fluttering two-dimensional panels on an airplanein pull-up maneuver

Abstract: The governing equations, derived using Lagrangian mechanics, include geometric nonlinearities associated with the occurrence of tensile stresses, as well as coupling between the angular velocity of the maneuver and the elastic degrees of freedom. Longtime histories, phase plane plots, and power spectra of the response are the dynamics tools used in studying the system considered here. The effect of the maneuver on the flutter speed and on the amplitude of the limit cycle are presented for different load conditions. A new type of limit cycle has been observed for the nonmaneuvering case. It is also shown that the presence of a maneuver can transform the panel response from a fixed point into a simple periodic or even chaotic state. It can also suppress the periodic character of the motion, transforming the response into a fixed point. For a prescribed time-dependent maneuver, a remarkable response transition between the different types of limit cycles is presented.

On reorienting linked rigid bodies using internal motions

Abstract: Kinematic algorithms are provided for reorienting some systems of linked rigid bodies floating in space. Since they are floating in space, they conserve both angular and linear momentum. The conservation of linear momentum is an integrable constraint; the conservation of angular momentum is not. The authors dualize the angular momentum constraint so that the problem of reorientation can be viewed as a steering problem for a drift-free control system which obeys these constraints. Explicit solutions via an algorithm are given for several sample systems. A hardware demonstration is also presented. >

Control of rotation velocity profile of tokamaks by application of slow electromagnetic waves

Abstract: Transport of a tokamak plasma may depend sensitively on its rotation velocity profile. Therefore a means for controlling the rotation profile may be useful. The paper describes a study of utilizing rotating islands, established deliberately by currents in external coils, as ‘‘stirrers’’ of the plasma and thereby influence the velocity profile. One of the main issues of the study is how large a stirring force rotating islands can provide. It is suggested that even relatively narrow islands can provide substantial stirring forces.

Angular velocities of sunspot-groups and solar photospheric rotation

Abstract: From an analysis of the Greenwich Photoheliographic Results sunspot-groups data from 1874 to 1976, it has been evidenced that the sunspot-groups angular velocity is not invariant with time during the first 2.5 1O 6 s of their life, showing a non-random negative acceleration. More precisely, 2 days old sunspot-groups have, at all the latitude strips, angular velocities which are on average, 0.3 degrees/day higher than reccurent sunspot. Moreover, the angular velocity difference between sunspot-groups of ages less than 8.6 10 5 s and reccurent sunspots decreases with time, and after 2 rotations, the angular velocity is almost equal to the plasma veloccity. The problem of the determination of the solar photospheric rotation is re-examined.