Showing papers on "Acceleration published in 1993"

Kinodynamic motion planning

Abstract: Kinodynamic planning attempts to solve a robot motion problem subject to simultaneous kinematic and dynamics constraints. In the general problem, given a robot system, we must find a minimal-time trajectory that goes from a start position and velocity to a goal position and velocity while avoiding obstacles by a safety margin and respecting constraints on velocity and acceleration. We consider the simplified case of a point mass under Newtonian mechanics, together with velocity and acceleration bounds. The point must be flown from a start to a goal, amidst polyhedral obstacles in 2D or 3D. Although exact solutions to this problem are not known, we provide the first provably good approximation algorithm, and show that it runs in polynomial time

Acceleration of the frame algorithm

Abstract: Shows how polynomial acceleration techniques which have been developed for the solution of large linear systems can be employed to improve and accelerate the frame algorithm. These methods permit a reduction in the number of necessary iterations by an order of magnitude when the frame algorithm is slow. The author gives several examples from the theory of irregular sampling, from wavelet theory and from Gabor theory where these methods are probably mandatory for efficient reconstruction. >

Ion Acceleration and Abundance Enhancements by Electron Beam Instabilities in Impulsive Solar Flares

Abstract: We show that a nonrelativistic electron beam in a hydrogen-helium solar flare plasma will excite H(+) electromagnetic ion cyclotron, shear Alfven, and R-X waves, in addition to waves resulting from the two-stream instability. The H(+) electromagnetic ion cyclotron and shear Alfven waves are able to selectively accelerate ambient He-3 and Fe, respectively, to MeV energies through first harmonic gyroresonance, and thereby account for the large (He-3)/(He-4) and Fe/C ratios seen in the energetic particles from impulsive solar flares. In this model, separate heating and acceleration mechanisms for either He-3 or Fe are not required, and Fe acceleration is quite efficient since it does not need to occur by second harmonic gyroresonance. The combination of the other two unstable modes is able to accelerate ions to hundreds of MeV if the particles become trapped in an electrostatic potential well of a two-stream wave.

Dynamic control of 3-D rolling contacts in two-arm manipulation

Abstract: When two or more arms are used to manipulate a large object, it is preferable not to have a rigid grasp in order to gain more dexterity in manipulation. It may therefore be necessary to control contact motion between the object and the effector(s) on one or more arms. This paper addresses the dynamic control of two arms cooperatively manipulating a large object with rolling contacts. In the framework presented here, the motion of the object as well as the loci of the contact point either on the surface of each effector or on the object can be directly controlled. The velocity and acceleration equations for three-dimensional rolling contacts are derived in order to obtain a dynamic model of the system. A nonlinear feedback control algorithm that decouples and linearizes the system is developed. This is used to demonstrate the control of rolling motion along each arm and the adaptation of grasps to varying loads.

Coordinate detecting apparatus having acceleration detectors

Abstract: A coordinate input device includes a coordinate detector which may include an acceleration detector for accurate determination of the spatial coordinates of a coordinate indicator. A three-dimensional acceleration in a first coordinate system is detected by a first acceleration detecting unit and is converted into an input coordinate system in accordance with the attitude of the coordinate indicator. The effect of gravity is removed and the acceleration is integrated to obtain the spatial coordinates of the coordinate indicator. Even if the coordinate indicator is tilted, accurate coordinate input can be performed.

Enhanced acceleration in a self-modulated-laser wake-field accelerator

Abstract: An alternative configuration of the laser wake-field accelerator is proposed in which enhanced acceleration is achieved via resonant self-modulation of the laser pulse. This requires laser power in excess of the critical power for relativistic guiding and a plasma wavelength short compared to the laser pulse length. Relativistic and density wake effects strongly modulate the laser pulse at the plasma wavelength, resonantly exciting the plasma wave and leading to enhanced acceleration.

Control of Sliding‐Isolated Bridge with Absolute Acceleration Feedback

Abstract: This paper presents an experimental and analytical study of hybrid control of bridges using sliding bearings, with recentering springs, in parallel with servohydraulic actuators. A new control algorithm with absolute acceleration feedback, based on instantaneous optimal control laws, is developed. The developed control algorithm is implemented in a shake-table study of an actively controlled sliding-isolated bridge. The objective of implementing the hybrid system is to evaluate its advantages in addition to those due to the passive sliding system. The experimental system used in the shake-table test is described and the results of the experiments are presented. It is shown that substantial reduction of response acceleration is possible, using hybrid control, while confining the sliding displacement within an acceptable range, and eliminating almost completely postearthquake permanent offsets. Comparisons of the results of hybrid system with results of passive system are presented. The advantages of hybrid control, in addition to those due to passive control, are discussed.

Particle acceleration in reconnecting current sheets

Abstract: We study motions of charged particles in reconnecting current sheets (CS) which have both transverse (perpendicular to the current sheet plane) and longitudinal (parallel to the electric current inside the sheet) components of the magnetic field. Such CS, called non-neutral, are formed in regions of magnetic field line reconnection in the solar atmosphere. We develop an analytical technique which allows us to reproduce previous results concerning the influence of transverse fields on particle motion and acceleration. This technique also allows us to evaluate the effect of the longitudinal field. The latter increases considerably the efficiency of particle acceleration in CS. The energizing of electrons during the main phase of solar flares can be interpreted as their acceleration in non-neutral CS.

Disk drive and method for minimizing shock-induced damage

Abstract: A disk drive has a fall detection control system that detects when a disk drive is in a free fall, and takes precautionary protective action to minimize physical damage from any resulting shock upon impact. The disk drive includes an accelerometer device that measures acceleration of the disk drive along three mutually orthogonal axes x, y, and z and resolves the measurement into respective vectors a x , a y , and a z . In one embodiment, a processor is programmed to (1) compute a net acceleration a net of the disk drive, (2) compare the net acceleration a net with the selected acceleration threshold level, (3) measure a duration that the net acceleration a net exceeds the acceleration threshold level, (4) compare the measured duration with a selected reference time period, and (5) output the warning signal when the measured duration exceeds the reference time period. Upon receipt of the warning signal, a controller initiates protective routines in preparation for shock.

Performance of a butterfly in take-off flight

Abstract: The flight of a butterfly, Pieris melete, was observed in the take-off phase and was analyzed theoretically from aerodynamic and kinetic viewpoints. A vortex method, which was recently developed by the present authors, was used in this analysis. During the downstroke, the butterfly generates mainly a vertical force. The acceleration of the butterfly9s body during the first half of the downstroke is especially large, and this acceleration is mainly caused by a large unsteady pressure drag acting on the wings. This large unsteady pressure drag is generated by the vortices shed into the flow from the outer edges of each wing of a pair; it is increased by the interference effect between a pair of wings when the opening angle is small. This force can be estimated by the previous quasi-steady analysis when the force coefficient is changed to 4. In addition to the unsteady pressure drag, an aerodynamic force due to added mass is generated and this is also increased by the interference effect between a pair of wings. During the upstroke the butterfly generates mainly a horizontal force. The change of direction of the forces during the down- and upstrokes is controlled by variation in the inclination of the stroke plane. The moment, which is created by the aerodynamic force acting on the wings and by abdominal motion, changes the thoracic angle, that is the inclination of the stroke plane.

Basic consideration of vibration suppression and disturbance rejection control of n-inertia system using SFLAC (state feedback and load acceleration control)

Abstract: SFLAC (state feedback and load acceleration control) is proposed for vibration suppression and disturbance rejection control of n-inertia system. An n-inertia system is a model of a steel rolling mill, flexible arm, large scale space structure, etc., and its control will be an important problem in the future motion control. The main idea of SFLAC is to control the load acceleration which can be estimated by the state observer including the disturbance estimation. A simple PI speed controllers and SFLAC based on the reduction models using 2 and 3 inertia moments are designed. The effectiveness of SFLAC is demonstrated showing some simulation results. >

Vibration control of a two-link flexible robot arm

Abstract: Analysis and experimentation is described for a two-link apparatus in which both members are very flexible. Attention is focused on endpoint position control for point-to-point movements, assuming a fixed reference frame for the base, with two rotary joints. Each link is instrumented with acceleration sensing and is driven by a separate motor equipped with velocity and position sensing. The control perspective adopted is to implement a two-stage control strategy in which the vibration control problem for fine-motion endpoint positioning is considered separate from the gross-motion, large-angle slew problem. In the first stage the control law shapes the actuator inputsfor the large-angle movement in such a way that minimal energy is injected into the flexible modes, while in the second phase an endpoint acceleration feedback scheme is employed in independent joint controlfor vibration suppression at the link endpoints.

Ground Motion Model for the 1989 M 6.9 Loma Prieta Earthquake Including Effects of Source, Path, and Site

Abstract: The objective of this study is to assess the effects of source finiteness, crustal wave propagation, and site response upon recorded strong ground motions from the 1989 Loma Prieta earthquake. Our analysis uses band limited white noise (BLWN) with random vibration theory (RVT) to produce site‐specific estimates of peak acceleration and response spectral ordinates for both a point‐source and finite‐source model. Effects of nonlinear soil response are modeled through an equivalent‐linear approach. The point‐source model additionally accommodates crustal propagation effects in terms of direct‐plus‐postcritical reflections.

Orthogonal acceleration — a new direction for time-of-flight mass spectrometry: Fast, sensitive mass analysis for continuous ion sources

Abstract: The current renaissance of time-of-flight mass spectrometry involves mainly pulsed laser ion sources. In the mainstream of mass spectrometry where continuous ion sources are used, problems arising from dispersions in ion initial location, velocity and time, have hindered exploitation of the advantages of time-of-flight. Orthogonal acceleration is a method which overcomes these problems for most continuous ion sources and provides greater resolution and sensitivity than quadrupole or single-sector magnetic scanning analysers.

Crash/non-crash discrimination using frequency components of acceleration uniquely generated upon crash impact

Abstract: In a crash detection apparatus, the output signal of an accelerometer is integrated at intervals and a velocity signal is produced. Those frequency components of the accelerometer output which appear uniquely during a vehicle crash are extracted and their amplitude is squared to produce an impact energy signal. An airbag is operated when the velocity signal exceeds a first threshold, or when a sum of the velocity and impact energy signals exceeds a second threshold, or operated when the impact energy signal exceeds a third threshold. In a modified embodiment, the accelerometer output is integrated both at longer and shorter intervals to produce a long-term and a short-term velocity signal. The airbag is operated when the long-term velocity signal exceeds a first threshold, or when the short-term velocity signal and the impact energy signal simultaneously exceed a second and a third threshold, respectively.

Ion injection and acceleration at parallel shocks : comparisons of self-consistent plasma simulations with existing theories

Abstract: We present a simulation study of particle acceleration by parallel collisionless shocks and compare our results with existing shock acceleration theories, in particular, diffusive and shock drift acceleration. We extend the earlier work in this field by drawing attention to the similarities and discrepancies between the results obtained from the more realistic, self-consistent simulations and these well-established theories

Design and performance of Sandia's contactless coilgun for 50 mm projectiles

Abstract: A multistage, contactless coilgun is being designed to demonstrate the applicability of this technology to accelerate nominal 50-mm-diameter projectiles to velocities of 3 km/s. Forty stages of this design (Phase 1 coilgun) will provide a testbed for coil designs and system components while accelerating 200 to 400 g projectiles to 1 km/s. The Phase 1 gun was successfully qualified by operating 40 stages at half energy (10-kJ stored/stage) accelerating 340 g, room-temperature, aluminum-armature projectiles to 406 m/s. The design and performance of the Phase 1 coilgun, coil development, projectile design, capacitor banks, firing system, and integration are discussed. >

Driving force controller for an electric vehicle with electric motors provided for all driving wheels individually

Abstract: A driving force controller for an electric vehicle calculates the optimal driving force of each driving wheel based on a formula in response to the detected wheel acceleration and the difference between the wheel speed and the vehicle speed, or alternatively calculates the optimal driving force of each driving wheel based on fuzzy theory by using predetermined membership functions pertinent to the wheel acceleration, speed difference and driving force in response to the detected wheel acceleration and speed difference. The driving force controller thereby controls the driving force of the driving wheel in accordance with the calculated driving force, and prevents slipping of the driving wheel.

Constant speed traveling apparatus for vehicle with inter-vehicle distance adjustment function

Abstract: An apparatus includes an inter-vehicle distance sensor for measuring a distance from a self vehicle to a vehicle traveling ahead, and a relative speed is calculated on the basis of the inter-vehicle distance data detected by the inter-vehicle distance sensor. When a variation of the relative speed is small, it is recognized that a vehicle is present ahead of the self vehicle. An acceleration/deceleration is obtained from a stored acceleration/deceleration basic map on the basis of a difference between the inter-vehicle distance and a target inter-vehicle distance, and the relative speed with the vehicle ahead, and an acceleration/deceleration correction coefficient is calculated from a correction map set with adjustment constants in correspondence with the measured inter-vehicle distance. An acceleration/deceleration is calculated by multiplying the acceleration/deceleration with the correction coefficient. A new target vehicle speed is calculated on the basis of the calculated acceleration/deceleration, and a previously set target vehicle speed.

Method and device for generating an input command for a motion control system

Abstract: A method and device of achieving motion cycle time reduction that takes motor capabilities, load inertia and gravity into account and, at the same time, produces acceptable tool tip vibration upon stopping. This cycle time reduction is especially applicable to short motions of a robot where the entire motion consists of acceleration and deceleration and there is no constant velocity region. The method and device provide open loop limiting factors for axis jerk, acceleration and velocity, taking into account robot position, payload and inertia.

Optimum damping in linear isolation systems

Abstract: Optimum isolation damping for minimum acceleration response of base-isolated structures subjected to stationary random excitation is investigated. Three linear models are considered to account for the energy dissipation mechanism of the isolation system: a Kelvin element, a linear hysteretic element and a standard solid linear element, commonly used viscoelastic models for isolation systems comprising natural rubber bearings and viscous dampers. The criterion selected for optimality is the minimization of the mean-square floor acceleration response. The effects of the frequency content of the excitation and superstructure properties on the optimum damping and on the mean-square acceleration response are addressed. The study basically shows that the attainable reduction in the floor acceleration largely depends on the energy dissipation mechanism assumed for the isolation system as well as on the frequency content of the ground acceleration process. Special care should be taken in accurately modelling the mechanical behaviour of the energy dissipation devices.

Tunnel effect wave energy detection

Abstract: Methods and apparatus for measuring gravitational and inertial forces, magnetic fields, or wave or radiant energy acting on an object or fluid in space provide an electric tunneling current through a gap between an electrode and that object or fluid in space and vary that gap with any selected one of such forces, magnetic fields, or wave or radiant energy acting on that object or fluid. These methods and apparatus sense a corresponding variation in an electric property of that gap and determine the latter force, magnetic fields, or wave or radiant energy in response to that corresponding variation, and thereby sense or measure such parameters as acceleration, position, particle mass, velocity, magnetic field strength, presence or direction, or wave or radiant energy intensity, presence or direction.

Study of the parametric oscillator driven by narrow‐band noise to model the response of a fluid surface to time‐dependent accelerations

Abstract: A stochastic formulation is introduced to study the large amplitude and high‐frequency components of residual accelerations found in a typical microgravity environment (or g‐jitter). The linear response of a fluid surface to such residual accelerations is discussed in detail. The analysis of the stability of a free fluid surface can be reduced in the underdamped limit to studying the equation of the parametric harmonic oscillator for each of the Fourier components of the surface displacement. A narrow‐band noise is introduced to describe a realistic spectrum of accelerations, that interpolates between white noise and monochromatic noise. Analytic results for the stability of the second moments of the stochastic parametric oscillator are presented in the limits of low‐frequency oscillations, and near the region of subharmonic parametric resonance. Based upon simple physical considerations, an explicit form of the stability boundary valid for arbitrary frequencies is proposed, which interpolates smoothly between the low frequency and the near resonance limits with no adjustable parameter, and extrapolates to higher frequencies. A second‐order numerical algorithm has also been implemented to simulate the parametric stochastic oscillator driven with narrow‐band noise. The simulations are in excellent agreement with our theoretical predictions for a very wide range of noise parameters. The validity of previous approximate theories for the particular case of Ornstein–Uhlenbeck noise is also checked numerically. Finally, the results obtained are applied to typical microgravity conditions to determine the characteristic wavelength for instability of a fluid surface as a function of the intensity of residual acceleration and its spectral width.

Apparatus for controlling vehicle driving power

Abstract: An engine controller includes a accelerator stroke detector, vehicle speed and vehicle acceleration sensors, first and second model learning units and a drive control unit. The first model learning unit constructs a vehicle acceleration model that exhibits and updates vehicle acceleration characteristics as required by a driver. The first unit includes a first learning program for updating acceleration model, and generates a first output (Gx) in response to the detected accelerator stroke and vehicle speed according to the first program. The first unit calculates a deviation (ΔG) between the detected vehicle acceleration (G) and the first output (Gx), and modifies the first output (Gx) to decrease the deviation (ΔG) to provide an updated acceleration model as required by the driver. The second model learning unit is for constructing a sensitivity model used to regulate the opening angle of an engine throttle valve. The second unit includes a second learning program for updating the sensitivity model and generating a second output (Thx) in response to the detected accelerator stroke and vehicle speed. As a consequence, the output (Thx) is modified to decrease the deviation (ΔG) which provides for an update to the sensitivity model. The drive control unit controls the throttle angle referring to a target value determined on the basis of the second output (Thx).

Band limited control of a flexible structure using piecewise trigonometric input signals

Abstract: A method and apparatus for moving a member provides parameters related to a given destination position of the member and corresponding to a switch time, a final time, an acceleration amplitude, and a deceleration amplitude. These parameters are used to specify a piecewise continuous function of time as an input signal. The input signal feeds a motor to move the member. The final time, switch time, acceleration amplitude, and deceleration amplitude are specified by iteratively providing minimal values for the switch time and final time while providing maximum acceptable values for the acceleration amplitude and deceleration amplitude for each possible given change in a characteristic of the movable member. A pre-shaped input signal is thereby provided which is bandwidth limited such that its energy is concentrated below the frequency of the lowest system resonance, since the signal is a piecewise continuous function comprising concatenated raised cosine and constant functions. The input signal may be asymmetrical and may have acceleration and deceleration amplitudes which differ in magnitude, and thus is useful in systems where it is desirable to the limit frequency content of an input signal while compensating for the effects of back EMF voltage. Since only four parameters are needed to specify the input signal, the signal is easy to construct, and it thus practical for use in high density disk drive applications.

System and method for diagnosing characteristics of acceleration sensor

Abstract: An apparatus for diagnosing the characteristic of an acceleration sensor and a method for diagnosis thereof are disclosed. The acceleration sensor includes a movable electrode (or mass part) displaced in accordance with an acceleration and a fixed electrode disposed opposite to the movable electrode. In a diagnosis mode, a signal for diagnosis is applied to the fixed electrode so that an electrostatic force as a force corresponding to a predetermined acceleration is generated between the fixed electrode and the movable electrode. In the case where the acceleration sensor is sound, the movable electrode or mass part is normally displaced. A failure of the acceleration sensor, the deterioration thereof in performance, a change in characteristic thereof caused from the lapse of time, or the like is self-diagnosed by detecting a change in capacitance between the movable electrode and the fixed electrode upon generation of the diagnosis signal. The force corresponding to the predetermined acceleration may be an electromagnetic force or a mechanical oscillation based on a piezoelectric element.

A lifetime projection method using series model and acceleration factors for TDDB failures of thin gate oxides

Abstract: The series model combined with the Weibull distribution is shown to be suitable for characterizing time-dependent dielectric breakdown (TDDB) failures and for projecting the failure rate under normal operating conditions. The validity of existing models for acceleration factors is examined through long-term lifetests with a wide range of stress fields for 11-nm oxides. The resulting curve is found to estimate field acceleration more accurately for lower field regions. The activation energy is also essentially independent of oxide field for thin and near-defect-free oxides. >