Showing papers on "Rotational speed published in 1998"

Compressor Surge and Rotating Stall: Modeling and Control

Abstract: This work gives a comprehensive overview of the achievements in the field of modelling and active control of instabilities in compressions systems over the last decade. Existing models of unstable compression systems are in most cases restricted to constant speed compressors. Here, two models are derived that take time varying rotational speed into account - one for centrifugal compressors and one for axial compressors. The main focus of the modeling element is the inclusion of non-constant speed in existing dynamic models of unstable compression systems, and the study of surge and rotating stall in connection with this. The focus of the control element is the use of a close coupled valve as a means of stabilising surge and rotating stall. Little work has yet been published on this.

Plant control system

Abstract: A plant control system using response specifying control that makes it possible to independently set a follow-up behavior for an output value of a plant when a target output value of the plant changes and a convergent behavior for a difference between a target output value and an output value when the output value of the plant changes. The control system has a controller for determining a clutch stroke on the basis of a model equation of a clutch device such that a target rotational speed and an actual rotational speed of the clutch device coincide with each other. The controller includes a target value filter for carrying out filtering computation on a target rotational speed to calculate a filtering target value that converges to the target rotational speed with a response delay, and a response specifying control unit that determines the clutch stroke by response specifying control such that the filtering target value and the clutch rotational speed coincide with each other.

Control strategy for variable-speed, stall-regulated wind turbines

Abstract: A variable-speed, constant-pitch wind turbine was investigated to evaluate the feasibility of constraining its rotor speed and power output without the benefit of active aerodynamic control devices. A strategy was postulated to control rotational speed by specifying the demanded generator torque. By controlling rotor speed in relation to wind speed, the aerodynamic power extracted by the blades from the wind was manipulated. Specifically, the blades were caused to stall in high winds. In low and moderate winds, the demanded generator torque and the resulting rotor speed were controlled to cause the wind turbine to operate near maximum efficiency. A computational model was developed, and simulations were conducted of operation in high turbulent winds. Results indicated that rotor speed and power output were well regulated.

Disk reproducing device

Abstract: PURPOSE: To improve an accessing speed at a reproducing time by controlling a disk recorded at a constant linear velocity to a constant angular velocity and changing a reference clock frequency corresponding to the transmission speed of a digital regenerative signal. CONSTITUTION: The rotation of a motor 2 is controlled so as to be a constant angular velocity with a rotational speed detection signal S1 from the motor 2 by a motor control circuit. Further, an error signal S2 is supplied to a control circuit 6 after a signal from an optical pickup 4 is amplified by a preamplifier 7 and a regenerative signal is supplied to a clock reproducing circuit 8 and the clock of a transmission speed frequency synchronizing with the regenerative signal is generated and outputted to a signal processing circuit 9. The code data of the regenerative signal is detected in the processing circuit 9 and sent to a micro computer 10 and a moving amount till a reproducing position is operated based on an access instruction and access operation is instructed to the control circuit. Thus, the motor is rotated at a constant angular velocity and a motor control time for making a constant linear velocity is eliminated and a reproduction accessing speed is improved. COPYRIGHT: (C)1993,JPO&Japio

Transient Thermal Response of a Rotating Cylindrical Silicon Nitride Workpiece Subjected to a Translating Laser Heat Source, Part I: Comparison of Surface Temperature Measurements With Theoretical Results

Abstract: Laser-assisted machining (LAM), in which the material is locally heated by an intense laser source prior to material removal, provides an alternative machining process with the potential to yield higher material removal rates, as well as improved control of workpiece properties and geometry, for difficult-to-machine materials such as structural ceramics. To assess the feasibility of the LAM process and to obtain an improved understanding of governing physical phenomena, a laser assisted machining facility was developed and used to experimentally investigate the thermal response of a rotating silicon nitride workpiece heated by a translating CO 2 laser. Using a focused laser pyrometer, surface temperature history measurements were made to determine the effect of rotational and translational speed, as well as the laser beam diameter and power, on thermal conditions. The experimental results are in good agreement with predictions based on a transient three-dimensiona numerical simulation of the heating process. With increasing workpiece rotational speed, temperatures in proximity to the laser spot decrease, while those at circumferential locations further removed from the laser increase. Near-laser temperatures decrease with increasing beam diameter, while energy deposition by the laser and, correspondingly, workpiece surface temperatures increase with decreasing laser translational speed and increasing laser power. In a companion paper (Rozzi et al., 1998), the detailed numerical model is used to further elucidate thermal conditions associated with laser heating and to assess the merit of a simple, analytical model which is better suited for on-line process control.

Dynamics of Spindle-Bearing Systems at High Speeds Including Cutting Load Effects

Abstract: Increased use of high speed machining creates the need to predict spindle-bearing performance at high speeds. Previous spindle-bearing models simplify either spindle or bearing dynamics to the extent of prohibiting a detailed analysis of a spindle with high speed motion. At high speeds, centrifugal loading in the bearing causes stiffness softening, creating a change in natural frequency. Therefore, spindle modeling requires a comprehensive representation of the dynamics of shafts with complex geometry rotating at high speeds and supported by non-linear bearings. This paper presents a coupled system of spindle and bearing dynamic models with numerical solution. Spindle dynamics are modeled using the influence coefficient method of discrete lumped masses, based on Timoshenko beam theory. Both linear and rotational bearing stiffness are included in the spindle model through solution of the angular-contact bearing model. The parameters of cutting loads, tool mass, and rotational speed are analyzed, and all are shown to affect the natural frequency. The computer model is both rapid and robust, and shows excellent agreement with experimental analysis.

Ultrasonic diagnostic device

Abstract: PROBLEM TO BE SOLVED: To improve a frame rate by controlling a rotation speed in one rotation in an ultrasonic diagnostic device for mechanically scanning an ultrasonic wave vibrator. SOLUTION: An ultrasonic wave probe 10 is a probe to be inserted to a blood vessel for instance and the ultrasonic wave vibrator 16 provided on the tip of a rotary wire 14 is rotationally scanned. The rotation speed is controlled by a rotation speed control part 24. The rotation speed control part 24 sets a low rotation speed in a part of a display area inside the entire rotation scanning range of an ultrasonic wave beam 100 and sets a high rotation speed in the other non-display area. Since the vibrator 16 is rotated at a high speed in a useless range for not performing imaging, the frame rate is improved.

Rolling contact bearing with rotational speed measuring device

Abstract: A rolling contact bearing with rotational speed measuring device, in particular a wheel bearing for motor vehicles for telemetric transmission of energy and signal between bearing and environment, insensitive to tolerances of the bearing and its surrounding parts, with simple and cost-effective construction and small dimensions. A first telemetry unit is integrated in the inter-ring seal. It comprises pulse transmitter, rotational speed sensor, telemetry electronics and a miniature coil, which is inductively coupled with a further telemetry unit, which is fitted axially outside the bearing, and which supplies the first telemetry unit with energy and receives its signals.

Disk drive with actuator load/unload controller

Abstract: A disk drive with means to prevent accidental landing of a head/slider on the disk surface is described. In one embodiment a shock sensor is provided to sense external shocks received by the mechanism. During loading (positioning) of the actuator bearing the head/slider over the disk, if a shock is sensed, loading is stopped and an immediate unloading is performed to return the actuator to the withdrawn position. In another embodiment the unload operation is performed when the rotational speed of the disk is changed. In another embodiment the unload operation is performed when the rotational speed of the disk drops below a threshold. A circuit and method for detecting when the rotational speed of the disk drops below a threshold is also provided. The unloading in the various embodiments may be performed using velocity control or without velocity control.

Acceleration sensing device

Abstract: An acceleration sensing device includes a rotational speed sensor which is mounted on a substrate and detects rotational speed, at least one oscillating structure with a deflectable seismic mass, and an acceleration sensor that detects linear acceleration and has at least one additional seismic mass which is suspended on flexible elements so that it can be deflected. The seismic masses of the two sensors are deflected independently of one another.

Wind speed estimation based variable speed wind power generation

Abstract: Significant variation of the resource kinetic energy, in the form of wind speed, results in a substantially reduced energy capture in a fixed speed wind turbine. In order to increase the wind energy capture in the turbine, variable speed generation (VSG) strategies have been proposed and implemented. Typically, VSG strategies vary the rotational speed of the turbine, by controlling either a mechanical or electrical parameter to maintain a constant tip-speed ratio of the turbine. This is known as a maximum power point tracking (MPPT) controller. Traditionally, the MPPT controller is based upon a simple, but slow, search or perturbation algorithm to determine the optimal rotational speed of operation. In this paper, a wind speed estimation-based MPPT algorithm is proposed that employs a heuristic model of both the turbine and the generator to estimate the wind speed. A local search/perturbation of the rotational speed is employed to attain fine tuning of the desired optimal tip-speed ratio tracking. While this algorithm is more complicated than the search based method, it can still be implemented inexpensively. The ease of implementation guarantees fast control updates and ensures maximum power point operation for all wind speeds within the design limitations. The controller has been verified for efficacy on a 1.5 kW laboratory VSG wind generator.

Non-volatile over speed control system for wind turbines

Abstract: A method and apparatus for non-volatile overspeed protection is described. The present invention provides a method and apparatus for non-volatile overspeed detection to provide turbine rotational speed safety during a power outage. In one embodiment, aerodynamic braking is used to slow rotation of a rotor of the wind turbine. If an overspeed condition continues after application of aerodynamic braking, mechanical braking is used to reduce the rotational speed of the rotor. Power is supplied by a non-volatile power source to continue overspeed detection during a power outage. A low-pressure trigger valve is used to apply a mechanical brake when hydraulic pressure in the braking system falls below a predetermined threshold.

Critical Speed for Floppy Disks

Abstract: This paper uses Lyapunov's method to determine the critical speed of a flexible spinning disk enclosed in a housing that hydrodynamically couples the transverse motion of the disk to the motion of the thin films of air surrounding the disk. Depending on the clamping ratio, this critical speed is three to ten times higher than the critical speed in the absence of hydrodynamic coupling and does not depend on the strength of the hydrodynamic coupling. Despite the nonlinearity of the underlying model, the critical speed problem is linear and tractable. The linearized free-vibration problem is also computed to verify the stability prediction and to examine linearized damping and stiffness as possible design criteria. The results are relevant to the design of both conventional computer floppy disks and the emerging generation of 100+ MB floppies.

Control device for brushless DC motor

Abstract: A control device controls operation of a brushless DC motor in such a way that the motor is started and accelerated up to a predetermined rotational speed by applying driving voltage formulated based on a synchronous signal under a startup-drive-mode and the driving mode is switched, after the predetermined rotational speed is established, to a self-controlled-drive-mode in which the driving voltage is formulated based on signals indicating an angular position of the rotor relative to the armature. In the transient period for switching-over from the start-up-drive to the self-controlled-drive, phase difference between the driving voltage and the rotor position signal is detected for a period covering more than one rotation of the rotor, the switching-over is carried out only when the phase difference is sufficiently small to avoid a motor stall or an excessive shock. Preferably, a pulse-width-modulated voltage is used as the driving voltage, so that the phase difference can be controlled by changing a duty ratio of the driving voltage.

Balancing device for use on washing machines

Abstract: A speed dependent response control balancing device of the present invention provides control of vibrations in a rotatable member such as a rotatable basket (10) of a washing machine. The balancing device (20) has two compartments including an annular ball race (22) and a reservoir (24). A plurality of balls (26) are positioned within the annular ball race (22) and move within the ball race to counteract the imbalance of the basket. A varying amount of viscous fluid (40) is delivered from the reservoir into the ball race depending on a rotational speed of the balancing device. Accordingly, the reaction or 'quickness' of the response of the balls within the ball race changes with the rotational speed of the balancing device to provide quick response during a start-up period and slower response at high rotational speeds.

Inhomogeneities in silicon carbide distribution in stirred liquids—a water model study for synthesis of composites

Abstract: An experimental study was conducted on the mixing quality of two-phase slurries in the model SiC–water system using a gravimetric technique with a view to determining the influence of impeller geometry and baffles on the uniformity of distribution of SiC in the mixture. A three-blade paddle with different blade angles and a variable-pitch blade impeller (A-3) were used for stirring the mixture at various rotational speeds. The results show that SiC concentration variation during stirring in the absence of baffles was 7.5 vol.%, whereas in the presence of four vertical baffles the concentration variation was reduced to 2 vol.%. The power consumption for homogeneous mixing varied between 17.5 and 175 W vol.−1 depending upon the type of impeller and its rotational speed. A semi-empirical correlation for obtaining uniform mixing has been developed based on the Reynolds number, the power number and the Froude number for stirred SiC–water slurries. The results on inhomogeneity of silicon carbide in water concentration during mixing are in close agreement with the modeling studies by previous workers on the water–SiC system, and with limited experimental studies on the real molten aluminum–SiC system used to cast metal–matrix composites.

Design, construction and characterization of a flightworthy piezoelectric solid state adaptive rotor

Abstract: The development of a new type of flightworthy adaptive rotor system is presented. By building upon earlier adaptive rotor work, a new miniature solid state adaptive rotor (SSAR) was built using directionally attached piezoelectric (DAP) torque-plates controlling Hiller servopaddles. These servopaddles change the rotor disk tilt and thereby induce changes in forces and moments for flight control. To demonstrate the concept, a 23.5 in diameter helicopter rotor was built using DAP servopaddles at the hub. The servopaddles were constructed from PZT-5H piezoceramic actuator sheets bonded symmetrically at . An aluminum substrate and a high temperature cure was used to provide precompression. Analytical modeling was accomplished by laminated plate theory along with strip theory aerodynamics and inertial relations. Because propeller moments are proportional to servopaddle deflections at a fixed rotational speed, it was possible to cancel them out by balancing an aeroelastic coupling between the center of mass, aerodynamic center and elastic axis. Bench testing of the SSAR showed that the rotor system could produce static servopaddle deflections in excess of with good agreement between theory and experiment. With the spinning rotor, the servopaddles demonstrated dynamic capability in excess of . As the rotor speed was increased, deviations between linear theory and experiment also increased. Nonetheless, the rotor still demonstrated servopaddle deflections at full rotor speed (1600 RPM). A detailed weight statement of the conventional and SSAR systems shows that the SSAR helicopter experienced a 40% reduction in flight control system weight, which resulted in an 8% cut in total aircraft gross weight, a 26% drop in parasite drag and a drop in flight control system part count from 94 components down to five.

Oil pressure supply device for vehicle drive system

Abstract: An engine and a motor are connected to the drive wheels of a vehicle via an automatic transmission. The drive wheels are driven using one of or both of the motor and the engine depending on the running state. The automatic transmission varies the drive ratio by the discharge pressure of the oil pressure pump. The oil pressure pump is driven by a second motor. When the automatic transmission is varying the drive ratio, the discharge of the oil pressure pump is increased by increasing the rotational speed of the second motor and thus the required oil for varying the drive ratio is maintained.

High-performance position detection and velocity adaptive measurement for closed-loop position control

Abstract: This paper presents a new solution for processing the pulses from an optical encoder attached to a motor shaft, and deriving the rotational speed information. An adaptive method allows the evaluation of the motor rotational speed with very good accuracy even at very low speeds. The adaptation also of the sampling period, according to the instant rotational speed, results in better response times at medium or high rotational speeds. The measurement accuracy at low speeds using the proposed method is improved, compared to currently known methods. Another significant advantage of using the proposed circuit is that it can be implemented in specific hardware, thus, reserving the full computational power of the controlling digital signal processor (DSP) for high-level control tasks and for future software expansions.

Electric power steering system

Abstract: PROBLEM TO BE SOLVED: To provide an electric power steering system capable of improving the feeling of steering without using any angle sensor. SOLUTION: In a system for driving an assist motor 40 by means of a motor driving command value obtained by adding a steering torque differential command value T2 decided by a first differentiator 24 to a basic assist current command value T1 decided by the output of a torque sensor 20 for detecting steering torque and the output of a car speed sensor 30 and then adding the assist torque to steering torque, a cogging frequency calculating means 52 is provided for calculating a cogging frequency by detecting the rotational speed of the assist motor 40, a center frequency variable type band-pass filter 53 is provided for detecting pulsation torque in a center frequency by coinciding the center frequency with the calculated frequency and a second differentiator is provided for differentiating its output and advancing its phase. Thus, a compensating current command value based on the output of the second differentiator is added to a motor driving command value.

Radially oriented motor for a fluid balance ring

Abstract: A radially mounted motor is provided in a closed system fluid balance ring for high rotational speed washing machines. The motor is mounted at an orientation of 90° relative to the rotational axis of the washing machine spinner. Such an orientation prevents adverse effects on the motor contacts from centrifugal forces generated by the rotating spinner. A 90° orientation also eliminates deflection of the motor shaft and excessive friction on the motor bearings. The angular orientation of the motor assures proper functioning of the closed system fluid balance ring of the washing machine. The balance system also includes a valve to control movement of fluid within the ring. The valve is mounted at an angle with respect to a tangent of the spinner so as to prevent detrimental effects from the centrifugal forces of the rotating spinner.

Wheel assembly for in-line skate with device for detecting rotational speed

Abstract: Device for detecting the rotational speed of a wheel of an in-line skate, the wheel being supported by rotating rings of two rolling bearings with fixed rings 9 of the two rolling bearings being secured to an axle mounted on a plate. The detection device includes a sensor and an encoder which are arranged in a volume bounded axially by the two rolling bearings and radially by a cylindrical surface which is coaxial with the rolling bearings and has a diameter represented by the external diameters of the outer rings of the rolling bearings.

Method for determining the rotational speed of a motor vehicle wheel rotating around a rotating axis

Abstract: The invention relates to a method for determining the rotational speed of a motor vehicle wheel (4) which rotates around a rotating axis (2), using an accelerometer (10). The accelerometer (10) is arranged on the motor vehicle wheel (4) at a distance (r) to the rotating axis (2) in such a way that the force-sensitive axis of the accelerometer (10) is vertical to the rotating axis and vertical to the centrifugal force, which acts upon the accelerometer (10) when the motor vehicle wheel (4) rotates around the rotating axis (2). The rotational speed of the motor vehicle wheel (4) is measured by directing the rotating axis (2) in a horizontal manner so that a periodically occurring measuring signal is generated by the gravitational force in the accelerometer (10). The frequency of said signal corresponds to the speed at which the motor vehicle wheel (4) rotates around the rotating axis 92). The invention also relates to an air pressure control system in which the rotational speed of a motor vehicle wheel is measured.

Toroidal type automatic transmission for motor vehicles

Abstract: Even in the case where a driver switches a select lever from D range to N range and returns it back to D range during the running of a vehicle, a speed change control device prevents the operation of sudden speed change caused by a difference between a transmission input rotational speed and the actual input rotating speed of a toroidal transmission unit while in the N range. Accordingly, an automatic transmission comprises a forward-reverse switching mechanism, an impelling mechanism and a toroidal transmission unit which are sequentially arranged from the driving source side of a vehicle, and further comprises a speed change control device for controlling the operation of the above. A notch as a rotational speed signaling section is provided on the outer periphery of a loading cam, for example, among rotating members in the area from an output member of the above forward-reverse switching mechanism to an input disc of the above toroidal transmission unit, and the notch is detected by a rotation sensor arranged in the vicinity of the outer periphery to detect the rotational speed of the loading cam and input the same to the speed change control device.