Showing papers on "Feedback loop published in 1998"

Design and evaluation of a feedback based phased array system for ultrasound surgery

Abstract: A driving system has been designed for phased array ultrasound applicators. The system is designed to-operate in the bandwidth 1.2 to 1.8 MHz, with independent channel power control up to 60 W (8 bit resolution) for each array element. To reduce power variation between elements, the system utilizes switching regulators in a feedback loop to automatically adjust the DC supply of a class D/E power converter. This feedback reduces the RF electrical power variation from 20% to 1% into a 16 element array. DC-to-RF efficiencies close to 70% for all power levels eliminates the need for large heat sinks. In addition to power control, each channel may be phase shifted 360/spl deg/ with a minimum of 8 bit resolution. To ensure proper operation while driving ultrasound arrays with varying element sizes, each RF driving channel implements phase feedback such that proper phase of the driving signal is produced either at the amplifier output before the matching circuitry or after the matching circuitry at the transducer face. This feedback has been experimentally shown to increase the focal intensities by 20 to 25% of two tested phased arrays without array calibration using a hydrophone.

Impedance based combination of visual and force control

Abstract: We propose a simple and efficient control algorithm that combines visual servo control and force feedback within the impedance control approach. The control scheme involves, at the low level, a position based impedance controller with an external force sensor feedback loop. The reference trajectory fed to this impedance controller is generated online by a vision based control loop. In spite of its simplicity, this approach provides satisfactory experimental behavior. Peg in hole insertion experiments involving large initial errors, are performed using a 7 axis robot manipulator without any computation of the peg trajectory.

Electronic mail in a working context

Abstract: Electronic mail, email, is one of the most widespread computer applications today.While email in general is very popular among its users, there are also drawbacks withemail usage: an increasing amount of messages that overwhelm users, systems that aretoo complex for naive users and at the same time do not support the needs of experiencedusers.In order to answer the main research question “Which design solutions couldimprove the situation of individual email users in a working context when it comes tocommunication and handling large numbers of incoming and stored email messages?”three studies conducted in email users’ working environment are described. The studiedorganisations are one academic research laboratory, one technical company, andone primary medical service organisation. The studies are focused on email usage,organisation of email messages, novice versus experienced users’ needs, managers’email usage, and information and communication overflow.The results indicate that the different strategies used to handle email are a matter ofa balance between advantages and disadvantages of these strategies. The choicebetween them is depending on the users’ total work situation and cannot be understoodby investigating the email communication alone.One advantage of email is the cognitive comfort it brings to its users by liberatingthem from thinking about tasks that can be solved by sending an email message, butthis advantage disappears when the sender cannot trust that the receiver will act uponthe message.Users develop their handling of email with experience and work position. Themedia that managers use to handle the increased communication that follows with ahigher position are email and meetings. One habit that do not change with position isto allow incoming messages to interrupt other work tasks, despite the asynchronousnature of email. This is particularly remarkable for managers who often complain thatthey need more uninterrupted time. The interruptions may partly be attributed to thelack of functionality in email systems to adapt the interfaces to the users’ work habits.In this case incoming messages result in a signal regardless the importance of them.Email is a part of an information and communication flow. Some users have problemshandling this flow. Overflow problems could be diminished by making senders ofmessages more aware of the receivers’ communicative situation. Email systems couldprovide feedback to senders of messages based on the receivers’ perception of his/hersituation.One of the studies indicates that it may be even more complicated to replace an oldemail system than introducing an email system for the first time in an organisation.The investment experienced users have made in the old system may be substantial.A model of time usage for organisation of email messages is also presented in orderto compare different strategies.Several design solutions are suggested with respect to folder usage, sorting emailmessages into folders, reducing the number of stored messages, and tailoring the emailsystem to the user’s work habits.

Non-contact power transmitting device having simplified self-oscillation feedback loop which interrupts power transmission when no load is present

Abstract: A power supplying section has a signal transmitting secondary coil which is not inductively coupled to a power transmitting primary coil, and actuates as a feedback coil of a switching element. A load section has a power transmitting secondary coil arranged so as to be confronted with the power transmitting primary coil when the load section is attached to the power supplying section, and also has a signal transmitting primary coil so as to be confronted with the signal transmitting secondary coil when the load section is attached to the power supplying section. When the load section is not attached to the power supplying section, the voltage is not induced in the signal transmitting secondary coil as the feedback coil, and the switching of the switching element is intermittently carried out.

Amplifier linearization using RF feedback and feedforward techniques

Abstract: The performance of feedback as a distortion reduction technique is highly dependent on the integrity of the feedback path. Any error or noise generated in this path is directly reflected into the output of the amplifier. Linearized RF power amplifiers (PAs) using Cartesian feedback require a demodulator in the feedback loop, and this is a potential source of linear errors, nonlinear errors, and noise. RF feedback with Cartesian compensation is proposed as a technique for overcoming some of these problems. The scheme is most suited to systems requiring an RF input. In addition, the RF nature of the input, feedback, and error signals enables the addition of a feedforward loop to further improve the linearization capability while still maintaining good efficiency. Design equations and simulation results are given for such a system. Disadvantages include the limited bandwidth (estimated at 1 MHz) and the need for additional circuits to generate the RF input signal when included in an integrated transmitter.

A Temperature Controller for VAV Air-Handling Units Based on Simplified Physical Models

Abstract: A feedforward controller based on simplified physical models is described for air-handling units to supplement conventional PI control. Inverse static models of the controlled processes produce feedforward control action and the PI feedback loop compensates for modeling errors and unmeasured disturbances. The models are configurable from plant design information and they operate using the sensor signals typically available to an air-handling unit controller. The incorporation of feedforward control reduces the reliance on the feedback loop and makes the tuning of the PI controller less critical. Low gain (default) control parameters may then be used in the feedback loop, thereby eliminating the need for on-site tuning. This paper describes the control scheme and models, and presents results from tests carried out using a simulated air-handling unit.

Multiple feedback loop ring oscillator and delay cell

Abstract: Disclosed is a multiple feedback loop ring oscillator and delay cell with high oscillation voltage. It is an object of the present invention to implement a new ring oscillator for the VCO of a high speed PLL and a proper delay cell with a high speed and low noise. The apparatus is composed of multiple feedback loop ring oscillator that 4 delay cells which have the first main input stage, the second main input stage, the first subsidiary input stage, the second subsidiary input stage, the third subsidiary input stage, the forth subsidiary input stage, the first output stage and the second output stage is connected to the main loop and subsidiary loop. The present invention has advantages that it can be operated in high speed, it has a low power sensitivity, there is no power noise because there is no variation of a supply current and it can improve noise characteristics.

Settling time analysis of third order systems

Abstract: Several operational transconductance amplifiers often have a third order transfer function. The use of these amplifiers for several applications, such as in switched-capacitor circuits requires the minimization of the settling time to a step response. This problem is studied in this work. First, the closed loop transfer function of a system with an the open loop 3/sup rd/ order transfer function is obtained, and a mapping from the closed loop parameters to the open loop parameters is derived. Second, the closed loop step response is deduced. Third, the dynamic settling error is studied based on numerical simulations. The described procedure can be used to find the optimal location for the open loop poles and zeros that minimizes the settling time for a specific amplifier structure.

Peak current mode control applied to the forward converter with active clamp

Abstract: The forward converter with clamp is nowadays one of the most useful topologies when low output voltage is required due to the possibility of using self driven synchronous rectification. This paper shows a study of the peak current mode control when the main MOSFET current is sensed instead of the current passing through the output inductor. A dynamic study is accomplished and the control problems are shown. Finally, several practical ways to close the feedback loop avoiding the dynamic drawbacks is also presented.

Feedback control of laser intensity noise

Abstract: A fully quantum-mechanical model of feedback to the pump source of a four-level laser is developed with a view to predicting the achievable intensity noise reduction. For solid-state lasers, the model shows that quantum noise sources due to laser dynamics have a significant impact on the optimization of the feedback loop, Experimental results obtained with a diode pumped neodymium:yttrium aluminum garnet (Nd:YAG) laser are found to be in good agreement with the theoretical model. The ultimate limit to the noise suppression comes from the quantum noise due to the measurement processes in the feedback loop. A scheme to overcome this limit using a squeezed vacuum is theoretically demonstrated to be a highly efficient method of generating bright intensity squeezed light, particularly in the kHz regime where bright squeezing is otherwise difficult to obtain. [S1050-2947(97)08111-0].

Optimal conditions for imaging in scanning tunneling microscopy: Theory

Abstract: The scanning tunneling microscopy ~STM! feedback system is analyzed to look for the optimal conditions for measurement The typical feedback circuit normally used in STM and the parameters involved on it are studied, and their relative importance into the loop are discussed The analysis of the role of each parameter demonstrated the importance of a detailed knowledge of the instrument to assure that the images obtained are reliable We obtained equations that involve the main parameters of the loop, and yield the optimal conditions for imaging taking into account stability, signal amplitude, and phase shift Combining the stability conditions with the imaging conditions obtained in this work, we found values for the feedback parameters to perform optimal STM measurements Moreover, with this work, we highlight the importance to include in further publications the value of the main parameters used to obtain STM images The conclusion of our work is that in some cases ~in particular atomic resolution and fractal analysis ! STM users should pay more attention to the setting of the instrument © 1998 American Institute of Physics @S0034-6748~98!02411-3# Scanning probe microscopy ~SPM! techniques, mainly scanning tunneling microscopy ~STM! and atomic force microscopy ~AFM!, have become today the standard techniques for characterization of surface materials with atomic resolution Commercial instruments are widely disseminated around the world and their use and importance cover many fields of science These instruments become increasingly compact and complex Consequently, the users look to them as ‘‘black boxes’’ In this way, the parameters in the feedback loop are most of the time obtained by trial and error However, to obtain ‘‘real copies’’ of the surface topography, it is necessary to keep in mind the main characteristics and the limits of the instrument Pioneering efforts on the STM feedback system analysis were made on the base to find out the stability region 1 and the transfer function to obtain the conditions for a critical damping 2 to avoid instabilities Other works proposed finding out the optimal feedback conditions experimentally—obtaining the critical damping conditions 3 —or using a mathematical model with complex equations, 4 without clear conclusions about how to use their results under real conditions Park and Barret 5 studied the stability of the tunnel loop by using a resonant model but finally they were not able to acquire the stability region for imaging Along this line, we discussed in previous works the optimal conditions in which to have stability, during scanning in the STM, in order to avoid artifacts, instabilities, resonance, or noise in the image 6 We emphasized the real parameters involved in it and their experimental determination 7 Therefore, an extensive analysis of a typical feedback circuit was made, finding conditions and rules for stability during imaging Because ‘‘an image says more than a thousand words,’’ it is important to be sure of the image quality Thus, a second part was missing in our previous work: the measurement conditions when the feedback loop is under conditions of stability Therefore, the aim of this work is to present a study on the correct use of the STM feedback system from the point of view of the measurement conditions As far as we know, this is the first study where the physical parameters used for measurement and the mechanical properties of the STM device have been related between them and with the images obtained

Multichannel radio device, a radio communication system, and a fractional division frequency synthesizer

Abstract: A new architecture for such a type of synthesizer is proposed not having the drawbacks of such known synthesizers and having the same phase noise properties as ordinary integer divide by N synthesizers. The novel architecture has a main PLL with a first integer frequency divider in its feedback loop and further an auxiliary PLL having a second integer frequency divider in its feedback loop.

Distortion control feedback loop utilizing a non-linear transfer function generator to compensate for non-linearities in a transmitter circuit

Abstract: A transfer function generator provides the ability to provide a non-linear response in a feedback loop to compensate for non-linearities introduced elsewhere in the system. The transfer function generator includes a non-linear function generator configured to provide an output current that is a non-linear function of an input signal representing an error to be corrected. The transfer function generator can also include a linear function generator configure to provide a linear output current as a function of an input current representing the error corrected. Tuning devices can be provided to adjust the turn-on level of the non-linear function generator and the output level of the linear function generator to allow the transfer function generator flexibility in implementation.

Fluorescent-lamp excitation circuit with frequency and amplitude control and methods for using same

Abstract: A power-supply and control circuit is provided for driving a fluorescent lamp from a low-voltage direct current (DC) power source such as a battery. The circuit includes a converter that converts low-voltage DC to high voltage alternating current (AC). The converter includes a feedback ceramic step-up transformer that amplifies the AC signal to a level sufficient to illuminate the lamp, and also provides a feedback signal that can be used to monitor the resonance frequency of the transformer. The power supply and control circuit also includes a first feedback loop that regulates the lamp current amplitude and a second feedback loop that forces the converter to operate at the transformer's resonant frequency.

Linear servo-controlled pressure generator for forced oscillation measurements

Abstract: In respiratory input impedance measurements, the low-frequency range contains important clinical and physiological information. However, the patient's spontaneous ventilation can contaminate the data in this range, leading to unreliable results. Unbiased estimators are a good alternative to overcome this problem, provided that the generator is considered linear. This condition is not fulfilled by most existing generators as they are based on loudspeakers, which have strong nonlinearities. The present work aims to contribute to the solution of this problem, and describes a pressure generator that minimises the nonlinearities by an optical sensor placed in a position feedback loop. The static evaluation shows a high linearity for the optical system. The well known frequency response of pressure transducers is used in the dynamic evaluation of the instrument. The analysis of the generator shows that the use of position feedback improved the frequency response. The total harmonic distortion (THD) measurement shows that closed loop resulted in an effective decrease in the nonlinearities. The reduction of THD achieved by the servo-controlled generator can contribute to the practical implementation of the unbiased estimators, increasing the reliability of the impedance data, especially in the low-frequency range. This system is compared with conventional generators and with another servo-controlled system.

Joint multiuser detector with decoding and feedback in asynchronous CDMA systems

Abstract: A joint multiuser detector with decoding and feedback for the convolutionally coded asynchronous code-division multiple-access (CDMA) system is proposed in this paper. This approach consists of generalized multistage processing and a decision feedback loop. The performance is verified by simulations in Rayleigh fading channels.

DSP based implementation of a digitally-controlled single phase PWM inverter for UPS

Abstract: This paper presents a new method to realize a digitally-controlled PWM inverter used in an online uninterruptible power supply (UPS). This digitally-controlled PWM inverter has been implemented using a digital signal processor (DSP). This implementation includes PWM pulse generation, voltage feedback loop (outer loop) and average current feedback loop (inner loop). Simulation and experimental results are given to verify the DSP based PWM inverter design and implementation.

Control loop for adaptive multilevel detection of a data signal

Abstract: A closed feedback loop controls the slicing, or detecting, of an incoming data signal. Detected signal information about the positive and negative peaks of the incoming data signal is processed to generate positive and negative peak reference signals which serve as reference signal levels for establishing the thresholds at which signal slicing takes place.

Transconductance control circuit, particularly for continuous-time circuits

Abstract: Embodiments of the invention provide a transconductance control circuit, particularly for a continuous-time filter, comprising a transconductor across which a constant voltage is input. The transconductor is connected to a digital-to-analog converter (DAC) to set a reference current. A feedback loop is provided between an output of the transconductor and an input. In particular, the circuit further comprises a means for mirroring the reference current set by the DAC both to the feedback loop and to at least one cell of a cascade-connected filter.

Dynamic power equalization of many wavelength-division-multiplexed channels in a fiber-optic system

Abstract: A dynamic power equalization module ( 10 ) for an optical network is provided. It includes a module input ( 16 ) for receiving an optical transmission ( 14 ) containing a combination of different channels (C 1 -C n ). Each channel (C 1 -C n ) has a different characteristic wavelength (λ 1 -λ n ) and different varying power. A power equalization device that is polarization insensitive is connected between the module input ( 16 ) and a module output ( 20 ). The power equalization device is driven by RF acoustic signals ( 26 ). A feedback loop ( 22 ) receives at least a portion of output from the module output ( 20 ) and generates, based upon a comparison of relative powers of the different channels (C 1 -C n ), the RF acoustic signals ( 26 ) which drive the power equalization device. The power equalization device is driven such that it dynamically controls transmission of the different channels (C 1 -C n ) to substantially equalize power differentials therebetween. The power equalization device includes a parallel array of acousto-optic modulators (AO 1 -AO n ).

Scan loop control design for a spin-stabilised seeker

Abstract: A scan loop model for a spin-stabilised seeker is introduced, which includes gyrodynamics with direct- and cross-spring constants for considering the autoerection effect of the gyro. The LQG/LTR and H∞ controllers are designed for the seeker scan loop system which has model uncertainty and is subject to external disturbances. The performance of LQG/LTR controller can be improved by obtaining uniform singular values over all frequencies for the target feedback loop. The H∞ controller is designed in the framework of the standard H∞ optimisation problem with model matching. The proposed H∞ method can reflect not only frequency domain specifications but also time domain ones, such as transient response characteristics and multivariable interaction between output channels, differently from the mixed sensitivity problem. It is shown that the designed LQG/LTR and H∞ controllers offer good performance and robustness properties, and both controllers are very effective in the seeker scan loop system.

Vibration Control of Structures With Closely Spaced Frequencies by a Single Actuator

Abstract: A variable gain direct velocity feedback is proposed to control vibrations in structures with two closely spaced natural frequencies using a single actuator. First, limitation of the conventional constant gain velocity feedback is discussed based on perturbation analysis of the free response of structures with two vibration modes and a single actuator. Then, a variable gain feedback is constructed from the physical intuitions obtained from these solutions. The variable feedback gain is derived in terms of the state of the system while the feedback loop remains direct velocity feedback Numerical studies confirm the efficiency of the proposed method.

Absolute Stability of Feedback Systems in Hilbert Spaces

Abstract: The problem of absolute stability of a feedback loop of an abstract differential system in Hilbert spaces is considered. Applications of Popov’s type frequency domain criteria and of the Kalman-Yakubovich Lemma for the construction of Lyapunov functions are illustrated, in two situations pertaining to distributed systems. Finally, a new criterion for absolute stability of a class of parabolic systems with boundary feedback is presented.

Self-optimizing and adaptive digital signal processor based algorithms in scanning tunneling microscopy

Abstract: A self-optimizing proportional integral differential feedback loop and an adaptive scan generator have been implemented in a digital signal processor board EVM56k from Motorola for the control of a scanning tunneling microscope. The self-optimizing feedback loop uses an evolutionary algorithm to optimize the step response of the system. The variation of the target step response strongly determines the results of the optimizing process and allows to optimize either for highest scan speed or best signal-to-noise ratio. In combination with the improved adaptive scan generator, the adjustment of the scan velocity to the local topography of the sample increases image contrast and quality considerably.

Robust controller design for a variable displacement hydraulic motor

Abstract: Presents the robust control of a variable displacement hydraulic motor (VDHM). A feedback control structure consisting of two nested loops is employed. The inner feedback loop controls the position of the rocker arm which actuates the wobbler plate of the motor. The outer feedback loop regulates the motor shaft velocity such that shaft speed is guaranteed at steady state despite external torque loads. The control loops are closed in succession closing the inner loop first. For each loop design, step response data is collected from a VDHM laboratory test stand to generate analytical systems level models. Based on these models, feedback controllers are designed using classical loop shaping techniques. Feedback control, as opposed to feedforward control, maintains motor shaft velocity under nonpredictive torque loading conditions. In addition, the feedback structure eliminates the need for extensive system calibration when considering system parameter changes that result from component aging.

Synchronization of multiple ROS for image registration in a single pass system

Abstract: A single pass ROS system provides a plurality of latent images which may subsequently be developed in different colors. A method and apparatus is provided for aligning ROS units in a single pass printing system, so that each ROS unit is aligned along the process or X-axis. After this alignment, the images formed by each ROS unit will be in proper registration within the prescribed tolerances. A signal in a closed feedback loop regulates the angular velocity and phase of the rotating polygon mirror of the first ROS unit. The same signal is also the reference signal to the feedback loops of the other rotating polygon mirrors of the other ROS units to synchronize all of the rotating polygon mirrors. The position of the scan lines formed by their respective ROS units are fixed relative to one another and thus, lacking any other error sources, are registered in the process direction. A proportional integral derivative controller, the motor polygon assembly and a speed detector form the synchronization system for each ROS unit. The proportional integral derivative controller produces the synchronized signal for the MPA as a function of the proportional feedback signal, the integral feedback signal and the differential feedback signal. The speed detector in the feedback loop has an invertor, a feedback gain and a zero order hold to convert the velocity/phase signal from the MPA into a feedback signal. The feedback signal, a weighted summed feedback signal from a feedback adder from all the ROS units and a reference signal are input to the proportional integral derivative controller.

Method for adjusting power of transmitter, and control arrangement

Abstract: The invention relates to a method for transmitter power control and a control arrangement employed for transmitter power control. The control arrangement comprises a control element (1) controlled by a control signal, a sampling means (3) for taking samples of a signal from the control element (1). The control arrangement further comprises a detector (4), an adder (5) and a loop filter (6). The adder (5) and loop filter (6) form a controller for receiving a signal which is transmitted by the detector (4) and forms part of a feedback signal for controlling the control element (1). Between the input and output of the controller, the control arrangement comprises a parallel loop which, when being activated, keeps the feedback loop closed when the sample signal is outside the dynamic range of the detector (4). Keeping the feedback loop closed enables transmitter power control without discontinuity points.