Slew Rate Limit Research Articles

The X-Space Formulation of the Magnetic Particle Imaging Process: 1-D Signal, Resolution, Bandwidth, SNR, SAR, and Magnetostimulation

The magnetic particle imaging (MPI) imaging process is a new method of medical imaging with great promise. In this paper we derive the 1-D MPI signal, resolution, bandwidth requirements, signal-to-noise ratio (SNR), specific absorption rate, and slew rate limitations. We conclude with experimental data measuring the point spread function for commercially available SPIO nanoparticles and a demonstration of the principles behind 1-D imaging using a static offset field. Despite arising from the nonlinear temporal response of a magnetic nanoparticle to a changing magnetic field, the imaging process is linear in the magnetization distribution and can be described as a convolution. Reconstruction in one dimension is exact and has a well-behaved quasi-Lorentzian point spread function.The spatial resolution improves cubically with increasing diameter of the SPIO domain, inverse to absolute temperature, linearly with saturation magnetization, and inversely with gradient. The band width requirements approach a megahertz for reasonable imaging parameters and millimeter scale resolutions, and the SNR increases with the scanning rate. The limit to SNR as we scale MPI to human sizes will be patient heating. SAR and magnetostimulation limits give us surprising relations between optimal scanning speeds and scanning frequency for different types of scanners.

Plasma Startup Design of Fully Superconducting Tokamaks EAST and KSTAR With Implications for ITER

Recent commissioning of two major fully superconducting (SC)-shaped tokamaks, Experimental Advanced Superconducting Tokamak (EAST) and Korean Superconducting Tokamak Advanced Research (KSTAR), represents a significant advance in magnetic fusion research. The key to commissioning success in these complex and unique tokamaks was as follows: 1) use of a robust, flexible plasma control system (PCS) based on the validated DIII-D design; 2) use of the TokSys design and modeling environment, which is tightly coupled with the DIII-D PCS architecture for first-plasma scenario development and plasma diagnosis; and 3) collaborations with experienced internationally recognized teams of tokamak operations and control experts. We provide an overview of the generic modeling environment and plasma control tools developed and validated within the DIII-D experimental program and applied through an international collaborative program to successfully address the unique constraints associated with the startup of these next-generation tokamaks. The unique characteristics of each tokamak and the machine constraints that must be included in device modeling and simulation, such as SC coil current slew rate limits and the presence of nonlinear magnetic materials, are discussed, along with commissioning and initial operational results. Lessons learned from the startup experience in these devices are summarized, with special emphasis on ramifications for International Thermonuclear Experimental Reactor (ITER).

A Detailed Dynamic Model of a Six-Axis Shaking Table

This article describes the modeling of a 5 m × 5 m 6 degree-of-freedom (DOF) shaking table and the subsequent computer simulation of the system's dynamic characteristics. The simulation model is required to aid the development of a closed-loop controller with a bandwidth specified up to 120 Hz, and thus high order dynamics including valve response and structural effects are included. Significant nonlinearities associated with the hydraulic and mechanical components are also included (e.g., spool slew rate and saturation limits, valve overlap, manifold and valve body pressure losses, friction, and geometric nonlinearities). Some model parameters are found from physical knowledge; others are determined experimentally, and methods for estimating key parameters from experimental data are developed. The simulation is implemented using Simulink® and its multi-body mechanical simulation tool SimMechanics®. The simulated response compares well with the measured response of the table.

Transducers for acoustical impulse measurements

The measurement of impulsive noise signals as for example from gunshots or airbag deployments requires special considerations when selecting transducer. The high frequency content in short impulses requires high bandwidth to correctly capture high rise times and small dimensions of the transducer to avoid diffraction. For high level impulses with very rapid rise time, the wide frequency range requires the use of preamplifiers with high slew rate capabilities and the capacitance and length of cables must be considered carefully. Slew rate limitations and bandwidth limitations can drastically change the peak value of an impulse. It is thus necessary to consider the whole measurement chain from transducer to AD‐converter to ensure the correct measurement of the impulse.

Bounded attitude stabilization: Real-time application on four-rotor mini-helicopter

This paper deals with the global stabilization of a rigid body by means of a bounded quaternion-based feedback. In addition to input bounds, the nonlinear control takes into account the slew rate limits. The proposed control scheme is generic and can be applied to all systems falling in the framework of rigid bodies. Furthermore, its extreme simplicity rendering it suitable for embedded implementation. It is also shown that the control strategy can be applied to attitude stabilization of a four-rotor mini-helicopter despite gyroscopic effects appear that are not present in the rigid body framework. Several real-time experiments have been performed on a real mini-helicopter in order to show the effectiveness of the proposed control approach.

Attitude Control of Large Angle Maneuver for Microsatellite Using Variable Speed Control Moment Gyros

研究了变速控制力矩陀螺(VSCMG)作为执行机构的微小卫星多目标快速姿态机动的控制问题.控制力矩陀螺(CMG)可以在不增加功耗、质量和体积的条件下为微小卫星提供独特的控制力矩、角动量和姿态机动能力,这有助于微小卫星变得更加机动灵活.首先建立了以变速控制力矩为执行机构的航天器姿态动力学模型,采用修正Rodrigues参数描述姿态.在考虑执行机构饱和、机动速率限制、控制带宽限制等情况下,设计了基于Lyapunov理论的非线性姿态反馈控制器.以采用VSCMG为执行机构的某微小卫星为例进行了数值仿真,结果表明卫星在机动中达到了快速和稳定的要求,提出的非线性姿态反馈控制器有很好的鲁棒性和有效性.

A fast large dynamic range shaping amplifier for particle detector front-end

The paper describes a fast shaping amplifier with rail-to-rail output swing. The circuit is based on a CMOS operational amplifier with a class AB output stage. A baseline holder, incorporating a closed-loop unity gain buffer with slew rate limitation, performs the AC coupling with the preamplifier and guarantees a baseline shift smaller than 3 mV for unipolar output pulses of 3 V and 10 MHz rate.

High-speed CMOS unity-gain current amplifier

A high-performance CMOS unity-gain current amplifier is proposed. The solution adopts two feedback loops to reduce the input resistance and a nested-Miller technique to provide frequency compensation. A design example using a 0.8μm process and a 2V supply is given and SPICE simulations show a bandwidth of 75MHz, no slew-rate limitations and a settling time better than 50ns, irrespective of the current amplitude. Input and output resistances are better than 0.1Ω and 15MΩ, respectively. The input-referred white noise spectral density is 10pA/Hz.

A 10-bit, 200-MSPS, 105-mW pipeline A-to-D converter

The optimum bit/stage configuration is an important issue in the design of a low-power pipeline analog-to-digital converter (ADC). Prior to this work, power considerations based on a linear-model have been reported [1]. In this letter, the slew-rate limitation, a non-linear effect, is taken into consideration in low-power design. In the case of a 10-bit, 200-MSPS ADC using 90-nm CMOS technology, the lowest power bit-arrangement was found to be 1.5bit/stage. A test chip was fabricated for confirmation, and a power dissipation of 105mW was achieved.

Shaped Time-Optimal Feedback Controllers for Flexible Structures

This paper describes the design of closed-loop control laws for servomechanisms with one dominant flexible mode. An input shaping technique is employed to alter the rigid body phase-plane trajectory that is used in time-optimal servomechanisms. The resulting controllers lead to near time-optimal performance without unwanted residual vibrations. After the basic technique is outlined for a system with one undamped flexible mode, extensions are given considering different acceleration and deceleration capabilities, damping, and slew rate limits.

Shaped Time-Optimal Feedback Control for Disk-Drive Systems With Back-Electromotive Force

In this paper, we describe the design of closed-loop control laws for disk-drive systems that account for back-electromotive force (back-EMF) by using a phase-plane approach. The time-optimal control law for a rigid body is shaped by using input shaping ideas to address the flexible mode, and then the altered rigid body phase-plane trajectories resulting from this shaping are calculated and used to determine a closed-loop controller. Extensions are made to account for damping and slew rate limits. Simulation results show that this control approach leads to near-time-optimal performance without unwanted residual vibrations, good robustness to modeling errors, and faster time response than the previously developed extended proximate time-optimal servomechanism (XPTOS) control, especially when the flexible dynamics are dominant.

Slew-rate removal technique for low-noise front-end preamplifiers

A novel slew-rate removal technique for monolithic front-end preamplifiers for detector readout is presented. It is based on the insertion of a feed-forward path in the gain stage that removes the slew-rate limitation without affecting noise, linearity or stability performances. The paper discusses the design steps of a low-noise high-speed voltage preamplifier in BiCMOS technology and compares the proposed solution with other slew-rate enhancement circuits. The simulated performances in terms of step response, noise, linearity and time-walk are presented and discussed.

Low-noise slew-rate free voltage preamplifier with current-limited continuous reset

A novel low-noise BiCMOS voltage preamplifier for the readout of high-resolution silicon detectors has been developed and characterized. This preamplifier features a feed-forward path in the gain stage that completely removes the slew-rate (SR) limitation without affecting the stability, the linearity or the noise performance. A transconductance amplifier biased at a very low current provides a low-noise current-limited continuous reset. The measured step response of the realized prototypes shows no SR limitation and a linearity error better than 0.1% within the tested output dynamic. Coupling this preamplifier to a silicon drift detector we measured a room temperature energy resolution of 165 eV FWHM at the 5.9 keV line.

Rapid Multitarget Acquisition and Pointing Control of Agile Spacecraft

This paper describes the study results of developing an attitude control system for agile spacecraft which require rapid retargeting and fast transient settling. In particular, a nonlinear feedback control logic is developed for large-angle, rapid multi-target retargeting maneuvers subject to various physical constraints, including the actuator saturation, slew rate limit, control bandwidth limit, etc. Simulation results for an agile spacecraft equipped with control moment gyros demonstrate the effectiveness and robust performance of the proposed nonlinear feedback control system.

On the Design and Analysis of Ship Stabilizimg Fin Controller

A ship stabilizing fin controller based on the Internal Model Control (IMC) method is described in this paper. The proposed method directly shapes the output sensitivity function which relates the wave disturbance to the ship roll motion to achieve good disturbance rejection. The adopted IMC method gives a controller that depends explicitly on the model parameters and a design parameter that specifies the desired system response. Moreover, under the IMC structure, the sensitivity functions depend linearly on the design transfer function and this makes it easy to satisfy the internal stability condition. A reference conditioning technique is employed in the design that takes the limited actuator authority into the controller design consideration to avoid unknowingly pushing the actuator beyond its saturation and slew rate limitation boundaries. Numerical results indicate that very good roll reduction is achieved for sinusoidal disturbance and reasonable roll reduction is obtained for a narrow band type of disturbance generated by passing a white noise sequence through a second order shaping filter.

Adaptive sigma-delta modulation with one-bit quantization

A method for improving the signal-to-noise ratio (SNR) of sigma-delta modulators with one-bit quantization is presented. The two-level feedback signal of a standard sigma-delta modulator is replaced by a multilevel signal, which is a superposition of two parts. One part s(n) represents a rough estimate of the instantaneous amplitude of the input signal (prediction signal), and the other y/sub b/(n) is the sign of the quantizer output, multiplied with constant b. Compared to a nonadaptive modulator, the amplitude of y/sub b/(n) is reduced. Therefore, less noise power is introduced in the quantizer, and the SNR is considerably enhanced. Signal s(n) is derived numerically from the quantizer output y/sub 0/(n) according to a particular adaptation algorithm. Except for the DC-level of s(n), sequence y/sub 0/(n) contains the full digital information of the modulator input signal. From y/sub 0/(n), a digital multilevel sequence w/sub 0/(n) can be calculated, which represents the digital modulator output. The price paid for the improved SNR is a moderate slew rate limitation of the input signal. The approach is basically suited for a wide class of sigma-delta modulators. Here, simulation results and an example for a practical implementation of an adaptive sigma-delta modulator of first order are presented.

Globally Asymptotically Stable Reorientation Controller with Control Constraint and Slew Rate Limit

Globally Asymptotically Stable Reorientation Controller with Control Constraint and Slew Rate Limit

Gain-frequency characteristics of transistors based on flux flow in hysteretic long Josephson junctions (LJJ)

Transistors based on one dimensional flux flow in hysteretic long Josephson junctions (LJJ) and deriving output from the spatial average over the length can be modeled as a section of transmission line. Time domain analyses made on these transmission line sections with both the ends terminated with typical resistance values reveal a fundamental gain-frequency relationship unique to all devices whose output voltage is equal to the spatial average over the length of the junction. The maximum frequency of a transistor depends on the transit time of carriers and the parasitic elements. The analysis shows that the frequency response of a flux flow transistor is related but not equal to the inverse of the transit time of fluxons. Secondly the step response of these transmission line sections varies linearly with time, which indicates a slew rate limitation. The slew rate that affects the high frequency response of a flux flow device is shown to be a function of the critical current density of the junction and material parameters. Analysis made on niobium-lead junctions indicates that the slew rate peaks at an optimum current density level. The results of these analyses and performance comparisons are presented.

Feedback linearization design of a ship steering autopilot with saturating and slew rate limiting actuator

A full non-linear model including sea-state modelling is used in the design for a ship steering autopilot. This has been done before. However, rather than a conservative design to avoid amplitude and slew rate limit in the rudder, we show how these limits can be accommodated without otherwise compromising the performance. Thus, saturation and slew rate limiting are accepted as inevitable consequence of high performance rather than something to be avoided at all cost. Copyright © 1999 John Wiley & Sons, Ltd.

An internal model control approach to the design of yaw-rate-control ship-steering autopilot

This technical communication is concerned with the design of inland ship-steering autopilots characterized by turning rate regulation rather than heading regulation found on most ocean-going vessel autopilots. The autopilot design is based on the internal model control approach which allows clear connections between the controller structure and that of the ship model to be established. To fully utilize the limited rudder power without introducing the controller wind-up, which may lead to undesirable long transients, an inverse of the rudder saturation (SAT) and slew rate limitation (SRL) is implemented in the controller. Specifically, an inversion by feedback technique is employed by implementing the noninverted dynamics in a local feedback loop. This resolves the difficulty associated with inversion of the SAT and SRL mathematically. Consequently, high turning rate maneuver can be achieved in case of emergency encounters without causing the controller wind-up. This feature is particularly important for inland ships, since unexpected encounters with other ships are quite common and the capability of quick response is vital to ensure safe maneuvers.