Differential Pulse Width Research Articles

High Spatial-Resolved φ-OTDR System Based on Differential Pulse Width Sequence Technique

High Spatial-Resolved φ-OTDR System Based on Differential Pulse Width Sequence Technique

Investigation on positioning control strategy and switching optimization of an equal coded digital valve system

This article concerns high accuracy positioning control with switching optimization for an equal coded digital valve system. Typically, pulse number modulation control cannot realize micro-positioning due to the characteristics of step-wise flow variation, therefore, a new position controller consisting of a model-based pulse number modulation and a differential pulse width modulation strategy is proposed to control the position of a hydraulic cylinder at high and low velocity cases, respectively. In addition, in order to solve several problems caused by the pulse number modulation and differential pulse width modulation, such as increased number of switchings and large difference among number of switchings of valves, a switching optimization consisting of a switching cost function, a circular buffer and a circular switching method is proposed. An adaptive weight of the switching cost function is proposed for the first time to reduce the total number of switchings under different pressure differences and its design criterion is presented. A circular buffer and a new circular switching method are used to improve the degree of equal distribution of switchings when the pulse number modulation and differential pulse width modulation are used, respectively. Comparative experimental results indicated that the average and the minimum positioning error for the proposed controller are only 10 and 1 μm, respectively. The number of switchings and the degree of equal distribution of switchings are significantly optimized. Moreover, the pressure fluctuations caused by the proposed controller remain acceptable.

Fast distributed Brillouin optical fiber sensing based on pump frequency modulation

We present a fast distributed Brillouin optical fiber sensor based on pump frequency modulation. The frequency shift of the probe is fixed, while the pump is fast scanned using an arbitrary waveform generator (AWG). Thus, the bandwidth requirement of the AWG is reduced to several hundred megahertz without any expense to the acquiring speed. Combining with differential pulse width pair (DPP) technology, a vibration measurement is implemented in a 230-m polarization-maintaining fiber with a sampling rate of 2.6 kHz and 50 cm spatial resolution. A vibration signal up to 31 Hz is identified successfully with a strain resolution of 15 µε.

Viscosity-adjusted estimation of pressure head and pump flow with quasi-pulsatile modulation of rotary blood pump for a total artificial heart

Estimation of pressure and flow has been an important subject for developing implantable artificial hearts. To realize real-time viscosity-adjusted estimation of pressure head and pump flow for a total artificial heart, we propose the table estimation method with quasi-pulsatile modulation of rotary blood pump in which systolic high flow and diastolic low flow phased are generated. The table estimation method utilizes three kinds of tables: viscosity, pressure and flow tables. Viscosity is estimated from the characteristic that differential value in motor speed between systolic and diastolic phases varies depending on viscosity. Potential of this estimation method was investigated using mock circulation system. Glycerin solution diluted with salty water was used to adjust viscosity of fluid. In verification of this method using continuous flow data, fairly good estimation could be possible when differential pulse width modulation (PWM) value of the motor between systolic and diastolic phases was high. In estimation under quasi-pulsatile condition, inertia correction was provided and fairly good estimation was possible when the differential PWM value was high, which was not different from the verification results using continuous flow data. In the experiment of real-time estimation applying moving average method to the estimated viscosity, fair estimation could be possible when the differential PWM value was high, showing that real-time viscosity-adjusted estimation of pressure head and pump flow would be possible with this novel estimation method when the differential PWM value would be set high.

Measurement Method of Vehicle Shaft Revolution Speed Based on Capacitive Grating Sensor

Due to the narrow interior space of vehicle, the compact structure limited the method of revolution speed measurement based on photoelectric and magnetoelectric, so a new measurement method based on capacitive grating sensor is presented here. The sensor will output alternating capacitance signal by fixed the mobilizable grating on the shaft and fixed the stator grating on the bracket. The capacitance signal will turn into the corresponding sine wave signal to the speed through differential pulse width modulation circuit, subtraction circuit and low-pass filter circuit, and will output a square wave of the same frequency with the sine wave through phase locked loop circuit. Then the speed measurement will be realized by counting the signal pulse. Experiments show that this method has the characteristics of non-contact measuring and high sensitivity.

Practical resolution analysis of perpendicular recording

The zigzag magnetic transition due to the magnetic clusters has been found to enlarge the differential pulse width (dPW50). In order to simulate the resolution or dPW50 precisely with magnetic cluster effect, a micro-track model was employed in the manner that local transition positions were determined by magnetic clusters. The magnetic cluster size was set to be the average diameter of the circles, which fit the magnetic clusters on MFM images in shape. Simulated transition jitter based on the distribution of the center position of circles is compared with experimentally measured value by time domain analysis of readout waveform. The calculated resolution of the transition model with magnetic cluster was successfully validated by the measured resolution along with the jitter with reasonable accuracy.

Simulation and Control Design of a Railway Vehicle Tilting System using Differential Pulse Width Modulation Control of Air Springs

SUMMARY A short review of electronically controlled pneumatic suspensions for railway application suggests that a better knowledge of the physics involved and how to control them could be of interest. The point of view adopted in this paper is to consider the air spring used in railway vehicle suspension as an autonomous actuator, including in aclosed loop arrangement a height sensor, 2 solenoid valves- 1 for supply, I for exhaust -driven by DPWM, and electronic controller. Physical modelling of the actuator is developped here, as well as how to obtain a third order control model to be used as a basis for state feedback design. Linear controller is then simulation checked against non linearities as a 1/4 vehicle secondary suspension. At last, full vehicle non linear simulation with unbalanced lateral acceleration sensing and four air springs tilt control leads to conclusion about the global behaviour of the system in a realistic context.

Digital Control of Hydrostatic Transmission System Driven by Differential Pulse Width Modulation.

This study deals with a hydrostatic transmission (HST) consisting of a variable displacement axial piston pump connected in a closed circuit to a fixed displacement axial piston motor. For the variation of the swashplate angle of the pump, a hydraulic rotary actuator is adopted. This actuator is driven by two on-off solenoid valves based on the differential PWM method, which thus makes the HST system easier to accomodate a digital control algorithm. In order to control the two variables of angular displacement and angular velocity of the motor, two control systems are designed using the method of the optimal control scheme. It is verified by experiment and digital simulation that the two systems have good control performance.

Digital control of an HST system with load cylinder operated by differential pulse width modulation

This study deals with an HST system which is driven by differential PWM method. In this system, for achieving a linear-motion control, the hydraulic motor in generic HST was replaced with a load cylinder. Two kinds of control algorithm are employed and verified for controlling the cylinder displacement of the modified HST system.

Digital Control of Electrohydraulic Servo System Operated by Differential Pulse Width Modulation

In the preceding papers, the authors proposed a new method of differential PWM for a hydraulic actuator operated by two 3-way solenoid valves. An arbitrary pulse width of the pressure difference across both sides of the actuator piston was realized by adjusting the switching time of each valve. The actuator operated by differential PWM shows good linearity as a control element, achieving accurate positioning. This study, as an application, deals with a hydraulic servo system composed of a 4-way spool valve and a load cylinder, where the spool valve is driven directly by the differential PWM actuator. The servo system is designed based on the optimal regulator method of the state variable model. The system performance is investigated through simulations and experiments. Consequently, it is shown that the actuator, operated by differential PWM, plays the role of a linear control element, and that the servo system is well designed by the optimal regulator.

Digital control of hydraulic actuator system operated by differential pulse width modulation.

This study deals with an electrohydraulic servo system which is operated by two 3-way high-speed solenoid valves in the PWM digital mode. It has often been pointed out that there are practical problems to be solved in the conventional PWM systems, such as serious nonlinearities in the valve characteristics. In order to overcome such problems, a new concept of PWM control, that is, a differential PWM method, is proposed in this study. The strategy of this method is to eliminate/minimize significant nonlinearities, such as the dead zone, which regularly appear with conventional methods. In the new method, the pressure difference for driving the actuator is given by pulse trains, their widths modulated by duty input to the valves. The dynamic characteristics of the system driven by the propoded method are investigated by experiment and digital simulation. Consequently, the availability of the proposed method is confirmed well.

A gyroless sounding rocket control system with sub-arc-second pointing stability

The Solar Pointing Aerobee Rocket Control System (SPARCS) has been developed to satisfy the demand from solar experimenters for a lightweight system to point payloads precisely at the sun. A unique feature of SPARCS is that it uses no gyros, during despin and acquisition, as well as during fine pointing. Both attitude and rate are derived from the direction cosine outputs of sun sensors and magnetometers by a simple arrangement of solid-state circuits. Both flight and laboratory results for SPARCS are presented to demonstrate that pointing stability, the jitter amplitude, approaching 0.1 arc-sec with good disturbance response can be achieved. The flight results, from a continuing, successful flight program, show that ±1 arc-sec pointing stability has been achieved by SPARCS I. The laboratory results, from hardware investigations conducted to obtain sub-arc-second pointing for SPARCS II, an improved system, show that stability better than ±0.1 arc-sec has been achieved. Pneumatic systems which use conventional Pulse Width Pulse Frequency (PWPF) valve drive electronics and Fixed Pressure Regulators (FPR) are compared with new systems investigated which include the use of Differential Pulse Width (DPW) valve drive electronics, a Variable Pressure Regulator (VPR) with adaptive control system electronics, and a Fluidic Proportional Thruster (FPT). The new systems investigated are not primarily limited by the pneumatics, as is the PWPF system; they are primarily limited by the noise in the control electronics, which is about 0.1 arc-sec for SPARCS II.

Signal Transduction with Differential Pulse Width Modulation

The Differential Pulse Width Modulation System presented here is a signal transduction scheme applicable to a wide range of data acquisition processes for either large systems such as industrial process control, aircraft flight testing, computerized medical information centers, etc. or individual users seeking low cost, compact measuring instruments. In this scheme, a variable capacitance or equivalent sensor, actuated by the physical quantities to be measured, is combined with an integrated circuit containing mainly logic elements, to generate a series of pulses with fixed height in voltage but varying width in time so that the difference/sum ratio of the width between two adjacent pulses is proportional to the input. Signals thus modulated can be converted readily into analog output by simple low-pass filtering and can also control a simple up-down counter to give digital output, bypassing the conventional analog-digital converter. For portable recording, this differential pulse width scheme facilitates the use of inexpensive tape recorders at no sacrifice in accuracy, since there is no need for precision speed control.

Air Damped Capacitance Accelerometers and Velocimeters

This is a companion paper serving as an extension of an earlier presentation entitled ``Signal Transduction With Differential Pulse Width Modulation''1. In that paper, a scheme was introduced to streamline the data acquisition system bridging a variety of physical parameters to be measured with several forms of signal processing. The essential part of that scheme involves the generation of a differential pulse width modulated signal with integrated logic circuits utilizing d. c. excitation to produce analog output with significant power, a pulse width modulated signal suitable for transmission or tape recording, or a digital output suitable for computer coupling.