Automatic controls and regulators: A compilation

Devices, methods, and techniques for control and regulation of the mechanical/physical functions involved in implementing the space program are discussed. Section one deals with automatic controls considered to be, essentially, start-stop operations or those holding the activity in a desired constraint. Devices that may be used to regulate activities within desired ranges or subject them to predetermined changes are dealt with in section two

Electrohydraulic servovalves – past, present, and future

In 2016 it is 70 years since the first patent for a two-stage servovalve was filed, and 60 years since the double nozzle-flapper two-stage valve patent was granted. This paper reviews the many alternative servovalve designs that were investigated at that time, focusing on two-stage valves. The development of single-stage valves – otherwise known as direct drive or proportional valves – for industrial rather than aerospace application is also briefly reviewed. Ongoing research into alternative valve technology is then discussed, particularly focussing on piezoelectric actuation and the opportunities afforded by additive manufacturing

A review of electro-hydraulic servovalve research and development

This paper provides a review of the state of the art of electro-hydraulic servovalves, which are widely used valves in industrial applications and aerospace, being key components for closed loop electrohydraulic motion control systems. The paper discusses their operating principles and the analytical models used to study these valves. Commercially available units are also analysed in detail, reporting the performance levels achieved by current servovalves in addition to discussing their advantages and drawbacks. Adetailed analysis of research that investigates these valves via computational fluid dynamic analysis is also provided. Research studies on novel control systems and novel configurations based on the use of smart materials, which aim to improve performance or reduce cost, are also analysed in detail.</p

A review of electro-hydraulic servovalve research and development

This paper provides a review of the state of the art of electro-hydraulic servovalves, which are widely used valves in industrial applications and aerospace, being key components for closed loop electrohydraulic motion control systems. The paper discusses their operating principles and the analytical models used to study these valves. Commercially available units are also analysed in detail, reporting the performance levels achieved by current servovalves in addition to discussing their advantages and drawbacks. Adetailed analysis of research that investigates these valves via computational fluid dynamic analysis is also provided. Research studies on novel control systems and novel configurations based on the use of smart materials, which aim to improve performance or reduce cost, are also analysed in detail.</p

Modification of the rotary machining process to improve surface form

Planing and moulding operations carried out within the woodworking industry make extensive use of rotary machining. Cutter-marks are produced on the timber surface which are generally accepted as unavoidable. More noticeable surface defects may be produced by such factors as cutter-head imbalance, and until recently most research has concentrated on removing these defects. When a high quality finish is required, a further machining operation, such as sanding, is often required to remove cutter-marks. What is required, is a modified machining process which combines a surface closer to the ideal fixed knife finish, whilst retaining the flexibility, practicality and cost effectiveness of rotary machining. [Continues.

A dual lane piezoelectric ring bender actuated nozzle-flapper servo valve for aero engine fuel metering

Amongst many other high performance flow control applications, servo valves are used to control aero engines by metering the fuel delivered from the fuel pump. Conventionally, a fuel metering servo valve has a pilot stage with an electromagnetic torque motor moving a flapper which differentially restricts a pair of nozzles to create a hydraulic signal (i.e. a pressure difference). These valve pilot stages use mature, optimised technology such that to achieve improvements requires a novel approach. Torque motors in particular present reliability and manufacturing difficulties, and news solutions should ultimately allow a reduction in manual assembly and set-up, improve repeatability, and eliminate failures associated with fine wire devices. In this paper, a pilot stage actuated by piezoelectric ring benders is proposed, designed, built and tested, and test results are compared with a model used to predict pressure-flow characteristics. A particular challenge is the need to include redundancy, and thus a pair of ring benders is used, allowing isolation between duplicated electrical control channels. Another challenge is the mounting of the ring bender, which has to flex to allow the outer edge of the ring bender to deform, yet be stiff enough to adequately react against generated forces. O-ring mounts made from three different elastomer materials are compared in this study. In aerospace, an added complication is the large range of fuel temperature; F70 fluorosilicone O-rings have been chosen with this in mind, and successfully demonstrated in the range -50 C to +180 C. With one active and one inactive ring bender to simulate a failure condition, the new dual lane pilot stage achieves +/-50 μm displacement under test, giving control port flows up to +/-0.6 l min -1, and a control port pressure variation of 40 bar using a 100 bar supply pressure difference (supply minus return pressure). This research establishes that a piezoelectric aero engine fuel valve is feasible, and in particular, that piezoelectric ring bender actuators with elastomeric mountings are highly suited to this application. </p

Design and analysis of a high performance valve

Most valves available in the fluid power industry today are capable of achieving either a large flow rate or a quick response time; however, often they are unable to deliver both simultaneously. Commercially available valves that can produce both at the same time require complex geometries with multiple actuation stages and piloting pressures, making them expensive components. To establish their active usage in applications across the fluid power industry, a reduction in price for these components is paramount. The Energy Coupling Actuated Valve (ECAV) is capable of solving the large flow rates with fast actuation speeds trade-off by utilizing a new, high performance actuation system. The Energy Coupling Actuator (ECA) is an innovative actuation system that separates the kinetic energy source mass from the actuation mass. Intermittently coupling the actuator to a constantly rotating disk creates an energy transfer from the rotating disk’s kinetic energy to the normally stationary actuator. This intermittent coupling process is controlled by changing the magnetic field inside the actuator’s two coils. Magnetorheological (MR) fluid resides in a 0.5mm fluid gap between the spinning disk and the actuator, and when the magnetic flux builds across this gap, it causes the actuator to move rapidly in a translational movement. The MR fluid changes to a solid between the gap and frictionally binds the actuator to the disk, causing the actuator to move up or down, depending on which coil is actuated on the spinning disk. The liquid-solid conversion from the MR fluid occurs in less than one millisecond and is completely reversible. The shear strength of the fluid is proportional to the magnetic field strength inside the system. The actuator is connected to either a poppet or spool assembly for valve actuation, and the position is controlled through intermittently binding the actuator to the disk. Two valve prototypes, one poppet and one spool type, were machined, and concept validation has been done in both simulation and experimentally. Experimental results show that the poppet reaches a 4mm displacement in 19.8ms opening and 17ms in closing under 33 L/min flow. The spool valve experimentally transitioned in 4.8ms at the same flow rate

Non-linear control of a hydraulic piezo-valve using a generalized Prandtl-Ishlinskii hysteresis model

The potential to actuate proportional flow control valves using piezoelectric ceramics or other smart materials has been investigated for a number of years. Although performance advantages compared to electromagnetic actuation have been demonstrated, a major obstacle has proven to be ferroelectric hysteresis, which is typically 20% for a piezoelectric actuator. In this paper, a detailed study of valve control methods incorporating hysteresis compensation is made for the first time. Experimental results are obtained from a novel spool valve actuated by a multi-layer piezoelectric ring bender. A generalized Prandtl-Ishlinskii model, fitted to experimental training data from the prototype valve, is used to model hysteresis empirically. This form of model is analytically invertible and is used to compensate for hysteresis in the prototype valve both open loop, and in several configurations of closed loop real time control system. The closed loop control configurations use PID (Proportional Integral Derivative) control with either the inverse hysteresis model in the forward path or in a command feedforward path. Performance is compared to both open and closed loop control without hysteresis compensation via step and frequency response results. Results show a significant improvement in accuracy and dynamic performance using hysteresis compensation in open loop, but where valve position feedback is available for closed loop control the improvements are smaller, and so conventional PID control may well be sufficient. It is concluded that the ability to combine state-of-the-art multi-layer piezoelectric bending actuators with either sophisticated hysteresis compensation or closed loop control provides a route for the creation of a new generation of high performance piezoelectric valves.<br/

A fault-tolerant triple-redundant voice coil motor for direct drive valves: Design, optimization, and experiment

AbstractA direct drive actuator (DDA) with direct drive valves (DDVs) as the control device is an ideal solution for a flight actuation system. This paper presents a novel triple-redundant voice coil motor (TRVCM) used for redundant DDVs. The TRVCM features electrical/mechanical hybrid triple-redundancy by securing three stators along with three moving coils in the same frame. A permanent magnet (PM) Halbach array is employed in each redundant VCM to simplify the system structure. A back-to-back design between neighborly redundancies is adopted to decouple the magnetic flux linkage. The particle swarm optimization (PSO) method is implemented to optimize design parameters based on the analytical magnetic circuit model. The optimization objective function is defined as the acceleration capacity of the motor to achieve high dynamic performance. The optimal geometric parameters are verified with 3D magnetic field finite element analysis (FEA). A research prototype has been developed for experimental purpose. The experimental results of magnetic field density and force output show that the proposed TRVCM has great potential of applications in DDA systems

A parsimonious model for the proportional control valve

A generic non-linear dynamic model of a direct-acting electrohydraulic proportional solenoid valve is presented. The valve consists of two subsystems-s-a spool assembly and one or two unidirectional proportional solenoids. These two subsystems are modelled separately. The solenoid is modelled as a non-linear resistor-inductor combination, with inductance parameters that change with current. An innovative modelling method has been used to represent these components. The spool assembly is modelled as a mass-spring-damper system. The inertia and the damping effects of the solenoid armature are incorporated in the spool mode1. The model accurately and reliably predicts both the dynamic and steady state responses of the valve to voltage inputs. Simulated results are presented, which agree well with experimental results