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Transistorized alternating current servomechanism design offers a number of advantages over other types because of their small size, low weight, high reliability, precision accuracy, and wide range of control. These lecture notes describe a cryogenic oxygen flow control servomechanism subsystem typical for an auxiliary power unit fuel system. Three possible types of feedback for this type of subsystem are: position feedback accomplished by gear tiain and synchro-transformer, position with velocity feedback accomplished by adding a rate generator and position feedback with compensating network. Servomechanisms employing any of these three types of subsystems can provide the oxygen flow control desired. The differences in performance relate primarily to steadiness of flow with the companion heat modulation. The damping ratio parameter can be used to achieve a reasonable response time and maintain a reasonable value for overshoot. Low damping ratio gives fast response but large overshoots. High damping ratios give low overshoot but slow response. This paper discusses transistorized servomechanism design for the basic position servo, plus rate feedback or network compensation. Included are design and application considerations, step-by-step design procedures, and the solution to sample design examples

The mechanical tension in the anode wires of a multiwire proportional chamber must be sufficient to prevent wire displacement due to electrostatic forces between wires but must not exceed the breaking strength of the wires. A technique is described for interferring the tension by measuring the mechanical resonant frequency of the wires. It employs a servomechanism which uses the small capacitance change of the selected wire to tune a variable frequency oscillator to the mechanical resonance. Since it is not necessary to observe the wires visually, the technique is applicable to closed chambers in inaccessible locations.

The synchronized astable multivibrator bridge using time delay between pulses, is a new temperature- stabilized linear transducer and a measuring device with a digital counter of R or C parameter changes or corresponding nonelectric quantities. It is used as an error detector, compatible with an electronic relay, bistable multivibrator or corresponding flip-flop integrated circuit, in a simple and reliable on-off servomechanism whose hysteresis or dead zone corresponds to relative changes of a variable element of about 10-5. This servomechanism is convenient for measurement, control, command or recording, especially for remote operations. Applied with thyristors it can be used as a sensitive and contactless thermostat or switcher.

The multi-functional externally powered arm prostheses currently available in the UK, suitable for fitting to children suffering from congenital deficiencies of both upper limbs, are all powered by compressed carbon dioxide gas's2. Arm articulation is accomplished by using three-way control valves in association with differential area piston actuators, or two three-way valves mounted back-to-back with double acting actuators, in closed loop position controlled servo-mechanisms. Several advantages are associated with the use of hydraulic fluid as the powering medium for such devices3 These mainly accrue from the relative compressibility of the two media. The virtually incompressible nature of hydraulic fluid results in safe operation of systems at higher working pressures and consequently results in better power to weight ratios. Thus hydraulically powered position control systems, designed to conform to the prosthetic requirements of safety, compactness and lightness, are able to meet load, response and stability specifications whch exceed the capabilities of their pneumatic counterparts. The output stiffness of hydraulic servos is also much greater, which decreases their disturbance by external loads. The construction of a hydraulically powered arm prosthesis has not been possible to date due to lack of a suitable power source. However, recent successful development of a prototype miniature hydraulic power unit indicates that portable hydraulically powered systems are viable'? 7 1 Energy storage for this hydraulic supply is accomplished by electric batteries which offer great advantages in ease of recharging or replacement compared with compressed carbon dioxide storage cylinders. This should make such a system popular in the United States where, due to the logistic difficulties of supplying gas cylinders, most externally powered prostheses are actuated by electric motors, resulting in heavier arm systems with poor dynamic performance. Other areas of hfficulty in implementing a hydraulic arm prosthesis include the development of suitable control valve and actuator system^^^^"^ and the adaptation of suitable terminal devices to make them compatible with the arm structure and hydraulic power. This article describes the current state of the hydraulic prosthesis under construction at University College London, under the four main headings of arm structure, portable power supply, valve and actuator system and terminal device. It should be stressed that this project is aimed at producing a prototype hydraulic arm and that the arm now nearing completion will not be used for clinical trials, but could form the basis of a system which, suitably modified to permit small batch production, could be used by bilateral dysmelics.

The load input tensile tester, performance of which is not influenced by the mechanical properties of the material to be tested had been designed and manufactured.The ability of this tester are investigated through experiments.This tester is proved to test the mechanical properties of textile fabrics un'ler the load input which is an arbitrary function of time when the following conditions are satisfied : i) To avoid the velocity error of the tester, the servo mechanism should satisfy the inequality : 1/Ks+Kpf >1iii) To make the performance of the tester to be independent of the properties of the test material to be tested, a compensation circuit of the servo system should satisfy the conditions : K0T2Tpf>>KpfT1Gc (s) =aT2s+1/T2s+1, T2>1

Semiautomated tasks frequently require humans to perform highly repetitive boring jobs such as placing objects into machine fixtures. The use of an electromechanical hand design is discussed which may operate in conjunction with industrial robots, part feeders, and minicomputers to perform some of these jobs. Flexibility is achieved with the same hardware by using different control algorithms for differently shaped objects. The design principle which permits simplicity is that the motion which is used to adjust object orientation is also instrumental in the detection of orientation. A ``hand'' was built and a control algorithm to orient a specific object was developed. The control algorithm first recognizes orientation by computing asymmetries and then conditionally adjusts a positional servomechanism in the hand to bring the object to a standard orientation. Tests verified hand performance and indicated restrictions on object shape. Regardless of the initial angle (360° range) about the uncontrolled axis, the computer-controlled hand adjusted this angle to within ±3°. For the prototype, object shape is primarily restricted by the requirement that objects must have their principal axes directed to within ±10° by conventional part feeders and sorters.

Previous studies of multi-variable servomechanism problems, using modern control theory, have relied almost exclusively on optimal control techniques to formulate and solve the problem. In that way, servo tracking has been obtained as a by-product of minimizing some contrived optimization functional. In this paper, a new servo theory is proposed which makes use of simple linear algebraic methods, rather than optimal control methods, to formulate, study, and solve the multi-variable linear servomechanism problem. The result is a new, algebraic procedure for designing high-performance output-feedback servo controllers for multi-input, multi-output, possibly time-varying linear plants. Moreover, when the plant is also subjected to external disturbances, the servo controllers designed by this new procedure will continue to provide consistently accurate tracking of complex servo command inputs—even though the disturbances are persistent acting, unknown and unmeasurable.

Some apparatus and instrumentation have been developed for improving the relevance of dynamic test data obtained from human muscle specimens. In the first part of this paper the background is given and a special clamping and mounting arrangement is described which allows a small specimen to be made ready for test in less than a minute. The second part describes a new timing and sequencing instrument for regulating the electrical and mechanical stimulations applied to the specimen. The mechanical displacements are controlled by a type of servomechanism which can be driven from an f.m. tape recorder.

A new definition of transmission zeros for a linear, multivariable, time-invariant system is made which is shown to be equivalent to previous definitions. Based on this new definition of transmission zeros, new properties of transmission zeros of a system are then obtained; in particular, it is shown that a system with an unequal number of inputs and outputs almost always has no transmission zeros and that a system with an equal number of inputs and outputs almost always has either n-1 or n transmission zeros, where n is the order of the system; transmission zeros of cascade systems are then studied, and it is shown how the transmission zeros of a system relate to the poles of a closed loop system subject to high gain output feedback. An application of transmission zeros to the servomechanism problem is also included. A fast, efficient, numerically stable algorithm is then obtained which enables the transmission zeros of high order multivariable systems to be readily obtained. Some numerical examples for a 9th order system are given to illustrate the algorithm.

A typical high performance phase-locked capstan speed control system of an analog instrumentation magnetic tape recorder/reproducer is analyzed. Attention is given to component parameter variations, particularly in the dc motor-capstantachometer assembly. A detailed model of the electro-mechanical components of the tape moving system is developed and is adjusted using comparisons of the transfer function calculations and experimental closed loop measurements for a range of parameter values.

In the case of applying a lever which swings about the horizontal axis by propotional control of an electric servomechanism to a manipulator's arm etc., it is difficult to position the manipulator's arm correctly according to the unbalance due to the grasping and releasing an object. In this paper, a balancing device using a movable counterweight is proposed for the purpose of positioning the arm correctly, and its characteristics and stability are studied. As a result of analysis, it is confirmed that such a balancing device is available for the manipulator's arm and automatic balancing device.

The additional complications of hydraulic elements have not prevented servomechanism engineers from resorting frequently in recent years to the use of high-pressure hydraulic motors in place of electric motors. The reasons for this trend are examined in relation to the performance demanded in many modern servomechanisms, particularly these in which a high natural frequency must be associated with small overall size and weight, and the methods adopted for driving hydraulic motors are described. The combination of the well-established electronic servo ‘ shaping ’ techniques and servo amplifiers with a hydraulic motor is achieved by means of an electromechanical transducer and examples of this element are described. Some special features of hydraulic components are dealt with, such as the effects of stiction and hydrodynamic forces in piston valves, and in addition the serious destabilizing effects of the integrating action of certain hydraulic elements on a servo loop, and its reduction with subsid...

A servo system is described whereby a rotating drum has its angular speed and angular position controlled to fine limits by using a crystal oscillator as a stable reference. The device was developed for use as a ?magnetic storage system? forming part of a digital computing machine; it has, however, other possible applications. The various components and their functions are described individually and an overall analysis developed. The theoretical performance is compared with that obtained experimentally, and a discussion of the factors affecting the final accuracy is included.

WHEN a servomechanism contains an on-off relay or contactor as a controlling device, it is called a contactor servomechanism. Among the great advantages of this type of servomechanism are its simplicity and low cost.1 One of the great disadvantages, however, is that it falls in the category of nonlinear systems. Unfortunately, the state of the art at present is such that these systems do not lend themselves to analysis as readily as do conventional linear ones. Fig. 1 shows a diagram of a typical contactor servomechanism. Fig. 2 shows the block diagram of this same system.

Design considerations relating to the construction of a high performance servomechanism are discussed here. In particular, the improvement in performance that may be achieved through the use of lead networks* and the valuable guides to system synthesis afforded by sinusoidal analysis1-5 are demonstrated. Direct reference to an armature-controlled d-c motor system** designed by the author is made and its dynamic characteristics are considered in detail in order to show the correlation between theory and practice as applied to a servomechanism design.

In the preceding paper, we have already discussed a relay servomechanism operating on sampled data. In this paper is treated the cycling phenomenon of on-off control operating on sampled signals of a process, whose characteristic is approximated by a first-order system with a dead time. Such a system has been practically used as a chopper bar galvanometer type control system for a long time. The experiment was carried out using a water level control system and the result of the analysis is shown to be in very good agreement with that of the experiment. Optimum performance of this system is defined and a method to obtain it is considered.

NUMERICAL POSITIONING controls for machine tools have in recent years demonstrated their ability to effect considerable economies in many industries; hence, further applications of these controls to machines may be expected.

After a theoretical discussion of the basic physical principles involved in the dew-point method of hygrometry, which serves to establish the inherent advantages of the technique, the paper describes the operating principles and the design of an improved, automatic, electronic dew-point hygrometer for laboratory or field use. The instrument makes use of photoelectric detection of condensation on a cooled, polished metal mirror combined with a radio-frequency induction heating system and an all-electronic proportional heat-control servo system. The instrument makes possible the continuous and automatic measurement of atmospheric water-vapor under all conditions of temperature with nearly constant accuracy and small lag.

This paper concerns an objective, analytical and experimental investigation of a novel control technique, namely, the feedforward technique. Following a brief literature survey outlining the genesis of the technique, a detailed analysis of an ideal feedforward servomechanism model is presented. In the analysis Liapunov's direct method has been used for the determination of the stability of the system. An estimate of the settling time of the system has also been made using the Liapunov function. Next, the experiments that were carried out on a simulated feedforward mechanism model are reported. The paper concludes with a suggestion on the possible use of this technique in the design of a model reference adaptive system, investigation on which is underway.

A step change in light intensity evokes a damped oscillation in the human corneoretinal potential. A mathematical model has been developed to describe this damped oscillation. The present study was conducted in order to explore the linearity of the servomechanism hypothesized in this model.

It is generally known that the design of linear systems for stochastic optimization for mean-square-error minimization leads to optimal systems that are insufficiently damped to be of practical utility. It is shown here that a modified definition of error, employing a properly chosen single-time-constant ideal, leads, on mean-square-error stochastic optimization, to systems which have much better damping characteristics. The procedure is illustrated by a typical gain-optimization problem in a servo system.

A brief review of existing methods and their limitations is followed by a description of what is believed to be a new approach to the problem of thyratron control. This approach enables a linear control of firing point to be achieved over the whole range from 0–180 deg. and details of a practical circuit are given together with some experimental results.

The self-aligning moment at the king-pin can be transmitted to the steering wheel as the restoring moment through the powered steering system, if a bilateral servomechanism is used as its servo-unit. In this paper the influence of this restoring force on the stability of the lateral motion of an automobile is studied, making us of the root-locus method. The results show that (1) the motion may become unstable, if the restoring force is not given to the steering whel, (2) there is an optimum ratio of the restoring moment at the steering wheel to the king-pin moment, and (3) the restoring force can be given by a spring installed to the steering mechanism, but in this case the lateral motion may become unstable at high speed.

A servomechanism has been designed and built for controlling the output of an artificial ventricle. Venous pressure was selected as the primary parameter of control because of experimental and clinical studies which report this mechanism to assume control under certain conditions in which neural and/or hormonal control mechanisms are attenuated. In this control system, venous pressure, as measured with a pressure transducer, is compared to an “ideal” venous pressure, usually 0 mm Hg. An error signal is thus generated, amplified, and integrated with respect to time. The integrated error signal is fed into a programable d-c power supply. The power supply output runs a small, positive-displacement artificial ventricle. The pump output is controlled by setting the venous pressure. Studies in a mock circulation setup in which venous return was varied over a wide range demonstrated how either blood loss or pooling of blood in the periphery will lead to a diminished ventricular output while the venous pressure is maintained at the same level. This situation has its clinical analogues. It is anticipated that the use of two such venous pressure-controlled artificial ventricles as a heart replacement in the experimental animal will permit changes in heart output in accord with tissue demands both at rest and during exercise. venous pressure regulation Submitted on February 28, 1963

In a-c servomechanisms tandem compensation is effected by the use of a-c notch-type networks, which operate on the modulating envelope by virtue of being resonant at, and sufficiently symmetrical around, the carrier frequency. However, if carrier frequency drifts away from the notch, the two sidebands of suppressed-carrier-modulated signal around it are no longer symmetrical. The adverse effects of such drifts have been analyzed by a number of authors. This problem is of great importance in air-borne installations where closely regulated carrier-frequency supply would increase the weight, cost, space, and complexity of the equipment. It would be most economical to design a network which would provide satisfactory compensation for a predetermined carrier drift.

An alternative method for determining the angular position of a rotating shaft is introduced. The required information is obtained from the envelopes of a modulated carrier at the stator terminals of an ac servomechanism. Essentially, a single-phase constant amplitude carrier signal is applied to the rotor winding; with zero stator current, the amplitude of the transformed carrier at any stator winding depends on the cosine of the angle between the rotor and stator windings, provided the ratio of rotor speed to carrier frequency is small. The stator envelopes may be decoded by analog methods to give a single analog signal calibrated to indicate the shaft position within a 360° range. An example of the application of this method to static drives for ac machines is included.

The design and performance of a servosystem for controlling pressures from a few mm Hg to atmospheric pressure is given. The technique used is applicable to maintaining a predetermined constant pressure for an indefinite period with high vapor pressure substances (i.e., liquid gases) in the system or for the automatic scan of pressure with a shaft rotation as the input. The fluctuation of the system pressure during cycling of the servomechanism is considerably less than 1% over most of the pressure range and is about 0.1% (±0.05%) for pressures near 30 cm Hg absolute.

The balance described is particularly well suited for use in an analytical laboratory in which repetitive weighings are made to an accuracy of one part in 5000. It is characterized by rapidity of operation, and robustness of suspension. Its regular use should enble substantial savings in time and labour to be made. The beam is balanced by an electronic servo system with a fast response speed and excellent long-term reliability.

A certain type of hydraulic remote position controller contains two resonant systems in its sequence. These are caused by the presence of resilience in the shaft connecting oil motor and mechanical load and by hydraulic resilience of the link between oil motor and oil pump. An idealized analysis of the system yields a sixth-order linear differential equation. When equalizing networks and possible non-linear effects are considered, the solution of the system equation by mathematical methods over a large range of parameters becomes impracticable. To ease the problem of computation an electronic simulator was designed. The paper includes a description of the simulator, and also an outline of the experimental work carried out to check its performance.

IN HIS PREVIOUS PAPERS1?3 the first author has given a general analysis of nonlinear coupled circuits and applied the method to the analysis of servomechanisms with nonlinear feedback control. This paper reports the results of a stability study of a third-order servomechanism with multiplicative feedback control. The nonlinearities in the control system, and hence the differential equations representing the system, are introduced by the multiplication of certain quantities, or variables, of the system. For example, if the actuating signal e is multiplied by itself, one obtains e2, which in turn introduces a nonlinear term in the final differential equation representing the feedback control system.

A servomechanism must hold its error or the difference between input and output, to as small a value as possible. If a large error appears as a result of a rapid change in the value of an input position signal, then high acceleration and high output speed are desirable, and these in turn are favored by a low damping ratio. When the error is near zero, the speed should be reduced rapidly so that overshoot does not occur, and this requires a high damping ratio. Thus the use of nonlinear damping which has some inverse relationship to the error has been proposed by several investigators.1?5

For a given parabolic dish antenna the servo system has been designed theoretically to maintain the antenna speed of 15 r.p.m. constant in azimuth and attempt has been made for determining the size of antenna drive motor and optimum gear ratio. To facilitate the determination of gear ratios for different motor powers and torque, the plots have been presented.

An idealization of a servomechanism which is used in a digital positioning circuit is analyzed. The loop consists of an ideal integrator, a finite time delay and a nonlinear signal limiting element. An exact solution is derived. Also, a simple approximate solution and an error term are obtained. Finally, curves are given which express the time necessary to zero in on the final position from a given initial position as a function of the loop parameters.

This paper presents a method for obtaining dead-beat response of third-order servo systems. It has been shown that among the three state variables, viz. error, error rate and error acceleration of a third-order system following a step input signal, the last two reach simultaneously zero values at intervals of one time period of damped osecillation if the real part of the complex root be equal to the real root of the closed-loop characteristic equation. Dead-beat response can be obtained on reducing the finite value of error to zero, when the above condition is achieved for the first time, by processing the input signal and applying the same with the help of a switching circuit. The results of simulator study of a proposed third-order system have also been given.

The paper describes novel piezoelectric devices for micro-movement applications. Such devices are ceramic composite plates, cylindrical tubes, composite discs etc which appear as servo controllers in closed-loop systems. The basic representatives of composite plate actuators are the bimorph and multi-morph ceramics. These are suitable for micro deflection. One of their applications is the laser beam triple deflector which is outlined in detail and which proves the applicability of ceramic elements as actuators in closed loop systems. Another group of piezoelectric elements is represented by the crystal microstep reversible motor which is suitable for linear translatory movement in the order of microns. The driving element is either a piezoelectric tube or bimorph discs. In both cases the steps are controlled by logic signals which are derived from a rotary switch in the case of simple remote control system or from more complex devices as digital or analogue computers in the case of closed loop servo systems. Finally the dynamics of composite plate actuators, like bimorph and multimorph are developed by applying and modifying D’Alambert-Timoshenko equation of vibration. The method presented considers further aspects of the ceramics which are piezoelectric, electrostatic and electromechanical in nature.

IN THE design of a positional servomechanism, the desired result is a system whose output member will follow exactly the instantaneous position of the input member. This, of course, imposes requirements on the system when in the dynamic or transient state which cannot be realized.

Servomechanism errors in a 2-dimensional contouring system are analyzed to determine the position error of a tool center negotiating a corner formed by two straight lines. The results establish the feed rate which will permit a specified tolerance on path error to be met. Transient response intormation from analog computer tests is summarized in nomographic form to permit convenient consideration of the maximum tool center path error during the design of the servomechanisms.

This paper considers the problem of controlling a multi-input, multi-output, linear, time-invariant dynamic system subjected to disturbances belonging to a known class of signals. The objective is to find a feedback control law which makes the outputs of the system track command signals belonging to a known class with zero steady-state error and a satisfactory transient response. Necessary and sufficient conditions for the existence of a state feedback control law that achieves this objective are obtained. The problem of stabilizing the closed-loop system while tracking with zero steady-state error is solved, the problem of controlling the system using output feedback is discussed and sufficient conditions for its solution are obtained. In addition, it is shown that if certain of the above conditions are not satisfied for a given system and class of disturbance and command input signals, then they cannot be satisfied using dynamic (integrator) compensation.

An important class of automatic control devices whose use is not restricted to any one field is that known as servomechanisms. Defined technically, a servomechanism is an automatic control system having a controlling element actuated by some function of the difference between the actual and desired response of the controlled element. By the use of operational methods in handling physical transients, the servo systems are readily analyzed and quantitative design characteristics obtained. I t is the purpose of this paper to show the use of the Laplace transformation in the analysis and design of servomechanisms. The treatment is divided into three main par ts : (a) the fundamental theory of servomechanisms; (b) the Laplace transformation; and (c) application to a simple servomechanism. Because of military secrecy, the most interesting applications are restricted and cannot be treated publicly. For this reason, the subject matter of this paper is based entirely on accessible literature, and the example chosen is typical of applications in various fields including the military. THEORY OF SERVOMECHANISMS IN A BROAD SENSE, automatic control devices are used to replace human labor by supplying power of proper form and accurate amount to perform a given task with little or no direction. In fact, they are usually more reliable and accurate and economically cheaper than their human counterpart. Automatic control mechanisms may be classified on the basis of the type of control requirements. In the open-cycle type the controlling quantity is independent of the controlled quantity—for example, a time-actuated traffic signal. When the controlling quantity is dependent upon the controlled quantity, the control is of the closed-cycle type. A simple example would be a thermostat. Combinations of both types are also used, such as in a clock-set thermostat. The power requirements of the two types are quite different. Open-cycle devices are usually quite simple and rugged, since the controlling mechanism has sufficient power to operate the device directly. Closedcycle devices are usually more complex, since the controlling mechanism is some form of measuring instrument and has insufficient power to operate the device. Hence, some sort of power or torque amplifier is required to give instrument indications at higher power levels. Presented at the National Fall Meeting, I.A.S., Dayton, Ohio, November 9-10, 1944. * Assistant Professor of Mathematics and Mechanics, College of Engineering and Commerce. Now Ensign, Aircraft Electrical Division, Naval Research Laboratory. For example, in the automatic piloting of ships or aircraft, a measuring instrument sensitive to compass settings must eventually control the ship itself. For purposes of technical definition, a servomechanism is an automatic control system having a controlling element actuated by some function of the difference between the actual and desired response of the controlled element. The power-amplifying device that tends to. make this difference, or error, zero is called a servomotor or "servo." The component parts can be visualized better with the help of the block diagram in Fig. 1. If, in particular, it is desired to keep the corrected input constant, the servomechanism is called a "regulator." The physical behavior of the servo and controlled system is always such as to affect the quantity under consideration and its successive rates of change with respect to time. The interrelation between the different quantities and the effects of the system components on them is expressed conveniently in the following manner. If F(p) is the transfer polynomial operator for the servo and if G(p) is the transfer polynomial operator for the system, where p = d/dt, then e(t) = i(t) o(t) c(t) = F{p)e{t) o{t) = G{p)[c{t) + d(t)] Solving for the error as a function of the operators on the input e{t) = [*(*) -G(p)d(t)]/[l + F(p)G(p)] and o{t) = [F(p)G(p)m + G(p)d(t)]/[1 + F(p)G(p)] Since G(p) is a function of the system and changes only with it, the basic problem of design in automatic control is to determine a servo having the required transfer operator such that the system is stable and the error lies within specified limits.

The analysis of Non-linear Control Systems with Random inputs is of very great practical interest. In such an analysis statistical linearization techniques are useful since they are simple to use, being based on the linear transformation of random functions. Mathematical methods for this transformation are quite straightforward. This technique results in the non-linear element being replaced by an equivalent linear gain. There are methods available for the analysis of ‘zero-memory’ or interialess non-linearities. A method is proposed for the analysis of an important ‘memory’ type non-linearity, a relay with hysteresis. This type of non-linearity is important in practice since relay or on-off servos are an important class of systems.

The electronic photometer of a recording spectrophotometer is described in detail. Sources of error of the circuit and experimental measurements of the inherent noise of the system are discussed. A segmented diode circuit is described for converting data in absorption to units of optical density with an accuracy of better than 1 percent. The electronic circuit of the servo system to correct the nonlinearity of the wavelength scale is also described.