Designing and analysis ACS (курсовая работа на английском языке)


Содержание работы

Annotation


Contents

Annotation. 2

Contents. 3

Introduction. 4

The description of the analogousand initial data. 5

Functional diagram.. 6

Actuator RD – 25FA.. 11

The block diagram.. 12

Design part 16

Development of technological process. 20

The economic substantiation. 26

Safety of habitability. 28

List of the literature. 32

The appendix. 33


Introduction

Tens thousand various types of automatic control systems (ACS) are applied now in aircraft and an astronautics which provide high efficiency of productions.

Modern ACS represents the complicated dynamic systems ensuring high accuracy of improvement of control signals in conditions of action of various disturbing interferences. At large values of disturbances and levels of interferences normal operational conditions are upset, accuracy is reduced, and parameters of quality of transients in systems are worsened in comparison with the given specifications. Designing such ACS represents difficult enough problem as devices enter in them and objects of control of a various physical nature.

For obtaining proper characteristics ACS the designer should find conciliatory proposals, as requirements to accuracy and parameters of quality of transients mutually exclusive.

Stability is necessary, but an insufficient condition of normal functioning ACS. Presence of stability testifies only that the transient called by action of external effect or existence of nonzero entry conditions, is damping. But thus are not determined neither damp time, or maximum deflection of a controlled variable, number of oscillations. Namely these parameters also characterize regulation processes course quality.

The large help in designing and analysis ACS to the engineer is given with software Simulink included in mathematical packet Mat Lab.


The description of the analogous and initial data

Frequency of natural oscillations

Damping ratio

Requirements:

-Overshoot   .

-Settling time

Limitations:

           An angle of an elevator deflection:

                   

           A speed on of a control surface deflection:

                   


Functional diagram

Fig. 1.1.Functional diagram of the servomechanism:

ОА – operational amplifier,

AED – amplifier of the electric drive,

FSR – phase-sensitive rectifier,

ALF – amplifier of low frequency,

M – motor,

G – generator,

IP – induction potentiometer,

EMC – electromagnetic coupling of coupling,

R – reduction gearbox.

A servomechanism may be broadly defined as a closed-loop control system in which a small power input controls a much larger power output in a strictly proportionate manner. In applying such a mechanism to the automatic control of an aircraft, the system must be capable of continuous operation and have the ability to

1)  detect the difference between an input and an output (error detection);

2)  amplify the error signals;

3)  control the closing of the servo loop by providing the feedback.

There are two main classes of servomechanisms:

1)  position control,

2)  speed control.

Position Control Servomechanism

    A block diagram of a position control servomechanism is illustrated in Fig. 1.2, and from this it will be noted that it is one in which a load has to be rotated through an output angle  corresponding to an input angle  of a controlling shaft. The controlling shaft is, in this example, mechanically coupled to the wiper arm of a potentiometer, the signal output of which is fed to a servomotor via an amplifier.  The output angle of the load is measured by the second potentiometer whose wiper arm is mechanically coupled to an output shaft.

    The potentiometers are electrically connected such that when their wiper arms occupy corresponding angular positions the servomechanism is in a “null” or zero signal condition. When it is required to move the load to a particular angular position  the controlling shaft is rotated through the appropriate number of degrees; thus the mechanism is no longer at a “null” and an error signal corresponding to angle  is produced and fed to the amplifier. The amplifier has an amplification factor of , and therefore the input to the servomotor is increased to . As the motor positions the load, the output shaft rotates the wiper arm of the second potentiometer to produce a signal corresponding to an angle . This signal is fed back to the amplifier thereby reducing the input error signal to the amplifier so that the real output from this unit to the servomotor is . When the load finally reaches the position required, the servomechanism will then be at a new “null” condition.

Speed Control Servomechanism

    A speed control servomechanism is one in which error signals are produced as a result of a difference between voltages corresponding to input and output speeds, such signals been used to control the speed of the servomotor and load. Referring to Fig. 1.3, it will be noted that the system differs from that used for position control in that the servomotor also drives a device known as a tachogenerator.

    When it is required to operate the load, the servomotor is driven by an amplified input error voltage, , and the motor accelerates the load towards the required speed. At the same time, the motor drives the tachogenerator which produces an output voltage, , in proportion to its speed of rotation. The output voltage, , is fed back to the amplifier thereby reducing input error voltage and so producing a real output from the amplifier equal to . The servomotor in this class of servomechanism is therefore controlled by differences in voltages, and will speed up or slow down until the difference is zero.

 Transient Responses of Servomechanism

    The transient response of servomechanism represents the behavior of the load when a change is made to the input. Let us consider two types of inputs: step and ramp inputs as shown in Fig. 1.4.

    The transient response of the position control servomechanism when its controlling shaft is instantly changed to a new angular position  from an initial position  is shown in Fig. 1.4a. Because of the load (i.e. controlling surfaces) an angular change at the servomechanism output will not be able to follow exactly that at the input, with the result that a large error signal is produced initially. This causes the load to be accelerated to its required position , and thereby reduces the error to zero (instant ). At this point however, and although the acceleration is zero, the control surfaces have reached a steady rate of change, and so it overshoots resulting in an increase of error in the opposite sense to decelerate the load until it comes to rest in the opposite direction (instant ). By this time the error signal is equal to the original error signal but of opposite polarity, and so the load is accelerated back towards the required position and produces another overshoot, and so on. If the frictional losses in the system are negligible, a continuous oscillation is produced.

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