Consider now transient response of the servomechanism to a ramp input (Fig.1.4b). In the early stages of the input (instant ), and while the error signal is small, the load accelerates slowly and lags behind the input. The signal increases as the lag increases, thereby building up the acceleration. Eventually the input and loud speeds are equal (instant ), but since a substantial position error exists, the load continuous to accelerate. Then the acceleration is reduced, and the load attains a constant speed (instant ) at zero position error with no error signal, and so on. Thus, as in the case of a step input, a continuous oscillation is produced.
If there are coloumb and viscous frictions the oscillations are damping (Fig.1.4). But using only inherent friction light damping is achieved. It is necessary, therefore, to use special approaches to restrict the oscillations.
The actuator is intended for activity in a structure of the servomechanism as an actuator of the autopilot and mechanically connected to a control system of an airplane.
The main characteristics:
Voltage across the winding of excitation of the engine
Voltage across the winding of control of the engine
The firing moment of the engine
Voltage across the winding of excitation of a tachogenerator
Steepness of voltage output of a tachogenerator not less
Steepness of voltage output of the induction potentiometer not less
Power of engine DG – 25B
Efficiency of the reduction gearbox
The given block diagrams of linear and non-linear servomechanisms we find in mathematical packet MATLAB 6.1 as follows:
1. We start MATLAB;
2. In a command line we write Demos;
3. In menu MATLAB Demos Simulink it is chosen Aerospace in which menu it is chosen Electrohydraulic Servomechanisms;
4. We receive schemes of linear and non-linear servomechanisms;
Drawing of transient characteristics (of linear servomechanism) is made under following scheme
From the received schedules it is visible, that the system is steady.
Research of frequency response of servomechanisms
Research of frequency response we shall conduct on linear model.
To draw frequency characteristics it is necessary to receive a transfer function of a servomechanism.
Transfer function of closed-loop system is
where - transfer function of disconnected system
proceeding from this
The logarithmic amplitude frequent characteristic,
The logarithmic phase frequent characteristic,
The amplitude-phase frequent characteristic,
Drawing LAFC, LPFC , MPFC with the help of commands Bode, Nyquist.
From the received schedules it is visible, that the system is absolutely steady.
The principal diagram of the final cascade of the servomechanism amplifier
Fig. 2.1. The final cascade of the amplifier
It is necessary to choose transistors for obtaining in load of voltage and a current .
We choose the amplifier of general application . Its basic parameters:
3. Maximum voltage on a collector
Taking into account values , we choose transistors и . Their basic parameters:
These transistors meet the requirements on permissible
, transistors can be used without heat rejections.
6. Power supply voltage of the amplifier
At transistors are open for currents:
, that is the amplifier provides a current of load
10. Maximum voltage of transistors:
11. Power, which dissipates on transistors:
Taking into account the received values, we choose transistors
12. Currents of bases of transistors:
13. Currents of dividers and also should exceed considerably. We receive .
14. Resistance of resistors it is considered, taking into account :
The analysis standard TP and selection of operations
Analyzing standard TP, we choose operations for worker TP .
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