Week 4: Servo Systems Flashcards
In an aircraft with cable and pulley controls how is the autopilot servo connected to the control cables?
With a bridle cable
What basic requirement of a closed-loop system (not present in open loops) enables present load position to be sensed?
Feedback
An error signal is the difference between what two quantities fed to the CT (error detector)?
Input and feedback
The output of the summing point must contain information that controls what 2 factors of load movement in a position servo?
Amount and direction of rotation
In a typical velocity servo block diagram what device is placed in the feedback loop that is not present in the position servo?
Tachometer
What are the 2 common methods used in a feedback loop to anticipate control surface movement?
Back EMF feedback
Tach Gen feedback
In a servo system using BACK EMF feedback, the servo is driven with what type of signal?
Square wave with varying pulse widths
What type of servo is commonly used in Transport Category aircraft?
Hydraulic servos
Why are DEMODULATOR circuits used in some servo systems?
Convert AC error to DC error
What is the purpose of sensors and gyros?
Detect changes in aircraft attitude
What is a servo system?
Uses weak control signal to move a large load with great accuracy
Servo systems can be either:
electromechanical, electrohydraulic, hydraulic, pneumatic
Control systems are classified as?
Closed or open loop
Which control system is used most and why?
Closed loop because more accurate, quick, and has automatic feedback
Synchro devices compares what 2 signals?
Electrical applied to stator
Mechanical applied to rotor
What is the name given to the electrical output of a CT?
Error signal
In a DC position servo system, the ______ and ______ of a DC error signal respectively are used to determine the amount and direction the load will be driven
amplitude and polarity
The oscillation of the load around the desired position will result in what?
Hunting/overshooting
In a velocity servo loop when it is in null position what is still present and what is happening?
Error signal still present and load is moving
When would you use a velocity servo loop?
When load is required to be driven at constant/variable speed
How is the speed governed in a velocity servo loop?
Level of error signal present
What is time lag?
response between input and movement of load
How do you decrease time lag?
Increase gain of servo amp
What may introduce additional time lag?
Weight of the load
How do we eliminate overshooting?
Damping
How do we dampen things?
Introduce a voltage in opposition to signal voltage
Physical restraint on servo output
What does friction clutch damping use and how does it work?
Flywheel, when it slips it disconnects
This type of damping has 2 types and uses electro-magnetic force
Magnetic Clutch damping
This type of damping “anticipates” the amount of overshoot and corrects the overshoot by introducing a voltage in the error detector that is proportional to the rate of change of the error signal.
Error Rate Damping
In Error rate damping, when does max damping occur?
Max rate of change of error signal present
The output voltage of the tachometer can be used to do what?
Anticipate sudden movement changes of the load
What is the electromechanical device that can generate an error-voltage?
Tach Gen/ Rate Gen
What is the purpose of MODULATORS?
Change DC error signals to AC error signals
