SERVOMECHANISMS Flashcards
What is a servomechanism (servo)?
A servomechanism (servo) is an electromagnetic device that converts electricity into precise controlled motion using negative feedback mechanisms.
In which systems are servomechanisms commonly used?
Servomechanisms are commonly used in aircraft systems such as control surfaces, helicopter rotor heads, and aircraft wheel steering.
What is a synchro?
A synchro is a type of rotary electrical transformer sensor used to measure the angle of a rotating machine, transforming the angular position of a part into a voltage or vice versa.
Give an example of an open-loop system.
An example of an open-loop system is a power-assisted braking system where the driver’s judgement determines the braking force.
Describe an open-loop system.
An open-loop system is a control system where human interface between input and output determines accuracy, response time, and stability, with no automatic feedback.
Describe a closed-loop system.
A closed-loop system is an automatic error-actuated power control system that uses feedback to limit overshoot, improving accuracy, response time, and stability.
Give an example of a closed-loop system.
An example of a closed-loop system is an automatic clothes iron that regulates its temperature to stay within a specified range using feedback from a temperature sensor.
What is deadband in control systems?
Deadband is an area of a signal range where no action occurs, used to prevent oscillation or repeated activation-deactivation cycles.
What is null voltage in servomechanisms?
Null voltage is the induced voltage in the rotor at the minimum coupling position due to mechanical imperfections, winding errors, and distortions in the magnetic circuit.
Explain time lag in servomechanisms.
Time lag is the delay between the input signal and the actual movement of the load, which can be influenced by the weight of the load and the gain of the servo amplifier.
Define feedback in the context of servomechanisms.
Feedback refers to the system providing information about its load to the operator or input, allowing the system to correct differences between the state of the receiver and the transmitter signal.
What is hunting in servomechanisms?
Hunting refers to the overshoot and undershoot that occurs as the receiving device tries to match the transmitter signal, resulting in oscillation around the desired point.
What does follow-up mean in servomechanisms?
Follow-up is the behavior where a servomechanism returns the load position to the demanded position upon detecting an error.
What is damping in servomechanisms?
Damping is a force within an oscillating system that opposes motion, reducing hunting in servomechanisms to enhance stability without significantly reducing efficiency.
What are the two types of synchro systems?
- Torque systems: Provide mechanical output sufficient to align indicating devices or move light loads without power amplification.
- Control systems: Provide voltage for conversion to torque through an amplifier and servomotor, driving heavier loads.
What is the primary function of a torque synchro system?
A torque synchro system provides a mechanical output sufficient to align an indicating device, actuate a contact, or move a light load without power amplification.
What are the two main categories of synchros based on their load?
- Torque synchros: Used to produce turning force or torque to move light loads like dials and indicators.
- Control synchros: Used to move heavy loads, requiring additional components like amplifiers and motors.
What is the primary function of a control synchro system?
A control synchro system provides a voltage for conversion to torque through an amplifier and servomotor, driving heavier loads such as flight control surfaces.
How are synchros used as transmitters and receivers?
Synchros can be used as transmitters to provide input to a position control system or as receivers to provide an output from a position control system.
What distinguishes a synchro receiver from a synchro transmitter?
A synchro receiver has low friction bearings to accurately follow the movement of the transmitter and includes a damping mechanism to prevent oscillation.
What are the main components of a synchro’s construction?
A synchro consists of a laminated stator core carrying three coils in a star configuration and a laminated rotor with a winding connected via slip rings to external connections.
What are the advantages of using synchros?
- Long-distance capabilities
- Easily routed wiring
- Low electrical power usage
- Lightweight
- Cost-effective
What is the purpose of a torque transmitter (TX)?
A torque transmitter (TX) converts the rotor position into an electrical signal from the stator, which is then supplied to a torque receiver (TR), torque differential transmitter (TDX), or torque differential receiver (TDR).
What is required for torque to be present in a synchro system?
Torque is only present when current flows through the stators, generating magnetic fields. For this to occur, there must be a differential angle between the transmitter rotor and the receiver rotor.
How does the torque moment change with the rotor angle difference?
The torque moment increases as the rotor angle difference increases up to 90°, where it reaches its maximum value. After 90°, the torque moment starts to decrease as the angle approaches 180°.
What effect do bearing friction and brush friction have in a synchro system?
Bearing friction and brush friction have a negative effect on precision, especially when the differential angle between the transmitter and receiver rotors is small.
Why must a synchro system be designed with low electrical resistance?
The system must be designed with low electrical resistance to allow sufficiently large currents to flow, as torque moments are proportional to the currents.
How does a differential transmitter (TDX) differ from a torque transmitter (TX)?
A differential transmitter (TDX) has three coils wired in a star shape on the rotor and is used to add or subtract angles. Unlike a torque transmitter (TX), it does not generate torque but rather transmits the difference or sum of angles.
What happens in a TX-TDX-TR system when the TDX is at electrical zero?
When the TDX is at electrical zero, it passes the voltages applied to its windings without change. The TX stator voltages are the same as those at the TDX rotor, and the TDX rotor voltages equal and oppose the TR stator voltages, resulting in no current flow and no torque in the TR rotor.
What is the effect of turning the TX rotor to 240° in a TX-TDX-TR system?
Turning the TX rotor to 240° induces maximum voltage into the S1 winding of the TX, which is then passed through the TDX to the TR. The TR rotor turns anti-clockwise to the 240° position, following the TX rotor exactly when the TDX rotor is at 0°.
How do you subtract angles using the TX-TDX-TR system when the TDX rotor is at 120°?
When the TDX rotor is at 120°, the system behaves as follows: The maximum voltage is induced in R1 of the TDX, which is connected to S1 of the TR, causing the TR rotor to turn to the position calculated by subtracting the TDX angle from the TX angle.
What happens in a TX-TDX-TR system when the TDX rotor is at 30° and the TX rotor is at 75°?
The TR rotor turns to 45° because the TDX subtracts the 30° from the 75° of the TX rotor, resulting in a difference of 45°.
Describe the setup for addition in a TX-TDX-TR system.
For addition, the S1 and S3 leads between the TX and the TDX are reversed, and the R1 and R3 leads between the TDX and the TR are also reversed. This setup causes the TR rotor to turn to a position that is the sum of the TX and TDX rotor angles.
