4.3 Servomechanisms Flashcards
What is a servo mechanism?
electromagnetic device that converts electricity into precise controlled motion using negative feedback mechanisms
What can servos be used to generate?
Linear or circular motion
What is a synchro mechanism?
type of rotary electrical transformer sensor used to measure the angle of a rotating machine, such as an antenna platform
What is an open loop?
human interface between input and output determines system accuracy, response time, and stability.
What do manually operated servo systems struggle with?
Overshoot, leading to poor response times and instability
What is an example of an open loop system?
Power assisted braking system, no auto feedback just the drivers judgment.
What is a closed loop system?
automatic error-actuated power control system
In a closed loop system what is the input?
Target at which the system is aiming for
In a closed loop system what is the controller?
Compares input to output
In a closed loop system what is the actuator?
Reacts to the controllers instructions
What is the error signal?
The amplified signal that is the difference between the input and the output.
What is the null voltage?
The mechanical imperfections in the transducer stator and rotor windings that should have no induced voltage but a little is.
What is the deadband?
An area of signal range where no action occurs, it prevents oscillation
How can the time lag be reduced?
Increasing the gain of the servo amplifier
What is the hunting?
Oscillation occurs as it overshoots, then undershoots, the movement gets smaller each swing until stable.
What is follow up?
behaviour of a servomechanism upon detection of an error.
What are the two different types of synchro system?
Torque systems and control systems
What happens in a toque system?
transmitted signal does the usable work without further amplification.
What happens in a control system?
synchro will provide a voltage for conversion to torque through an amplifier and a servomotor
What is the main difference between a transmitter or receiver synchro?
Receiver has low friction bearings to follow the movement of the transmitter accurately.
What is a synchro by definition?
Electromechanical transducer
What are simple synchro’s used for?
Dials and pointers
What components are required for heavier loads?
Amplifiers and motors
Would you use a control synchro for a heavy or light load?
Heavy
Due to shafts being cumbersome and hard to route, teleflex could be used what are the negatives to flex?
Friction and they can’t take heavy loads
What designation system do synchro system wires use?
ARINC (Aeronautical Radio Incorporated)
What colour is Stator 1:X wire?
Blue
What colour is stator 2: Z wire?
Black
What colour is Stator 3: Y wire?
Yellow
What colour is Rotor 1:H wire?
Red and white
What colour is rotor 2 : C wire?
Black and white
What are the advantages of synchros?
Long distance
Routing
Small power
Lightweight
Cost
What types of closed loops are there?
Positional
Rate
Computing
What degree intervals are the stator windings placed at?
120
How is the turning moment produced to move the rotor in the receiver?
Created by the interaction between the magnetic fields of the stator and the rotor.
What happens when the two rotors are aligned?
The voltage is equal and opposite since they are wired in parallel and no current flows.
When is torque present?
When current flows through the stators, generating magnetic fields.
How is a torque movement acheived?
There has to be a differential angle between the transmitter rotor and receiver rotor
What is the task of a differential transmitter?
Add or subtract angles.
If both shafts are moved in the same direction what does the differential transmitter do?
Subtract
In a differential transmitter the coupling and translations are chosen in which way?
That max voltages between two stator terminals are of the same magnitude as the max voltage between two rotor terminals.
Indicating mechanisms take too much torque to turn, how can more torque be produced?
Addition of a servo mechanism
What are the three types of control synchros?
Control Transmitter CX
Transformer CT
Differential Transmitter CDX
What is the difference between a CX and CDX and a TX and TDX?
C have higher impedance
Why do control windings have a higher impedance?
control systems draw far less current and provide an output voltage to a control transformer that outputs an error signal that controls a servo motor, which can drive a large load.
What is a control transformer?
accurately governs some type of power amplifying device used for moving heavy equipment
What two signals does the CT (transformer) compare?
Electrical signal applied to the stator and the mechanical signal applied to the rotor
What is a resolver?
rotary electrical transformer used for measuring degrees of rotation
What are the digital versions of a resolver?
Digital resolver and rotary pulse encoder
What do resolvers allow you to monitor?
Flying control positions
Control input positions
Throttle position
How does a resolver system differ from a control transmission?
Consists of a two phase stator and three phase rotor free to turn within the field of the stator
How is a resolver transmitter rotor powered?
26V/115V 400Hz single phase AC
What does LVDT stand for?
Linear Variable Differential Transformer
What is an LVDT?
common type of electromechanical transducer that can convert the rectilinear motion of an object (to which it is coupled mechanically) into a corresponding electrical signal.
What does rectilinear mean?
Motion restricted to a straight line
What are the advantages of DC operated LDVTs?
Ease of installation
Simpler data
Use dry cell batteries
Lower cost
What are the advantages of AC LDVTs?
Smaller
More accurate
Operate well at high temps
Which law is a fundamental part of LDVTs?
Lenz- Secondary coils are parallel but with opposing polarity
What does RVDT stand for?
Rotary Variable Differential Transformer
What are RVDTs used for?
Produce electrical signal from rotational movement.
What does an E and I bar offer?
Electrical signal from both linear and rotational movements.
Why are E and I bars laminated?
To reduce the effects of eddy currents
What is a common use of an induction transmitter?
Prox switch
Magnetic prox switches are divided into what?
Integrated (vane)
Seperated
What is a vane type prox switch?
Object passes through groove, object tends to be flat and ferromagnetic.
What are the benefits of vane type?
high detecting accuracy, the switch exhibits less constraint conditions and greater ease-of-handling
What is a capacitive sensor?
Can detect solid or liquid targets
What are the four main parts of capacitive sensors?
Body
Face
Light
Cable
What was the first DC servo system?
Desynn system
What are the three types of desynn transmitters?
Toroidal resistor- rotary
Micro Desynn- linear for pressure
Slab- Pressure
