synchros and resolvers
DESCRIPTION
synchro resolver machine tool feedbackTRANSCRIPT
Synchros
It is the name given to a variety of rotary, electromechanical, position-sensing devices.
a variable coupling transformer. Functions –
supplying data by positioning dials and pointers control devices in servo systems.
Types Torque synchro
to move light loads such as dials, pointers, or similar indicators. Control synchro
designed to move heavy loads such as gun directors, radar antennas, and missile launchers,machine tools.
Torque synchros include transmitters (CG), differentials (CD) and receivers (CR).
Control synchros include transmitters (CG), differentials (CD) control transformers (CT), resolvers (CS), linear transformers (LT) and
the two hybrid units: transolvers (CSD) and differential resolvers (CDS).
Construction of synchro transmitter-receiver Each synchro contains a rotor, similar in appearance to the
armature in a motor, and a stator, which corresponds to the field in a motor.
The synchro stator is composed of three Y-connected windings (S1, S2, and S3).
The rotor is composed of one single winding (R1 and R2).
TRANSMITTER The magnitude of the induced voltage depends on the angle
between the rotor fields and the resultant axis of the coils forming that stator phase.
VS1-3 = KVR2-1 sin θVS3-2 = KVR2-1 sin (θ+ 120°)VS2-1 = KVR2-1 sin (θ + 240°)
where K is the maximum coupling transformation ratio (TR), which is defined as TR=Vout(max.)/Vin
θ is the rotor position angle. VS1-3 is the voltage from the S1 terminal to the S3 terminal. The transmitter, therefore, supplies information about the rotor
position angle as a set of three output voltages.RECEIVER An instrument which will measure the magnitude of these voltages,
examine their time-phase relationships, and return them to their original form: a shaft position.
Such a device is the synchro receiver (CR). These two units form the most basic synchro system.
Torque in receiver The torque developed in a synchro receiver results from the tendency of two
electromagnets to align themselves The strength of the magnetic field produced by the stator determines the torque. The field strength depends on the current through the stator coils. As the current through the stator is increased, the field strength increases and more
torque is developed Synchro torque receivers, commonly called synchro receivers, are electrically
identical to torque transmitters of the same size except for the addition of some form of damping
The rotor is connected to the same ac source as the transmitter and assumes a position determined by the interaction of its magnetic field with the magnetic field of the stator.
Control synchros
Control synchros by themselves cannot move heavy loads.
These devices are used for providing and dealing with control signals in servo systems where accurate angular transmission to a mechanical load is required.
There are three types of control synchros: the CONTROL TRANSMITTER (CX), the CONTROL TRANSFORMER (CT), and the CONTROL DIFFERENTIAL TRANSMITTER (CDX).
Working The Control Transmitter is really a high
impedance version of the Torque Transmitter . A Control Transformer is a high impedance
version of the Torque Receiver with the rotor winding aligned at 90 degrees from that of a TR.
The output voltages from the CX are normally fed to a Control transformer (CT) to form a Control Chain.
If the control transformer rotor angle is not the same as that of the transmitter, a voltage proportional to the sine of the angular difference appears on the control transformer rotor.
Synchros are more commonly used in machine tools than resolvers A single synchro can represent an angular rotation unambiguously in very
narrow range(4-6mm) A number of synchros are coupled with gears having reduction ratio 10:1 As the table moves,the switching system switches from one to the other till
only fine control works
Resolver
The Resolver is a form of synchro (Resolvers are very often called Synchro Resolvers) in which thewindings on the stator and rotor are displaced mechanically at 90º
The Resolver therefore exploits the sinusoidal relationship between the shaft angle and the output voltage.
The simplest Resolver would have a rotor with a single winding and a stator with 2 windings at 90º to each other.
If we assume that the rotor is excited by an AC reference voltage:
A Sin ω t
Then the voltages appearing on the stator terminals will be:
S1 to S3 = V Sin ω t Sin θ and S4 to S2 = V Sin ω t Cos θ, θ is resolver shaft angle
These voltages are known as Resolver format voltages
Resolver with two rotor windings Either one of rotor windings or one of stator windings shorted. Known as Data Transmission Resolvers, Control chain
a Resolver Transmitter (Symbol TX) and a Resolver Control Transformer (Symbol RC)
Application in machine tools
If rotor is coupled to the lead screw of machine tool, the voltages in stator indicate angle of rotation and hence displacement of table.
Selsyn transducer-3 stator windings
Difference between synchro and resolver
Synchro
3 stator winding Stators 120 deg apart Output taken from
stator
Resolver
2 stator winding Stators 90 deg apart Output taken from
stator or rotor
Comparison with other angular transducers
Cost ,in descending order Absolute optical Encoders Synchros and Resolvers Potentiometers Contact Encoders
Resolution and Accuracy High accuracy
Static and Dynamic Mechanical Loading Less in the case of the optical encoders and the
Synchros and Resolvers than in the case of the potentiometer and the contact encoders
Environmental Considerations The combination of synchro and its associated
electronics meet more stringent temperature, humidity, shock and vibration specifications than any other shaft angle transducer.
This is one of the main reasons why Synchros and Resolvers are preferred for Military and Aerospace applications.
Noise Immunity High degree of noise immunity If true transformer
isolation is used at the conversion end No 3 or 4wire long distance problem