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SYNCHROS AND RESOLVERSJenny
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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 pointerscontrol devices in servo systems. Types Torque synchroto move light loads such as dials, pointers, or similar indicators.Control synchrodesigned to move heavy loads such as gun directors, radar antennas, and missile launchers,machine tools.
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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).
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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).
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TRANSMITTERThe 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 VS3-2 = KVR2-1 sin (+ 120)VS2-1 = KVR2-1 sin ( + 240)where K is the maximum coupling transformation ratio (TR), which is defined as TR=Vout(max.)/Vin 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.RECEIVERAn 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.
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Torque in receiverThe torque developed in a synchro receiver results from the tendency of two electromagnets to align themselvesThe 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 dampingThe 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.
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BASIC SYNCHRO SYSTEM OPERATION
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TORQUE DIFFERENTIAL SYNCHRO SYSTEMS
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TX-TDX-TR
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TX-TDR-TX
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Control synchrosControl 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).
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Control transmitter (cx)The Control Transmitter is really a high impedance version of the Torque Transmitter and is possibly the most common of all synchros.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.
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Synchros in machine tools
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Working
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Servo system using control chain
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Synchros are more commonly used in machine tools than resolversA 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 10:1As the table moves,the switching system switches from one to the other till only fine control works
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Digital synchro
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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 90The 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 90 to each other.
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If we assume that the rotor is excited by an AC reference voltage:A Sin tThen the voltages appearing on the stator terminals will be:S1 to S3 = V Sin t Sin and S4 to S2 = V Sin t Cos , is resolver shaft angleThese voltages are known as Resolver format voltages
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Resolver with two rotor windingsEither 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)
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Resolver control chain
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Application in machine toolsIf 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
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Difference between synchro and resolver3 stator windingStators 120 deg apartOutput taken from stator2 stator windingStators 90 deg apartOutput taken from stator or rotor
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Comparison with other angular transducersCost ,in descending orderAbsolute optical EncodersSynchros and ResolversPotentiometersContact EncodersResolution and AccuracyHigh accuracy
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Static and Dynamic Mechanical LoadingLess in the case of the optical encoders and the Synchros and Resolvers than in the case of the potentiometer and the contact encodersEnvironmental ConsiderationsThe 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 ImmunityHigh degree of noise immunityIf true transformer isolation is used at the conversion endNo 3 or 4wire long distance problem
