ASSIGNMENT:2 question1

What is a Synchro? Is it related in any way to a stepper motor?

The term synchro is a generic name for a family of inductive devices which work on the principle of a rotating transformer. A synchro is an electromagnetic transducer commonly used to angular position of a shaft into an electrical signal. It is commercially known as a selsyn or an autosyn.

The basic synchro unit is usually called a synchro transmitter. Its construction is similar to that of a three phase alternator. The stator is of laminated silicon steel and is slotted to accommodate a balanced three-phase winding which is usually of concentric coil type that is, three identical coils are placed in the stator with their axis 120° apart and is star connected. The rotor is of dumbbell construction and is wound with a concentric coil. An ac voltage is applied to the rotor winding through slip rings. This voltage causes a flow of magnetizing current in the rotor coil which produces a sinusoidally time varying flux directed along its axis and distributed sinusoidally in the air gap along the stator periphery. The synchro transmitter acts like a single phase transformer in which the rotor coil is the primary and stator coils form the three secondary’s.

The stepper motor is a special type of synchronous motor which is designed to rotate through a specific angle ,called a step, for each electrical pulse received from its control unit. Typical step sizes are 7.5°, 15° or larger. The stepper motor is used in digitally controlled position control systems in open loop mode. The input command is in the form of a train of pulses to turn a shaft through a specified angle.

The advantages of using stepper motors are:

  1. Their compatibility with digital systems.
  2. No sensors are needed for position and speed sensing as these are directly obtained by counting input pulses and periodic counting if speed information is needed.

Since stepper motors are essentially digital actuators, there is no need to use analog to digital or digital to analog converters in digital control systems. They are used in paper feed motors in type writers and printers, positioning of print heads, pens in X-Y plotters and recording heads in computer disk drives.

Reference: control systems.(nagrath and gopal)


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