PRESENATTION ON SERVOMOTORS

MADE BY :-JASDEEP KOUR

WHAT IS A SERVOMOTOR

• A servomotor (servo) is an electromechanical device in which an electrical input determines the position of the armature of a motor.

• Servos are used extensively in robotics and radio-controlled cars, airplanes, and boats.

• It consists of the Stator windings and the Rotor . The Rotor rotates with respect to the stator windings which are placed in the magnetic field being created by these current carrying coils

PICTORIAL REPRESENTATION OF A SERVOMOTOR

DIAGRAM OF A SERVOMOTOR

PARTS OF A SERVOMOTOR

• A servo motor consists of several main parts, 1.the motor and gearbox, 2. a position sensor, 3. an error amplifier 4. motor driver and 5. a circuit to decode the requested position.• Figure below contains a block diagram of a

typical servo motor unit.

BLOCK DIAGRAM OF A TYPICAL SERVOMOTOR SYSTEM

Pulse width to voltage converter

• The control pulse is feed to a pulse width to voltage converter. This circuit charges a capacitor at a constant rate while the pulse is high.

• When the pulse goes low the charge on the capacitor is fed to the output via a suitable buffer amplifier. This essentially produces a voltage related to the length of the applied pulse.

• The circuit is tuned to produce a useful voltage over a 1ms to 2ms period. The output voltage is buffered and so does not decay significantly between control pulses so the length of time between pulses is not critical.

Position Sensor

• The current rotational position of the servo motor output shaft is read by a sensor.

• This is normally a potentiometer (variable resistor) which produces a voltage that is related to the absolute angle of the output shaft.

• The position sensor then feeds its current value into the Error Amplifier which compares the current position with the commanded position from the pulse width to voltage converter.

Error Amplifier

• The error amplifier is an operational amplifier with negative feedback.

• It always try to minimise the difference between the inverting (negative) and non-inverting (positive) inputs by driving its output is the correct direction.

• The error amplifier output is used to drive the motor; If it is positive the motor will turn in one direction, if negative the other

HOW DOES A SERVOMOTOR WORKS

• The servo motor has some control circuits and a potentiometer (a variable resistor, i.e pot) that is connected to the output shaft. The potentiometer allows the control circuitry to monitor the current angle of the servo motor.

• If the shaft is at the correct angle, then the motor shuts off. If the circuit finds that the angle is not correct, it will turn the motor the correct direction until the angle is correct

Cont……

• . The output shaft of the servo is capable of travelling somewhere around 180 degrees.

• . The amount of power applied to the motor is proportional to the distance it needs to travel.

• So, if the shaft needs to turn a large distance, the motor will run at full speed. If it needs to turn only a small amount, the motor will run at a slower speed. This is called proportional control

WORKING OF A SERVOMOTOR

CONT…

• . The amount of power applied to the motor is proportional to the distance it needs to travel.

• So, if the shaft needs to turn a large distance, the motor will run at full speed. If it needs to turn only a small amount, the motor will run at a slower speed. This is called proportional control

REQUIREMENTS OF A GOOD SERVOMOTOR

The requirements of a servomotor to be used for feedback control systems are:-

1. Linear relationship between electrical control signal and the rotor speed over a wide range

2. Its response should be as fast as possible3. It should have linear torque – speed

characterstics4. Its operation should be stable without any

oscillations or overshoots

TYPES OF SERVOMOTORSERVOMOTOR

A.C SERVOMOTOR

D.C SERVOMOTOR

SPECIAL SERVO

MOTOR

ARMATURE CONTROLLED FIELD CONTROL

FIELD CONTROLLED D.C SERVOMOTOR While deriving the transfer function of the field

control d.c servomotor the following assumptions are taken in to account:-

1. Constant armature current is fed to the motor2. Flux produced is proportional to field current i.e 3. Torque is proportional to the product of flux

and armature current

CIRCUIT DIAGRAM OF A FIELD CONTROLLED D.C SERVOMOTOR

APPLICATION OF A SERVOMOTOR

• The servomotor in this application has an encoder attached to its shaft that is used to provide velocity data as well as positioning data.

• The pulse train from the encoder is sent to the frequency-to-voltage converter, and the output voltage signal from the converter is sent to the summing junction.

• A position setpoint is set in the up/down counter, which is converted from a digital value to an analog voltage.

• The voltage is sent to the summing junction as a reference signal.

servomotor that moves a welding index table

CONTD…

• The summing junction compares the position reference signal to the velocity feedback signal and produces an error signal that is sent to the op amp as the inverting input signal.

• If the error is negative, it means the motor hasn't moved the table into the correct position, and additional voltage will be sent to the motor from the output signal from the op amp. The output signal from the op amp must go through a pulse-width modulator (PWM) circuit, a control logic circuit, and a motor control circuit.

CONTD…

• When the motor shaft moves the table, the encoder will indicate that the table is at a new position.

• The position loop compares the set point position (the desired position) in the up/down counter buffer with the actual position that is reported by the encoder.

• The amount of difference is converted from a digital signal to an analog voltage and sent to the summing junction

CONT…

• When the encoder indicates that the indexing table is at the correct position, the setpoint signal and the feedback signal will cancel each other and the resulting signal value will be zero, which means that no voltage is sent to the motor so it will stop at that position.

Application of a servomotor controlling the speed of material

Application of a beverage-filling station controlled by a servomotor

packaging system with random timing functions controlled by a servomotor.

THANK YOU