SERVO MOTORS

SERVO MOTORSPresented by:Rajesh DopplapudiSc.no:142113214Rajesh DopplapudiSc.no:1421132141Contents:Introduction2. Servo structure3. Servo terms4. Servo centering5. Mechanism6. Servo types7. Modified servos8. Applications9. Servo drivesServo drives2A servo motor is a mechanical motorized device that can be instructed to move the output shaft attached to a servo wheel or arm to a specified position.Inside the servo box is a DC motor mechanically linked to a position feedback potentiometer, gearbox, electronic feedback control loop circuitry and motor drive electronic circuit.servo looks like a plastic rectangular box with a rotary shaft coming up and out the top of the box and three electrical wires out of the servo side to a plastic 3 pin connector.Introduction:Introduction3

Structure of servomotorStructure of servomotor4Servos are controlled by sending pulse width signals (PWM) from an external electronic device that generates the PWM signal values, such as a servo controller.PWM signals sent to the servo are translated into position values by electronics inside the servo.A pulse width signal (PWM) of approximately 1.5 mS (1500 uS) is the "neutral" position for the servo.neutral is defined to be the point where the servomotor has exactly the same amount of potential rotation in the counter clockwise direction as it does in the clockwise direction.BASIC TERMS:Servo Speed is defined as the amount of time ( in seconds) that a servo arm attached to the servo output shaft will move from 0 to 60 degrees.Servo Torque is defined as the total push / pull power a servo can apply on a 1" servo arm when moving.Servo Power is defined as the amount of DC Voltage needed to operate a Servo without damage.Servo Centering:Automated Servo Center Position:The best and easiest way to set a servo's center position is to connect the servo to a servo checker or tester.2. Manual Servo Center Position:Obtained by drawing reference lines through the servo arm or servo wheel center point at different positions.Obtained by drawing reference lines through the servo arm or servo wheel center point7

Carefully remove the servo arm from the servo if not needed for instillation or place the servo arms on top of the servo shaft, secure it with servo screw and install the servo as needed.8

MechanismAs the name suggests, a servomotor is aservomechanism. It is aclosed-loopservomechanism that uses position feedback to control its motion and final position.The motor is paired with some type ofencoderto provide position and speed feedback. In the simplest case, only the position is measured. Mechanism9The very simplest servomotors use position-only sensing via apotentiometerandbang-bang controlof their motor; the motor always rotates at full speed (or is stopped).Present servomotors measure both the position and also the speed of the output shaft. They may also control the speed of their motor, rather than always running at full speed. These servo motors uses position control in addition with PID algorithm.These servo motors uses position control in addition with PID algorothm.10Servo motors and are constructed out of basic DC motors, by adding:Some gear reduction.A position sensor for the motor shaft.An electronic circuit that controls the motor's operation.

Types of servo motors:Positional rotation servo motor:Servos come in many sizes and in three basic types:The output shaft rotates in about half of a circle, or 180 degrees.It has physical stops placed in the gear mechanism to prevent turning beyond these limits to protect the rotational sensor. Radio-controlled cars and water- and aircraft, toys, robots, and many other applications.Types of servo motors

122. Continuous rotation servo motorIt can turn in either direction indefinitely.The control signal, rather than setting the static position of the servo, is interpreted as the direction and speed of rotation.You might use a servo of this type on a radar dish if you mounted one on a robot. Or you could use one as a drive motor on a mobile robot.:These servo motors are not easy to find, but we can sometimes find them at hobby stores where they are used as actuators in larger model airplanes.3. Linear servo motor:This is also like the positional rotation servo motor, but with additional gears (usually a rack and pinion mechanism) to change the output from circular to back-and-forth.Types of servo motors by electrical analogy:D.C. Servomotor:-

Shunt wound d.c. motorSeries wound d.c. motor Compound wound d.c. motor

2. A.C. Servomotors:-

Induction motor a.c. motorSynchronous a.c. motorTypes of servo motors by electrical analogy15DC Servo motors:DC servo motors are controlled by DC command signals applied directly to coils.The magnetic fields that are formed interact with permanent magnets and cause the rotating member to turn.One type of PM uses a wound armature and brushes like a conventional DC motor, but uses magnets as pole pieces.Another type uses wound field coils and a permanent magnet rotor.DC Servo motors16AC Servo Motors:Controlled by AC command signals applied to the coils.AC Brushless Servo MotorOperates on the same principle as single-phase induction motor.The stator has two distributed windings displaced 90 electrical degree apart.One winding is the reference phase and is connected to a constant voltage source.The other winding is the control phase and is supplied with a variable voltage of the same frequency as the reference phase but is phase-displaced by 90 electrical degree.Servomotors vs Steppermotors:A servomotor consumes power as it rotates to the commanded position but then the servomotor rests. Stepper motors run warm to the touch because they continue to consume power to lock in and hold the commanded position.Servomotors are generally used as a high performance alternative to the stepper motor.The lack of feedback of a stepper motor, it can only drive a load that is well within its capacity, otherwise missed steps under load may lead to positioning errors and the system may have to be restarted or recalibrated.Servomotors vs Steppermotors:18Modified Servos:Servo motors can also be retrofitted to provide continuous rotation:remove mechanical limit (revert back to DC motor shaft)remove pot position sensor (no need to tell position)This is done by removing the feedback sensor, and replacing it with an equivalent circuit that creates the same readings as the sensor being at 90 degrees

Applications of Servo motorMachine Tool (Metal Cutting)Metal formingAntenna PositioningWoodworkingTextilesPrintingRope/Twine manufacturingMedical equipmentServo drives are designed to offer among other things, exact control, optimum torque as well as a rich set of features to complement the linear positioning systems and rotary servomotors. Servo drives :Servo drives can be used by a machine to offer excellent quality motion control in a very dynamic application.

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