What is Servo, servomotors and example of applications

What is Servo?

Servo is the systems where the feedback or error-correction signals help control mechanical position, speed or other parameters. The function of the servo is to receive a control signal that represents a desired output position of the servo shaft, and apply power to its DC motor until its shaft turns to that position. It uses the position-sensing device to determine the rotational position of the shaft, so it knows which way the motor must turn to move the shaft to the commanded position. The shaft typically does not rotate freely round and round like a DC motor, but rather can only turn for example 300 degrees.
We often use servodrive to control servomotor

What is servodrive ?

In typical application the servo drive receives a command signal from a control system device,
servo motoramplifies the signal, and sends electric current to a servo motor in order to produce motion proportional to the command signal. Typically the command signal represents a desired position, torque or speed. A sensor which is attached to the servo motor reports the motor’s actual status back to the servo drive. The servo drive then compares the actual motor status with the commanded motor status. It then alters to
correct for any deviation from the commanded status.
Where we can use Servos?

2 examples based on Parker Servo Products:

1. Rotary Indexer
Description: An engineer for a pharmaceutical company is designing a machine to fill vials and wants to replace an old style Geneva mechanism. A micro stepping motor will provide smooth motion and will prevent spillage. The indexing wheel is aluminum and is 0.250-inch thick and 7.5″ in diameter. Solving the equation for the inertia of a solid cylinder indicates that the wheel has 119.3 oz-in2. The holes in the indexing wheel reduce the inertia to 94 oz-in2. The vials have negligible mass and may be ignored for the purposes of motor sizing. The table holds 12 vials (30° apart) that must index in 0.5 seconds and dwell for one second. Acceleration torque is calculated to be 8.2 oz-in at 1.33 rps2. A triangular move profile will result in a maximum velocity of 0.33 rps. The actual torque requirement is less than 100 oz-in. However, a low load-to-rotor inertia ratio was necessary to gently move the vials and fill them

Product Solutions from Parker:
Drive Indexer SX Drive Indexer*   Motor S83-135
* The 6200, AT6200, and Model 500 are other
indexer products that have been used in these
types of applications.
Servo application for rotary control
2. Labelling Machine using linear solution

Description: Bottles on a conveyor run through a labelling mechanism that applies a label to the bottle. The spacing of the bottles on the conveyor is not regulated and the conveyor can slow down, speed up, or stop at any time.
Machine Requirements:
• Accurately apply labels to bottles in motion
• Allow for variable conveyor speed
• Allow for inconsistent distance between bottles
• Pull label web through dispenser
• Smooth, consistent labelling at all speed
A motion controller that can accept input from an encoder mounted to the conveyor and reference all of the speeds and distances of the label roll to the encoder is required for this application. A servo system is also required to provide the torque and speed to overcome the friction of the dispensing head and the inertia of the large roll of labels. A photosensor connected to a programmable input on the controller monitors the bottles’ positions on the conveyor. The controller commands the label motor to accelerate to line speed by the time the first edge of the label contacts the bottle. The label motor moves at line speed until the complete label is applied, and thendecelerates to a stop and waits for the next bottle.
Product Automation Solutions:
Controller     Motor
APEX6152*      APEX604
labelling machine with servo drive

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