How to select a Servomotor for your application

Here is a little background on what a servo motor is.
A servomotor is an electric drive with a feedback mechanism. The feedback loop allows the motor input current to be adjusted automatically to properly position the servo shaft when the sensors tell the controller that it’s time to move the shaft or that the motor is not performing as it should.


For example, say you were driving a car up a hill. You as the driver are the Controller. The speedometer is the sensor and the motor is (of course) the motor. You adjust the power to the motor based on the feedback you receive from the sensor, pushing harder on the gas pedal to maintain your speed up the hill.
Servomotors are available as either AC or DC. The main things that have to be considered when making a servomotor from any electric drive are:

• They must be able to operate at a wide range of speeds without overheating
• They have to be able to hold torque on a load at zero speed
• They have to be able to operate at low speeds for a long time

Servomotors are generally considered to have the following advantages:

• Wide range of speeds
• Hold torque at zero speed
• Operate at low speeds for long time

While servo motors can deliver excellent performance and high speed in a small size, the additional controls in the feedback mechanism make them cost more than stepper motors [insert link]. Another challenge you may face in selecting a servomotor is tuning the motor to ensure that it is performing optimally for your application.
When you are selecting your servomotor, you’ll need to consider:

• What shaft speed you’ll need. Manufacturers identify their shaft speeds as the no-load speed at the rated terminal voltage.
• The terminal voltage
• The continuous current you have available, which is the maximum rated current that can be supplied to the motor without overheating
• The continuous torque you will need in constant running conditions
• The continuous output power, which is the mechanical power your application requires.
• Of course, you’ll also need to consider your physical space in terms of shape, diameter and housing length

Even if you carefully specify your motor, the tuning stage may take you a while. You may have to purchase a few samples in different sizes and test them before placing a larger order. And working with the engineering teams at a motor manufacturer may be the right way to go if you have a specialized application.
There are lots of types of servomotors. Some of the most common types and their applications include:
- Permanent magnet and shunt wound motors which provide constant speed with varying load, so they are a good fit for machine tools, fans and blowers.
- Series wound motors provide high starting torque, so they are good for constant loads such as in heavy industrial applications.
- Compound wound motors provide a heavy starting torque and are typically used where adjustable speed is not required, such as in elevators and hoists.
That’s a high-level outline on selecting a servomotor for your application. For more details, watch some of the related videos in this section.

from : http://www.engineering.com