Stepper Motors

Stepper Motors

Stepper Motors

A Stepper Motor (or Steper Motor) is a brushless, synchronous electric motor that can divide a full rotation into a large number of steps. The Motors Position can be controlled presicely without any feedback mechanism (see Open - loop Controller), as long as the motor is carefully sized to the application.

Stepper Motors are smiliar to switch reluctance motors (which are very large stepping motors with a reduced pole count, and generally closed loop communtated) fundamentals of operation Stepper Motors operate differently from DC brush motors, which rotate when voltage is applied to their terminals. Stepper Motors, on the other hand effectively have multiple "toothed" electromagnets arranged around a centrl gear-shaped piece of iron.

The electromagnets are energized by an extenal control circuit, such as a microcontroller. To make the motor shaft turn, first one electromagnet is given power, which makes a gears teeth magnetically attracted the electromagnet's teeth. When the gear's teeth are thus aligned to the first electromagnet, they are slightly offset from the next electromagnet.

So when the next electromagnet is turned on and the first is turned off, the gear rotates slightly to align with the next one, and from there the process is repeated. Each of those slight rotations is called a "Step", with an integer number of steps making a full rotation. In that way, the motor can be turned by a precise angle.

http://www.KelingInc.Net are experts in the functioning of stepper motors and can help consult in their best use of whatever your applications is. Here is an important list concerning stepper motors.

1. Stepper Motors are constant power devices

2. As motor speed increases, torque decreases (most motors exhibit maximum torque when stationary, however the torque of a motor when stationary "Holding Torque" defines the ability of the motor to maintain a desired position whileunder external load.

3. The torque curve may be extended by using current limiting drivers and increasing the driving voltage (sometimes referred to as a 'Chopper" circuit; there are several off teh shelf driver chips capable of doing this in a simple manner).

4. Steppers exhibit more vibration than other motor types, as the discrete step tends to snap the motor from one position to another(called a dentent). The vibration makes stepper motors nosier than DC motors.

5. This vibration can become very bad at some speeds and can cause the motor to lose torque or lose direction.

This is because the rotor is being held in a magnetic field which behaves like a spring. On each step the rotor over shoots and bounces back and forth, "ringing" at its resonant frequency. If the stepping frequency matches the resonant frequency then the ringing increases and the motor comes out synchronism, resulting in positional error or a change in direction. At worst there is a total loss of control and holding torque so the motor is easily overcome by the load and spins almost freely.

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