A common use for the stepper motor is in the household computer printer and the motor that makes your hard drive or CD-ROM go round and round. A stepper motor in the printer, moves the paper in and out and pulls the printing cartridge head across the surface of the paper in order to print. In the hard drive or CD-ROM, the motor accurately spins the disk so the read and write head can precisely place the information for storage and run your favorite programs.
Function
A stepper motor can run in either direction, clockwise or counterclockwise. The voltage that controls the motor's speed is generally of a Direct Current (DC) type. Varying the DC voltage to the motor windings also varies the speed. You may recognize this as you hear the CD-ROM or hard drive speed up or slow down. This is the stepper motor speed controller at work.
Types
Built within the stepper motor itself are positions or steps. These steps are also called pulses. A stepper motor is classified by how many pulses per full revolution have been built in to the motor windings. The motor windings are what create the magnetic waves that cause a motor to rotate. The pulses are the position of the motor as it goes around in a 360-degree circle or single revolution. A stepper motor can be classified in resolution as 1000 steps per 360-degree revolution. In other words, for every full revolution of the motor shaft there are 1000 points to detect that position.
Features
A stepper motor can also be rated not only by the pulses per revolution but also torque value. The torque value is given either in inch pounds or foot-pounds. A 12-inch pound motor would be able to lift 12 pounds, one inch from the center of the motor shaft. Or, one pound can be lifted, 12 inches from the center of the motor shaft. A 12-inch pound torque value, will equal a one-foot pound value.
Identification
A stepper motor can also be rated by the control voltage. This control voltage or pulse power is what turns the motor. The DC voltage is actually pulsed, so many times per second, for the motor to move. A positive pulsed voltage may move the stepper motor in a clockwise rotation. A negative pulsed voltage will then rotate the motor in a counterclockwise rotation. Varying the amount of voltage will then regulate the speed.
Effects
Think of the end shaft of the stepper motor attached to the face of a clock, with the end shaft connected to hour dial indicator. The motor will always start at the 12 o'clock position. he stepper motor is rated for 24 Volts DC and has a resolution of 1000 pulses per revolution. By regulating the control signal, this motor will rotate as follows. The full speed of the motor would be at 24VDC. If the controller outputs 12VDC at 500 pulses, the motor will then move a half of a revolution at half speed, to the 6 o'clock position. Applying a --12vdc signal at 500 pulses, it then returns back to the 12 o'clock spot.
Considerations
Giving the stepper motor a control signal of 24vdc with 10,000 pulses will rotate the motor at full speed with a full 10 revolutions. Each one of the pulses is accurately counted by the stepper motor controller. So regardless of the direction of the stepper motor, if the controller is as fast as the motor, it will always know the position of the end shaft. This allows the stepper motor to constantly run, in either direction. Their positions are known to accurately read or write information to a hard drive or CD-ROM.
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