Stepper motors rotate a set number of degrees in response to electronic pulses, allowing precise control without feedback. They are used in disk drives, machine tools, and robotics for their high torque and reliability. The motor consists of electromagnets arranged around a permanent magnet, with each pulse charging and discharging the electromagnets to rotate the rotor. The motor has three step modes: full step, half step, and microstep, with each allowing for greater accuracy but potentially losing torque.
Stepper motors are motors that rotate a set number of degrees in response to an electronic pulse. This method allows the rotational speed and magnitude to be precisely controlled without using a feedback system. Stepper motors are often used in disk drives, machine tools and robotics. They are popular for their high torque at low speeds and because they tend to be extremely reliable in all environments.
A stepper motor is basically a circle of electromagnets arranged around a single permanent magnet, called a rotor. A pulse of electricity is sent to each electromagnet in turn, charging it. This causes the magnet to rotate towards that electromagnet. That electromagnet is discharged and then a charge is sent to the next one. By charging and discharging the electromagnets, the rotor rotates 360 degrees on its axis. If the electronic pulses are fast enough, continuous rotation of the rotor is achieved.
One movement of the rotor is called a step. Each rung is the same size, with no more than 3-5 degrees variance. Since each pulse is a discrete event, the variations do not add up over time and cause a severe loss of accuracy. This means that stepper motors can never be more than 5 degrees away from perfect accuracy.
The rotational speed of the motor can be changed by varying the pulse frequency. If the pulses stop, such as when no power is being sent to the motor, the rotor will line up with the closest magnet and stay there. The attraction between the magnet and the metal is sufficient to keep the shaft from rotating.
Stepper motors generally have three step modes. Full step mode causes the rotor to move one full step for each pulse. Many standard stepper motors are 200-step, which means that each pulse moves the rotor 1/200th of a circle 360 degrees. A standard stepper motor set to full step mode will therefore rotate approximately 1.8 degrees for each pulse.
Half Step mode allows the operator to double the number of steps per full rotation. A standard 200-step motor set to half-step mode will actually have 400 steps, because the rotor moves a half-step for each pulse. Microstep mode divides the rotation into even smaller steps. Each division of a pulse allows for greater accuracy, but also causes the motor to lose some of its torque.
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