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Information About Stepper Motor Driver

Introduction to Stepper Motors and Drives

A stepper motor is a brushless, synchronous electric motor that converts digital pulses into mechanical shaft rotation. Every revolution of the stepper motor is divided into a discrete number of steps, in many cases 200 steps, and the motor must be sent a separate pulse for each step. The stepper motor can only take one step at a time and each step is the same size. Since each pulse causes the motor to rotate a precise angle, typically 1.8°, the motor's position ca n be controlled without any feedback mechanism. As the digital pulses increase in frequency, the step movement changes into continuous rotation, with the speed of rotation directly proportional to the frequency of the pulses. Step motors are used every day in both industrial and commercial applications because of their low cost, high reliability, high torque at low speeds and a simple, rugged construction that operates in almost any environment.

Stepper Motor Advantages

  1. The rotation angle of the motor is proportional to the input pulse.
  2. The motor has full torque at standstill (if the windings are energized).
  3. Precise positioning and repeatability of movement since good stepper motors have an accuracy of 3 to 5% of a step and this error is non-cumulative from one step to the next.
  4. Excellent response to starting/stopping/reversing.
  5. Very reliable since there are no contact brushes in the motor. Therefore the life of the step motor is simply dependant on the life of the bearing.
  6. The stepper motors response to digital input pulses provides open-loop control, making the motor simpler and less costly to control.
  7. It is possible to achieve very low speed synchronous rotation with a load that is directly coupled to the shaft.
  8. A wide range of rotational speeds can be realized as the speed is proportional to the frequency of the input pulses.

Types of Step Motors

There are three bas ic types of step motors: variable reluctance, permanent magnet, and hybrid. This discussion will concentrate on the hybrid motor, since these step motors combinethe best characteristics of the variable reluctance and permanent magnet motors. They are constructed with multi-toothed stator poles and a permanent magnet rotor (See figure A). Standard hybrid motors (such as the models offered by OmegamationTM) have 200 rotor teeth and rotate at 1.8º stepangles . Because they exhibit high static and dynamic torque and run at very high step rates, hybrid step motors are used in a wide variety of commercial applications including computer disk drives, printers/plotters, and CD players. Some industrial and scientific applications of stepper motors include robotics, machine tools, pick and place machines, automated wire cutting and wire bonding machines, and even precise fluid control devices.

Driver Technology Overview

The stepper motor driver receives step and direction signals from the indexer or control system and converts them into electrical signals to run the step motor. One pulse is required for every step of the motor shaft. In full step mode, with a standard 200-step motor, 200 step pulses are required to complete one revolution. The speed of rotation is directly proportional to the pulse frequency. Some drivers have an on-board oscillator which allows the use of an external analog signal or joystick to set the motor speed. Speed and torque performance of the step motor is based on the flow of current from the driver to the motor winding. The factor that inhibits the flow, or limits the time it takes for the current to energize the winding, is known as inductance. The effects of inductance, most types of driver circuits are designed to supply a greater amount of voltage than the motor's rated voltage. The higher the output voltage from the driver, the higher the level of torque vs. speed. Generally, the driver output voltage (bus voltage) should be rated at 5 to 20 times higher than the motor voltage rating. In order to protect the motor from being damaged, the step motor drive should be current-limited to the step motor current rating.

Choosing a Stepper Motor and Drive

The choice of a step motor depends on the application's torque and speed requirements. Use the motor's torque-speed curve (found in each drive's specifications, example in figure C) to select a motor that will do the job. Every stepper drive in the Omegamation line shows the torque-speed curves for that drive's recommended motors. If your torque and speed requirements can be met by multiple step motors, choose a drive based upon the needs of your motion system- step/direction, stand-alone programmable, analog inputs, microstepping- then choose one of the recommended motors for that drive. The recommended motor list is based on extensive testing by the manufacturer to ensure optimal performance of the step motor and drive combination. More items… Can you submit more information?

power by how it works

20th Jan 2015

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