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Stepper Motor Overview

The rotor of a permanent magnet stepper motor consists of permanent magnets and the stator which has two pairs of windings. Just as the rotor aligns with one of the stator poles, the second phase is energized. The two phases alternate on and off and also reverse polarity.

There are four steps:

  • One phase lags the other phase by one step. This is equivalent to one-forth of an electrical cycle or 90°
  • Poles are formed using a single magnet mounted in-line with the rotor axis and two pole pieces with many teeth
  • The teeth are staggered o produce many poles
  • The stator poles of a real stepper motor also have many teeth. The teeth are arranged so that the two phases are still 90° out of phase
BrushedDC_Block_640x480v2
Recommended Products for Stepper Motor Control and Drive
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Microchip offers a complete line of dual full bridge drivers designed to drive bipolar stepper motors. These can be easily interfaced to any microcontroller.

Microchip’s award winning 8-bit PIC® MCUs are an excellent solution for traditional stepper motor control.

  • For 8-bit PIC MCUs for Stepper Motor Control Start with the: PIC16F917

For advanced closed loop stepper motor control Microchip’s dsPIC® family of digital signal controllers (DSCs) offer DSP performance and advanced motor control peripherals to enable sub micro stepping, high-speed rotation and full torque output.

Microchip offers both MIPS and ARM Cortex MCU's for high performance, 32-bit motor control. These devices feature high performance peripherals tailored for high speed, closed loop motor control.

Stepper Motor Control Application Notes and Software
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Stepper Motor Control Development Tools
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For Microchip single-chip stepper motor drivers

For 8-bit dsPIC DSCs

  • F1 Bipolar Motor Add On for the F1 LV Eval Platform
  • F1 Unipolar Motor Add On for the F1 LV Eval Platform

For 16-bit PIC MCUs

Key Characteristics of the Stepper Motor
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  • Easy to position - moves in steps based on pulses supplied to the stator windings
  • Direction of rotation is changed by reversing the pulse sequence
  • Speed is controlled by the frequency of pulses or pulse rate
BrushedDCMotorDesignFlowchart
How it Works
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In simplified terms, the rotor of a stepper motor consists of permanent magnets with poles and a stator with windings. The rotor is constructed using a single magnet mounted in line with the rotor axis and two pole pieces with many teeth. The teeth are staggered to produce many salient poles.

The stepper motor is easy to position and moves in steps based on pulses supplied to the stator windings. The direction of rotation is changed by reversing the pulse sequence and speed is controlled by the frequency of pulses or pulse rate. The "Micro Stepping Details" below demonstrates this principle for a stepper motor using full step commutation. Just as the rotor aligns with one of the stator poles, the second phase is energized. The two phases alternate on and off, and also reverse polarity. There are four steps. One phase lags the other phase by one step. This is equivalent to one fourth of an electrical cycle or 90°. Stepper motors have a high holding torque but they cannot run at high speeds.

Stepper Motor Control
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Input:
  • Inputs are typically pulses digital communications speed
Control:
  • Basic I/O for full-step and half-step control
  • Comparators for over-current detection
  • Capture/Compare/PWM for micro stepping (or half stepping)

Feedback:

  • Limits switches for homing and safety
Driver:
  • Multiple Switches (MOSFETS)
Micro Stepping Details
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microstepping

Each stepper motor will have a defined step angle associated with it. In the example we can see that with 2 phases, we have a step angle of 90°. If we implement some basic techniques we can improve the resolution of the motor by decreasing the stepping angle.

>Increases step resolutionDivides a full step into sub-steps
>Smoother transitions between stepsLimits noise
Reduces anti-resonance problems
>Maximum torqueLow step rates
High step rates
Design Flow Chart
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StepperMotorFlowChartLarge
Applications
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  • Idle speed adjust
  • Exhaust gas re-circulation
  • Duct airflow vanes
  • Mirror control
  • Telescopes
  • Antennas
  • Toys