Hurst Manufacturing

The term, hybrid, is due to the motor being operated under the combined principles of permanent magnet and variable reluctance. The most popular step angle for the hybrid stepping motor is 1.8 degrees, or 200 steps per revolution.

The Hybrid Stepper is the motor solution for precision movements or higher speed applications in factory and office automation.

The construction of a hybrid stepper motor is characterized by having a coil, multi-toothed stator and rotor poles with a permanent magnet. This construction offers small step angle, sufficient torque and speed.

A 200 step per revolution (1.8°) step motor with 2 phases "on" (4 phase instant) has 50 rotor teeth on each rotor yoke. These are referred to as poles. The stator has 8 poles. A phase state in a motor with permanent magnets is considered a single polarity current or voltage. A cycle is considered a positive and negative current or voltage.

These motors are usually wound with a bifilar winding, this makes it possible to drive a motor from a single polarity voltage without using reversing switches or transistors to reverse the current to the motor windings. Each of the poles has 2 windings and is mistakenly called a 4 phase motor because of this. If the motor is driven from a bipolar drive or ac power source only 1 winding per pole is required.

• Higher Torques than variable reluctance and permanent magnet step motors
• Allows for small step angles (higher rps)
• Highly Accurate - step angle error is small and non-cumulative

The DC power supply is switched to each phase in sequence to operate a stepping motor. Ordinary DC or AC power supplies will not run a stepping motor unless the driving circuit includes a switching circuit. The signal circuit is used to generate pulses, change or stop frequencies and to generate reversing signals. The logic circuit distributes signal pulses to each wire according to the number of phases and the excitation method.

Unipolar Drives Motor phase winding current is switched in only one direction (typically to ground).

• Simple low cost drive circuit
• Requires a center tap winding
• Lower output Torque
• 6 & 8 lead motors

  Bipolar Drives Motor phase winding current is switched in both directions

• Higher cost drive circuit
• No center tap winding required
• Higher output torque
  • Approx 1.4 X Unipolar Drive
• 4, 6 & 8 lead motors
• 8 Lead motors are more efficient when used with a bi-polar drive
  Stepping Methods

  Full/Half Stepping Steps the motor by alternating phase windings in fully on or fully off mode

• Full Stepping (1 Phase)
  • Energize 1 phase at the same time
  • 1 Phase stepping uses half the power devices as 2 phase stepping
• Full Stepping
  • Energize 2 phases at the same time
  • Rotor step is function of motor pole count
• Half Stepping
  • Sequences 2 phases "on" and "off"
  • Rotor step 1/2 of full step value
  • 5-10% less torque than with full step control

  Microstep Stepping Gradually energizes a phase to create smaller subdivisions of each full-step.

• Requires sophisticated control electronics
• Resonance speeds become an issue
• 20-30% less torque than with full step
• Motor design becomes significant