24/12/2021

Hybrid Stepper Motor

 

The characteristics of Hybrid stepper motor is combined that of variable reluctance ( VR ) stepper motor and permanent magnet ( PM ) stepper motor.

Construction

  • Its stator is similar to that of single stack VR stepper motor. 
  • The phase winding of stator is either Mono-filar or Bifilar. 
  • The rotor is made of three sections, in which two sections are similar to that VR stepper motor.  
  • The permanent magnet is placed between these two sections. 
  • The distance between north pole section and south pole section is at half tooth pitch in the vertical axis direction. 
  • The torque is generated due to combined magnetic flux of stator and permanent magnet. 

hybrid-stepper-motor.png



Operation

  • The stator has 4 poles in which two winding XX’ and YY’ are energized as shown in the Figure ( a ) and ( b ). 
  • Let us consider that the six north pole of rotor is placed at one side and other six south pole at other side on axial magnet.

Step angle

= [( Nr – Ns ) / ( Nr × Ns )] 360o

= [( Nr – Ns ) / ( Nr × Ns )] 360o

= [( 6 – 4 ) / ( 5 × 4 )] 360o

= 36o

  • The direction of flux in this motor is from stator pole – air gap – rotor half –air gap – stator  pole and stator core. Figure shows initial position of rotor for 36 degree step angle.

Step 1

  • The stator winding X is energized through VX ( + ) such that upper part of stator winding becomes south pole and it attracts north pole of rotor . The step angle during step 1 is zero degree. 
  • The stator Y winding is kept deenergized during this condition.

Step

Energization of winding

Step angle

X

Y

1

VX ( + )

0

00

2

0

VY ( + )

360

3

VX ( - )

0

720

4

0

VY ( - )

1080

5

VX ( + )

0

1440

6

0

VY ( + )

1800

     Single Phase ON – Full Step Operation of Hybrid Stepper Motor

Step 2

  • The stator winding X is deenergized and stator winding Y is energized through VY ( + )  in order to rotate rotor at 36 degree in the clockwise direction.

Step 3

  • The stator winding again energized in the negative direction such that Vx ( - ) , the rotor again rotates through 36 degree step angle resulting total rotation of 72 degree in the clockwise direction.

Step 4

  • The stator winding again energized in the negative direction such that VY ( - ) , the rotor again rotates through 36 degree step angle resulting total rotation of 108 degree. 
  • Similarly the step position 5 and step position 6 is explained.

Features

The following are the features of Hybrid Stepper Motor.

  • As there are large number of poles, small step angle is achieved. This will result in good resolution.
  • Low excitation voltage requires in the Hybrid Stepper Motor as compared to VR stepper motor.
  • Good damping characteristic due to permanent magnet
  • Better detent, holding and dynamic torque characteristic as compared to PM stepper motor and VR stepper motor
  • Due to higher detent torque, rotor becomes standstill even if power is switched off.
  • Cost of Hybrid stepper motor is higher as compared to PM stepper motor   

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