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 of Hybrid Stepper Motor

• 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. 

Operation of Hybrid Stepper Motor

• 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 )] 360^o

= [( Nr – Ns ) / ( Nr × Ns )] 360^o

= [( 6 – 4 ) / ( 5 × 4 )] 360^o

= 36^o

• 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 V_X ( + ) 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 V_Y ( + )  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 V_Y ( - ) , 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 of Hybrid Stepper Motor

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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