electric machines

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STEPPER MOTOR INTERFACING WITH 8086
HARIKRISHNAN G. P. Lecturer ECE
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8255 -PPI

• Programmable Peripheral Interface

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• Functional configuration of each port is
  controlled by the command word.
• Control Word Register can only be written into,
  no read operation is allowed.
• 8255 offers 3 modes
• Mode 0 Basic I/O
• Mode 1 Strobed I/O
• Mode 2 Strobed bidirectional I/O
• 24 I/O lines organized as 3-ports having 8 I/O
  lines each

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8255 MODE INSTRUCTION FORMAT
PORT C LOWER) 1- Input 0- Output
Mode select 0 - Mode 0 1 Mode 1
PORT C (UPPER) 1- Input 0- Output
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STEPPER MOTOR

• Rotor able to assume discrete stationary angular
  positions.
• Rotor motion in stepwise-manner from one
  equilibrium position to the next.
• Two types of Stepper-Motor.
• Reluctance type
• Permanent Magnet type (PM).
• PM type consists of multiphased stator and two
  part permanent magnet rotor.
• Two phase stepper-motor consists of two pairs of
  stator poles
• Each of 4 poles has its own windings.
• Excitation generates N S poles at diametrically
  opposite side.

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S

• 4-pole structure with 3-pair rotor poles
• Two end faces

N
S
S

• N-Pole twisted w.r.to S-Pole by one pitch.
• 12 stable positions in which S-pole of rotor can
  lock with N-pole of Stator

N
S
N
N
S
N
Stepper-Motor Cross-sectional view
S
S
N
N
N
S
Rear-View
Front-View
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• Ns is no. of stator poles
• Nr is no. of pairs of rotor poles
• 3-Schemes for Stepping a stepper-Motor
• Wave Scheme.
• 2-Phase Scheme.
• Half-Stepping or Mixed Scheme.

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Energizing of Coils in 4-Pole Stepper-Motor
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Wave Scheme
N-Pole
S-Pole
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Wave Scheme

• A single phase is activated at a time.
• The same number of steps as the full step drive,
  but the motor will have significantly less than
  rated torque. It is rarely used.
• 30o for each step.

Anticlockwise Anticlockwise Anticlockwise Anticlockwise Anticlockwise Clockwise Clockwise Clockwise Clockwise Clockwise
Step A1 A2 B1 B2 Step A1 A2 B1 B2
1 1 0 0 0 1 1 0 0 0
2 0 0 0 1 2 0 0 1 0
3 0 1 0 0 3 0 1 0 0
4 0 0 1 0 4 0 0 0 1
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2-Phase Scheme

• step angle is 30o but is offset by 15o in the
  two-phase scheme.
• 12 steps required to move rotor 360o.

N-Pole
S-Pole
Anticlockwise Anticlockwise Anticlockwise Anticlockwise Anticlockwise Clockwise Clockwise Clockwise Clockwise Clockwise
Step A1 A2 B1 B2 Step A1 A2 B1 B2
1 1 0 0 1 1 1 0 1 0
2 0 1 0 1 2 0 1 1 0
3 0 1 1 0 3 0 1 0 1
4 1 0 1 0 4 1 0 0 1
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Stepper Motor Wiring

• Most stepper motors have 6 wires, however there
  are motors with 4, 5, or 8 wires also.
• Each of the four coils is made up of one length
  of wire with two ends.
• One end is called live and the other end is
  called common.
• In a five-wire stepper motor all four commons
  are joined together, in a six-wire stepper motor
  two pairs of common wires are joined together,
  and in an eight-wire stepper motor none of the
  four common wires are joined together.

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Programming a Stepper

• Basics
• VLIM-013A supports Stepper motor interface.
• Board consists of 3-parts
• Address decoding.
• Stepper-Motor driving circuitry.
• Operating voltage selections.

8255 PPI 0C Port A 0D Port B 0E Port C 0F
Control Register
According to torque range from 2Kg -20Kg 12V,
24V, 6V
TIP 122 Darlington pair used
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Software Experiments

• To run a stepper motor at different speeds

MOV AL, 80H OUT 0026H, AL L3 MOV SI,1050H
MOV BL, 04H L2 MOV AL,SI OUT 0020H,
AL CALL L1 INC SI DEC BL JNZ L2 JMP L3 L1 MO
V CX, 0A03 L4 DEC CX JNZ L4 RET
INPUT
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• To run a stepper motor for required angle within
  460o which is equivalent to 256 steps

MOV AL, 80H OUT 0026H, AL MOV CL,
064 L1 MOV SI, 1200H MOV BL, 04 L2 MOV
AL,SI OUT 20, AL DEC CL JZ L4 MOV DX,
0505 L3 DEC DX JNZ L3 INC SI DEC BL JNZ L2 J
MP L1 L4 HLT
INPUT
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• To rotate the motor in both forward and reverse
  direction

MOV AL, 80H OUT 0026H, AL L1 MOV CL,
050 FWD MOV SI, 1200H CALL ROTATE DEC CL JNZ
FWD CALL DELAY MOV CL, 050 REV MOV SI,
1300H CALL ROTATE DEC CL JNZ REV CALL DELAY J
MP L1
ROTATE MOV BL,04 L2 MOV AL, SI OUT 0020,AL M
OV DX, 0505 L3 DEC DX JNZ L3 INC SI DEC BL JN
Z L2 RET DELAY MOV DX, 0FFF L4 DEC DX JNZ L4
RET
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INPUT
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