How Stepper Motor Works
A stepper motor is an electro-mechanical device which converts electrical pulses into mechanical movements. The shaft of a stepper motor rotates in step increments when electrical pulses are applied to it in the proper sequence.
Themotors rotation has several direct relationships to these applied input pulses. The sequence of the applied pulses is directly related to the direction of motor shafts rotation.
How to test the speed of the motor shafts rotation is directly related to the frequency of the input pulses and the length of rotation is directly related to the number of input pulses applied.
STEPPER MOTOR COIL DETAILS:
A Pole A and B are both energized with north up drawing and rotor’s south pole to the up position: this known asfull step.
If pole A had been turend off instead of reversed, the rotor would have rotated only 45 degree clockwise to line up with the field created by Pole B; this is known as as Half step.
Stpper motors obtain small angle step increments by using large numbers of poles. Stator pole reversal can be accomplished by reversing the current flow direction in the winding or by using alternate halves of a ceter-tapped winding
Full-step sequence.
| STEP | SW1 | SW2 | SW3 | SW4 |
| 1 | OFF | ON | OFF | ON |
| 2 | OFF | ON | ON | OFF |
| 3 | ON | OFF | ON | OFF |
| 4 | ON | OFF | OFF | ON |
| 1 | OFF | ON | OFF | ON |
Half-step sequence
| STEP | SW1 | SW2 | SW3 | SW4 |
| 1 | OFF | ON | OFF | ON |
| 2 | OFF | ON | OFF | OFF |
| 3 | OFF | ON | ON | OFF |
| 3 | OFF | OFF | ON | OFF |
| 5 | ON | OFF | ON | OFF |
| 6 | ON | OFF | OFF | OFF |
| 7 | ON | OFF | OFF | ON |
| 8 | OFF | OFF | OFF | ON |
| 1 | OFF | ON | OFF | ON |
Stepper motors may be classified by their motor construction, drive topology, and stepping pattern.
There are three main types of stepper motor construction.
They differ in terms of construction based on the use of permanent magnets and/or iron rotors with laminated steel stators.
These include:are
- Permanent Magnet Stepper
- Hybrid Synchronous Stepper
- Variable Stepper.
STEPPER MOTOR CIRCUIT:-
Program for stepper motor:-
Address Starts from: 8200 90,A0,03 74,82 F0 90,A0,00 74,09 F0 51,1F 74,05 F0 51,1F 74,06 F0 51,1F 74,0A F0 51,1F 80,EA 79,10 78,FF D8,FE D9,FA 22.
Stepper Motors vs. Other Motors
1. Brushless
– Stepper motors are brushless. Motors with contact brushes create sparks, undesirable in certain environments.
2. Holding torque
– Stepper motors have very good low speed and holding torque. Stepper motors are usually rated in terms of their holding torque and can even hold a position (to a lesser degree) without power applied, using magnetic ‘detent’ torque.
3. Open-loop positioning
– Stepper motors can run ‘open-loop’ without the need for any kind of encoder to determine the shaft position. Compared to servos (Closed loop systems- systems that feed back position information), stepper motors are very easy to control.
The position of the shaft is guaranteed as long as the torque of the motor is sufficient for the load, under all its operating conditions.
4. Load independent
– The rotation speed of a stepper is independent of load, provided it has sufficient torque to overcome slipping. The higher RPM a stepper motor is driven, the more torque it needs, so all stepper motors eventually start slipping at some RPM.
Slipping is usually a disaster for steppers, because the position of the shaft becomes unknown. For this reason, software usually keeps the stepping rate within a maximum top rate. In applications where a known RPM is needed under a varying load, steppers can be very handy.
Stepper Motor Details Click Here.
Advantages
1. The rotation angle of the motor is proportional to the input pulse.
2. The motor has full torque at standstill (if the windings are energized)
3. Precise positioning and repeatability of movement since good stepper motors have an accuracy
4. Excellent response to starting/stopping/reversing.
5. Very reliable since there are no contact brushes in the motor.
6. The motors response to digital input pulses provides open-loop control, making the motor simpler and less costly to control.
7. It is possible to achieve very low speed synchronous rotation with a load that is directly coupled to the shaft.
8. A wide range of rotational speeds can be realized as the speed is proportional to the frequency of the input pulses.
Disadvantages
1. Resonances can occur if not properly controlled.
2. Not easy to operate at extremely high speeds.
Related Link: Dc Motor.
