3. INTRODUCTION
Stepper Motors
A stepper motor or step motor or stepping motor is a brushless DC
electric motor that divides a full rotation into a number of equal steps. The
motor's position can then be commanded to move and hold at one of
these steps without any position sensor for feedback (an open-loop
controller), as long as the motor is carefully sized to the application in
respect to torque and speed.
Switched reluctance motors are very large stepping motors with a
reduced pole count, and generally are closed-loop commutated.
5. Stepping motors are electromagnetic, rotary, incremental devices
which convert digital pulses into mechanical rotation. The amount
of rotation is directly proportional to the number of pulses and the
speed of rotation is relative to the frequency of those pulses.
Stepping motors are simple to drive in an open loop configuration
and for their size provide excellent torque at low speed.
The benefits offered by stepping motors include:
a simple and cost effective design
high reliability
maintenance free (no brushes)
open loop (no feed back device required)
known limit to the 'dynamic position error'
6. construction
A stepper Motor is basically a synchronous Motor. In stepper
motor there is no brushes. This motor does not
rotate continuously, instead it rotates in form of pluses or in
discrete steps. That's why it is called stepper motor. There are
different types of motors available on the basis of steps per
rotation, for example- 12 steps per rotation, 24 steps per rotation
etc. We can control or operate Stepper motor with the feedback or
without any feedback. A simple image of stepper motor is shown
in above picture.
7. Interfacing Stepper Motor with 8051 using
Keil C – AT89C51
A Stepper Motor is a brushless, synchronous DC Motor. It
has many applications in the field of robotics and
mechatronics. The total rotation of the motor is divided into
steps. The angle of a single step is known as the stepper
angle of the motor. There are two types of stepper
motors Unipolar and Bipolar. Due to the ease of operation
unipolar stepper motor is commonly used by electronics
hobbyists. Stepper Motors can be easily interfaced with a
microcontroller using driver ICs such as L293D or ULN2003.
9. Driving Unipolar Stepper Motor with 8051
Unipolar stepper motors
can be used in three
modes namely the Wave
Drive, Full Drive and Half
Drive mode. Each drive
have its own advantages
and disadvantages, thus
we should choose the
required drive according to
the application and power
consumption.
10. Wave Drive
In this mode only one electromagnet is energized at a time. Generated
torque will be less when compared to full drive in which two electromagnets
are energized at a time but power consumption is reduced. It has same
number of steps as in the full drive. This drive is preferred when power
consumption is more important than torque. It is rarely used.
Wave Drive Stepping Sequence
Step A B C D
1 1 0 0 0
2 0 1 0 0
3 0 0 1 0
4 0 0 0 1
11.
12. Full Drive
In this mode two electromagnets are energized at a time, so the
torque generated will be larger when compared to Wave Drive.
This drive is commonly used than others. Power consumption
will be higher than other modes.
Full Drive Stepping Sequence
Step A B C D
1 1 1 0 0
2 0 1 1 0
3 0 0 1 1
4 1 0 0 1
13.
14. Half Drive
In this mode alternatively one and two electromagnets are energized, so it is a combination of
Wave and Full drives. This mode is commonly used to increase the angular resolution of the
motor but the torque will be less, about 70% at its half step position. We can see that the
angular resolution doubles when using Half Drive.
Half Drive Stepping Sequence
Step A B C D
1 1 0 0 0
2 1 1 0 0
3 0 1 0 0
4 0 1 1 0
5 0 0 1 0
6 0 0 1 1
7 0 0 0 1
8 1 0 0 1
17. Interfacing Using L293D
This is the circuit diagram of driving a bipolar stepper motor
using 8051 microcontroller using L293D. 24MHz crystal is
connected to provide the required clock for the microcontroller.
10μF capacitor and 10KΩ is used to provide Power On Reset
(POR) for the 8051 microcontroller. L293D is connected to pins
P2.0, P2.1, P2.2, P2.3 of the microcontroller and two pairs of
L293D are enabled by tieing EN1, EN2 to 5V. Logic Voltage
(5V) is connected to Vss pin and Motor Supply (12V) is
connected to the Vs pin of L293D. Center Tap of each windings
of stepper motor is shorted and connected to the motor supply.
Now we can energize each winding of the motor by making
corresponding pin of L293D LOW.
19. Interfacing Using ULN2003
In this circuit instead of L293D, ULN2003 is used. Working is
similar to the previous circuit, when an input (say 1B) is HIGH
corresponding output pin (1C) will be grounded. Thus we can
energize any winding of stepper motor.
