RF CONTROLLED STEPPER MOTOR
A stepper motor is an electromechanical device, which converts
electrical pulses into discrete mechanical movements. The shaft or spindle of a
stepper motor rotates in discrete step increments when electrical command
pulses are applied to it in the proper sequence. The motors 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.
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.
We can use the stepper motor to control the motion of a robot but
the biggest hurdle is the wired control. We can control the stepper motor
wirelessly through RF link. In this project we are controlling the stepper
motor wirelessly through RF link. We are using RF module and AT89S52
microcontroller to achieve this motive.
Following are the main components of this project:
1) RF Module
2) Microcontroller.
3) Output mechanical transducer
(stepper motor).
Stepper
motor:
A stepper motor (or step motor) is a brushless, synchronous
electric motor that can divide a full rotation into a large number of steps.
The motor’s position can be controlled precisely, without any feedback
mechanism (see Open-loop controller). Stepper motors are similar to switched
reluctance motors (which are very large stepping motors with a reduced pole
count, and generally are closed-loop commutated.)
Fundamentals of Operation:
Stepper motors operate differently from DC brush motors, which
rotate when voltage is applied to their terminals. Stepper motors, on the other
hand, effectively have multiple “toothed” electromagnets arranged around a
central gear-shaped piece of iron. An external control circuit, such as a
microcontroller, energizes the electromagnets. To make the motor shaft turn,
first one electromagnet is given power, which makes the gear’s teeth
magnetically attracted to the electromagnet’s teeth. When the gear’s teeth are
thus aligned to the first electromagnet, they are slightly offset from the next
electromagnet. So when the next electromagnet is turned on and the first is
turned off, the gear rotates slightly to align with the next one, and from
there the process is repeated. Each of those slight rotations is called a
“step,” with an integer number of steps making a full rotation. In that way,
the motor can be turned by a precise angle.
Stepper motor characteristics:
1. Stepper motors are constant power devices.
2. As motor speed increases, torque decreases.
3. The torque curve may be extended by using current limiting
drivers and increasing the driving voltage.
4. Steppers exhibit more vibration than other motor types, as the
discrete step tends to snap the rotor from one position to another.
5. This vibration can become very bad at some speeds and can cause
the motor to lose torque.
6. The effect can be mitigated by accelerating quickly through the
problem speeds range, physically damping the system, or using a micro-stepping
driver.
7. Motors with a greater number of phases also exhibit smoother
operation than those with fewer phases.
Applications:
Computer-controlled stepper motors are one of the most versatile forms
of positioning systems. They are typically digitally controlled as part of an
open loop system, and are simpler and more rugged than closed loop servo
systems.
Industrial applications are in high speed pick and place equipment
and multi-axis machine CNC machines often directly driving lead screws or ball
screws. In the field of lasers and optics they are frequently used in precision
positioning equipment such as linear actuators, linear stages, rotation stages,
goniometers, and mirror mounts. Other uses are in packaging machinery, and
positioning of valve pilot stages for fluid control systems.
Commercially, stepper motors are used in floppy disk drives,
flatbed scanners, computer printers, plotters, slot machines, and many more
devices.
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