Unipolar Stepper Motor
Páginas: 9 (2075 palabras)
Publicado: 3 de enero de 2013
http://www.tigoe.com/pcomp/code/circuits/motors/stepper-motors/
Stepper Motors
A stepper motor is a motor controlled by a series of electromagnetic coils. The center shaft has a series of magnets mounted on it, and the coils surrounding the shaft are alternately given current or not, creating magnetic fields which repulse or attract the magnets on the shaft, causing the motor to rotate.This design allows for very precise control of the motor: by proper pulsing, it can be turned in very accurate steps of set degree increments (for example, two-degree increments, half-degree increments, etc.). They are used in printers, disk drives, and other devices where precise positioning of the motor is necessary.
There are two basic types of stepper motors, unipolar steppers and bipolarsteppers.
Unipolar Stepper Motors
The unipolar stepper motor has five or six wires and four coils (actually two coils divided by center connections on each coil). The center connections of the coils are tied together and used as the power connection. They are called unipolar steppers because power always comes in on this one pole.
[pic]
Bipolar stepper motors
The bipolar stepper motorusually has four wires coming out of it. Unlike unipolar steppers, bipolar steppers have no common center connection. They have two independent sets of coils instead. You can distinguish them from unipolar steppers by measuring the resistance between the wires. You should find two pairs of wires with equal resistance. If you’ve got the leads of your meter connected to two wires that are notconnected (i.e. not attached to the same coil), you should see infinite resistance (or no continuity).
Like other motors, stepper motors require more power than a microcontroller can give them, so you’ll need a separate power supply for it. Ideally you’ll know the voltage from the manufacturer, but if not, get a variable DC power supply, apply the minimum voltage (hopefully 3V or so), apply voltageacross two wires of a coil (e.g. 1 to 2 or 3 to 4) and slowly raise the voltage until the motor is difficult to turn. It is possible to damage a motor this way, so don’t go too far. Typical voltages for a stepper might be 5V, 9V, 12V, 24V. Higher than 24V is less common for small steppers, and frankly, above that level it’s best not to guess.
To control the stepper, apply voltage to each of thecoils in a specific sequence. The sequence would go like this:
|Step |wire 1 |wire 2 |wire 3 |wire 4 |
|1 |High |low |high |low|
|2 |low |high |high |low |
|3 |low |high |low |high |
|4 |high|low |low |high |
To control a unipolar stepper, you use a Darlington Transistor Array. The stepping sequence is as shown above. Wires 5 and 6 are wired to the supply voltage.
[pic]
To control a bipolar stepper motor, you give the coils current using to the samesteps as for a unipolar stepper motor. However, instead of using four coils, you use the both poles of the two coils, and reverse the polarity of the current.
The easiest way to reverse the polarity in the coils is to use a pair of H-bridges. The L293D dual H-bridge has two H-bridges in the chip, so it will work nicely for this purpose.
[pic]
Once you have the motor stepping in one...
Stepper Motors
A stepper motor is a motor controlled by a series of electromagnetic coils. The center shaft has a series of magnets mounted on it, and the coils surrounding the shaft are alternately given current or not, creating magnetic fields which repulse or attract the magnets on the shaft, causing the motor to rotate.This design allows for very precise control of the motor: by proper pulsing, it can be turned in very accurate steps of set degree increments (for example, two-degree increments, half-degree increments, etc.). They are used in printers, disk drives, and other devices where precise positioning of the motor is necessary.
There are two basic types of stepper motors, unipolar steppers and bipolarsteppers.
Unipolar Stepper Motors
The unipolar stepper motor has five or six wires and four coils (actually two coils divided by center connections on each coil). The center connections of the coils are tied together and used as the power connection. They are called unipolar steppers because power always comes in on this one pole.
[pic]
Bipolar stepper motors
The bipolar stepper motorusually has four wires coming out of it. Unlike unipolar steppers, bipolar steppers have no common center connection. They have two independent sets of coils instead. You can distinguish them from unipolar steppers by measuring the resistance between the wires. You should find two pairs of wires with equal resistance. If you’ve got the leads of your meter connected to two wires that are notconnected (i.e. not attached to the same coil), you should see infinite resistance (or no continuity).
Like other motors, stepper motors require more power than a microcontroller can give them, so you’ll need a separate power supply for it. Ideally you’ll know the voltage from the manufacturer, but if not, get a variable DC power supply, apply the minimum voltage (hopefully 3V or so), apply voltageacross two wires of a coil (e.g. 1 to 2 or 3 to 4) and slowly raise the voltage until the motor is difficult to turn. It is possible to damage a motor this way, so don’t go too far. Typical voltages for a stepper might be 5V, 9V, 12V, 24V. Higher than 24V is less common for small steppers, and frankly, above that level it’s best not to guess.
To control the stepper, apply voltage to each of thecoils in a specific sequence. The sequence would go like this:
|Step |wire 1 |wire 2 |wire 3 |wire 4 |
|1 |High |low |high |low|
|2 |low |high |high |low |
|3 |low |high |low |high |
|4 |high|low |low |high |
To control a unipolar stepper, you use a Darlington Transistor Array. The stepping sequence is as shown above. Wires 5 and 6 are wired to the supply voltage.
[pic]
To control a bipolar stepper motor, you give the coils current using to the samesteps as for a unipolar stepper motor. However, instead of using four coils, you use the both poles of the two coils, and reverse the polarity of the current.
The easiest way to reverse the polarity in the coils is to use a pair of H-bridges. The L293D dual H-bridge has two H-bridges in the chip, so it will work nicely for this purpose.
[pic]
Once you have the motor stepping in one...
Leer documento completo
Regístrate para leer el documento completo.