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In many Robot Applications Stepper Motors are Best Solution because you can
controls the rotation & speed of Motor very easy.
But it has 2 Disadvantages:
1- They can't reach high speeds.
2- They are not Common for using in High Power and High Speed Applications
BUT if You Want to Precise rotation speed and torque it is better to use
Sync AC Motors or Inductive AC Motors. these motors speeds and torque
are Independent in wide range of Load change.
But These motors Have some Disadvantages :
1- They are common in big sizes.
2- They are expensive
3- Controler circuits are complicated.
4- it's Better to design FeedBack Controller circuits for very presice torque.
I recommend these books:
a-Electric Machinery fundamentals 3rd (Chapman Stephan)
b-Power control circuits Manual (Marston)
You should search for servo drive. Usually servo drive comes with it's own controller. Servo driver manufacturers:
1) Pacific Scientific ( **broken link removed** )
2) Hitachi ( **broken link removed** )
If precise torque is the goal, then you can use a DC motor and supply it with a constant current, that wil give you a constant torque. A switching regulator is desirable, since it has better efficiency.
Yes nicleo. In brush DC, brushless DC or AC servos current control gives you direct torque control. Altough current variation in stepper motor windings afects torque, you can't control the force exerted against the load that way. That's simply because the torque in stepper motors has a very non linear profile between torque detents.
A possible solution if you *really* want to use a stepper is to use some sort ef elasticity between motor and load, a spring for example, and use the stepper to compress it more or less.
Controlling the motor torque can be done with a constant current. Since it is a robot, I expect efficiency will be an issue, so a a switching regulator will be needed in the end. After you experiment please post how things are going and I will suggest something.
For now I would breadboard the circuit shown and test to see if this is realy what is needed, namely current control.
The motor current is simply:
Im=(Vdac-Vbe)/R1
You should select R1 so as to obtain the maximu current required for the motor when Vdac is at maximum (I suppose 5V).
Vdac is the voltage you get from the DAC (I suppose you will have a DAC). For testing you can just use a pot and vary the voltage from 0 to 5V. The battery shown will be your bench supply for now. Adjust the voltage to about 10-12V. Do not worry about details now. You just need to test the concept. Later we can deal with the other issues such available voltage, power, etc.
The transistor shown may get hot, depending on the motor current and power suply voltage. I suppose a 2N2219 or similar should do the trick. A heatsing may be required.
I've made a H bridge controller . but it seems hoter while reduce speed . Maybe the wave at gate of MOSFET not good . Can you help me to make my curcuit better
I'm using SLA7042M from Allergro and my customized code uon PIC16F84 to generate necessary signal for the Micro stepping driver.
the driver can drive a unipolar stepping motor from full step boosted torq mode to 1/8 step which combination to the 1.8 degree per step can give you a very accurate positioning in any application.
You can go through my code and it is possible to build your own controller by compare the driver data sheet and I/O from the code
I'm using this driver to control the 3 axis of my sherline milling machine using 3 controller attached to a PC running Linux and EMC.
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