Moror controller design

formatting link

I'm a hobbyist without much electronic experience.

In the above design for a motor controller, what is the anticipated input where it says "Input voltage from computer"?

Can it be, is it meant to be, a PWM signal voltage? TIA

Reply to
Rich
Loading thread data ...

"Rich" schreef in bericht news: snipped-for-privacy@mid.individual.net...

No, it should be a DC voltage. It's a lineair circuit. No PWM.

petrus bitbyter

Reply to
petrus bitbyter

I wonder why the author put "Input voltage from computer".

I guess that voltage is the reference voltage, and is equivalent to a setpoint?

Could come from a regulated DC supply?

Reply to
Rich

Interesting circuit to say the least.

it requires a +/- 0..? some very low voltage to control the direction and speed.

My guess is that the control voltage average range is 150:1 of the supply voltage. so, if you were to use a 12 volt supply for example, that would be like +/- 0.08 volts for max speed either direction. I could be wrong in that area, that's just a quick observation.

Also, after looking at it, it's very possible that first network is intended for a PWM wave form, but still, the input voltage needs to be low.

The oscillator is a nice addition to perform a locked rotor effect.

formatting link
"

Reply to
Jamie

Well, I cannot tell whether it's designed for a PWM reference voltage input, I'm too green.

Perhaps someone can give a definitive answer.

Thanks fot the laugh BTW. You know, the "Club". :c)

Reply to
Rich

I'm glad you like my club girl :)

As with the circuit, either will work ..

PWM or variable DC how ever, the level of the voltage still looks to be very low. There is a lot of gain in the circuit.. That gain can be reduced greatly to accommodate higher input voltages.

formatting link
"

Reply to
Jamie

"Rich" schreef in bericht news: snipped-for-privacy@mid.individual.net...

"Input voltage from computer" suggests what it says, but does not tell a thing about that voltage itself. From the circuit I can tell only that it requires a constant or slowly changing, low DC voltage. As far as the circuit concerns that voltage is used to control the moter speed, no matter where it comes from, no matter what you name it.

If you have a PWM signal available it may be used if you add an appropriate low pass filter.

The principles used are well known in analog controll technics but FAIK digital technics (PWM) are more often used this days. As the articles tells little or nothing about the environment in which this circuit is used, I can only hope it performs well. I think I'd use a micro but I can be mistaken.

petrus bitbyter

Reply to
petrus bitbyter

Hi. Well I posted also to sci.eng.control and someone said" The input referred to would be an analog voltage, with value proportional to the target speed."

I take "analogue voltage" to mean simple a steady, unvarying dc voltage.

However, you can add a small sawtooth component to the to the reference voltage, so the voltage controlling the motor will not necessarily be steady dc.

And then one thinks, can in fact this circuit work with a PWM reference voltage. It's still perhaps somewhat unclear.

Reply to
Rich

"Rich" schreef in bericht news: snipped-for-privacy@mid.individual.net...

Well, that's the voltage I meant.

Wrong, I sine wave for instance is also a analog voltage.

The sawtooth component is added by the circuit already, made by opamp 22.

Only if you add the appropriate low pass filter. The circuit is not designed for PWM input.

petrus bitbyter

Reply to
petrus bitbyter

to me the circuit looks wrong for a PWM input

motor voltage is measured by 12 and current by 11 current multiplied by the motor resistance is subtracted from voltage in 21 to get a measure of back emf.

22 is an oscilator which creates a sawtooth that is added to the input anf then that is compared with the back emf (from 21) of the motor in 31 thus producing a PWM signal which is used to drive 32 and the half-bridge
Reply to
Jasen Betts

Okay.

I am thrown off by that sawtooth generator. Because of the inclusion of that, the circuit obviously works with some degree of varying dc voltage, because it's potentially such a voltage that is feeding the difference amplifier (marked 31). Then of course I got to wondering whether it will go "all the way", and work with a square wave input.

Thanks for the help. Rich

Reply to
Rich

What is clear, is that the circuit will handle an input other than steady dc voltage. But looks like not a fully-chopped dc voltage.

I'm going to draw the circuit out again and see more clearly how it works what it's possibilities are. Just why it won't work with a PWM input.

Reply to
Rich

Wait a minute, you say it produces itself a PWM signal, so the motor does get PWM driven.

I'll try to figure out how exactly the cicuit produces PWM.

Reply to
Rich

It's PWM's by running the DC voltage from the input and the triangle wave from the Schmitt trigger (lower left) into a comparator.

Hope This Helps! Rich

Reply to
Rich Grise

See my earlier post.

Cheers! Rich

Reply to
Rich Grise

OK. :-)

None of these other responders know what they're talking about. The Schmitt trigger (lower left) produces a triangle wave, which is summed with the DC input (yes, "input voltage from computer" is DC.) by the 10K and the 4.7 uF, and sent to the comparator (the upper left difference amlpifier), where it's compared with the error voltage from the lower left difference amplifier, producing PWM at its output. This drives the motor with PWM. (IOW, the circuit makes its own PWM.) The rest of the circuit is just a fancy-schmancy way of reading the motor voltage and current to determine its actual speed for the feedback signal.

If you redraw it, please give the parts reference designators. ;-)

Hope This Helps! Rich

Reply to
Rich Grise

Hi. If you assume that the reference input is a steady dc voltage, and no other signal is involved, then the drive will deliver a constant voltage to the motor. Under these circumstances this is not a PWM motor controller. Even when the motor is loaded, leading to an error voltage, it's still not a PWM controller.

But, the circuit has a provision to introduce a triangle wave and therefore the drive voltage to the motor can begin to take on an element of PWM. I'm not sure it's PWM as a square wave applied to the motor, but I think it can be something akin to PWM. So, the motor is driven something akin to PWM. I think.

Of course you could not have the triangle wave generator and let the computer supply something akin to PWM.

I'm still not convinced the motor in this circuit is meant to recieve a square wave voltage. *That's what I think of when I think of a PWM controller*.

But on the other hand I'm not certain either that it cannot handle a square wave input from (say) a computer or other source.

I think I am convinced something akin to PWM drives the motor.

Just my thoughts as a not a learned electronics hobbyist.

Reply to
Rich

Really, if that is the case, why does it specify it to be a holding signal to prevent the motor from moving?

I think you better look at the circuit a little closer..

The signal you're talking about is an injected signal to cause the motor to produce a locked magnetic position to hold it self in place. If you notice, there is a pot there that allows you to adjust it or remove it if you wish.

The input signal only offset's this effect if you are using it, other wise, the input signal just normally biases the drive +/- with no mag locking effects. You must remember that locking a DC motor requires an alternation of polarity. It's very obvious that injecting a signal like that isn't going to drive the motor either way but causing it to bind in place.

In short, with out the optional inserted signal, the motor will free spin at 0 bias..

Further more, there is no voltage comparator in the input circuit that I noticed ?

In any case, if you look at Vector control motors, its a common practice to set the AC motor at 50% of Max current at all times even at 0 speed, this helps regulate position at low RPM's and offers smoother torque control at low RPM's..

With this DC motor, you really don't need the torque control since DC motors have that at the low end how ever, it offers the ability to control swing loads and free spin.

That's my take on it, I'll stick with it.

formatting link
"

Reply to
Jamie

Here's a simpler circuit that describes how the triangle wave and the DC level are combined to produce the PWM output for the motor.

formatting link
Although I find it interesting that the Electronics Design circuit does that with passive components rather than driving separate inputs to a comparator. Mike

Reply to
amdx

Thanks for the link, it's great. That is going to be very helpful I'm sure.

formatting link

So, very often a PWM motor controller will use a comparator fed with a triangle (or sawtooth) waveform, as well as a dc reference voltage, to turn on and off a transistor thus producing a PWM supply to the dc motor. This is PWM because whatever the waveform, the voltage is turned off at some point. If the voltage to the motor does not go to zero, that is not strictly PWM motor control. I believe this is correct.

I think the reference voltage is called a "setpoint" in a closed loop system, because it determines the set speed of the motor.

formatting link

Not sure precisely how this circuit produces a PWM drive to the motor, but it does not use a comparator. It does have a reference input and a sawtooth generator by which PWM is created. Now, unless someone says different this circuit is a PWM controller because the voltage to the motor during a duty cycle does go to zero. That I think is an essential characteristic of a PWM controller.

Reply to
Rich

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.