motor driver evolution question...

[Matt McColley]

Well the more I learn, the more questions I generate....

apologies if this is in the wrong forum.... but benchtop machines is one of the most active an seems to be frequented by a lot of sharp cookies.

So I'm looking at different motor characteristics and types of drivers and am wondering....

1. terminology.... are L/R drivers, resistance limited drivers, high frequency switching drivers and chopper drivers all different names for the same thing?

2. am I correct in my understanding that Keling's drivers and Gecko drivers are "chopper" drivers?

3. can any stepper motor be used with either a bi-level or a chopper driver? or is the motor design specific to one type of driver?

4. Why do chopper drivers seem to dominate? The torque curves for motors paired with bilevel drivers I'm looking at seem to hold their torque MUCH better.

5. Does a driver have to utilyze high frequency switching in order to accomplish micro-stepping? (if so, this would answer Q4)

6. Why is micro-stepping so desireable, when you lose so much torque at higher speeds? Can't you just half step with a bilevel driver and utilyze screw pitch and gear/pully ratios to get the requied resolution?

As I've noted before, I now know just enough to be a hazzard to myself and others

Thanks in advance for any light you can shed on the subject.

[escott76]

I'm not going to be much help for most of this, but for Q6 the answer is it isn't always best to microstep, as some of the better drives will morph to half or full step when going fast. I know the G540 and 203's do this.

[Matt McColley]

some of the better drives will morph to half or full step when going fast. I know the G540 and 203's do this

That's cool... I didn't know that

[kreutz]

Originally Posted by escott76 I'm not going to be much help for most of this, but for Q6 the answer is it isn't always best to microstep, as some of the better drives will morph to half or full step when going fast. I know the G540 and 203's do this.

That is a misconception. The fact that they morph into different waveforms does not mean that they are not still micro-step drives. No micro-steps are lost at any speed.

Micro-stepping current waveforms are used at low speeds as a mean of having smoother motor response and make the stepper motor less prone to resonances. So, it is always best to micro-step unless your PC does not provide the required step frequency for the speeds you are aiming at.

At higher speeds the current waveform cannot follow the sinusoidal reference anymore and is where morphing takes place (as a means to improve torque at those speeds).

By the way, also the Mardus-Kreutz (unipolar micro-stepper drives) and Kreutz-4 and derivatives (K-41DIY) bipolar micro-stepper drives use waveform morphing vs speed.

Best regards,

Kreutz.

[kreutz]

Originally Posted by Matt McColley 1. terminology.... are L/R drivers, resistance limited drivers, high frequency switching drivers and chopper drivers all different names for the same thing? 2. am I correct in my understanding that Keling's drivers and Gecko drivers are "chopper" drivers? 3. can any stepper motor be used with either a bi-level or a chopper driver? or is the motor design specific to one type of driver? 4. Why do chopper drivers seem to dominate? The torque curves for motors paired with bilevel drivers I'm looking at seem to hold their torque MUCH better. 5. Does a driver have to utilyze high frequency switching in order to accomplish micro-stepping? (if so, this would answer Q4) 6. Why is micro-stepping so desireable, when you lose so much torque at higher speeds? Can't you just half step with a bilevel driver and utilyze screw pitch and gear/pully ratios to get the requied resolution?

6- Was answered on a prior post.
5- No, you can microstep using chopper and linear (analog) type of current control.
4- Chopper drives are more efficient, but stepper motors tend to heat up more with chopper drives due to magnetic losses. Bi-level drives are more complex.
3- You can use any "hybrid stepper" motor with any of the drives. Micro-stepper drives are better used with higher quality low torque ripple stepper motors, otherwise the rotor movement is not going to be equally spaced on each micro-step.
2- Yes.
1- They are all terms that refer to the method used to regulate current on the drives, they are not the same. L/R and resistance limited refer to the same principle. Chopper and high frequency switching refer also to the same type of drives.

The term "high frequency" is very relative, in the early 80's 20 Khz was considered high frequency switching, nowadays there are dc/dc switchers on the Mhz range and class-d audio amplifiers on the 100's of Khz and up.

[HimyKabibble]

Greatly simplified, of course, but....

1. terminology.... are L/R drivers, resistance limited drivers, high frequency switching drivers and chopper drivers all different names for the same thing?

The two most common ways of limiting current in stepper motors are:

a) a series resistor - These are L/R drivers and resistance limited drivers. This approach has the advantage of being very simple and cheap - a few FETs, and a few big power resistors. You see these often in very cheap unipolar drives. It has the disadvantage of being extremely inefficient - at least half the total input power is wasted - and generates a great deal of waste heat as a result. It also becomes impractical at higher current levels, as the resistors, and the amount of heat they generate, becomes unamanagable. Also, they will be limited in top speed, and high-end torque, due to their inability to saturate the coils at high step rates.
b) "Chopper", "Switching" or "PWM" drivers - This is by far the most common and best method to control a stepper. The electronics is a lot more complex, but it provides the best combination of performance, and efficiency.

2. am I correct in my understanding that Keling's drivers and Gecko drivers are "chopper" drivers?

Yes.

3. can any stepper motor be used with either a bi-level or a chopper driver? or is the motor design specific to one type of driver?

I don't know, but I suspect so. Some may not work particularly effectively, particularly those with high inductance coils, but I'd guess almost any motor would at least work.

4. Why do chopper drivers seem to dominate? The torque curves for motors paired with bilevel drivers I'm looking at seem to hold their torque MUCH better.

I think that's explained above - Performance and efficiency.

5. Does a driver have to utilyze high frequency switching in order to accomplish micro-stepping? (if so, this would answer Q4)

No, it can be done by other means, but, again, the other means are inefficient.

6. Why is micro-stepping so desireable, when you lose so much torque at higher speeds? Can't you just half step with a bilevel driver and utilyze screw pitch and gear/pully ratios to get the requied resolution?

Micro-stepping provides smoother torque, by approximating a sinusoidal current waveform in the coils. This reduces "cogging", and also mitigates mid-band resonances, which can cause lost steps.

Regards,
Ray L.

[Matt McColley]

very interesting! I understand about half of it, but still very interesting.

Are all Bi-Polar drivers analog?

Am I correct in thinking that in the evolution of driver types, chopper drives have won the battle?

or...

are there certain applications that are still seen as being more suitable for Bi-Level drivers?

[HimyKabibble]

Originally Posted by Matt McColley very interesting! I understand about half of it, but still very interesting. Are all Bi-Polar drivers analog? Am I correct in thinking that in the evolution of driver types, chopper drives have won the battle? or... are there certain applications that are still seen as being more suitable for Bi-Level drivers?

Virtually all bi-polar drivers are PWM these days, very few are "analog". Chopper drives have definitely "won the battle". The only place you'll see analog/LR drives are on very, very low-end products.

Regards,
Ray L.

[Matt McColley]

Does PWM stand for pulse width modulating?

if so, I'll be my 10 year old Anaheim Automation driver are in fact PWM, as their spec. sheet calls out a minimum pulse width of 15 micro-seconds.

so I'll rephrase my quesion.....

Have chopper drivers won the driver wars and made PWM drivers obsolete? Or, are their applications better suited for PWM drivers.

This whole line of inquirey is based upon me trying to figure out whether my salvaged (10 year old, but unused) Anaheim Automation DPK series drive pack should be considered for a router table build.

Here's a link to the Drive packs spec. sheet.

http://www.anaheimautomation.com/man...rs%20Guide.PDF

[ger21]

Originally Posted by Matt McColley Does PWM stand for pulse width modulating? if so, I'll be my 10 year old Anaheim Automation driver are in fact PWM, as their spec. sheet calls out a minimum pulse width of 15 micro-seconds.

PWM and the 15us pulse width are two different things. The pulse width is the length of the step signal required. Most newer drives only require 1 or 2 us for the step pulse.

[HimyKabibble]

Originally Posted by Matt McColley Does PWM stand for pulse width modulating? if so, I'll be my 10 year old Anaheim Automation driver are in fact PWM, as their spec. sheet calls out a minimum pulse width of 15 micro-seconds. so I'll rephrase my quesion..... Have chopper drivers won the driver wars and made PWM drivers obsolete? Or, are their applications better suited for PWM drivers. This whole line of inquirey is based upon me trying to figure out whether my salvaged (10 year old, but unused) Anaheim Automation DPK series drive pack should be considered for a router table build. Here's a link to the Drive packs spec. sheet. http://www.anaheimautomation.com/man...rs%20Guide.PDF

Matt,

Yes, PWM = Pulse Width Modulation. A chopper drive *is* a PWM drive. PWM drives have been around for a long time, but only in the last 5 years or so have become cheap enough for widespread hobby use.

Regards,
Ray L.