stepping motor with high resolution

Contact Hurst and ask for a list of distributors or area reps, who are in the business of selling in smaller quantities.

Also consider a standard motor with a microstepping drive. This is the more common approach to the problem. Some of the drives provide for

-- Gordon

Cosmin,

What about a standard motor and a gear (or belt) reduction?

Jeff.

Gord>> Does anyone know where to buy such a motor? The best match I came

--Gooogle on the term "differential screw" (I think that's right); it's a sneaky way to get high resolution with low tech stuff.

While I think some of the mechanical means suggested make some sense for DC motors, for steppers a $150-200 circuit can provide finer control with no backlash or mechanical setup. What's especially nice about microstepping drives is that (most) also function in full-step mode. You're not limited to a set top speed because nothing is geared down. Under software control the motor will drive at full speed (e.g. 200 cps), so you don't have to sit there for a blue moon as your motors re-home. Then, under microstep mode they move in fractions of a step.

For a CNC rig, which is my , geared down stuff means $$$ wasted in operating time.

-- Gordon

steamer wrote:

Gordon:

While I am no expert on micro-stepping, but I have implemented my own CNC 4-axis drive electronics using microstepping.

You can get some additional stepper resolution using microstepping, but you do eventually reach a point of diminishing returns. At some point the friction in the system will be greater than the torque required to move a microstep. It is extremely unlikely that you will be able to divide a step into 1/256. 1/32 is probably pushing it.

For me the primary reason for implementing micro-stepping is to avoid resonance issues. If you use ripple-step, full-step, or even half step drive electronics to drive a stepper motor, there are some speeds at which the stepper motor will not want to run; instead, it freezes up and makes a horrible noise. Determining the speed at which resonance occurs is difficult because it depends upon many system wide factors such as friction, axis inertia, etc. The typical solution is to use micro-stepping electronics to avoid these resonance effects. I am at a loss of words to describe why micro-stepping avoids resonance effects, but suffice to say that is one of the primary reasons people go through the hassle of doing micro-stepping electronics for stepper motors.

For the original application that started this thread, I suspect that resonance effects are not an issue.

-Wayne

Gordon:

While I am no expert on micro-stepping, but I have implemented my own CNC 4-axis drive electronics using microstepping.

You can get some additional stepper resolution using microstepping, but you do eventually reach a point of diminishing returns. At some point the friction in the system will be greater than the torque required to move a microstep. It is extremely unlikely that you will be able to divide a step into 1/256. 1/32 is probably pushing it.

For me the primary reason for implementing micro-stepping is to avoid resonance issues. If you use ripple-step, full-step, or even half step drive electronics to drive a stepper motor, there are some speeds at which the stepper motor will not want to run; instead, it freezes up and makes a horrible noise. Determining the speed at which resonance occurs is difficult because it depends upon many system wide factors such as friction, axis inertia, etc. The typical solution is to use micro-stepping electronics to avoid these resonance effects. I am at a loss of words to describe why micro-stepping avoids resonance effects, but suffice to say that is one of the primary reasons people go through the hassle of doing micro-stepping electronics for stepper motors.

For the original application that started this thread, I suspect that resonance effects are not an issue.

-Wayne

Dittos.

I think you'll be hard-pressed to find a commercial drive that offers less than 1/16.

It avoids resonance while accelerating the motor by providing a smoother transition between steps; the motor is not snapping to multi-degree angles and initiating a wobble which will develop into resonance at the right frequency.

However there is another issue. The original poster wanted a stepper motor with 0.1 degrees resolution. The fact of microstepping is that the intermediate "steps" can be wildly inaccurate. Adding any load to the system makes things worse. No, I agree with an earlier poster that gearing is the answer. Not only does it allow high resolution, but it provides greatly improved torque to prevent the load from making the position droop or the motor skip steps. Stock Drive Products has a number of methods for doing this, with backlash essential nil.

The original poster also specified that this will be run in full step mode, so it appears they are already aware of microstepping and do not wish to use it, either for simplified drive electronics or the unreliable microstep resolution I mentioned above.

Wait a minute! The OP said 0.1 degree resolution, not accuracy to 0.1 degree. Different stuff. I'm of the school of thought that considers these two words, while interrelated, don't mean the same thing, from an engineering standpoint.

I'm impressed that industry is able to achieve *resolutions* for things like 1200 dpi inkjet printers, and 2400x4800dpi flatbed scanners, while still providing for fast re-homing speeds, and while using the cheapest steppers China manufactures. They achieve these resolutions with microstepping. Actually a microstepping driver and clever software.

The original poster didn't indicate the load requirements, and while he did say full step mode, that could have been just from the spec sheets for the motor he was interested in. Most stepper motors list specs for full step mode, as a matter of consistency. Otherwise it's like comparing apples to oranges.

One would assume most people know the concept of a gear system, being familiar with driving a car. To me that's the obvious approach to something like this, while a solution in software is not. This is why I suggested it. As he didn't mention an application, the OP will have to decide if the particulars of his system merit one approach or another.

-- Gordon

I really don't think that's a good example. Inkjets and scanners only have to maintain a constant speed across the imaging area, and the resolution (in direction of travel) comes from how fast they shoot ink or sample the CCD. They are not homing the imaging head to each pixel location on the page at 1200 dpi. A microstepping driver merely makes it easier to keep the speed smooth, and not have annoying ripples in the image where stepper resonance appeared.

The constant speed you refer to still has a minimum step angle resolution, which directly gives the product its higher dpi functionality. They go hand-in-hand.

The OP did use the term "resolution" and not accuracy, and it's not difficult or expensive to achieve 0.1 degree resolution with a standard stepper and a microstepping drive. Highland, AllMotion, AMS, and several others sell programmable step drives that support 1/8 to 1/256 microsteps, some with encoder feedback to improve accuracy. These are fairly commonplace in factory automation applications where certain resolutions are needed yet without sacrificing rehoming speeds.

If the OP really does need *accuracy* to 0.1 degrees, and doesn't care about the overall speed of the system, then I agree certain geardown approaches may be preferred (i.e., for an astrodrive for a telescope). In any case, the OP now has several suggestions to pick through.

-- Gordon

Ok, I've seen a few of your suggestions, but there are many problems, I think.

First, I cannot buy a microstepping driver, someone said $150-$200, I don't have the money, I'm way past my limit, I had to buy other stuff.

Someone commented about 0.1 value being "0.1 degree resolution" or "accuracy to 0.1 degree". I actually need to position a laser module (a small one, looks like an R6 batt) accurately, so this means at least that accurately.

Anyway, I can't really see microstepping doing a fine job at doing this, because of reasons others already mentioned, and also because of stepper motor quality. I need an advised opinion on this, but I've measured the stepper motor coils, and 3 of them have 80ohms, one has

With the information you have given us so far, I would suggest gearing down your stepper motor using either gears or pulleys. At some point in time the friction, backlash, and slop in your system will overcome your ability to accurately position the laser. Whether or not you can get it down to .1 degree accuracy is going to be more of a testiment to your mechanical construction abilities.

If you give us a little bit more information about your application, we might be able to give you better suggestions.

-Wayne

Cosm> Ok, I've seen a few of your suggestions, but there are many problems, I > think.