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I'm looking for a stepper motor with an integrated high-resolution encoder for some force-feedback experimentation. Maybe something like this: http://www.opticalencoder.com/pdf/CM-300.pdf

It need not be a large motor, and I was hoping to get the thing for $50 or less.

Can anyone point me to somewhere I can buy small quantities of such a thing?

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What do you want a stepper with encoder in it for? The whole point of a stepper is you don't need an encoder - you know how far it turns with each pulse (the ones I use are 7.5° per step). Sensors (typically optical) are used to detect absolute limits so the system knows when the device (whatever is being driven by the stepper) is in a known position. All other positions are X number of steps relative to that known position. –  Majenko - not Google Jul 17 '11 at 14:57
    
But if the motor is being turned by an external force, say my fingers, there's no way to tell its position, correct? –  laslowh Jul 17 '11 at 15:03
    
That is why most things which use steppers move to a known position first before they do anything else (for example, watch how your printer powers up - you'll see it moves the head until it reaches a predefined position first) –  Majenko - not Google Jul 17 '11 at 15:05
    
@Matt - Seems my answer is a bit like your comment. Sorry, didn't mean to steal it; must have been writing while you posted. Why didn't make it an answer anyway? –  stevenvh Jul 17 '11 at 15:10
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There seems to be a "lost in translation issue here". @laslowh seems to want to specifically want to move the stepper with external force AND to subsequently know its position. Applications could include use as a rotary encoder - a PM stepper will output a bipolar waveform when turned by hand and output level is high even at low rates (say step / second). Having eg your volume control "knob" zero and return to its position occasionally in order to determine where it was would be novel but disconcerting. –  Russell McMahon Jul 17 '11 at 16:19

5 Answers 5

I've never noticed a four-phase stepper, whether unipolar or bipolar, which included a rotary encoder. Many brushless motors, however, combine what's effectively a 3/6-phase stepper with a 3/6-phase rotary encoder. Perhaps that's what you need.

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Links Steven style. I like them raw :-)

Festo Stepper motors with integral encoder

Oriental motor USA more of same

Parker Sy56 Still more of same


ADDED July 18th 2011:

In view of the almost universal comments re "not available", "doesn't exist" etc, I've referenced below a real world example. Adding a position encoder is essentially trivial - largely a mechanical issue. Some reasons as to why you may want to are explained below by a quote from Festo. Or, it may be because you want to turn the shaft by hand ;-).

As an alternative to Feto's fine but no doubt somewhat costly offering it would be easy enough [tm] to add an encoder disk to an existing stepper if required.

Here's an example of a real world product from Festo. There will be lower cost Asian emulators.

Festo EMM-ST closed loop stepper motors

They say:

  • True servo performance based on stepper technology, without the traditional issues of resonance, heating, and loss of step, inherent in conventional stepper systems. This new stepper motor series offers long service life and reliable performance. The two phase hybrid stepper motor offers high torque, with options for an integrated brake and incremental encoder feedback. External gearboxes are available for all motor sizes together with adapter kits for all Festo electromechanical actuators.

And here

  • A key advantage of using closed loop feedback is that the stepper motor is always operating at maximum efficiency and cannot suffer step loss; if the motor is overloaded, the position controller automatically compensates for following error and maintains position tracking. This means that unlike an open loop stepper system, it is not necessary to oversize the motor to handle an application's peak torque demands, allowing use of smaller, less expensive units. Other operational benefits include better smoothness, lower acoustic noise levels, and absence of mechanical resonance. Although many stepper drives offer the options of closed loop facilities, these generally only offer alarm functionality in case of step error. The CMMS-ST offers true servo functionality with full control of current, speed and position.

Catalog Stepper motors EMMS-ST catalog

__ End of July 18th add on __


An electronic pulse counting position determiner could be built - with due care this would seldom if ever get lost. A comparator with very very light hysteresis will toggle when applied across a PM stepper winding as the coil voltage passes through zero. Even at VERY slow speeds (< 1 step/second) the signal will be well above what a comparator requires.

An up down counter or microcontroller can determine position by tracking transitions. Two windings (probably) required to get quadrature signal for direction.

Detent action caused by motor saliency means that rotor tends to jump in position when lightly coupled to drive (such as fingers) enhancing low speed output. So much so that depending on stepper used signal may be enough to drive logic level circuitry directly.

Start up position detection can be managed by stepping to an endpoint, as already suggested, or by having syynchronisation contacts or optical detectors.

Depending on application the need for absolute position detection may be eliminated by making the stepper the decoder but storing position information electronically. eg a volume control can show the volume level on a bar graph. The stepper drives this but its absolute position is of no relevance. In other systems the absolute position matters 0 eg use as a postion encoder for a "vernier caliper"* or "dial gauge"* or machine table etc. Traditionally synchronisation is achieved with a reset button.

*Interestingly - no vernier on the vernier-caliper and no dial on the dial-gauge due to electronics invasion.

Many digital "vernier" caliper users will have absolutely no idea what a "vernier" is or that the concept even exists.

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I read "can" and "could", but I still think the product OP wants doesn't exist, for the reasons Russell and I give. Rotating a stepper motor controlled shaft by hand is not normal use. You'll have to resync after you do that. –  stevenvh Jul 17 '11 at 16:38
    
See above for example of real world product. –  Russell McMahon Jul 18 '11 at 5:14
    
Well, that seems to prove me wrong :-(. If it uses an incremental encoder it still will have to synchronize upon power-up. And it just radiates "expensive!". –  stevenvh Jul 18 '11 at 5:22
    
@RusselMcMahon, when you update it works much better to just put everything together instead of spreading it out over a number of updates. Write the answer for those that find this question later so that they have one contiguous and detailed answer. Besides that, looks like an answer you put time into. –  Kortuk Jul 18 '11 at 12:46

I've never seen a stepper with an encoder integrated. Normally you won't need one either, since the stepping should tell you all about the rotation. In any case incremental encoders aren't useful. For absolute position there's often a single index point on the shaft, either using an optical sensor (like reflective), or magnetic (Hall effect sensor). To synchronize the motor rotates until the index point is found, and from then on it's the (micro)steps which tell you where you are. If you don't run your motor to fast and don't overload it the pulses should be a reliable measure, and you shouldn't have missing pulses.

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Thanks for the answer. Please see comments on question above. –  laslowh Jul 17 '11 at 15:05

I don't believe such a device is commonly available. In general the position of a stepper motor is calculated by counting the number of steps the stepper has performed.

Stepper motors come with a specified number of degrees per step - the ones I am working with at the moment are 7.5°/Step, which makes for a total of 48 steps for one complete turn.

In order to determine the exact position of the item being moved by the stepper it is usually moved to a known position as the first operation. For instance, the print head of a printer will be moved fully to one end of its movement until it breaks an infra-red beam of a photointerruptor (for example). From then on the position is counted relative to that location.

If there is a chance that the stepper motor will be moved by some external source between operations then it should be re-calibrated before the second operation by moving it to the known position again.

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JVL has a wide range of intergrated stepper motors. You can choose between single turn encoder or multiturn encoder (absolute encoder). Besides the encoder the motors also has intergrated controller and a mini PLC with I/Os. Stepper motors from JVL have up to 409.600 steps/rev. This is one of highest microstepping resolutions available. They are not cheap, but you get everything in one compact package and are often used in test environments since you can control everything. http://www.jvl.dk/List/308/Quick-Step-Integrated-Stepper-Motors/ It is also possible to turn off the motor but still turn it and read the encoder position.

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Downvoted as this appears to be advertising on a 3 year old post. –  David Feb 4 at 17:09

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