# Ideas for precisely moving a small object in 2 dimensions?

We would like to precisely control the position of a small object in a X-Y plane. The object we are moving contains a LED diode and some optics. The restrictions are:

• The total area is 9mm x 6mm
• We'd like to position the object within ±0.1 mm within this area.
• We will move stepwise (Move 0.1 mm, wait there a while, move another 0.1mm...)
• Expensive components are OK :)
• However, we have very limited size - the smaller the solution, the better.
• The object we are moving is very light (only a few grams) and can be altered as needed.

Our ideas so far:

1) Building a miniature X-Y table. We're thinking this could be designed to satisfy the positioning requirements, but the total solution (including stepper motors etc) would probably be larger than we were hoping for.

2) Using electromagnets. Given that our object is very light, we might be able to control its position using reasonably sized electromagnets.

Can you think of any other way of attacking this problem?

The question is similar to this question, which assumes a much larger scale (30x30 cm).

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To be clear, you need automatic positioning, right? Otherwise small manual x-y tables are not hard to come by. – HL-SDK Jan 13 '14 at 14:59
What kind of speed do you need on the movement? – Dave Tweed Jan 13 '14 at 15:09
Yes, automatic positioning, not manual. Also, the movement will be stepwise: We'll move 0.1mm, wait there, move another 0.1mm, etc. No particular speed requirements. I'll update the question to reflect this - thank you! – user2078515 Jan 13 '14 at 15:26
Consider combining a "Pantograph" & a larger "X-Y table". The resolution of the X-Y table will be proportionately reduced. If attention is given to keeping bearings tight, this may solve your design requirements. Jewelers engrave plaques miniaturizing them, as do map makers. – Optionparty Jan 13 '14 at 16:48

For a really small X-Y table, a pair of the tiny stepper motors used for camera lens focusing would serve well:

These steppers have a 6 mm slide span, and allow better than 0.01mm precision:

These slightly larger steppers have an 18 mm slide span, and precision of around 0.025 mm.

In each case, microstepping allows the precision to be improved by a factor of 8 to 32, depending on the specific driver and drive mode chosen.

If the 22 mm overall length of the larger stepper is a concern, with a little research, a 9 or 10 mm slide span stepper, in the same 5 to 7 mm motor size, can surely be found.

Using a StepStick microstepping driver, I have been able to get practically vibration-free operation from the smaller stepper mentioned above. Results should be similar for other such lens focusing steppers.

This will permit an X-Y table to be fabricated with a footprint comparable to the movement dimensions mentioned in the question, i.e. around 15 mm x 22 mm including motors, with the motors placed under the table.

As a matter of fact, an actual X-Y table would not be required, since the object to be moved is small: A single-axis sliding base served by the first stepper would work, with the device being moved along the perpendicular axis directly by the slider tab of the second stepper.

Bonus: If microstepping is not required, these steppers work even when driven directly off an atTINY45 microcontroller's GPIO pins, since their required operating current is in the 3 to 8 mA range. One just needs to add flyback diodes to protect the pins.

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Thank you! You were also right in that there are motors to be found with ~6 mm motor size and ~10 mm span length, for instance these ones – user2078515 Jan 14 '14 at 9:04
@user2078515 Well, those are marked as used, I hope you noticed that. Should still be fine for trying out. – Anindo Ghosh Jan 14 '14 at 9:48

As an alternative to stepper motors, piezoelectric materials are used for extremely high precision movements, like aligning lasers. The operating principle is rather simple: piezoelectric materials change dimensions in the presence of an electric field. An advantage is that the thing to be moved can be directly attached to the piezoelectric actuator, thus there are no moving parts like gears to have play or backlash in them.

There are also linear piezoelectric stepper motors which "walk" on a shaft. The operating principle is best described by video. You can find manufacturers by searching for "piezoelectric stepper".

However, I suspect when you try to source the parts, you will find miniature magnetic steppers to be more economical while still sufficiently precise. Piezoelectric actuators are pretty specialty stuff.

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Phil, Could you please suggest any piezo XY Stage manufacturers other than Physik Instrumente? Their XY stages seem to max out at 1.8 x 1.8 mm. – Anindo Ghosh Jan 13 '14 at 21:32
@AnindoGhosh I don't know of any off-hand. I've never purchased the things, just considered them. I think the piezo option of more academic interest than anything for this application. – Phil Frost Jan 14 '14 at 22:38