Mechanically Coupling a Stepper Motor to a Cylindrical Knob/Micrometer

Hi All,

I am completely new to everything Arduino, motor and, frankly, mechanical.

I'm trying to mechanically couple a NEMA 17 Stepper Motor (link here) to a cylindrical knob (a micrometer) of a translation stage (link here). The diameter of the shaft of the motor is 5mm, whilst the diameter of the cylindrical knob is roughly 2cm. The surface of the knob is quite rough, and the diameter of the knob isn't uniform along it's length (see picture of cylindrical knob here).

My initial idea is to add a shaft converter of around 2cm in diameter to the motor (something like this ; I know it's a 5mm to 8mm converter, but its diameter is 19mm, and I can't find a direct/cheap 5mm to 2cm converter) and then put a clamp across this and the knob. I've also considered adding gears to the ends of the motor shaft and knob. I wanted to see if more experienced members of the community knew if there is standard way to couple two objects like this, as I imagine this is quite a common occurrence in engineering, or know of a better way to do this that isn't ridiculously expensive (i.e. that isn't more than a few hundred dollars)

However, the difficult part is that when the knob is turned, it will MOVE OUT/IN (i.e in a direction parallel to its length). The maximum range of this movement during operation is roughly 1cm to 2cm, but even allowing movement for a few millimeters would be extremely helpful.

There are only 2 ways I can think of to accommodate this:

  1. Using a clamp/shaft converter that allows compression/extension along its length (perhaps some kind of spring mechanism), and keep the motor fixed in place.

  2. Use a rigid clamp/shaft converter, but allow the motor to move with the knob as it turns, so that the distance between the motor and the knob remains constant.

However, I'm struggling to find concrete ways to implement these solutions, and wondering if there is a better/standard way to achieve this.

IN SUMMARY

  1. How do you couple the shaft of a stepper motor to a cylindrical knob/micrometer?

  2. How do you allow for lateral compression/extension in such a system?

If there is a better place for me to put my post, I would be grateful if you could direct me towards it. I'm using an Arduino Uno/Easy Driver to drive the motor.

Thank you for your time.

If the micrometer drives an otherwise standard translation stage (the link doesn't work for me), it would be much simpler just to buy a stage without the micrometer attachment, i.e. a simple shaft intended for coupling directly to a stepping motor.

Otherwise, plan on paying $$ for a machinist to fabricate a custom solution.

Image from Original Post. See this Simple Image Posting Guide

...R

Can you mount the motor on the part that slides when the knob is turned so that the relationship between the motor and the knob remains constant when the system moves?

...R

Many years ago, one of my customers manufactured and sold a similar product, but the stepper motor was tiny, not like the monster you picture. You need to use one of the other stages offered by the company, the PT1B, which has a shaft that you can connect to. They also offer the motor drive and coupling for that stage. You will have to duplicate that coupling.

The advantage of a stepper motor driving a microscope stage is much finer movement can be made that is possible with a manual adjustment. I think the stepper motor followed the stage movement, just as the one in your link does.

Paul

You just need to clamp on a bit of rubber pipe to the micrometer knob and the coupler, gives damped and
compliant coupling without any modifications.

MarkT:
You just need to clamp on a bit of rubber pipe to the micrometer knob and the coupler, gives damped and
compliant coupling without any modifications.

MarkT:
You just need to clamp on a bit of rubber pipe to the micrometer knob and the coupler, gives damped and
compliant coupling without any modifications.

Yes, that would do the coupling, but not take care of moving the stepper along with the micrometer movement.

Paul

The max current also needs to be very carefully controlled to prevent it trying to torque the micrometer.
You could also employ some rubber/flexible tube in the coupling to help with that.
Or fit a slip ring system (mini clutch)

Thought I posted this reply 3 days ago seems it was sat in my drafts folder.
Darned forum software GRR

Hmm, I missed the movement in and out issue with my earlier answer, sorry about that...

Hmm, its a challenge. You can get couplings with dog-teeth that would be suitable, but normally
only allow for a few mm of in-out movement - this is likely to be a custom job, based on something
like this:

You'd make a longer version and glue the rubber piece at the end of one set of jaws so its always
in contact with the other. And then use the rubber pipe trick.

There are two hex-head set screws in the top left of the image in Reply #2. Why not make a bracket that fits on those screws and mount the motor on that so it moves with the micrometer?

...R

Robin2:
There are two hex-head set screws in the top left of the image in Reply #2. Why not make a bracket that fits on those screws and mount the motor on that so it moves with the micrometer?

...R

Those don't move, Robin. They are part of the stage that is fixed. The top of the picture shows where the micrometer shaft goes to connect to the moving part of the stage.

For information, the moving part of the micrometer is a screw that is turned by the knob. A 1 inch micrometer will move the knob.handle 1 inch as the screw turns. That is where the motor connection problem occurs.

Paul

Paul_KD7HB:
Those don't move, Robin.

Does that mean it is only the black rectangle immediately next to the micrometer screw that moves with the screw?

Heath-Robinson or Rube Goldberg would epoxy a motor mount to that.

...R

Robin2:
Does that mean it is only the black rectangle immediately next to the micrometer screw that moves with the screw?

Heath-Robinson or Rube Goldberg would epoxy a motor mount to that.

...R

Nope, that fixes the micrometer frame to the fixed microscope stage. I think I have some old pieces to a depth micrometer and will take some pictures that show what is inside the black rectangle.

Paul

If the OP could post a photo of the micrometer at its outer position it would be a big help.

And maybe a picture that shows more of the device

...R

Finally found the micrometer adjusters. Right where I put them! The shinny part just to the right of the black knurled part is the mounting area. That is what the black cube in the OP's picture is holding and locating.

micrometer adjuster.JPG

The knurl is a locking ring. Everything to the right of the mounting ring turns with the micrometer knob.

Hope that helps and hope I can get the picture to display.

Paul

micrometer adjuster.JPG

If the little knob is a tension clutch knob, then you might connect to it using some little round Velcro pieces attached to the knob and the stepper motor with a drop of hot glue (generally easy to remove if needed). If the stepper motor is small it can just slide when the micrometer shaft goes in and out.

Something like this would take care of almost all the issues.

it would give you direct drive to the clutch of the micrometer no matter where it is positioned.

A little better selection here

ballscrewbob:
Something like this would take care of almost all the issues.

it would give you direct drive to the clutch of the micrometer no matter where it is positioned.

A little better selection here

Only usable if there is no angle involved. Those are not constant velocity u-joints, when at an angle, they will alternate between slow and fast as they turn. While a full turn of the stepper motor will result in a full turn of the micrometer, any intermediate stepper rotation will result in either more or less movement of the micrometer shaft.

Paul

Paul_KD7HB:
The knurl is a locking ring. Everything to the right of the mounting ring turns with the micrometer knob.

First, many thanks.

Second, why isn't the OP taking the trouble do tell us this stuff - he's the guy with the problem!

Third, do you mean that the black part (and the short silver part to its right) is stationary and everything to left and right of the black part moves in and out of it when the big knurled part (at the left) is turned.

I would really like to see a picture of the OP's machine that better illustrates how it works.

I suggest we take a holiday until he returns :slight_smile:

...R

Paul_KD7HB:
Only usable if there is no angle involved. Those are not constant velocity u-joints, when at an angle, they will alternate between slow and fast as they turn. While a full turn of the stepper motor will result in a full turn of the micrometer, any intermediate stepper rotation will result in either more or less movement of the micrometer shaft.

Paul

They are made to operate over different angles. The second link has a little more in terms of pictures.
Being as the issue is driving the micrometer from the clutch on the end of it, it would drive that until the clutch engages and thus have reached the measurement point. There are distinct clicks when the clutch on these micrometers engage and that load can even be varied by adjusting the end screw on the clutch.

As it is a "fixture" micrometer either inline or a slight angle between the drive shaft and the stepper motor is acceptable. Most micrometer movements are either 1" or 25mm so you only need one of the smaller driver shafts to attain full travel as most seem to have enough travel to accomodate that.

Engineer / millwright this end.