Low-cost linear scanner

[WalterMo]

This should be a beta version of my first linear scanner. It's really a low-cost device and nearly all components were got from a home-improvement market.
The reason to build it was that I wanted to have the possibility to remotely could change the intersection angle from plus to minus by mounting a small servo at the slide. Also it could be possible, if the scanner is controlled by a microprocessor, to dynamically adapt the intersection angle during the scan.

The main part of the scanner is a ball bearing telescopic slide normally used for drawers for their easy opening. Its basic length is 31cm. Removing also a plastic stopper at the other side of the rail I could get a travel of 42cm. The price for a pair was 7€.
The drive was made by a 1.8° stepper motor in 1/8 step width mode. Using a driving wheel at the motor shaft with a diameter of 26mm the vertical laser movement was 0.051mm per step. This resolution can simply increased by using a smaller wheel. To avoid a slippage at the driving wheel the string was wounded 2 1/2 times around it.

So far, so good. But there is a fundamental problem: The plasic cage which is fixing the balls doesn't return to its initial position. That means, by its own weight it is moving from scan to scan more and more down and the travel is reduced. Then it must be pushed back by hand. Therefore I am searching for another kind of low-cost translation gage. Do you have an idea?

Walter

[WalterMo]

To prove that the linear scanner is really fine working I have made a scan of a 3-D picture made of sand of different colours and glued onto a wooden plate. I have got it as a present from a guest scintist from Algiers some years ago.
The size was 30cm x 20cm and the maximal elevation (at the Tuareg's hand) about 11mm.

[Khalid Khattak]

Walter a very ingenius design.. I am really impressed by the work you posting.. Your linear scanner reminds me that you are not rotating the laser but giving translation motion to whole laser support rig.. You rotate laser only to keep it true for linear motion..

What motor you are using and what controller you using to controll that motor?

Great work and good aspiration. Thanks

[WalterMo]

The controller was the same as presented here:
viewtopic.php?f=6&t=1124&start=0

The motor driver board came from:
http://cgi.ebay.de/3-St-Schrittmotor-St ... 3ca4bd37c8

and the Shinano motor STH-56D111 came from:
http://www.pollin.de/shop/p/OTk0OTg4/Mo ... toren.html

[Kirch]

Hi Walter,
If I understand what you are trying to do I would suggest that you
try a better drawer slide-
I make alot of cabinets for people and what you have there is on the low end of quality. The parts don't really glide as smoothly as they could-
A company called Accurde also make slides similar to what you have that have a self closing action. A spring that pulls them closed shut. Don't know how it would work vertically , if there is enough "oomph".

Blum makes some well engineered slides.
I'd recommend them but I am not familiar with a slide similar to what you have pictured here. I use their slides all the time but am only using a system that works horizontally.
They have a prety good online presence and you can get stl. files from them to get an idea of how they go together. Same with accuride for that matter.



Best,
Karl

[Khalid Khattak]

Hi Walter,
Thanks for showing.. I am using SLA7062 based controller cards with a breakoutboard to control my homemade CNC via Mach3 software.. Controlling my motors via Mach3 is best for CNC purposes but Mach3 consume all resources to run CNC i.e. if you are running any other program in the background that will interfere the Mach3 and the motor will loose steps..Offcourse DAVID also consumes windows resources that the reason i do not want to try both on the same computer.. Else Mach3 has KERNEL speed of more than 35000 and its enough.. I can use my controller upto 1/16 and that will create a good difference in scanning.. BUT i don't want to use Two computer for this purpose..

CAn you kindly tell me do you able to repetion scan with your setup?.. Do not your software and controller consumes resources when David is scanning?..

I thought you have made your own controller but you have sent me the Link of another controller card? Are you not using H-bridge to control your stepper motor?

Thanks

[RAYA]

Hi Walter

You are a multiporpuse man with multiporpuse hands.

It is not clear for me why you imegrate from planless scanning to a mix of linear/rotation system which can not use for planless scanning .

Your design is not clear fully with one image only ,I didn`t catch you full exactly.

Ray

[Khalid Khattak]

RAY..He can do planless scanning in this set-up too.. sometime we use larger calibration panel so we have to change the laser position to get high intersection angle..In that case he can remotly do make the laser high..and you see he has laser mounted with gearbox and motor, in planless case he will use the laser to rotate..and the painting he done seems to me his planless scan..

Regatrds

[RAYA]

Hi

I don`t think Walter wants to use rotation motion ,I think he wants to remotly componsate low intersection when cam/laser distance decrease in linear motion scanning.

With linear/rotation system it is very clear that you can have planless scanning if using one of them only.

Ray

[WalterMo]

Hi Karl,
I came to that low cost slides a few days ago when I was looking for a horizontally shifting platform for my photo camera. Greg showed us a software for easily making 3-D images:
viewtopic.php?p=9084#p9084
First I purposed to present my linear scanner by a 3-D photo but I think not all of us have stereo spectacles at hand.

And I was really astonished how precise and smooth-running this slide was. Therefore I came to the idea to use them for a linear scanner. I think the problem is that I used it vertically. The cage with the balls is free and not connected (only by the balls) to the rails. Normally it should have half the speed as the two rails. But as I said in my first post above the cage has an own weight working downwards. During first horizontally made tests I didn't noticed this behaviour.
I know that noble types of slides which close the drawer the last centimeters automatically. They are working at another system, not with a lot of balls but with two wheels at each side. And they can only be used horizontally.

Walter

[WalterMo]

Hi Ray and Khalid Khattak,
As Ray just mentioned: „A multipurpose man“. I try to be it and therefore I don't want to be fixed only to planeless scanning. Every method has its advantages and disadvantages. Let's pick out the best of all (which is often the easiest).
This linear scanner can only be used for planeless scanning if there isn't any slippage between cord and driving wheel. Better would be to use a drive belt or a threaded spindle. But both aren't of low cost.
My controller isn't equipped with a microprocessor but with an up/down counter. Therefore it's also suitable for planeless scanning.

The now presented linear scanner wasn't primarily designated for planeless scanning. Only, when the object is small, it should give the possibility to remotely changing from a positive intersection angle (laser above the camera) to a negative one (below the camera). And who knows, using a microprocessor like the Arduino with a PWM output, it should be possible to adapt the intersection angle during the travel way. That means to let it constant by controlling the attached servo with the laser.

Walter

[RAYA]

Hi Walter

I had in mind before to use used and cheap long vernier (measurment device) for linear motion with using motorized screw to move it.

It has good slide accuracy but not find in new tool market.

Ray

[WalterMo]

Now I have improved my linear scanner.
It's also low-cost and all components are coming from the home-improvement market.
There is no limit now of the travel. The whole length of the 2m long aluminium rail can be used for scanning. That means it can be used as a full-sized scanner for persons.

The sleigh consists of an aluminium base plate with four wheels which normally will be used for ropes. They are made of polyamide and are smooth-running. The rail on which they are moving, is a 40mm wide and 6mm thick anodised aluminium profile. It is mounted with a small gap onto a 25mm x 25mm aluminium carrier. This space between the two aluminium parts is necessary for the returning cord.

Inside the nave of the wheels are brass sleeves to enable a precise and easy rotation of the wheels. These sleeves are clamped by the screws. The holes in the base plate are a bit bigger than the diameter of the screws to enable a fine adjustment for a perfect run.

Walter

Edit: Because these kind of pulleys are normally fabricated by injection moulding take care of burr on the running surface. You can carefully remove it with a fine round file.

[Khalid Khattak]

Very nice walter:)..thanks for showing us...Kindly, tell me what is the black thing on which you have attached the laser?

[jantje]

Khalid
As it is connected with 4 wires I assume it is a stepper with gear.
Best regards
Jantje