Questions about linear rail drive gear

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lothman
Posts: 958
Joined: Sat Feb 14, 2009 7:00 am
Location: Stuttgart/Germany

Re: Questions about linear rail drive gear

Post by lothman »

chris_ma wrote:
Thu Sep 16, 2021 5:38 am
the full range of distance adjustment I need is about 50cm, so a KR26 unfortunately wont be long enough, and the KR30H and KR33 have 6mm or 10mm ball screws, what's why i'm wondering if step size could be reduced with gears or belts (I aim for about 10um step size)
on a spindle with 6mm pitch you need 600 steps per revolution for 10µm stepsize, this should be easy by a driver which provides microsteps and a 400 steps/revolution stepper motor. On the other hand 10µm stepsize limits you to 5x magnification. But at 1/8 microsteps you will get 8x400=3200 steps per revolution, what provides a stepszize of 1,87µm with a 6mm pitch spindle - this should be sufficient for a 20x NA0,4 lens.

elf
Posts: 1416
Joined: Sun Nov 18, 2007 12:10 pm

Re: Questions about linear rail drive gear

Post by elf »

mjkzz wrote:
Thu Sep 16, 2021 2:54 am
elf wrote:
Wed Sep 15, 2021 11:02 pm
I can see why that would happen :shock: Fix is pretty simple, just add a mechanical brake which is activated whenever the stepper is disabled. Wire it on the Enable pin the same as you would an NC limit switch.
Sure, there are motors specifically for this kind of situation, I think they are called self-braking or self-locking (I do not know their English name), these motors have brake mechanism around their shaft. But that is going to increase cost and redesign of controller.

The rail is superb in terms of performance, smooth, backlash free (not noticeable), wobble free (even under 10x), and I can get meter long ones . . . and best of all, most of it are off the shelf from companies like ratrig in EU, OpenBuilds in the US.
Having the brake built into the motor would be a more expensive option. Investigate using a small solenoid. If it pressed against a plate with a shape matching the belt, it wouldn't need a lot of force.
Having the system crash down like it currently is could be very expensive if the lens is damaged.

mjkzz
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Re: Questions about linear rail drive gear

Post by mjkzz »

I like DIY, but for a braking system like this, I prefer off the shelf solution because I can NEVER get it to work the way I want, Another solution to this is just NOT using it vertically. :D

Hopefully this information is useful for @skarabaeus and those interested.

ray_parkhurst
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Re: Questions about linear rail drive gear

Post by ray_parkhurst »

One thing to consider is that smaller pitch rail screws will give more resistance to unwanted movement. I have an XY stage with 6mm pitch, and it is relatively easy to make the rail move with pressure on the carriage. My KR2602 rails are more difficult, but still possible. My KR2001 rails are quite difficult to move, and take significant force to overcome the static friction in the system. Coupling a motor to this gives more resistance to movement, as the motor mimics additional static friction. So if you want to avoid things like counterweights and brakes, I'd recommend going with a 1mm pitch rail if possible. Of course the best thing is to simply assemble the rail and motor, and measure the amount of force against the carriage required to make it move. This is your absolute maximum weight limit for the vertical system.

lothman
Posts: 958
Joined: Sat Feb 14, 2009 7:00 am
Location: Stuttgart/Germany

Re: Questions about linear rail drive gear

Post by lothman »

mjkzz wrote:
Wed Sep 15, 2021 10:25 pm
OK, here is a video (part of another) on my personal account, showing how dangerous it is with VERTICAL belt driven setup. Though the motor and driver are still powered after powering off the Raspberry Pi, the idle power was set to 0.15A (I think) which is not enough and when RPi is powered off, it sets the drivers to idle state and booom, it crashes down fast. Of course, one can set idle power to be much higher, but that can be more problematic than beneficial (motor over heat when idling), etc. Plus, when there is a power outage, it won't help.

https://youtu.be/fD8NirPtYGI
Peter,
PLEASE make this lovely stand alone controller available?
controller.jpg

Adalbert
Posts: 2427
Joined: Mon Nov 30, 2015 1:09 pm

Re: Questions about linear rail drive gear

Post by Adalbert »

Hello Skarabaeus,
Does the use of planetary gears make sense
I would say yes, and I use one 100:1 in my rail for the very high NA.
viewtopic.php?p=186841#p186841
Best, ADi

skarabaeus
Posts: 10
Joined: Fri May 15, 2020 5:54 am
Location: Austria

Re: Questions about linear rail drive gear

Post by skarabaeus »

Hello friend,
Many thanks to all of you, I have learned a lot, but what the philosopher's stone really is (best solution) is still unclear to me :shock: . So that I can really sleep peacefully, I will probably have to test all versions of belts, gears and direct drives. When I have found out more details, I will report on my results

best regards gerold

chris_ma
Posts: 570
Joined: Fri Mar 22, 2019 2:23 pm
Location: Germany

Re: Questions about linear rail drive gear

Post by chris_ma »

I would say for low magnification pretty much every approach works, for medium mag as well but you'll want quality components and careful assembly, and for high mag the microscope focus block is probably your best bet.
chris

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