# stepper question, precision

Posted by mfzandstra
 stepper question, precision March 22, 2013 04:44AM Registered: 11 years ago Posts: 9
Hi,

I am currently exploring some things for perhaps doing an SLS printer. I'm unsure if I will be capable of designing something like that to the end, but it's the process that counts to me on this moment.

As a starting point, the laser probably is easier to control if it's static within the printer, pointing in a direction that is unrelated to the printing surface itself and beamed by mirrors unto the printing surface at an precisely calculated point. The last mirror(s) should be rotated to make the angle required.

If I calculate with an distance of 10 cm of the printing surface, the mirror must be moved quite precisely to step 0,1 mm to the left; the angle would be 0,057 degrees. Since I have a few spare 28YBT-48's laying around, I would like to use these. But I'm not totally sure about it's accuracy, since I normally never use steppers for these precise work. If you check the link, the stepper should do 5,625 degrees in one step, correct? And I can divide one step in 64 smaller steps? So that would be 0,0879 degrees per devision. The code I have is in 16 steps, and more like the one in this code example. Any ideas how to make those 1/64 steps? It would save me some work with gears.

Regards,

Michael
 Re: stepper question, precision March 22, 2013 06:17AM Registered: 13 years ago Posts: 7,616
Microstepping is part of the stepper driver, not of the code sending the Step signals. You have to find such a stepper driver providing such a high microstepping rate.

 Generation 7 Electronics Teacup Firmware RepRap DIY
 Re: stepper question, precision March 22, 2013 10:48AM Registered: 15 years ago Posts: 332
Microstepping isn't very accurate - you won't get an exactly linear angle change going from one full step to another through all the in-between steps. You'd probably be better off having a fixed angle mirror that you slide along an axis, or maybe using a galvanometer if the mirror is light enough.
 Re: stepper question, precision March 22, 2013 11:40AM Admin Registered: 16 years ago Posts: 13,870
... you can get 3-phase and 5-phase-steppers with 1000 full-steps per revolution, that are much more precise.

I have some drivers and motors from Precitec (Berger&Lahr), where 3-phase steppers are driven with 325Volts and have configurable fullsteps (200, 400, 500, 800 and 1000), optionally enhanced with 1/10 microstepping (then from 2000 to 10000 steps per rev) with up to 200kHz stepping clock -- what's better angular precision than most galvos can provide ...

Viktor
--------
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 Re: stepper question, precision March 22, 2013 01:46PM Registered: 11 years ago Posts: 9
Thanks for all the replies. I'm thinking about using the spare steppers that are laying around over here. I think the 28YBT-48's will be good enough for some testing and playing. With some gearing I should be able to move the mirrors precise enough, without using a lot of steps / microsteps. After reading some other documents, the more microsteps the controller has, the less accurate the movements become.

I've been looking at some steppers with more steps and though very promising, the price isn't worth it at this moment of time. Maybe if I have a working model with the cheap motors that will become an option.
 Re: stepper question, precision March 23, 2013 08:16AM Registered: 13 years ago Posts: 7,616
Computer hard disks have something similar to a galvanometer inside to move the read/write head. I'd be surprised if there wasn't some open source project out there on how to make them work outside a disk housing.

 Generation 7 Electronics Teacup Firmware RepRap DIY
 Re: stepper question, precision March 23, 2013 03:55PM Admin Registered: 16 years ago Posts: 13,870
... this are 'voice-coil actuators' - activation/moving and measuring is made by driving or induced currents in coils, placed in the gap between two strong magnet poles ...

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]
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