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Paint dispenser with DC motor and encoder

Posted by o_lampe 
Paint dispenser with DC motor and encoder
January 05, 2019 03:24AM
I want to design a peristaltic pump to dispense laquer. I picked a geared DC motor with encoder to do the job.




I think, my Duet-boards can drive it without H-bridge, but how do I config the two encoder lines in RRF for speed control? Even add another (analog or encoder ) input for fine tuning...

Thanks for reading

Edited 1 time(s). Last edit at 01/05/2019 03:33AM by o_lampe.
Re: Paint dispenser with DC motor and encoder
January 05, 2019 03:29AM
A general question about peristaltic pumps:
Are they able to build up any pressure?
I don't want to spray the paint, but have a oozeless tip in mind, where the opening is held close by a springloaded delrin ball.
The pressure has to lift up the ball.
Re: Paint dispenser with DC motor and encoder
January 05, 2019 03:44AM
Quote

Even add another (analog or encoder ) input for fine tuning...

Got it! The dispenser has to act like a extruder and by adjusting extruder ratio, I can tune it while it runs. The encoder-wheel of a simple 12864LCD will work too, I hope?

Edited 1 time(s). Last edit at 01/05/2019 03:45AM by o_lampe.
Re: Paint dispenser with DC motor and encoder
January 05, 2019 05:50AM
Peristaltic pumps manage a medium pressure. The limit is where back pressure causes the tube, typically silicone rubber, to bulge and jam the rollers. I think that a peristaltic pump should be fine for spraying and the most significant problem may be that the output is somewhat pulsitile.

I tried a number of the motors that you show for a toggle mechanism on a 3D printer but found that the minimum speed was a substantial fraction of the full speed: a 12V motor became very eratic to start even at 5V and speed control even when started was not good at less than rated voltage. I did try several motors of various reduction ratios but the motor part aways had the same problem. Lacking the funds to get a Maxon ironless motor to do this I built my own stepper motor to fit the same mountings - I will try to put the STL files on Thingiverse in the next few day if this option helps.



Mike
Re: Paint dispenser with DC motor and encoder
January 07, 2019 11:24AM
Thanks for sharing your experience with these motors. It's probably the stiction of the worm drive that causes this behaviour.
It's the same with fan motors running on PWM. You have to start them with 50-100% to make them spin, than you can go down to even 10%. But they wouldn't start at 10% at all.
Re: Paint dispenser with DC motor and encoder
January 07, 2019 11:27AM
Quote

the most significant problem may be that the output is somewhat pulsitile.

It would be cool to sync the pulsing with the XY speed to compensate that. In my case it would only be one axis I had to compensate.
Re: Paint dispenser with DC motor and encoder
January 07, 2019 11:43AM
Paint sprayers pull the paint they need with the vacuum created by the air discharge through the nozzle. Is there some reason you have to pump the paint?

You can buy cheapo peristaltic pumps from China for $10 or so. Some use silicone tubing, others use something called BPT. The BPT tubing lasts much longer than silicone (see pg 23)


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Paint dispenser with DC motor and encoder
January 09, 2019 03:34AM
The reason for not spraying the paint is: selective coating. I want to ooze the paint while the toolhead meanders across the selected area.
I think, that requires an encoder to sync with acceleration/deceleration moves
Re: Paint dispenser with DC motor and encoder
January 09, 2019 04:55AM
Quote
o_lampe
The reason for not spraying the paint is: selective coating. I want to ooze the paint while the toolhead meanders across the selected area.
I think, that requires an encoder to sync with acceleration/deceleration moves

I fail to see why a stepper wouldn't do it ?


"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
Re: Paint dispenser with DC motor and encoder
January 09, 2019 12:59PM
Peristaltic pumps don't provide continuous flow. You might need some other technology...


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
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