June 20, 2014
A SCARA robot is primarily used for assembly and can be programmed to handle precise installation work repetitively. SCARA stands for Selective Compliant Assembly Robot Arm or Selective Compliant Articulated Robot Arm. However robotic arms for manufacturing or research often are priced between $10k to $40k.
British inventor Sean (Clanzer) has been hard at work for over a year now designing his own MK3 Prototype Scara Arm 3D Printer. It is not fully functional yet, but he is at the point where it is time to get the resolution and backlash out of the system.
With the MK1 he used 50:1 planetary gearboxes, and with the MK2 he built an arm with a combination of belts and pulleys to build up the ratio, But again backlash was appearing. So he ended up using harmonic gear drives for the MK3 prototype.
The Harmonic gear drives are expensive and commonly used on commercial robots, but Sean and his team have now sourced a company that can produce them at a reasonable price if they order quantities. This will allow Sean to get the price of a Scara Arm 3D Printer within range that is affordable to the hobbyist and small businesses market.
In the pictures below you can see the MK3 prototype that has some off the shelf Harmonic gear drives that are 30:1 and when combined with micro stepping and 0.9degree motors should give a 0.013mm resolution, according to Sean. "But the custom made Harmonic gear drive examples we have ordered and are on the way to us, are 50:1 which will take us up to 0.007mm resolution." Sean said.
"This is more than enough resolution for most tasks from Pick & Place to 3D Printing."
The next generation MK4 Scara arm will incorporate these new drives and also the arms will be slimmed down a bit compared to the MK3, Sean told 3der.org.
For 3D Printing it has a 250mm x 250mm heated bed platform and 200mm height, making it a reasonable printing area. For other tasks the arms extend out to 400mm and can be rotated a full 360 degree around the base Axis.
"The MK3 is now accurate and stable enough to allow us to continue with the software/firmware development and complicated calculations that are needed to make the machine run smooth." Sean explained.
"We are investigating two avenues at the moment.
"First one is to go with an Open Source controller board such as the Smoothie Board and allow existing 3D control applications such as Pronterface and Repetier-Host to be used with the machine. But we still have development time to invest into this solution and all code will become Open Source.
"Or we use our own already proved motion controllers and focus on a dedicated application.
"Both of these options are being explored at the moment, but we are hoping to have a production model available within the next 3 months." Sean said.
The pictures show the MK3 Scara Arm fitted with extruder and heated bed, but these can easily be removed and swapped out for other modular attachments, such as syringe and gripper attachments.
This is not the first 3D printer Sean has developed. In 2012 he built a CNCDudez RouterStrap 3D printer based on one of his CNC frame and used it to ice a cake.
Posted in 3D Printers
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Sam is a critic and has a point, but experimental designs lead to further innovation. The articulated arm is extremely open, and has the potential to be very elegant. It opens up many possibilities.
Andreas wrote at 6/23/2014 10:05:39 AM:
Looks quite massive right now, and accelerating/decelerating mass is a problem with most robots. I think if he optimizes the design to keep stability while minimizing moving masses this thing could get very quick, and that is very interesting for high resolution printing with low layer thickness. All it needs after that is a dual-head extruder for printing support material or multiple colors and he could have a winner.
Wild Bob wrote at 6/21/2014 8:37:00 PM:
But if total backlash is less than half the printer resolution backlash is no longer an issue.
Nick wrote at 6/21/2014 5:24:39 PM:
RepRap Morgan is a SCARA.
Sam wrote at 6/21/2014 3:40:27 AM:
No matter how you slice it, an articulated arm with serial joints will always have more backlash than a cartesian system that is balanced. I don't know why people are so horned up on trying to do articulateds for printing.
clovis ray wrote at 6/20/2014 5:58:14 PM:
Hi, I really like Sean's scara arm printer, very ingenious , and looks like it would have many uses, in my case, I would need to print out custom parts, for new designs of devices, not yet developed,
Bri wrote at 6/20/2014 2:05:17 PM:
Has someone released a SCARA already?
Sum-Ting Wong wrote at 6/20/2014 11:14:42 AM:
That must be bloody fast!
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