Quattro Parallel Concept - Tilting slider mounts for boolean 4th and 5th DOF control
Posted by mobile chernobyl
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Quattro Parallel Concept - Tilting slider mounts for boolean 4th and 5th DOF control March 21, 2014 04:58PM |
I also posted this on the Google group but thought it would be good to cover both forums...
I've been stalking this forum ever since I got my Cartesian printer late last year - my goal for that printer was simply to fool around and print a vitamin kit for a Delta.
I have to admit though - usually it's not the juice I'm after but rather the squeeze.
The concept of the delta was fascinating, I had never even heard of it until I saw the kickstarter campaign by Deltaprintr and realized they were in my current hometown, Brooklyn!
I've kind of wanted to develop a multi hot end delta as well, and through some more research found out about the Adept Quattro 4 armed parallel robot (4-RSS by the looks of it). I didn't really understand at the time just by looking at the design that the effector plate in a 4-RSS design cannot have more then 3DOF if it's a radially symmetrical design like it is.
The interest in extra X and Y tilt DOF stemmed from my observance in how the stratasys hot end features a solenoid to push it's support material hot end down into place, so it doesn't drag under normal printing. I know printers like the maker bot and plenty of other desktop designs out there have multiple print heads on the same plane, but I figured, go big or go home right?
I've searched around quite a lot to see if anyone was using this quattro design, fully aware that it's not the simplest way to build a parallel robot with 3 DOF (everyone seems to be most scared away by it's inverse kinematics!). I've seen versions which aren't exactly 3D printers in use, mostly of the 4-RSS design (i.e. pretty much exact copies of the adept Quattro), similar to the 3-RSS used in material transport delta PKM 'bots. I didn't really see any 4-PSS design like our 3-PSS style delta printer with a Prismatic joint vs the PKM industry standard Revolute joint.
So I set out, first off just playing around in Solidworks with some numbers of joint lengths I had calculated, trying to see what all the stigma was about. First I made a conventional delta bot using standard dimensions so I could play around with it in "3 space" and quickly added another upright! It works! haha - that was simple I thought.
Now what I really wanted was a way to "tilt" the hot end, so I could either have 2 or 4 hot ends, with only 1 hot end tip at a time on the "printing plane". There's surely a bunch of ways to do this - gimbal on the effector plate with X and Y actuators? nah - why add weight to the effector? wasn't that the point of going Delta in the first place? some sort or rotating cam deal? more weight... How about control each arm individually like a Stewart Platform PKM does? that means 8 servos/steppers to control! I guess I could just use a stewart PKM, but that's a lot of trouble to go through just to have a 4th and 5th DOF for X and Y tilt of the effector plate!
I started playing around with mounting the parallel arm spherical joints on the prismatic(slider) side on an additional revolute joint. That worked really well! With a 4-PSS style robot, adding an R makes it a 4-PRSS and now I have the ability to tilt the effector to take advantage of a multi-hot end with splayed tips. I chose 5 degrees off the central axis just to keep it simple!
-Just a note to add here, the revolute joints are not free-acting. This is why the design works. If they were you would have too many DOF for the input. Since this design only concerns tilting the head a given -/+ amount of degrees - it's basically a boolean option so I'll be using some method of actuation to trigger it - that is where I currently stand in the design process! Any input is greatly encouraged - I really want to make this into a real physical printing design!
So just thought I'd share my idea! Actuating the +/- action on the slider is something I'm still trying to think about. Electronic solenoid actuation with spring return, pneumatic cylinder actuation with spring return have been floating around my head, but these, if mounted ON the sleds add weight to the slides and therefor are not preferred. Another concept, albeit much more complicated, is to have a semi-syncronous bobbin and filament set running with the carriage drive setup. By incrementing or decrementing the semi-syncronous set of pulleys +/- 5 deg, the rotating ball mount assembly, which would be attached to this additional set, you would effectively perform the same thing as the carriage mounted actuators but instead you would be adding no weight to the carriage, and only minimal rotating weight to the pulley/bobbin setup. Incrementing/Decrementing could be accomplished either by a planetary gear/differential gear setup (complicated!!) such as that found in the lego kits. Another method is to have a sprague clutch style indexing ramp and spring. Under normal use the pulleys would be seperate, but if actuated by a linear actuator pushing on a thrust bearing you could "force" the pulleys together, and up a ramp, seperting them by about 5-10 degrees. This design might suffer from axial thrust issues when being driven in the opposite directly of the ramps, and accidentally start incrementing them though perhaps? All ideas haha...
The hot end is probably worth it's own subject, but that's a ways off and the splayed design just complicated the hell out of it. But I will say this - it's water cooled and should weigh 100 grams or less for 4 hot ends, and the working bits (surfaces immediately in contact with the filament extrusion) are all based on working designs. It's definitely going to take some testing but it's based on existing designs that deal with hot temperatures on the regular - but it's aim is to take advantage of 3d printing shapes that would normally be unmanufacturable. Ultimately the goal is to have the hot end assembly BE the effector plate (and the design would be adaptable for anyone's printer if your CAD savvy!)
This design works for the conventional 3-PSS style Delta printers as well! only you need to actuate 2 of the 3 in opposing fashion radially. (The 4 arm design works very simply by having the opposing 2 arms actuate the same way. it also only has 5DOF, a 3 arm delta would have 6 DOF and require 6 inputs - 3 stepper/servo and 3 actuators)
This design for a 3-PSS like the common delta printer is probably not a surprise though as there is a large amount of research on 6DOF PKM out there!
Edited 1 time(s). Last edit at 03/21/2014 05:00PM by mobile chernobyl.
I've been stalking this forum ever since I got my Cartesian printer late last year - my goal for that printer was simply to fool around and print a vitamin kit for a Delta.
I have to admit though - usually it's not the juice I'm after but rather the squeeze.
The concept of the delta was fascinating, I had never even heard of it until I saw the kickstarter campaign by Deltaprintr and realized they were in my current hometown, Brooklyn!
I've kind of wanted to develop a multi hot end delta as well, and through some more research found out about the Adept Quattro 4 armed parallel robot (4-RSS by the looks of it). I didn't really understand at the time just by looking at the design that the effector plate in a 4-RSS design cannot have more then 3DOF if it's a radially symmetrical design like it is.
The interest in extra X and Y tilt DOF stemmed from my observance in how the stratasys hot end features a solenoid to push it's support material hot end down into place, so it doesn't drag under normal printing. I know printers like the maker bot and plenty of other desktop designs out there have multiple print heads on the same plane, but I figured, go big or go home right?
I've searched around quite a lot to see if anyone was using this quattro design, fully aware that it's not the simplest way to build a parallel robot with 3 DOF (everyone seems to be most scared away by it's inverse kinematics!). I've seen versions which aren't exactly 3D printers in use, mostly of the 4-RSS design (i.e. pretty much exact copies of the adept Quattro), similar to the 3-RSS used in material transport delta PKM 'bots. I didn't really see any 4-PSS design like our 3-PSS style delta printer with a Prismatic joint vs the PKM industry standard Revolute joint.
So I set out, first off just playing around in Solidworks with some numbers of joint lengths I had calculated, trying to see what all the stigma was about. First I made a conventional delta bot using standard dimensions so I could play around with it in "3 space" and quickly added another upright! It works! haha - that was simple I thought.
Now what I really wanted was a way to "tilt" the hot end, so I could either have 2 or 4 hot ends, with only 1 hot end tip at a time on the "printing plane". There's surely a bunch of ways to do this - gimbal on the effector plate with X and Y actuators? nah - why add weight to the effector? wasn't that the point of going Delta in the first place? some sort or rotating cam deal? more weight... How about control each arm individually like a Stewart Platform PKM does? that means 8 servos/steppers to control! I guess I could just use a stewart PKM, but that's a lot of trouble to go through just to have a 4th and 5th DOF for X and Y tilt of the effector plate!
I started playing around with mounting the parallel arm spherical joints on the prismatic(slider) side on an additional revolute joint. That worked really well! With a 4-PSS style robot, adding an R makes it a 4-PRSS and now I have the ability to tilt the effector to take advantage of a multi-hot end with splayed tips. I chose 5 degrees off the central axis just to keep it simple!
-Just a note to add here, the revolute joints are not free-acting. This is why the design works. If they were you would have too many DOF for the input. Since this design only concerns tilting the head a given -/+ amount of degrees - it's basically a boolean option so I'll be using some method of actuation to trigger it - that is where I currently stand in the design process! Any input is greatly encouraged - I really want to make this into a real physical printing design!
So just thought I'd share my idea! Actuating the +/- action on the slider is something I'm still trying to think about. Electronic solenoid actuation with spring return, pneumatic cylinder actuation with spring return have been floating around my head, but these, if mounted ON the sleds add weight to the slides and therefor are not preferred. Another concept, albeit much more complicated, is to have a semi-syncronous bobbin and filament set running with the carriage drive setup. By incrementing or decrementing the semi-syncronous set of pulleys +/- 5 deg, the rotating ball mount assembly, which would be attached to this additional set, you would effectively perform the same thing as the carriage mounted actuators but instead you would be adding no weight to the carriage, and only minimal rotating weight to the pulley/bobbin setup. Incrementing/Decrementing could be accomplished either by a planetary gear/differential gear setup (complicated!!) such as that found in the lego kits. Another method is to have a sprague clutch style indexing ramp and spring. Under normal use the pulleys would be seperate, but if actuated by a linear actuator pushing on a thrust bearing you could "force" the pulleys together, and up a ramp, seperting them by about 5-10 degrees. This design might suffer from axial thrust issues when being driven in the opposite directly of the ramps, and accidentally start incrementing them though perhaps? All ideas haha...
The hot end is probably worth it's own subject, but that's a ways off and the splayed design just complicated the hell out of it. But I will say this - it's water cooled and should weigh 100 grams or less for 4 hot ends, and the working bits (surfaces immediately in contact with the filament extrusion) are all based on working designs. It's definitely going to take some testing but it's based on existing designs that deal with hot temperatures on the regular - but it's aim is to take advantage of 3d printing shapes that would normally be unmanufacturable. Ultimately the goal is to have the hot end assembly BE the effector plate (and the design would be adaptable for anyone's printer if your CAD savvy!)
This design works for the conventional 3-PSS style Delta printers as well! only you need to actuate 2 of the 3 in opposing fashion radially. (The 4 arm design works very simply by having the opposing 2 arms actuate the same way. it also only has 5DOF, a 3 arm delta would have 6 DOF and require 6 inputs - 3 stepper/servo and 3 actuators)
This design for a 3-PSS like the common delta printer is probably not a surprise though as there is a large amount of research on 6DOF PKM out there!
Edited 1 time(s). Last edit at 03/21/2014 05:00PM by mobile chernobyl.
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Re: Quattro Parallel Concept - Tilting slider mounts for boolean 4th and 5th DOF control March 21, 2014 05:58PM |
Quote
A2
Alternative idea to the prismatic(slider).
To alternate between multiple hot ends, mount the hot ends on a revolving plate, and splayed as you have noted.
The plate is at an angle (cam), and revolves like the lens on a microscope with a small servo, or NEMA 8 stepper motor.
NEMA 8 Frame Size(20 x 20 mm)
1.8° Step Angle
Torque - Up to 4.25 oz-in
That idea crossed my mind exactly! haha
I figured... why add weight at the worst place for inertia though? keep thinking, thinking, that's when I came up with this idea - which effectively does the exact same thing and add's no weight to the effector. The reason I decided to post it now is that my mind is overrun with ideas on how to "activate" the tilting revolute pivot on the prismatic slider. As-is it only needs to shift between -5 deg and +5deg. I really like the idea of using a pneumatic cylinder from my background skills, but I realize not everyone wants to add an air system to a pretty much purely electrically actuated machine lol. Discussing mechanics and reading about them on these forums is exciting to me so I'm anxious to see what creative ideas get manifested.
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