gripper design for picking up a paint brush

[forgetcolor]

I'm working on a gripper design that can pick up a paintbrush.  The gripper will be attached to a CNC-like cartesian robot for manipulation of the brush in 3D.  I've built the CNC but this is my first attempt at designing anything like a gripper.  Here's a drawing of what I'm thinking:



The solenoid would be a pull solenoid, which would open the gripper.  The spring would hold the gripper closed on the brush (the circle with an X in it) when the power to the solenoid is off.  Everything except the piston would be fixed in place.

I need the length to the right of the brush to be a max of about 3".  I haven't quite figured out my needed stroke length, but I'm thinking 1" is more than enough, maybe less.  I want to be able to use a variety of size brushes, but I can cut them and attach them to a standardized cylinder for the gripper to grab on to.

So my questions are:

1. does this look reasonable?
2. any ideas to improve or a completely different direction that my be preferable?
3. any pointers to appropriate solenoids?
4. any ideas on how to figure out the necessary strength of the solenoid vs. the spring tension?

Answers (or commentary) to as few as 1 or maybe even 0 of those questions are appreciated!

[Cristi_Neagu]

You could look into something like a mechanic pencil head... A solenoid pushes the 3 heads out, and, because they're elastic, they spread. You put in the brush, solenoid pulls the heads back in, and they squeeze together.
Would be a bit harder to implement, but it has the advantage that, unlike your design, when you change the brush size, the axis of the brush doesn't change (with your design, a bigger brush would shift the axis to the right).

Good luck.

[forgetcolor]

good points.  if i understand you correctly, i think i might be able to mitigate the axis (center point?) of the brush changing with different brush sizes as long as every brush has an identically-sized collar and that the brush is centered in the collar?  in other words, embed and center the brush handles in 1" diameter cylinders, then pickup the cylinders with the gripper.  if i calibrate home with one the centers of all should line up.  i can keep track of the varied brush diameters in software.

[Admin]

I'm working on a gripper design that can pick up a paintbrush.

Just pick it up? Or also use the paint brush? Or just use the paintbrush after you put it in the gripper? Where would the brush be before the gripper picks it up?

(these are two very different tasks)

[forgetcolor]

both pick it up, and then hold it while it's being used.  the gripper will be attached to the mounting plate of a CNC machine.  the brushes will be held in tall narrow cylinders so that they stay upright and so that the machine knows where to get them and where to put them back.

[Admin]

How much space do you have between each brush in the CNC rack? ie, how fat can the robot fingers be?

[Cristi_Neagu]

good points.  if i understand you correctly, i think i might be able to mitigate the axis (center point?) of the brush changing with different brush sizes as long as every brush has an identically-sized collar and that the brush is centered in the collar?  in other words, embed and center the brush handles in 1" diameter cylinders, then pickup the cylinders with the gripper.  if i calibrate home with one the centers of all should line up.  i can keep track of the varied brush diameters in software.

That sounds right to me. It would be more efficient, i think, to use the collar idea. Then you won't need to worry about making the program remember where's the center of one brush, and then having to remember to add that offset everywhere... It's just simpler to have one standard dimension.

[forgetcolor]

How much space do you have between each brush in the CNC rack? ie, how fat can the robot fingers be?

great question i haven't been thinking about in relation to the gripper.  i've planned for the paintwells (cups holding wet paint) to be about 1 1/8" in diameter and spaced 2" on center.  i've planned the containers for the brushes to be behind each respective color (different brush for each color).  but as designed, the gripper might not have enough left/right room to get in there and grab the brush.  I may need to extend the gripping surfaces out in front somehow so the gripper mechanism isn't running into other brushes.

i can spread the brushes and colors out more but then i might be limiting my total colors more than i want to.

[forgetcolor]

hmm, i could also rotate the gripper design so that the left side in the drawing becomes the back side (against the mounting plate on the CNC), with the solenoid assembly jutting out in the air.  it's not ideal, but it keeps the brush close to the plate (essential for using as much of the table as possible) and it makes the gripper narrow so it can fit between other brushes.  but visually it's really not my choice.

[Admin]

Just an out of the box thought . . . what if you modified the brushes to be easier to grip?

For example, drill a 1" diameter hole into the handle of each brush.

Then your 'gripper' is a long rod that goes into the hole, and the rod expands inside to lock onto the brush.


(just an idea to get you thinking out of the box, not necessarily a good idea in itself)

[SmAsH]

Speaking of out of the box, an electromagnet? With permanent magnets in the brushes?