Grippers for a Bioloid

[JonHylands]

So, one of the things I am working on for BrainBot is to add grippers to the robot, one on each arm. These grippers are for object manipulation and, more importantly, to allow the robot to "inspect" objects it is holding using its stereo vision.

So, I needed to design a two-degree of freedom gripper - one degree is the normal fingers open/close motion, and the other is a rotating wrist. I have designed this gripper, and had the first one printed on a 3D printer. There is still a bunch of work to do, but as you can see its coming along. It has a recess in the fixed finger for a pressure sensor, and will plug onto the Bioloid bus just like everything else.

This is a render of the CAD model it is based off of:



And here's the actual "printed" gripper shell:





To give a sense of scale, the main gripper body is 20mm wide and 93mm long...

I'm going to be machining the second one out of Delrin, just to compare how they turn out. The motor in the bottom is the wrist rotator, and the linear actuator (the large orange thing in the middle) is a Firgelli actuator, available here:

http://www.robotshop.ca

I have ordered a couple of those, and will take more pictures and post them here once I get it more assembled.

- Jon

[JonHylands]

So, I got a pair of Firgelli actuators in the mail today, and I put one in place on the printed gripper:



It looks pretty nice...

I decided machining the grippers, although technically possible, is more trouble than its worth (or, more to the point, takes longer than the printed version costs).

- Jon

[JonHylands]

More fun with grippers...

Here's a short movie (929 KB) of me manually applying 5 volts to the linear actuator on the gripper, and making it close and open.

http://www.bioloid.info/Gripper-Actuator-01.wmv

The wrist rotator is simply a GM-14a gearmotor from Solarbotics, but I need to use a couple gears to get the rotation axis to the point that the whole gripper rotates around. I have been looking for commercial gears for a while, but haven't managed to find what I really need. I decided to try making my own gears on my CNC mill, and it works pretty well.



Details here: http://www.huv.com/blog/2007/04/more-grippers.html

- Jon

[Robo1]

I like what you up to.

I've been using printed parts for a while as long as there don't have small bits < 5mm then they should be fine.

Love the Firgelli actuators makes a change to see them used rather then a normal servo.

bren

[Pev]

They look great and seem to work really well.

Can I show my ignorance and ask what you mean by printed parts? I assume this is some sort of method of printing a 3d design to a cutting machine???

Pev

[JonHylands]

3D printing is a very cool, relatively new technology. Basically, you have something that looks like a CNC milling machine. Instead of having a cutting head, it has a printing head. It takes a spool of ABS "wire" (about 2-3mm diameter) and feeds it down into the print head. The print head melts the plastic, and extrudes it out a very small nozzle, so the printer has the ability to lay down a "line" of ABS. Because the print head can move in three dimensions, it can lay down thin layers of ABS, which when built up form 3D shapes.

Look at this site: http://www.reprap.org

- Jon

[Robo1]

I just love 3D printers.

I'm currently using one to design my new biped. I just have to give a CAD if to the man that runs the machine come back the next day and it's just there. The only limitation is your imagination it can literally build any shape.

When I get some time I will up data my home build thread, things are coming along nicely.

Bren

[billyzelsnack]

Very cool.

Seems like you could have a hybrid machine that had a glue head and a cutting head. Do a a rough layer pass with the glue and clean it up with the cutting pass.

[JonHylands]

Well, you could do that, but in reality the model I had printed has internal hollows which you just can't machine. There is a channel that goes from the indent on the bottom gripper (for the pressure sensor) through the base, and into the PCB enclosure.

http://www.xardas.com/Examples.html for some examples of things this guy has printed.

- Jon

[billyzelsnack]

I mean that you do a pass of glue. Then a pass of cutting. So internal features would work too.

[JonHylands]

Ahh, okay, I understand. The problem is, in order to do internal hollows, the machine actually lays down a soluble support layer inside the hollows to hold up the solid areas above it - otherwise, the liquid ABS would just run into the hollow when you tried to cover it over.

Once the piece is done, you place the part in a dissolving tray, and the support structures go away.

There really isn't much need for a cutting phase - anything you can cut, you can just not put ABS there.

- Jon

[JonHylands]

So, much progress has been made on the grippers - I plan on finishing them later today. Here's where I am right now:

This is a picture of the underside, showing the mounted PCB, and the wrist gearmotor. The PCB has an ATmega168 onboard, 2 h-bridges, and a pile of connectors.



Here's some detail on the wrist setup.



And finally, here's a short movie, showing both the gripper and wrist under control of the on-board ATmega168...

phpBB [media]

- Jon

[limor]

when do we get to see it mounted it on the BrainBot..

[JonHylands]

Hey limor,

Probably tomorrow... I'll post it here...

- Jon

[Pev]

Brilliant gripper - look forward to seeing it on BrainBot