Sunday, June 22, 2025
Prototype Micron Gripper (printed at macro scale)
We're starting to approach the point where it's worth considering practical things to make. Using the Blacksmith analogy, the first thing should be a micron scale gripper - essentially a pair of tongs to hold your work with.
I went for something totally minimalist. The prototype here uses a syringe body 6.5mm in diameter as a sleeve, and an actuator shaft of 4mm dia. The jaw spacing is 3mm. Here is the prototype on a 10mm grid in the open and closed configurations:
This is an ad hoc prototype so things are a bit scrappy, please excuse. The sleeve acts on the sloping arms at the base of the gripper, and a single flexure pair bends to allow the jaws to meet. By changing the length of the jaws, I can vary the range of motion.
This was printed on a Prusa Mk4. When printed on a RepRapMicron, I would use a blunt 0.5mm hypodermic needle as the sleeve, and a 0.24mm stainless steel wire as the actuator. I'm sure I'll change dimensions, but just a quick comparison. Scaling down by a factor of (6.5/0.5) 13, this would result in a gripper approximately 1.5 mm x 1.2mm which we know the μRepRap is capable of making with an accuracy of better than 50μm worst case (though the precise layer height is TBA).
The jaw spacing would be about 230μm, which is a bit small for the present capabilities IMHO but this is just an example.
Current concept is to mount it on the probe holder with a micro hobby servo to do the actuating so I don't have to put my shaky hands on it. Some support infrastructure is obviously needed but I'm nowhere near designing that yet.
To attach the gripper to the actuator wire, I would give it a light coating of UV resin before putting it in contact with the printed gripper. When it's in the right location, the resin is cured. Probably needs more contact area for the bond, and a bit more room to prevent the resin blob contacting the sleeve. This also gives a handy way to keep hold of the part when I separate it from the print bed.
Blacksmiths don't just use one pair of tongs - they have dozens. Consequently I'd expect there to be a variety of grippers. Apart from anything else I can foresee a number of them pinging off the end of the actuator wire into the universe beyond forever...
