I've got a half complete project for etching PCBs automatically. I've got a set of three tanks (develop, etch and wash) and a servo controlled mechanism for moving the board between the tanks.
The coding side of the project isn't causing problems, but the mechanical side is a bit flaky (the home-made mechanism is a bit lose and imprecise) so sometimes the boards get dropped in between two tanks, or they don't get lowered far enough.
On the plus side it's cheap, and looks easy to hack, on the down side I suspect that it's going to be very imprecise, and very hard to persuade to repeat exactly the same movements time-after-time. My guess is that there's probably no feedback mechanism, and it's only the eye of the operator that can determine the position of the gripper.
Advice please!
Just to make it clear, I'm not actually interested in a robot arm for the sake of a robot arm. I'm just looking for a mechanism to move a PCB between three tanks - the movements aren't complicated, up and down in the tank, and left and right between the tanks. Would I be better off re-engineering my servo mechanism to remove the slack, or would a robot arm be better? or is there another may of doing it?
I know nothing about that robot arm that you linked to but I wonder is it designed for repeated long term use or is it just a toy that will work until people get tired of it.
Can you post a photo or a video of your existing arrangement?
The tanks are quite heavy (when full) so it makes more sense to move the lightest item (the pcb)
I wonder is it designed for repeated long term use or is it just a toy
I doubt it's designed for repeated long term use, but I don't make all that many PCBs, so whatever else may go wrong, I wouldn't expect it to wear out.
I have seen these robot arms in person before. They seem robust enough, but they are certainly in the toy category. Note that they are quite small and are by no means fast, but that may be fine for your application. You might be able to add you own motor controllers and potentiometers/encoders to make it fully autonomous, but at that point you be equal in work and $ to somthing more purpose built.
Im not ture if you will understand this but ill have a go.
Imagine a pair of wheels mounted vertically above another pair, connected by something , a bit like a bycicle chain.
Pcb mounted on hangars , with hooks attatched to the rope.
As pulley rotates hooks engage on hangars which are lifted clear then moved sideways as it travels around the top pulley before descending to next tank.
Times two gives 3 tanks , times four gives feed and removal option.
Iv seen this arrangement but have no idea what its called
I just remembered, the hook is a u shaped receptacle pivoted with a weight below , so it always stays vertical, so the hangar does not fall off.
Edit
A similar arrangement is where the pulleys are mounted howisontaly with a bar between them, bar picks up all the hangars at once and walks them to the next tank.
Boardburner2:
Im not ture if you will understand this but ill have a go.
Imagine a pair of wheels mounted vertically above another pair, connected by something , a bit like a bycicle chain.
Pcb mounted on hangars , with hooks attatched to the rope.
As pulley rotates hooks engage on hangars which are lifted clear then moved sideways as it travels around the top pulley before descending to next tank.
Times two gives 3 tanks , times four gives feed and removal option.
Iv seen this arrangement but have no idea what its called
I think you've the right idea with the chain, but I would use two (one either end of the tank) and hang the PCB horizontally between them. The chains can be made to follow the path the PCB will take, using free running rollers to raise or lower the chain in the correct places. The PCB can sit in a dense (so it doesn't float) plastic tray with some holes in, suspended from the chain on something like cable ties or thin plastic cord. If the width of each tank is set correctly, there would be no need to adjust the speed or stop the chains when the PCB is in each tank. The mechanism can be extended beyond the last tank so that the completed PCB is tipped off the tray to land safely on a piece of foam plastic.
At the price of this arm, I would definitely attempt to use it.
if I was making a tank that would be handling lots and lots of boards, I would go for a gantry type system. move carriage over tank, lower board(s), wait, or shake or raise/lower. then lift and move to the next tank.
that arm is much easier to make, and would get your weeks or months of use. in the mean time, you can make boards while planning your next device.
for that price, you could get two and some spare parts.
Thanks for the suggestions, I'm beginning to think I'll have to go for some form of overhead gantry for the side-side movement, and a servo arm for the up-down dunking of the board in the tank.
Something that perhaps I should have mentioned earlier, is that the tanks are very thin (about 20mm) to save space and keep the amount of etchant and developer fluid to a minimum. This means that the PCBs cannot move sideways until they have been complete removed from the tank.
To ensure even etching the pcb needs be right in the center of the tank, so I need to sure I can achieve a dunking accuracy to +-1 or 2mm, and I'm not sure I'm going to get this from a robot arm.
OhMyCod:
Something that perhaps I should have mentioned earlier, is that the tanks are very thin (about 20mm) to save space and keep the amount of etchant and developer fluid to a minimum. This means that the PCBs cannot move sideways until they have been complete removed from the tank.
To ensure even etching the pcb needs be right in the center of the tank, so I need to sure I can achieve a dunking accuracy to +-1 or 2mm, and I'm not sure I'm going to get this from a robot arm.
Cheers
Ok, large crank or pantograph for the big lift and small crank for accurate side to side at top, bit like piston engine with wobble.
Another thought though, if you are bubble etching you will need removable covers as i can see mist carry over between the tanks causing chemistry problems.
