Hi All,
I've been thinking for ages that a really low cost pick and place machine would be great but up until recently couldn't come up with something that breaks the stepper motor barrier. I say barrier because a) they aint cheap, b) they need drivers which aint cheap and c) programs to drive them.
So here's the idea for overcoming the stepper motor barrier. What I realised, which potentially removes the steppers, was that for a pick and place machine you don't need to know where the business end (picker / placer) is until it's at the target position - once at the target position you need to know it's arrived but that is all.
Ages ago I made a capacitive sensor that measures distance. You can put the capacitor in an oscillator and measure the frequency really easily. So if you make a long capacitor (out of PCB say) and have a 'U' shaped secondary plate* that moves with the axis you get to know where the axis is; rather than stepping to a 'feed forward' position using steppers. Then all you need is a signal generator (read DDS) and output that to a phase detector that's looking at the oscillator whose frequency is dependent on the position of the axis. Once 'locked' you are ready to pick or place (or whatever else).
The thing is, for this idea you can just use belts and simple DC servo motors, with audio amplifiers driving the servo motors. In turn that also means that the weight of the whole thing can be small allowing it to move really quickly. DC servos have more torque than steppers so there's room for some real fun
Instead of being code driven (to make steps) it would be analogue using PID loops to move the axes. A processor would send tell a DDS what frequencies to generate and then wait for the 'locked' signals to arrive.
Anyone interested in discussing it further, to come up with something to actually build?
I have built CNC milling machines in the past but not pick and place. I bet there are much more challenging things to consider than just the movement of the business end.
* three parallel strips, two side strips are grounded with a tapered centre strip. The U shaped piece couples the ground to the tapered piece so the whole assembly is corrected for slight deviations from centre and shielded. Centre tapered strip is the oscillator capacitor to ground.