This is part 2 in the development of a pick-and-place machine for electronics assembly. Part 1 is available here.
The new head
The new head is much more simplistic than the old version. This version uses a stepper motor with a hollow shaft instead of a tube with a GT2 pulley on it.
In the CAD model to the left you can see the Shapeoko spindle mount plate in black. The main mount for the head is shown in a semi-transparent grey with the stepper motor and mounts for two cameras.
At the bottom you can see an adapter that converts the stepper motor shaft into a tapered fitting for the pick and place tip. The blue disk in the center is a magnet that holds the taper and head assembly. This allows the machine to be able to adjust the tip depending on the part being placed.
Here you can see what everything looks like on the machine today:
We also mounted an upward going Z-axis limit switch that’s screwed in to the spindle mounting plate. This will kill the power to the motor drivers if we accidentally command the machine to kill itself.
The brass fitting in the vacuum line allows the motor to turn the nozzle continuously without turning the plastic tubing going to the vacuum.
The new feeder
The new feeder swaps out the solenoid and pawl for a thin, pancake stepper motor. The stepper motor advances the paper tape of parts with precision control. This model also includes a small reel in front to collect the clear film that keeps the parts in there little holes. This is driven by a small DC hobby motor, but we’ve also made it to where a second stepper motor could replace this DC motor if it doesn’t work in this design.
I just got the circuit boards for the control board in earlier this week, so I’ll make those up tomorrow. But for now you can see a video about the construction and initial testing on the new feeder:
We started with the “mechanical kit” from inventables.com. We also got their NEMA 17 stepper motors, stepper motor cable, GT2 belting, and GT2 pulleys. With shipping this comes to about $440.
When the box arrived it was obvious that it was not treated well on its journey:
That hole there, that was the escape hatch that all of the stepper motors used. After filing a lost articles claim with the shipper, I notified the folks at inventables.com and they put replacement steppers in the mail that same day. Hats off to the instructables.com gang!
During assembly I broke a tap in the makerslide. I was going to EDM it out, but the machine was being used to make money. Also, I was a little concerned about damaging the threads that were already there, so I ended up dissolving the tap with some alum. I got the idea from here. The called it flocculant at the pool supply store. I used the Baquacil product shown here.
I put the makerslide in a stand and then suspended it on a hot plate with an automatic magnetic stirrer. You want to get the tap to where it has bubbles coming off of it. Add alum until you can’t get any more to dissolve in the water. It took several hours to dissolve to where the tap fell out.
At the end the slide was a little discolored where it was exposed to the alum, but the threads were undamaged.
I have a video on YouTube showing the bubbles and the steel turning into black dust particles:
The first head on the Shapeoko worked pretty well. It’s shown here to the left. The vacuum tube comes in and connects to a tubing adapter, twist adapter, then another adapter that connects to a hollow aluminum tube. This tube had a GT2 pulley on it. The stepper motor connected to the left of the base had a GT2 belt that would turn the pulley on the vacuum tube and orient the picked up part along the A-axis.
The aluminum rod goes between two switches. A wide washer on the aluminum rod can trigger the switches. The height of the buttons on the switches is different, but close. When the part gets placed the first button triggers. The second button is just slightly higher and is used as a limit switch killing power to the Z-axis stepper driver if something bad happens.
There is also a webcam shown, a Logitech C920.
To the right you can see several, rather large countersunk holes. These were sized to fit dispensing tubes for solder paste.
The CAD model probably makes it easier to see what’s going on. In the center there’s a teal colored washer with a thick diameter. This presses up on the switch buttons as the tip of the vacuum needle touches the circuit board. The three plungers shown wouldn’t be used together. The idea was just to have a hole to accommodate the various sizes of dispensers from multiple manufacturers.
Below is a wider angle shot of the setup. At the bottom you can see the four stepper drivers that control each of the axes. We did get this setup working with LinuxCNC and OpenPnP. The stepper controllers were driven by the parallel port on the PC shown at the back-right of the table behind the Shapeoko.
Unfortunately we were not able to get the proprietary nvidia driver working with the real time kernel in our LinuxCNC distro and this was slowing down our vision processing. So we started looking for a way to move away from LinuxCNC. We also were using a solder-less breadboard for the electronics that are controlling our vacuum, blower, and the solenoids that direct the air and wanted to get away from needing the breadboard or building a circuit board to replace it.
We considered getting a GRBL controller since a lot of folks are using this with OpenPnP but decided to get a Smoothieboard instead. The big points that made us go the smoothie route were:
One board that can control all of our stepper motors
The same board can control our vacuum, blower, and fans (onboard mosfets with screw terminals)
So, we tore apart the PnP that we spent so much time wiring together to come up with iteration 2.
What about part feeders?
The last bit of parts we need for our next version of our feeder are scheduled to arrive with FedEx on Thursday, so we’re really excited about that. However, for this first version of the PnP we tried to use a solenoid based solution for our feeders:
The control board at the top-left drives a hobby, DC motor that was used to pull up the tape on the reel. It also controlled the voltage to the solenoid. The solenoid was connected to a pawl that grabbed the teeth on the ratchet behind the sprocket that fed the tape. A second ratchet is shown here in this picture on top of the sprocket.
This feeder was functional, but the solenoid was not strong enough to consistently advance the reel. Adding in gearing would have made this solution too slow for production use. Larger solenoids would not have fit in the narrow spacing that we wanted to keep for the feeder. It was cool to watch though with the pawl acting as a hand grabbing and pulling the ratchet. Another downside was that the solenoid doesn’t allow for precision control of how far the tape gets advanced each time.
The CAD rendering below shows the assembly a little better. The pawl (purple in the CAD) is basically a hook that gets stuck in the angled teeth of the ratchet shown in green. When the solenoid fires it pulls the ratchet and the sprocket that moves the tape forward.
Stay tuned and I’ll bring you up to date on our second version of the head and feeders.