In order for this project to be successful, we must define a set of criteria, and then break the problem down into a set of little problems that can be tackled, one by one.
We chose a Delta robot configuration over a more conventional Cartesian design. This allows us more speed, less BOM cost going bearings and linear slides, and easier build / configuration. This will be covered in more detail in a future post.
I've taken the RepRap philosophy to heart. There are no swiss-machined parts and crazy Japanese bearings in this machine. I've spent weeks pulling my hair out trying to figure out the cheapest way to build a PnP machine without sacrificing quality. The original RepRaps used 608 bearings and LM8UU linear bearings because they're the cheapest, most-available type out there. They built their machines around these parts, rather than designing the machine first, only to be pigeon-holed into a weird bearing size. The best part is that the popularity of the RepRap movement has brought down the prices of these parts even further.
I've designed FirePick Delta around the following parts:
- Roller bearings: Use primarily 608 for anything load-heavy. Available for $0.30 each online. Use 623's for anything tiny.
- Linear bearings: Use LM8UU or LM6UU (8mm and 6mm, respectively). Available for $0.60 each online.
- Timing belts: GT2 belts and pulleys. Zero backlash, super cheap and available.
- Motors: Use NEMA 17 stepper motors whenever possible, because they're the most common. Available for $6.80 online.
- Custom parts, brackets, etc.: 3D print them. Design them without overhangs so they they can be printed without support. Since this is a Pick and Place machine, we can print with ESD-safe conductive ABS plastic :)
- Limit switches: Vishay TCST2103 optical endstops are quite common in the RepRap community, and can be extremely accurate.
- Frame: Misumi HFS5-series extrusion with select CO2 laser-cut acrylic pieces.
ACCURACY AND SPEED
SMT parts are getting smaller and smaller every year. If we made a crappy machine, it would be outdated by the time we'd finish it. We've taken the proactive approach, and created a set of simulations that test various configurations for accuracy and speed, that uses monte-carlo trials and evolutionary algorithms to "find" a correct delta geometry that fits our needs. We are attempting a design that *should* be able to place 0201 components! Although we'll be happy if it places 0402's and QFN's. I'll be talking more about this in a future post.
OPEN SOURCE vs. CLOSED SOURCE
We will keep it open and pay it forward. This gives us the ability to leverage the following Open Source projects in our design:
- OpenPnP - Is a project to create the plans, prototype and software for a completely Open Source SMT pick and place machine that anyone can afford.
- FireSight - A high-level computer vision framework designed for Pick and Place machines, powered by OpenCV. No programming experience required - A pipeline of image operations is specified with a JSON structure. The results of the operations are returned as a JSON structure.
- FireFUSE - FireFuse is the FUSE driver for all FirePick machines. FireFuse maps all hardware input/output functions for FirePick to individual files in the /dev/firefuse virtual f Read more »