The Crousel is a mechanism for pogo-testing and/or programming 60 small circuit boards without human intervention. Drawing its inspiration from the slide projectors of days gone by, 60 boards are loaded into a removable circular cartridge. The desired test is contained in another modular cartridge that holds the pogo pins, a microcontroller, and interfaces with the mother Crousel using a simple 6-line parallel protocol that initiates the test and returns the results. Upon commencing the process, the Crousel advances to drop a single board into the channels, presses the board against the pogo pins, waits for the results of the test, then sorts the board into a "good" or "bad" bin at the bottom.
At it's heart, a simple arduino uno runs the show along with some inexpensive pneumatic actuators, a solenoid or two, and strategically placed photointerrupters that detect any sort of mechanical jam. If the desired test is less than a second, the Crousel runs at about a 3 second cycle time per board. We've run thousands of boards through the first model with no indications of things slowing down!
The Crousel in Use
The initial jig was built for the Motherboard-A of Cubelets. The engineering team spent about 200 hours in design and development of the first Crousel jig. This jig replaced a repetitive task that was error prone and a drain on the user who was carrying out the test. The previous test required an assembly team member (elf) to hold each PCB in the jig until programming was complete at which point the elf would check for pass or fail of the board. More than 50% of the elf's time was spent holding the PCB in the jig and waiting for the screen to show green or red. With the current jig the elf is able to set up a run of circuit boards and allow it to program and test the boards until either a jam is detected of until the jig is out of boards.
With the Crousel, each board is able to be programmed and tested in approximately 10.4 seconds compared to nearly 27 seconds using the previous method. This is a gain equal to $.0412 for each board, not to mention the increase in happiness of the assembly worker. The total amount allocated for development of the Crousel was calculated to be approximately $7,717.75. If the Crousel was only developed for this unique board it would require 187,120 boards to go through the jig in order to recoup the investment in the jig. The engineering time spent developing the Crousel is such a large part of this cost that if a second jig were produced it would only require 22,991 boards to pay off the copy of the original. Spinoffs that test other PCB's would require some additional engineering resources but would be able to recoup the cost of the jig much more quickly than the original in about 41,660 PCB's.
The original Crousel should pay itself off in April of 2014 if nothing else is to be taken away from the project. Fortunately a large portion of the project is able to be utilized in other Crousel jigs as well as throughout the FARKUS system. It is difficult to quantify the amount of R&D that is transferable to other elements of the system but if 50% of the original Crousel is transferable, then the quantity of boards to recoup the investment would drop to 102,261. The mechanisms and lessons learned from the Crousel will benefit FARKUS as a whole in helping automate our factory to build robot construction kits. As of July 2013 more than 12,000 boards have been tested using the Crousel.
|Cost of Engineering per Hour||$35|
|Return per Board||$0.041245|
|Hourly Elf Payrate||$9|
|First Jig||Second+ Jig|
|Hours into development||200||8|
|Maintenance per Month||$24.75||$24.75|
|Total (with Maintenance)||$7,717.75||$948.25|
|Number of Boards to Recoup Costs||187,120||22,991|
Bill of Materials
|Micro ATX Power supply||$30||Newegg.com|
|MicroRax struts and connectors||$50||microrax.com|
|Acrylic (for laser-cut parts)||$80||Mcmaster.com|
|Pneumatic manifold, pistons, tube, fittings, and solenoid valves (3 channels)||$200||Mcmaster.com|
|Standoffs, nuts, bolts, springs, shafts, bearings||$30||Mcmaster.com|
|Photointerruptors, buttons, LEDs, wires||$20||Sparkfun.com|
|Arduino Uno and Power shield||$50||Sparkfun.com|
|3d printed material cost||$30||Various|
Pogobed Test Module
One of the primary advantages to the Crousel is how flexible and reusable it is. Each circuit board design that is to be tested in the crousel requires a board-specific test module. Using a Nintendo 64-esque card-edge connector, these modules slide in and out of the mother crousel for quick changeover between builds. The electronics on the pogo module are tailor-made to accomodate to the board-under-test, but we provide the basic template to get you started. We've also implemented all of the PC <-> Crousel communication on both devices. Developing test modules is simple.
Below you'll find schematics and a PCB layout for the very same board we use in production at Modular Robotics to test and program the Motherboard that is inside each and every Cubelet. Want to play around? The AutoCAD Eagle Schematic and Board files are available for download as well.