For part two I’m going to cover the building/assembly and wiring of my custom control electronics enclosure for the Liteplacer. Part one of this series can be found here, and covers the mechanical assembly of the Liteplacer kit.
I designed this enclosure in Solidworks after some careful measuring of all the goodies that go inside. With .dxf files in hand, I paid a visit to my buddy Jon and his big router table. The large vented backplate was cut from 0.125″ aluminum, the end panels and cover were cut from 0.060″. The engraving of the end panels was done on the router table using a diamond point tool. The width of the control box matches the small HP computer that will mount vertically just below.
Next order of business was to fire up my little press brake and put the appropriate bends in these freshly cut parts.
I’m pretty happy with how all the pieces ended up fitting together. I could have made the enclosure just a tad longer though, since it got a little tight inside by the time everything was mounted & wired.
The power supply I used is a 10A/24VDC Delta unit, which happens to be a bit overkill but it’s what I had to work with. Also, since I’m going to be running a larger 12VDC powered vacuum pump rather than the one that comes with the kit, I mounted a small 12VDC power supply inside.
The vacuum configuration I’m going to run will include a reservoir and an adjustable vacuum switch to power the pump only when needed. This necessitated a couple changes to the way the vacuum pump FET was wired up. I ended up using some IRF3708’s for the pump and solenoid valve instead of the STD30NF06L FET’s that were included with the Liteplacer kit. I put together a perf board to hold these goodies, and mounted it to a couple of the available threaded holes in the big power supply. The 1N4007 freewheeling diode in the diagram above will be mounted at the vacuum pump motor rather than the perf board for the sake of simplicity.
Connections to the stepper motors, limit switches, solenoid valve, vacuum pump, vacuum switch, and LED ring lights are brought out the rear panel via Amphenol C 091 A Series connectors in 3, 4, and 6 pin varieties.
The USB connector on the Tiny-G board lines up nicely with the provided opening. One cable gland secures the incoming power cord, and the other is for the IEC pigtail that brings AC power back out to the PC. The one thing I neglected to consider when designing the enclosure was a place to provide power for the monitor. I fixed this by manually cutting a square hole in the 0.125″ backplate to accommodate a single AC outlet. This works but it did make the area behind the front panel more cramped than I had planned.
The front panel houses a pair of lighted rocker switches. One provides power to the machine via the main power supply, and the other controls power to the vacuum pump. Three push to reset circuit breakers reside along the bottom. These provide independent protection for the machine power, the vacuum pump, and the PC/Monitor. While certainly more than required protection wise, it is nice to have things broken out like this when it comes time to troubleshoot a problem.
The emergency stop I used is a GCX1131 from Automation Direct. I currently have it wired up to the reset input on the Tiny-G motion control board like is shown in the Liteplacer instructions. However I’ll probably be changing this to interrupt power to the 24VDC supply instead. If you look closely you’ll notice that I have a green contact block (normally open) on the e-stop. This works for resetting the board, but it’s a no no in the industrial control world because the machine won’t stop if a wire in the safety circuit comes loose. The Liteplacer instructions do however make a point to mention this issue.
With the enclosure all buttoned up, the next step of the project will be to assemble all of my nice new 80/20 extrusion to create the frame that will house everything. I’ll also need to make up some brackets to mount the PC. That’s all for today, thanks for reading!