Homebuilt pcb printer from cheap HP printer
Hello CNC zone. Hopefully I'm posting this in the right place, if not I'll move it right away. I've been reading quite a bit of the diy servo drives of both the atmega and arm stm32f103c8t6, the arm micro seems like a good choice but when I thought about how I would add drive circuitry that would be customized to each motor and how I would have to etch and design each circuit board, I thought of recycling a cheap desktop printer and computer into a dedicated pcb printing and inspection station for whatever drive circuitry I need at the time. My grandmother gave me her old hp deskjet 1512 as well as an old, cheap desktop computer to go along with it when my grandpa died. This setup seems to offer several advantages over traditional photoresist and etch methods, including:
Quick design, printing directly allows me to forgo the uv exposure and possibility of errors from improper exposure, so I can go straight to etching once the ink dries
Easy customization and repeatability, with printing directly from my computer I can easily tweak a few traces or components with the click of a button, or I can set it up to print off a whole series of pcbs nonstop as long as I have the blank pcbs and ink available.
Better reliability, I'm working on a program in Linux that can scan the finished pcb, both after printing and after etch, and compare to the master image on the computer to speed up the troubleshooting process if the circuit doesn't work as planned, most likely the longest part of my most likely overly ambitious project.
I will be posting the entirety of this project from the first screwed removed, any and all troubleshooting, the design refinements, and the software whenever I get around to that part.
Part of the inspiration for a dedicated pcb printer is finding the trays on eBay to send a pcb through a standard printer, though there were several issues with the design and use that came up in all of the reviews I read, most of which involved the stability of the tray and repeatability of the print. My plan is to harvest the required components from inside of the printer, design my own rigid pcb tray, and use a linear drive mechanism similar to the axis of a router to either send the pcb through the machine or move the machine over the pcb, hopefully with the improved rigidity the prints will be quite consistent and repeatable. Depending on the drive units and sensors in the printer itself I may have to make some slight tweaks to my design, such as how the linear drive is actuated or the overall shape and design of the tray itself. I'm hoping I can find some way to extract a signal from the controller when a print is finished that I can send to a microcontroller to automatically load and unload pcbs when I want to do multiple prints. We'll see how the project progresses as I learn more about the printer and how the components work together. So without further ado, let's begin the teardown process.
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Re: Homebuilt pcb printer from cheap HP printer
First is a picture of our organ donor, a pretty simple desktop printer, luckily it makes pretty good prints on paper, but the wife an I want to keep our wireless printer for home use, so its either into the trash or into the shop. Second pic has the simple controls, oddly enough the power button doesn't seem to do anything, but the other three buttons work exactly as advertised. Last you can see the scanner side of things, along with the four screws holding the thing together, we'll start with those and see what we find under the hood.https://uploads.tapatalk-cdn.com/201...861c1616cb.jpghttps://uploads.tapatalk-cdn.com/201...d9fa5f0ddc.jpghttps://uploads.tapatalk-cdn.com/201...644b0724b4.jpg
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Re: Homebuilt pcb printer from cheap HP printer
Right underneath the panel are two ribbon connectors linking the button panel and the scanning head to the main control board, both will have to be removed to safely lift the top panel off. It looks like a rectangular choke on the wide ribbon linked to the scanner side of things, it would be a good idea to keep an eye on it so it doesn't fall off or go missing.https://uploads.tapatalk-cdn.com/201...5ad8adef60.jpghttps://uploads.tapatalk-cdn.com/201...ec4278c8e2.jpghttps://uploads.tapatalk-cdn.com/201...c8b3b9a900.jpg
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Re: Homebuilt pcb printer from cheap HP printer
On the bottom of the top panel it looks like the top is pretty simple, the ribbon goes right to the scanner head itself and directly to the buttons themselves, since there's no ic on the button pcb it seems easy enough to simply leave that part unconnected, though the controller may need a pull-up resistor or something to function properly so some trial and error may be necessary. The scanner part seems simple enough, once I pop off the top half of the panel I can just lift out the entire assembly, motors and everything, it would seem easy enough to either reuse the original panel or to cut out the gear track to use myself. I'll try to get some better pictures of the scanning unit later.https://uploads.tapatalk-cdn.com/201...57772bd299.jpghttps://uploads.tapatalk-cdn.com/201...2443286d77.jpghttps://uploads.tapatalk-cdn.com/201...38f9c0f787.jpg
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Re: Homebuilt pcb printer from cheap HP printer
Under that top panel you can see the main part of the printer that we'll be using for our pcb's, it holds the print head, all the sensors, and the control board with power and serial connections. I'm going to try to upload a quick video of the details under the hood here. You can see an optical encoder on the back of the print head. It's hard to see unless I tilt it with my finger but there's a clear plastic strip with encoder lines printed on it so the print head can find it's location at all times. I'm assuming it is a quadratic encoder with a simple brushed dc motor on it. The motor doesn't need to locate the print head accurately each time since the controller with just activate the ink jet when it happens to be in the right place. This seems easy enough to interface with on the off chance that we'll need to modify the design slightly. I found a set of gears to the side of the slot that the paper goes in on the back, I'm not sure if it is used to feed the paper or if it's attached to an encoder to provide feedback on paper movement, maybe to identify the size of sheet? The gears turn pretty freely but there's enough that it seems like the kind used for a drive mechanism so we'll see what happens when we start this thing up. In addition there's a pair of toothed tabs toward the bottom of the tray where the edge of the paper falls when it's inserted into the slot, I've taken a picture both with and without paper, so that's another part of this reverse engineering process we'll have to pay attention to once we can see it running with the hood open. Finally, there's what looks like a print head cleaning area to the side, with some foam blocks and a linkage connecting to a rubber wiper, I'd love to see how that works since that seems pretty essential to maintain consistent and repeatable prints for pcb use.https://uploads.tapatalk-cdn.com/201...5e5a9a0281.jpghttps://uploads.tapatalk-cdn.com/201...3e58788246.jpghttps://uploads.tapatalk-cdn.com/201...bdbde760f8.jpghttps://uploads.tapatalk-cdn.com/201...2be1b0aee3.jpghttps://uploads.tapatalk-cdn.com/201...ce81385d76.jpghttps://uploads.tapatalk-cdn.com/201...1d7448df8c.jpghttps://uploads.tapatalk-cdn.com/201...6f57783d5c.jpghttps://uploads.tapatalk-cdn.com/201...477d2a5e2f.jpghttps://uploads.tapatalk-cdn.com/201...fca423cff2.jpg
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Re: Homebuilt pcb printer from cheap HP printer
So I don't have a link to the video yet, but I started it up with the panel off and the plastic piece with the foam cleaning pads seems to have a homing switch of some kind since the print head travels back and forth until it slides the whole assembly over, which also activates the linkage for the rubber wiper too. I didn't get to it in my first video, but for some reason whenever I turn on the printer and try to print something with the panel off, I am continuously given a paper error, which means either empty tray or misfeed. Since neither is true and we didn't have the issue when we used the printer last, I realized and confirmed through trial and error that the controller with throw a misfeed error if the scanning head is disconnected. Unfortunately this limits us in how we can set up the linear stage that feeds the pcb to a moving table design rather than moving gantry, though I was figuring I'd have to do it that way anyways, moving table would take up more room, though I doubt it would make much of a difference. I haven't taken it apart enough to be sure, but it looks like the majority, if not all of the printer mechanism can be taken out as a single unit and then just pick and choose which part I need and which ones I can toss. My main concern now is the linkage on that cleaning head. When the machine starts up the print head moved left until it slides that black plastic assembly over, at which point the black rubber wiper lifts up. As soon as the printer is ready to print, the thin black roller towards the front spins a couple times, tripping a latch that drops the wiper below the level that the paper would be at. This is fine for printing on paper, however since that area will be taken up by the space needed by my linear stage instead, I don't think I can keep the rubber wiper the way it is unless I add in a small groove or something on my tray to make room for it, and that's not including what I may need to modify on the rollers that trip the latch on the wiper or any sensors that are needed to confirm the print is ready/operational. Anyone's thoughts on this are greatly appreciated.
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