Z Axis Optical Endstop for Geeetech Prusa I3 Pro by DougInAZ

Last crawled date: 3 years ago

Update 1/28/18 I added a retainer to secure the stop flag in its holder. I relied on a friction fit on an earlier version and when I replaced it, I found there wasn't anything to secure the flag. You can mount it either way in the holder, depending upon whether you are using a printed flag or a thinner one made out of plastic or card-stock.
Added 5/29/18. Originally I used a printed flag that was painted at the end. After a long while, I started getting inconsistent Z homing. I believe the paint was scratched somewhere along the line, and it was no longer opaque. I replaced it with a flag made out of credit-card plastic and it the Z-home consistency was restored. FWIW, I also painted the end if the flag black with a black marking pen.
UPDATE 1/30/17 The holes in the printer frame and/or the holes in the bracket that mounts to the printer frame are over-size for the 2.5 mm screws that Geeetech originally furnished for the micro switch. Also, the holes on the frame of my printer appear not to be parallel to the horizontal line of the printer frame. There isn't any problem with the frame bracket being out of square with the frame as far as the flag actuating the optical module, but the over-size holes allow the optical module to be moved up and down if the bracket holding the optical module is bumped inadvertently. This can move the end point and allow the extruder to end up too high or low when homed. I've found it is best to push the bracket to its lowest position and then make sure the screws are tight. Another potential fix is to switch to 3 mm screws and/or place some contact cement on the bracket before mounting it to the frame and make sure it is in the lowest position when fixed in place.
UPDATE 12/29: I've been using this for almost a month now, and am very pleased with the way it works. It seems very repeatable. Between this and the nut keepers on the printer bed, my printer bed holds adjustment much better than it used to when I got it a year ago.
After having two micro switches fail in less than a year of use, the option of using an optical sensor end stop switch seemed like a worthwhile thing to try. Switches that do not provide a consistent switch point can be tolerated in the X and Y axis, but precision is a necessity in the Z axis if your bed control is manual.
The two printed assemblies here, plus a purchased optical module provide an optical endstop that replaces the microswitch on the Z axis of Geeetech I3 Pro printers. It can probably be adapted to other printers that use the same metal brackets as the Pro series on the X carriage.
First, my thanks to Ablapo for his design, http://www.thingiverse.com/thing:27544, which provided the inspiration. I wish I could have used it as-designed in my printer.
Besides the printed parts, The following parts are needed:
1 Ramps 1.4 Optical Endstop and cable, eBay, Aliexpress or other.
1 square post for connecting 5V power to endstop cable (or solder to board (recommended))
Misc soldering tools and shrink tube.
2 #4 x 1/2 inch SAE sheet metal screws or similar size metric sheet metal or machine screws for mounting optical switch to the printed bracket..
1 3MM cap screw as furnished by Geeetech for Z-Endstop adjustment (to provide adjustment of optical sensor).
1 Spring, as furnished for Z-End stop by Geeetech;
1 6d Finishing Nail or similar smooth steel rod approximately 0.092 in. diameter to stabilize the position of the optical sensor.
2 short #4 sheet metal screws or machine screws to hold the stop flag coarse adjustment in the movable carriage. These are not needed if the flag is glued or friction-fitted into the flag holder.
Steel washers, 3mm 3 for the spring and cap screw. a couple more if you use screws to hold the flag into the bracket.
The assembly that is mounted on the X axis carriage holds the stop flag which enters the gate in the optical switch when nearing the stop point. This assembly allows a coarse height adjustment of the stop flag. It can accommodate a wide range of extruders by raising or lowering the stop flag fixed position. This allows the fine adjustment on the fixed assembly to have a limited adjustment range without the spring being too tight or too loose.
The assembly mounted on the frame attaches to the mounting holes that were used for the microswitch. It provides fine Z-adjustment of the optical sensor using a 3mm machine screw. A smooth steel rod on the sensor holder moves in a clearance hole and keeps the sensor in alignment.
The optical sensor is powered by 5vdc which can be tapped from the main controller board or the display panel. The newer GT256 control boards have 3 pins available for powering a BL Touch. That is an easy place to get 5 VDC. The other two wires of the optical sensor connect to the existing wires that connected to the micro switch. These two wires provide a 5v ground and the output signal used by the processor board. Use a voltmeter connected to 12v low to determine which is the signal and mark it for connection to the optical module.
I added a knob for adjustment, but the screw furnished with the printer may not be long enough to use it without compressing the spring more than desirable. If you want to use a knob, use a longer screw with a nut run up tightly against the head and insert it in the bottom of the fixed frame piece. Put the knob on the top of the movable piece, where the adjustment cap screw head is in the pictures. It looks like there will have to be a spacer under the knob to clear the sensor. You can use the washers included; they can be scaled up in size ant thickness to do the job.
It's worth mentioning that the photos show development parts and in most cases are not the same as submitted here; I never updated the parts on my printer. If I screwed up, and the changes don't work, please let me know, so I can fix it.
The LED on the sensor lights when the flag is not blocking the path. In practice, the LED never extinguishes. When the flag triggers it momentarily, the end point is sensed and the stepper motors stop. In my case, the LED remains lighted after the motors stop, however it is not at full brightness, which indicates there is a lot of noise in the module. A capacitor across the module might be helpful, but the switch point seems very repeatable as noted by the stopped position of the stepper motors. If anyone tries to correct this situation, let me know so I can add your findings. This printer is an EMI nightmare; it drives my digital caliper crazy if it is within several feet of it.
UPDATE 12-2-16
I added knob2. This offers another way of adding a knob to the adjusting screw. It is attached to the head of the cap screw by heating the screw with a soldering iron and pressing it into the knob. If it comes off when it cools, a drop of CA glue might be enough to keep it in place more or less permanently. The best way to get it on straight is to drop the hot screw into a clearance hole in a piece of wood or other material and then press the knob firmly in place over the head. It can be reheated (at the base of the head) and repeated as necessary. The hole in the front of the printer base for the Y carriage belt adjustment is a good hole to use. Put a washer on the screw to make sure the screw is fully supported when you press against it.
UPDATE 12-3-16
I shortened the vertical blade on the X carriage base to get it out of the way of the knob and added it as Base 2.... The change shouldn't interfere with use on the target printer.
Notes:
The pitch of a 3mm adjustment screw is 0.5 mm or 0.020 in. A quarter turn of the knob or screw moves the Z set point 0.125 mm or 0.005 in.
The downside of using a square pin connector on the power to the optical module is that if the power connector happens to get knocked off, the carriage will crash into the bed when homed.
I'm not using the latest parts, but when I see something that can be improved, I make a change. The downside is that I may upset something that I don't see. The only way I'll know is if I get feedback. If you run into something that doesn't fit or work well, please let me know and I'll try to fix it.
12/6 added photo of Knob2 pressed onto the original z-adjust screw.