Finishing the microscope with a stronger and stiffer Z-axis and framing

[00:00:00]So, as I previously hinted, I wanted to further improve the microscope because I experienced excess vibrations and the lack of stiffness. When I published the previous work, I had already ordered the new parts that are used in this final upgrade. Finally, I achieved the rocksolid microscope with all the three of its axis motorized and able to achieve a 1 micrometer step size with the new Zaxis linear actuator and frame.

[00:00:23]The hardware is considered finished. I'm happy with all the moving parts of the microscope now and if there are future updates, they will be focused on software related updates. The previous Zaxis upgrade replaced the microscope's original Zaxis. It was a rack and pinion mechanism driven by the focus adjusting knob for coarse adjustments. I used this knob, attached the timing pulley to it, and drew it with a stepper motor by a timing belt. It was okay, but the speed and accuracy were not the best, and there was a noticeable backlash. Then I replaced this wall mechanism with a customuilt linear actuator based on an SFU 1204 ball screw. I used some support bearings, some 2040 extrusion profiles, an 8 mm shaft, and some 3D printed parts to build it. It worked better in terms of speed and accuracy than the previous mechanism, but I basically traded off stability. I noticed wobbly movement and excess vibrations. This most probably came from the not too stiff 3D printed parts, especially the one that supported the wall microscope, which without the camera and cables weighed 2.37 kg. Since I wasn't entirely satisfied with the DIY build, I decided that I was going to rebuild the Zaxis with better, stiffer parts. I reimagined the wall mechanism using similar but better built parts.

[00:01:42]The main idea, driving the microscope with a ball screw remained. I found a nice linear actuator with a 100 mm stroke length that seemed promising. It had a Nema 23 stepper motor, which is a bit stronger than the Nema 17 I used previously, but it is still possible to drive it with the TMC 2209 driver. It had an SFU6005 ball screw, a step larger than the previous one. This is actually a bit bad because its pitch is 1 millm larger 5 mm. So I lose some resolution.

[00:02:12]But with the available micro stepping, it does not really matter. It had two MGM12 type linear guides that supported the aluminum block that accommodates the ball nut and everything was mounted on a 2080 extrusion profile which made mounting and assembly easier. The linear actuator came with some pre-installed nuts for the V slot, but I had to replace them because I needed more of them. and in a different slot from where they were. I just had to unscrew the four bolts at the end of the actuator and remove and replace them. Since the previous build suffered from vibrations, I decided to make the microscope mount as sturdy as possible. I bought a 15 mm thick aluminum plate for this purpose.

[00:02:52]Having it this thick is not only because I want it to be sturdy, but I also want to provide a sufficient overhang so I don't have the same problem with the Y-axis as I had before. The plate will sit on top of the actuator's balnut block and will support the microscope.

[00:03:07]The aluminum block for the ballnut has four M5 threaded holes. Plus, I will need three M4 holes for mounting the microscope. The distances and tolerances are rather strict, and I'm not the best machinist in the town. But I had everything drawn in Fusion 360. So, I drew a sheet that contained the seven holes I needed to drill. I made the 3D printed template so that it tightly snaps on the aluminum block. Once the sheet was on the plate, I took the drill bits, the 4 mm and 5 mm ones, and marked where the holes should be drilled. To be extra sure, I did not directly drill the 4 mm and 5 mm holes. I used center drills first in two steps to be sure that I had the holes aligned as well as possible. I must mention that I do not have the best drilling equipment. Apart from a wonky chuck, I do not have a proper vice to hold the specimen. So, I had to improvise. After reading about drilling holes in aluminum, I also placed a piece of wood under the block to avoid making an ugly hole when the drill bit goes through the plate. It worked well. Furthermore, I had to make sure that the heads of the M4 bolts that are supporting the microscope are sunk into the plate. So, I drilled their hole with an 8 mm bit. This was necessary because otherwise I could not mount the aluminum block on the linear actuators block. It had to have a flat bottom. The other four screws go through the plate from the top side. So their holes were untouched. To make the wall structure stiffer and more stable instead of using two separate 2040 profiles as previously, I used a single piece of 2080 C beam profile. This piece is much stiffer due to its shape and due to the fact that it contains more material in a single piece. I originally bought the 750 mm piece and then got it cut into two pieces. A 400 mm piece and the rest.

[00:04:57]The 400 mm piece became the vertical part. The other will be the horizontal part and the base for the XY stage. I bought some corner brackets for joining the pieces together. I can use this bracket both for the C beam profiles and the linear actuator which makes the wall assembly much simpler. I first attached the linear actuator to the vertical piece. I used all the possible mounting positions. So in total 20 screws hold the linear actuator and the vertical beam together. Eight are in the vertical beam and 12 are in the linear actuator.

[00:05:29]It should be strong enough. Then I moved on to the microscope. I removed the microscope from the previous rig and attached the previously drilled aluminum block to it using three M4 bolts.

[00:05:40]Everything fit smoothly and the heads of the bolts did not stick out. This is very important because this side of the block should sit on the actuator's block. So, it should be totally flat. In the following step, I mounted the block with the microscope on it onto the linear actuator. I just used four long enough M5 bolts and washers. To make my work easier, I removed the light source from the microscope. This made the mounting easier because the microscope was more balanced and it allowed me to access one of the four screws. I could not access it otherwise. After finishing the last screw, I mounted the light source back onto the microscope. It is held in place by a single set screw.

[00:06:18]Finally, I attached the bottom profile to the microscope. I use the same corner brackets that I used for attaching the linear actuator to the vertical piece. I attached the bracket to the top side of the bottom profile where the aluminum profile has the 2080 wide section and not where it has the two ears. There is a roughly 10 mm gap left between the two brackets in case I want to move the actuator further down. But as it can be seen when the actuator is at its bottom position, the shortest lens is almost touching the bottom profile. So once the XY stage is mounted, I will be able to move close to the subject and I won't need to move all the way to the end of the actuator's range. So the last step is to mount the XY stage. I did not change anything in the 3D printed mount because the stage is still mounted on a 2080 profile. I still use four bolts. It is enough. Once the stage is mounted, it becomes clearer how much space remains between the lenses and the stage. If I move the actuator all the way towards its end, I can move the lenses through the hole on the XY stage. So, the distance between the stage surface and the lenses is sufficient. If you remember, this was an issue in the previous project because I had to print another longer microscope holder piece.

[00:07:31]After all, with the initial piece, the microscope was several cm about the usable working distance of the lenses.

[00:07:38]There was no way to bring the lenses to within their working distance. This is not an issue with this build. Once the XY stage was in place, I could notice that the microscope became somewhat unbalanced. This is because the light source, the two stepper motors of the XY stage, and the cable for the XY stage are all located on the right side of the setup. To counter this unstable condition and prevent tipping, I reused the 1080 profile from the previous build and attached it to the back of the vertical beam in a way that hinders the wall structure from tipping towards the right side. With this extra stabilizer, the setup became very sturdy. Since there is a new stepper motor in the linear actuator, I had to do some soldering as well. My control circuit is equipped with a four pin GX16 socket.

[00:08:23]So, I soldered the corresponding mail plug. I put heat shrink tubes on both the individual wires plus an extra to hold everything together. Once everything was put together, I made a test homing along the Y-axis. This was a big issue in the previous build because I could not use the wall positive range of the stage along the Y-axis. With this build, I have enough overhang so that the XY stage can be in the center and I can have the full range of the Y-axis.

[00:08:50]This means that in both the positive and the negative directions, the stage can move 33 mm from the center. It is a bit tight towards the vertical axis, but there are still a few millm to spare.

[00:09:01]Probably I could move the bracket down to be extra safe, but I think it is fine this way. The limit switch is pressed before the stage physically touches the bracket and the stage won't move at extremely high speeds to create enough inertia to hit the bracket so it will be okay. I also tested the homing along the Z axis. This is still done by the TMC 2209 drivers stall guard feature. There are no limit switches. The actuator slowly travels up until it hits the support bearing. When the motor stalls, it creates back EMF which is detected by the driver circuit and the motor is stopped. Then the motor drives the microscope down by 50 mm which is the center of the actuator's range. And then this point is considered as the zero point of the Z axis. Similar to the previous setup, I attached the diode gauge to the microscope and then send the Z axis to different positions to see how accurately it could move. Overall, I'm fairly satisfied with it. The numbers did not match the last digits, but they were close enough. Then I did more testing through my software as well. I was especially interested in the backlash. So I tested the Z axis by first focusing on the subject under the microscope and then moving it up by let's say 10 mm from this position and then back to the initial position where the subject was in focus. It was almost always in focus after moving it back to the initial position. There was a tiny backlash but when I notched the Z axis by 10 micrometers I could get the subject back in focus immediately. So this means two things. The stage and with this all three axis have 10 micrometer step resolution and the backlash is somewhere around 10 micrometers which is acceptable for me.

[00:10:41]Actually the X and Y axis are a bit better. They have at least 1 micrometer resolution. I'm pretty sure that with some tuning and adjustments I could improve this, but I'm already satisfied with the result. Furthermore, the vibrations disappear. Not only the vibrations from the movement itself along the Z axis. I also noticed that the wall microscope tolerates the vibrations much better. I used to notice vibrations even with the original setup when I touched the table or walked around it. Now they are absent. I think that the wall setup became stiffer overall. So the vibrations are much better dampened. I wrote a detailed article about the project on my website and also uploaded some extra pictures.

[00:11:22]So make sure that you visit my website.

[00:11:24]link is in the description. Also, if you like these projects, please consider becoming a channel member to support me in publishing more of these videos. I hope you like the video. I hope you learned something and see you in the next video.