projekte:dvdlsm:start
Unterschiede
Hier werden die Unterschiede zwischen zwei Versionen angezeigt.
| Beide Seiten der vorigen RevisionVorhergehende ÜberarbeitungNächste Überarbeitung | Vorhergehende Überarbeitung | ||
| projekte:dvdlsm:start [2021/02/07 00:20] – [Electronics] thasti | projekte:dvdlsm:start [2021/02/07 22:25] (aktuell) – [Laser Diodes, Lens and Actuators] thasti | ||
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| ~~NOTOC~~ | ~~NOTOC~~ | ||
| - | ====== DVD-Drive-Based | + | ====== DVD-Drive |
| - | {{ : | + | {{ : |
| Due to an abundance of one specific type of DVD drives, plans were made to give a useful afterlife to these devices. A laser scanning microscope seemed to be the most useful project. | Due to an abundance of one specific type of DVD drives, plans were made to give a useful afterlife to these devices. A laser scanning microscope seemed to be the most useful project. | ||
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| ==== Laser Diodes, Lens and Actuators ==== | ==== Laser Diodes, Lens and Actuators ==== | ||
| - | The OPU houses two laser diodes. As this is just a DVD/CD reader, the lasers are not very powerful but provide sufficient power for microscopic | + | The OPU houses two laser diodes. As this is just a DVD/CD reader, the lasers are not very powerful but provide sufficient power for microscopy |
| The primary lens is positioned using electromagnetic actuators. These come in the form of three coils, which tilt or move the coil proportionally to the current flowing though them. Their polarity and required full-scale DC actuation current can be easily found by using a lab power supply. | The primary lens is positioned using electromagnetic actuators. These come in the form of three coils, which tilt or move the coil proportionally to the current flowing though them. Their polarity and required full-scale DC actuation current can be easily found by using a lab power supply. | ||
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| It was conjectured that the smaller inner quadrants were responsible for the low-sensitivity outputs, while the outer segments would produce a large amplitude (due to their larger light collection area). | It was conjectured that the smaller inner quadrants were responsible for the low-sensitivity outputs, while the outer segments would produce a large amplitude (due to their larger light collection area). | ||
| - | In a second reverse engineering session, the exact pinout was determined by means of selective illumination: | + | In a second reverse engineering session, the exact pinout was determined by means of selective illumination: |
| {{: | {{: | ||
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| ==== OPU Modification ==== | ==== OPU Modification ==== | ||
| - | A breadboard header was added to the OPU, fanning out all required signals to the custom electronics on a ribbon cable. The analog output signals are separated on one side, while the current inputs for the laser diode and the lens actuators are kept to the other side. This should help mitigate electrical coupling between these signals, even though the diode outputs are actively driven by the PDIC. | + | The whole top assembly of the DVD drive is reused. This includes not only the OPU, but also the linear (worm gear) axis driven by a stepper motor and its base plate. |
| + | |||
| + | The other axis (below the drive mechanism) is built from a commercial precision linear actuator that was donated to the project. Other people have simply used another DVD drive in its place, which would certainly be a possibility here. | ||
| {{: | {{: | ||
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| The main laser microscope class provides a few methods for focus control and scanning a predefined area to an image file. The focusing is the most interesting aspect here. Generally, the focusing first performs a wide scan of the Z-height to find the linear region of the focus error detector. Following that, it implements a simple PI control scheme for successively minimizing the focusing error. | The main laser microscope class provides a few methods for focus control and scanning a predefined area to an image file. The focusing is the most interesting aspect here. Generally, the focusing first performs a wide scan of the Z-height to find the linear region of the focus error detector. Following that, it implements a simple PI control scheme for successively minimizing the focusing error. | ||
| - | Given that relatively large areas should be possible, focus tracking is required. Initially, the software uses a relatively simple algorithm to achieve this: | + | As relatively large scan areas should be possible, focus tracking |
| - | * Given a rectangular scan area, place a virtual grid inside this area with at least N points per millimeter | + | * Inside the rectangular scan area, place a virtual grid with at least N points per millimetre |
| - | * At each grid point, perform | + | * At each grid point, perform |
| * Least-Squares-Fit a 3D plane through all the points on the grid | * Least-Squares-Fit a 3D plane through all the points on the grid | ||
| - | * During the actual scan, calculate the optimal Z-height for a given position | + | * During the actual scan, calculate the optimal Z-height for a given position |
| Another noteworthy aspect is the Y-Axis (implemented using the DVD drive motor and mechanism). Given this whole mechanism is a made from a few cheap plastic pieces, | Another noteworthy aspect is the Y-Axis (implemented using the DVD drive motor and mechanism). Given this whole mechanism is a made from a few cheap plastic pieces, | ||
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| - | Higher | + | Higher |
| {{: | {{: | ||
| - | Scan of an I2C test chip from my colleage | + | Scan of an I2C test chip from my colleague |
| {{: | {{: | ||
| - | This picture shows some of the aforementioned nonlinearity in one axis, which introduces periodical distortions in the image. These could be corrected in principle, but I didn't bother. The nice CERN logo was placed on the top metal layer, and is composed | + | This picture shows some of the aforementioned nonlinearity in one axis, which introduces periodical distortions in the image. These could be corrected in principle, but I didn't bother. The nice CERN logo was placed on the top metal layer, and some of the lower level metals |
| Also from this chip, here's a few very small scans performed at 200 nm step size. Small metal filling patterns on the top metal layer are imaged, each of which is only about a two micron wide square. Lithographic imperferfections can clearly resolved using this imaging technique. The horizontal (black) lines were caused by the erratic X-axis stage, sometimes going to places it was not told to go... | Also from this chip, here's a few very small scans performed at 200 nm step size. Small metal filling patterns on the top metal layer are imaged, each of which is only about a two micron wide square. Lithographic imperferfections can clearly resolved using this imaging technique. The horizontal (black) lines were caused by the erratic X-axis stage, sometimes going to places it was not told to go... | ||
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| + | Finally, here are two videos of the device in Action: | ||
| + | * Focusing: https:// | ||
| + | * Scanning: https:// | ||
| + | ===== Summary ===== | ||
| + | For not a lot of money, a rather capable little laser microscope could be built. At some point, more scanned objects will be added to the collection above. If you are interested in replicating this project or a part of it, all developments are publicly available in the following repositories: | ||
| + | * Hardware: https:// | ||
| + | * FPGA Gateware: https:// | ||
| + | * PC software: https:// | ||
| + | ===== References ===== | ||
| + | I'm of course not the first one to build something like this. Here's some sources of my own inspiration: | ||
| + | * http:// | ||
| + | * https:// | ||
| + | * https:// | ||
| + | * https:// | ||
projekte/dvdlsm/start.1612657230.txt.gz · Zuletzt geändert: 2021/02/07 00:20 von thasti