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Assembling: Laser alignment and focusing

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iliasam edited this page Jun 4, 2020 · 11 revisions

Here we need to do two steps - make laser alignment and lens focusing.

Laser alignment

  1. Connect "GND" and "DATA" lines of the "Motor PCB" to the USB-UART converter (connect "DATA" to its RX line). Connect converter to the PC.

  2. Disconnect motor from the scanning head - rotation is not needed.

  3. Connect external power lines to the Lidar.

  4. Load "test1_capture_image" firmware to the MCU.

  5. Reboot power and ensure that a led at the USB-UART is blinking (if it is present).

  6. Run "LidarRawDataCapture.exe" from the "PC_utility". Select proper serial port and press "CONNECT" button. When data packet is received by this utility, packet counter at the bottom of the utility form is increased.

  7. It is very possible that there would not be any image because laser is not aligned. Try to move laser beam vertically by pressing to the bottom of the laser holder (there is a place for a screw there). See picture (screws are not shown):
    I'm calling one of the directions "good", because that movement cold be achieved by tighten the alignment screw. Another direction - "bad", because that movement cold be achieved by untwisting the alignment screw and untwisting is limited.

  8. If you can see that a peak is appearing at the chart when moving holder in the "good" direction, just place a suitable screw to the hole at the laser holder to hold it in that position. Turn it to get maximum amplitude of the peak.
    Example of the peak image at the chart:

    Asis X is representing pixels of the image sensor and Y is ADC signal.

  9. If there is a peak appearing at the chart when moving holder in the "bad" direction, that means that the surface marked "A" of the laser holder is badly produced. You need to disconnect laser holder from the PCB and refine it with a needle file. Don't make a mistake with direction! Try to make step 8.

  10. When you get a stable peak at the chart, you can do lens focusing. Turn the lens at the lens holder to get the maximum amplitude of the peak. Fasten it with a screw (there must be a special hole at the lens holder).

When you are making alignment process, it is important to keep peak near the right side of the plot (100-110 pixels) then the object is far enough. Also you need to check:

  • That peak is moving left when you decreasing the distance
  • Peak it still present at min distance
  • "Peak Float Max Pos" value is calculated at the all range of the distances

You can check that laser is working using phone camera. Laser beam could be seen at a certain position of camera. See video: https://yadi.sk/i/UbTX5m8ad9eUsA

You can try use "test2_capture_image" to increase laser power (it could be dangerous for your eyes!)
You can see laser spot at the paper with that firmware:

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