Project
| # | Title | Team Members | TA | Documents | Sponsor |
|---|---|---|---|---|---|
| 10 | Active feedback control for laser pointing stability |
Hao Yan Ruomu Hao Sean White |
Yangge Li | design_document1.pdf final_paper1.pdf proposal1.pdf video1.mp4 video2.mp4 |
|
| # Problem A label-free diagnostic tool used in medical area, infrared microscopy is based on the fact that molecular bonds in tissues and cells have a unique spectral signature in IR. However, the beam pointing could be affected by external factors like the drift of modules or vibration by sound. Because this technique requires a high level of sensibility, it is crucial to maintain the stability of the laser beam. Also, since various QCLs would be used in the technique, they need to be aligned co-linearly with respect to each other. # Solution Overview A closed-loop feedback control system could be adopted to solve this problem. The position information could be obtained from a quadrant photodiode sensor passed to the processing unit. This sensor can generate a difference signal that can be used as the error signal in a PID controller. The microcontroller will then output a voltage to the servo drivers to correct the beam position. # Solution Components ## Microcontroller We can implement the control algorithm within the microcontroller. It should take the input error signal and compare it with the expected position, from either a LUT from the system or a stored equation. We could also use one that can be recognized by Matlab Simulink, so we could just download the code converted from block diagram to the microcontroller. This has the advantage that the controlling schemas would be easier to write and debug. ## ADC & DAC An ADC is needed to convert the input error signal from the quadrant photodiode sensor to a digital signal for the microcontroller. A DAC is needed to output the correction voltages to the servo drivers. This would require the Vcc and GND pins for the PCB. Depending on the number of outputs from the microcontroller, MUXs could be used and the microcontroller should generate the select bits for them. ## PCB It should integrate our microcontroller and ADC/DAC chips together and possibly fit the physical requirements from the project team. The microcontroller could be mounted as a sister board with ADC TTL as peripherals. It would be unlikely (at least for now) that we’d need additional memory or routing for it. This PCB will be integrated with the current laser system. # Criterion for Success Our Solution will need to stabilize the beam to get consistent and clear images the research team can use despite external factors. For the modular design, the ADC and DAC should successfully convert the signals. The microcontroller should be able to calculate the correct output for any given test inputs. The PCB board should have all the routing correctly working and without thermal or mechanical issue. |
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