Introduction
ScanImage's advanced imaging modes (Arbitrary Line Scanning, Multiple Region of Interest (MROI) Imaging) rely on accurate positioning of the involved scanners (Galvos, piezos/voice coils). These scanners ship with controllers that implement simple PID loops to ensure tracking accuracy. However, these controllers cannot fully compensate for the dynamic behavior of the scan system, such as system lag and mechanical damping. These effects accumulate in a tracking error, which can result in a warped image geometry for frame scans, and an incorrect trajectory during line scans. To compensate for the tracking error, ScanImage can optimize the scanner command waveform using Iterative Learning Control.
During the optimization, ScanImage sends a command waveform to the scanners, measures the position sensor feedback of the scanner, and updates the command waveform based on the calculated tracking error. This process is repeated iteratively until the tracking error is within an acceptable range.
Wiring
The command waveform optimization feature requires a connected position feedback sensor for each scanner. This section describes how to set up the feedback sensors for commonly used scanner controller boards.
Cambridge Galvo mirrors
The galvo position and offset inputs are located on connector J1 of the Cambridge Technologies 671 series galvo controller board. Assuming these inputs are configured to be non-inverting single ended (W4 1-3 and 4-6 jumpered), the following wiring scheme can be used:
Pin | Signal | MDF Section | MDF Variable | Recommended MDF Value |
|---|---|---|---|---|
| J1.2 (X,Y) | Signal GND | - | - | - |
| J1.3 (X) | X Galvo position | LinScan / ResScan | XMirrorChannelID / galvoAOChanIDX | 0 |
| J1.3 (Y) | Y Galvo position | LinScan / ResScan | YMirrorChannelID / galvoAOChanIDY | 1 |
| J4.2 (X) | X Galvo position feedback | LinScan / ResScan | XMirrorPosChannelID / galvoAIChanIDX | 5 |
| J4.2 (Y) | Y Galvo position feedback | LinScan / ResScan | YMirrorPosChannelID / galvoAIChanIDY | 6 |
| J4.3 (X,Y) | Signal GND | - | - | - |
Fast-Z
Wire the controller's position feedback signal to the DAQ terminal defined in the Machine Data File variable 'fastZAIChanID'.
Operation
Before starting a scan, open the Waveform Controls window and select 'Update Waveforms'. The checkbox 'Optimized' indicates if ScanImage has previously performed an optimization for the current command output. In this case, the optimized waveform will be used for the scan. In case there is no optimized waveform in the ScanImage cache, choose 'Optimize' to start an optimization run.
API
ScanImage ships with two default optimization algorithms, which are located in
+scanimage\+mroi\+scanners\+optimizationFunctions
| Name | Used for | Comment |
|---|---|---|
| deconvOptimization | Galvos | fast convergence, relies on linear scanner behavior |
| proportionalOptimization | FastZ (piezos) | slower convergence, can optimize non-linear systems |
The functions take the desired waveform and the current scanner feedback as an input, and generate an updated command waveform based on the tracking error. These functions are called iteratively until the output 'done' equals true. Data can be passed in between calls by using the variable 'optimizationData'.
When controlling a scanner with an analog command waveform, scanner lag and damping result in a tracking error (A). This results in warped image geometry for frame scanning and an incorrect trajectory for line scanning. ScanImage can automatically optimize the scanner command waveform to minimize the tracking error (B).
The Cambridge Technologies 671 series galvo controller boards expose the sensor feedback on pin J4.2.
Attachments:
waveform optimization.png (image/png)
waveform optimization.png (image/png)
671 series galvo controller feedback wiring.png (image/png)