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synchronized_zaxis_focus_sweeps

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synchronized_zaxis_focus_sweeps [2016/05/24 21:59]
vik
synchronized_zaxis_focus_sweeps [2019/04/18 23:35] (current)
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 +====== Synchronized Z-axis Focus Sweeps ======
  
 +Focus sweeps provide a simple way to integrate many focal planes in a single image. ​  It is possible to generate accurate position and exposure control using some specialized scanning firmware and hardware encoder comparisons with the MS2000WK controller and an ASI Z-axis drive.  ​
 +
 +===== Required Configuration =====
 +
 +The following components are required:
 +  * MS2000WK controller with firmware** SCAN MODULE**
 +  * Mechanical Z-axis Drive
 +  * Camera with TTL gated exposure mode
 +
 +===== Procedure =====
 +
 +The user should familiarize themselves with the [[commands:​scan|SCAN]],​ [[commands:​scanr|SCANR]],​ [[commands:​scanv|SCANV]] and [[commands:​ttl|TTL commands]].  ​
 +
 +As an example, let us assume that we would like to take a 200ms exposure over a swept focal range of 10μm. ​ The exposure time will determine the sweep speed.
 +
 +\begin{equation} Speed = \frac{Focal Range}{Exposure Time} \\
 +
 +Speed = \frac{0.010 mm}{0.200 sec} = 0.05 mm/sec \end{equation}
 +
 +The following commands will set up the single Z-axis scan at the correct speed:
 +
 +''​SCAN X=0 Y=0 Z=1''​ X and Y axes not used; Z-axis is fast-scanned axis
 +
 +''​SCANR X=0.0 Y=0.01''​ sets the start and stop positions for the fast-scanned axis to 0.0 and 0.010 mm respectively
 +
 +''​SCANV Z=100''​ the scan will be repeated 100 times
 +
 +''​SPEED Z=0.05''​ set the scan speed to value calculated above
 +
 +''​SCAN''​ start the scan
 +
 +At this point the controller will begin successive scans of z-axis followed by rapid retraces. ​ To trigger a camera, some TTL exposure control is required. ​ There are two ways this can be accomplished.
 +
 +  - Use TTL OUT0 (internal SV1-2) and the command [[commands:​ttl|TTL Y=5]] to select a gated output during the “uniform velocity” portion of the move as determined by the built in trajectory generator. ​ This provides a reasonably accurate gate pulse, with perhaps 3-6 ms jitter and 0.2 to 2m systematic position error compared to what is desired. ​
 +  - Use the SCAN SYNC (internal SV1-7) output directly. ​ For this to work on the Z-axis, JP1 – Pin 2 must be connected to the Z-channel encoder flag output, pin 22 of IC24.  This is a special hardware modification that must be made for Z-axis synchronized sweeps. ​ This method has the advantage that the precise encoder locations of the start and stop positions (as defined by the SCANR command) determine the edges of the SYNC pulse.
 +
 +With either (or both) method(s), you should be able to display the TTL trigger pulses on an oscilloscope.  ​
 +
 +There may be some reason you wish to pause between successive sweeps. ​ An arbitrary time delay can be added using the [[commands:​wait| WAIT command]]. ​ For example[[commands:​wait| WT Z=1000]] would add a one second delay time between successive sweeps.
 +
 +The basic setup parameters for your sweep can be stored into nonvolatile memory in the controller using the command [[commands:​saveset|SS Z]].  ​
 +
 +A scan can be initiated, stopped, and restarted just by using the [[commands:​scan|SCAN command]] without any other arguments.
 +
 +===== Overshoot Parameter =====
 +
 +The overshoot parameter is set using [[commands:​scanv|SCANV F=overshoot]]. ​  The stage will travel a distance on each side of the uniform-speed scan equal to the acceleration ramp distance multiplied by //​overshoot//​. ​  The default value is ''​overshoot=1.0''​ so the ramp regions are exactly excluded from the uniform speed section of the move.  A value of ''​overshoot > 1''​ provides additional distance for the speed to settle into a constant velocity. ​ Scans with ''​overshoot < 1''​ will have non-uniform speed at the beginning and end of the scan.
 +
 +
 +{{tag>​advanced_feature ms2000 scan_module tiger}}
Address: 29391 W Enid Rd. Eugene, OR 97402, USA | Phone: +1 (541) 461-8181