3 ms·

Anyone know why the mirrors in the displays oscillated instead of spinning? Was it just a matter of it somehow being easier to keep the phase and frequency corr

Anyone know why the mirrors in the displays oscillated instead of spinning? Was it just a matter of it somehow being easier to keep the phase and frequency correct with oscillation? Because it seems like it would be much simpler mechanically to spin them.

laumars 11y ago
My guess would be that there would be a brief pause between scanlines where the angle of the mirror was acute. Where as oscillation ensures there is always a section of the viewable screen being rendered. But this is just an educated guess so I too would be interested to read the actual reason.
deelowe 11y ago
Galvos were fairly common back on those days. For such a simple device (it's just a voicecoil) you can get very precise alignment assuming it's well designed mechanically (e.g. properly damped). Not sure about spinning mirrors like those used in barcode scanners, but I'm guessing gavos were preferrable at the time for things like this. Galvos were heavily used in laser light shows back then which would have been very popular when this was being designed. To be honest, when I heard single line LED display utilizing 2 mirrors (one for each eye), my first thought was "Just like a laser light display." Clever, but relatively evolutionary if you know how existing tech worked at the time. The other reply below/above isn't correct about there being a pause between scans. A common implementation for rotating mirrors is to use an octagonal mirror [1]. With that implementation, there's no pause. The image just jumps immediately back to the left/right. The issue is more likely controlling the speed of the motors would be difficult to keep synced with the requisite precision. [1] http://cdn.iopscience.com/images/0034-4885/76/8/086801/Full/rpp437052f02_online.jpg http://cdn.iopscience.com/images/0034-4885/76/8/086801/Full/...
cma 11y ago
Maybe the mirror would hit the optics otherwise and would have to be moved back, resulting in smaller field of view, requiring more sophisticated optics.

laumars 11y ago

My guess would be that there would be a brief pause between scanlines where the angle of the mirror was acute. Where as oscillation ensures there is always a section of the viewable screen being rendered. But this is just an educated guess so I too would be interested to read the actual reason.

deelowe 11y ago

Galvos were fairly common back on those days. For such a simple device (it's just a voicecoil) you can get very precise alignment assuming it's well designed mechanically (e.g. properly damped). Not sure about spinning mirrors like those used in barcode scanners, but I'm guessing gavos were preferrable at the time for things like this. Galvos were heavily used in laser light shows back then which would have been very popular when this was being designed. To be honest, when I heard single line LED display utilizing 2 mirrors (one for each eye), my first thought was "Just like a laser light display." Clever, but relatively evolutionary if you know how existing tech worked at the time. The other reply below/above isn't correct about there being a pause between scans. A common implementation for rotating mirrors is to use an octagonal mirror [1]. With that implementation, there's no pause. The image just jumps immediately back to the left/right. The issue is more likely controlling the speed of the motors would be difficult to keep synced with the requisite precision. [1] http://cdn.iopscience.com/images/0034-4885/76/8/086801/Full/rpp437052f02_online.jpg http://cdn.iopscience.com/images/0034-4885/76/8/086801/Full/...

cma 11y ago

Maybe the mirror would hit the optics otherwise and would have to be moved back, resulting in smaller field of view, requiring more sophisticated optics.