of the early attempts at developing a small mechanical scanner was the Vibratory
scanner. In this device, a small mirror, "rocked" in the "horizontal"
direction and simultaneously, in a "vertical" direction, perpendicular
to the first. The mirror, usually about 1/4" square, was controlled
by a pair of electromagnets driven by appropriate sweep signal frequencies. Because
of the added weight of the rocking frame, it was always driven by the framing
sweep signal because it was the lower frequency of the two. Therefore, the rocking
mirror was always driven by the line sweep signal. To improve the efficiency of
the scanner, the mirror mounting and the rocking frame were made resonant to the
two sweep frequencies. A light source, modulated by the picture signal was reflected
by the vibrating mirror onto a screen. Pictures as large as 3 feet square and
with up to 240 lines were claimed with this system.
The main failing of the
Vibratory scanner was that it produced a sine wave scanning action, not compatible
with signals from cameras equipped with the usual Nipkow disk or electronic pickup
tubes such as the Image Dissector or Iconoscope. In addition, sine wave scanning
produces undesirable shading of the image. Similar scanners were attempted using
Piezo-Electric crystals or Electrostatic drivers instead of electromagnets. They
suffered from the same problems.