Unified Optical Scanning Technology

Chapter 4.5 - Scanner Devices and Techniques: Oscillatory (Vibrational) Scanners

4.5 OSCILLATORY (VIBRATIONAL) SCANNERS

The scan nonuniformities that can arise from minute errors of rotating mirrored or holographic facets may be avoided by eliminating all but one facet. This changes a polygon to a monogon, which adapts well (per Fig. 4.7) to internal drum scanning. It achieves a very high duty cycle when executing a large scan angle within a cylindrical image surface. The same scan, however, when projected through a flat-field lens per Figure 1.8 or 1.9, allows only a limited scan angle, resulting in a limited duty cycle from a monogon. If the mirror is oscillated rather than rotated through a full cycle, the wasted scan interval may be reduced. This component must, however, satisfy system speed, resolution, and linearity. Such devices include the familiar galvanometer and resonant scanners [Ayl, Bei2, Mon1, Rei] and the less frequently encountered piezoelectrically driven mirror transducers [Bei2,Rei] and the 'fast-steering" larger mirrors driven by push-pull pairs of voice-coil type actuators [Ber,New,Swe].

The typical mirror mounting position places its reflecting surface coincident with the rotating axis (Fig. 1.8). In this orientation, with the plane of the input and output beams perpendicular to the rotating axis, the optical scan angle Θ is twice that of the rotation angle Φ (magnification m = 2). In rare, although useful alternate instances, the mirror reflecting surface is positioned nominally at 45° to the rotating axis (Fig. 1.9). In this condition, with the illuminating beam coaxial to (or derived from focus on) the rotating axis, the optical scan angle Θ is equal to the mechanical rotation angle Φ, exemplifying radial symmetry. Along with some distinctions in performance (see, e.g., Section 4.3.5.5 re image rotation), the effects on scanner-lens relationships are discussed in Section 4.6.

 

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