High duty cycle synchronized multi-line scanner

Details High duty cycle synchronized multi-line scanner High duty cycle synchronized multi-line scanner

1998-01-21

2001-09-11

Spyrou, Cassandra (Department: 2872)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S017000, C359S216100

Reexamination Certificate

active

06288817

ABSTRACT:

BACKGROUND
1. Field of the Invention
This invention relates to line scanners and methods for scanning multiple synchronized scan lines using scanners having high duty cycles that conserve illumination source energy.
2. Description of Related Art
Many devices such as printers, inspection devices, and medical equipment contain line scanners. For example, a typical laser printer contains a line scanner that scans a digitally modulated laser beam to form an image on a media such as paper, film, or plates, and in the medical industry, a line scanner in an X-ray machine scans an X-ray beam through a patient or sample to form lines of an image. A typical line scanner includes a scanning element such as a polygon mirror or a holographic disc on which an input beam from a laser or other light source is incident. The scanning element redirects the input beam, for example, by reflection or diffraction, to project a scan beam. Movement such as rotation or oscillation of the scanning element moves or scans the scan beam along a scan line in an image area. Line scanners often include pre-scan and post-scan optical systems that adjust the focus or collimation of the input and scan beams as well the linearity of the scan line and the uniformity of scan rate.
An important property of a line scanner is the duty cycle which is defined by the ratio of the time that the scan beam is imaging to the total operating time. Generally, a line scanner has a periodic motion that includes a dead time during which the line scanner is not directing the scan beam toward the image area. Thus, duty cycles for line scanners are generally less than 100% and typically range from about 20% to 70%. The duty cycle of a line scanner can limit the useful output illumination per unit of input power from a laser or other light source. Accordingly, a low duty cycle line scanner requires either a higher power light source, more efficient optics, or a slower scan rate to provide a fixed amount of useful illuminating energy density. Accordingly, line scanners having high duty cycles are sought.
Another important property of line scanners is the imaging area or scan line length. Conventionally, creating long scan lines to cover a large imaging area requires either a large line scanner or multiple smaller line scanners operated in series. Using multiple line scanners (or scan heads) to create a long scan line has a number of advantages including the ability to design smaller or more compact systems with less expensive scanning heads. However, multiple-head systems often require elaborate and expensive line-connecting optics or electronics to control the relative positions of the scan lines from the various scan heads and to synchronize the independently operating scan heads. This is due in part to the lack of synchronization of the motion of the light sources and the scanning optics in the multiple scan heads. U.S. Pat. No. 5,654,817 describes a system employing multiple scan heads for large area imaging. Line scanners that are compact and do not require expensive line connecting optics or electronics are desired.
SUMMARY
In accordance with an embodiment of the invention, a high duty scanner has a single compact scan head capable of creating multiple synchronized scan lines. The scan lines are easily connected because a single scanning element provides a common reference for the multiple scan lines and in some embodiments because a common light source is oriented relative to each input beam so that motion of the light source manifests itself in each scan line in both the same direction and magnitude to provide synchronization. One embodiment of the invention redirects an input beam to increase the duty cycle of a scanner. In particular, pre-scan optics move an input beam from a first area for incidence on a scanning element to a second area for incidence on a scanning element. In alternate embodiments, the first and second areas contain portions of a single scanning element or alternatively portions of two separate scanning elements. Moving the input beam from the first to the second area occurs when the scanning beam reaches the end of a scan line but the scanning element has not positioned another facet in the first area for the start of another scan line. Upon movement of the input beam, the second facet immediately directs the scan beam into the image area for another scan line or for an extension of a scan line originated from the first facet. Moving the input beam thus can increase the duty cycle by increasing the time during which the scan beam is in the image area. The scan line length increases when second facet extends a scan line the first facet previously started.
Alternatively, multiple input beams either derived from a common light source and beam splitters or from multiple light sources, are directed to multiple separated areas on a single scanning element to generate multiple synchronized scan lines. Timing of the multiple scan lines depends on the relative positions of the incident areas of the multiple input beams so that scan lines can be simultaneously or sequentially scan.
The synchronized scan lines can be used separately in applications such as color laser printing or can be aligned for formation of a single extended scan line. Whether simultaneous input beams or alternating input beams are used, a single scanning element and/or light source simplifies alignment of multiple scan lines for formation of an extended scan line because many variations of the scanning element and light source are common to all of the scan lines that constitute the extended scan line.
In one embodiment of the invention a scanner includes a scanning element such as a holographic disc or a polygon mirror and an illumination system that directs a first input beam to a first area and a second input beam to a second area. The first and second areas are separated from each other and situated so that portions of the scanning element move through the first and second areas during a scanning operation. First and second scan beams respectively originate from deflections of the first and second input beam by portions of the scanning element in the first and second areas. The input beams encountering the scanning element are oriented so that motion of both scan beams are synchronized for a given light source motion, and thus motion of the light source does not affect synchronization or alignment of the scan beams. Post-scan optics direct the first and second scan beams to illuminate first and second scan lines which can be used separately or aligned for joining that forms of an extended scan line. When the scan lines are aligned, a beam detector assembly can be positioned between the scanning element and an image plane in which the extended scan line is formed and in a gap between a path of the first scan beam to the end of the first scan line and a path of the second scan beam to the start of the second scan line. In one embodiment, the detector assembly is mounted on the back of a mirror having a first mirrored section positioned to reflect the first scan beam, a second mirrored section positioned to reflect the second scan beam, and a transparent section between the first and second mirrored sections.


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