Apparatus for scanning a document

An apparatus for scanning documents combines digitizing circuitry with a scanning platen to achieve precise selection of image areas on large documents. A vacuum system holds the document in place against a perforated scanning surface during registration and scanning. The assembly of scanning surface, vacuum chamber, and digitizing circuitry move as a unit beneath a fixed scanning apparatus. The apparatus further has a mechanical structure which allows the table assembly to rotate about a pivot axis toward an operator to reduce parallax error in mapping image areas.

BACKGROUND OF THE INVENTION 
The invention relates generally to scanning documents and in particular, to 
apparatus for scanning selected portions of large documents. 
Various systems have been used for selecting portions of a document to be 
scanned. According to one approach, the original document is placed on a 
digitizer pad where the area to be scanned is mapped by an operator using, 
for example, a cross-hairs device to define coordinates of selected 
boundaries, and the coordinates are entered into a computer through the 
digitizing mechanism. The document is then transferred to a scanning 
table, using a known registration, and the stored coordinates are 
recalled. As the document is scanned, only the area within the designated 
boundaries is recorded, while the area outside the designated boundaries 
is excluded. 
Errors often occur in this procedure as the original document is 
transferred from the digitizing pad to the scanning table surface. The 
precise coordinates recorded from the digitizer may not precisely match 
the scanned area if the document has been placed out of registration on 
the scanning table, or if the document moves during registration or 
scanning, for example, because of air currents. 
Additionally, since the procedure described above can be used with 
documents having a width of eighteen inches or more, errors are often made 
in mapping a selected image area, since an operator may be viewing the far 
side of a document from an angle as he leans over the digitizer pad. As a 
result, incorrect coordinates may be selected for the desired image area. 
A primary object of the invention is an apparatus which ensures that the 
precise coordinates chosen on the digitizer pad match the scanned area of 
the document. Another object of the invention is an apparatus which aids 
the operator in accurately designating coordinates of the image area to be 
scanned. Further objects of the invention are a simple, accurate, and 
reliable scanning apparatus. 
SUMMARY OF THE INVENTION 
The invention relates to an apparatus which combines digitizing circuitry 
with a scanning platen in one moving assembly unit. A digitizer is 
installed beneath the surface of a scanning platen so that a document, 
once placed on the platen, can be both digitized and scanned without being 
repositioned. A vacuum chamber is created between the scanning platen and 
the active digitizer surface, so that the document is held in place 
through a vacuum at holes on the surface of the platen. The assembly of 
digitizer, vacuum chamber, and perforated scanning platen move as a unit 
beneath the fixed scanning apparatus. 
In another aspect of the invention, the apparatus features a mechanism for 
tilting the table on which the scanning optics, scanning platen, and 
digitizer rest. A linear actuator enables the operator to rotate the table 
at an angle of up to 20.degree. to thus rotate the document toward him for 
more precise coordinate selection using, for example, a cross-hairs device 
.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to FIG. 1, the invention relates to a laser scanning apparatus 8 
for effecting precision recording of designated portions of a scanned 
document 16. The apparatus 8 has a base 10, a table assembly 12, a 
scanning optics assembly 14, a control console 15, and a moveable platen 
assembly 18. 
In the illustrated embodiment, the document 16 is placed on the moveable 
platen assembly 18 where coordinates of a selected image area are mapped 
and stored electronically. The moveable assembly is supported by a table 
support 19 of table assembly 12 and moves along a guide rail 20, driven by 
a motor 22 and lead screw 30. The moveable assembly 18 carries the 
document underneath scanning optics assembly 14. When the document is 
scanned, the electronically stored coordinates are recalled and only the 
image area designated by the coordinates is recorded. An elevation 
mechanism 24 allows the scanning optics of assembly 14 to be adjusted, as 
is well known in the art, with respect to the thickness of the document 
being scanned. 
Referring to FIG. 2, the mechanics for moving the document beneath the 
scanning assembly are shown. The moveable assembly 18 moves along a guide 
rail structure 26, contact being through bearing assemblies 27, 28, and 
29. The assembly rolls along guide rail 20 when the lead screw 30, which 
passes through a coupling 31, is rotated by drive motor 22. The guide rail 
is supported by the table support 19 at rail supports 32. The moving 
assembly contacts the guide rail 20 through bearing assemblies 27, 28 to 
control horizontal movement and is supported by guide rail 20 through 
bearing assembly 29 to fix the vertical position. 
Referring to FIGS. 3 and 1A the moveable assembly 18 is also guided and 
supported in the vertical direction on each side by support bearings 34. 
The bearings 34 contact guide rods 37a, 37b supported by side supports 
37c, 37d of table base 19. 
Referring to FIG. 4, a vacuum connection 38, is attached to a vacuum pump 
40 at one end, and vacuum connector 41 which is in fluid communication 
with two vacuum channels 42 at an end of assembly 18. FIGS. 5 and 6 shows 
the vacuum system in more detail. The document is held in place on a 
perforated top plate 44 of the moveable assembly by suction created at 
holes 45 through which air is drawn into a vacuum chamber formed between 
the bottom surface of the top plate and the digitizer structure 47. FIG. 6 
shows the perforated top plate 44, a plurality of spacer strips 56, and a 
digitizer wire grid 50. A protective sheet 58 covers the wire grid 50. A 
nonmetallic base 52 supports the wire grid 50 and the protective sheet 58. 
The nonmetallic base 52 is surrounded by a supporting aluminum extrusion 
edging structure 62. 
Vacuum chamber 46 is connected to vacuum channels 42, which are separated 
from each other by an angle 62 which contains evenly distributed holes, 
for example six. As noted above, vacuum channels 42 are attached to the 
vacuum connection 38 of FIG. 4. 
Again referring to FIG. 5, the digitizer pad is a wire grid 50, such as 
that commercially available from Numonics Corp. The wires of the grid 
cross at right angles. Nonmetallic base 52 separates the digitizer pad 50 
from a supporting steel plate 54. Perforated top plate 44 is separated 
from the wire grid of digitizer pad 50 by a plurality of parallel, spaced, 
spacer strips 56, as shown in further detail in FIG. 6. 
As described above, perforated top plate 44 holds documents up to 18" wide. 
In the preferred embodiment of the invention, a cross-hair device is slid 
over and in contact with the document 16. Since the cross-hairs are spaced 
from the document surface, the angle of view can adversely affect the 
precision of the marking device. Preferably, the operator's view should be 
directly over the cross-hairs. When an operator selects points on the far 
side of a document from the near side of the table, it is difficult and/or 
impractical to view the document in this ideal manner. According to the 
invention, therefore, table assembly 12, which supports the digitizer and 
the document to be scanned as well as the scanning optics assembly and the 
control console, is designed to rotate toward the operator about a pivot 
axis 63. Referring to FIG. 7, pivot connections at pivot points 64a and 
64b allow the table to be rotated about the fixed axis 63. In the 
illustrated embodiment, referring to FIG. 7A, a linear actuator 66 lifts 
one side of the table opposite pivot points 64a, 64b to an angle of 
between 0.degree.-20.degree.. Linear actuator 66 is supported by base 10 
at 68 and hingedly connects to table assembly 12 at 70. The degree of 
rotation is determined under operator control. Thereafter, the operator 
can precisely locate the points of interest anywhere on the document 
without parallax error. 
Additions, subtractions, deletions, and other modifications of the claimed 
invention will be apparent to those practiced in the art and are within 
the scope of the following claims.