Transparent sheet-like pad with reflective grid layer to provide position information to an optical reader

A sheet-like pad having a grid pattern constituted by X-axis grid lines and Y-axis grid lines perpendicular to the X-axis grid lines, and adapted to be placed between a document and an optical reader of a type which comprises an optical scanner for scanning the document to read an image on the document while the document is radiated with first rays of light emitted therefrom and a position sensor for reading the grid pattern for locating the position of the optical reader on the document while the document is radiated with second rays of light emitted therefrom. The sheet-like pad comprises a film-like base having upper and lower surfaces opposite to each other, reflective layers formed on the upper surface of the base for periodically reflecting the second rays of light in first and second directions perpendicular to each other, and a protective layer formed on the upper surface of the base so as to overlay the reflective layers. Each of the base and the protective layer is made of material capable of passing therethrough both of the first and second rays of light.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to an optical reader for reading 
characters and/or graphic presentations which comprises an optical scanner 
having a position sensor, and more particularly, to a sheet-like pad for 
use with the optical reader. More specifically, the present invention 
relates to the sheet-like pad adapted to be laid below the optical reader 
for providing position information to the position sensor as the optical 
reader is moved above the sheet-like pad. 
2. Description of the Prior Art 
An optical reader of the type referred to above includes an optical scanner 
for reading, and providing an electric signal indicative of alphanumeric 
characters and/or graphic presentations depicted or reproduced on a sheet 
such as, for example, a sheet of paper. An example of this type of optical 
reader hitherto proposed is disclosed in, for example, Japanese Laid-open 
Patent Publication No. 1-500553 and U.S. Pat. No. 4,751,380. 
The position sensor used in the prior art optical reader is an important 
tool to enable the optical reader to reproduce characters and/or graphic 
presentations accurately at required positions, by optically monitoring 
positional information imparted to the sheet or paper, when the characters 
and/or graphic presentations are printed out, displayed on a display 
device and/or stored in a data storage unit. In order for the positional 
information to be read by the optical scanner, a specially processed 
transparent film generally known as a sheet-like pad is utilized in 
association with the optical scanner. 
The sheet-like pad referred to above has a grid pattern formed thereon or 
therein, having a plurality of equally spaced X-axis grid lines and a 
plurality of equally spaced Y-axis grid lines perpendicular to the X-axis 
grid lines. When in use, the sheet-like pad is laid beneath the optical 
scanner, particularly the position sensor, so that the latter can move 
above the sheet-like pad. As the position sensor is moved above the 
sheet-like pad traversing the grid lines, the position sensor counts the 
number of the grid lines which have been traversed thereby. The number of 
the grid lines so counted by the position sensor is converted into an 
electric signal representative of positional information which is 
subsequently issued by the optical scanner as a whole. 
The sheet-like pad of the type used in the above described manner in 
association with the optical reader is required to satisfy the following 
requirements. 
In the first place, the sheet-like pad must have a property that infrared 
rays of light emitted from the position sensor can be reflected by the 
sheet-like pad in a quantity greater than a predetermined value. Secondly, 
the grid pattern on the sheet-like pad should be such that a light 
responsive element sensitive to the infrared rays of light emitted from 
the position sensor can recognize the grid lines. In other words, the grid 
pattern on the sheet-like pad should include reflective and non-reflective 
areas alternating at predetermined intervals, said reflective areas being 
effective to reflect the infrared rays of light emitted from the position 
sensor. Finally, the sheet-like pad must have a transparency required for 
the optical scanner to receive rays of light, that is, must have a high 
light transmissivity with respect to visible rays of light. 
An example of a prior art sheet-like pad hitherto designed to satisfy all 
of the foregoing requirements is schematically illustrated in FIGS. 12 to 
14, reference to which will now be made for the purpose of discussion of 
the prior art believed to be pertinent to the present invention. 
Referring first to FIG. 12 showing a perspective view of the prior art 
sheet-like pad 11, the sheet-like pad 11 is in the form of a film and has 
a periodic grid pattern of X-axis and Y-axis grid lines 12 forming square 
areas of uniform size thereon. FIG. 13 illustrates, on an enlarged scale, 
a portion of the sheet-like pad 11, and the grid lines generally 
identified by 12 are areas capable of absorbing infrared rays of light 
while the square areas of uniform size delimited by the grid lines 12 and 
generally identified by 13 are reflective area capable of reflecting the 
infrared rays of light. 
As best shown in the sectional representation of FIG. 14, the sheet-like 
pad 11 is a multi-layered structure including a base layer 15 of polyester 
film, an infrared reflective layer 16, formed on one surface of the base 
layer 15 and capable of reflecting the infrared rays of light, and a 
protective layer 18. The infrared reflective layer 16 is of a multilayer 
structure including an Au-Ag alloy layer and an InO.sub.2 layer. The grid 
lines 12 forming the grid pattern are in the form of infrared absorbing 
layers 17 formed on one surface of the infrared reflective layer 16 
opposite to the base layer 15 by the use of any known screen printing 
technique. The infrared absorbing layers 17 forming the grid lines 12 
contain a dyestuff having an infrared absorbility extremely higher than 
its absorbability to the visible rays of light. The dyestuff contained in 
the infrared absorbing layer 17 may be a commercially available dyestuff 
such as, for example, IRA-870 manufactured and sold by EXCITON CHEMICAL of 
U.S.A. 
The protective layer 18 is for the purpose of protecting square portions of 
the infrared reflective layer 16, which essentially form the square areas 
13, and the infrared absorbing layers 17, which essentially form the grid 
lines 12, from damage which may be brought about by the contact of the 
optical reader with the sheet-like pad 11, and for this purpose, this 
protective layer 18 is formed on the infrared reflective layer 16 so as to 
overlay the infrared absorbing layers 17. 
With the prior art sheet-like pad 11 so constructed as hereinabove 
described, as best shown in FIG. 14, infrared rays of light 20 emitted 
from the position sensor so as to be incident upon the sheet-like pad 11 
at an angle of incidence of 30.degree. relative to the normal to the 
surface of the sheet-like pad are reflected in part by the non-reflective 
square areas 13, i.e., respective portions of the infrared reflective 
layer 16 which are not occupied by the infrared absorbing layers 17 
forming the grid lines 12, and in part absorbed by the grid lines 12. On 
the other hand, visible rays of light 21 radiated by the optical scanner 
so as to be incident upon the sheet-like pad 11 at an angle of incidence 
of 45.degree. relative to the normal to the surface of the sheet-like pad 
11 are allowed to pass through both of the infrared reflective layer 16 
and the infrared absorbing layers 17. Accordingly, the visible rays of 
light 21 pass through the sheet-like pad 11 to reach a document 22 placed 
underneath the sheet-like pad 11 and are then reflected by the document 
22. The visible rays of light 21 so reflected by the document 22 carry 
image information descriptive of alphanumeric characters and/or graphic 
presentations on one surface of the document 22 and, hence, form the 
imagewise rays of light. The imagewise rays of light reflected from the 
document 22 subsequently pass through the sheet-like pad 11, specifically 
through only the infrared reflective layer 16 or both of the infrared 
reflective layer 16 and the infrared absorbing layers 17, and are 
eventually detected by the optical scanner. 
Thus, while the infrared rays of light radiated by a infrared light source 
built in the position sensor are repeatedly reflected and absorbed so that 
the infrared light receiver also built in the position sensor can provide 
an electric signal (binary signals) synchronized with a periodic structure 
of the grid lines 12, the counting of the binary signals generated from 
the infrared light receiver in the position sensor can result in a 
detection of the position of the optical reader on the document. 
The prior art sheet-like pad 11 of the above described structure has been 
found to have problems. Specifically, since the visible rays of light 21 
pass through the infrared reflective layer 16 at least twice with portion 
of the visible rays of light 21 passing additionally through the infrared 
reflective layers 17 as indicated by broken lines 21a in FIG. 14, 
attenuation of light takes place and, therefore, the efficiency of 
utilization of the rays of light tends to be lowered. 
Also, in order for the infrared absorbing layers 17 forming the fine grid 
lines 12 to be formed on the infrared reflective layer 16 in the form of 
the periodic structure by the use of the screen printing technique, the 
screen printing is required to be repeated several times while work 
parameters such as, for example, the temperature of material for the 
infrared absorbing layers 17, the condition of the base layer 15 and the 
infrared reflective layer 16, the printing speed and the printing 
direction are strictly managed and controlled. Accordingly, it is not easy 
to manufacture sheet-like pads of uniform quality. It is eventually 
pointed out that the conventional screen printing is ineffective to 
provide the grid pattern of grid lines 12 which satisfies a required 
dimensional precision. 
Furthermore, the formation of the infrared reflective layer 16 over the 
entire surface of the base layer 15 by the use of a coating technique 
requires an increased consumption of a coating material, resulting in an 
increased cost of manufacture of the sheet-like pad. 
SUMMARY OF THE INVENTION 
The present invention has been developed with a view to substantially 
eliminating the above discussed problems inherent in the prior art 
sheet-like pad and is intended to provide an improved sheet-like pad of a 
type having a grid pattern constituted by X-axis grid lines and Y-axis 
grid lines perpendicular to the X-axis grid lines, and adapted to be 
placed between a document and an optical reader of a type which comprises 
an optical scanner for scanning the document to read an image on the 
document while the document is radiated with first rays of light emitted 
therefrom and a position sensor for reading the grid pattern for locating 
the position of the optical reader on the document while the document is 
radiated with second rays of light emitted therefrom. 
In accordance with the present invention, the sheet-like pad comprises a 
film-like base having upper and lower surfaces opposite to each other, 
reflective layers formed on the upper surface of the base for periodically 
reflecting the second rays of light, and a protective layer formed on the 
upper surface of the base so as to overlay the reflective layers. The 
reflective layers may be formed either in a grid pattern with the grid 
lines constituted by the reflective layers or in a matrix of rows and 
columns leaving square areas defined by the reflective layers and 
delimited by non-reflective grid lines, through which lines the first and 
second rays of light can pass. Each of the base and the protective layer 
is made of material capable of passing therethrough both of the first and 
second rays of light. 
With the sheet-like pad constructed according to the present invention, no 
infrared absorbing layer hitherto employed in the prior art sheet-like pad 
is required and, therefore, the first rays of light emitted from the 
scanner will not pass through the infrared absorbing layer, and that a 
portion of the first rays of light merely pass through the reflective 
layers once or twice according to the present invention. Therefore, an 
attenuation of the first rays of light can be advantageously minimized, 
permitting a maximized utilization of the rays of light. Particularly in 
the case where the reflective layers from respective square areas 
delimited by the non-reflective grid lines forming the grid pattern such 
as in the second mentioned preferred embodiment of the present invention, 
the total area of surface occupied by the reflective layers can be made 
smaller than that of the system wherein the grid lines are defined by the 
reflective layers, thereby achieving an increased efficiency of 
utilization of the rays of light used in the system as a whole. 
Also, the reflective layers can be formed into the requisite structure by 
the use of any known photo-etching technique, and therefore, the 
sheet-like pad according to the present invention can readily and easily 
be assembled or manufactured with a stabilized quality. The use of the 
photo-etching technique should achieve a high dimensional precision of the 
reflective layers as compared with the conventional screen printing. 
In addition, since the reflective layers are formed into the requisite 
structure, the amount of material used to form the reflective layers can 
be less as compared with the prior art sheet-like pad in which the 
reflective layers are formed all over the base layer.

DETAILED DESCRIPTION OF THE EMBODIMENTS 
Before the present invention is described, an optical reader with which the 
present invention can be utilizable will first be described with 
particular reference to FIGS. 1, to 7. Referring first to FIG. 1 showing a 
bottom plan view of the optical reader 25, the latter comprises a housing 
26 accommodating therein an optical scanner 27 operable with first rays of 
light such as visible rays of light and a pair of position sensors 28 
positioned on respective sides of the optical scanner 27 and operable with 
second rays of light such as infrared rays of light. The housing 26 of the 
optical reader 25 includes a bottom wall having defined therein a 
generally rectangular light receiving window 29 associated with the 
optical scanner 27. The bottom wall of the housing 26 also has a pair of 
apertures, one for each of the position sensors 28, through which aperture 
light projecting and collecting lenses 30 and 31 are exposed to the 
outside. The optical scanner 27 and the position sensors 28 are 
electrically connected with an external signal processing circuit through 
respective lead lines 23 and 24. 
As best shown in FIG. 2, the optical scanner 27 and the position sensors 28 
are so arranged and so positioned that the optical scanner 27 can read a 
document 32 to be read and the position sensors 28 can read positional 
information originating from a sheet-like pad 33 positioned so as to 
intervene between the optical reader 25 and the document 32. 
The optical scanner 27 referred to above comprises, as best shown in FIG. 
3, a scanner casing 35 accommodating therein a pair of light sources 36 
for radiating the document 32 with visible rays of light L1, a light 
receiver 37 comprised of an array of photosensitive light receiving 
elements operable to detect imagewise rays of light originating from the 
light sources 36 and subsequently reflected by the document 32 within a 
predetermined time and also to convert the detected imagewise rays of 
light into an electric signal, and a lens assembly 38 for focusing the 
reflected visible rays of light L1 on the light receiver 37. The scanner 
casing 35 is not only to support the required component parts of the 
optical scanner 27 therein, but also to shield the interior of the scanner 
casing 35 from external rays of light which would otherwise constituted an 
external disturbance to the rays of light emitted by the light sources 36 
and utilized by the light receiver 37. The light receiver 37 is 
electrically connected with an image signal processing circuit 39 
positioned outside the scanner casing 35 and operable to perform an image 
processing and also to store processed image signals. 
Each of the position sensors 28 comprises, as best shown in FIG. 4, a 
sensor casing 41 accommodating therein, a light source 42 for radiating 
the sheet-like pad 33 with infrared rays of light L2, a light projecting 
lens 30 operable to project the infrared rays of light L2 from the 
infrared light source 42 therethrough towards the document 32 accurately 
in a required light quantity and in a required width, an infrared light 
receiver 43 comprised of an array of photosensitive light receiving 
elements for sensing the infrared rays of light L2 which have been 
reflected from the document 32, a light collecting lens 31 operable to 
converge the infrared rays of light L2, reflected from the document 32 and 
travelling towards the infrared light receiver 43, so as to be accurately 
received by the infrared light receiver 43, and a reflecting mirror 44 
interposed between the light collecting lens 31 and the infrared light 
receiver 43 for reflecting the infrared rays of light L2, collected by the 
light collecting lens 31, towards the infrared light receiver 43 so as to 
be focused thereon. 
As is the case with the scanner casing 35 referred to hereinbefore in 
connection with the optical scanner 27, the sensor casing 41 is not only 
to support the required component parts of the position sensors 28 
therein, but also to shield the interior of the sensor casing 41 from 
external rays of light which would otherwise constitute an external 
disturbance to the rays of light emitted by the infrared light source 42 
and utilized by the infrared light receiver 43. The infrared light 
receivers 43 of the position sensors 28 are electrically connected with a 
position signal processing circuit 45 positioned outside the sensor casing 
41 and operable to perform an arithmetic operation and a storage of 
position signals. 
The array of the photosensitive light receiving elements forming the 
infrared light receiver 43 in each of the position sensor 28 are generally 
identified by 47 in FIG. 5 and are arranged in a pattern as shown in FIG. 
5. The pattern so far shown in FIG. 5 is made up of a pair of first 
divided, rectangular pattern areas 48 and 49, confronting with each other 
in an X-axis direction, and a pair of second divided, rectangular pattern 
areas 50 and 51, confronting with each other in a Y-axis direction 
perpendicular to the X-axis direction, and twelve photosensitive light 
receiving elements 47 are arranged in that pattern with each six elements 
47 positioned within each rectangular pattern area 48 to 51. More 
specifically, assuming that the photosensitive light receiving elements 47 
forming the infrared light receiver 43 are respectively designated by A, 
B, C, D, E, F, I, J, K, L, M and O as shown in FIG. 5 although the 
characters A to F and I to O are used as respective symbols allocated to 
output signals from the photosensitive light receiving elements as seen 
below, the elements A, B, E, I, J and M and the element C, D, F, K, L and 
O are positioned within the first divided, rectangular pattern area 48 and 
the first divided, rectangular pattern area 49, respectively, whereas the 
elements A to F and the elements I to O are positioned within the second 
divided, rectangular pattern area 50 and the second divided, rectangular 
pattern area 51. 
The relationship between the pattern of the photosensitive light receiving 
elements 47 and grid lines 55 forming a grid pattern on the sheet-like pad 
33 is shown in FIG. 6. Referring to FIG. 6, the width W of grid line 55 
extending in the X-axis direction is so chosen as to be within the range 
of 90 to 100% of the interval Py between the adjoining second divided 
pattern areas 50 and 51 oriented in the Y-axis direction as shown in FIG. 
5, and the same is with the width W of grid line 55 extending in the 
Y-axis direction which is equal to the width W in the X-axis direction and 
which is chosen to be within the range of 90 to 100% of the interval Px 
between the adjoining first divided pattern areas 48 and 49 oriented in 
the Y-axis direction. 
When respective outputs A to F and I to O from the twelve photosensitive 
light receiving elements 47 are processed in the position signal 
processing circuit 45 (FIG. 4) according to equations shown in FIG. 7 to 
provide two-phase electric signals XA, YA, XB and YB. The detection of 
set-up and set-down of each of the electric signals XA and XB can result 
in a detection of an X-axis coordinate defined by the grid lines 55 on the 
sheet-like pad 33, whereas the detection of set-up and set-down of each of 
the electric signals YA and YB can result in a detection of a Y-axis 
coordinate defined by the same grid lines 55. 
Referring now to FIGS. 8 and 9, there is shown the sheet-like pad 33 
designed according to a first preferred embodiment of the present 
invention. As shown in FIG. 8, the sheet-like pad 33 has a grid pattern 
comprised of grid lines 55 some extending in the X-axis direction and the 
remainder in the Y-axis direction. Each neighboring X-axis oriented grid 
lines 55 are spaced a predetermined pitch (periodicity) D2 and each 
neighboring Y-axis oriented grid lines 55 are spaced a predetermined pitch 
(periodicity) D1. 
The details of the sheet-like pad 33 having the above described grid 
pattern are best shown in FIG. 9. As shown therein, the sheet-like pad 33 
comprises a multi-layered structure including a base layer 56 capable of 
passing both of the rays L1 and L2 therethrough and having an upper 
surface formed with a grid pattern of X-axis oriented and Y-axis oriented 
reflective layers 57 laid so as to cross with each other, said reflective 
layers 57 forming the grid lines 55. Each neighboring reflective layers 57 
oriented in the X-axis direction and in the Y-axis direction are spaced an 
equal distance from each other. The multi-layered structure of the 
sheet-like pad 33 also includes a transparent protective layer 58 formed 
on the base layer 56 so as to overlay the grid-patterned reflective layers 
57, which layer 58 is made of material of a property capable of passing 
both visible and infrared rays of light L1 and L2 therethrough. 
With the sheet-like pad 33 so constructed as hereinabove described, as 
shown in FIG. 9, the infrared rays of light L2 emitted from the position 
sensor 28 so as to be incident upon the reflective layers 57 at an angle 
of incidence of 30.degree. relative to the normal to the surface of the 
sheet-like pad 33 are reflected by the reflective layers 57 in an 
extremely great quantity while the rest of the infrared rays of light L2 
are passed therethrough. Also, the infrared rays of light L2 similarly 
emitted from the position sensor 28 so as to be incident upon portions of 
the base layers 56 delimited by the reflective layers 57 are passed 
therethrough without being substantially reflected thereby. Thus, the 
infrared rays of light L2 emitted from the position sensor 28 are in part 
reflected by the grid-patterned reflective layers 57 and in part passed 
through those portions of the base layer 56 delimited by the 
grid-patterned reflective layers 57 and, therefore, the position sensor 28 
can provide binary signals (the respective waveforms of which are shown in 
FIG. 7) synchronized with the periodic structure of the grid lines 55. By 
counting the electric signals from the position sensors 28, the position 
of the optical reader on the document can be detected. 
On the other hand, visible rays of light L1 radiated by the optical scanner 
27 so as to be incident upon the reflective layers 57 at an angle of 
incidence of 45.degree. relative to the normal to the surface of the 
sheet-like pad 33 are reflected by the reflective layers 57 in an 
extremely small quantity while the rest of the visible rays of light L1 
are allowed to pass therethrough. Also, the visible rays of light L1 
similarly emitted from the optical scanner 27 so as to be incident upon 
those portions of the base layer 56 delimited by the grid-patterned 
reflective layers 57 are allowed to pass therethrough without being 
reflected thereby. Thus, the visible rays of light L1 having passed 
through the sheet-like pad 33 are subsequently reflected by the document 
32 placed beneath the sheet-like pad 33 with the reflected visible rays of 
light L1 consequently carrying image information descriptive of 
alphanumeric characters and/or graphic presentations on one surface of the 
document 32. The imagewise rays of light subsequently pass through the 
sheet-like pad 33, having passed in a major quantity through the 
reflective layers 57 and are eventually detected by the optical scanner 
27. 
The sheet-like pad 33 according to another preferred embodiment of the 
present invention is shown in FIGS. 10 and 11. As shown in FIG. 10, the 
sheet-like pad 33 has a grid pattern comprised of grid lines 55a some 
extending in the X-axis direction and the remainder in the Y-axis 
direction. Each neighboring X-axis oriented grid lines 55a are spaced a 
predetermined pitch (periodicity) D2 and each neighboring Y-axis oriented 
grid lines 55a are spaced a predetermined pitch (periodicity) D1. Unlike 
the grid lines 55 in the foregoing embodiment of the present invention, 
the grid lines 55a in this preferred embodiment are delimited by generally 
square reflective layers 57a operable to reflect the infrared rays of 
light L2 and formed, as will be described later in detail, on the base 
layer 56 in a generally dot-like pattern. 
Referring now to FIG. 11, the sheet-like pad 33 according to the embodiment 
shown therein comprises a multi-layered structure including the base layer 
56 having an upper surface formed with a generally dot-like pattern of 
X-axis oriented and Y-axis oriented reflective layers 57a laid thereon so 
as to leave the discrete grid lines 55a defined by portions of the base 
layer 56 and capable of passing both the rays L1 and L2 therethrough. Each 
neighboring rows of reflective layers 57a oriented in the X-axis direction 
are spaced an equal distance from each other and, similarly, each 
neighboring columns of reflective layers 57a oriented in the Y-axis 
direction are spaced an equal distance from each other. The multi-layered 
structure of the sheet-like pad 33 also includes a transparent protective 
layer 58 formed on the base layer 56 so as to overlay the patterned 
reflective layers 57a, which layer 58 is made of material of a property 
capable of passing both visible and infrared rays of light L1 and L2 
therethrough. 
Even though the sheet-like pad 33 is so constructed as hereinabove 
described with reference to FIGS. 10 and 11, it can work in a manner 
similar to that according to the foregoing embodiment shown in and 
described with reference to FIGS. 8 and 9. Specifically, the infrared rays 
of light L2 emitted from the position sensor 28 are in part reflected by 
the patterned reflective layers 57a and in part passed through the 
discrete grid lines 55a, i.e., those portions of the base layer 56 
delimited by the reflective layers 57a and, therefore, the position sensor 
28 can provide binary signals which are subsequently counted to provide 
information descriptive of the position of the optical reader on the 
document 32. 
In accordance with the present invention, where any one of the pitches D1 
and D2 between each neighboring grid lines 55a and 55a is within the range 
of 0.33 to 0.34 mm, the width W of each reflective layer 57 should be 
chosen to be within the range of 0.16 to 0.17 mm as will be described 
later and should not be smaller than 0.16 mm. Because of this, in the 
first preferred embodiment shown in and described with reference to FIGS. 
8 and 9, the total area of surface occupied by the reflective layers 57 
forming the grid lines 55 will be relatively large. In contrast thereto, 
in the second preferred embodiment shown in and described with reference 
to FIG. 10 and 11, since the reflective layers 57a leave respective 
portions of the base layer 56 not occupied by the reflective layers 57a 
thereby to define square areas of uniform size in the grid pattern, the 
total area of surface occupied by the reflective layers 57a is relatively 
small. In practice, where each pitch D1 and D2 and the width W are chosen 
to be 0.34 mm and 0.17 mm, respectively, the total area of surface 
occupied by the reflective layers according to the second preferred 
embodiment of the present invention was found to be one third of that 
according to the first preferred embodiment of the present invention. 
Accordingly, since the amount of the visible rays of light L1 passing 
through the reflective layers 57a is small, the efficiency of utilization 
of the visible rays of light L1 according to the second preferred 
embodiment of the present invention is extremely higher than that 
according to the first preferred embodiment thereof. 
In order for the position sensor 28 to exhibit a high operating precision, 
the reflective layers 57 or 57a should have a high reflectivity to the 
infrared rays of light L2 and also has a high light transmissivity to the 
visible rays of light L1. The reflectivity exhibited by each reflective 
layer 57 or 57a when near-infrared rays of light of 880 nm in wavelength 
are radiated so as to be incident upon such reflective layer 57 or 57a at 
an angle of incidence of 30.degree. relative to the normal to the surface 
of the sheet-like pad 33 is preferred to be equal to or higher than 20% 
and the light transmissivity exhibited by the same reflective layer 57 or 
57a when visible rays of light of 570 or 660 nm in wavelength are radiated 
so as to be incident upon such reflective layers 57 or 57a at an angle of 
incidence of 45.degree. relative to the normal to the surface of the 
sheet-like pad 33 is preferred to be equal to or higher than 40%. 
Summarizing the foregoing, where the near-infrared rays of light of 880 nm 
in wavelength and the visible rays of light of 570 or 660 nm in wavelength 
are utilized, each reflective layer 57 or 57a employed in the practice of 
the present invention is preferably of a type capable of reflecting 20% or 
a higher amount of the near-infrared rays of light and passing 40% or a 
higher amount of the visible rays of light. 
Each reflective layer 57 or 57a capable of reflecting the infrared rays of 
light as hereinbefore described may be in the form of a single reflective 
layer made of material capable of exhibiting a high reflectivity relative 
to the infrared rays of light and a high light transmissivity relative to 
the visible rays of light, such as, for example, gold, silver, copper or 
chromium. Alternatively, each reflective layer 57 or 57a may be in the 
form of a multi-layered structure comprising a dielectric layer of high 
refractive index made of, for example, Ta.sub.2 O.sub.5 or TiO.sub.2 and a 
dielectric layer of low refractive index made of, for example, MgF.sub.2 
or SiO.sub.2 or a metallic layer made of, for example, Au or Cu, which 
have respective appropriate thicknesses and which are alternately laid one 
above the other so that the reflective layer 57 or 57a as a whole can 
exhibit a high reflectivity relative to the infrared rays of light and a 
high light transmissivity relative to the visible rays of light. 
Where the reflective layer 57 or 57a is in the form of the single 
reflective layer, either a copper layer of a thickness within the range 
of, for example, 30 to 60 .ANG. or a gold layer of a thickness within the 
range of, for example, 40 to 80 .ANG. is preferred. On the other hand, 
where the reflective layer 57 or 57a is in the form of the multi-layered 
structure, a three-layered structure including TiO.sub.2, Au and TiO.sub.2 
layers laid one above the other in the order given above from the base 
layer 56 is preferred. 
In any event, the reflective layers 57 or 57a can be formed by forming an 
infrared reflective layer uniformly over the entire surface of the base 
layer 56 by the use of a vacuum evaporation method, a sputter coating 
method or an electro-depositing method and then removing unwanted portions 
of the reflective layer by the use of a photo-etching method to form the 
patterned reflective layers 57 or 57a. 
Both of the base layer 56 and the protective layer 58 are made of polyester 
or glass and are of a type that the light transmissivity exhibited 
thereby, when the visible rays of light of 570 or 660 nm in wavelength are 
radiated so as to be incident upon such layer 56 or 58 at an angle of 
incidence of 45.degree. relative to the normal thereto, and the light 
transmissivity exhibited thereby when the near-infrared rays of light of 
880 nm in wavelength are radiated so as to be incident upon such layer 56 
or 58 at an angle of incidence of 30.degree. relative to the normal 
thereto can be equal to or higher than 50%, preferably 70% or higher. 
Where the pitch D1 or D2 shown in FIGS. 8 and 10 is within the range of 
0.33 to 0.34 mm, the width W of each reflective layer 57 or 57a is 
preferred to be within the range of 0.16 to 0.17 mm. If the width W is 
smaller than 0.16 mm, it will give a small quantity of the infrared rays 
of light L2 reflected thereby and, therefore, the detection of the grid 
pattern, that is, the positional information, by the position sensors 28 
will be difficult. On the other hand, if the width W is greater than 0.17 
mm, the light transmissivity to the visible rays of light L1 will be 
lowered to such an extent that the optical scanner 27 will fail to read 
the image at high precision. 
In the practice of the present invention, the first and second rays of 
light L1 and L2 are preferred to be visible rays of light and infrared 
rays of light, respectively. 
Again, in the practice of the present invention, the reflective layers 57 
or 57a may suffice to be so patterned as to provide a periodic structure 
extending in X-axis and Y-axis directions perpendicular to each other and, 
therefore, may be formed in the form of a pattern of dots with upper and 
lower dots displaced relative to an intermediate dot in a direction 
parallel to the X-axis direction. 
From the foregoing full description of the present invention made in 
connection with the preferred embodiments thereof, it is clear that no 
infrared absorbing layer hitherto employed in the prior art sheet-like pad 
is required and, therefore, the first rays of light emitted from the 
scanner will not pass through the infrared absorbing layer, and that a 
portion of the first rays of light merely pass through the reflective 
layers once or twice according to the present invention. Therefore, an 
attenuation of the first rays of light can be advantageously minimized, 
permitting a maximized utilization of the rays of light. In particular, 
where the reflective layers form respective square areas delimited by the 
grid lines forming the grid pattern such as in the second mentioned 
preferred embodiment of the present invention, the total area of surface 
occupied by the reflective layers can be made smaller than that of the 
system wherein the grid lines are defined by the reflective layers, 
thereby achieving an increased efficiency of utilization of the rays of 
light used in the system as a whole. 
It is also clear that, since the reflective layers can be formed into the 
requisite periodic structure by the use of any known photo-etching 
technique, the sheet-like pad according to the present invention can 
readily and easily be assembled or manufactured with a stabilized quality. 
The use of the photo-etching technique should achieve a high dimensional 
precision of the reflective layers as compared with the conventional 
screen printing. 
In addition, since the reflective layers are formed into a matrix-like 
periodic structure, the reflective layers can be minimized and be 
therefore rendered inexpensive as compared with the reflective layers 
formed all over the base layer. 
Although the present invention has been fully described in connection with 
the preferred embodiments thereof with reference to the accompanying 
drawings which are used only for the purpose of illustration, those 
skilled in the art will readily conceive numerous changes and 
modifications within the framework of obviousness upon the reading of the 
specification herein presented of the present invention. Accordingly, such 
changes and modifications are, unless they depart from the spirit and 
scope of the present invention as delivered from the claims annexed 
hereto, to be construed as included therein.