U.S. patent number 3,670,633 [Application Number 05/091,192] was granted by the patent office on 1972-06-20 for recording apparatus.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Philip L. Chen, Lawrence J. Mason, Louis F. Paradysz, George R. Simpson.
United States Patent |
3,670,633 |
Mason , et al. |
June 20, 1972 |
RECORDING APPARATUS
Abstract
An alphanumeric recording system wherein a character disc having
transparent character images thereon is rotated through an exposure
zone so that selected characters may be projected by the
energization of a flash lamp. The projected image is collimated and
directed to a recording zone through which move lens-mirror units
at a constant speed intercept the projected image and focus it onto
a photoreceptive recording medium. The character disc rotates at a
rate such that with the slits therein associated with respective
characters inter-character spacing is assured. Dead time in the
recording process is eliminated by the use of the collimated
projected character image and plural interception of that
image.
Inventors: |
Mason; Lawrence J. (Webster,
NY), Simpson; George R. (Webster, NY), Paradysz; Louis
F. (East Randolph, VT), Chen; Philip L. (Penfield,
NY) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
22226537 |
Appl.
No.: |
05/091,192 |
Filed: |
November 19, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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791050 |
Jan 14, 1969 |
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Current U.S.
Class: |
396/555; 355/40;
396/552; 396/559 |
Current CPC
Class: |
G06K
15/12 (20130101) |
Current International
Class: |
G06K
15/12 (20060101); B41b 013/00 (); G03b
027/70 () |
Field of
Search: |
;95/4.5R ;355/40 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Matthews; Samuel S.
Assistant Examiner: Wintercorn; Richard A.
Parent Case Text
This application is a continuation-in-part of application, Ser. No.
791,050, filed Jan. 14, 1969 now abandoned.
Claims
What is claimed is:
1. An apparatus for recording alphanumeric characters
comprising:
a. an exposure zone;
b. an opaque character member having an axis of rotation and an
arcuate character area having a uniform radius therefrom and
including at least one set of uniformly spaced alphanumeric shaped
transparent areas;
c. a field stop optical member having an axis of rotation and a
transparent spiral segment;
d. motive means for driving said character member and said field
stop optical member at a uniform rate through said exposure
zone;
e. said character member and said field stop optical member being
positioned relative to each other and to said exposure zone such
that said spiral segment and said character area overlying
intersect each other in said exposure zone and pass coincidently
therethrough;
f. a selectively energizable flash lamp positioned relative to said
exposure zone such that light from said lamp passes through the
areas of intersection of said spiral segment and said character
area;
g. first optical means positioned relative to said exposure zone
for collimating the light passing through one of said alphanumeric
shaped transparent areas thereat;
h. second optical means for focusing at least a portion of said
collimated light at a focal plane; and,
i. a light responsive recording medium positioned at said focal
plane to receive a focused image of the alphanumeric shaped
transparent area at said exposure zone.
2. Apparatus as defined in claim 1 wherein said second optical
means includes:
a. a drive member;
b. a recording zone;
c. a mask positioned adjacent said recording medium in said
recording zone and having an aperture therein with one dimension
equal to one dimension of said recording zone;
d. at least two lenses attached to said drive member and adapted to
be driven thereby through said recording zone and spaced apart on
said drive member by a distance equal to said one dimension of said
recording zone.
3. Apparatus as defined in claim 1 wherein said character member is
in the form of a disc, the plane of which is substantially
perpendicular to the collimated light from said first optical
means, and said disc having detectable indicia thereon, each one of
said indicia being positioned uniquely with respect to its
associated alphanumeric shaped transparent area.
4. Apparatus as defined in claim 3 wherein the center of adjacent
ones of said alphanumeric shaped transparent areas being uniformly
spaced from each other and adjacent ones of said indicia being
uniformly spaced from each other, the spacing of said adjacent
indicia being different than the spacing of said adjacent
transparent areas.
5. Apparatus for recording alphanumeric characters at the rate of B
characters per second and H characters per inch along a recording
zone I inches inlength in response to code groups having C bits per
group received at the rate of F bits per second where F/C = B,
comprising:
a. an opaque character disc rotatable about an axis and having a
character area concentric thereabout including D sets of
alphanumeric shaped transparent areas centered in uniformly sized
character spaces;
b. an exposure zone defined by a portion of said character
area;
c. motive means for rotating said disc at the rate of G revolutions
per second equal to B/D;
d. a light responsive recording medium;
e. a recording zone I inches in length measured in a predetermined
direction;
f. flash lamp means responsive to said code groups for transmitting
light through said exposure zone;
g. collimating means for collimating light passing through said
exposure zone;
h. a drive member;
i. motive means for moving said drive member through said recording
zone in said predetermined direction at a constant speed K equal to
B/H inches per second, and,
j. at least two lens means attached to said drive member and spaced
apart therealong by I inches and responsive simultaneously to
different portions of said collimated light for focusing said
portions at said recording medium when in said recording zone.
6. Apparatus as defined in claim 5 for recording alphanumeric
information in parallel lines corresponding to J lines per inch
further including motive means for moving said recording medium
through said recording zone at a rate L equal to (B)/(JHI) inches
per second.
7. Apparatus as defined in claim 5 wherein said character disc
includes indicia, each of said indicia associated with a respective
one of said character spaces and identifying the position of its
respective character space in said set by the unique relative
position of the character space and its respective index, the
center of adjacent ones of said character spaces being equal to an
amount Q and the spacing between adjacent indicia being equal to
[(Q/N) + Q] where N equals the number of transparent areas in said
set.
8. Apparatus as defined in claim 7 further including:
a. input terminal adapted to receive said code group
b. counter means for storing a count representative of a received
code group;
c. detection means positioned relative to said character disc for
altering the count in said counter means in response to the passage
of said indicia;
d. trigger means responsive to a predetermined count in said
counter means for energizing said flash lamp means when the
transparent area in said exposure zone corresponds to the character
represented by said received code group.
9. Recording apparatus comprising:
a. a pattern disc having an axis of rotation and at least one set
of light modulating patter areas uniformly spaced on an arcuate
portion thereof concentric with said axis, each of said areas
having uniquely positioned relative thereto an index, the index
associated with one area not differing in configuration from the
index of another area;
b. motive means for moving said set of light modulating areas
through an exposure zone;
c. means including flash lamp means for selectively directing light
at said exposure zone through only one of said areas at any one
time;
d. collimating means for collimating light passing through said
exposure zone from said flash lamp means;
e. an endless drive member;
f. a light responsive recording medium having a recording area;
g. means for moving said drive member through a path of which a
portion is substantially parallel and proximate to said recording
area;
h. a recording zone defined by said recording area and said portion
of said path; and,
i. a pair of optical units attached to said drive member and spaced
therealong by a distance equal to the dimension of said recording
area in the direction of said path portion, each of said optical
units including a lens and a mirror in fixed relation to each
other, the path of said drive member being so positioned that,
during passage through said parallel portion of said path, each
lens simultaneously intercepts a portion of said collimated light
which is focused by only one lens on said recording area, said
mirror positioned to reflect the light passing through said lens
toward said recording medium.
10. Apparatus as defined in claim 9 wherein said means including
flash lamp means comprises a field stop disc having an axis of
rotation and a transparent spiral segment, said field stop disc
being positioned parallel relative to said disc and to said arcuate
portion thereof; and
motive means for moving said spiral segment through said exposure
zone simultaneously with said pattern disc.
11. Apparatus as defined in claim 10 further including means for
moving said recording medium in a predetermined direction, which
forms an obtuse angle with that portion of said path proximate to
said recording area.
12. Apparatus as defined in claim 10 further including:
a. an input terminal adapted to receive binary bit groups
representative of patterns to be recorded;
b. means responsive to the passage of said indicia for generating a
signal;
c. trigger means responsive to said signals and said bit groups for
energizing said flash lamp means.
Description
This invention relates generally to information recording and
specifically to information recording utilizing optical projection
techniques.
There has been a long standing need for information recording
apparatus which are capable for fulfilling a number of operational
requirements and standards. One such requirement is a recording
speed which effectively utilizes costly transmission mediums such
as standard voice line communication links. However, another
requirement which is a function of speed is a quality of recording
commensurate with conventional typewriter quality. Several
corollary requirements are also noteworthy. These relate to the
external noise level during operation of the machine and the
versatility of the apparatus itself in regards, for example, to
character font and upper and lower case capabilities.
Typical communication links for alphanumeric data such as Teletype
networks employ impact printers which are capable of only upper
case alphanumeric characters and record alphanumeric information at
a substantially slow rate in a rather noisy manner.
It is, therefore, an object of the present invention to provide
improved recording which is of a high quality and capable of
substantially high speeds.
It is another object of the present invention to provide an
improved information recording apparatus which is capable of upper
and lower alphanumeric character recording.
These objects and other objects which may become apparent may be
appreciated more readily upon reading the following detailed
description in conjunction with the attached drawings wherein:
FIG. 1 is a side view of apparatus in accordance with the
principles of the present invention;
FIG. 2 is a front view of the apparatus shown in FIG. 1 with some
parts broken away;
FIG. 3 is a top cross-sectional view of FIG. 2 taken along section
lines 3--3;
FIGS. 4 and 5 illustrate sequential relationships between a
character disc and an optical field stop disc during operation of
the apparatus illustrated in the above figures;
FIG. 6 is a schematic representation of the logic circuit for the
apparatus in which the present invention may be utilized.
Reference will now be made in detail to the mechanical structures
illustrated in FIGS. 1, 2 and 3 which depict in detail the
significant portions of an alphanumeric character recorder in
accordance with the principles of the present invention.
FIG. 1 shows in somewhat more detail than FIGS. 2 and 3 exemplary
xerographic process stations which are conventional in nature and
actually form no part of the present invention. However, they are
illustrated to provide a point of reference for the present
invention in a practical environment. Not all of the details of the
xerographic process have been illustrated but sufficient details of
those stations illustrated and other desirable stations not
illustrated may be obtained from U. S. Pat. No. 3,187,651, which
issued to Eichorn et al. on June 8, 1965, assigned to the same
assignee as the present application. Basically, a conventional
xerographic drum 2 is shown to rotate in the direction indicated by
the arrow to pass successive portions under the influence of a
pre-exposure corotron 4 and to an exposure station which is
represented by the slit mask 6 where the previously charged
xerographic drum is selectively discharged in accordance with the
intensity of the image at the exposure station. The latent
electrostatic image thereby produced may then be conventionally
developed with electroscopic marking particles using a suitable
developing apparatus such as a cascade developer represented by the
housing 8.
The developed latent image is then moved to a transfer station
where a transfer corotron 10 transfers the electroscopic marking
particles onto a copy sheet which is held on a copy sheet conveyor
12 by means of a suitable gripper mechanism 14 shown in more detail
in the aforementioned patent. The copy sheet can originate from an
appropriate copy sheet tray 16 under the influence of a feed-out
roller 18 and paper guides 20. After transfer a conventional
radiant fuser 22 may be employed to permanently affix the
transferred image onto the copy sheet.
Referring now specifically to the mechanical structure with
particular reference to FIG. 2 which best depicts this structure
which is partially shown in FIGS. 1 and 3, the xerographic drum 2
which is rotated by motive power applied to its shaft 24 provides
the final receptor of optical information projected onto it via
slit mask 6.
As noted before, the xerographic aspects of the present disclosure
do not constitute a portion of the inventive concept herein
disclosed. For example, any photoresponsive medium may be used to
receive and record the optical projections. Therefore, the
xerographic drum may be replaced by a suitable photographic medium
or any other light responsive medium. It goes without saying that
in certain situations depending upon the type of recording medium
utilized a drum configuration is not necessarily desirable and a
flat plate adapted for movement could also be employed.
The source of the optical projections which are received by the
xerographic drum 2 originate from a pattern disc 26 which is driven
rotatively so as to pass an annular pattern area 28 successively
through an exposure zone. As will be described hereinafter, this
area 28 is composed of sets of transparent light modulating
patterns capable of optical projection. The exposure zone is
aligned with the center line of the image path designated in FIG. 2
by reference numeral 30. Other elements further define this
exposure zone such as the optical field stop disc 32 which is
driven about its axis represented by a drive shaft 34 as shown in
FIG. 2. As shown best in FIG. 3 the optical field stop disc 32 is
generally opaque to a particular illumination utilized in the
recording apparatus and has transparent portions 36 thereon which
corresponding to segments of a spiral. Each segment 36 has a radius
from the center of the disc 32 which corresponds to the following
equation:
R= R.sub.o + KO
where R is the radius of the segment measured from the center of
the disc 32, R.sub.o is the shortest radius of the segment as
measured from the center of disc 32, K is a constant and O is the
angle subtended by R and R.sub.o. As shown in FIG. 3, disc 32 has
three such segments 36, each of which correspond to a set of light
modulating patterns on disc 26 which are used in the recording
operation. In a particular example of this disclosure, each set
includes alphanumeric characters comprising two alphabets, upper
case and lower case.
As will be seen again in FIG. 3 referring to the disc 26, there are
three transparent slits 38 in an otherwise opaque disc with, of
course, the exception of the character area 28 and other slits.
These slits, as will be seen in more detail hereinafter, designate
the beginning and end of a alphanumeric character set on the disc
26. The angle subtended by any one of the segments 36 on the
optical field stop disc 32 is equal to 120.degree.. Therefore, as
shown in FIG. 3 where the character area 28 of disc 26 and any
portion of a segment 36 of disc 32 intersect proximate to the
center line 30 of the image path, the exposure zone will be
defined. It can be readily understood that although the character
area 28 is concentric about the axis and drive shaft 40 of
character disc 26, the exposure zone previously defined will vary
about the center line 30 of the image path as a function of the
aforementioned equation since the spiral segments 36 will vary in
their distance from the center of disc 32. This will be seen in
greater detail hereinafter in connection with discussion of FIGS. 4
and 5. It is sufficient at this time to describe the exposure zone
as being the intersection of any of the segments 36 and the
character area 28 of disc 26 at or near the center line 30 of the
image path.
Both disc 32 and 26 may be formed by etching photographic emulsion
which is adhered to one side of a lightweight normally transparent
disc-shaped material such as plexiglass. The emulsion side of the
discs 26 and 32 face each other and are very closely spaced so as
to permit the segments 36 and the character area 28 to be as
proximate to the object plane of the projection optical system as
is possible.
This projection optical system is represented by a collimating
optical assembly generally designated by reference numeral 42 which
acts to collect the light passing through the selected portion of
the character disc 26 and collimate it for reflection by a main
mirror 44. The light from main mirror 44 is then acted upon by two
identical lenses 46. These may be achromatic doublets of
conventional design and as seen in FIGS. 1 and 3 are substantially
rectangular in area. They serve to focus via mirrors 48 the light
reflected by mirror 44 onto the image plane represented by the
surface of xerographic drum 2 exposed through slit mask 6. As is
shown in FIG. 2, a support member 49 holds the lens 46 and the
mirror 48 in a fixed relationship relative to each other to insure
proper optical alignment throughout the operation of the
apparatus.
The source of the light which has been described as passing through
the optical system is generated by a suitable flash lamp 50 which
may suitably be a xenon lamp housed in a conventional light box 52
so as to permit light to exit through an optical assembly 54 and
into the exposure zone previously referred to.
The description of the optical arrangement can be summarized by
saying that a character in the pattern area of disc 26 is
illuminated and this object character in the character plane is
imaged at infinity by the collimating action of assembly 42. The
main mirror 44 reflects this collimated light to lens 46 which
images that character via mirror 48 onto the image plane at the
surface of the drum 2 or other photoreceptor.
Referring now specifically to FIGS. 1 and 2, the manner in which
the optical projections from the character disc 26 are spatially
recorded on the surface of drum 2 will be described. As noted
hereinabove, lens 46 and mirror 48 are formed into an integral unit
by an appropriate support member 49. This support member is, in
addition, attached to a carriage 56 which is fixed to a flexible,
endless drive member 58, which may be a chain as illustrated in the
drawings. The chain engages two sprocket wheels 60, one of which
may be driven by a suitable source of motive power not shown to
move the chain 58 through its particular path as shown best in FIG.
2. A plurality of carriages 56 are shown attached to the chain 58
and, as will be seen hereinafter this number of such carriages and
associated optical units can not be less than two and may be
larger.
FIG. 2 depicts two of these units in the optical path formed by the
reflected light from mirror 44 which in part is directed by either
one of the units onto the surface of drum 2 at the beginning or end
of the slit in the mask 6. The movement of the chain viewing FIG. 2
is in a clockwise direction as indicated by the arrows. Therefore,
the lens-mirror assembly on carriage 56 on the left can be
considered as having completed the projection of a line of
alphanumeric information and the identical assembly on the right
can be considered as having completed the projection of a line of
alphanumeric information and the identical assembly on the right
can be considered as initiating the next line of recorded
information. Because of the finite speed at which chain 58 drives
these lens-mirror assemblies along the axis of drum 2, it is
necessary in order to achieve line recordings which are
substantially perpendicular to the edges of drum 2 to skew the
plane of the chain 58 with respect to the drum's axis which is
represented in FIG. 3 by reference numeral 62. The amount of skew
is a function of the chain's speed and the linear velocity of the
drum. In this way, in the final copy the horizontal lines of
alphanumeric information will be equally spaced and substantially
perpendicular to the side edges of the copy sheet.
Because of the high speed capabilities of the recording apparatus
permitted by the present invention the speed at which the chain 58
is driven may cause certain vibrations which adversely affect the
quality of the final copy. In order to minimize these effects, a
stabilizing plate 64 is employed upon the edge of which in effect
rides carriages 56 by way of wheels 66 which are best shown in
FIGS. 1 and 2. These wheels are rotatively mounted on the same pins
which attach carriage 56 to the chain 58. Because of the tension in
the chain 58, the wheels 66 of the carriages 56 maintain continuous
contact with the edge of the stabilizing plate 64.
In the recording zone of the apparatus defined as shown in FIG. 2
by that space between the mirrors 48 of the two lens-mirror units
shown providing exposure of the drum 2, additional stabilizing
flanges 68 are employed to provide positive restraint on both the
upper and lower portions of the periphery of wheels 66. As seen
better in FIG. 1 flanges 68 are attached appropriately to
respective ones of the stabilizing plates 64. This insures the very
minimum of vibration in the recording zone by chain 58 and
carriages 56 thereby providing little, if any, blur in the image
projected on the surface of drum 2. It is recognized that the
stabilizing provisions are not necessary to the operation of the
system but only enhance the quality of the resultant recording.
At this point, the operation of the apparatus as depicted in the
drawings may be summarized as follows. Through appropriate logic
control circuitry yet to be described, input signals representative
of alphanumeric information are received by the recording apparatus
and decoded so as to indicate what particular alphanumeric
character is to be projected and recorded onto the surface of
xerographic drum 2 at any instant of time. This indication is
compared with the ever changing status of the character disc in the
exposure zone so that when the selected character is properly
positioned at this zone, the flash lamp 50 is energized. The image
of the selected character is then projected through the optical
system via optical assembly 42, mirror 44, lens 46, and mirror 48
to selectively discharge the xerographic drum in accordance with
the optical information. During this time one of the lens-mirror
assemblies on carriage 56 is moving from right to left as seen in
FIGS. 2 and 3 so that a series or sequence of alphanumeric
characters may be recorded in a line substantially parallel with
the axis of drum 2.
Due to the speeds involved, it is necessary to provide proper and
uniform spacing between adjacent alphanumeric characters appearing
in a word, for example. Since the motion of the driving chain 58 is
at a constant velocity in contradistinction to being incrementally
stepped, it is possible when using prior art techniques that two
alphanumeric symbols separated by some distance on the character
disc 26 may be recorded sequentially with a spacing which would be
different from the spacing between two projected characters which
occupy adjacent positions on the disc 26. Expressed differently,
since the disc 26 is continuously rotating at a uniform speed, the
time which elapses between the character A, upper case, being at
the exposure zone and the lower case Z being at the recording zone
is considerably greater than the time elapsing between the upper
case A and B sequentially being presented to the exposure zone.
Since the carriages 56 are moving constantly, this difference in
time means the lens-mirror unit moves a different amount.
As will be seen in more detail in the description of the electronic
circuitry which controls the recording process, the apparatus of
the present invention is designed to project one alphanumeric
character per set of alphanumeric characters. Therefore, the
spacing problem is involved each time it is desired to sequentially
record any two characters.
However, the present invention solves this problem by utilizing
character slits shown best in FIGS. 4 and 5 to which reference is
now made. As shown there, each slit is on a radian of disc 26 and
extends from the periphery of disc 26 a short distance toward the
center of the disc. Each alphanumeric character in the character
area 28 is centered in a character space which is uniform in size
for all characters. Therefore, the centers of adjacent characters
are uniformly spaced from each other. The character slits vary in
their alignment with a particular character space. As will be noted
the spacing of adjacent character slits is uniform. However, the
spacing or the alignment between a particular character slit and
its respective character space varies depending upon the position
of the respective character in the character space in its
respective set. This can be seen upon close examination of FIGS. 4
and 5.
Character slit 69 associated with the space occupied by the upper
case character A is located 0.5/52 of a character space to the
right of the left-most portion of that character space. Examining
the character slit 70 associated with the space occupied by the
upper case character M it can be seen that this slit is removed
from the left-most portion of that space by slightly less than
one-fourth of the width of that character space. In FIG. 5 the
character slit 72 associated with the lower case character M is
shown to be removed approximately three-fourths the width of a
character space from the left-most side of the character space
occupied by this character. Turning then to the lower case
character Z, character slit 74 associated with that character is
located 0.5/52 of a character space to the left of the right-most
side of that space. The character slits for those alphanumeric
characters intermediate the characters previously referred to have
associated with them similar slits which are positioned uniformly
from the preceding slit.
The changing relationship of successive character slits with
successive characters is easily appreciated when it is considered
that each alphanumeric character both upper and lower case is
centered in a uniform sized character space. The character slits as
noted previously are uniformly spaced from adjacent slits but the
spacing of these slits is somewhat greater than the spacing between
the centers of adjacent character spaces. Therefore, in the example
used in this description wherein each alphanumeric character set
contains 52 symbols or characters plus one blank space, and the
center of adjacent characters are spaced apart by a unit designated
by the constant Q, the character slit spacing between adjacent
slits can be represented by Q/52 plus Q. Therefore, referring to
FIGS. 4 and 5, it can be ascertained that if character slit 69
associated with upper case character A is aligned with an initial
or zero position then character slit 70 associated with the
character upper case M is then spaced along the periphery of disc
26 from character slit 69 by an amount equal to 12 (Q/52 + Q). In a
like manner character slit 72 associated with lower case character
M is spaced from character slit 69 by an amount equal to 38 (Q/52 +
Q) and character slit 74 is similarly spaced from character slit 69
by an amount equal to 51 (Q/52 +Q).
Having described the unique relationship between a particular
character slit and its respective character space with which it is
associated, the function of these character slits in accordance
with the present invention will now be described. As noted
hereinabove, the various slits referred to, both the character
slits and slits 38 on the character disc 26, are transparent areas
in the normally opaque surface of the emulsion side of the
character disc 26. Therefore, these slits transmit light from an
appropriate source of constant illumination which is not shown in
the figures but may be a conventional low voltage lamp. The light
which is transmitted by these particular slits is detected by a
conventional pair of photocells or photodiodes which are located
inside the photocell assembly designated by reference numeral 78.
One photocell (referred to hereinafter as the clear photocell)
exclusively monitors light passing through slit 38 while the other
photocell (referred to hereinafter as the character photocell)
monitors exclusively light passing through the character slits. As
will be seen hereinafter in connection with the description of the
logic control circuitry, slit 38 is utilized to generate a signal
to reset or clear a character counter which generates a full count
when the selected character is in the exposure zone. As can be seen
from the depiction of FIG. 3, the photocells are located
120.degree. from the center of the exposure zone or from the center
line 30 of the image path. This is done so as to remove the
photocells from the exposure zone so that they will not obstruct
the light passing therethrough. Placing them 120.degree. from this
position is equivalent to their being at this position since three
character sets are used on the character disc 26. When, for
example, the character photocell detects character slit 70 as shown
in FIG. 4, the control logic through the use of a counter, which at
this point registers a full count knows that the upper case
character M is in the exposure zone. As noted hereinabove, the
exposure zone is actually defined by the intersection of the
character area 28 of character disc 26 and a portion of one of the
spiral segments 36 of the optical field stop disc 32. As shown in
FIG. 4 this exposure zone may extend anywhere from the point
represented by reference numeral 80 to the point represented by
reference numeral 82. This space between these two points along a
radian of disc 26 passing through center line 30 of the image path
defines the upper and lower limits of the exposure zone.
As will be brought out in the discussion of the logic circuitry,
the count of the character slits determines precisely when the
flash lamp 50 will be triggered. Since the position of character
photocell in assembly 78 is fixed relative to the center line 30 of
the image path, the character slit associated with the particular
character in the exposure zone which is projected by the light from
the flash lamp 50 will always be in the same position relative to
center line 30 and coincident therewith. However, because of the
unique relationship between a particular character and its
respective character slit, the position of the projected character
in the exposure zone will vary. For example, when the flash lamp is
triggered to project the image of the upper case character A, the
character itself will be to the right side as FIGS. 4 and 5 are
viewed of its respective character slit and of the exposure zone.
In other words, the projected character will be closer to point 80
as shown in FIG. 4 than point 82. In the other extreme, when lower
case character Z is projected, it will be to the left, as FIGS. 4
and 5 are viewed, of its respective character slit and closer to
side 82 of the exposure zone than side 80 thereof.
The particular function of the character slits is best explained in
relation to actual operating parameters within which the apparatus
illustrated is capable of operating. An initial factor which is
fixed in value is the bit rate possible for transmission over
standard voice grade telephone lines, viz., 2,400 bits/second.
Typical alphanumeric codes use 8 bits/character which dictates a
maximum transmission and recording rate of 300 characters/second.
Since the character disc carries three character sets and one
character per set is projected, the disc must rotate at a rate of
100 revolutions/second in order to achieve the 300 character/second
recording rate (3 characters/revolution is the maximum recording
rate). For typical typewriter spacing, 10 character/linear inch of
drum surface is required. If 84 characters are desired per line
then the recording zone limited by slit mask 6 is 7 inches. This
results in a drive speed for chain 58 of 25 inches/second. At this
speed, the chain, and hence the optical units attached thereto,
will progress approximately one character space during the time
disc 26 moves the equivalent of one character set through the
exposure zone. This is realized when it is considered that the
chain 58 moves at the rate of 300 character spaces/second while
disc 26 moves one character set through the exposure zone in one
three-hundredth of a second at the rate of 100
revolutions/second.
With the preceding factors and parameters understood, the problem
of uniform spacing of recorded characters can be better
appreciated. Since the tangential velocity of a typical 4-inch
diameter disc is approximately 1,200 inches/second, one aspect of
the spacing problem is overlap in the recording of two characters
on the disc occurring very close to one another, e.g., lower case
character Z and upper case character A. The amount of time elapsing
between the projection of these two characters is so small as to be
negligible for practical considerations. However, in spite of this
fact, proper spacing of these two characters is accomplished in
accordance with the principles of the present invention. Let the
center of the exposure zone which corresponds to the center line 30
of FIGS. 1 and 2 and the intersection of disc center lines 84 and
86 in FIGS. 4 and 5 represent a zero position. To the left of this
zero position are negative values of distance and to the right
thereof positive values. These negative and positive values relate
distance of the center of a character space from its associated
character slit when that character slit is at the zero position
(when the lamp 50 is energized if it is desired to record the
character in that character space). Since the position of the
character spaces are predetermined relative to their character
slits, a table of distance values can be attributed to each
character in a character set. With 52 characters per set, values
from +25.5 to -25.5 can be given the characters as follows:
A+25.5 N+12.5 a- 0.5 n-13.5 B+24.5 O+11.5 b- 1.5 o-14.5 C+23.5
P+10.5 c- 2.5 p-15.5 D+22.5 Q+ 9.5 d- 3.5 q-16.5 E+21.5 R+ 8.5 e-
4.5 r-17.5 F+20.5 S+ 7.5 f- 5.5 s-18.5 G+19.5 T+ 6.5 g- 6.5 t-19.5
H+18.5 U+ 5.5 h- 7.5 u-20.5 I+17.5 V+ 4.5 i- 8.5 v-21.5 J+16.5 W+
3.5 j- 9.5 w-22.5 K+15.5 X+ 2.5 k-10.5 x-23.5 L+14.5 Y+ 1.5 l-11.5
y-24.5 M+13.5 Z+ 0.5 m-12.5 z-25.5
These values represent the numerator in a ratio having 52 as the
denominator so that the character space is divided into 52
increments. As noted hereinabove, upper case character A has its
character slit 69, 0.5/52 of a character space to the right of the
left-most edge of its character space. Therefore, the center of
this character is 25.5/52 of a character space from its character
slit in a direction previously defined as positive. Similarly, the
lower case character z is given a value of -25.5/52. Therefore, if
the sequence of characters is "zA," the distance between these two
characters on the drum must be equal to one character space. If it
is less than this amount, the recorded characters will overlap; if
greater than this amount, the spacing between the recorded
characters will be incorrect. This can be expressed by the simple
equation:
D.sub.A - D.sub.z + d = 1 (where D= distance traveled by the
lens-mirror assembly)
which translates when using the above table to:
(+25.5/52) - (-25.5/52) + d = +51/52 + 1/52 = 52/52 = 1
In the sequence such as "Az," it can be demonstrated that there
will be only one character space between characters on the drum as
follows:
D.sub.z - D.sub.A + d = 1
Again using the above Table, D.sub.z = -25.5/52 and D.sub.A =
+25.5/52. In this particular sequence one character space is moved
by the chain 58 per passage of a character set through the exposure
zone. There d will be equal to 52/52 or one character space, as the
character set including the aforementioned blank space containing
the projected character A passes the exposure zone, plus another
amount of 51/52 required to move the second character set through
the exposure zone to bring the lower case character z thereto. So d
will equal (52/52 + 51/52) and the three term equation translates
to:
(-25.5/52) - (+25.5/52) + (52/52 + 51/52) = 1
(-51/52) + (103/52) = 52/52 = 1
This demonstration with the two sequences of characters establishes
the effectiveness of the character slits in insuring that the space
between the recording of any two characters in the set is
substantially uniform regardless of the distance separating their
stencils on the character disc.
With the explanation of the character disc and the function of the
character slits therein given above, it can be appreciated that
since the exposure zone is actually two character spaces wide,
something must insure that only one character is projected at a
time. As FIGS. 4 and 5 are viewed, it can be seen that two
characters are usually in the exposure zone between points 80 and
82 with the exception of the first and last characters of the sets.
In order to eliminate the possibility that two characters will be
projected, optical field stop disc 32 is employed. Its utilization
can best be seen with reference to FIGS. 3, 4 and 5 which show the
relationship between the two discs. Disc 32 rotates in a direction
as indicated by the arrow and has it rotation synchronized with
that of the character disc so that one of the spiral segments 36
passes through the exposure zone coincidently with the passage
therethrough of one of the character sets on disc 26. This is
evident from the positions of the discs as depicted in FIG. 4 or 5.
While FIGS. 4 and 5 do not show two characters in the exposure
zone, it can be pictured when the character disc is advanced so
that, for example, upper case characters A and B are in the
exposure zone together. In that situation, the optical field stop
disc 32 would block character A's projection and permit the
projection of character B via transparent segment 36.
Now that the mechanical aspects of the apparatus depicted in FIGS.
1 to 5 has been described, one facet of this apparatus will be
explained which lends it the capability of very high speed
recording. This capability is partially due to the role played by
the moving optical system comprised of the lens-mirror units
including lens 46 and mirror 48 attached to the drive chain 58 via
members 49 and 56. However, by itself this optical system could not
achieve the ultimate speed capability but in cooperation with the
collimating optical assembly 42 it is all possible.
The recording zone in a typical recorder may be approximately seven
inches long and is defined by the opening in the slit mask 6 in the
direction of the drum's axis. The spacing of the lens-mirror units
is such that the distance between the focal paths in the plane of
the slit mask of the two units closest to the recording zone is
exactly equal to the dimension of the slit mask's opening measured
in the direction of the axis of the recording drum 2. In other
words, viewing FIG. 2 of the two lens-mirror units intercepting the
collimated image projection reflected by mirror 44 the one on the
left is focusing whatever character is being projected onto the
slit mask and the one on the right is just focusing the same
character image through the slit mask's opening and onto the drum
surface. In exactly this manner dead time between the recording of
adjacent lines of alphanumeric information is eliminated or reduced
to such an infinitesimal amount that in practice it is
non-existent. Consequently, as the lens-mirror unit on the left
completes the recording of one line of information, the unit on the
right is just beginning the next line of information. From this
explanation it can be appreciated that the spacing of the
lens-mirror units on the drive chain is somewhat critical.
It is helpful in the discussion to refer back to the parameters
offered to show a practical environment of the recording apparatus.
In the example being used, the lines of alphanumeric information
recorded have a vertical density of 6 lines per inch. Therefore the
drum must move through the recording zone at approximately 0.625
inches per second.
As noted hereinabove, the spacing of the lens-mirror units along is
not enough to insure this high speed and nonexistent dead time
between successive line recordings. The collimated character
projection is also important. From the above discussion of the
precise spacing of these lens-mirror units, it is essential that
each lens 46 focuses the same character being projected at that
instant of time. This is made possible by utilizing Huygens' theory
that the wave front of light emission can at any future time be
determined by assuming that every point on a given wave front acts
as the center of a new disturbance emanating from that point. In
other words, a new wave front can be found by treating each point
of the old wave front as a new source of light from which a
secondary wavelet emanates in all directions. Therefore, when the
light emitted by flash lamp 50 is collected and translated by the
optical arrangement 54, which includes conventional condenser or
collector lenses, through the transparent character shaped area in
the exposure zone, that wave front so shaped by the transparent
area includes a multiplicity of individual light sources
corresponding to the points of the character's area. These light
sources radiate light in all directions but the collimating
assembly 42 acts to collimate it so that many images of the
projected character are focused at infinity by this assembly 42. By
means of mirror 44 and lenses 46, two of these images are
intercepted and focused by the two lens-mirror units as one leaves
and one enters the recording zone. In this manner, the projected
character image is instantly available to the unit on the right as
the next line is being recorded immediately after the preceding
line's recording was completed.
Having described the mechanical aspects of the present invention
and the function of the character slits, reference will now be made
to FIG. 6 which schematically depicts the logic circuitry employed
to control the recording process. As noted hereinabove, the
apparatus of this invention can be used on the receiving end of a
standard voice grade telephone link over which is transmitted coded
groups of binary bits representative of information or data, for
example alphanumeric data as well as various control words. Such
bit groups are received by the circuit of FIG. 6 at an input
terminal 3 which serially supplies these bits to the input of a
conventional shift register 5 and to a conventional clock bit
recovery circuit 7. The latter provides suitable recovered clock
pulses to a counter 9 of conventional design which has a full count
capacity equal to the number of bits employed to represent a
particular alphanumeric character. In the particular example used
in this description, eight bits have been referred to as
constituting a bit group. Circuit 7 also supplies these recovered
clock pulses to the shift input of the shift register 5 which shift
the bits of the bit group thereinto. In addition to the shift
register 5 and the counter 9, the recovered clock pulses are also
provided as an input to gate 11 and detector 13.
As for the detector, these pulses actually serve to enable an input
gate in the detector 13 so that the detector can decode certain
code words temporarily stored in the shift register 5. Code words
such as SYNC and START are decoded by this conventional detector
circuit 13 which may be comprised of various gate combinations as
is well known in the art. As shown in FIG. 6, the two outputs of
the detector 13 are labeled "Start" and "Sync." Each of these
outputs will be energized when the proper word is detected as being
stored in the shift register 5.
In addition to the parallel output to the detector 13, shift
register 5 also has a parallel output to a conventional eight stage
digital register 15 which, in turn, has parallel outputs to another
identical register 17 and so on until an eighth such digital
register 19 is reached. These registers serve as a very short
buffer for the code groups before and during the recording
process.
Before the actual receipt of coded information is described, a
description of the link between the logic circuit of FIG. 6 and the
mechanical side of the recording apparatus will be given. As was
described in connection with FIGS. 1, 2, and 3, photocell housing
78 houses two photodetectors referred to as a clear photodetector
and a character photodetector which detect the presence of slits 38
and the character slits, respectively, of the character disc 26.
These two photocells or photodetectors are coupled to suitable
amplifiers 21 and 23, respectively, via input terminals 25 and 27
associated therewith.
The character photocell and amplifier 23 provide a signal each time
one of the character slits passes the photocell. This signal
constitutes what will be referred to as simply a clock pulse, in
distinction to the recovered clock pulse. Such a clock pulse is
supplied to many sub-systems of the circuit of FIG. 6. The
character counter 29 receives them to index its count. In addition,
the flash lamp trigger gate 31 and the register load circuits 33
receive these clock pulses to respond in a particular manner to be
described hereinafter.
The clear photocell and amplifier 21 provide a clear signal
indicative of each time one of the slits 38 on the character disc
passes housing 78. These signals serve many roles, one of which is
to clear or reset the character counter 29 to its initial
condition, for example, zero. The eight logic gates represented by
block 35 are enabled by a delayed clear signal, which permits the
complement of the contents of the eighth register 19 to be loaded
into the character counter 29. In addition, these clear pulses or
signals serve as one input to gate 37 and to set flip-flop 39 for
purposes to be described hereinafter.
In continuing this description of the links between the mechanical
apparatus and the logic control circuit of FIG. 6, reference must
be made to output terminal 41 which, via an inverter 43, couples
the output trigger signal generated by trigger gate 31 to the flash
lamp 50 previously referred to in connection with the description
of FIGS. 1 and 2. Also, mention is appropriate of output terminal
45 which is coupled to suitable control relays initiating
particular sub-systems in the xerographic process area such as the
pre-exposure corotron and xerographic drum drive thereby preparing
the photoreceptor for the recording step as well as other drives
for the chain 58 and discs 26 and 32.
In operation, the circuit of FIG. 6 receives sync bit groups first
which are shifted into shift register 5, detected by detector 13,
and indicated as a pulse to an in sync circuit 76 which may be of
any suitable design to monitor a sequence of received sync pulses.
An in sync condition is indicated by a signal at terminal 51 which
can be coupled to other circuits responding to such a condition.
This in sync signal is provided to reset all the flip-flops
included in the register load circuits 33 as well as flip-flops 55
and 57. By way of inverter 59 coupled to terminal 51, an inverse
signal of opposite polarity to that of the in sync signal is
supplied to reset flip-flop 61. Practically, this means that once
the recording apparatus reaches an in sync condition, the
flip-flops mentioned above as being coupled to terminal 51 are
placed in an initial reset condition.
After this in sync condition is reached, a START word is
transmitted to the recorder which, like the SYNC words, is shifted
into shift register 5 and detected by detector 13. It should be
noted that because of the design of the logic controlling the
loading of the eight digital or buffer registers, none of the SYNC
words are initially translated to these registers from the shift
register 5. The same is true for this first START word. However,
this first START word does act to enable gate 11 and, upon the
trailing edge of the output signals therefrom, places flip-flop 55
in a set condition. This occurs on the trailing edge of one of the
recovered clock pulses. However, due to the propagation time
inherent in the flip-flop 55 gate 63 remains disabled. As noted
before in connection with output terminal 45, this first START word
is required when a xerographic recording medium is utilized to
permit preparation of the xerographic process stations. In
addition, the pulse at output terminal 45 is also used to begin the
chain drive which moves the lens-mirror units through the recording
zone.
After the first START word, additional SYNC words may be
transmitted and then the second START word is sent. This word is
decoded by detector 13 and gate 11 is once again enabled. However,
since the reset input of flip-flop 55 is wired directly to ground
potential, the output of gate 11 has no effect on its set condition
in which it remains. But the enabling of gate 11 does now effect
the enabling of gate 62 and, upon the trailing edge of the pulse at
its output, flip-flop 57 is set. This generates a high level signal
at its set output which enables one input of gate 65.
The other inputs to this gate 65 originate from the counter 9,
character photocell amplifier 23, and latch 67 consisting of gates
69 and 71. The first two of these inputs can be considered at a
high level. As for the latch, its gate 69 monitors two inputs: one
from counter 9 and the other from gate 71. This second gate 71
monitors the output of gate 69 and the reset output of flip-flop 53
in the register load circuit 33 which controls the loading of the
second buffer register 17. Since flip-flop 53 is initially in a
reset condition by action of the in sync signal, it supplies a high
level signal to gate 71. The results of these inputs on latch 67 is
to provide a high level signal to gate 65 to be translated into a
trailing edge by gate 65 and inverter 73 thereby setting flip-flop
61. A high level condition is then created at the output side of
inverter 75, the input of which is coupled to the output of gate
77. This high signal is sufficient to enable the loading of the
first buffer register 15 with the contents of shift register 5.
This would be the first character after the second START word.
Before detailing the action of the register load circuits 33, it
may be helpful to briefly describe their function. Once a word is
loaded from the shift register 5 into the first buffer register 15,
the loaded word then effectively "slides" through the buffer
registers until it reaches the last, or eighth register in the
example of FIG. 6, or an empty register immediately "upstream" from
a loaded or full register. How this is accomplished will now be
described. For simplicity and ease of understanding the circuit of
FIG. 6, not all of the circuits 33 have been illustrated in the
same detail as the first one. It is to be understood that each such
circuit associated with the buffer registers (with the exception of
register 19) has the same design as the one detailed in FIG. 6 in
the dashed block 33.
With the output of gate 77 experiencing a level transition from
high to low to high the output of gate 79 goes high and then low
providing a trailing edge to the toggle input of flip-flop 53
thereby setting this flip-flop. This trailing edge coincides with
the trailing edge of one of the clock pulses supplied to gate 65.
With flip-flop 53 set, the output of latch 67 goes low effectively
disabling gate 65. Also, via inverter 81 coupled to the set output
of flip-flop 53, a resetting pulse is supplied to flip-flop 61.
Gate 83 monitors the clock pulses, the set output of flip-flop 53,
and an output from the next circuit 33 "downstream." This output
comes from the reset output of the flip-flop included in that
particular load register circuit 33. Since that flip-flop would be
initially in a reset condition, this is a high level signal.
Therefore, with flip-flop 53 in an initially set condition, the
output level of gate 83 goes high-low-high and, accordingly, the
output level of inverter 85 goes low-high-low providing an enabling
pulse to the second buffer register 17 to permit the word to
continue its "slide" toward the last of the buffer registers. This
same operation continues to let the word go from one buffer
register to the next succeeding one until it ends up in the eighth
register 19. Meanwhile, with the high-low-high sequence from the
output of gate 83 and a high signal from gate 77, the output of
gate 79 goes low-high-low providing a resetting edge to the toggle
input of flip-flop 53 thereby preparing it for the next received
bit group at input terminal 3.
This same preparatory cycle is accomplished in the remaining
circuits 33 by the action of gate 83 as conveyed by the output
therefrom which is an input to gate 79's counterpart in the next
successive downstream circuit 33.
The technique of loading the last or eighth register 19 differs
somewhat from that which has been described in connection with the
other buffer registers. The loading of this register 19 is
controlled in the first instance by gate 87 which has two inputs;
from two other gates 89 and 91. When either of these two gates
generates a low level signal at its input to gate 87, then a load
pulse will be generated by the latter to load register 19.
As seen from FIG. 6, gate 89 monitors an output from the preceding
register load circuit 33 which comes from inverter 85's counterpart
therein. In addition to this, it monitors the reset output of
flip-flop 93. As will be seen hereinafter, this flip-flop is in a
reset condition at this time and hence a high level signal is at
one of the inputs to gate 89. Since the output of the inverter in
the circuit 33 just upstream from the last register goes through
the same level changes as was described in connection with inverter
85, that input to gate 89 will experience a low-high-low level
transition. During the high level, the output of gate 89 will be
low thus providing a high level load pulse at the output of gate 87
effecting the loading of the last register 19.
As the inverter in the last circuit 33 goes through the
low-high-low sequence of level changes, a trailing edge is coupled
to the toggle input of flip-flop 95 which acts to set this
flip-flop. This puts a high level signal on the input of gate 37
coupled to the set output of this flip-flop 95. This gate 37 has
two other inputs, one of which comes from the set output of the
flip-flop in the last circuit 33. The other input is from the clear
photocell amplifier 21.
The role of gate 37 is to indicate to flip-flop 93 when the last
two buffer registers are loaded so that the recording process can
begin.
This signal from gate 37 is not translated to flip-flop 93 until a
character set begins its pass through the exposure zone previously
described, i.e., a clear signal is supplied to gate 37 from the
clear photocell. At this point flip-flop 93 will be set and a
signal will emanate from the set output of this flip-flop and be
translated to one input of gate 97. Before following through the
explanation of this gate and its other input, reference should be
first made to what other events take place at the initiation of the
signal.
As noted hereinabove, the clear signal clears the character counter
29 after a predetermined time from which, dictated by delay circuit
99, the complement of register 19 is transferred or loaded into
counter 29 via gates 35 enabled by the delayed clear pulse.
The complement of the register 19, when once loaded into the
character counter 29, is augmented by one as each character in the
particular character set passes through the exposure zone. The code
for the characters is so chosen that when the counter reaches its
full count, the character represented by the code word in register
19 will be at the exposure zone. For example, if the desired
character to be recorded was an 13 case character M, then its code
or bit group could be 00001101 which would have "slid" into
register 19. Upon the generation of the next clear pulse, the
complement of this number, 11110010, would be loaded via gates 35
into the character counter 29. As each character in the set passed
the character photocell, its respective character slit would be
detected and a clock pulse generated which would be supplied to
counter 29 to increase its contents by one. Therefore, after 13
character slits were detected and the upper case character M was at
the exposure zone, the contents of the counter 29 would be 11111111
or a full count. This condition would be detected by a series of
gates represented in FIG. 6 by block 101 and indicated by a full
count signal supplied to the trigger gate 31. The other inputs to
this gate need be satisfied before the character in the exposure
zone would be projected onto the xerographic drum 2 by lamp 50.
One input is from flip-flop 103 which is set upon the coincident
occurrence of two events: a signal from flip-flop 93 and a high
level signal from input terminal 105. This latter signal can be
generated in several ways and is used to insure that the moving
optical systems will be in the right position relative to the
recording zone when projection begins. Therefore, a microswitch or
photocell system can be used to insure that when this signal is
generated the chain 58 is in a predetermined position.
Another input to the trigger gate 31 is from the clock pulse
source, character photocell amplifier 23.
The final input to this gate comes from the output of gate 107
which monitors the reset output of flip-flop 39 and the output of
trigger gate 31 itself. The output of trigger gate 31 is normally
high and flip-flop 39 is set by the clear pulse from amplifier
21.
Therefore, all inputs to gate 31 are high thereby providing a low
level signal at its output which is inverted by inverter 43 and
translated to lamp 50 via output terminal 41 as a high level
signal. The upper case character M is then projected onto the
recording medium.
When the lamp is flashed, a low level pulse disables gate 107 and
triggers monostable multivibrator 109 which, in turn, disables gate
91. Since the automatic set and reset inputs of the flip-flops used
in FIG. 6 are level sensitive, during the disabled condition of
gate 91, flip-flop 39 is reset. In addition, flip-flop 95 is reset.
Since the reset output of the flip-flop feeds back to the next
preceding register load circuit 33, specifically as one input to
gate 83 and the input gate associated with the set input of
flip-flip 53 therein, the output of this gate 83 goes low
permitting the output of its respective gate 79 to go high
providing the penultimate buffer register with a loading pulse.
Coincidently with this, the low level pulse from gate 91 also is
supplied as one input of gate 87 thereby permitting this gate to
supply the last register 19 with a load pulse also so that it can
accept the contents of the penultimate register. It may be noted
that affirmative loading is used in the stream of buffer registers
so that zeros can be loaded from one register to another without
first clearing the latter.
Before the above description was started using the upper case
character M as an example, the first word was located in the last
register. Therefore, suitable detecting gates can be incorporated
into detector 110 which monitors the contents of register 19. The
detector also detects other control words such as SPACE, STOP, and
SYNC. When it detects one of these words, it translates an inhibit
signal to output terminal 41 which effectively inhibits the
energization of the flash lamp even though all other conditions at
the input to gate 31 are satisfied.
The above description of a high speed alphanumeric recording
apparatus in accordance with the principles of the present
invention fulfills all the desirable requirements of a high speed
recorder that meets the standard of typewriter quality and
versatility.
While the foregoing description has referred to optically
detectable slits in the character disc 26, other detectable indicia
may also be used, for example, conductive areas, embossed areas, or
any other type of readily detectable marking or index.
While the invention has been described with reference to a
preferred embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the true
spirit and scope of the invention.
* * * * *