Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
_
Field of the Invention
The invention relates to-methods and apparatus for earsing
printed characters and more specifically to erasing by strik-
ing over the unwanted character.
20 STATEMENT REGARDING THE PRIOR ART
A great boon to typists, regardless-of skill level,
resulted when erasing shields and the unpleasant time con-
suming "rub~off" erasing procedure for typed characters gave
way to "strike-over" erasing, i.e., erasing that involves
a repeat striking of the unwanted character using either
a cover-up material or an adhesive tape that
x
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1 lifts the unwanted character off the paper. Such strike-over
erasing is faster and cleaner than the old procedure, and
generally results in less noticeable erasures in the end
product original.
Nevertheless, many sophisticated impact typing machines
do not feature strike-over erasing. One possible reason for
omission of this highly desirable feature is that the character
placement accuracy of moderately-high-speed impact printers,
such as the flexible-spoke ("daisy wheel") printing devices,
10 is not sufficient to achieve an apparently complete erasure.
More specifically, while type-bar and type-ball printers are
usually adjusted to permit a return impact within the "lift-
off zone" of a printed character--typically within +.005 cm of
the original impression--medium to high speed printers (say
those capable of printing at rates exceeding 30 characters
per second) are generally incapable of consistently providing
such strike-over accuracy. With flexible-spoke printers,
this accuracy problem is thought to result mainly from vib-
rations in the long slender spokes and from striker align-
20 ment variations these being additive to the usual carriagepositioning variations. Whatever the causes, it appears that
significantly increased strike-over accuracy is possible
only at an unduly high cost, if at all.
To avoid the above problems with overstriking characters
for erasure purposes, recourse has been taken to erase
techniques using block characters. These block characters
have specifically selected shapes that either singly or in
cooperating groups cover the impression area for any given
printed character. This special character overstriking
technique requires, however, the addition of erase characters
which are not useful for printing purposes and presents
problems because the necessary striking force to make such
characters
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1 effective for erasing, with their relatively large impact
areas, results in paper blemishes that impair the appearance
of the end product original.
Apparently because of the above outlined problems,
medium to high speed printing units, as was mentioned above,
typically do not feature strike-over erase and, if unwanted
characters have been printed, they must either be erased
with an abrasive eraser or painted over manually; otherwise,
the page must be repeated to achieve a clean copy.
10 SUMMARY OF THE INVENTION
The invention involves a recognition that, rather than
resort to special measures in seeking to increase the strike-
over accuracy of a typewriter for permitting quality erasure
of printed characters, quality erasure may be achieved at
normal placement accuracies by purposely missing the printed
character in a particular way. Indeed, we have found that
ordinary character placement accuracy is generally adequate
to assure complete erasures if the unwanted character is
overstruck slightly to one side and then slightly to the
20 other side in the escapement direction. This is believed to
be the case because such strike position shifting allows
the type element pressure pattern to remain generally along
the "embossed" contours of the printed character while never-
theless extending the erase zone along the axis where over-
strike inaccuracy is concentrated, i.e., the escapement axis.
With this double-strike erase approach, the placement shifts
on either side of the printed character are preferably a
fraction of the character escapement and a shift increment
in the range of 2 to 20 percent of the average character
esca~ement has been found
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l to be generally effective for achievin~ quality erasures.
Within such range, it appears that erasures are complete for
the various standard type fonts, as is, of course, desirable
for those machines featuring changeable type.
In a presently preferred implementation for a typewriter
having an escapement detector and using an escapement count
o code to control carrier position, the escapement detection
resolution is a fraction (1/10 or 1/12) of the escapement
for a character and advantage is taken of such resolution to
10 utilize the standard escapement control apparatus in effect-
ing erasures. More specifically, escapement position codes
are generated which represent positions that are a fraction
of the average character escapement from the position of the
unwanted character, so that the carriage may be driven to
such positions, for erase overstriking, by the normal escape-
ment control apparatus. Other functions such as type element
impacting and ribbon lifting are preferably triggered auto-
matically as part of an erase sequence as is discussed more
fully below. And, in a memory typewriter the character is
preferably selected automatically based on a code in memory
corresponding to the nominal erase position.
It should be appreciated that, as an alternative, the
technique of the invention may be implemented by moving the
type carrier to the position of the unwanted character (again
normal accuracy suffices) and then using a separately controll-
ed shifting apparatus mounted on the carrier to superimpose
the necessary escapement increments for erasing accordin~ to
the invention. Furthermore, it should be appreciated that
either the type unit(s) or the paper holder or both may be
transported to provide the relative motion for positioning.
It is also contemplated, for a hi~h-speed version of
the invention in a spoked wheel printer, that a special double
solenoid
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1 arrangement for the impact hammer (described more fully below)
may be introduced to permit a rapid second impact of the un-
wanted character for erasure purposes.
The invention will now be described in detail with ref-
erence to the drawing wherein:
FIG. lA and lB are cross-sectional representations for
teaching the basic erasure method according to the invention,
the sections being taken parallel to the escapement axis;
FIG. 2 is a simplified perspective representation of a
carrier drive suitable for implementing the invention;
FIG. 3 is a side view of a ribbon lift mechanism for
use according to the invention;
FIG. 4 is a system diagram in block form representing
in part a presently preferred implementation for the inven-
tion;
FIG. 5 is a system diagram representing a character
selection apparatus for a wheel-like type unit;
FIG. 6 is a system diayram in block form representing
in part, the presently preferred implementation for the
invention;
FIG. 7 is a flow chart indicating a preferred sequenc-
ing of operations for erasures according to the invention;
FIG. 8 is a side view of a dual solenoid hammer for a
special implementation according to the invention.
FIG. 9 is a front view of a carrier assembly implement-
ing an alternative for introducing sidewise shifting to
establish erase strike positions.
Referring to FIG. lA, a type character 10 is about to
impact a sheet of paper 12 on an erase stroke according to the
invention. An erase tape 14 is interposed between the char-
acter 10 and the paper 12 ~o serve in "lifting off !I the print
medium 16 (hereinafter referred to as "ink"~ of the unwanted
character. According to the invention,
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1 the type character 10 is the same one used for the unwanted
printing and a shift is introduced along the escapement axis
to establish a first erase position PEl at a distance al
to one side of the original printing position Pp. Another
shift is introduced to establish a second erase position
PE2 at a distance ~2 to the other side of the original
printing position Pp. By striking the character twice and
so shifting the strike positions in relation to the original
print position, as was discussed above, a complete erasure
10 can be achieved without a requirement for special overstrike
accuracy. Whats more, abnormal striking pressure is not
required and objectionable paper blemishes do not result,
at least with commonly used typing papers.
The following is a summary of test results for the
technique of the invention using a "daisy wheel" printer
(the Qume Model Q45). Escapement positions for the test
erasures were controlled to high accuracy using a micro-
meter positioning mechanism.
Test Set #l (Normal Printing Force):
Print Eont - Prestige Elite
Force Level - 34 lbs.
Print Ribbon - IBM Correctable Film Ribbon
Correction Tape- IBM Lift-Off Tape
Printed Character- Y & M
Minimum Shifts - + .002"
Maximum Shifts for Complete Erase -
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1 Paper Shift Increment (~ 2)
Patapar + .016 in.
Cranes Crest + .012 in.
Plover + .012 in.
Weston Opaque + .011 in.
Lancaster Bond + .010 in.
Test Set #2 (Heavy Printing Force):
_
Print Font - Diablo Manifold
Force Level - 54 lbs.
Print Ribbon - IBM Correctable Film Ribbon
Correction Tape - IBM Lift-Off Tape
Printed Character - Y & M
Minimum Shifts - + .002 in.
Maximum Shifts for Complete Erasure -
Paper Shift Increment
Cranes Crest ~ .010 in.
Plover + .010 in.
Patapar + .010 in.
LE9-77-003 -6a-
5S2
1 Based on these results, shift increments in a range of
2 to 20 percent of an average character escapement (typically
.08 to .10 in.) or 4 to 40 percent of a nominal character
width (around one half the escapement) are effective for
erasures with various grades of paper and the more difficult
to erase character, i.e., Y and M. Moreover, dual erase
strokes at normal positioning accuracy, but without side
shifts, do not provide reliably complete erasures.
Now referring to FIG. 2 a presently preferred mechanism
for implementing the invention includes a paper holder such
as a platen 20 and associated paper guide rollers 21. A
carrier 22 supports the character bearing type element 24
which is assumed to be a spoked ("daisy") wheel element.
Positioning of the carrier 22 along an escapement axis
parallel to the platen, established by a set of guide rails
26, is effected using a cable-pulley system 28 connected to
a drive motor 30, as is well known in the art. Pulses SE
indicating escapement increments are produced by a position
transducer 32 that is connected to the shaft of motor 30.
The angular resolution of the transducer 32 is preferably
chosen to correspond to 47.24 pulses per centimeter (120
pulses per inch of escapement).
To print a character at a print position ~Pp) along
the escapement axis, a selected character element 34 of the
type unit 24 is rotated by a motor 36 into alignment with a
hammer 38. Such rotation is controlled, as is discussed in
more detail below, based on position code signals Sw produced
by an position transducer 40.
Striking of the character is triggered by a signal SH
applied to an electromagnetic actuator 42 having an armature
44 that pivots to drive the hammer 38 into the selected
element (e.g., the element 34) of the type unit 24.
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1 Ribbon lifters 50 and 52 serve to position printing and
erase tapes respectively. Lifter 50 is caused to pivot by
an actuator 56
LE9-77-003 -7a-
~?~ 32
1 Ribbon lifters 50 and 52 serve to position printing and
erase tapes respectively. Lifter 50 is caused to pivot by an
actuator 54 in response to a lift signal SR and lifter 52 is
caused to pivot by an actuator 56 in response to the signal
ST.
Referring to FIG. 3, apparatus 100 for positioning a
printing tape or ribbon 102 (supplied from a cartridge 103)
between the platen 20 and the character element 34 preferably
includes an arm 50' coupled to the signal responsive actuator
54. The arm 50' drives guide linkage 106 to position the
ribbon 102. Apparatus 104 for positioning an erase tape
108 between platen 20 and the character element 3~ preferably
includes an arm 52' coupled to the signal responsi~e actuator
56. The arm 52' drives guide linkage 110 to position the
ribbon 108.
Referring to FIG. 4 a signal processing arrangment 120
serves in intializing control signals for implementing the
invention in a typewriter such as the Qume Model Q45. Erase
and character selection signals from a manually operable
keyboard 122 are supplied as data to a processor 124.
Responsively the processor 124 raises an erase bit in a
"ha~mer" register 126. An escapement code, representing
the pxesent escapement position, is entered in an "escape-
ment" register 128 and a type character position code along
with a direction bit (CW) are entered in a "selection"
register 130. (An "index" register 132 is shown for complete-
ness but will not be discussed further). Demultiplexing of
information from a processor data bus gate 134 is coordinated
by a command decoder 136 connected to the command bus of
processor 124 as is well known in the data processing art.
A sequence control 140 triggers data transfers, via a
"LOAD" signal, to a hammer buffer 142, an index move counter
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1 144, an escapement move counter 146, and a selection move
counter i48.
Referring to FIG. 5 circuitry for effecting code res-
ponsive selection of type characters includes a logic circuit
160 that sends signals SCW and SCCW to activate the motor 36
in either the clockwise or the
LE9~77-003 -8a-
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1 counterclockwise direction respectively according to the
state of signal CW from the selection counter. A selection
movement is initiated in response to an SSTART signal when
a non-zero code is entered in the selection move counter.
A decoder 162 generates a logic signal SEL~ to indicate when
the total ~5 in counter 148 has been reduced to zero, i.e.,
the selection is completed.
Pulses to decrement the counter 148 are sent from logic
circuit 160 based on the signal Sw of transducer 40. The
signal ~s indicates the distance from the commanded destina-
tion and as a refinement may be used by logic circuit 160
to control the speed of motor 36.
Referring to EIG. 6, printing ribbon lift logic 200
responds to the signal SEL~, which, as was discussed above,
signals completion of a selection, and the ERASE signal
(produced by the processor 124 in response to operator
actuation(s) of the keyboard 122) to control the position of
the print ribbon 102 (FIG. 3) via signal SR and the ribbon
lift apparatus 100.
Escapement movements for implementing the invention, as
was discussed above, preferably involve the normal typewriterescapement mechanism. An erase-and-tape-lift control 240
"tricks" the normal escapement control logic 242 into coopera-
tion by sending special erase control signals through gates
250, 252 and 256, and introducing erase shift values by
means of an encoder 258. More specifically, STARTE is a
special operation initiating signal for erase, LOADE is a
special load command for counter 146, REVE is an escapement
direction command signal for erase, and ECNTE is an incre-
menting signal to the counter 146 (similar signal labels
without the final E identify corresponding signals used for
normal operation).
LE9-77-003 -9-~
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1 The control 240 is sequential and may be implemented,
for example, in a microprocessor, preferrably the processor
124, using techniques well known in the art. A description
of the control 240
lQ
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1 is provided in FIG. 7 in terms of a sequence of cornparison
and command operations.
An erase sequence begins with an erase command (ERASE)
arriving at the buffer 342 (FIG. 4) and a selection code
arriving at the selection move counter ]48. When a type
character selection operation is completed by the selection
circuitry of FIG. 5, the signal SEL0 is set to logic ] and a
signal ERASE] is produced by a gate 244. Referring again to
FIG. 7, the control 240 first checks the state the signal
ERASE' (block 700) and for a logic ] condition, responds by
pulsing the signal LOADE to a logic ] state (block 702),
thereby causing the escapement value from the register ]28 to
be loaded in the move counter ]46 (see also FIG. 6).
A count pulse ECNTE is then applied at gate 250 (block
704) to decrement the counter ]46 and the signal REVE is set
to logic ~ (block 706) and passes through gate 254 to the
escapement control logic 242. Such a command sequence pre-
pares the way for an escapement movement to a position one
escapement increment ~preferably ]/]20") beyond the print
position of the unwanted character. Escapement movement is
triggered by raising the STARTE signal to a logic ] state
(block 708). The STARTE signal passes through a gate 256
(which also receives the normal START signal) to a gate 262.
At the gate 262, a MOVE signal is raised to logic ] if a
decoder 268 indicates that the total~ at the counter ]46 is
not zero (i.e., the inverse of the signal indicating arrival
at a d~stination (ESC0) is at logic ]).
The direction of escapement caused by the drive motor 30
is conditioned to be forward or reverse respectively by
signal DFWD and DREV. Motion of the drive motor 30 is
transmitted to the escapement apparatus 28 and the position
transducer 32 which produces the feedback signal SE. The
signal SE triggers
LE9-77-003 10
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1 a corresponding ECNT pulse, from a squaring circuit 265,
that decrements counter 146.
lOa
7~
1 When the escapement destination is achieved, the signal ESC0
is set to logic 1 and the test at block 710 of FIG. 7 is
satisfied.
Such destination is one escapement increment from unwanted
character position and is a first erase position according
to the invention. Signal STARTE is set to logic 0 (block 712)
and the erase tape lift signal ST is set to logic 1 (block
714). After a delay at device 266 that corresponds to the
operating time of tape lift apparatus 104, the signal ST
becomes (denoted ETUP after delay) indicates that the erase
tape is in operative position (see block 716). The signal
ETUP passes through gate 269 to the hammer control logic 264
(i.e., raises signal RR to logic 1). Such conditioning of
signals ESC~, R. R, SEL0 along with signal IHE remaining at
logic 0 causes the hammer control logic 264 to send out a
hammer pulse SH to the hammer actuator 42. The pulse SH is
also received by a monostable circuit 270 that produces a
signal H' after a delay corresponding to the hammer actuation
time, a ribbon and tape advance apparatus 272, and the control
240 (see block 718, FIG. 7).
An erase "on the fly" may be achieved by triggering the
hammer pulse SH in response to a signal ESCl that indicates
the carrier is one escapement increment from the destination.
With the first erase stroke now completed, the escapement
move counter 146 is loaded with a two increment count via
encoder 258 (block 720), which count represents the displace-
ment to the second striking position. The signal REVE remains
at logic 1 (block 722) and the signal STARTE is set to logic
1 (block 724~ so that an escapement operation similar to that
30 described above commences and continues until the signal
ESC0 goes to a logic 1 state (see block 726, FIG. 7) In this
condition the hammer control logic sends out a hammer actuat-
ing pulse SH and ~ogic 240 waits until the signal H'
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1 goes to a logic 0 state (see block 728, FIG. 7). With the
second erase stroke completed, the erase tape is lowered by
setting the signal ST to logic 0 (block 730).
To return to the unwanted character position, the signal
STARTE is set to logic 0 (block 732) and the escapement move
counter 146 is loaded with a one increment count via the
encoder 258 (block 734). The signal REVE is set to logic
0 (block 736) to cause forward escapement and the hammer
inhibit signal IHE is set to logic 1 (block 738~. Escape-
ment operation is then commenced by setting the signalSTARTE to logic 1 (block 740). Eor this condition, escape-
ment occurs until the position of the erased character (Pp),
is reached at which position the signal ESC0 is set to logic
1 by decoder 268 (see block 742, FIG. 7). The signal STARTE
is then set to logic 0 (block 744~ to complete the operation-
al sequence for control 240.
Referring to FIG. 8, a special hammer apparatus 400 for
high speed erase has dual solenoids 42 and 420 to permit
rapid repeat impacting of hammer 38 for erase operations.
The second hammer actuation indicated in the operating
sequence of FIG~ 7 would, for such implementation, actuate
the solenoid 420 by a signal S'H in order to avoid delay
(because of circuit inductance) between successive solenoid
firings. A set of abutments 422 and 424 serve to limit the
stroke of armature 44'.
As an alternative for establishing erase positions for
erasure according to the invention, the apparatus of FIG. 9
produces side shifts from a print position independently
of the normal carrier positioning apparatus. A carrier
frame 3Q0 supports a mounting frame 302 for sliding motion
paralleling the escapement axis by virtue of guide pins 304
which ride in elongate slots. Controlled escapement
direction shifts for erase are produced by a motor 306
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1 which drives an eccentric cam 30~ against camming surfaces
310 and 320 of mounting frame 302. Erase striking is timed
to occur at extreme escapement direction positions of the
cam 308.
The invention has been described in detail with reference
to the drawing but it will be appreciated that variations
and modifications are possible which come within the spirit
and scope of the inventionO For example, either lift-off
or cover-up media may be used to apparently remove the unwanted
printed character and the erase positioning apparatus may
either involve the normal carrier drive or independent
shift apparatus. Further, the type unit may be a type bar,
type ball, daisy wheel, or any other variety used for impact
printing. And, in a typewriter having a storage for codes
representing type characters on a line the means for select-
ing a type character for erase may be a table look up logic
that extracts the code corresponding to the erase position.
LE9-77-003 ' 3
