Note: Descriptions are shown in the official language in which they were submitted.
I i70374
1 Background of the Invention
The present invention relates to a calligraphic writer
and more particularly to such a device in which writing is per-
formed from a moving carriage on which the pen driving servo-
mechanisms are mounted.
Calligraphic character writing systems are known in
which a pen or stylus together with driving servomechanisms are
transported on a carriage from character position to character
position and, as each position i8 traversed, the servomechanisms
are energized by respective control voltages to effect tracing
out of the desired character. Such devices are described for
example in U.S. Patents Nos. 3,182,126; 3,342,936 and 3,3~9,176
to Ascoli et al; and ~.S. Patent No. 4,150,902 to Brescia. A
related form of graphical plotter is shown in U.S. Patent No.
3449,754 to Stutts.
As is understood, the vectors or line segments which
make up a chara~ter will typically be stored in digital form in
digital memory devices. So-called read only memories are usually
preferred, packaged in a form which permits them to be easily
exchanged, e.g. to effect the changing of character fonts. In
t~e prior art character writing or printer systems as disclosed,
however, it appears that the carriage is moved from ~ne position
to the next and stopped to allow writing of each character. This
then permits the vectors which typically make up each character
to be defined with respect to a fixed frame of reference. While
the possibility of writing while the carriage is moving has been
suggested e.g. in the Brescia patent, no structure implementing
this function is disclosed. Clearly, writing from a moving
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1 carriage has a substantial advantage in total throughput of the
machine since the time spent accelerating and decelerating the
carriage is deducted from the time available for writing. This
loss of time sets an upper limit on the ~verall speed of the
device which limits throughput no matter what improvements are
made in the speed of the servomechanisms which drive the pen and
stylus. As will be understood by those skilled in the art, the
coding of vectors in digital form could be implemented 80 that
the vector orientations themselves take into account the moving
frame of reference. In this way the character resulting from
writing from a moving carriage would have the desired shape not-
withstanding th~ moving frame of reference. However, as will
also be appreciated by those skilled in the art, such a compen-
sation would be fixed in the original coding of each character
and would be valid for a single carriage speed only.
Among the several objects of the present invention may
be noted the provision of a high speed calligraphic character
writer; the provision of such a character writer in which writing
is effected from a carriage while the carriage is in motion; the
provision of such a writer in which writing is performed by a
stylus driven in transverse directions by a pair of servomotors
carried on a carriage which is moving at a freely selectable
velocity; the provision of such a system which i8 highly
reliable and which is of relatively simple and inexpensive
construction. Other objects and features will be in part
apparent and in part pointed out hereinafter.
1 170374
1 Summary of the Invention
Briefly, the present invention involves a character
writer in which each of a series of successive characters is
represented by a plurality of digital data words, each word
defining a vector. The writer employs a mechanism which writes
on a platen from a carriage which is traversed across the platen.
A pair of linear transducers are carried on the carriage for
moving a stylus in essentially transverse directions, thereby
permitting movement of the stylus within a predetermined region
relative to the carriage. Means are provided for driving the
carriage across the platen at a selectable speed and for genera-
ting a voltage which varies in proportion to displacement of the
carriage, starting from a preselectable point corresponding to
the edge of a character location along the platen. A pair of
voltages are generated from each of the data words, which volt-
ages represent velocity components along the transverse
direction. A pair of integrators are provided for generating,
from the velocity voltages, respective relative position
voltages. The carriage displacement voltage is summed with at
least one of the relative position voltages, thereby to obtain
respective control voltages representative of position with
respect to the carriage. The transducers are driven to effect
stylus movement which is, relative to the carriage, proportional
to the control voltages and which is, relative to the platen,
proportional to the relative position voltages and is essentially
independent of the velocity of the carriage.
Brief Description of the Drawings
Fig. 1 is a diagram of a calligraphic writing mechanism
used in the present invention;
~ ~7037~
1 Fig. 2 is a schematic diagram of control circuitry
employed in operating the mechanism of Fig. 1 in accordance with
the present invention; and
Fig. 3 is a block diagram of a generalized microcom-
puter system appropriate for providing data to the circuitry of
Fig. 2 and for generally supervising operation of the apparatus.
Corresponding reference characters indicate
corresponding parts throughout the several views of the drawings.
Description of the Preferred Embodimen~
Referring now to Fig. 1, a carriage mechanism is indi-
cated generally by reference character 11. Carriage 11 is
slideably mounted on a pair of rails 13 and 15 so as to be
moveable along a platen, indicated generally by reference
character 17. Platen 17 may, for example, be of the character of
a typewriter roller through a fixed platen, independent of the
paper feed mechanism, could also be used.
Carriage 11 carries a pair of linear transducers or
servomotors 21 and 23 which are adapted for moving or positioning
a pen or stylus 25. The servomotors are oriented for moving the
stylus 25 along essentially transverse axes. The servomotor 21
moves the stylus along an axis parallel to the carriage motion
(the X-axis) while the servomotor 23 moves the stylus along the
transverse or vertical axis (the Y-axis). Each of the linear
transducers 21 and 23 is responsive to a control signal for mov-
ing the stylus along the respective transverse axis and includes
also means for generating a feedback or position signal. In the
presently preferred embodiment, optical feedback transducers are
~ 170374
1 employed, similar to those described in the Brescia patent iden-
tified earlier. Carriage 11 will typically also include a third
drive mechanism (not shown) for loading and unloading the stylus
to effect writing or not and to vary the loading on the stylus.
At the outset, it may be noted that writing is effected
by moving the carriage along the platen 17 from character posi-
tion to character position and writing in each character position
by energizing the linear servomechanisms 21 and 23 to move the
stylus 25 along in accordance with a set of vectors defining the
character. The definition of these vectors is preferably stored
in diqital form in a suitable digital memory, e.g. a so-called
read only memory, which may be readily interchanged to effect
changing frorn one font to another. The stylus 25 may be in the
form of a pen to effect direct writing or, preferably, will press
through a carbon film ribbon to effect writing on paper supported
by platen 17.
Carriage 11 is moved along the length of platen 17 by a
d.c. servomotor 27 which drives a timing belt 29 passing over a
pair of rollers 31 and 33. This is the means for providing move-
ment along a row of characters, i.e. in the horizontal direction.Movement of the paper in the transverse direction, e.g. vertical,
is provided by means of a stepping motor 35 which rotates the
- roller platen 17.
In order to provide a feedback mechanism for sensing
movement of the carriage and for keeping track of its position,
the servomotor 27 is provided with a shaft encoder 37. Encoder
37 is of the type providing squarewave signals in phase quadra-
1 1 7037~
1 ture, as indicated at A and B, so that both motor speed anddirection of rotation can be determined. These positional infor-
mation signals are provided to the overall control processor of
Fig. 3 as control signals as well as to the servo control cir-
cuitry of Fig. 2.
As indicated previously, the definitions of the vectors
which make up each character are preferably stored in digital
form in a read only memory and are then utilized by a micropro-
cessor controller to generate the actual data which controls the
stylus-driving servomechanims and the carriage drive. The
general organization of this microprocessor system is illustrated
in Fig. 3. The system illustrated is bus-oriented, that is,
memory devices, I/0 ports, and the processor are all connected to
a common data and control bus. This bus is indicated generally
by reference character 41, the processor itself being indicated
at 43. In one embodiment of the invention, processor 43 was an
Intel 8085 microprocessor and the memory and I/0 components were
implemented using integrated circuits from the same family of
devices. As is understood, the advantage of using a
microprocessor-driven controller is that the mode of operation
may be flexibly changed under software control, without extensive
hardware redesign. In implementing its control function, the
processor utilizes random access memory for storing operating
parameters, such memory being indicated by reference character
45. Fixed data, i.e. data defining the vectors which make up
each character in a font, is stored in so-called read only
memory, such memories being indicated in Fig. 3 at reference
characters 46-49.
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1 Digital data for defining the operation of the control
circuitry of Fig. 2 is provided from the microprocessor system
through latched output ports 51 and 52. Port 51 provides data
for the pen servos while the port 52 provides carriage speed
information. As is common to such systems, various control
signals are needed by the processor to determine the state of the
mechanism and various control signals are provided out to the
mechanism controllers. A bi-directional port for this purpose is
indicated by reference character 53. A third I/O port 54 is pro-
vided for vertical control, i.e. the controller which drives the
stepping motor 35. However, this mechanism forms no part of the
present invention and is not disclosed in detail herein.
Preferably, the vector defining data is stored in terms
of direction and length of vector. Among the functions performed
by the microprocessor system of Fig. 3 is to expand the data and
generate respective X- and Y-axis components. These values are
specified to four bits of accuracy each and are applied, respect-
ively, to the digital to analog converters (DACs) 61 and 63 of
Fig. 2. The values provided to the control circuitry represent
velocity components. To get displacement values, the voltages
obtained from the DACs 61 and 63 are integrated by the circuits
indicated at 71 and 73, respectively~ Each of these circuits
comprises an inverting amplifier and an integrating capacitor, Cl
and C3, respectively. The capacitors Cl and C3 can be dis-
charged, i.e. to reset the integrators, by means of respective
analog switches. The dual analog switch which performs this
function, together with its control circuitry, is as indicated
generally by reference character 75. The resetting switch cir-
1 17037q
1 cuitry 75 is operated by a control signal, designated ~ESET,which is one of the signals obtained from the control port 53 of
the microprocessor controller of Fig. 3.
The output signals from the integrators 71 and 73 are
applied, through respective current-limiting resistors Rl and R3,
to error amplifiers 75 and 77. The error amplifiers 75 and 77
are responsive to the difference between the integrator output
signals and the respective position signals obtained from the X
and Y linear servomechanisms 21 and 23. The error amplifiers, in
turn, drive, in conventional fashion, X- and Y-axis power ampli-
fiers 76 and 78.
The quadrature output signals obtained from the shaft
encoder 37 are each applied to one input of a respective com-
parator 81 and 83. A suitable intermediate reference voltage is
applied to the other input of each comparator. The output from
comparator 81 is applied directly as one input to an exclusive OR
gate 85 and, in delayed form, as the other input to gate 85. The
delay is effected by a filter comprising a resistor R6 and capa-
citor C6, with s~uaring up being performed by a buffer gate 87.
The function of this delay and gating circuitry is to provide, at
the output of gate 85, a brief pulse for each transition, posi-
tive or negative, in ~he input signal A. A completely similar
circuit provides, in re~ponse to the input signal B, a
corresponding pulse train at the output of an exclusive OR gate
89. The pulse trains obtained from the gates 85 and 89 are com-
bined in an exclusive OR gate 91. The output of this gate
comprises a pulse for each transition in either of the input
signals (A or B). In effec~, a factor of four multiplication in
1 17037~
1 the pulse rate is provided as compared with the pulse rate of
either one of the input signals. If the carriage were driven by
a stepper motor instead of the d.c. servomotor 27, the pulse
signal used to advance that motor might be used in place of the
pulse train generated by the shaft encoder 37.
The pulse train obtained from the gate 91 is applied to
a counter 101 so that the counter generates a digital value which
varies in proportion to displacement of the carriage. This
counter 101 is reset along with the resetting of the integrators
71 and 73 at the start of each character. Thus, the digital
value held by the counter in one sense represents displacement
across the character position. The digital value in counter 101
is converted to an analog signal voltage by a digital to an~log
(D/A) converter 103, the transfer being buffered by a latch 105
which is loaded in synchronism with the counting to minimize
ripple-through effects. In one sense, the output voltage from
the D/A converter 103 comprises a ramp as the carriage moves
across the platen. This ramp voltage, however, is not a time
dependent function in the usual sense, but rather is proportional
to actual displacement of the carriage and thus, in the time
domain, will vary as the speed of the carriage varies.
The rarnp voltage obtained from D/A converter 103 is
mixed in or summed with the X axis position signal obtained from
the integrator 73, the ramp ignal being applied, through a
resistor R9, to a summing junction S at the input of error
amplifier 77. The addition of this carriage displacement com-
ponent into the vector-defining voltage allows the writing of
characters from the moving carriage without requiring alteration
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1 170374
1 of the basic vector encoding scheme and, in a manner, allowing
the velocity of the carriage to change. Because of this compen-
sation, the carriage can be driven re~atively rapidly when simple
characters are being written and more slowly for more complex
characters. In this way, the throughput of the machine can be
substantially increased as compared with the situation which
would exist if the speed of the carriage had to be kept constant,
as would be the case if compensation were built into the vector
encoding scheme. In such a case the single speed chosen would
have to be relatively low, i.e. selected to permit forming of the
most complex character to be written.
Selection of carriage speed is performed by the micro-
processor system of Fig. 3, a data word representing the desired
carriage speed being output through the port 52. This data, at
five bits of accuracy, is applied to a digital-to-analog con-
verter 111. The output signal from converter 111, which is an
analog voltage representing desired speed, is compared with a
voltage representing actual speed. This latter voltage is
obtained by a frequency-to-voltage converter 113 driven by the
pulse train from gate 91. As described previously, the pulse in
this train is generated at a rate which is proportional to the
speed of the carriage, being derived from the shaft encoder asso-
ciated with the carriage drive motor 27. The output voltages
from the frequency-to-voltage converter 113 and the ~/A converter
111 are applied, through respective mixing resistors Rll and R13,
to a summing junction T to derive an error signal. This error is
amplified as indicated at 117. The amplified error signal is
mixed with an a.c. component obtained from a dither oscillator
1 170374
1 119 at the input of an amplifier 121 which, in turn, drives a
power amplifier controlling the servomotor 27.
The embodiment illustrated includes provision for
forming characters of different sizes from the same font data,
i.e. the digital data being applied directly to the digital-to-
analog converters 61 and 63. For this purpose, the converters
are of the so-called multiplying type in which the output voltage
is proportional, not only to the digital value applied, but also
to an analog reference voltage. A four bit data word, again
obtained from the microprocessor controller of Fig. 3, is applied
to a decoder 72 which generates two separate one-of-four selec-
tion signals. Each of these set of signals is applied to a
respective quad switch 74 and 76 to select one of four predeter-
mined voltages for application, as a reference voltage, to the
respective digital analog converter 61 or 63. The predetermined
voltages are obtained from a voltage divider comprising resistors
R21-R24. The resistors R21-R24 are selected to produce voltages
corresponding to desired typesizes rather than to perform a nor-
mal digital-to-analog conversion. The nature of the decoding is
such that only one switch in each of the packages is on at any
one time so that the reference voltage applied to each digital-
to-analog converter 61 or 63 may be independently selected.
Accordingly, since the horizontal and vertical scaling factors
can be selected separately, characters of different aspect ratios
can be formed from the same data as well as merely scaling the
characters.
In the embodiment illustrated, the axis o~ one of the
linear servotransducers driving the stylus is parallel to the
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~ 17037.~
1 direction of carriage movement and the other axis is essentially
perpendicular thereto. Accordingly, the displacement based com-
pensation signal only needs to be mixed with one of the two
control signals driving the servotransducers in order to obtain
the desired moving frame of reference. On the other hand, those
skilled in the art will appreciate that an arrangement could be
utilized in which the axes of both linear servotransducers were
at an angle, e.g. 45 to the direction of carriage movement,
though perpendicular to each other. In such a case, displacement
compensation components of appropriate magnitude would be æummed
with each of the servocontrol signals, observing appropriate
polarity. Such an arrangement should be understood to be within
the scope of the present invention. Similarly, it should also be
understood that it is relative motion between the platen and the
stylus mount which is significant and that either component might
actually be moved even though movement of the stylus mount
(carriage) is disclosed in the preferred embodiment.
Summarizing, it can be seen that the present invention
facilitates the digital encoding of character defining vectors
with respect to a seemingly fixed frame of reference. High speed
writing of characters from a moving frame of reference, the
carriage, is then accomplished by summing, with at least one of
the writing servocontrol voltages, a compensating voltage which
-- represents displacement across a character position. Thus, co~-
pensation for the moving frame of reference is achieved essen-
tially independently of carriage speed.
In view of the foregoing, it may be seen that several
o~jects of the present invention are achieved and other advan-
tageous results have been attained.
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1170374
1 As various changes could be made in the above construc-
tions without departing from the scope of the invention, it
should be understood that all matter contained in the above
description or shown in the accompanying drawings shall be
interpreted as illustrative and not in a limiting sense.
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