Note: Descriptions are shown in the official language in which they were submitted.
"` ~ 2fi(~8~1
IMI'A~T MECHANIS~I ~OR QUIET IMPACT PRINT~R
liIELD ~F THE INVENTION
This invention relates to the impact mechanism for an improved serial
irnpact printer and, more particularly, to a novel prin~er designed to
substantially reduce impact noise generation during the printing operation
BACKGROIJND OF THE lNYENTlON
The office environment has, for many years, been the home of
objectionable noise generators, viz. typewriters and high speed impact
printers. Where several such devices are placed together in a single room,
~5 the cumlllative noise pollution may even be hazardous to the health and
well being of its occupants. The situation is well recognized and has been
addressed in the technical community as well as in governmental bodies.
Attempts have been made to reduce the noise by several methods:
enclosing impact printers in sound attenuating covers; designing impact
20 printers in which the impact noise is reduced; and designing quieter
printers based on non-impact technologies s~lch as ink jet and thermal
transfer. Also, legislative and regulatory bodies have set standards for
maximum acceptable noise levels in ofFlce environments.
Typically, impact printers generate an average noise in the range of 70 to
just over 80 dBA, which is deemed to be intrusive. When reduced to the 60-
70 dBA range, the noise is construed to be objectionable. Further redllction
of the impact noise level to the 50-60 dBA range uollld improve the
designation to anno;ing. Clearly, it would be desirable to reduce the impact
noise to a dB~ value in the low to mid-40's. The "A" scale, by which the
sound vallles have been identified, represents hllmanly perceived levcls of
lolldness as opposed to absolute alues of sollnd intensity alld uill be
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disc~lssed in more detail below. When considering so~md energyrepresented in dB (or dBA) ~Inits, it should be borne in mind that the scale
is logarithmic and that a 10 dB difference means a factor of 10, a 20 dB
difference means a factor of 100, 30 dB a factor of 1000 and so on. We are
5 looking for a very aggressive dropoff in printer impact noise.
The printing noise referenced above is of an imp~llse character and is
primarily prod~lced as the hammer impacts and drives the type character
pad against the ribbon, the print sheet and the platen with sufficient force
10 to release the ink from the ribbon. The discussion herein will be directed
solely to the impact noise that masks other noises in the system. Once sllch
impact noise has been substantially reduced, the other noises will no longer
be extraneous. Th~ls, the design of a tr~lly quiet printer requires the
designer to address reducing all other noise sources, such as those arising
~s from carriage motion, character selection, ribbon lift and advance, as well as
from miscellaneous clutches, solenoids, motors and switches.
Since it is the impact noise which is modified in the present invention, it is
necessary to understand the origin of the impact noise in conventional
20 ballistic hammer impact printers. In such typical daisywheel printers, a
hammer mass of about 2.5 grams is driven ballistically by a solenoid-
act~lated clapper; the hammer hits the rear surface of the character pad and
impacts it against the ribbon/paper/platen combination, from which it
rebounds to its home position where it mllst be stopped, usllally by another
`- 25 impact. This series of impacts is the main source of the objectionable noise.
Looking solely at the platen deformation impact, i.e. ~he hammer against
the ribbon/paper/platen combination, the total dwell thne is typically in the
vicinity of 100 microseconds. Yet, at a printing speed Or 30 characters per
30 second, the mean time available between character hllpacts is about ~0
milliseconds. Clearly, there is ample opportllnity to significantly stretch the
imp,lct dwell time to a substantially larger fraction of the printin~, cycle than
.~260~16~L
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is typical of conventional printers. For instance, if the dwell time were
stretched from 100 microseconds to 6 to 10 milliseconds, this would
represent a sixty- to one hundred-fold increase, or stretch, in pulse width
relative to the conventional. By extending the deforrning o~the platen over
a longer period of time, an attendant reduction in noise output can be
achieved, as will become apparent in the following discussion.
The general concept - reduction in impulse noise by stretching the
deforrnation pulse - has been recognized for many decades. As long ago as
o 1918, in U.S. Patent No. 1,261,751 (Anderson) it was recognized that q~liet
operation of the printing runction in a typewriter may be achieved by
increasing the "time act~lally llsed in making the impression". Anderson
llses a weight or "moment~lm accum~llator" to thrllst each type carrier
against a platen. Initially, the force applying key lever is str~lck to set a
linkage in motion for moving the type carriers. Then the key lever is
arrested in its downward motion by a stop, so that it is decoLlpled from the
type carrier and exercises no control thereafter. An improvement over the
Anderson actuating linkage is taught in Going, U.S. Patent No. 1,561,450. A
typewriter operating upon the principles described in these patents was
commercially available.
Pressing or squeezing mechanisms are also shown and described in ~J.S.
Patent No. 3,918,568 (Shimodaira) and U.S. Patent No. 4,147,438 (Sandrone
el al) wherein rotating eccentric drives Llrge pLlshing members against the
character/ribbon/sheet/platen combination in a predetermined cyclical
manner. It shoLlld be apparent that an invariable, "kinematic" relationship
(i.e. fixed interobjcct spacings) between the moving parts renders critical
impoltallce to the platen location and tolel-ances thereon. That is, if the
throat distance between the pLIshing member and the platen is too great, the
ribbon and the sheet will not be pressed with s~lfricient force (if at all) for
acceptable print qllali2y and, conversely, if the throat distance is too close,
~he pllslling member will callse the character pad to emboss the image
1 !36~
receptor sheet. Sandrone et al teaches that the
kinematic relationship may be duplicated by usiny a
solenoid actuator, rather than a fixed eccentric (note
alternative embodiment of Fiyures 1~ through 17).
Pressing action may also be accomplished by
simultaneously moving the pla1en and the pushing member,
as taught in U.S. Patent No. ~L,203,675 (Osmera et al).
In addition, Sandrone et al states that quiet operation
o relies upon moving a small mass and that noisy operati.on
is generated by large masses. This theory is certainly
in contravention to that applied in Anderson and Going
(supra) and in U.S. Patent No. 1,110,346 (Reisser) in
which a mass multiplier, in the form of a flywheel and
linkage arrangement, is set in motion by the key levers
to increase the effective mass of the striking rod which
impacts a selected character pad.
A commercially acceptable printer must have a number of
attributes not found in the prior art. First, it must
be reasonably priced, therefore tolerance control and
the number of parts must be minimized. Second, it must
have print quality comparable to, or better, than that
conventionally available. Third, it must have the same
or similar speed capability as conventional printers.
The first and the last factors rule out a printer design
based upon squeeze action since tolerances are critical
therein and too much time is required to achieve
satisfactory print quality.
It is an object of an aspect of the present invention to
provide a novel impact mechanism for a quiet impact
printer that is orders of magnitude quieter than that
typical in today's mar~etplace, and which nevertheless
achieves the rapid action and modest cost required for
office usage.
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SUMMARY OF THE INVlENTION
An aspect of this invention is as follows:
An impact mechanism in an impact printer, for
delivering a printing force to drive a character element
against a platen by means of a print tip normally spaced
from the surface of said platen by a throat distance and
movable toward and away from said platen, said character
element and said print tip being supported upon a
carriage mounted upon said printer for reciprocating
movement in a path substantially coextensive with the
axial length of said platen and substantially parallel
to the axis of said platen, said impact mechani.sm being5 characterized by comprising;
a bail bar of substantially the same length as said
platen, extending in a direction substantially parallel
to the axis of said platen, said bail bar having an axis
of rotation substantially parallel to the axis of said
platen and being constrained to limited angular movement
about its axis for movement toward and away from said
platen,
means for interconnecting said print tip and said
bail bar so as to move said print tip toward and away
from said platen as said bail bar is rocked, said means
for interconnecting being supported upon and movable
with said carriage and including means at a first end of
said means for interconnecting for providing intimate
moving contact with said bail bar in the direction of
carriage movement and in both directions of movement of
said bail bar, an interposer mounted upon and movable
with said carriage and being further movable in an
arcuate path toward and away from said platen, a second
end of said means for connecting being attached to said
interposer, wherein said print tip is supported upon
said interposer for movement in said arcuate path, and
drive means connected to said bail bar for
imparting said limited angular movement thereto at a
predetermined velocity so as to move said print tip
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therewith at a predetermined velocity as it is moved
from a home position, across said throat distance and
then to deform said platen.
By way of added explanation, the quiet impact pxinter of
the present invention comprises, in one form, a novel
impact mechanism for delivering a printing force to
drive a character
086
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element against a platen by means of a print tip movable toward and away
from the platen. The character element and the print tip are supported
upon a carriage mounted upon the printer for reciprocating movement in a
path substantially parallel to the axis oî the platen. The impact mechanism
5 includes a bail bar mounted for rocking movement toward and away frorn
the platen, its axis of rocking being substantially parallel to the axis of the
platen. The print tip and the bail bar are interconnected so as to move the
print tip toward and away from the platen as the bail bar is rocked. A prime
mover is connected to the bail bar for imparting controlled rocking
10 movement thereto so as to impart the desired velocity to the print tip as it
moves from a home position to the surface of said platen and then moves to
deform said platen.
THEORY OF OPERATION OF THE INVENTION
As is the case in conventional ballistic hammer printers, the improved
printer of this invention also is based upon the principle of kinetic energy
transfer from a hammer assembly to a deformable member. The mass is
accelerated, gains momentum and transfers its kinetic energy to the
20 deformable member which stores it as potential energy. In sllch dynamic
systems the masses involved and speeds related to them are substantial, so
that one cannot slow down the operation withollt seeing a signirlcant
change in behavior. Taken to its extreme, if such a system is slowed eno~lgh
its behavior disappears altogether and no printing will occ~lr. In other
25 words, a kinetic system will only work if the movable mass and its speed are
in the proper relationship to one another.
Another attribLlte of the kinetic system is that it is self levclling. By this we
mean that the moving mass is not complctely limited b~ the drive behind it.
30 Motion is available to it and the moving mass will continlle to move lln~il
an cncolmter with the platen is made, at which time the e~change bctween
their energies is accomplished. Thcrefore, since the point of contact wilh the
6- ~L26~
platen is unpredictable, spatial tolerances are less critical, and the printing
action of the system will no~ be appreciably altered by minor variations in
the location of the point of contac~
5 Kinetic energy transfer systems ~re to be distinguished from kinematic
systems in which the masses involved and the speeds related to them are
much less important. The latter are typically represented by cam-operated
structures in which the moving elements are physically constrained in an
invariable cyclical path. They will operate as effectively at any speed. It
o doesn't matter how slowly the parts are moved. All ~hat is important is the
spatial relationship between the relatively movable parts. The cycle of
operation will continue unchanged even in the absence of the deformable
member. Consider the effect of a platen spacing which is out of tolerance. If
the platen is too close, the invariant motion will cause embossing of the
15 paper; if the platen is too far, printing will not be of satisfactory q~ality, or
printing may not take place at all.
~n order to understand the theory by which noise reduction has been
achieved in the novel impact printer of this invention, it would be helpful
21) to consider the mechanism by which sound (impulse noise) is generated and
how the solmd energy can be advantageously manipulated. In a
fundamental sense, sound results from a mechanical deforrnation which
moves a transmitting medium, such as air. Since we will want to maintain
the amplitude of platen deforrnation s~lbstantially the same as in
25 conventional ballistic impact printers in order to insllre high quality
printing, we will only consider the velocity of the deformation. As the
deforming surface moves, the air press~lre changes in its vicinity, and the
propagating pressllre distllrbance is perceived by the ear as sollnd.
Immediately adjacent the surface there will be a slight rarefaction (or
30 compression3 of the transmitting medillm, becallse the sLIrro~lnding air can
fill the void (or move ollt of the way) only at a f nite rate, i.e., the faster the
derorma~ion occurs, the greater will be the distllrbance in the medillm.
. 7 ~l260~631
Th~ls, the resulting pressllre difference and the res~llting sound intensity
depend upon deformation velocity~ not merely ~Ipon amplitude of
deforrnation. Intuitively we know that a sharp, rapid impact will be noisy
and that a slow impact will be less noisy. As the duration of the de~orrning
5 force pulse is increased, the velocity of the deforming sur~ace is reduced
correspondingly and the soLlnd pressure is reduced. Therefore, since the
intensity of the sound waves, i.e. the energy created per unit time, is
proportional to the product of the velocity and pressure, stretching the
deforming pulse red~lces the intensity of the sound wave.
Taking this concept as our starting point, we consider the impact noise
source, i.e. the platen deforrnation when hit by the hammer. The
intervening character, ribbon, and paper will be neglected since they travel
as one with the hammer. It has just been explained that sound intensity can
15 be redllced by stretching the contact period, or dwell, of the impact. We
also know that we have a substantial time budget (about 15 milliseconds)
for expanding the conventional (100 microsecond) cont~ct period by a
factor of abo~lt 10Q. Furthermore, it is well known that manipulation of the
time dornain of the deformation will change the frequency domain of the
20 sound waves emanating therefrom. In fact, as the impulse deformation time
is stre~ched, the sollnd freq~lency (act-lally, a spectrum of so~lnd
freq~lencies) emanating from the deformation is proportionately reduced. In
olher words, in the abovè example, stretching the contact period by 100
times would red~lce the corresponding average frequency of the spectrllm
25 by 100 times.
As the dcformation p~llse width is increased and the average fi-equency and
freqllency spectrllm is reduced, the impact printing noise is lessened as the
res~llt of l~vo phenomena. The first pllenomenon has been described above,
30 namcly, red~lction of the so~md wave intensity, arising from the
proportionality of sollnd pressllre to the velocity of the deformation. A
rcdllc~ion factor of abollt 3 d~ pcr octave of average freq~lency red~lction,
- 8~ ~ 26~36~
has been calculated. The second phenomenon, arises from the
psychoacoustic perception of a given sound intensity. It is well known that
the human ear has an uneven response to sound, as a function of frequency.
For very loud sounds the response of the human ear is almost flat with
5 frequency. But, at lower loudness levels the human ear responds more
sensitively to solmd freqllencies in the 2000 to S000 Hz range, than to either
higher or lower frequencies. This "roll-off" in the response of the human
ear is extremely pronounced at both the high and low frequency extremes.
o A representation of the combined effect of the sound intensity and the
psychoaco~lstic perception phenomena is illustrated in Fig~lre 1 wherein
there is reproduced the well known Fletcher-Munson contours of equal
loudness (dBA), plotted against intensity level (dB) and freq~lency (Hz) for
the average human ear. The graph has been taken from page 569 of
"Acoustical Engineering" by Harry F. Olson published in 1957 by D. Van
Nostrand Company, Inc.. At 1000 Hz, the contours, which represent how
the frequencies are weighted by the brain, `are normalized by
correspondence with intensity levels (i.e. 10dB = 10dBA, 20dB = 20dBA,
etc.). As stated above, both dB aTId dBA are logarithmic scales so that a
difference of 10 dB means a factor of 10; 20 dB means a factor of 100; 30
dB means a factor of 1000, and so on.
The following example illustrates the above described compound red~lction
in perceived impulse noise, achieved by expansion of the dwell time of the
impact force. Consider as a stalting point the vicinity of region "a" in
Figure 1 which represents a conventional typcwriter or printer impact noise
level generated by an impact pLllse of aboLlt 100 microseconds. It has a
lo~ldness level of abollt 75 dBA al a freqllency of abollt S000 Hz. An
e~pansion of the impact dv~ell time ~o abo~lt 5 milliseconds represents a S0-
îold dwell time increase, res~llting in a comparable 50-fold ~abo~lt 5.5
octaves) fiequency rcd~lction to abo~lt 100 Hz. This fieq~lency shift is shown
the linc indicatcd by arrow A. A redllction factor o~ aboLI~ 3dB per octave,
~ ~60~36
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attributed to the slower deformation pulse, decreases the noise intensity by
about 16.5 dB, along the line indicated by arrow B, to the vicinity of region
"b" which falls on the 35 dBA contour. Thus, by stretching the impact tirne,
the sound intensity per se has been decreased by about 16.5 dB, but the
s shift in the average frequency (to about 100 ~z) to a domain where the ear
is less sensitive, results in the compound effect whereby impact noise is
perceived to be about 40 dB quieter than conveDtional impact printers.
In order to implement the extended dwell time, with its attendant decrease
~o in deformation velocity, it was found to be desirable to alter the impacting
member. The following analysis, being a satisfactory first order
approximation, will assist in understanding these alterations. For practical
purposes, the platen, which generates noise during the deforrnation impact,
may be considered to be a resilient deformable member having a spring
15 constant "k". In reality it is understood that the platen is a viscoelastic
material which is highly temperature dependent. The platen (spring) and
impacting hammer mass "m" will move together as a single body during the
deformation period, and may be viewed as a resonant system having a
- resonant frequency "f" whose pulse width intrinsically is decided by the
20 resonant frequency of the platen springiness and the mass of the hammer.
In a resonant system, the resonant frequency is proportional to the square
root of k/m (or f2 = k/m). ~here~ore, since the mass is inversely
proportional to the sq~lare of the frequency shift, the 50-fold frequency
reduction of the above example would require a 2500-fold increase in the
2S hammer mass. This means, that in order to achieve print quality (i.e. same
deformation amplitude) comparable to the conventional ballistic-type
impact printer it would be necessary to increase the mass of the typical
hammer weighing 2.5 grams, to abo~lt 13.75 pounds. The need to control
such a large hammer mass, while Xeeping the system inexpensive, would
30 appear to be implausible.
Having seen that it is necessary to mate~ lly increase the mass, it is quickl~
- 10 - ~Z~;O~
understood that the quantitative difference we have effected is no longer
one of degree, bllt is rather one of kind, signifying an entirely different, andnovel, class of impact mechanism. The novel approach of the present
invention makes the implausible quite practical. Rather than increasing the
s hammer mass per se, a mass transforrner is utili7ed to achieve a mechanical
advantage and to bring a large effective, or apparent, mass to a print tip
through a unique drive arrangemen~ In addition to an increase in the
magnitude of the effective mass, quality plinting is achieved by the
metering of sllfficient kinetic energy to the platen to cause the appropriate
o defolTnation therein.
In the impact printer of the present invention, a heavy mass is set in motion
to accumulate momentum, for delivery to the platen by the movable print
tip, throllgh a sllitable linkage. The entire exc~lrsion of the print tip includes
15 a throat distance of about 50 mils from its home position to the surface of
the platen and then a deformation, or penetration, distance of abollt S mils.
The stored energy, or momentum, in the heavy mass is transferred to the
platen dllring defonnation and is completely converted to potential energy
therein, as the print tip is slowed and then arrested. As the print tip is the
20 only part of the kinetic energy delivery system "seen" by the platen, it views
the print tip as having the large system mass ~its effective mass). It shollld
be apparent, of collrse, that relative motion between the print tip and the
platen may be accomplished, alternatively, by moving either the platen
relative to a fixed print tip, or by moving both the print tip and the platen
25 toward and away from one another.
In the preferred form of the present invention, the total kinetic energy may
be metered o~lt incrementally to the mass transformer. A first portion of the
energy will move the print tip rapidly across the throat distance and a
30 second portion of the energy will be provided at the initiation of the
dcforrnation period. By controlling the prime mover, the traverse of the
throat distance may be accomplished by initially moving the print ~ip
31 ~6~
rapidly and then slowing it down immediately before it reaches the platen
surface. This may be done by havil~g regions of different velocity with
transitions therebetween or it coul~ be done by continuously controlling the
velocity. It is desirable to slow the print tip to a low or substantially zero
5 velocity irnmediately prior to the initiation of contact in order to decrease
the impact noise. However, since its velocity at the initiation of contact
would be too low for printing, an augmentation of kinetic energy mllst be
irnparted at that point in order to accelerate the print tip into the platen foraccomplishing the printing.
Alternatively, it is possible to provide the mass transforrner with the total
kinetic energy it will need to cross the throat distance and to effect
penetration of the platen. This energy would be metered out to the mass
transformer by the system prime mover at the home position (i.e. prior to
15 the initiation of the deforrnation period) and will set the mass transforrnerin motion. In order to carry out this procedure, a large force would have to
be applied and it is apparent that more noise will be generated.
A major benefit may be obtained when we bifurcate the total kinetic energy
20 and meter it ~or (a) closing down the throat distance (before contact), and
(b) effecting penetration into the platen (after contact~. Namely, the contact
velocity will be low, resulting in inherently quieter operation. The metering
may be accomplished so that the velocity of the print tip may be
substantially arrested immediately prior to contact with the platen, or it may
25 have some small velocity. What is important is that uporl derterrnination
that contact has been made, an augmentation force is applied for adequate
penetration.
We find that under certain conditions the application of the allgmentation
30 kinetic energy allows us to obtain the same penetration force and yet
sllbslantially decrease the effective mass, and thlls the system mass. In order
to llnderstalld why this is possible, the effect of momentllm on deformation
~z~o~
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should be explored. In the following two examples, it is assumed that the
same maximum platen deforTnation is effected, in order that comparable
print quality is achieved. First consider a squeeze-type printer wherein the
deforrning force is applied so slowly that its momentum is negligible. As the
5 print tip begins to deforrn the platen, its force is greater than, and
overcomes, the platen restoring counterforce. When the print tip deforrning
force equals the platen restoring counterforce, the print tip mass will stop
moving and the counterforce will prevail, dr~ving the movable members
apart. This will occur at the point of maximum platen deforrnation.
Now consider the kinetic system of the present invention, wherein the print
tip is accelerated into the platen. It may either have a finite velocity or zerovelocity at its moment of arrival. Then, as the accelerating print tip begins
to exert a force on the deforrning platen, it experiences the platen restoring
15 counterforce. Initially the print tip deforming force will be greater than the
platen restoring collnterforce. However, unlike the previous exarnple, the
print tip force equals the platen restoring counterforce at the mid-point (not
at the end) of its excursion. From that point, to the point of maximum
deformation, the print tip's momentum will continue to carry it forward,
20 while the greater counterforce is decelerating it. At the point of maximum
defolmation, all the print tip kinetic energy will have been converted to
potential energy in the platen and the restoring force will begin to drive the
print tip ollt.
25 We find that it is only necessary to apply half of the platen deforming forcewhile the system momentllm, in effect, applies the remaining half. We also
find that since the hammer mass would have a longer excursion, if we want
to limit penetration to the same amplitude, we must shorten the dwell time
for the same penetration. Since, as stated above, the mass relates inversely
30 to the square Or the frequency, doLlbling the frequency allows us to reduce
the mass by one-qllarter.
~ 26,~f~fi'1
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Typical values in our unique impact printer are: an effective hammer massat the point of contact of 3 pounds (1350 grarns), a contact period of 4 to 6
milliseconds, and a contact velocity of ~ to 3 inches per second (ips). By
comparison, typical values of these pararneters in a conventional impact
5 printer are: a harnmer mass of 3 to 4 grams, a contact period of S0 to 10D
microseconds, and a contact velocity of 8~ to 10~ ips. Even the IBM ball-
type print element, the heaviest conventional impact print hammer, and its
associated driving mechanism has an effective mass of only 50 grams.
o We believe that a printer utilizing our principal of operation would begin to
observe noise reduction benefits at the following parametric limits: an
effective mass at the point of contact of 0.5 pounds, a contact period of 1
millisecond, and a contact velocity of 16 ips. Of course, these values would
not yield optimum results, but there is a reasonable expectation that a
15 printer constructed to these values would have some attributes of the
present invention and will be quieter than conventional printers. For
example, one would not obtain a 30 dB (1000x) advantage, but may obtain
a 3 dB (2x) noise reduction. The further these values move toward the
typical values of our printer, the quieter the printer will become.
BRIl~F DESCRIPTION OF T~IE DR~\WINGS
The advantages of the present invention will be understood by those skilled
in the art through the following detailed description when taken in
25 conjunction with the accompanying drawings, in which:
Figure 1 is a graph showing contour lines of equal loudness for the norrnal
human ear;
Figure 2 is a perspective view of the novel impact printer of the present
nventlon;
- 14 . ~26C~1~6~,
Figure 3 is a side elevation view of the novel impact printer of the present
invention showing the print tip spaced from the platen;
Figure 4 is a side elevation view sirnilar to Figure 3 showing the print tip
s impacting the platen, and
Figure 5 is an enlarged perspective view of the back of the print tip.
DETAILED DESCRIPT~ON OF THE ILLUSTRATED EMBODIMEN~
The graph of Figure 1 has been discussed above with reference to the
theory of noise reduction incorporated in the present invention. Our novel
irnpact printer will be described with particular reference to Figures 2
through 5. The illustrated printer includes a platen 10 comparable to those
~s used in conventi~nal impact printers. It is suitably mounted for rotation in
bearings in a frame (not shown) and is connected to a drive mechanism
(also not shown) for advancing and retracting a sheet 11 upon which
characters may be imprinted. A carriage support bar 12 spans the printer
from side to side beneath the platen. It may be fabricated integrally with
20 the base and frame or may be rigidly secured in place. The carriage support
bar is forrned with upper and lower V-shaped seats 14 and 16 in which rod
stock rails 18 and 20 are seated and secured. In this manner, it is possible to
form a carriage rail structure having a very smooth low friction surface
while maintaining relatively low cost.
It is important that the support bar 12 extends parallel to the axis of the
platen so that the carriage 22 and the printing elements carried thereon will
be accurately located in all lateral positions of the carriage, along the lengthof the platen. A cantilever support arrangement for the carl iage is provided
by four sets of toed-in rollers 24, two at the top and two at the bottom,
which ride llpon the rails 18 and 20. In this manner, the carriage is
unobtrllsively supported for moving several motors and other control
~ ;~608~i4
- 15-
mechanisms for lateral movernent relative to the platen. A suitable carriage
drive arrangement (not shown) such as a conventional cable, belt or screw
drive may be connected to the carriage for moving it parallel to the platen
10 upon the support bar 12, in the direction of arrow C
The carriage 22 is shown as comprising side plates 25 secured together by
connecting rods 26 and supporting the toed-in rollers outboard ~ereof.
Althollgh the presently preferred form is somewhat differently configured,
this representation has been made merely to more easily illustrate the
o relationship of parts. There is shown mounted on the carriage a printwheel
motor 27 having a rotatable shaft 28 to which print~Yheel 30 is securable,
and a ribbon cartridge 32 (shown in phantom lines) which supports a
marking ribbon 33 intermediate the printwheel and the image receptor
sheet 11. A ribbon drive motor and a ribbon shi~ing mechanism, which are
lS also carried on the carriage, are not shown.
In conYentional printers the carriage also supports the hammer and its
actuating mechanism. In our unique arrangement, the carriage only
supports a portion of the hammer mechanism, narnely, a T-shaped print tip
20 34 secured upon an interposer member 36. The interposer is in the forrn of
a yoke whose ends are pivotably mounted in carriage 22 on bearing pin 38
so as to be constrained for arcuate movement toward and away from the
platen 10. The print tip 34 includes a base 40 and a central, cutwardly
extending, impact portion 42 having a V-groove 44 in its striking surface for
25 mating with V-shaped protrusions on the rear surface of printwhee1
character pads 45. Thus, upon impact, the mating V-shaped surfaces will
provide fine alignment for the characters by mo-ing the flexible spokes
either left or right as needed for accurate placement of the character
impression upon the print line of the receptor sheet II. The outer ends of
30 the base 40 are secured to mounting pads 46 of the interposer 36, for
leaving the ccntral portion of base unsupported. A strain sensor 47 is
secured to the central portion of the base directly opposite the impact
;0l36
- 16-
portion 42. Suitable electric olltput leads 48 and 50 are connected to thesensor and the print tip base, respectively, for relaying electrical signals,
generated by the sensor, to the control circuitry of the printer. Preferably,
the sensor comprises a piezoelectAc wafer adhered to the base. It is well
5 known that the piezoelectric crystal will generate an electric signal
thereacross when subject to a strain caused by a stress. Thus, as soon as the
~mpact portion 42 of the print tip pushes ~he character pad 45, the ribbon
33 and the image receptor sheet 11 against the deformable platen 10, the
platen counterforce acting through the impact portion, will cause the beam
10 of the print tip base 40 to bend, generating a voltage across the piezoelectric
crystal strain sensor 47 and sending an electrical signal to the control
circuitry, indicative of the moment of arrival of the print tip at the platen
surface.
The remainder of the hammer force applying mechanism for moving the
print tip comprises a mass transforrner 52, remotely positioned from the
carriage. It includes a push-rod 5~ extending between the interposer 36 a~d
a rockable bail bar 56 which rocks about an axis 57 extending parallel to the
axis of the platen 10. As the bail bar is rocked toward and away from the
2Q platen, the push-rod moves the interposer in an arc about bearing pin 38,
urging the print tip 34 toward and away from the platen. A bearing pin 58
mounted on the upper end of the interposer 36, provides a seat for the V^
shaped driving end 60 of the push-rod 54. The two bearing surfaces 58 and
60 are urged into intimate contact by springs 62. At the opposite, driven
25 end 64 of the push-rod, there is provided a resilient connection with an
elongated driving sllrface of the bail bar, in the form of an integral bead 68.
The bead is formed parallel to the rocking axis 57 of the bail. One side of
the bead provides a transverse bearing s~lrface for a first push-rod wheel 70,
journalled for rotation on a pin 71 secured to the push rod. The opposite
30 side of the bead provides a trans~erse bearing surface for a second pusll-rod wheel 72, spring biased thcreagainst for insllring that the first wheel
intimately contacts the bead. The aforcmentioned biasing is effcctcd by
~L26~l36
- 17-
providing the driven end of the push-rod with a clevis 74 to receive the
tongue 76 of pivot block 78, held in place by clevis pin 80. The second
wheel 7~ is supported upon bearing pin 82 anchored in the pivot block. A
leaf spring 8~, cantilever mounted on a block 86 urges the pivot block 78 to
bias the second wheel 72 against the bead 68 and effecting intimate contact
of the first push-rod wheel 70 against the bail bar bead 68.
Rocking of the bail bar about its axis 57 is accomplished by a prime mover,
such as voice coil motor 88 through lever arm 90 secured to a flexure
o connector 92 mounted atop movable coil wound bobbin 9~ on mounting
forrnations 96. The voice coil motor includes a central magnetically
permeable core 98 and a surrounding concentric magnet 100 for driving
bobbin 94 axially upon support shaft 10~ guided in bushing 104 in response
to the current passed through the coil windings. The voice coil motor 88 is
securely mounted on the base of the printer. Suitable electronic logic and
circuitry, represented by the controller 106, is connected to the voice coil
motor for energizing it in the proper sequence and at the proper
magnitudes to move the print tip to the surface of the platen and then to
deform the platen over the desired velocity trajectory.
The operation will now be described. Upon receiving a signal to initiate an
irnpact, current is passed through the the coil wound bobbin 94 in one
direction for drawing it downwardly in the direction of arrow D and for
pulling lever arm 90 to rock bail bar 56 about its a~is 57 in the direction of
- 25 arrow E. Rocking movement of the bail bar causes bead 68 to drive pllsh-
rod 54 toward the platen 10, in the direction of arrow F. Since the push-rod
is maintained in intimate contact with the interposer 36, the motion of the
push-rod is transmitted to the print tip 34 which is driven to impact the
deformable platen. As the carriage 22 is moved laterally across the printer,
3, in the direction of arrow C, by its drive arrangement, the push-rod is
likewise carried laterally across ~he printer between the interposer and the
bail bar uith driving contact being maintained by the sprillg biased wheels
- 18~
70 and 72 straddling the bead Mil. Conversely, when current is passed
through the coil wound bobbin 94 in the opposite direction, it will be urged
upwardly in the direction of arrow D for drawing the print tip away from
the platen.
It can be seen that the magnitude of the effective mass of the print tip 34,
when it contacts the platen 10, is based primarily upon the momentum of
the heavy bail bar 56 which has been set in motion by the voice coil motor
88. The kinetic energy of the moving bail bar is transferred to the platen
o through the print tip, during the dwell or contact period, in which the
platen is deformed and wherein it is stored as potential energy. By
extending the length of the contact period and substantially increasing the
effective mass of the print tip, we are able to achieve impact noise reduction
of about lOOO-fold, relative to conventional impact printers, in the manner
described above.
Movement of the print tip is effected as described. By accurately controlling
the timing of energization of the voice coil motor through suitable control
circuitry, the voice coil motor may be driven at the desired speed for the
20 desired time, so as to impart kinetic energy to the print tip. Thus,
appropriate amounts of kinetic energy may be metered out prior to the
cor~tact or both prior to the contact and after contact. For example, a first
large drive pulse may accelerate the bail bar and the print tip with sufficient
kinetic enegy to cause the print tip to cross the 50 mil throat distance and
25 deforrn the platen by the desired amount (about 5 mil). Alternatively, an
incremental drive p~llse may rnerely meter out sufficient kinetic energy to
accelerate the print tip across the throat distance through a presclected
velocity profile which could cause the print tip to reach the platen with
some predetermined velocity or may substantially arrest the print tip at the
30 surface of the platen (compensating, of course, for the interposed character
pad, ribbon and paper). As described above, the moment of arrival of the
print tip at the platen is indicated by the signal emanaling fiom the
~;a~6~L
piezoelectric sensor 46. Subsequent to that signal, an additional application
of kinetic energy may be provided by the voice coil motor to accelerate the
print tip into the defo~nable platen surface to a desired distance and for a
desired dwell time so as to cause the marking impression to be made. The
5 application of force at the time of contact enables contact to be rnade at a
lower velocity (generating less noise) than that which would have been
needed if there were no opportunity for subsequent acceleration.
CONCLUSION
It should be understood that the present disclosure has been made only by
way of example and that numerous changes in details of construction and
the combination and arrangement of parts may be resorted to without
departing from the true spirit and the scope of the invention as hereinafter
,5 claimed.
