Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention is directed to a daisy type print wheel
apparatus and more specifically to the technique of driving and stopping the ~ !
print wheel.
A typical daisy wheel printer is shown in patent 3,954,163 where
a servo system stops the print wheel at each printing position and allows a
hammer to strike the printing element. However, feedback control or servo
systems are relatively expensive.
Other more mechanical techniques of stopping the daisy type print-
ing wheel momentarily while the hammer is striking the wheel are illustrated
in three other patents. Herterich patent 3,677,386 drives the print wheel
by a crown gear arrangement and when the hammer engages the tongue of the
daisy type print wheel the crown gear is withdrawn from driving a relation-
ship with the print wheel. In a German patent 1,461,514 OLS the print
elements are on the periphery of a disk and there is some type of spring-like
clutch element between a drive shaft and a print shaft in a complex mechanical
arrangement. Here apparently the ribbon is pressed against the type wheel to
produce an impression. Finally in Hugel patent 3,353,647 a light friction
motor normally rotates the daisy type print wheel with the wheel being
stopped by some type of mechanical interference relationship.
All of the above three devices are mechanically cumbersome and will
not provide high speed and accurate placement of the type characters.
It is therefore an object of the invention to provide an improved
printing apparatus utili~ing a daisy type print wheel.
The invention provides printing apparatus comprising: a daisy type
print wheel including a plurality of print elements carried on spokes radiat-
ing out from the wheel axis such print elements being oriented to lie in a
plane perpendicular to said axis and including a fixed portion of magnetic
material; means for rotating said wheel around its axis including drive shaft
means; print hammer means adapted to impact a selected print element while
such element is stopped; magnet means producing a magnetic field mounted for
rotation with said drive shaft means and said wheel; brake means separate
from said print hammer means and having only a single movable component which
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interfaces with said print wheel, for acting on said wheel for stopping its
rotation and selecting one of said print elements for positioning such -
element to be hit by said hammer means; magnetic material means connected to
said drive shaft means and juxtaposed with said magnet means and rotatable
with said fixed wheel portion in a physical relationship to provide a sub-
stantial magnetic coupling force between said wheel and said drive shaft
means and for allowing said wheel and shaft means to have relative rotary
motion therebetween when said brake means is actuated.
Figure 1 is a plan view of apparatus of one embodiment of the
present invention;
Figure 2 is substantially taken along the line 2-2 of Figure 1 and
shows a portion of the device in section for clarity;
Figure 3 is a detailed view of a portion of Figure 1,
Figure 4 is a side view of Figure 3;
Figure 5 is an exploded view of a portion of another embodiment of
the invention.
Figure 6 is an assembled view of some of the parts of Figure 5;
Figure 7 is an elevation view showing the embodiment of Figures 5
and 6 in the practical printing apparatus;
Figure 8 is a side view of Figure 7;
Figures 9A and 9B are a portion of Figure 7 to better illustrate
its operation;
Figure 10 ls a block diagram illustrating the operation of both
embodiments of the invention; and
Figure 11 is a block diagram along with a typical print format
illustrating the operation of the invention.
Figure 1 in combination with the cross-section of Figure 2 illus-
trates one embodiment of the invention with a typical daisy wheel 10 mounted
for rotation on an axis 11 extending from a base 21. The daisy wheel or
print wheel has radially extending spokes 12 extending from axis 11 with
print elements 13 carried on the end of each spoke.
As illustrated in Figure 2 when the print element 13 is opposite a
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platen 14 paper and ribbon therebetween (not shown) printing occurs by
actuation of the print hammer 16 hitting print element 13 and moving it
against the ribbon and paper in a manner well-known in the art. Print hammer
16 shown in dashed
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outline is pivoted at 17 and constitutes a lever which is actually actuated by aprint hammer solenoid 18. Such hammer may be almost identical in con-
struction to the type shown in Ragland patent 3,696,739.
Platen 14 is retained on a post 19 affixed to the base 21 of the carriage. The
5 carriage itself has a scan along the line of printing to the left in the direction
shown and is movable or slidable on the main traverse shaft 22. In order to
sense the location of the individual print elements 13 there are provided both aspoke sensor 23 and an index sensor 24. Spoke sensor 23 operates on a
photoelectric principle with a light source and a photocathode sensing the
10 passage of each spoke 12. Index sensor 24 indexes the spoke count once each
revolution by sensing a short spoke 12'. Such technique is illustrated in Figure6 of Wagner patent 3,669,237 entitled "Double Helical Printer".
In order to brake the rotation of print wheel 10 a character selector lever 26 is
mounted on the base 21 and pivoted at point 20. As will be discussed in detail
15 below the character selector engages the spokes 12 or printing elements 13 tostop the wheel. When this occurs a drive shaft 27 driving the print wheel 10
continues to rotate. However, a slipping action is provided by means of
annularly shaped permanent magnet 25 as shown in Figure 2. This is mounted
for rotation with shaft 27 which is, of course, coaxial with the axis 11, by
20 means of a disk 28 of magnetic material affixed to and extending from shaft
27. Disk 28 has affixed to itself in turn a T-shaped insert 29 of non-magnetic
copper material which finally is affixed to a backing plate 31 to which
permanent annular ring 27 is affixed. In other words, rotating with print wheel
shaft 27 as a unit is the metal disk 28, copper insert 29, print wheel backplate25 31 and permanent magnet 25. Drive shaft 27 is journaled in bearings 30 on base
21 and driven by a pulley 35.
Print wheel 10 is composed of light-weight plastic material except for a T-
shaped metal insert 32 of magnetic material such as cold rolled steel. Insert
32 is journaled on a narrow stub end 33 of shaft 27 so that print wheel 10 and
30 its insert 32 may be pulled off or easily removed from the rest of the
assemblage. One benefit of this is the replacement of the print wheel with,
for example, one having a different character font. More importantly,
however, as discussed above when the spokes 12 of the print wheel are engaged
by character selector 26 it allows the stopping of print wheel 10 while the shaft
35 27 and it drive motor (not shown) may continue to rotate. When the brake is
released the print wheel can immediately again resume its rotation for the
next printing position due to the magnetic coupling force established between
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drive shaft 27 and print wheel 10. Specifically this is accomplished by a
magnetic field path starting from one pole of magnet 25 to the metal insert
32, through the steel magnetic stub end 33, through disk or plate 28 back to
the other pole of magnet 25. Magnet 25 is polarized north-south in the axial
5 direction as is apparent. The copper spacer 29 allows for control of the
magnetic coupling force and at the same time the copper material serves as a
good bearing surface since the T-shaped insert 32 is stopped while the insert 29is still being rotated by shaft 27.
The entire carrige on its base 21 may be rotated downward from platen 14 for
10 repair, inspection, replacement of the print wheel 10, etc. in the direction
shown by the arrow 21a in Figure 2.
Figures 3 and 4 illustrate character selector 26 in greater detail. As shown in
both of the figures the end 26a of the selector has four teeth which intersect
effectively with the spokes or character elements 13 of the print wheel 10. By
15 intercepting the print wheel spokes at their extreme ends the greatest
leverage is accomplished. Figure 4 shows the technique of rotating the
selector from its rest position in solid outline to its activated or stopping
position in dashed outline. This is accomplished by pivoting the selector
around the axis 20 by means of a solenoid 34 which acts against a spring 36.
20 As discussed above this technique has been disclosed in the above Ragland
patent.
Another embodiment of the invention is illustrated in Figure 5 in exploded
view where a daisy type print wheel 10' has a T-shaped metal insert 32' of
magnetic material press fitted into a recess 37. Figure 6 shows simple cross
25 sectional view of at least the magnetic coupling force structure which couples
the drive shaft 27' to the print wheel 10'.
Referring to both figures, a drive spindle 38 has a narrowed end 39 on which
insert 32' is journaled for rotation. Permanent magnet 41 is press fit in an
aluminum collar 43 and polarized north south across its axis. In the same
30 manner as illustrated in Figure 2 with the other embodiment of the invention,a brass bearing and magnetic spacer T-shaped unit 43 is press fit into the inneraperture 44 of magnet 41 serving both as a bearing and as a magnetic spacer to
control the magnetic field. The steel drive spindle 38 with its narrowed stub
end 39 is mated to bearing 43 by a pin 46 so no relative rotational movement
35 can occur between them. Finally spindle 38 is fixed to drive motor shaft 27'
driven by drive motor 47.
Thus to summarize, the steel drive spindle 38 brass bearing and magnetic
spacer 43, aluminum collar 42,and permanent magnet 41 are all driven as a
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common unit by drive shaft 27'. A magnetic coupling force is provided as
illustrated in Figure 6 by the magnetic field lines 48 which extend out of the
north pole through the insert 32' through the end 39 of the steel drive spindle
38, through the magnetic spacer 43 and into the south pole of magnet 41. Thus
5 far this embodiment is almost identical to that of Figure 2.
However, the braking action is different. Specifically, an annular portion 49 ofmagnetic mterial, such as cold rolled steel is affixed to the daisy wheel 10' byseveral pins 51 extending from one surface thereof which fit into the mating
apertures 52 carried by print wheel 10'. An inner ring portion 53 acts as a
10 braking surface when it is attracted by the cup type electromagnetic brake orring solenoid 54. The pin arrangement 51,52 allows a slight axial displacement
of annular portion 49 carried by the print wheel for stopping the print wheel
rotation.
An outer ring 55 having bars marked thereon provides an indexing function to
15 locate the position of the daisy wheel. This location may provide greater
flexibility in locating photoelectric apparatus as compared to the other
embodiment of the invention.
Figures 7 and 8 and especially Figure 8 show the action of the cup type
electromagnetic brake 54 more clearly. The plan view of Figure 7 in
20 conjunction with the side view of Figure 8 illustrate the use of this
embodiment in actual printing apparatus. A carriage 56 has a metal base plate
57 on which all of the elements shown in Figure 5 are mounted. Carriage 56
moves on a main traverse shaft 58. Also the entire carriage may be moved
downward away from the fixed platen 59 to a~low for access. The scan is
25 normally from right to left and is provided by carriage drive roller 61 which is
of a hard rubber material. The ribbon supply and take-up reels 62,63 provide
the ribbon for the printing. As illustratred in Figure 8, paper 64 is held
between a presure roller 66 and a paper drive roller 67. ~ hammer lever 68 is
provided similar to that in the other embodiment. In addition photoelectric
30 devices 69 and 71 scan the ring 55 to provide for indexing and counting
functions.
The means for scanning the carriage as well as including the drive roll 61 also
include a friction wheel shown in print and return positions 72 and 73,
respectively. This is shown more clearly in Figures 9A and 9B where friction
35 wheel 72,73 rotates on the roll 61 and describes a helical path 74 depending on
the angle of the wheel itself. Figure 9B illustrates a typical holder 74 on
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which wheel 72,73 is journaled so that the pitch at which the wheel is set may
be effectively changed. In other words, in Figure 7 the return pitch indicated
at 73 is much greater than the print pitch indicated at 72 to thus provide for areasonably low scan movement during printing and a fast return. And, of
5 course, the direction of pitch whether it is positive or negative provides for movement in one direction or the reverse direction.
In operation since the hammer and carriage are actuated or moved at constant
rates recovery problems are minimized. The variable factor illustrated in
Figure 10 is the character select function which actuates the selector lever.
10 This is true in both embodiments of the invention. Moreover since the selector
lever, in the case of the first embodiment, is of relatively light-weight
aluminum and the select or brake function in the other embodiment is a cup-
type electromagnetic type brake these braking mechanisms can easily be
varied in time. The circuit of Figure 10 for actuating this character select
15 function includes a basic clock counter 76 or timer receiving a clock input on
line 77. An ASCII character to be printed is inputed on line 78 to a read-only
memory where it is translated to a command position on a seven line input to a
print character register 81. The actual print character sequence is based on
ASCII sequence but instead of merely having an "alpha stick'l and a "numeric
20 stick" the 48 different possible characters are divided into four sticks by
arrangement of the binary logic so that if the next character selected is within16 positions of the last character previosusly printed the print wheel will rotate
fully another time and assures the select unit has timefor recovery.
The output of the print character register 81 is compared in a comparator 82 to
a5 the clock counter which is reset by an index input to the print wheel and when
the two inputs coincide a select command occurs on line 83. As discussed
above, in the case of the embodiment of Figure 8 the electromagnet 54 is
energized and in the case of the embodiment of Figure 1 the character selector
26 is actuated. In order to provide for effective character selection the period30 of rotation of the print wheel must be les than the time required between print
hammer actuations. In other words, the print wheel must rotate at fast
enough speed so that a character may be selected well before the print
hammer is periodically actuated. For example, assume a character density of
ten characters per inch with a scan rate of five inches per second. This is in
35 effect a printing rate of 50 characters per second or the time for selection is
less than 20 milliseconds. Assuming the print wheel has a rotation of 3,600
revolutions per minute a single rotation will occur 1/60 of a second or 16.5
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milliseconds which is less than the 20 millisecond time between effective print
hammer actuations.
Moreover, by varying the constant rate of the print hammer actuation to
another constant rate as illustrated in Figure 11 proportional spacing for the
5 purpose of both left and right justification may be achieved. This is
accomplished with the use of a microprocessor 84 which has both a ROM read
only memory input 86 and a random access memory input 87. Random access
memory 87 would typically contain a line of, for example, 32 characters.
Depending on how many characters were actually to be printed the print
10 hammer drive circuit 88 can be varied between a ten characater per second
output on line 89 from the print clock 91 or a five per second rate on line 92
from the divide-by-two unit 93 which is connectd to print clock 91. A selector
94 determines which of the rates is to be selected. Thus the density is doubled
as illustra~ed by the five per second print line compared to the ten per second
15 print line. Assuming different spacing is desired a control line 96 from
microprocessor 94 drives the print hammer circuit 88 to provide an
intermediate hammer actuation rate. The carriage is schematically indicated
at 97 which carries the print hammer and, of course, has a constant scan rate.
With such a hammer actuation rate of five to ten per second the recovery rate
20 is much less critical.
Thus an improved printing apparatus has been provided.
