Hammers abstract
A dot line printer has a plurality of print hammers accommodated
in a hammer bank, which make dot impressions on a sheet of print
paper as the hammer bank reciprocally moves in a print line direction
perpendicular to the direction in which the sheet of print paper
is fed. To print L dot lines at a time with each of forward and
backward movements of the hammer bank, the print hammers are divided
into a preselected number of groups so that each group includes
N number of print hammers where L and N are integers equal to or
greater than 3. The print hammers in each group are displaced one
dot line distance from one another in the sheet feeding direction.
The print hammers in each group are further displaced in the print
line direction by respective predetermined distances from their
home positions so that the respective hammers in each group do not
impinge upon the sheet of print paper simultaneously. The print
hammers equal in number to the least common multiple of L and N
or integer multiples of the least common multiple thereof are integrally
formed into a module structure to facilitate the manufacture and
management of the hammer assemblies.
Hammers claims
What is claimed is:
1. A dot line printer comprising:
a hammer bank, said hammer bank comprising a plurality of print
hammers, each having a print pin;
means for moving said hammer bank back and forth in a shuttling
direction;
holding means for holding said plurality of print hammers in non-printing
positions with magnetic attractive force;
a plurality of electromagnetic coils provided in one-to-one correspondence
to said plurality of print hammers;
means for supplying a current of a predetermined duration to each
of said plurality of electromagnetic coils thereby creating a magnetic
field which counteracts the magnetic attractive force produced by
said holding means thereby releasing the print hammers from their
non-printing positions for making dot impressions on a sheet of
print paper; and
means for moving said sheet in a line to line direction,
wherein said plurality of print hammers of said hammer bank are
divided into a plurality of groups so that each group includes N-number
print hammers where N is an integer equal to or greater than 3
said N-number print hammers in each group being displaced by a distance
corresponding to one dot line in the line to line direction so that
L dot lines are printed with each of forward and backward movements
of said hammer bank where L is an integer equal to or greater than
3 and wherein said printer further comprises;
means for releasing said N-number print hammers, in each of said
groups, in a predetermined successive order, so that only 1/N of
said plurality of print hammers are fired simultaneously, and wherein
positions of (N-1) print hammers in each group are displaced in
the shuttling direction from respective home positions by (n-1)/N.multidot.D),
where n is a number indicative of an order in which one of said
(N-1) print hammers is released, n being an integer in a range of
from 2 to N, and D represents a number of dots printable per unit
length, as measured in the shuttling direction, to compensate for
the successive releasing of the print hammers, said home positions
being imaginary positions of said print hammers spaced equidistant
from one another, by a predetermined distance.
2. The dot line printer according to claim 1 wherein said print
hammers equal in number to at least common multiple of N and L are
formed into a module structure.
3. The dot line printer according to claim 1 wherein said print
hammers equal in number to an integer multiple of a least common
multiple of N and L are formed into a module structure.
4. The dot line printer according to claim 1 wherein N is an odd
number.
5. The dot line printer according to claim 1 wherein L and N are
equal to 6 and 9 respectively, and wherein said print hammers in
each group are arranged so that adjacent print hammers are released
with a time delay of 4t and 5t where t represents a time interval
at which said print hammers in each group are successively released.
6. The dot line printer according to claim 1 wherein L and N are
equal to 6 and 3 respectively, and wherein said print hammers in
each group are arranged so that adjacent print hammers are released
with a time delay of t where t represents a time interval at which
said print hammers in each group are successively released.
7. The dot line printer according to claim 1 wherein L and N are
equal to 6 and 4 respectively, and wherein said print hammers in
each group are arranged so that adjacent print hammers are released
with a time delay of one of t and 2t where t represents a time interval
at which said print hammers in each group are successively released.
8. The dot line printer according to claim 1 wherein N is an odd
number N.sub.o which is expressed as N.sub.o =2n.sub.o +1 where
n.sub.o is an integer equal to or greater than 1 and wherein a
minimum firing time difference t.sub.o between adjacent print hammers
in said group is determined by
where T is a repeatability of the print hammer.
9. The dot line printer according to claim 1 wherein N is an even
number N.sub.e which is expressed as N.sub.e =2n.sub.e where n.sub.e
is an integer equal to or greater than 2 and wherein a minimum
firing time difference t.sub.e between adjacent print hammers in
said group is determined by
where T is a repeatability of the print hammer.
Hammers description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a dot line printer,
and more particularly to a dot line printer for printing L dot lines
at a time during each of forward and backward movements of a hammer
bank accommodating therein a plurality of print hammers juxtaposed
along a print line, and for minimizing the number of print hammers
simultaneously fired, where L is an integer equal to or greater
than 3.
2. Description of the Prior Art
In a dot line printer, a print hammer which is a plate-like leaf
spring having a print pin at its tip end is held in a non-printing
position by a magnetic attraction of a permanent magnet against
elastic deformation of the print hammer. The print hammer is released
from the non-printing position with a supply of a release current
to an electromagnetic coil. The print pin thus impinges upon a sheet
of print paper, thereby making a dot impression thereon.
As disclosed in Japanese Patent Publication (Kokoku) No. 55-10385
there is a problem such that if adjacent print hammers are allowed
to be fired at the same time, duration of the current supplied to
the electromagnetic coil needs to be prolonged or the peak level
of the current needs to be increased. To obviate such a problem,
this Publication proposes displacing columnar printing types embossed
on the periphery of a drum in the circumferential direction with
respect to printing types in adjacent column so that adjacent print
hammers are not fired at the same time.
Another proposal for solving this problem is disclosed in Japanese
Patent Publication (Kokai) No. 58-11177 and Japanese Patent Publication
(Kokoku) No. 62-28755 wherein a plurality of print hammers are
divided into two groups and respective ones of the print hammers
in a second group are displaced from their home positions by a distance
corresponding to one half of a reciprocal of a print density (hereinafter
referred to as "a half dot") where the print density is
represented by a number of printable dots per a unit length. Displacement
of the second group print hammers by the half dot reduces electric
power consumption and lowers the peak level of the current flowing
in the electromagnetic coil. As a consequence, a small-capacity
power source can be used for the dot line printer.
However, high speed dot line printers have an increased number
of print hammers, say nearly 300 so that the number of simultaneously
fired print hammers increases in due course even if the hammers
are divided into two groups, thus electrical and mechanical influences
caused by the increased number of the hammers are still outstanding
in the high speed dot line printers. More specifically, as the number
of simultaneously fired print hammers is increased, a total amount
of currents flowing in the coils is increased, thus requiring a
large-capacity power source. Further, mechanical impact increases
as the larger number of print hammers impinge upon a platen at a
time. This increased mechanical impact may cause the print gap between
the print hammers and the sheet of paper to widen, thus lowering
print quality. Magnetic interaction between adjacent hammers is
another problem in such high speed printers, because the pitch between
the hammers is made small so as to accommodate the increased number
of print hammers.
SUMMARY OF THE INVENTION
The present invention has been made to solve the aforesaid problems,
and accordingly it is an object of the present invention to provide
a high speed dot line printer which minimizes the number of print
hammers simultaneously fired.
Another object of the present invention is to provide a dot line
printer which can afford good printing quality.
To achieve the above and other objects, there is provided a dot
line printer which includes a plurality of print hammers, holding
means for holding the plurality of print hammers in non-printing
positions with magnetic attractive force, and a plurality of electromagnetic
coils provided in one-to-one correspondence to the plurality of
print hammers. Each of the plurality of electromagnetic coils are
supplied with a current having a predetermined duration to release
the print hammer from the non-printing position and to thus make
a dot impression on a sheet of print paper by cancellation of the
magnetic attractive force with a magnetic field produced by the
current flowing in the electromagnetic coil. The plurality of print
hammers are accommodated in a hammer bank reciprocally movable with
forward and backward movements in a first direction perpendicular
to a second direction in which the sheet of print paper is fed.
The plurality of print hammers are divided into a plurality of groups
so that each group includes N-number print hammers where N is an
integer equal to or greater than 3. The N-number print hammers in
each group are displaced by a distance corresponding to one dot
line in the second direction so that L dot lines are printed with
each of forward and backward movements of the hammer bank where
L is an integer equal to or greater than 3. Further, positions of
(N-1) print hammers in each group are displaced in the first direction
from respective home positions by respective predetermined distances
so as to prevent the N-number print hammers from being released
simultaneously, where the home positions are imaginary positions
of the print hammers apart a predetermined equi-distance from position
of adjacent print hammer.
More specifically, the positions of (N-1) print hammers in each
group are displaced in the first direction by (n-1)/(N.multidot.D)
from respective home positions, where n is a number of order in
which one of the (N-1) print hammers is released, where n is an
integer in a range of from 2 to N, and D represents a number of
dots printable per a unit length.
With the arrangement of the print hammers as described above, the
number of print hammers simultaneously fired are reduced to one
N-th (1/N), so that the electrical and magnetic influences which
may otherwise be caused if a large number of print hammers are simultaneously
fired can be suppressed to an allowable low level. Furthermore,
by forming the print hammers equal in number to a least multiple
of L and N into a module structure or by forming the print hammers
equal in number to an integer multiple of the least multiple of
L and N into a module structure, the print hammers can be fabricated
with the use of the same kind of module structure hammer assemblies.
The above and other objects, features and advantages of the present
invention will become more apparent from the following description
when taken in conjunction with the accompanying drawings in which
preferred embodiments of the present invention are shown by way
of illustrative examples.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing dot print hammers;
FIG. 2 is a side view showing the print hammer shown in FIG. 1;
FIG. 3 is a front view showing a print hammer assembly used in
a dot line printer according to a first embodiment of the present
invention;
FIG. 4 is a front view showing a print hammer assembly in a dot
line printer according to a second embodiment of the present invention;
and
FIG. 5 is a front view showing a print hammer assembly in a dot
line printer according to a third embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An example of a dot print hammer is shown in FIGS. 1 and 2. The
print hammer is a plate-like leaf spring 1 having a print pin 2
attached to free end portion of the leaf spring 1. The lower portion
of the leaf spring 1 is sandwiched between a front yoke 4 and a
yoke base 5 and fixedly secured thereto by virtue of screws. A permanent
magnet 6 and a comb-like yoke 7 are fixedly secured to the yoke
base 5. The front yoke 4 leaf spring 1 yoke base 5 permanent
magnet 6 and the comb-like yoke 7 constitute a magnetic circuit.
The upper portion of the leaf spring 1 is magnetically attracted
to the pole of the comb-like yoke 7 against elastic deformation
of the leaf spring 1 by virtue of the permanent magnet 6. With energization
of a release coil 8 the leaf spring 1 releases from the pole of
the yoke 7 and the print pin 2 impinges upon a sheet of print paper
(not shown), thereby making a dot impression thereon.
In the following description, a dot line printer of the present
invention is assumed to print with a print density of 180 dpi (dots
per inch) and 6 dot lines are simultaneously printed with each of
forward and backward movements of a hammer bank in which the print
hammers are accommodated.
FIG. 3 shows an arrangement of the print hammers according to a
first embodiment of the present invention. A plurality of module
structure print hammer assemblies 10 (only two being shown in FIG.
3 for the sake of brevity) are arranged in alignment with one another
along a print line perpendicular to the direction in which a sheet
of print paper is fed. Each print hammer assembly 10 is made of
a single sheet of leaf spring, wherein 18 print hammers extend upwardly
from a common base portion. Print pins denoted by numerals 21 through
29 are secured to upper free end portions of the print hammers by
means of welding or caulking. The positions of 6 print pins are
displaced vertically or in the paper feeding direction from one
another by a distance corresponding to one dot line so that 6 dot
lines are simultaneously printed with each of forward and backward
movements of the hammer bank. 18 print hammers in each hammer assembly
10 are grouped into two wherein the leftside 9 hammers belong to
the same group and the rightside 9 hammers belong to another group.
8 hammers in each group which are successively fired in an order
of from second to ninth and are displaced horizontally in a print
line direction by respective predetermined distances from their
home positions as indicated in Table 1 below so that the hammers
in the same group do not impinge on the sheet of paper simultaneously.
The number of the print hammers "18" included in each
assembly 10 is a least common multiple of "6" and "9"
where "6" is the number of simultaneously printable dot
lines with each of forward and backward movements of the hammer
bank, and "9" is the number of the print hammers contained
in each group. The numerals of the print pins indicate an order
in which the print hammers are fired in succession.
The hammer assemblies 10 are mounted on a hammer bank which is
reciprocally moved in the print line direction by a shuttle mechanism
including a motor and a cam or by a linear motor. Representing repeatability
or flight time of each hammer by T (milliseconds), fire start interval
of the respective print hammers in each group is set to t=T/9. That
is, the fire start times at which the respective print hammers in
each group start firing are delayed every t=T/9. The repeatability
or flight time T is defined by a period of time starting from the
release of the print hammer from the non-printing position to the
return to the original non-printing position upon making a dot impression
on the sheet of print paper. The speed of the hammer bank v (inch/millisecond)
is determined based on both the dot density which is 180 dpi in
the instant case, and the repeatability T, i.e., v=(1/180)/T inch/millisecond.
A distance x that the hammer bank moves from the time when a particular
hammer is fired to the time when the subsequent hammer is fired
is given by:
Table 1 below indicates distances (D1) of the print pins 22 through
29 measured from the position of the print pin 21 distances (D2)
of the print pins 22 through 29 measured from the respective home
positions, and distances (D3) of the respective print pins 22 through
29 measured from the position of the immediate leftside print pin.
The home positions of the print pin are defined by imaginary print
pin positions arranged at a predetermined equi-interval which in
the following case is 0.1 inch.
TABLE 1 ______________________________________ D1 D2 D3 ______________________________________
Print pin 22 0.1 .times. 7 - x x 0.1 + 5x Print pin 23 0.1 .times.
5 - 2x 2x 0.1 + 5x Print pin 24 0.1 .times. 3 - 3x 3x 0.1 + 5x Print
pin 25 0.1 - 4x 4x 0.1 - 4x Print pin 26 0.1 .times. 8 - 5x 5x 0.1
- 4x Print pin 27 0.1 .times. 6 - 6x 6x 0.1 - 4x Print pin 28 0.1
.times. 4 - 7x 7x 0.1 - 4x Print pin 29 0.1 .times. 2 - 8x 8x 0.1
- 4x ______________________________________
Assuming that the print pin 21 is fired when the rightwardly moving
hammer bank is instantaneously at some location, the print pin 22
is subsequently fired after expiration of time t (=T/9) from the
firing of the print pin 21. During the period of time t, the hammer
bank moves rightwardly a distance x. The print pin 22 is the seventh
pin counted rightwardly from the print pin 21 and the home position
of the print pin 22 is apart by 0.7 inch from the position of the
print pin 21. Therefore, the position of the print pin 22 is leftwardly
displaced by a distance x from its home position as can be seen
from Table 1. The print pin 27 is the immediate leftside print pin
of the print pin 22 and the position of the print pin 27 is leftwardly
displaced by a distance 6x from its home position, so that the position
of the print pin 22 is apart by 0.1+5x from the position of the
print pin 27. In this manner, assuming that print commands for the
print pins 23 through 29 are present, these print pins are successively
fired each time with a delay of time t with respect to the firing
of the immediate preceding print pin. After expiration of time t
after the firing of the print pin 29 the print pin 21 has returned
to its original position and is placed ready for the subsequent
firing.
With the hammer arrangement as shown in Table 1 the number of
the print hammers which simultaneously impinge upon the sheet of
print paper is reduced to one ninth (1/9). If the total number of
print hammers is 300 maximum number of the print hammers which
impinge upon the sheet of print paper at a time is 34. As the number
of the simultaneously fired print hammers are greatly reduced, the
peak level of the current flowing in the coils is reduced, so a
small-capacity power source suffices for the dot line print having
the hammer arrangement as described above. Further, the mechanical
impact upon the platen is reduced, high print quality can be maintained
at all times.
In the first embodiment describe above, the print hammers in each
group are fired in a predetermined scrambled order, but they can
be fired in a regular order from left to right. In the latter case,
the positions of the print pins 22 through 29 relative to the position
of the leftmost print pin 21 are determined depending on the firing
order.
A second embodiment of the present invention will be described
with reference to FIG. 4. A plurality of module structure print
hammer assemblies 101 are arranged in alignment with one another
in the print line direction. Each print hammer assembly 101 is made
of a single sheet of leaf spring, wherein 6 print hammers extend
upwardly from a common base portion. The positions of 6 print pins
in the module structure are displaced vertically or in the paper
feeding direction from one another by a distance corresponding to
one dot line so that 6 dot lines are simultaneously printed with
each of forward and backward movements of the hammer bank. 6 print
hammers in each hammer assembly 101 are grouped into two wherein
leftside 3 hammers belong to the same group and the rightside 3
hammers belong to another group. 2 hammers in each group which are
successively fired in an order of from second to third are displaced
horizontally or a print line direction by respective predetermined
distances from their home positions as indicated in Table 2 below.
The number of the print hammers "6" in each assembly 101
is a least common multiple of " 6" and "3" where
"6" is the number of simultaneously printable dot lines
with each of forward and backward movements of the hammer bank,
and "3" is the number of the print hammers contained in
each group. The numerals of the print pins indicate an order in
which the print hammers are fired in succession.
In the arrangement shown in FIG. 4 fire start interval at which
the respective print hammers in each group start firing is set to
t=T/3. That is, fire start times at which the respective print hammers
in each group start firing are delayed every t=T/3. A distance x
that the hammer bank moves from the time when a particular hammer
is fired to the time when the subsequent hammer is fired is given
by:
where the print density is also assumed to be 180 dpi.
Table 2 below indicates distances (D1) of the print pins 32 and
33 measured from the position of the print pin 31 distances (D2)
of the print pins 32 and 33 measured from the respective home positions,
and distances (D3) of the respective print pins 32 and 33 measured
from the position of the immediate leftside print pin.
TABLE 2 ______________________________________ D1 D2 D3 ______________________________________
Print pin 32 0.1 .times. 1 - x x 0.1 - x Print pin 33 0.1 .times.
2 - 2x 2x 0.1 - x ______________________________________
With the hammer arrangement as shown in Table 2 the number of
the print hammers which simultaneously impinge upon the sheet of
print paper is reduced to one third (1/3). If the total number of
print hammers is 300 maximum number of the print hammers which
impinge upon the sheet of print paper at a time is 100.
A third embodiment of the present invention will be described with
reference to FIG. 5. A plurality of module structure print hammer
assemblies 102 are arranged in alignment with one another in the
print line direction. Each print hammer assembly 102 is made of
a single sheet of leaf spring, wherein 12 print hammers extend upwardly
from a common base portion. The positions of 6 print pins in the
module structure are displaced in the paper feeding direction from
one another by a distance corresponding to one dot line so that
6 dot lines are simultaneously printed with each of forward and
backward movements of the hammer bank. 12 print hammers in each
hammer assembly 102 are grouped into three wherein leftside 4 hammers
belong to a first group, intervening 4 hammers belong to a second
group, and rightside 4 hammers belong to a third group. 3 hammers
in each group which are successively fired in an order of from second
to fourth are displaced horizontally or a print line direction by
respective predetermined distances from their home positions as
indicated in Table 3 below. The number of the print hammers "12"
in each assembly 102 is a least common multiple of "6"
and "4" where "6" is the number of simultaneously
printable dot lines with each of forward and backward movements
of the hammer bank, and "4" is the number of the print
hammers contained in each group. The numerals of the print pins
indicate an order in which the print hammers are fired in succession.
In the arrangement shown in FIG. 5 fire start interval at which
the respective print hammers in each group is set to t=T/4. That
is, fire start times at which the respective print hammers in each
group start firing are delay every t=T/4. A distance x that the
hammer bank moves from the time when a particular hammer is fired
to the time when the subsequent hammer is fired is given by:
where the print density is also assumed to be 180 dpi.
Table 3 below indicates distances (D1) of the print pins 42 through
44 measured from the position of the print pin 41 distances (D2)
of the print pins 42 through 44 measured from the respective home
positions, and distances (D3) of the respective print pins 42 through
44 measured from the position of the immediate leftside print pin.
TABLE 3 ______________________________________ D1 D2 D3 ______________________________________
Print pin 42 0.1 .times. 2 - x x 0.1 - 2x Print pin 43 0.1 .times.
1 - 2x 2x 0.1 + x Print pin 44 0.1 .times. 3 - 3x 3x 0.1 - 2x ______________________________________
With the hammer arrangement as shown in Table 3 the number of
the print hammers which simultaneously impinge upon the sheet of
print paper is reduced to one third (1/4). If the total number of
print hammers is 300 maximum number of the print hammers which
impinge upon the sheet of print paper at a time is 75.
While the above embodiments assume that 6 dot lines are simultaneously
printed with each of forward and backward movements of the hammer
bank, the hammer arrangements can be modified so that 4 or 8 dot
lines can be simultaneously printed. Further, although in the embodiments
described above, odd numbers 9 and 3 and an even number 4 are selected
as the number of the print hammers in each group, the number thereof
may be arbitrarily selected if it is an integer equal to or greater
than 3. The number of the print hammers in each module structure
can be a least common multiple of N and L or integer multiples of
the least common multiple of N and L where N represents the number
of hammers in each group and L is the number of simultaneously printable
dot lines. As described below, it is desirable to select odd numbers
for the number N rather than selecting even numbers.
Forming the print hammers into a module structure on a group basis
requires at least two kinds of hammer assemblies except the case
that N is a number dividable with L, resulting in complicatedness
in the manufacture and intricateness of the management of different
kinds of print hammer assemblies. Further, if the print hammers
are formed into a module structure with a number greater than the
least common multiples of N and L excluding the cases of the integer
multiples of the least common multiples, a problem is encountered
such that the number of hammers included in one module is too large
to accurately manufacture the module structure, and is therefore
undesirable.
Assuming that an odd number N.sub.o (N.sub.o =2n.sub.o +1 where
n.sub.o is an integer equal to or greater than "1") is
selected as the number of print hammers in each group, the minimum
firing time difference t.sub.o between adjacent print hammers is
given by:
On the other hand, assuming that an even number N.sub.e (N.sub.e
=2n.sub.e where n.sub.e is an integer equal to or greater than "2")
is selected as the number of print hammers in each group, the minimum
firing time difference t.sub.e is given by:
Since a larger firing time difference is desirable in terms of
reducing the magnetic interaction between adjacent print hammers,
it can be concluded that odd numbers are better than even numbers
if a relationship of t.sub.o -t.sub.e >0 is met. ##EQU1## That
is, when N.sub.o >N.sub.e /2 t.sub.o becomes greater than t.sub.e.
Therefore, when even numbers are selected, the number of print hammers
to be included in each group must be two times as many as the number
of print hammers in the case of selecting odd numbers so as to keep
the same firing time interval. Consequently, it can be concluded
that odd numbers are desirable as the number of the print hammers
to be included in each group. If even numbers are selected, problems
may be encountered such that the hammers cannot be accurately formed
into a module structure and driving control of the hammers is complicated.
In accordance with the present invention, the print hammers belonging
to the same group are separately fired at different times, and the
number of the simultaneously fired print hammers is reduced to 1/N
where N is the number of print hammers included in each group. As
a consequence, electrical and mechanical influences can be greatly
suppressed and dot line printers capable of affording a high print
quality can be provided at low cost. Furthermore, the fabrication
of the print hammers can be achieved by the module structure print
hammer assemblies of the same kind, the manufacture and the management
of the print hammer assemblies can be facilitated.
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