Printing head device

A printing head device according to the present invention includes a plurality of printing pins corresponding to respective dots, a plurality of first pin drive plates having the printing pins fixed thereon and having surfaces on which first electrodes are formed, a plurality of second pin drive plates having second electrodes opposing to the first electrodes with predetermined gaps therebetween, a first drive plate support member for supporting the first pin drive plates through elastic members, respectively, and a second drive plate support member for supporting the second pin drive plates. Further, the second drive plate support member is vibrated repeatedly in a direction toward a top end of the printing pin by a drive unit. A drive circuit applies a voltage based on a printing signal between the first and second electrodes of the first and second pin drive plates with the vibration timing of the drive unit to generate Coulomb force between the first and second electrodes. With this construction, it is possible to enable the printing pins to perform a print by a single drive unit and to miniaturize the printing head.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a printing head device of a dot-impact 
type printer and, particularly, to a printing head capable of being 
miniaturized. 
2. Description of the Related Art 
In a conventional dot-impact type printer, a printing head having a 
plurality of printing wires and a drive mechanism for driving the printing 
wires is put in a facing relation to a recording sheet through, for 
example, an ink ribbon and prints a dot pattern of such as characters on 
the recording sheet by selectively driving the printing wires while the 
head is running. FIG. 12 is a cross section of a typical conventional 
printing head and FIG. 13 is a plan view thereof showing an arrangement of 
printing elements fixed in the printing head. The printing head shown in 
FIG. 12 includes the printing elements 80 shown in FIG. 14 in a printing 
head housing 81 and arranged in an annular region as shown in FIG. 13. 
Each printing element 80 includes a printing wire 82, a leaf spring 83 for 
driving the printing wire, an armature 84, a drive coil 85, a core 86 and 
a yoke 87. The printing wire 82 is fixedly secured to a top end of the 
leaf spring 83 and has a top end which can protrude through a guide 88 
provided in a top end of the printing head. The armature 84 is fixedly 
secured to the leaf spring 83 which, in turn, is fixedly secured in 
between the printing head housing 81 and the core 86. The drive coil 85 is 
wound on the core 86 and can be selectively driven according to a dot 
print signal. 
When magnetic flux generated by a current flowing through the coil 85 
passes through a magnetic circuit constituted with the armature 84, the 
core 86 and the yoke 87, the armature 84 is attracted to the core 86. 
Therefore, the top end of the printing wire 82 collides with the ink 
ribbon and the recording sheet (which are not shown) to print the latter. 
In such conventional printing head, however, the magnetic circuit must be 
provided every printing wire, causing a miniaturization of the printing 
head to be very difficult. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a printing head in which 
the number of magnetic circuits can be substantially reduced, allowing a 
miniaturization thereof. 
A printing head device according to the present invention comprises a 
plurality of printing pins corresponding to dots, a plurality of first pin 
drive plates which have the printing pins and have a surface on which a 
first electrode is formed, respectively, a plurality of second pin drive 
plates having a second electrode which faces to the first electrode 
respectively, a first drive plate support member for movably supporting 
the respective first pin drive plates, and a second drive plate support 
member for supporting the plurality of the second pin drive plates. The 
second drive plate support member vibrates repeatedly in a direction 
toward top end of the printing pin by means of a drive unit. A drive 
circuit applies a voltage which corresponds to a print signal between the 
first and second electrodes of the first and second pin drive plates with 
a timing of vibration of the drive unit to produce Coulomb force between 
the first and second electrodes. As a result, the first pin drive plate 
having the printing pin is attracted by the second pin drive plate 
according to the printing signal and moved together with the drive unit in 
the direction toward the top end of the printing pin. 
Since, according to this construction, it is possible to print by using one 
drive unit for a plurality of printing pins and the first and second pin 
drive plates themselves are not bulky, thereby a miniaturization of the 
printing head becomes possible. 
When the first drive plate support member is provided with an elastic 
member for movably supporting each of the first pin drive plates in which 
the printing pins are fixed, and the elastic member is of an electrically 
conductive material, it is possible to electrically connect the first 
electrode of the first pin drive plate to the drive circuit through the 
elastic member. Therefore, the elastic member functions not only to 
support the first pin drive plate but also to electrically connect the 
electrode to the drive circuit, resulting in an improved wiring efficiency 
.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a perspective view of a printing head according to an embodiment 
of the present invention, with a housing being shown by chain lines and 
FIG. 2 is a cross section of the printing head taken along a line A--A in 
FIG. 1. In these figures, the printing head of this embodiment is a 
printing head device of a dot-impact type printer in which a dot pattern 
of such as character is printed on a recording sheet 41 through an ink 
ribbon 40 according to a printing signal. Printing drive mechanisms 100 
and 200 having identical constructions are fixedly arranged in parallel in 
a printing head housing 1 of aluminum. The printing drive mechanism 100 
(and 200) is constructed with a magnetic drive unit 2 having a single 
magnetic circuit for generating vibration and a pin drive unit 3 which is 
vibrated as a whole in a direction toward a top end of a printing pin 10 
(which is vertical to the recording sheet 41 as shown in FIG. 2) by the 
vibration transmitted from the magnetic drive unit 2. 
The magnetic drive unit 2 includes an arm 9 having a top end to which the 
pin drive unit 3 is fixed, a leaf spring 4 for supporting one end of the 
arm 9, a core 5 on which the leaf spring 4 is fixed, an armature fixed to 
a center portion of one surface of the leaf spring 4 and facing to the 
other end of the core 5 with a gap, a yoke 7 and a drive coil 8. The core 
5 is fixed to a base 1A which, in turn, is fixed to the printing head 
housing 1. The yoke 7 has legs forming a U-shape and has one end fixed to 
the core 5. Thus, the core 5, the armature 6 and the yoke 7 are 
magnetically coupled. The core 5, the armature 6 and the yoke 7 are of 
magnetic material. The armature 6 is arranged in a position between the 
legs of the U-shaped yoke 7 and is not fixed to the yoke 7. A distance 
between the leaf spring 4 and the yoke 7 is larger than a moving stroke of 
the printing pin 10 so that the leaf spring 4 does not contact with the 
yoke 7 during printing. The drive coil 8 is wound on and fixed to the core 
5 in the vicinity of the armature, so that the armature 6 is attracted 
magnetically to the end portion of the core 5 by current flowing through 
the drive coil. When the armature 6 is attracted to the core 5, the leaf 
spring 4 is deformed so as to move the arm 9 toward the recording sheet 
41. By ON/OFF switching current flowing through the drive coil 8, the pin 
drive unit 3 fixed to the arm 9 vibrates in a direction toward the top end 
of the printing pin 10. 
The pin drive unit 3 selectively drives a plurality of printing pins 10 
arranged in a row for a dot printing at the time of the movement of the 
arm 9. Each pin 10 is driven on the basis of the printing signal supplied 
to the pin drive unit 3 in concomitance with the movement of the arm 9. 
The pin drive unit 3 includes first pin drive plates 20 on which the 
plurality of the pins 10 are fixed individually, a first drive plate 
support member 11 of insulating material for supporting the first pin 
drive plates 20 through respective electrically conductive, elastic 
members 13, second pin drive plates 30 facing the respective first pin 
drive plates 20 with a predetermined gap, and a second drive plate support 
member 12 of metal material which fixes the second pin drive plates 30. 
The first drive plate support member 11 is fixed in the printing head 
housing 1 and the second drive plate support member 12 is fixed to the arm 
9. 
FIG. 3 is a front view of the pin drive unit 3 and a peripheral elements 
thereof in a state of before printing when looked in a direction B in FIG. 
1. In FIG. 3, each of the first pin drive plates 20 on which the pins 10 
are fixed, is arranged alternatively of the second pin drive plate 30 
fixed to the second drive plate support member 12 with a predetermined 
gap. The first and second pin drive plates 20 and 30 have on one surfaces 
thereof electrode films 21 and 31, respectively, which are facing to each 
other. As shown in FIG. 7, the first and second pin drive plates 20 and 30 
are formed by forming the electrode films 21 and 31 on ceramics plates 20A 
and 30A each being 1 mm thick or lesser, respectively, as the first and 
second electrodes. The electrode films 21 and 31 are formed by 
electrically conductive films 21B and 31B and insulating films 21C and 31C 
formed thereon, respectively. The conductive films 21B and 31B generate 
Coulomb force by a voltage applied thereto, with which they are attracted 
by each other. The insulating films 21C and 31C are provided in order to 
prevent the electrode films 21 and 31 from being short-circuited when they 
are in contact by Coulomb force. Either one of the insulating films 21C 
and 31C may be omitted. 
Each of the first pin drive plate 20 is movably fixed to the first drive 
plate support member 11 by an elastic member 13 as shown in FIG. 5. The 
first drive plate support member 11 has a connector 14 which fixes the 
elastic member 13 and is connected to a cable 15 electrically. As shown in 
FIG. 6, a pair of thin plates 13A of the elastic member 13 are connected 
to each other by a pair of spring members 13B. One of the thin plates 13A 
is inserted into a gap 14A provided in the connector 14 and fixed therein 
and the other thin plate 13A is fixed to the other surface of the first 
pin drive plate 20, on which there the electrode film 21 is formed. The 
conductive film 21B (FIG. 7) of the electrode film 21 is electrically 
connected to the conductive elastic member 13, so that the conductive film 
is electrically connected to the cable 15. 
Therefore, each of the elastic member 13 supports the first pin drive plate 
20 and has functions to move the printing pins 10 horizontally and 
vertically with respect to the recording sheet 41 and to electrically 
connect the electrode film 21 to the cable 15. 
In FIG. 3, each of the second pin drive plates 30 opposing to the first pin 
drive plates 20 is fixed, together with the electrode film 31, to the 
second drive plate support member 12 made of metal and grounded through a 
cable 16 connected to the second drive plate support member 12. 
When a drive (printing) signal is supplied through the cables 15 and 16, 
voltages are applied between the electrode films 21 and 31 selectively 
according to the printing signal and the first and second pin drive plates 
20 and 30 are attracted by each other. That is, the first pin drive plate 
20 having the printing pins 10 fixed thereon is attracted by the second 
pin drive plate 30 by deformation of the elastic member 13. In this case, 
Coulomb force F is represented by the following equation: 
EQU F=V.sup.2..epsilon. . S/2 . d.sup.2 (1) 
where V is a voltage between the electrode films 21 and 31, d is a distance 
between these electrode films, S is an area of each of the conductive 
films 21B and 31B of the electrode films 21 and 31 and e is permittivity. 
The arm 9 is moved in the direction toward the top end of the printing pin 
10 by a current supplied to the drive coil 8, when the printing signal is 
supplied to the electrode films 21 and 31. Therefore, when the printing 
signal has a voltage V so that the first pin drive plate 20 is held 
attracted to the second pin drive plate 30, the first pin drive plate 20 
and 30 move together with the arm 9 as shown in FIG. 4. At this time, the 
pin 10 protrudes from a bottom plate 1B of the printing head housing 1. 
However, when no voltage is supplied to the electrode film 21, the first 
pin drive plate 20 does not lower with the arm 9 and is kept at a position 
before printing, that is, the pin does not protrude from the bottom plate 
1B. Therefore, only the pin protruded from the bottom plate 1B pushes the 
ink ribbon 40 to transfer ink to the recording sheet 41. In this 
embodiment, the magnetic drive unit 2 is driven at the timing of the 
printing signal as mentioned and, since the first and second pin drive 
plates 20 and 30 of the pin drive unit 3 are selectively and 
simultaneously driven according to the printing signal, the pins 10 
transfer ink to the recording sheet 41 according to the printing signal. 
Coulomb force F depends upon pressure force of the pin 10 to the ink ribbon 
40. For example, the pin 10 presses the ink ribbon with a force of 10 
grams, the voltage V, the area S and the distance d may be made about 100 
V, about 1-2 mm and about 0.1 mm, respectively. 
When the printing pin 10 reciprocates vertically of the recording sheet 41, 
it is preferable in order to prevent lateral deviation of the pin that the 
reciprocation of the pin 10 is guided by a small guide hole. 
In the printing head of this embodiment, there is no need of providing a 
drive coil, a core and an armature every pin 10 and only one or two 
magnetic drive units are enough. Further, since the pin drive unit 3 can 
be miniaturized, it is possible to substantially reduce a size of the 
printing head compared with the conventional head. 
Now, a drive circuit of the printing head shown in FIGS. 1 and 2 will be 
described. FIG. 8 is a circuit diagram of a drive circuit of the printing 
head and FIG. 9 is a timing chart showing an operation of the drive 
circuit of the printing head. In these figures, a printing head drive 
circuit includes a drive coil driving circuit 50 for driving the drive 
coil 8, a pin drive plate driving circuit 51 for driving the first and 
second pin drive plates 20 and 30 and a drive control circuit 52. The 
printing head drive circuit is mounted on a electrical circuit board of 
the printer. The drive control circuit 52 produces control signals 55, 56, 
57 and 58 shown in FIG. 9 based on the printing signal. The control 
signals 55 and 56 are repeatedly produced in synchronous with a printing 
period and supplied to base terminals of transistors Tr1 and Tr2 of the 
drive coil driving circuit 50. The transistors Tr1 and Tr2 are turned on 
simultaneously with leading edges of the control signals 55 and 56, 
respectively. The transistor Tr1 is turned off after a time t1 lapses and 
the transistor Tr2 is turned off after a time t2 lapses from t1. When the 
transistors Tr1 and Tr2 are in on-states for the time t1, current flows 
from a power source E1 through the transistor Tr1, the drive coil 8 and 
the transistor Tr2, and thereby the armature 6 (FIGS. 1 and 2) is 
attracted by the core 5, lowering the arm 9. For a time from a time at 
which the transistor Tr1 is turned off to a time at which the transistor 
Tr2 is turned off, that is, the time t2, the power source E1 is blocked by 
the transistor Tr1. However, energy stored in the drive coil 8 flows 
through the drive coil 8, the transistor Tr2 and ground to a diode D1. 
Therefore, the lowered position of the arm 9 is maintained until the 
transistor Tr2 is turned off. The time t2 is necessary to stabilize an 
operation of the magnetic circuit by approximating a current waveform of 
the drive coil to a rectangular waveform. The drive coil 8 is driven every 
constant time t3 which is equal to a printing period. 
On the other hand, the control signals 57 and 58 are used to exchange 
on/off-states of switches S1 and S2 of the pin drive plate driving circuit 
51. Although a single pin drive plate driving circuit 51 is shown in FIG. 
8, a corresponding number of the pin drive plate driving circuits 51 to 
the number of the pins 10 are connected in parallel to each other to a 
power source E2. The control signals 57 and 58 are pulse signal trains 
which become high or low levels every constant time t3 based on the 
printing signal and the respective pins 10 are selectively driven by these 
signals. One of terminals of the switch S1 is connected to the power 
source E2 and the other terminal thereof is connected to the electrode 
film 21 of the first pin drive plate 20 through a resistor Rs. The 
electrode film 31 of the second pin drive plate 30 and the switch S2 are 
connected to a ground terminal of the power source E2, the switch S2, 
resistors Rp and Rs and the electrode films 21 and 31 forming a closed 
circuit. The cable 15 shown in FIGS. 1 and 2 connects the resistor Rs to 
the electrode film 21 and the cable 16 connects the electrode film 31 to 
the ground terminal of the power source E2. 
As shown in FIG. 9, the control signals 57 and 55 are synchronized while 
the control signals 58 and 57 are not. Therefore, only the switch S1 is 
closed during a time in which current flows through the drive coil 8 to 
apply a voltage between the electrode films 21 and 31 and make them 
attracted by each other by Coulomb force to thereby perform a printing 
operation as shown in FIG. 4. In this case, the switch S1 is not closed 
when the printing signal has no voltage. 
On the other hand, when the switch S1 is turned off and the switch S2 is 
turned on, charge stored between the electrode films 21 and 31 is 
discharged through the resistors Rs and Rp. In this manner, the on/off 
operation of the switches S1 and S2 are performed in synchronous with the 
operation of the drive coil 8. 
In the embodiment described above, the printing signal voltage is applied 
to the electrode film 21 through the elastic member 13 and the electrode 
film 31 is grounded through the second drive plate support member 12. 
However, the application of voltage and the grounding may be reversed. In 
such case, the second drive plate support member 12 may be made of an 
insulating material, the respective electrode films 31 may be connected to 
the resistor Rs of the pin drive plate driving circuit 51 and the 
respective electrode films 21 may be grounded at the ground terminal of 
the power source E1 through the elastic members 13. 
FIG. 10 is a cross section of a printing head according to a second 
embodiment of the present invention. This embodiment differs from the 
previously mentioned embodiment in the structure of a magnetic drive unit 
60. A permanent magnet 62 is fixed in series with a core 61 of the 
magnetic drive unit 60 and a leaf spring 63 is fixed below the core 61. 
The leaf spring 63 and the core 61 are fixed to a printing head housing 
68. An armature 64 is fixed on the leaf spring 63 and a gap is formed 
between the core 61 and the armature 64. The core 61, the permanent magnet 
62, a yoke 66 and the armature 64 constitute a magnetic circuit. The 
armature 64 is always attracted to the core 61 by the permanent magnet 62 
and thus an arm 69 fixed to a top end of the leaf spring 63 is shifted to 
an opposite side of a recording sheet 41. The drive coil 65 is wound on 
the core 61 such that, in response to the drive signal supplied thereto, 
magnetic force is generated in a direction in which magnetic force of the 
permanent magnet 62 is cancelled out. 
When there is no current in the drive coil 65, the leaf spring 63 deforms 
oppositely of the printing pin 10 to put the pin 10 remote from the 
recording sheet 41 at which no printing is performed. However, when a 
current flows through the drive coil 65 in synchronous with the printing 
signal, attraction of the armature 64 due to the permanent magnet 62 is 
released and the second drive plate support member 12 moves toward the 
recording sheet 41 immediately. When a voltage due to the printing signal 
is applied to the electrode films 21 and 31 of the first and second pin 
drive plates 20 and 30 as shown in FIG. 4, simultaneously with this 
movement, the first and second pin drive plates 20 and 30 are attracted by 
each other. As a result, the elastic member 13 deforms and the printing 
pin 10 moves together with the movement of the second drive plate support 
member 12, printing the recording sheet 41 through the ink ribbon 40. A 
drive circuit used may be the same as that shown in FIG. 9. 
According to this embodiment, it is possible to reduce the length of the 
arm fixed to the leaf spring, compared with the previous embodiment and, 
so, it is possible to stabilize the movement of the arm. 
FIG. 11 is a cross section of a printing head according to a third 
embodiment of the present invention. Although the magnetic drive units are 
used in the first and second embodiments, a drive unit to used in the 
third embodiment is a piezoelectric element. In FIG. 11, a drive unit 70 
includes a piezoelectric element 71, a support member 72 to which one end 
of the piezoelectric element 70 is fixed and a vibration amplifying member 
73 to which the other end of the piezoelectric element 71 is fixed and on 
a point of action of which a second drive plate support member 12 is fixed 
to amplify deformation of the piezoelectric element 71. One end of the 
vibration amplifying member 73 is fixed to the support member 72. The 
support member 72 is fixed to a printing head housing 74. Since 
construction of other portion than the drive unit 70 is the same as that 
of the first embodiment, details thereof are omitted. 
Before a drive signal is applied to the piezoelectric element 71, the 
printing pin 10 is separated from the recording sheet 41 and does not 
print at all. When the drive signal is supplied in synchronous with the 
printing signal, the piezoelectric element 71 is expanded and the second 
drive plate support member 12 moves immediately toward the recording sheet 
41. When a voltage due to the printing signal is applied to the electrode 
films 21 and 31 of the first and second pin drive plates 20 and 30 
simultaneously with the movement of the second drive plate support member 
12 as shown in FIG. 4, the printing pin 10 prints the recording sheet 41 
through the ink ribbon 40. In this embodiment, a piezoelectric element 
drive circuit is used instead of the drive coil driving circuit 50 in FIG. 
9 and the piezoelectric element 71 is driven with the same timing as that 
of the control signal 56. 
This embodiment does not require any magnetic circuit and further the 
vibration amplifying member 73 functions in the same way as the 
combination of the arm and the leaf spring. Therefore, the number of parts 
is smaller than that in the first or second embodiment. 
The present invention is not limited to the first to third embodiments 
mentioned above and various modifications are possible within the scope 
defined by the appended claims. For example, the configuration of the 
first and second pin drive plates 20 and 30 may be any so long as they are 
in the form of plate. Further, the printing pin 10 which is described as 
being fixed to the first pin drive plate 20 may be formed as a portion of 
the first pin drive plate 20.