WIRE DOT PRINTING HEAD

Abstract: A spring charge type of wire dot printing head, wherein a plurality of pairs of cores each consisting of a front core (35) and a rear core (36) are arranged toroidally on a base plate (44) and coils (39, 40) are wound alternately on one of these paired cores. Accordingly, the inductance of the coil (39, 40) can be increased and the reduction of current and power consumption can be accomplished.

Description: Industrial Field The present invention relates to a wire dot printing head for an impact printer, more particularly to a wire dot printing head for printing by driving the printing wire secured to the tip of an armature of the impact printer. Background Technology An impact printer executes printing on a printing media by driving a printing wire, by giving blows to the printing media through an ink ribbon, and with this force. Since the printing media are readily available and comparatively cheap as well, this impact printer is widely used for various kinds of output devices, such as those of data processing systems. The above-described impact printer is classified into a wire dot printing head type, a plunger type, a spring charge type and a clapper type. Among these types, the spring charge type is constituted such that the armature which secures the printing wire is supported so as to joggle freely by a bias leaf spring, that the armature is attracted in advance to a core by a permanent magnet against an elastic force of the above-described bias leaf spring, and that in case of printing a coil wound around the core is excited to generate a magnetic flux in an opposite direction to that of the permanent magnet, whereby the armature is released. The wire dot printing head having this construction has been recently desired to realize speeding up for printing. To meet this desire, this spring charge type wire dot printing head having high-speed responsiveness has been widely utilized. Fig. 1 is a cross-sectional view illustrating a conventional spring charge type wire dot printing head. In this drawing, between a guide frame 1 and a cap 2, a base 3, a ring 4, a permanent magnet 5, a magnet york 6, a spacer 7, a leaf spring 8 and an armature 9 are piled up in this order through a clamp spring 10. On the resilient portion of the leaf spring 8, an armature 11 is disposed, and on to the tip of the armature 11, the base of a spring wire 12 is secured. The tip of the printing wire 12 is guided by a wire guide 13 so as to be protrusile toward a platen. At the center of the base 3, a core 14 is disposed around which a coil 15 is wound. This coil 15 is fixed to a printed board 17 through a coil bobbin 16. The coil 15 is connected electrically to the printed board 17 through a coil terminal 18. Between the printed board 17 and the base 3, an insulation plate is inserted. Further, a numeral 20 denotes a wire felt disposed in the wire guide 13, through which the printing wire 12 passes. In the above-described construction, a magnetic circuit is formed, through which the magnetic flux generated by the permanent magnet 5 returns to the permanent magnet 5 after passing through the magnet york 6, the spacer 7, the armature york 9, the armature 11, the core 14, the base 3 and the ring 4. By this magnetic circuit, the armature 11 is attracted to the core and displaced. This displacement of the armature 11 accumulates distortion energy in the leaf spring 8 so that the leaf spring 8 is put under a biased condition. Under this biased condition, when the magnetic flux having an opposite direction to the magnetic circuits is generated by exciting the coil 15, the magnetic flux generated by the permanent magnet 5 and the magnetic flux generated by the coil 15 negate with each other. As the result, the force to attract the armature 11 is decreased. Accordingly, since the distortion energy accumulated in the leaf spring 8 is released and the leaf spring 8 reverts to an original position, the printing wire 12 fixed on to the tip of the armature 11 protrudes through the wire guide 13 to press an ink ribbon and a printing media (both not shown) against a platen. As the result, characters and graphic patterns can be printed out. However, in the wire dot printing head having the above-described construction, the magnetic flux leakage of the electromagnet which is used to negate the magnetic flux generated by the permanent magnet passes through both the adjacent armature and the core. Accordingly, the magnetic interference causes a change to the magnetic flux of the core. Further, the more a number of the dot wires printing in the same timing increases, the larger the change in the magnetic flux caused by the above-described magnetic interference grows. When releasing the armature in order to obtain this large magnetic flux change, larger exciting current is required in comparison with operating the respective dot wire independently. Accordingly, the calorific value of the printing head increases accompanied by an increase of power consumption. Further, though, accompanied by miniatualization of the printer, the printing head tends to be miniatualized, realization of the flexible design is now under the difficult condition due to the coil space being limited and the coil winding turns and diameters being restricted. An object of the present invention is to solve the above described problems by minimizing the magnetic interference and decreasing the power consumption and the calorific value. Further object of the present invention is to provide a wire dot printing head miniatualizing its size and improving its operational speed. Disclosure of the Invention A wire dot printing head of the present invention is defined in claim 1. Since either of the front core or rear core is wound around alternately by the coil, an inductance of the coil can be increased. Further, since the permanent magnet is disposed between the core and the base plate, the sectional area can be significantly reduced, so that the cost reduction can be achieved. Brief Description of the Drawings Fig. 1 is a cross-sectional view illustrating a conventional wire dot printing head; Fig. 2 is a partial plan view illustrating a wire dot printing head of the first embodiment of the preset invention; Fig. 3 is a cross-sectional view of A-A in Fig. 2; Fig. 4 is a cross-sectional view of B-B in Fig. 2; Fig. 5 is a partial perspective view illustrating a wire dot printing head of the first embodiment of the present invention; Fig. 6 is a partial plan view illustrating a wire dot printing head of the second embodiment of the present invention; Fig. 7 is a partial plan view illustrating a wire dot printing head of the third embodiment of the present invention; Fig. 8 is a partial perspective view illustrating a wire dot printing head of the second embodiment of this invention; Fig. 9 is a partial perspective view illustrating a wire dot printing head of the fourth embodiment of the present invention; Fig. 10 is a partial plan view illustrating the fourth embodiment of the present invention; Fig. 11 is a partial plan view illustrating a wire dot printing head of the fifth embodiment of the present invention; Fig. 12 is a cross-sectional view of B-B in Fig. 11; Fig. 13 is a cross-sectional view of C-C in Fig. 11; Fig. 14 is a partial perspective view illustrating a wire dot printing head of the fifth embodiment of the present invention; and Fig. 15 is an exploded perspective view illustrating a wire dot printing head of the present invention. Best Mode for Exploiting the Invention (First Embodiment) Fig. 3 is a cross-sectional view illustrating a wire dot printing head of A-A the first embodiment of the present invention and also a cross-sectional view in Fig. 2. Fig. 4 is a cross-sectional view of B-B in Fig. 2. Fig. 2 is a partial plan view illustrating a wire dot printing head of the present invention. Fig. 5 is a partial perspective view illustrating a wire dot printing head of the present invention. In the drawings, a numeral 31 denotes an armature for securing a printing wire 33 on to its tip, a numeral 32 denotes a leaf spring for securing the armature 31 on to its free tip by laser welding and so on; and a numeral 34 denotes a permanent magnet for attracting the armature. The permanent magnet 34 is disposed on the side of a front core 35. The core is constituted by a pair of cores having the front core 35 and the rear core 36 each pair of which is disposed in a circular form. The paired cores having the front core 35 and the rear core 36 are disposed at the center and on the periphery of the printing head corresponding to the armature 31. A numeral 37 denotes a ring for forming a fixed tip of the leaf spring 32; a numeral 38 denotes a magnet york disposed between the front core 35 and the permanent magnet 34. Further, a numeral 39 denotes a coil wound around the front core 35; and numeral 40 also denotes a coil wound around the rear core 36. The coils 39 and 40, as shown in Figs. 2 and 5, are wound alternately around the front core 35 or the rear core 36. 41 denotes a wire guide; 42 a metallic residual sheet inserted between the core 36 and the leaf spring 32 both to protect the core surface and to give an initial displacement to the leaf spring 32; 43 a guide frame positioning the wire guide 42; 44 a base plate on which the cores 35 and 36 and the permanent magnet 34 are mounted. The guide frame 43 and the base plate 44 are fixed with the screws 45 and 46 to the ring 37, with the leaf spring 32 in between. The operation of the wire dot printing head having the above-described construction will be explained hereinafter. While not printing, electric current is not applied to the coils 39 to 40. Magnetic flux generated by the permanent magnet 34 constitutes a magnetic flux loop passing through the magnet york 38, the front core 35, the armature 31, the rear core 36 and the base plate 44. This magnetic flux loop attracts the armature 31 to the cores 35 and 36 against the force of the leaf spring 32 and puts the leaf spring 32 biased to accumulate the distortion energy. Now, assume the printing by driving the optional dot wire 33, selectively. Among the front cores 35 wound around by the coil 39 as shown in Fig. 4 and the rear cores 36 wound around by the coil 40 as shown in Fig. 3 a core corresponding to the driven printing wire 33 is selected. Further, by applying electric current to the coil 39 or 40 wound around the above-described selected rear core 36, a magnetic flux loop is formed in an opposite direction of the magnetic flux loop generated by the permanent magnet. In this way, winding the coils 39 and 40 alternately around the paired cores constituted by the adjacent cores 35 and 36 provides installation space for the coils 39 and 40 being doubled as compared with that for the conventional wire dot printing head, resulting of inductance being increased, electric current to drive the coils 39 and 40 being decrease, and electric power consumption being able to be decreased. Further, since the adjacent coils 39 and 40 are disposed separately with each other, the magnetic interference generated while exciting is reduced. In this way, since the wire dot printing head of the first embodiment of the present invention is constituted such that a pair of cores constituted by the front core 35 and the rear core 36 and disposed to correspond to each armature, is disposed plurally in a circular form, that between either of the above-described front core 35 or the rear core 36 and the base plate 44, the permanent magnet is disposed, and that either of the above-described front core 35 or the rear core 36 is wound around alternately by the coil 39 or 40, inductance of the coil can be increased. Accordingly, both low electric current and low electric power consumption can be realized. Further, since, in this wire dot printing head, the permanent magnet 34 is disposed between the core 35 or 36 and the base plate 44, the sectional area becomes significantly small so as to the cost being reduced. Further, since the permanent magnet 34 is disposed adjacent to the operational gap, the magnetic flux leakage can be minimized so that the effective magnetic flux can be efficiently utilized. Further, since each of the adjacent coils 39 and 40 is disposed separately with each other, the magnetic interference caused by electromagnet can be reduced. (Second and Third Embodiment) Fig. 6 is an exploded plan view illustrating the second embodiment of the present invention, and Fig. 8 is an exploded perspective view illustrating an essential part of the second embodiment of the present invention. According to Figs. 6 and 8, a wire dot printing head is constituted such that the paired cores, which is constituted by the center core, that is, the front core 35 and the peripheral core, that is, the first rear core 36a or the second rear core 36b being disposed in a centripetal direction, are disposed in a circular form. The second rear core 36b and the first rear core 36a are disposed alternately in a circular form, and the sectional area S1 of the second rear core 36b is set to be smaller than the sectional area S2 of the first rear core 36a. Further, the second rear core 36b is wound around by the rear core coil 40, whereas the first rear core 36a is not wound around by a coil. Moreover, the front core 35 pairing with the second rear core 36b is not wound around by a coil, whereas the front core 35 pairing with the first rear core 36a is wound around by the front core coil 39. In this way, except that the sectional area S1 of the second rear core 36b is set to be smaller and the second rear core 36b is also set to be thinner, the other structures are all the same as those in the first embodiment. Accordingly, the other parts, such as an armature and a printing wire, omitted in the drawings for explaining this embodiment can be readily understood by reference to Fig. 3 - Fig. 5. The operation of the second embodiment will be explained hereinafter. As shown in Fig. 8, while not printing, the leaf spring illustrated with a dashed line is attracted to the front core 35 and the second rear core 36b by magnetic flux generated by the permanent magnet 34. Since the sectional area S1 of the second rear core 36b is set to be small, the magnetic flux volume passing through the second rear core 36b is smaller than that passing through the first rear core 36a. Accordingly, the force to attract the leaf spring 32 to both the front core 35 and the second rear core 36b becomes smaller than the force to attract the leaf spring 32 to both the front core 35 and the first rear core 36a. Under this condition, a printing wire (not shown) is driven. An electric current is applied to the rear core coil 40 or the front core coil 39 constituting the paired cores corresponding to a desired driving printing wire. When the electric current is applied to the rear core coil 40 or the front core coil 39, a magnetic flux in an opposite direction to the magnetic flux generated by the permanent magnet 34 passes through the second rear core 36b or the first rear core 36b, the leaf spring 32, an armature (not shown) and the front core to negate the magnetic flux generated by the permanent magnet 34. Since the magnetic flux generated by the permanent magnet 34 passing through the second rear core 36a is comparatively small, the magnetic flux to negate this can be made small. Accordingly, the current value of the electric current applying to the rear core coil 40 wound around the second rear core 36b can be decreased. Alternatively, current passing time for the rear core coil 40 can be made shorter. Further, as for the current passing time, by adjusting the size of the sectional area S1 of the second rear core 36b in order that the current passing times. at both the rear core coil 40 and the front core coil 39, necessary to release both the leaf spring 32 attracted to the paired cores made by the front core 35 and the second rear core 36b and the leaf spring 32 attracted to the paired cores made by the front core 35 and the first rear core 36a, are set to be equal with each other, the printing control can be much simplified. When the magnetic flux generated by the permanent magnet 34 is negated, the leaf spring 32 is released, and with the accumulated distortion energy, moves upward to protrude the printing wire secured on to the armatures (not shown). Referring to Fig. 7, the third embodiment of the present invention will be explained hereinafter. As shown in Fig. 7, this embodiment is characterized in that the sectional area S3 of the center core, that is, the second front core 35b in the paired cores made by winding the rear core coil 40 around the peripheral core, that is, the rear core 36, is set to be smaller than the sectional area S4 of the first front core 35a wound around by the front coil 39. The other structures are all the same as those in the first embodiment. In this embodiment similar to the second embodiment, by the magnetic flux generated by the permanent magnet, the leaf spring is attracted to both the second front core 35b and the rear core 36. Since the sectional area S3 of the second front core 35b is set to be smaller, the magnetic flux generated by the permanent magnet also becomes small. Accordingly, in case of driving the printing wire, as described in the second embodiment, the magnetic flux to negate the magnetic flux generated by the permanent magnet can be also minimized. As the result, the current value of the electric current applying to the rear core coil 40 wound around the rear core 36 can be decreased. Alternatively, the current passing time for the rear core coil 40 can be made shorter. As explained so far, in the above-described second and third embodiments, thought the sectional area of the rear core 36 or the front core 35 in the paired cores made by winding the coil 40 around the rear core 36 is set to b small, depending on the installation position of the permanent magnet 34, the present invention does not exclude making smaller the sectional area of the rear core 36 or the front core 35 in the paired cores made by winding the coil 39 around the front core 35. (Fourth Embodiment) Fig. 9 is an exploded perspective view illustrating an essential part of the fourth embodiment of the present invention; and Fig. 10 is an exploded plan view illustrating an essential part of the fourth embodiment of the present invention. In Figs. 9 and 10, the leaf spring 32 forms the first and the second leaf spring fragments 32a and 32b protruding in the centripetal direction to stretch relative to each of the paired cores. On to both the leaf spring fragment 32a stretching relative to the paired cores made by winding the rear core coil 40 around the rear core 36 and the second leaf spring fragment 32b stretching relative to the paired cores made by winding the front core coil 39 around the front core 35, similarly as the first embodiment, the armature 31 is fixed though, the width 11 of the resilient part 32a of the first leaf spring fragment 32a is set to be larger than the width 12 of the resilient part 32b₂ of the second leaf spring fragment 32b. Accordingly, the first leaf spring fragment 32a is required stronger force to be deflected than the second leaf spring fragment 32b being deflected so that the recovery force to revert to the original position becomes stronger. Since the other structures are all the same as those in the first embodiment, the explanation will be omitted. The operation of this embodiment will be explained hereinafter. While not printing, both the first leaf spring fragment 32a stretching relative to the paired cores made by winding the rear core coil 40 around the rear coil 36 and the second leaf spring fragment 32b stretching relative to the paired cores made by winding the front core coil 39 around the front core 35, are attracted by the magnetic flux generated by the permanent magnet 34. Since the magnetic flux volume passing through each of the paired cores is equal, the attracting force in this case is also equal with each other. With this attracting force, the first leaf spring fragment 32a and the second leaf spring fragment 32b are attracted to each of the paired cores. However, since the recovery force of the first leaf spring fragment 32a is stronger than that of the second leaf spring fragment 32b, the magnetic flux volume necessary to release the first leaf spring fragment 32a from the paired cores, that is, the coercive force, is smaller than that necessary to release the second leaf spring fragment 32b from the paired cores. Under this condition, the printing wire is driven. The electric current is applied to the rear core coil 40 or the front core coil 39 in the paired cores corresponding to the driving printing wire 33. When the electric current is applied to the front core coil 39 or the rear core coil 40, the magnetic flux in the opposite direction of the magnetic flux generated by the permanent magnet 34 passes to the rear core 36, the leaf spring fragment 32a or 32b, the armature 31 and the front core 35 to negate the magnetic flux generated by the permanent magnet 34. Though all of the magnetic flux generated by applying the electric current to the rear core coil 40, as described above, due to the magnetic flux leakage, is not used to negate the magnetic flux generated by the permanent magnet 34, the first leaf spring fragment 32a is released even though the magnetic flux generated by applying the electric current to the rear core coil 40 is small. This is because the coercive force at the leaf spring fragment 32a is small. Accordingly, the current value of the electric current applying to the rear core coil 40 wound around the rear core 36 can be decreased, or the current passing time for the rear coil 40 can be made shorter. By adjusting the coercive force of the first leaf spring 32a and further the width l₁ of the resilient part 32a₁ of the first leaf spring fragment 32a so that the current passing time at both the rear core coil 40 and the front core coil 39 wound around the front core 35, necessary to release both the first leaf spring fragment 32a and the second leaf spring fragment 32b, are set to be equal with each other, the current passing time control is much simplified more. As described above, according to the above-described fourth embodiment, the resilient part width of the first leaf spring fragment 32a corresponding to the paired cores made by winding the coil 39 around the rear core 36 is set to be larger so that the coercive force under the condition in which the first leaf spring fragment 32a is attracted also becomes small. Accordingly, the current value of the electric recurrent applying to the rear core coil 39 wound around the rear core 36 can be decreased, or the current passing time can be made shorter. (Fifth Embodiment) Fig. 11 is a plan view illustrating an essential part of the wire dot printing head of the fifth embodiment of the present invention; Fig. 12 is a cross-sectional view of B-B in Fig. 11; Fig. 13 is also a cross-sectional view of C-C in Fig. 11; Fig. 14 is a perspective view illustrating an essential part of the wire dot printing head; and Fig. 15 is a perspective take-down view illustrating an essential part of the wire dot printing head. Two kinds of cores 35 and 36, as shown in Figs. 12 and 13, are disposed alternately in a radial form as shown in Fig. 11 to constitute the printing head. In the drawings, 31 denotes an armature securing a printing wire 33 on its tip; 32 a leaf spring securing the armature 31 on its free tip by laser welding or the like. 34 a circular permanent magnet magnetized in a direction of its thickness; 35 a front core; 36 a rear core; 44 a round-shape base plate made from magnetic material securing the front core 35 and the rear core 36 alternately in a circumferential direction; 37 a spacer ring forming a fixed tip of the leaf spring 32; 38 a magnet plate securing the front core 35 and the rear core 36 alternately to the permanent magnet 34; 47 a screw for fixing the magnet plate 38, the permanent magnet 34 and the base plate 44; 47a a washer; 39 a coil wound around the front core 35; 40 also a coil wound around the rear core 36; 42 a residual sheet disposed to be inserted between the front core 35, the rear core 36 and the leaf spring 32 for protecting the surface of the core 35, and the armature 31; and 43 a guide frame disposed, along with the spacer ring 37, to form the fixed tip of the leaf spring 32 and further to position the wire guide 41. That is, in the base plate 44, installation holes for the front core 35 and the rear core 36 are formed alternately in the circumferential direction and into these core installation holes, the front cores 35 are inserted to fix themselves on every other hole, and further the rear cores 36 corresponding to the front core 35 adjacent to these front cores 35 are inserted into the rear core installation holes to fix themselves on every other hole in the same way. Meanwhile, also in the magnet plate 38, installation holes for both the front cores 35 and the rear cores 36 are formed alternately in the circumferential direction, and both the rear core 36 corresponding to the front core 35 fixed on to the above-described base plate 44 and the front core 35 corresponding to the rear core 36 similarly fixed on the base plate 44, are inserted into the installation holes for both the front cores and the rear cores to fix themselves on every other hole. These front cores 35 and rear cores 36 fixed on the magnet plate 38 are wound around respectively by the front core coil 39 and the rear core coil 40. This magnet plate 38 is formed so as to have the identical external shape as the permanent magnet 34. And, to avoid the interference from the front cores 35 and the rear cores 36 fixed respectively on the base plate 44, holes and helical grooves are formed in both of them. Accordingly, after placing the permanent magnet 34 and the magnet plate 38 where the front core 35 and the rear core 36 are inserted into their holes and helical groove to fix themselves upon the upper center of the base plate 44 and by fixing integrally with the screw 45, as shown in Fig. 11, each of the front cores 35 and the rear cores 36 is disposed to be fixed sequentially in the circumferential direction. Accordingly, in this embodiment, the first magnetic assembly constituted by the rear core 36 and the rear core coil 40 disposed on the front core 35 and the permanent magnet 34 fixed on the base plate 44 and the second magnetic assembly constituted by the front core 35 and the front core coil 39 disposed on the rear core 36 and the permanent magnet 34 fixed on to the base plate 44, are formed. Further , the front core 35 and the rear core 36 can be formed integrally with the base plate 44 and the magnet plate 38 respectively in one body. The operation of the wire dot printing head having the above-described construction will be explained hereinafter. When not printing, the electric current is not applied to the coil 38. As shown in Fig. 12, where the permanent magnet 34 is disposed, a magnetic flux loop 101 passing through the front core 35, the armature 31 the rear core 36 and the base plate 44 in this order is formed by the permanent magnet 34. As the result, the armature 31 is attracted to the front core 35 against the force of the leaf spring 32, and the leaf spring 32 is put under the biased condition to accumulate distortion energy. Meanwhile in Fig. 13, in the same way, a magnetic flux loop 102 passing through the rear core 36, the armature 31, the front core 35 and the base plate 44 in this order is formed by the permanent magnet 34 so that the armature 31 is attracted to the front core 35. In this case, the polarities of the adjacent magnetic flux loops 16 and 17 are in the opposite direction with each other. Next, in Fig. 14, when printing by driving the optional printing wire 33 selectively, the magnetic flux in the opposite direction of a magnetic flux loop 47 generated by the permanent magnet 34 is formed by applying the electric current to the exciting coil 40 corresponding to that printing wire 33, as shown with the arrow e. Since, at this time, the coils 39 and 40 are wound around the cores 35 and 36 which are disposed on the permanent magnet, most of the magnetic flux 102 generated by the permanent magnet 34 passes through the cores 35 and 36. That is, the magnetic flux leakage from the magnetic fluxes 101 and 102 generated by the permanent magnet 34 is so small that they can pass through inside the coils 39 and 40. As the result, the magnetic fluxes e and f generated by the coils 39 and 40 can negate effectively the magnetic flux generated by the permanent magnet 34. In the wire dot printing head having the above-described construction as shown in Fig. 15, since the integral-type permanent magnet 34 is used and the manufacturing process to magnetize after the assembly of the printing head can be adopted possible, the production cost can be decreased. Possibility for Industrial Use The present invention is suitable for use in various kinds of information processing devices, especially for use in the printing head of the printer to obtain hard copies readily. Among other things, the present invention is suitable for the serial printer with low power consumption and stabilized operation.

Claims: A wire dot printing head comprising: a base plate (44) made from magnetic material, a plurality of cores arranged in pairs, each pair (35, 36) of cores including a rear core (36) and a front core (35), the rear cores being disposed in a circular form on a periphery of the base plate (44) and the front cores being disposed in a circular form inside the circle of rear cores, a permanent magnet (34) disposed between the base plates (44) and the rear core (36) or the front core (35) of each pair of cores, a plurality of coils (39, 40) alternately wound around each second rear core (36) and each second front core (35) such that each pair of cores (35, 36) has only either its rear core or its front core provided with a coil, a plurality of spring means (32) associated with the plurality of pairs of cores, each string means (32) being disposed over the associated pair of cores (35, 36) to joggle freely by being released from the pair of cores or by being attracted to the pair of cores with a magnetic force depending on whether or not the associated coil is excited, a plurality of printing wires (33) associated with the plurality of spring means (32), each printing wire being fixed on a freely joggling part of the associated spring means (32), and a spacer ring (37) disposed on the base plate (44) outside the rear cores (36). The wire dot printing head set forth in claim 1, wherein the permanent magnet (34) is disposed between the base plate (44) and the core provided with the coil, and wherein the upper surface of the permanent magnet is the first pole and the lower surface thereof is the second pole. The wire dot printing head set forth in claim 2, wherein the permanent magnet (34) is formed to be in a plate shape connecting sequentially each of the cores provided with a coil. The wire dot printing head set forth in claim 1, wherein the permanent magnet (34) is disposed between the base plate (44) and the front core (35) or between the base plate (44) and the rear core (36). The wire dot printing head set forth in claim 1, wherein an area of a cross-section of the front core (35a) provided with a coil differs from an area of a cross-section of the front core (35b) not provided with a coil. The wire dot printing head set forth in claim 5, wherein an area of a cross-section of the front core (35a) provided with a coil is larger than an area of a cross-section of the front core (35b) not provided with a coil. The wire dot printing head set forth in claim 1, wherein an area of a cross-section of the rear core (36b) provided with a coil differs from an area of a cross-section of the rear core (36a) not provided with a coil. The wire dot printing head set forth in claim 7, wherein an area of a cross-section of the rear core (36b) provided with a coil is smaller than an area of a cross-section of the rear core (36a) not provided with a coil. The wire dot printing head set forth in claim 1, wherein the spring means is a leaf spring (32), a resilient part width (l₁) of the leaf spring disposed on the rear core (36) provided with a coil differs from a resilient part width (l₂) of the leaf spring disposed on the rear core (36) not provided with a coil. The wire dot printing head set forth in claim 9, wherein a resilient part width (l₁) of the leaf spring disposed on the rear core (36) provided with a coil is wider than a resilient part width (l₂) of the leaf spring disposed on the rear core (36) not provided with a coil.

Inventors: ANDOO HIROKAZU OKI ELECTRIC IN, KISHIMITO MITSURU OKI ELECTRIC, OOISHI NOBORU OKI ELECTRIC IND, UMEZAWA YOICHI OKI ELECTRIC IN, ANDOO, HIROKAZU OKI ELECTRIC INDUSTRY CO., LTD., KISHIMITO, MITSURU OKI ELECTRIC INDUSTRY CO.,, OOISHI, NOBORU OKI ELECTRIC INDUSTRY CO., LTD., UMEZAWA, YOICHI OKI ELECTRIC INDUSTRY CO., LTD.
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY COMPANY, LIMITED
Application year: 1990
Main classification: B41J2
IPC codes: B41J2