Dot Printer

Abstract

An apparatus comprising a plurality of dot forming needles each connected to one of a plurality of electromagnets of the clapper type arranged in a circle and controlled individually to actuate the needles selectively so as to perform dot printing by the needles on a recording sheet.

Description

BACKGROUND OF THE INVENTION

This invention relates to dot printers using a plurality of dot forming needles, and more particularly it is concerned with a dot printer of the type in which base portions of the dot forming needles are arranged in a circle.

In one type of mechanical dot printers known in the art, seven dot forming needles, for example, are arranged in a row lengthwise of a recording sheet and selectively actuated while being moved crosswise thereof, so that dot printing can be performed on the recording sheet through a carbon tape.

Generally, electromagnet means is used for actuating the dot forming needles. The electromagnet means used should be quick in response and should have a sufficiently high power to permit dot printing to be performed satisfactorily by the needles, because the time during which a row of dots is printed should be very short. Because of this, electromagnets of the plunger type which are high in efficiency have hitherto been in use in many dot printers of the prior art.

Some disadvantages are associated with the use of electromagnets of the plunger type. Specialized art is needed to work on materials to fabricate parts of the electromagnets, and it is difficult to obtain a small size in an electromagnet of the plunger type. Thus, the dot printers of the type using electromagnets of the plunger type are high in cost and large in overall size.

Electromagnets of dot printers of the prior art are arranged in a row so that the free ends of needles depending from the plungers of the electromagnets may be disposed in a row lengthwise of the recording sheet. In this arrangement, nearly all the needles depending from the electromagnets are more or less bent outwardly in going to their base portions except possibly for the center needle so that the needles are arranged segmentally as seen from the front or rear, because the free ends of the needles should be concentrated in a small area while their bases are connected to the electromagnets of large size. This arrangement of the needles has made it necessary to fit a tubular needle guide over each needle because each needle moves along a curved path. The use of the tubular needle guides has the disadvantage of offering resistance to the movement of needles and the frictional dragging of the guides on the needles causes a reduction in the efficiency of the electromagnets. Besides, the arrangement in which the electromagnets are disposed in a row requires more space than is necessary in the dot printer.

SUMMARY OF THE INVENTION

This invention has as one of its objects the provision of a dot printer which uses a plurality of electromagnets of the clapper type having a segmental cross-sectional shape and arranged radially to form a circle so that the base portions of the needles depending from the electromagnets may be disposed in a small circle to permit the free ends of the needle to be disposed adjacent one another in a row.

Another object of the invention is to provide a dot printer which is quick in response in spite of the fact that simple electromagnets of the clapper type is used, compact in size and low in cost.

According to the invention, there is provided a dot printer wherein the armature of each electromagnet of the clapper type is adapted to be moved away from the core of the electromagnet by separating means when the electromagnets are de-actuated, so that the mechanism can be simplified and the operation of the needle can be performed positively even if the stroke is very small. Besides, the electromagnets are segmental in cross-section and arranged radially to form a circle, so that it is possible to obtain a compact overall size in a dot printer.

In the present device, the needles are arranged in a small circle to form a small bundle and disposed substantially perpendicular to the plane of the recording sheet as the result of the arrangement in which the electromagnets are arranged radially to form a circle. This eliminates the need to use tubular needle guides, so that the working on the needles is simplified and the production cost is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of the dot printer comprising one embodiment of the invention;

FIG. 2 is a right side view of the dot printer shown in FIG. 1;

FIG. 3 is a sectional view of the cores of the electromagnets;

FIG. 4 is a front view of an electromagnet with certain parts being broken away;

FIG. 5 is a right side view of FIG. 4;

FIG. 6 is an exploded perspective view of an electromagnet showing its construction;

FIG. 7 is a plan view of one example of a recording sheet on which dots are printed;

FIG. 8 is a front view of the dot printer comprising another embodiment of the invention; and

FIG. 9 is an exploded perspective view of the dot printer shown in FIG. 8 showing the construction of its essential portions.

DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 1, the dot printer is shown as comprising drive means 1 comprising a plurality (seven in the embodiment shown) of electromagnets 2 of the clapper type each of which is firmly secured by a screw 3 to a mounting plate 4. Each electromagnet 2 comprises a coil 6 wound on a core 5 as shown in FIG. 4, the core 5 being segmental or triangular in cross-section as shown in FIG. 3 so that the coil 6 wound thereon is substantially segmental in cross-section. Flanges 7 and 8 secured to opposite ends of the core 6 prevent opposite ends of the coil 6 from being unwound from the core 5.

The screw 3 threadably connected to the left end portion of the core 5 loosely extends through an opening formed in the mounting member 4 and through an opening formed in a mounting portion of a yoke 9, and a plate spring 11 is mounted between the mounting portion 9a of yoke 9 and the mounting plate 4 so as to urge the mounting portion 9a into pressing engagement with the left end surface of core 5. The yoke 9 includes a portion 9b which is parallel to the axis of core 5 and which has firmly secured to its free end by two screws 13 (FIG. 6) a base of an L-shaped supporter 12. In supporter 12, at the junction of a longer portion 12b and a shorter portion 12a there is formed an opening 14 as shown in FIG. 6; a projection 15a formed in the base of an armature 15 extends through a portion of the opening 14 disposed on the shorter portion 12a.

The armature 15 has a free end portion which tapers in going toward its free end where two shoulders 15b, 15b are formed. A plate spring 16 adapted to urge the armature 15 to move away from the core 5 is formed at its opposite ends with projections 16a and 16b which are adapted to be brought into engagement with the shoulders 15b, 15b in the armature 15 and an edge of the opening 14 formed on the longer portion side of support 12 respectively. As shown in FIG. 4, the armature 15 is disposed parallel to the right end surface of core 5 with a very small clearance being interposed therebetween and normally urged by the biasing force of plate spring 16 to move away from the right end surface of core 5 into an inoperative position. An elongated needle 17 for performing dot printing is secured at its base to a free end 15c of armature 15.

The core of an electromagnet is usually circular in cross-section. However, the electromagnets used in the invention each have a core which is segmental in cross-section as shown in FIG. 3. This permits the electromagnets 2 to be arranged radially to form a circle without using more space than is necessary and thus permits an overall compact size to be obtained in a dot printer. The use of the armature 15 which includes a free end portion tapering in going toward the free end as shown in FIG. 6 permits the outer diameter of the drive means 1 to be greatly reduced when the electromagnets 2 are arranged radially to form a circle as shown in FIG. 2 and thus permits the armature to operate quickly when actuated because of low inertia. In addition, leakage of magnetism can be minimized from the closed magnetic circuit formed by the core 5, yoke 9 and armature 15.

The plate spring 16 which is adapted to urge the armature 15 to move away from the core 5 when the electromagnet is de-actuated as aforementioned serves concurrently as a guide for the armature, thereby permitting the size of the drive means 1 to be reduced. Moreover, since the biasing force of the plate spring shows a sudden change even if the stroke of the armature is small, it has particular utility with the electromagnet. That is, the biasing force of the plate spring is low in the initial stages of actuation of the electromagnet 2; hence the armature 15 and the rod 17 can operate quickly. Conversely, the biasing force of the plate spring is high when the electromagnet 2 is de-actuated, so that the speed of movement of armature 15 and rod 17 to their inoperative positions can be increased. Thus, the use of the plate spring is conducive to increased speed at which dot printing is performed.

Referring to FIG. 1 again, a carriage 18 is firmly secured to the mounting plate 4 and loosely mounted on guide shafts 19 and 21 connected at opposite ends to an immovable member (not shown). A pin 23 is loosely fitted in a boss 22 secured to the carriage 18, the pin 23 and boss 22 constituting a so-called click mechanism for stabilizing the pin 23 irrespective of whether the pin 23 is in or out of engagement with a feed screw 24 disposed juxtaposed to the right end of pin 23 in FIG. 1. The feed screw 24 extends through a relatively large aperture 18a formed in the carriage 18 and is supported by an immovable member (not shown) for rotation at a uniform rate. The right end of pin 23 is juxtaposed to the threaded portion of feed screw 24.

When the carriage 18 is in an inoperative position, the pin 23 is engaged at its left end, as shown in FIG. 1, with one arm end of a crank arm 25 which is connected at the other arm to an actuator of a solenoid 26.

A shaft 27 supporting the solenoid 26 and crank arm 25 is connected to a printer proper (not shown). When the solenoid 26 is energized, the pin 23 is brought into engagement with the feed screw 24 which rotates while the solenoid 26 is being energized, so that the pin 23 is moved by the rotating feed screw 24 to move the carriage 18 with the pin 23 along the guide shafts 19 and 21 axially thereof in a recording direction.

Firmly secured to a left end of the carriage 18 is a guide plate 28 formed with a plurality of openings through which the needles 17 loosely extend. A coloring ribbon 31, such as a carbon tape, red ribbon or the like, a recording sheet 32 and a backing plate 33 are disposed leftwardly of the free ends of needle 17 in FIG. 1.

In operation, when the solenoid 26 is energized, the crank arm 25 pivots clockwise about the shaft 27 in FIG. 1 to move the pin 23 rightwardly into engagement with the feed screw 24. When in engagement with the feed screw 24, the pin 23 is moved by the rotating feed screw 24 to move the carriage 18, magnets 2 and needles 17 along the guide shafts 19 and 21. As the magnets and needles move, an actuation signal is selectively supplied to electromagnets 2 in synchronism with the movement of needles 17. Those electromagnets to which the actuating signal is supplied are magnetized and the respective needles perform a dot printing operation. When the needles 17 perform a dot printing operation, they strike the recording sheet 32 through the ribbon 31 to form dots on the recording sheet.

More specifically, when a current is passed to the coil 6 in FIG. 4, a closed magnetic circuit is formed by the core 5, yoke 9 and armature to attract the armature to the core 5, so that the needle 17 moves leftwardly to strike the recording sheet through the ribbon. As the needles 17 strike the recording sheet 32 at high speed according to a predetermined program, a symbol 34 as shown in FIG. 7 is recorded on the sheet 32. The needles 17 have a very small stroke which is about 0.5 millimeter and operate at high speed such that about fifty symbols can be formed per second.

In the embodiment shown and described above, there are seven needles arranged in a row. It is to be understood, however, that the invention is not limited to this number of needles and that the needles may be five in number or any other number as desired and arranged in two rows with the adjacent needles of the two rows being staggered as shown in Japanese Patent Publication No. Sho 46-41357.

FIG. 8 and FIG. 9 show another embodiment of the drive means of the dot printer according to the invention. Secured to one end of a support post 34 is a guide plate 35 which is formed therein with a needle guide opening 35a as shown in FIG. 8. A cylindrical guide 36 formed therein with a needle guide opening 36a and fitted over the support post 34 is secured to the guide plate 35. Secured to the cylindrical guide 36 in ring form are a plurality of yokes 9 each comprising a mounting portion 9a having secured thereto a core 5 on which a coil 6 is wound and held in place by flanges 7 and 8.

As shown in FIG. 9, a supporter 12' is secured by a screw 13' to the free end portion of a portion 9b of each yoke 9 which is parallel to the corresponding core 5. The supporter 12' is formed at its free end portion with a plurality of projections 12a' and 12b' for receiving therein pins 37 and 38 respectively which pivotally support an armature 15' at its base.

A needle 17 extends through the guide openings 35a and 36a formed in the guide plate 35 and cylindrical guide 36 respectively, and has a coil spring 41 mounted at its base between stoppers 39 and 40. Referring to the upper one of the armatures 15' shown in FIG. 8, and to the needle 17 and spring 41 associated therewith, the coil spring 41 urges the needle 17 to press, through the stopper 40, the free end of armature 15' to cause the same to pivot counter clockwise about the shafts 37 and 38. The free end of armature 15' is positioned against a rubber cushion 42 provided at the inner side of a stopper 43 mounted at the other end of support post 34 and locked in this position by stopper 43.

When a current is passed to the electromagnets each comprising coil 6 and core 5 while the needles 17 having their free ends oriented toward the recording sheet are moved in the recording direction, the armature 15' of each electromagnet is attracted to the core 5, thereby causing each needle to move leftwardly in FIG. 8 against the biasing force of coil spring 41 to perform a dot printing operation. According to the invention, the needles 17 can be actuated to perform dot printing by the drive means constructed as aforementioned.

In place of moving the needles 17 by means of the feed screw 24 as described in the first embodiment to carry out dot printing, the recording sheet may be moved to carry out dot printing. In either case, the ribbon can be eliminated if the recording sheet is of the character such that it develops color upon being struck by the needles.

Claims

What I claim is:

1. A dot printer comprising:

a. a plurality of plungerless electromagnets of the clapper type each comprising a yoke formed of flat sheet material, a core secured to said yoke, a coil wound on the core, an armature having a base and an opposite free end, and non-resilient means for pivotally connecting the armature base to the yoke to allow pivotal movement of the armature toward and away from the core but to prevent movement of the armature transversely of the core axis, said base overlapping the yoke and maintaining contact with a continuous line thereof at all times, said opposite free end of the armature tapering in going from the base toward the free end, said armature being disposed substantially transversely of the core axis, said plurality of electromagnets being disposed radially to form a circle with the free ends of the armatures being disposed toward the center of the circle, said core having a triangular cross-section with an apex pointing to the center of the circle,

b. a plurality of needes for performing dot printing corresponding in number to the plurality of electromagnets, each of said needles having a free end and a base, and the needles being respectively operatively connected at their bases to the free ends of the armatures of the respective electromagnets,

c. resilient means for urging the armatures of the electromagnets to move away from the cores when the electromagnets are inoperative, and

d. guide means for guiding the needles to cause the free ends thereof to be aligned with one another and disposed in a row in face-to-face relationship with a recording sheet, said electromagnets being selectively magnetized and rendered operative for selective actuation of the needles to perform dot printing on the recording sheet by selective passage of current to the coils of the electromagnets respectively associated with the needles to be selectively actuated.

2. A dot printer as set forth in claim 1 wherein said means for urging the armatures of the electromagnets to move away from the cores when the electromagnets are inoperative comprises a plurality of plate springs each mounted between the armature and yoke of one of the electromagnets.

3. A dot printer as set forth in claim 1 wherein said means for urging the armatures of the electromagnets to move away from the cores when the electromagnets are inoperative comprises a plurality of coil springs each mounted on one of the needles.

4. A dot printer as set forth in claim 1 further including a carriage, a pin supported by said carriage, and a feed screw rotatable at a uniform rate, said electromagnets being mounted on said carriage together with said needles which are connected to the respective electromagnets, and said pin being adapted to be brought into and out of engagement with said feed screw during rotation of the screw at a uniform rate to move the carriage axially of the feed screw whereby the needles can be moved in a recording direction.

5. A dot printer as set forth in claim 4 further including a solenoid for driving said pin to bring said pin into and out of engagement with said feed screw.

6. A dot printer comprising:

a. a plurality of plungerless clapper-type electromagnets each comprising a yoke formed of flat sheet material, a core of triangular cross-section mounted thereon, an energizable coil wound on the core, an armature having a base and an opposite free end and disposed substantially transversely of the core axis, non-resilient means for pivotally connecting the armature base to the yoke to allow said free end of the armature to move toward and away from the core along the core axis but to prevent movement of the armature transversely of the core axis, said base overlapping the yoke and maintaining contact with a continuous line thereof at all times, said electromagnets being disposed in a circle with the armature free ends oriented toward the center of the circle and with the apices of the core cross-sections pointing to the center of the circle;

b. means for resiliently biasing the armature free end of each electromagnet away from the core thereof such that the armature free end moves toward and away from the core in correspondence with energization and de-energization, respectively, of the coil wound on the core;

c. a plurality of needles, equal in number to the electromagnets, each having a free end and respectively operatively interengaged with the armature free ends of the respective electromagnets for movement therewith such that the free end of each needle is advanced and retracted in correspondence with movement of its associated armature free end toward and away from its associated core, respectively; and

d. guide means for aligning the free ends of the needles in a straight row and for guiding each needle free end, in its position in said row, to produce a dot imprint on a recording medium upon advance of the needle free end as aforesaid, said electromagnet coils being selectively energizable for effecting selective advance of particular ones of said needles to produce on the recording medium a predetermined dot imprint pattern.

7. A dot printer as defined in claim 6, wherein said biasing means for each electromagnet comprises a plate spring acting between the yoke and armature of the electromagnet, and wherein each of said needles has a base secured to the free end of the armature with which it is operatively interengaged.

8. A dot printer as defined in claim 6, wherein each of said needles has an enlarged base bearing against the free end of the armature with which it is operatively interengaged, and extends therefrom through said guide means, and further including fixed structure through which said needles movably extend intermediate said armatures and said guide means, and wherein said biasing means comprises a plurality of helical springs respectively surrounding said needles, each of said springs being under compression between the base of the needle it surrounds and said fixed structure for urging the needle into a retracted position.