Printing Head With Springs for Pivotably Holding Printing Hammers

The present invention relates to an impact type dot matrix printer for forming characters, symbols, or the like in a dot matrix formation.

In a conventional print head of this kind, print hammers are supported so as to be rotatable at a right angle to the main surfaces thereof and have movable yokes (armatures) which are mounted opposite to coil cores (see Japanese Patent Publication No. 35474/1983). In another print head of this kind, print hammers are supported so as to be rotatable along the main surfaces thereof. This hammer includes an armature disposed opposite to each coil core. The hammer is fabricated by blanking and bending a plate and the armature is integrally formed with the hammer (see Japanese Patent Publication No. 42471/1981).

The first-mentioned print head is comprised of a number of components and cumbersome to assemble, because the movable yokes are manufactured independent of the print hammers and then rigidly attached to the hammers. The second-mentioned head is laborious to manufacture, insomuch as it requires blanking, bending and other steps. In either print head, leaf springs, press plates, screws, or other similar parts are required to support the print hammers. Therefore, the conventional print head consists of a number of components, and is not easy to assemble. In addition, it is so difficult to arrange the hammers closely and actuate the hammers with a sufficient large magnetic forces.

It is an object of the present invention to provide a print head which has print hammers arranged closely and actuated with a sufficiently large magnetic force.

The above object is achieved by a print head for use in a printer of the impact type, comprised of print elements biased rearward by return springs, print hammers arranged radially and striking corresponding print elements, and a yoke body disposed in front of the print hammers and having coil cores which are disposed opposite to corresponding print hammers and on which coils are wound to actuate the hammers. The head is characterized by a further provision of a yoke plate for enhancing the efficiency with which the print hammers are magnetically actuated. The yoke plate has tongue portions which extend radially inward from its outer peripheral portion. The tongue portions are arranged alternately with, and close to, the print hammers. The yoke body has a lateral wall extending rearward in a parallel relation to the cores. The outer peripheral portion of the yoke plate is in contact with the rear end surfaces of the lateral wall.

Since the tongue portions of the yoke plate extend between the print hammers, the magnetic flux emanating from a coil core forms a first magnetic path which passes from the corresponding print hammer and back to the same print hammer through the yoke body. In addition, a second magnetic path is formed which passes from the core through the hammer, the neighboring tongue portions of the yoke plate, the outer peripheral portion of the yoke plate and the yoke body, and back to the same core. The print hammers shaped in the form of a plate are angularly movable along their main surfaces. Even if the magnetic flux saturates inside the hammer, the magnetic path passing through the neighboring tongue portions of the yoke plate is formed. Thus, the cores attract the hammers with a sufficient large force. Hence, the hammers can be actuated efficiently.

Other objects and features of the invention will appear in the description thereof which follows.

FIG. 1 is a cutaway side elevation view of main portions of a print head according to the present invention;

FIG. 2 is a rear view of the yoke body shown in FIG. 1;

FIG. 3 is a rear view of the coil shown in FIG. 1;

FIG. 4 is a right side elevation view of the coil shown in FIG. 3;

FIG. 5 is a front elevation view of the head cover shown in FIG. 1;

FIG. 6 is a front elevation view of the press spring shown in FIG. 1;

FIG. 7 is a side elevation view of the print hammer shown in FIG. 1;

FIG. 8 is a front elevation view of the print hammer shown in FIG. 1;

FIG. 9 is a front elevation view of the yoke plate shown in FIG. 1;

FIG. 10 is a cutaway front elevation view of the yoke plate shown in FIG. 9, and in which some components have been mounted to the yoke plate;

FIG. 11 is a cross-sectional view of main portions of the print head shown in FIG. 1, for showing the manner in which the print hammer is actuated; and

FIGS. 12-16 are cross-sectional views of main portions of other structures for supporting the print hammer.

Referring to FIG. 1, there is shown a print head embodying the concept of the present invention. This head has a head frame 1 which is entirely made from a synthetic resin containing graphitic carbon. A guide plate support portion 1a protrudes from the center of the front half of the frame 1. The support portion 1a has a hollow 2 which is open at its lower end. The front wall 1b of the support portion 1a is provided with an opening 1c which is in communication with the hollow 2. The peripheral wall defining the front end of hollow 2 has a vertical groove 2a and a front guide 3 is inserted into the groove 2a. The guide 3 is introduced into the groove 2a from the bottom of the groove 2a and has a portion 3a protruding forward and fitted in the opening 1c. The front surface of the protruding portion 3a and the front wall 1b of the head frame 1 form a common plane. The protruding portion 3a has two rows of zigzag guide holes 3b in which the front ends of print elements 4, such as print wires, are slidably inserted. In this embodiment, twenty-four print elements 4 (only one is shown) are provided. The peripheral wall defining the rear end of the hollow 2 has a vertical groove 2b into which an intermediate guide 5 is inserted. When the head is assembled, the intermediate guide 5 is inserted into the groove from the bottom side. The intermediate guide 5 has twenty-four guide holes 5a arranged in an elliptic shape. The intermediate portions of the print elements 4 extend slidably through the guide holes 5a.

The head frame 1 further has a rear guide 1d disposed at the rear of the hollow 2 and spaced a given distance from the hollow 2, in order to guide the rear portion of the print elements 4. A post-like connector portion 1e protrudes rearwards from the center of the rear end guide 1d, which is provided with twenty-four guide holes 1f arranged in a circular shape. At the rear portions of the print elements 4 which extend through the holes 1f, return springs 6 are mounted. Thus, each print element 4 is biased rearwards.

A mechanism for striking the print elements 4 is now described. A first cylindrical yoke member 7 (FIG. 2) is mounted behind the head frame 1. A number of coil cores 7a corresponding to that of the print elements 4 (twenty-four in this embodiment) protrude rearward from the yoke member 7, and are arranged circumferentially on the yoke member 7. Each core 7a has a coil 8 (FIGS. 3 and 4) wound around respective one of the cores 7a to actuate the corresponding print hammer (described latter). Each core 7a further includes terminal pins 9a, 9b protruding toward the front surface of the yoke member 7. A flexible cable 10 is connected to the pins 9a and 9b. Radiating fins 7b are formed integrally on the outer periphery of the yoke member 7. The connector portion 1e extends through the center of the yoke member 7 and protrudes rearward.

A head cover 11 (FIG. 5) has a lateral wall opposed to the rear end surface of the lateral wall of the yoke member 7 which extend parallel to the cores 7a. The lateral wall of the cover 11 has twenty-four grooves 11a. The cover 11 has a center hole 11b through which the connector portion 1e extends. Twenty four guide protrusions 11c are formed around the center hole 11b. A press spring 12 (FIG. 6) is housed in the cover 11. The spring 12 has an annular hub 12a fitted around the protrusions 11c and twenty-four finger-like resilient arms 12b extending outwardly radially from the annular hub 12a. The distal ends of the resilient arms 12b extend into the grooves 11a in the cover 11. An annular damper 13 is received inside the protrusions 11c.

Twenty four print hammers 14 (FIGS. 7 and 8) are mounted in front of the resilient arms 12b of the press spring 12. Each hammer 14 having a shape, as shown in FIGS. 7 and 8, pressed out of a sheet plate. Each hammer 14 is radially arranged so that its inner end portion 14a is disposed between the neighboring protrusions 11c. The rear ends of the print elements 4 face corresponding front inner ends of the hammer 14. The radially outer end portions 14b of the hammers 14 are inserted in the grooves 11a. Each hammer 14 has an intermediate protruding portion 14c in its center in opposed relation to the corresponding. core 7a.

The outer peripheral portion 15a of a yoke plate or second yoke member 15 (FIG. 9) is in contact with the rear end surfaces of the lateral wall or dependent portion of the yoke member 7 depending laterally from an outer periphery of the first yoke member 7. The outer peripheral portion 15a is provided with grooves 15b facing the grooves or openings 11a. The outer end portions 14b of the hammers 14 are located within the corresponding grooves 11a and 15b such that the outer ends 14b of the hammers 14 are brought into contact with the end of the dependent portion of the first yoke member 7. Tongue portions 15c extend radially inward from the outer peripheral portion 15a and are arranged alternately with the hammers 14 to define a plurality of slots between adjacent tongue portions 15c to receive therein the hammers 14.

Referring to FIG. 5, the head cover 11 has protrusions 11d for placing the yoke member 7 and the yoke plate 15 in position. These protrusions 11d fit in positioning grooves 7c (FIG. 2) and in positioning grooves 15d (FIG. 9). Referring to FIG. 6, positioning protrusions 12c are integrally formed on the press spring 12 toward the head cover 11 and fit between the adjacent protrusions 11c (FIG. 5).

When the print head is assembled, the press spring 12 and the print hammers 14 are inserted into the head cover 11. Then, the rear surface of the outer peripheral portion of the yoke plate 15 is brought into contact with the front end surface of the lateral wall of the cover 11 in the arrangement shown in FIG. 10. Thereafter, the front surface of the outer peripheral portion of the yoke plate 15 is brought into contact with the rear end surface of the lateral wall of the yoke member 7.

The fringe of a fixing leaf spring 16 is brought into resilient contact with the rear surface of the cover 11. A screw 17 is passed through the leaf spring 16 and screwed into the connector portion 1e. Thus, the rear end surfaces of the print elements 4 are in contact with the front end surfaces of the radially inner end portions 14a of the hammers 14. The resilient arms 12b of the press spring 12 push or act on the rear end surfaces of the outer end portions 14b of the hammers 14, bringing the front end surfaces of the outer end portions 14b into resilient contact with the rear end surface of the lateral wall of the yoke member 7 to urge the radially outer end portions 14b against the lateral wall of the yoke member 7 to rotatably position the respective outer ends of the hammers in place relative to the lateral wall of the yoke member 7. In this way, the hammers 14 are received so as to be rotatable or pivotable about their radially outer end portions between front operating and rear rest positions in an axial direction transverse to the radial directions of the hammers 14.

We now describe the operation of one of the print elements 4 and its associated components. It is to be understood that any other print element 4 and its associated components function in the same manner. When the coil 8 corresponding to the print element 4 is not energized, the print hammer 14 is pushed rearwards in the rear rest position so that its inner end is in resilient contact with the damper 13 by the action of the return spring 6 of the print element 4. Under this condition, the intermediate protruding portion 14c is not in contact with the core 7a. When the coil 8 is energized to excite the core 7a, the protruding portion 14c of the print hammer 14 is attracted to the core and makes contact with it as shown in FIG. 11 in the front operating position. This moves the inner end portion 14a of the hammer 14 forward, pushing and actuating the print element 4 forward. The magnetic flux emanating from the core 7a passes from the protruding portion 14c of the hammer 14 to the yoke member 7 through the outer end portion 14b of the hammer magnetically coupled to the dependent portion of the yoke member 7, and then returns to the core 7a. Also, the flux originating from the core 7a passes form the protruding portion 14c of the hammer 14 to the yoke member 7 through the neighboring tongue portions 15c and the outer peripheral portion 15a of the yoke plate 15 magnetically coupled to the dependent portion of the yoke member 7, and then returns to the core 7a. Therefore, even if the hammer 14 is shaped in the form of a thin plate and does not have a sufficiently large area of cross section, the hammer 14 is actuated with a sufficiently large magnetic attraction, impacting the print element 4.

It is to be understood that the structure for supporting the print hammers 14 is not limited to the structure of the above embodiment, but rather various support structures as shown in FIGS. 12-16 can be employed. In the embodiment shown in FIG. 12, a small protrusion 14d is formed on the outer end of the print hammer 14. This protrusion 14b is fitted in a hole 15e formed in the yoke plate 15, so that the hammer 14 is rotatably received. In the embodiment shown in FIG. 13, a receiver member 15f for receiving the small protrusion 14d is manufactured independently and is fixed to the yoke plate 15. In the embodiment shown in FIG. 14, a vertically bent portion 15g is formed integrally with the yoke plate 15 and extends laterally from the outer peripheral portion of the plate 15. The bent portion 15g is received in a V-shaped groove 14e formed at the outer end of the hammer 14. In the embodiment shown in FIG. 15, the fringe 15h of the yoke plate 15 is received in a V-shaped groove 14f formed in the hammer 14. Thus, the hammer 14 is rotatably supported. In this case, the outer peripheral portion of the plate 15 is not bent but rather extended in the radially outward direction. In the embodiment shown in FIG. 16, a protrusion 14g which is formed on the outer end of the hammer 14 bears on the outer surface of the yoke frame 7. The hammer 14 can rotate about this protrusion. The yoke plate 15 has a groove 15j at its outer end. The outer end portion of the hammer 14 is fitted in the groove 15j and placed in position.

In accordance with the present invention, since a magnetic path passing form the core and back to the core through the print hammer and the yoke member is formed and, in addition, also a magnetic path passing from the core and back to the core through the print hammer, the yoke plate, and the yoke member is formed, a magnetic efficiency is improved. Hence, it is possible to obtain a sufficiently large force to actuate the hammers.