Single Element Print Head

1. Field of the Invention

This invention relates to a single element print head of a typewriter and more particularly to a single element print head having an apparatus for releasably attaching it to a drive shaft.

2. Description of the Prior Art

In a single element print head typewriter, as is shown in U.S. Pat. No. 2,895,584, characters and symbols arranged on the print head surface are properly chosen by a print head driving member and are printed on paper, in which the selection of print style can be made easily by changing the print head. In order to change the print head easily it is necessary to provide any convenient means releasably attaching the print head to a drive section, and this means itself should be easy in handling. To this end, various releasable attaching means such as those disclosed in U.S. Pat. Nos. 3,001,628 and 3,307,677 have been practically applied. This kind of attaching means is desired to be one which can be easily handled manually and which affords a sufficient coupling force to transmit the motion of the print-head-driving-section positively to the print head.

It is the object of this invention to provide an improved single element print head having an apparatus for releasably attaching the print head to a drive shaft, which apparatus possesses a superior manual handling feature and a positive coupling force.

FIG. 1 is an enlarged plan view showing the condition in which a print head drive shaft and a print head have been mounted according to this invention.

FIG. 2 is an enlarged plan view showing the condition in which a slide member has been moved from the state illustrated in FIG. 1.

FIG. 3 is an enlarged plan view showing the condition in which a cap, the slide member and a spring have been arranged on the print head.

FIG. 4 is an exploded perspective view illustrating the slide member, the spring and the print head drive sahft on an enlarged scale.

FIG. 5 is an enlarged perspective view of the cap.

Referring to FIG. 1, which is an enlarged plan view of a print head releasably mounted by utilization of the attaching means of this invention, the reference numeral 1 designates a print head drive shaft which is disposed on the carriage (not shown) in the typewriter body (not shown) and constitutes a part of a print head drive section. In the upper end portion of the print head drive shaft 1, as is shown in FIG. 4, is formed a grooved portion 2, under which is formed a mounting portion 3. A tapered slant face 2a is formed extending from the grooved portion 2 to the upper end of the print head drive shaft 1. A print head body 4 is formed of a truncated spherical shell having a plane upper wall and also having an outer peripheral surface on which are embossed a number of characters 5 (only a part of which are shown). In the central part of the print head body 4 is formed a through opening 6 extending through the upper wall thereof, into which is fitted the print head drive shaft 1 so that its grooved portion 2 projects upward from an upper end surface 4a of the print head, while at the same time a projection (not shown) formed on the mounting portion 3 engages a notch (not shown) formed in the lower part of the through opening 6 on its inner peripheral surface, whereby the print head body 4 and the print head drive shaft 1 are mounted together so as to be rotatable in a body. Consequently, the print head body 4 rotates with the rotation of the print head drive shaft 1 and performs a character selecting operation. A cap 7 is secured to the upper end surface 4a of the print head body 4. In the central portion of the cap 7, as is shown in FIG. 5, there is formed therethrough a guide portion 8 one end of which is open at the outer peripheral part, and on the bottom surface of the cap 7 is formed a generally annular holding groove 9. The guide portion 8 is composed of a first upper guide groove 8a and a second lower guide groove 8b of larger width, the first and second guide grooves 8a, 8b being stepped to each other. Formed on the bottom surface of the cap 7 are pins 10 adapted to fit in caulking holes 11 formed in the upper end surface 4a of the print head body 4. The pins 10 are used to couple the print head 4 with the cap 7 after going through the subsequent caulking process.

As illustrated in FIG. 4, a slide member 12 is provided at its upper portion with an operating portion 13 of about the same width as the first guide groove 8a and further provided at its lower portion with a guided portion 14 of about the same width and height as the second guide groove 8b. In the guided portion 14 is formed a guide passage 16 so that there is formed a cam means, which consists of a pair of cam surfaces 15 gradually diverging from the mutually nearest portion towards the mutually farthest portion, forming a shape of substantially a longitudinal section of a bullet, since the rate of diverging decreases as the diverging advances. Each of the cam surfaces has a recess in adjacent to its farthest portion. The slide member 12 is mounted so as to allow the operating portion 13 and the guided portion 14 to be guided by the first and second guide grooves 8a, 8b in the cap 7 respectively, and to allow the bottom surface of the guided portion 14 to slide along the upper end surface 4a. In other words, as a result of the cap 7 being secured with pins 10 to the upper end surface 4a, the slide member 12 is carried between the cap 7 and the upper end surface 4a so as to be movable along the first and second guide grooves 8a, 8b and the upper end surface 4a, so that the slide member 12 can slide between a first operating position in which, as illustrated in FIG. 1, an end face l3a of the operating portion 13 abuts an end face 8c of the guide portion 8 of the cap 7 and a second operating position in which, as illustrated in FIG. 2, the manual slide member 12 has been pulled out of the guide portion 8 to the fullest extent so that the arms of the spring 17 have been most widely opened.

A spring 17 is generally U-shaped or hair pin-shaped, having a base portion 17a of a loop shape capable of fitting in the holding groove 9, a pair of arms l7b extended in the same direction from the base portion 17a, and a bent end 17c formed at the free end of each arm 17b. The spring 17 has a resilience sufficient to permit both bent ends 17c to approach to each other, and it is mounted so that, after the slide member 12 has been inserted as above in the guide portion 8 of the cap 7, the base portion 17a of the spring 17 engages with, for being held in, the holding groove 9 of the cap 7, and the bent ends 17c are positioned within the guide passage 16. Thus the cap 7, which has been attached the slide member 12 and the spring 17, is fixed to the upper end surface 4a of the print head body 4 by means of caulking of the pins 10 got through the caulking holes 11, whereby the spring 17 is held between the cap 7 and the upper end surface 4a, and the slide member 12 is carried so as to be slidably guided by the upper end surface 4a and the guide portion 8.

When the slide member 12 is located in the first operating position as illustrated in FIG. 3, the arms 17b of the spring 17 extend over, and at the same time cross through the area of, the through opening 6 of the print head body 4 and the bent ends 17c are positioned in a front portion 16a of the guide passage 16, thus assuming the most closely approached state of the bent ends 17c. On the other hand, when the slide member 12 moves to the second operating position as shown in FIG. 2, the bent ends 17c of the spring 17 are moved along the cam surfaces 15, thus allowing the arms 17b to pass over, at the same time outside the area of, the through opening 6 of the print head body 4 until the bent ends 17c are rested in positioning recesses 16b of the guide passage 16 to assume the most widely open state of the beat ends 17c.

The following description is now provided for explaining how to attach and detach the print head, which has been assembled to a unit body including the print head body 4, the cap 7, the slide member 12 and the spring 17 put respectively in place, to and from the print head drive shaft 1.

First, the slide member 12 is moved to the second operating position as illustrated in FIG. 2 so that, as mentioned above, the arms 17b of the spring 17 pass outside the area of the through opening 6. This condition is maintained by engagement of the bent ends 17c of the spring 17 with the positioning recesses 16b of the guide passage 16 unless a force acting in the direction of arrow A is exerted on the slide member 12. In this condition, when the print head drive shaft 1 is inserted in the through opening 6 of the print head body 4 and a positional relationship of both is fixed by the afore-mentioned notch and projection (not shown), the grooved portion 2 of the print head drive shaft 1 projects upward from the upper end surface 4a and is positioned within the travelling locus of the arms 17b of the spring 17. Therefore, when the slide member 12 is returned to the first operating position as illustrated in FIG. 1, the spring 17 begins to change the form or posture, by virtue of its own resilience, along the contour of the cam surfaces 15 in such a manner that both arms 17b approach each other, and its changing of posture continues until the arms 17b come into pressure-engagement with the grooved portion 2 of the print head drive shaft 1. By the pressure-engagement of both arms 17b of the spring 17 with the grooved portion 2 of the print head drive shaft 1, the print head body 4 is fixed firm enough so as not to come off the print head drive shaft 1. In this way, the attaching operation of the print head to the print head drive shaft 1 is completed.

To detach the print head from the print head drive shaft 1, the slide member 12 is moved to the second operating position as illustrated in FIG. 2 whereby the arms 17b of the spring 17 are expanded by the action of the cam surfaces 15 to be disengaged from the grooved portion 2 of the print head drive shaft 1, that is, they assume the state shown in FIG. 2. Thus, the fixed state between the print head drive shaft 1 and the print head is released, thereby permitting the latter to be removed from the former.

According to the present invention, as set forth hereinbefore, the print head can be mounted and removed simply due to the easy manual movement of the slide member. In addition, the apparatus of the present invention is so simple in structure that its assembling manipulation is very easy.