Device to prevent the inadvertent coming-apart of the parts of a draftsman&#39;s ink writing instrument
FIELD OF THE INVENTION 
     The instant invention relates to a device for preventing the inadvertent coming-apart of the parts of a draftsman&#39;s ink writing instrument. 
     BACKGROUND OF THE INVENTION 
     Conventional draftsman&#39;s ink writing instruments are structured as shown in FIG. 1. In such conventional draftsman&#39;s ink writing instruments, an outer case 1 has three cylindrical stages of different external diameters and an axial through bore which likewise has three stages having different internal diameters. The largest diameter portion of the outer case 1 is referred to herein as the ink reservoir 2, and the part of the axial through bore contained therein functions as an ink reservoir. The medium diameter portion of the outer case 1 contains the medium diameter portion of the axial through bore and is referred to herein as an operation part 3. The small diameter portion of the outer case 1 contains the small diameter portion of the axial through bore and is referred to herein as the writing part 4. The writing part 4 contains an ink flow hole 7 which is open to the bottom of the outer case 1, while the ink reservoir part 2 is open at the top of the outer case 1. A tapered annular shoulder 5 is formed in the inner surface of the axial through bore between the reservoir and the portion of the axial through bore in the operation part 3. An external annular step shoulder 6 is formed on the outer case 1 at the level of the bottom of the tapered annular shoulder 5. Further, a tapered annular shoulder 8 is formed in the inner surface of the axial through bore at the juncture between the medium diameter portion and the small diameter portion thereof. 
     An ink flow stopping piece 9 is inserted in the outer case 1. The ink flow stopping piece 9 has a needle part 10 which is located in the ink flow hole 7 and the end of which projects through the ink flow hole 7. The ink flow stopping piece 9 also has a flowing down prevention part 12 which has a tapered flow stopping surface 11. The tapered flow stopping surface 11 valves the tapered annular shoulder 8 to prevent the flowing down of the ink. The flowing down prevention part 12 is of cylindrical shape and is sized so that an annular gap is present around it. A weight 14 is connected to the upper surface of the flowing down prevention part 12 by a connecting rod 13. 
     Such a conventional draftsman ink writing instrument prevents external leakage of ink by surface tension when the ink reservoir is filled with ink. The flowing down of the ink is prevented by the annular engagement of the tapered annular shoulder 8 with the corresponding tapered flow stopping surface 11 on the ink flow stopping piece 9, and the tapered flow stopping surface 11 is biased into engagement with the tapered annular shoulder 8 by the force of gravity operating on the weight 14. 
     When performing character or line writing with the conventional draftsman&#39;s instrument shown in FIG. 1, a grip holding member 18 is pivotally supported at the desired angle to the end of a fork-shaped holding member 16 attached to the end of a pen holder 15 by a pin 17 as shown in FIG. 2. The grip holding member 18 grippingly holds the outer surface of the operation part 3 of the outer case 1 with a forked grip holding part 19 attached to the end of the grip holding member 18. The grip holding member 18 keeps the ink flow stopping piece 9 from dropping out by holding the head of the weight 14 with the suspender 20 formed integrally with the forked grip holding part 19 and extending upwardly. 
     When it is desired to draw a circle, a leg 22 of a compass 21 holds the outer case 1 as shown in FIG. 3. An attachment 24 having a bore 23 is mounted on the leg 22 of the compass 21, and the operation part 3 of the outer case 1 is inserted into the attachment 24 and is gripped by tightening an adjusting screw 25. 
     When a draftsman performs character or line writing using the pen holder 15 or the compass 21, the needle part 10 is touched to the paper, forcing the ink flow stopping piece 9 upwardly, and the tapered flow stopping surface 11 separates from the tapered annular shoulder 8 to allow ink to flow down. The ink flows down the ink flow hole 7, and a line of the thickness corresponding to the outer diameter of the writing part 4 is formed. 
     In the above draftsman ink writing instrument, the needle part 10 required to write a fine line is itself very fine. The needle part 10 may be easily bent, particularly when the ink flow stopping piece 9 falls out of the outer case 1. Therefore, a U-shaped clip 26 has been conventionally fitted to the outer wall of the ink reservoir 2 so that the ink flow stopping piece 9 will not fall out when the apparatus is turned upside down. 
     However, a serious drawback of this conventional construction is that, because one side of the U-shaped clip 26 is placed in the ink reservoir, the ink may leak out due to capillary action. 
     Moreover, in those apparatuses intended to write thick lines, the needle part 10 is thick, and the total weight of the ink flow stopping piece 9 is large. In that case, the U-shaped clip 26 cannot stop the inadvertent coming out of the ink flow stopping piece 9. Therefore, the ink flow stopping piece 9 comes out when the apparatus is turned upside down, and the ink loses its surface tension and flows out of the ink reservoir. Such an eventuality may cause trouble by making stains on the paper surface or the draftsman&#39;s clothes. 
     OBJECT OF THE INVENTION 
     Therefore, this invention was devised to avoid ink leaking out by capillary action. Additionally, the ink will not flow out if the apparatus is placed upside down. 
     SUMMARY OF THE INVENTION 
     To avoid ink leaking out due either to capillary action or to the ink flow stopping piece inadvertently falling out due to its own weight, the subject invention provides a falling down prevention member which is axially and movably received in the upper, larger diameter part of the axial through bore. The falling down prevention member is sized and shaped so that it is resiliently biased against the inner surface of the upper, large diameter part of the axial through bore but will not pass downwardly beyond the tapered annular shoulder between the upper, larger diameter part of the axial through bore and the medium diameter, intermediate part of the axial through bore. Moreover, the falling down prevention member has an inserting hole sized, shaped, and positioned to receive the connecting rod and to permit the falling down prevention member to be slid radially into position around the connecting rod. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an enlarged longitudinal section of a conventional draftsman&#39;s pen. 
     FIG. 2 is an enlarged side view of the apparatus of FIG. 1 attached to a penholder. 
     FIG. 3 is a perspective view of the apparatus of FIG. 1 attached to a compass. 
     FIG. 4 is an enlarged longitudinal sectional view of a first embodiment of the present invention. 
     FIG. 5 is a perspective view on an enlarged scale of a falling down prevention member used in the first embodiment. 
     FIG. 6 is a perspective view of a falling down prevention member according to a second embodiment. 
     FIG. 7 is an enlarged longitudinal sectional view of a third embodiment. 
     FIG. 8 is a perspective view of the falling down prevention member used in the third embodiment. 
     FIG. 9 is an enlarged longitudinal sectional view of a fourth embodiment. 
     FIG. 10 is a perspective view of the falling down prevention member used in the fourth embodiment. 
     FIG. 11 is a perspective view of the falling down prevention member of a fifth embodiment. 
     FIG. 12 is a perspective view of the falling down prevention member of a sixth embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
     The First Embodiment 
     A first embodiment of the invention is illustrated in FIGS. 4 and 5. It is identical to the conventional draftsman&#39;s pen shown in FIG. 1 except that a falling down prevention member 30 inserted in the ink reservoir 2 has replaced the U-shaped clip 26. 
     The falling down prevention member 30 is composed of a thin metallic circular falling down prevention board 31 having a slightly larger diameter than the inner diameter of the ink reservoir 2. The circular falling down prevention board 31 has a U-shaped inserting hole 32 sized and shaped to allow radial insertion of the connecting rod 13. The diameter of the inserting hole 32 is smaller than the outer diameter of the flowing down prevention part 12. Straight line parts 33, 33 are formed on both sides of the circular falling down prevention board 31, and rectangular legs 34, 34 made of springy material (preferrably spring steel) project upwardly from the falling down prevention board 31. 
     Connecting rod 13 of the ink flow stopping piece 9 is inserted radially into the inserting hole 32, and the ink flow stopping piece 9 and the falling down prevention member 30 are inserted in the ink reservoir 2, as shown in FIG. 4. Axial movement of the falling down prevention member 30 is stopped at the tapered annular shoulder 5. Because the outer diameter of the falling down prevention board 31 is a little larger than the inner diameter of the ink reservoir 2, it is fixed firmly by friction. Further, the falling down prevention member 30 is attached rigidly in place by the spring force of the rectangular legs 34, 34. 
     When ink is filled in the ink reservoir 2, the ink passes through the inserting hole 32 in the falling down prevention board 31 and flows inbetween the flowing down prevention part 12 and the operation part 3. Contact of the tapered flow stopping surface 11 and the tapered annular shoulder 8 prevents flowing out of the ink. 
     In use, the ink flow stopping piece 9 is raised by touching the needle part 10 to the paper as in the conventional case, and the required character, etc., may be written. 
     When the pen is held upside down,, although the ink flow stopping piece 9 moves axially, the flowing down prevention part 12 contacts the falling down prevention board 31 of the falling down prevention member 30, preventing further axial movement of the ink flow stopping piece 9. Further, the ink is prevented from flowing out of the ink reservoir 2 by surface tension. 
     In the first exemplary embodiment, the falling down prevention board 31 has a circular form. However, the falling down prevention board 31 is not necessarily limited to having a circular form. Various forms can be adopted. 
     In the first exemplary embodiment, the falling down prevention member 30 can be fixed in place by contacting both rectangular legs 34, 34 elastically to the inside surface of the ink reservoir 2. Thus, the falling down prevention board 31 can be fixed in place without inclination by the rectangular legs 34, 34. 
     Because the falling down prevention member 30 is rigidly fixed in place, the coming out of the ink flow stopping piece 9 can be completely prevented when the apparatus is held upside down, and flow out of the ink can be prevented. 
     The Second Embodiment 
     A second exemplary embodiment will now be explained with reference to FIG. 6. The falling down prevention member 30a of the second exemplary embodiment has rectangular legs 34a, 34a formed from elastic material protruding axially from both sides of the falling down prevention board 31. The rectangular legs 34a, 34a are bent outwardly from bending lines 35, 35 to give sufficient friction to prevent the coming out of the ink flow stopping piece 9 when the falling down prevention member 30a is inserted in the ink reservoir 2. 
     Except as stated above, the second embodiment is identical to the first embodiment. 
     The Third Embodiment 
     A third exemplary embodiment is next explained with reference to FIG. 7 and FIG. 8. In this embodiment, the falling down prevention member 30b is formed by bending steel material having elasticity (such a piano-wire) as shown in FIG. 8. An inserting hole 32b has a width which allows insertion of the connecting rod 13 of the ink flow stopping piece 9. A circular falling down prevention part 36 has a diameter smaller than the outer diameter of the flowing down prevention part 12. Circularly shaped fixing parts 37, 37 have a diameter slightly larger than the internal diameter of the ink reservoir 2. The open ends of the fixing parts 37, 37 are bent in the upper direction to form legs 34b, 34b. 
     When the legs 34b, 34b of the falling down prevention member 30b structured as above are pressed inwardly, the diameters of the fixing parts 37, 37 become smaller. The ink flow stopping piece 9 and the falling down prevention member 30b are inserted into the outer case 1 until the falling down prevention member 30b contacts the tapered annular shoulder 5 at the bottom of the ink reservoir 2. Then the legs 34b, 34b are freed, and the fixing parts 37, 37 expand their diameter until they are strongly pressed against the inside of the ink reservoir 2 by their elastic force, and the falling down prevention member 30b is fixed in place by their frictional force. 
     When ink is filled in the ink reservoir 2, the ink passes through the gaps between fixing parts 37, 37 and the falling down prevention part 36. 
     Although the falling down prevention part 36 is shown as circular in FIG. 6, it should be noted that it can also be made in a U-shape. 
     In the third exemplary embodiment, the elastic force of the two fixing parts 37, 37 of the falling down prevention member 30b tends to expand in both directions to strongly hold the falling down prevention member 30b in the ink reservoir 2. 
     Because the legs 34b, 34b project upwardly, the legs 34b, 34b can be held during the operations of attaching and removing the falling down prevention member 30b from the ink reservoir 2, making the attaching and removing operations easy. 
     Further, the falling down prevention member 30b is fixed rigidly in place. Thus, the coming out of the ink flow stopping piece 9 can be prevented completely when the instrument is placed upside down. 
     The Fourth Embodiment 
     A fourth exemplary embodiment will now be explained with reference to FIGS. 9 and 10. The falling down prevention member 30c has a circular shape as shown in FIG. 10 and is formed with an outer diameter larger than the inner diameter of the ink reservoir 2. However, the thickly formed falling down prevention board 31c is made of a resilient material, such as plastic. An inserting hole 32c opens to one side of the falling down prevention board 31c in open ends 38, 38. As with the other embodiments, the inserting hole 32c has a width larger than the diameter of the connecting rod 13 of the ink flow stopping piece 9 and smaller than the diameter of the flowing down prevention part 12. The surfaces of the open ends 38, 38 of the falling down prevention board 31c have circular arc shapes. 
     After the connecting rod 13 of the ink flow stopping piece 9 is inserted into the insertion hole 32c, the open ends 38, 38 of the inserting hole 32c are squeezed. Consequently, the diameter of the outer circumference of the falling down prevention member 30c is made smaller. The falling down prevention member 30c is then inserted into the ink reservoir 2 until it is stopped by the tapered annular shoulder 5. The open ends 38, 38 are then released, permitting the falling down prevention member 30c to try to recover its original shape. The falling down prevention member 30c is thus pressed against the internal surface of the ink reservoir 2 and is strongly held in place by its elastic force. 
     The Fifth Embodiment 
     A fifth exemplary embodiment will now be explained with reference to FIG. 11. The fifth exemplary embodiment has a hollow space 39d between the inserting hole 32d and the circumference of the falling down prevention board 31d. Otherwise, the fifth embodiment is similar to the fourth embodiment. As for the material, any resilient material, such as natural rubber, synthetic resin, or spring metal may be selected. 
     The fifth exemplary embodiment allows ink to flow down through the hollow space 39d. When inserting or removing the falling down prevention member 30d to or from the ink reservoir 2, the operation of holding the falling down prevention member 30d and narrowing the inserting hole 32d may be performed easily by inserting a tool in the vicinity of open ends 38d, 38d of the hollow space 39d. 
     The Sixth Embodiment 
     A sixth exemplary embodiment will now be explained with reference to FIG. 12. The sixth exemplary embodiment has a hollow space 39e, as in the case of the fifth exemplary embodiment. However, the sixth embodiment is formed with sharp open ends 38e, 38e. Otherwise, the sixth embodiment is the same as the fifth exemplary embodiment in function and effect.