A mechanical pencil

Abstract: A mechanical pencil providing a cushioning action by means of a sleeve (24) disposed inside of an outer barrel (10). The mechanical pencil comprises an outer barrel, and a lead pipe (12) disposed inside the outer barrel. The lead pipe has a chuck (16) mounted in the end thereof. The pencil further comprises a chuck ring (22) mounted on the outside of the chuck, a sleeve (24) contacting a rear end of the chuck ring slidable relative to the outer barrel, and a spring (26) interposed between the sleeve and the lead pipe. The sleeve has a plurality of flexible pieces (24a) that spread outwardly in a radial direction. A part of each flexible piece (24a) is inserted into a stopper hole (11c) formed on an inner wall of the outer barrel. An inclined portion (24b) contacting the rear end of the stopper hole is formed on an outer surface of each of the flexible pieces.

Description: BACKGROUND OF THE INVENTION 1. Field of the invention This invention relates to a mechanical pencil, particularly to a mechanical pencil having a cushioning action when excessive force is applied to the lead, by retracting the lead into outer barrel for protecting the lead from damage. 2. Background Information This kind of a prior mechanical pencil is disclosed in Japanese Utility Model Publication No. 3-40633. The prior mechanical pencil comprises an outer barrel, a lead pipe disposed inside the outer barrel, a chuck at the end of it, and a chuck ring disposed outside of the chuck. A sleeve contacting to the rear end of the chuck ring is slidable relative to the outer barrel, and a spring is interposed between the sleeve and the lead pipe. The sleeve is provided with a cushion portion which can extend and shrink in an axial direction. The sleeve also has a plurality of engaging projections engaging stopper holes or inner wall steps formed on the outer barrel, in a rear part behind the cushion portion. The cushion portion comprises a cylindrical member which has a plurality of holes in a side surface of the cylindrical member. The holes allow the cushion portion to extend and shrink in the axial direction. When the engaging projection engages the outer barrel, the sleeve is biased forwardly by its own elastic force. When excessive force is applied to the lead projecting from the outer barrel when writing, the sleeve provides a cushioning action by shrinking rearward in the axial direction, retracting the lead into the outer barrel to prevent damage to the lead. When the sleeve is assembled in the outer barrel, it is inserted into the outer barrel from the rear so that the engaging projections of the sleeve engage the stopper hole it, the outer barrel. However, the engaging projections projecting outwardly in a radial direction must move in the outer barrel by being pressed inwardly until they reach the stopper hole. Therefore it is difficult to move them in the outer barrel without a jig because a large friction force is applied to the engaging projections when they move in the outer barrel. It takes a lot of time and slows productivity. Mechanical pencils according to the first part of claim 1 are described in EP-A-0168122 and EP-A-0093815. SUMMARY OF THE INVENTION To overcome the above disadvantages, it is an object of this invention is to provide a mechanical pencil having a sleeve providing a cushion action that can be assembled without any jigs and in which damaging of the lead is prevented if excessive force is applied to the lead in that the sleeve allows the lead to retract into the barrel when such excessive forces are applied. The mechanical pencil according to the present invention comprises an barrel, a lead pipe disposed in the barrel, a chuck at the end of it, and a chuck ring disposed outside of the chuck. A sleeve contacting the rear end of the chuck ring, is slidable relative to the barrel, and a spring is interposed between the sleeve and the lead pipe. The sleeve has a plurality of flexible pieces spreading outward in a radial direction. A part of the flexible pieces is inserted into a stopper hole formed on an inner side wall of the barrel. According to the invention a portion is formed as part of an outer surface of each of the flexible pieces, which portion is inclined in relation to the longitudinal axis of the sleeve, the other part of said outer surface being projecting from the outer end of the inclined portion parallel to a wall surface of the stopper hole, which wall surface is a rear wall surface seen from the end of the sleeve which end contacts the chuck ring. Preferably guide grooves are axially formed on the inner wall of the outer barrel to guide the flexible pieces of the sleeve into the stopper holes during assembly. When excessive force is applied to the lead projecting from the outer barrel during writing, the flexible pieces that spread outwardly in a radial direction bend inwardly in a radial direction. The inclined portion provided on each of the flexible pieces displaces relative to the stopper hole so that the sleeve displaces rearwardly in an axial direction, retracting the lead into the outer barrel, as a result this cushioning action prevents damage to the lead. When the sleeve is inserted into the outer barrel from the rear during assembly, the flexible pieces that outwardly spread in a radial direction easily bend in a radial direction so that it is possible to assemble it without any resistance force or any jigs. In a case where the outer surface including the inclined portion and the portion parallel to the end surface of the stopper hole is formed on each of the flexible pieces, the outer surface abuts the wall surface of the stopper hole at the rear end of the stopper hole when the sleeve is displaced rearwardly in an axial direction to a certain extent so that further displacement of the sleeve is prevented, thus the flexible pieces are protected from completely escaping from the stopper hole. The sleeve surely returns to the original position when the applied force is released. In a case where the guide grooves are axially formed on the inner wall of the outer barrel, the guide grooves help the flexible pieces to be surely inserted into the stopper hole during assembly. The above, and other objects, advantages and novel features of this invention will become apparent from the following detailed description and the accompanying drawings, in which like reference numbers indicate like or similar parts throughout wherein; BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a longitudinal cross sectional view of a first embodiment according to the present invention, which is a pencil having a barrel of double centric construction i.e. outer barrel and an inner barrel with stopper holes defined spaces between the two barrels. Fig. 2 is an enlarged view of a main part of the embodiment of Fig. 1, Fig. 3 is a cross sectional view of an outer barrel rotated 90 degrees about a center axis from the position shown in Fig. 1, Fig. 4 is a cross sectional view taken at 4-4 line of Fig 3, Fig. 5 is a cross sectional view of an outer barrel taken at 5-5 line of Fig. 6, Fig. 6 is an end view seen along arrow 6 of Fig. 5, Fig. 7 is a longitudinal cross sectional view of a second embodiment according to the invention, which is a pencil having just an outer barrel in the wall of which the stopper holes are defined as through holes, and Fig. 8 is another enlarged view of a main part of the embodiment of Fig. 1. DETAILED DESCRIPTION OF THE INVENTION Referring to Figs. 1 and 2, an embodiment of the invention is described below. Barrel 10, 10a has at the front portion a double concentric construction comprising an outer barrel 10 and an inner barrel 10a, with the inner barrel 10a forwardly extending to form front end 10a of barrel 10, 10a. At a rear end of a space 10b defined between the outer barrel 10 and the inner barrel 10a of the double concentric construction, two stopper holes 10c communicating with a central bore of outer barrel 10 are formed at 180 degrees angular positions (see Fig. 4) to each other, in which flexible pieces 24a are to be inserted as described hereinafter. The aim of the double concentric construction is to form outer barrel 10 with stopper holes 10c by molding, but stopper holes 10c may also be formed on an inner wall of outer barrel 10 by boring after molding outer barrel 10. Guide grooves 10e are axially formed on the inner wall of outer barrel 10 corresponding to stopper holes 10c (see Fig. 3). Lead pipe 12 is axially and movably disposed inside outer barrel 10. Lead pipe 12 has lead case 14 and chuck 16 connected to the front end of lead case 14. A knocking portion 18 is detachably mounted on a rear end of lead pipe 12 and eraser 20 is detachably mounted on a rear end of knocking portion 18. Chuck ring 22 is mounted outside of chuck 16 and sleeve 24 is provided to contact the rear end of chuck ring 22. Spring 26 is interposed between sleeve 24 and lead pipe 12 so that lend ripe 12 is biased rearwardly relative to outer barrel 10. Chuck 16, chuck ring 22 and spring 26 comprise a conventional lead advancing mechanism. Front end ripe 28 is disposed at a front end of inner barrel 10a to hold lead L protruding from the front end of barrel 10, 10a. As shown in Figs. 2, 5 and 6, sleeve 24 has two flexible pieces 24a in a rear part at 180 degrees angular positions from each other. Each flexible piece 24a spreads toward an outer radial direction, on the outer surface of which, are formed inclined portion 24b and step 24c adjacent to the outer top end of inclined part 24b. Step 24c has projecting surface 24d parallel to a wall surface of stopper hole 10c after assembly, which wall surface is the rear surface seen from the end of the sleeve contacting chuck ring 22. As shown in Fig. 2, a part of each flexible piece 24a is inserted in stopper hole 10c with inclined portion 24b of each flexible pieces 24a contacting rear end 10d of stopper hole 10c so that spreading of the outer surface of each flexible piece 24a is restricted. When assembling sleeve 24 into outer barrel 10, sleeve 24 is inserted into outer barrel 10 from the rear. At this time, flexible pieces 24a move along inner wall of outer barrel 10 and are bent inwardly in spite of the spreading force toward an outer radial direction because flexible pieces 24a are flexible and can be easily bent inward in a radial direction. It is thus possible to assemble sleeve 24 into outer barrel 10 without any resistance force and the need for jigs. On the other hand, in the prior mechanical pencil having engaging projections, they can not bend inwardly in a radial direction and are hard to press. Guide grooves 10e axially formed on the inner wall of outer barrel 10 surely guide flexible pieces 24a into stopper hole 10c during assembly. Sleeve 24 stops when it abuts the inner surface of outer barrel 10. At this time, flexible pieces 24a spread outwardly until inclined portion 24b of each of flexible pieces 24 contacts rear end 10d of stopper hole 10c and engages rear end 10d. Even if there is a dimension error in either sleeve 24 or stopper hole 10c of outer barrel 10, the dimension error is absorbed by the adjustable spreading range of flexible pieces 24a. When writing with the mechanical pencil according to this embodiment, in the case that excessive force is applied to lead L, lead pipe 12 having chuck 16 holding the lead L, chuck ring 22 and sleeve 24 are pushed rearwardly and flexible pieces 24a bend inwardly in a radial direction. Inclined portion 24b of each flexible piece 24a is displaced relative to rear end 10d of stopper hole 10c, as a result sleeve 24 displaces rearward in an axial direction, accompanied by lead L retracting into outer barrel 10. Such a cushioning action prevents damage to lead L. When sleeve 24 is displaced rearward in an axial direction to a certain extent, projecting surface 24d of step 24c abuts rear end 10d of stopper hole 10c so that axial displacement of sleeve 24 stops and sleeve 24 can not move any further. Accordingly, flexible pieces 24a are prevented from completely escaping from stopper hole 10c and surely resume their original positions when the force is released. Assuming the distance between the front end of sleeve 24 and rear end 10d of stopper hole 10c is set as "a", and the distance between the front end of sleeve 24 and projecting surface 24d is set as "a' ", the equation a'< a must be satisfied and the difference a-a' becomes the cushioning distance. Fig. 7 is a longitudinal cross sectional view of an another embodiment according to this invention. In this embodiment, outer barrel 30 has through holes 30a as stopper holes instead of providing the double concentric construction of the first embodiment. Otherwise the construction and operation are the same as the first embodiment. Fig. 8 is an another enlarged view of a front portion of this invention. Packing member 32 is inserted into space 10b defined between the outer portion and the inner portion of the double concentric construction of outer barrel 10. This packing member 32 covers space 10b. When the packing member 32 is differently colored from outer barrel 10, the appearance of the mechanical pencil becomes different and value of the design can be improved. As explained above, the radial displacement of the flexible piece of the sleeve is transduced into an axial displacement by the inclined portion for a cushioning action against excessive writing pressure. When inserting the sleeve into the outer barrel during assembly, the flexible pieces easily bend inwardly so that it is possible to insert the sleeve without any resistance force and the need for special jigs. As explained above, in this invention, a plurality of flexible pieces that spread toward an outer radial direction are provided in the sleeve, a part of the flexible pieces are inserted into a stopper hole provided on the inner wall of the outer barrel, and an inclined portion contacts the rear end of the stopper hole formed on the outer surface of the flexible pieces. When excessive force is applied to the lead, the sleeve allows the lead to retract into outer barrel, the cushioning action preventing damage to the lead. Having described the preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope of the invention as defined in the appended claims.

Claims: A mechanical pencil comprising a barrel (10,10a); a lead pipe (12) disposed inside the barrel (10,10a); a chuck (16) mounted on an end of said lead pipe (12); a chuck ring (22) mounted on an outside of said chuck (16); a sleeve (24) contacting the rear end of said chuck ring (22) slidably disposed relative to said barrel (10,10a); and a spring (26) interposed between said lead pipe (12) and said sleeve (24), said sleeve having a plurality of flexible pieces (24a) that spread outer in a radial direction, each of said flexible pieces (24a) being inserted into a stopper hole formed on an inner wall of said barrel for contacting a wall surface of said stopper hole (10c) which wall surface is a rear wall surface seen from the end of the sleeve (24) contacting the chuck ring, characterized in that the portion (24b) of each of the flexible pieces (24a) contacting the rear wall surface (10d) of the stopper hole (10c) is inclined in relation to the longitudinal axis of the sleeve (24) and a surface (24d) adjacent to the outer end of the inclined portion (24b) is projecting parallel to the rear wall surface (10d) of the stopper hole (10c). The mechanical pencil according to claim 1, including guide grooves (10e) axially formed on an inner wall of said outer barrel, said grooves guiding said flexible pieces of said sleeve (24) into said stopper hole (10c) of the barrel (10,10a) during assembly. A mechanical pencil according to claim 1 in which the stopper holes are through holes (30a) in the barrel (10). A mechanical pencil according to claim 1 in which each of the stopper holes (10c) is defined as space between a front surface (10d) of stop means of an outer barrel (10) and a rear end of an inner barrel (10a) of a barrel (10,10a) of double concentric construction in which the inner barrel extends forwardly from the outer barrel to form front end of the outer barrel.

Inventors: KAGEYAMA SHUHEI, KAGEYAMA, SHUHEI, Kageyama, Shuhei, Kawagoe factory 138
Applicants: KOTOBUKI & CO LTD, KOTOBUKI & CO. LTD.
Application year: 1996
Main classification: B43K21
IPC codes: B43K21