Mechanical pencil with lead breakage prevention mechanism

Abstract

To provide a mechanical pencil with a lead breakage prevention function in which a slider with a lead protection pipe is attached so that it can move back and forth, and the slider retracts according to writing, the mechanical pencil preventing the lead protection pipe from bending due to writing pressure, and allowing the slider to move smoothly and the lead to be extended with less knocking.SOLUTION: An outer pipe holder 18 having an outer pipe 19 is provided on a taper member 16, and a slider 20 having a lead protection pipe 17 is housed in the outer pipe holder so as to be movable back and forth. The lead protection pipe protrudes outward from the tip of the outer pipe. Inside the slider, there is provided a weak lead holding portion 25 with an extremely light load that does not interfere with writing while dragging the lead protection pipe. The outer surface of the slider is provided with a non-resistance sliding contact surface that does not generate resistance. The slider moves together with the lead, does not rattle, and can prevent the lead from breaking.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a mechanical pencil with a lead breakage prevention mechanism in which the outer periphery of the tip of the lead is covered with a lead protection pipe provided at the tip of the slider to prevent the lead from breaking, and the lead protection pipe and the slider are retracted as writing is performed. [Background technology]

[0002] A widely known mechanical pencil has a tapered member at the tip of the main body, a retractable lead protection pipe inserted through a tip opening in the tapered member, the rear end of the lead protection pipe fixed to a slider that moves back and forth within the tapered member, the tip of the lead inserted through the lead protection pipe to prevent lead breakage, and the lead protection pipe and slider retract as the lead wears (see, for example, Patent Document 1). Knock-type mechanical pencils typically use a collet chuck-type chuck as the lead advancement mechanism, a clamping ring (clutch) that clamps the chuck, and a chuck spring that biases the chuck backward. The chuck closes by slipping into the clamping ring, gripping the lead. When the chuck is knocked, it advances while still holding the lead, and midway through, the clamping ring releases the chuck's grip, allowing the lead to advance. This operation advances the lead to its advanced position, where it protrudes from the lead protection pipe.

[0003] When the knocking operation is stopped, the chuck retracts. If the lead is not held in the forward position, it will retract along with the chuck, requiring repeated knocking to advance the lead. Therefore, a lead holder is usually provided on the slider to temporarily hold the lead so that it remains in the forward position. Furthermore, as the chuck retracts, it gradually closes by slipping into the clamping ring, slightly retracting the lead. If the slider retracts due to this retraction force, the lead will not be able to be advanced. Patent Document 1 shows an example of a conventional slider. The inner surface of the slider is formed with a lead holder made of synthetic resin that slides against the outer surface of the lead with frictional resistance. The outer surface is provided with a resistance elastic piece made of synthetic resin that slides against the inner surface of a tapered member with frictional resistance. The frictional resistance of the resistance elastic piece that slides against the inner surface of the tapered member is set to be greater than the frictional resistance of the lead gripping piece that slides against the outer surface of the lead, preventing the slider from retracting when the lead is retracted.

[0004] When writing, the lead protection pipe hits the paper and retracts. The resistance force at this time is the sum of the resistance force of the lead holding member that temporarily holds the lead and the resistance force of the elastic resistance piece that holds the slider in place. Because this large resistance force is always acting on the lead protection pipe, the resistance force at the writing tip increases, increasing writing resistance and hindering smooth writing.

[0005] While the lead protection pipe prevents lead breakage as described above, mechanical pencils are also known that are designed to further prevent lead breakage when excessive load is applied to the writing tip of the lead. Figure 17 shows one such example. In Figure 17, a tapered member 102 connected to the tip of a main body 101 has a slider 104 inserted therein, which has a lead protection pipe 103 similar in configuration to that described in Patent Document 1. The slider's inner surface is provided with a lead holder 105 that temporarily holds the lead, and its outer surface is provided with a resistance elastic piece 106 that exerts a resistance greater than that of the lead holder. A retaining tube 109, which holds the lead-advancing mechanism including a chuck 107, a clamping ring 108, and a chuck spring 113, is biased forward by a cushion spring 110 that exerts an elastic force greater than the writing pressure. In the writing state, as shown in FIG. 17A, the slider 104 and lead protection pipe 103 advance and come into contact with the inner stepped portion 111 of the tapered member 102, causing the tip of the lead protection pipe 103 to protrude from the tapered member 102, allowing writing. As shown in FIG. 17B, when an excessive load acts on the tip in the direction of the arrow, the lead protection pipe 103 and slider 104 retract, and the slider 104 stops in the retracted position. At this time, the chuck 107, still holding the lead 112, is pushed by the lead 112 and retracts together with the retaining tube 109 against the cushion spring 110. The retraction distance at this time is L1. When the excessive load is removed, the retaining tube 109, which holds the chuck 107 and other components, advances due to the cushion spring 110. At this time, the lead 112 held by the chuck 107 also advances, as shown in FIG. 17C. When advancing, the chuck 107 does not push the slider 104, so the slider remains stopped in the retracted position due to the resistance force of the resisting elastic piece 106. In this state, the lead protection pipe 103 does not protrude from the tip of the tapered member 102, so only the lead 112 advances and protrudes from the tip of the tapered member 102. The protruding distance at this time is a distance L2, which corresponds to the above-mentioned L1. Therefore, the tip portion is not protected by the lead protection pipe 103 and is exposed outside the tapered member, making the lead more likely to break.

[0006] To ensure visibility during writing, the lead protection pipe is typically used with the pen protruding approximately 3 to 4 mm from the tapered member. Therefore, depending on the writing angle, the writing pressure from the tip of the lead acts laterally on the lead protection pipe, applying a force to the lead protection pipe in a direction that bends the lead protection pipe, with the part of the lead protection pipe that contacts the tip of the tapered member as a fulcrum. This force acts as a resistance between the outer surface of the lead protection pipe and the tip of the tapered member, and also acts on the slider through the lead protection pipe, pressing the slider sideways and hindering its linear movement. Such a lateral force prevents the slider from moving linearly, which can be one of the causes of lead breakage. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Utility Model Application Publication No. 63-21082 (claims and drawings for utility model registration) Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved by this invention is to provide a mechanical pencil with a lead breakage prevention mechanism that has a slider with a lead protection pipe at the tip that protects the lead, and that moves the slider forward when the lead is advanced and moves back as writing progresses, allowing the lead to be advanced with a small amount of knocking, does not cause large drag resistance when writing, allows the slider to move back smoothly, and allows the lead protection pipe and slider to move stably without bending or tilting. [Means for solving the problem]

[0009] According to the present invention, a mechanical pencil with a lead breakage prevention mechanism is provided, which comprises a main body housing a lead-advancing mechanism including a chuck and a clamping ring, a tapered member attached to the tip of the main body, a slider mounted within the tapered member so as to be movable back and forth and having a lead protection pipe that protrudes from the tip of the tapered member when the slider moves forward, and an outer pipe attached to the tip of the tapered member so as to surround the tip of the lead protection pipe, the outer surface of the slider forming a non-resistance sliding surface that slides against the inner surface of the tapered member without generating resistance, and the inner surface of the slider having a weak lead holding part that has a weak holding force that prevents the lead advanced by the chuck from falling under its own weight.In this invention, the direction in which the lead is advanced from the tapered member will be described as "front" or "front end," and the direction in which the lead is stored within the main body will be described as "rear."

[0010] The lead holding force of the weak lead holder is set to a load of approximately a few grams, which is small enough that it does not get in the way when writing while dragging the lead protection pipe. The outer pipe is fixed to a tapered member or attached to an outer pipe holder inserted into the tapered member. The outer pipe holder is fixed within the tapered member or is provided so that it can move back and forth. When provided so that it can move back and forth, the rear end of the outer pipe holder faces a retaining tube that holds the chuck and tightening ring, and this retaining tube is urged forward by a cushion spring with a spring pressure greater than the writing pressure. [Effects of the Invention]

[0011] The present invention is configured as described above. A slider with a lead protection pipe that protrudes from the tip of the tapered member when advanced is provided within a tapered member at the tip of the main body, and is movable back and forth. An outer pipe is provided at the tip of the tapered member to surround the tip of the lead protection pipe. The outer surface of the slider is formed with a non-resistance sliding surface that makes sliding contact with the inner surface of the tapered member, and the inner surface of the slider is provided with a weak lead holder that has a weak holding force that is weak enough to prevent the advanced lead from falling under its own weight. With this configuration, when the chuck of the lead advancement mechanism is knocked, the outer surface of the lead advanced by the chuck comes into contact with the weak lead holder within the slider. Because the outer surface of the slider is provided with a non-resistance sliding surface that makes contact with the inner surface of the tapered member without creating resistance, the slider is advanced by the lead entering the weak lead holder, and with a single knock, the lead is advanced to the advanced position, allowing writing to be performed with the lead protected by the lead protection pipe. Furthermore, taking into account the retraction distance of the lead when the knock is retracted, the lead advance distance by the knock operation is the lead advance amount required for normal writing plus the retraction distance. When the lead protection pipe comes into contact with the paper during writing, a non-resistance sliding surface is formed on the outer surface of the slider and the lead retention force of the weak lead retainer is extremely weak, so the lead protection pipe and slider retract easily, reducing drag resistance when writing and making writing easier.

[0012] In addition, the lead protection pipe attached to the front of the slider is covered on its outer periphery by an outer pipe attached to the tapered member, and protrudes outward through the outer pipe, providing protection. Therefore, even if a force that would bend the lead protection pipe acts during writing, the outer pipe protects it, eliminating the risk of the lead protection pipe bending. This prevents the slider from tilting, preventing the lead protection pipe from bending when dropped. As described above, the slider's linear movement is ensured, further preventing lead breakage. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view showing an embodiment of the present invention. [Figure 2] 10 is a partial cross-sectional view and a partial enlarged explanatory view of an embodiment in which an outer pipe holder is not used. FIG. [Figure 3] 1A to 1C show an embodiment of a slider, in which A is a plan view, B is a half cross-sectional view, and C is a right side view. [Figure 4] 10A to 10C show another embodiment of the slider, in which A is a plan view, B is a half cross-sectional view, and C is a right side view. [Figure 5] Shows the outer pipe holder, A is a plan view, B is a half cross-sectional view, C is a partial longitudinal cross-sectional view, and D is a right side view. [Figure 6] 10A and 10B show another embodiment of the outer pipe holder, in which FIG. 10A is a plan view, and FIG. 10B is a half cross-sectional view and an enlarged explanatory view of a portion thereof. [Figure 7] 6 is an explanatory diagram of a state in which the slider shown in FIG. 3 and the outer pipe holder shown in FIG. 5 are assembled into a tapered member. [Figure 8] FIG. 8 is an explanatory diagram of a state in which the outer pipe holder and the like shown in FIG. 7 are retracted. [Figure 9] 7 is an explanatory diagram of a state in which the slider shown in FIG. 4 and the outer pipe holder shown in FIG. 6 are assembled into a tapered member. [Figure 10] FIG. 10 is an explanatory diagram of a state in which the outer pipe holder and the like shown in FIG. 9 are retracted. [Figure 11] The diagrams show the lead advance mechanism. A is the state when the lead protection pipe is stored, B is the state when it is knocked, C is the state when the chuck starts to return, and D is the state when writing. [Figure 12] Shows the writing state, A is the start of writing, B is a side view when the lead protection pipe is retracted. [Figure 13] The cushion mechanism is shown in A (writing state) and B (when the cushion spring is compressed). [Figure 14] 1A and 1B are side views showing the operation of the cushion mechanism, with A showing the state in which the cushion spring has contracted and the lead protection pipe has retracted, and B showing the state in which the cushion spring has expanded and the lead protection pipe has returned to its writing position. [Figure 15]Shows the protection mechanism for the outer pipe. A is a side view of the core protection pipe stored inside the outer pipe, B is a side view of the pipe when dropped, C is an explanatory diagram of the core protection pipe stored inside, and D is an explanatory diagram of the pipe when dropped. [Figure 16] FIG. 10 is a cross-sectional view of a mechanical pencil that does not have a cushioning mechanism. [Figure 17] The figures show a conventional mechanical pencil, with A showing the pencil in writing mode, B showing the lead retracted when excessive load is applied to the tip of the lead protection pipe, and C showing the state after the excessive load has been removed. DETAILED DESCRIPTION OF THE INVENTION

[0014] FIG. 1 shows one embodiment of the present invention. The cylindrical main body 1 has a clip 3 on the outside of a larger-diameter rear section 2. The front section 4, with a smaller inner diameter than the rear section 2, houses a chuck 5 and a clamping ring 6, which constitute a lead-advancing mechanism, as is well known. A lead tank 8 with an eraser 7 attached to its rear end is inserted into the rear section 2 of the main body, and the chuck 5 is fixed to the front end of the lead tank 8. The chuck 5 grips a lead 9 when retracted into the clamping ring 6. The chuck 5 and clamping ring 6 are inserted into a retaining tube 10, which is inserted into the front section 4 of the main body and can move back and forth. A chuck spring 12 is provided between the inner step 11 of the retaining tube 10 and the front end of the lead tank 8 to bias the chuck 5 rearward. A cushion spring 14, with a spring pressure greater than normal writing pressure, is provided between the rear end of the retaining tube 10 and a shoulder 13 inside the main body. A grip 15 is provided around the outer periphery of the front section 4 of the main body. A tapered member 16 is screwed onto the front end of the main body 1, and a lead protection pipe 17 made of a stainless steel pipe or the like protrudes from the tip of the tapered member 16. With the above-described configuration, when the lead tank 8 is knocked, the chuck 5 moves forward, as is well known, and as it moves forward, the clamping ring 6 releases the chuck from its clamping, sending the lead 9 forward and protruding from the lead protection pipe 17, allowing writing to be performed.

[0015] An exterior pipe holder 18 is provided within the tapered member 16, and an exterior pipe 19, with an inner diameter that covers the outer periphery of the lead protection pipe 17, is fixed to the tip of the exterior pipe holder 18. The exterior pipe 19 is made of a thin metal pipe material, such as a stainless steel pipe, with a strength sufficient to resist the bending force acting on the lead protection pipe 17 during writing. The exterior pipe 19 preferably has an inner diameter that allows the outer surface of the lead protection pipe 17 to slide against it, but has an outer diameter that is small enough not to interfere with visibility. The length of the exterior pipe 19 is such that, when the lead protection pipe 17 is extended during writing, the tip of the exterior pipe 19 is positioned behind the tip of the lead protection pipe 17. The exterior pipe holder 18 may be fixed within the tapered member 16, but is preferably movable back and forth so that it can retract when an excessive load is applied to the exterior pipe 19. As shown in FIG. 2, the exterior pipe 19 may be directly fixed to the tip of the tapered member 16 without using the exterior pipe holder 18. A slider 20 is housed within the exterior pipe holder 18 so as to be movable back and forth, and the lead protection pipe 17, which is inserted into the exterior pipe 19 and protects the lead 9, is fixed to the tip of the slider 20. In the embodiment shown in Figure 2, the slider 20 is housed within the tapered member 16 so as to be movable back and forth, and a protruding portion 21 for preventing the slider 20 from slipping out rearward is provided on the rear inner surface of the tapered member 16.

[0016] FIG. 3 shows one embodiment of a slider 20. The slider 20 has a tip-side tube portion 22 and a rear-side tube portion 23 with a larger diameter than the tip-side tube portion 22. The lead protection pipe 17 is fixed to an attachment hole 24 provided in the tip-side tube portion 22. A cylindrical weak lead holder 25 is provided inside the rear-side tube portion 23 to temporarily hold the lead 9. Like conventional mechanical pencils, the weak lead holder 25 has a longitudinal slit to elastically hold the lead 9. However, the weak lead holder can also be made of an elastic material such as rubber (not shown). The lead retention force provided by the weak lead holder 25 of the present invention is set to be much weaker than that of lead holders of conventional mechanical pencils. Specifically, the lead retention force is set to be extremely weak, for example, a few grams, so that the lead 9 does not fall under its own weight when the tip of the main body 1 is pointed downward. The weight is set to be such that it does not get in the way when dragging the lead protection pipe 17 while writing. Furthermore, in conventional mechanical pencils, a resisting elastic piece is provided on the slider that inscribes the tapered member with a large elastic resistance to prevent the slider from being pulled backward when the chuck retracts, but the rear side tube portion of the present invention does not have such a resisting elastic piece. The rear side tube portion 23 of the present invention inscribes the inner surface of the outer pipe holder 18, but is formed with a non-resisting sliding surface 26 so as to prevent contact resistance between the rear side tube portion 23 and the outer pipe holder 18. In the embodiment shown in Figure 3, a retaining claw 27 is provided on the outer surface of the rear side tube portion 23 to prevent it from falling off the outer pipe holder 18, but the rear end surface may also be used as a retaining abutment 28, as in the embodiment shown in Figure 4.

[0017] Referring to Figure 5, the exterior pipe holder 18 is formed as a cylindrical body sized to be inserted into the tapered member 16. At its tip, a tapered mounting portion 29 is formed that protrudes from the tip opening of the tapered member 16, and an mounting hole 30 for the exterior pipe 19 is formed inside the tapered member 16. A shoulder 31 is formed on the outer surface of the exterior pipe holder 18, which abuts against the inner surface of the tapered member 16 to prevent slippage. A small-diameter portion is formed behind the shoulder 31, and a stopper 32 is provided at its rear end to abut against the tip of the retaining tube 10. The small-diameter portion is provided with a retaining groove 33 into which the retaining claw 27 (see Figure 3) provided on the slider 20 fits. A stopper 34 is formed on the inner surface of the exterior pipe holder 18, against which the tip of the front-side tube portion 22 abuts when the slider 20 advances. A rear-side sliding surface 35, against which the non-resistance sliding surface 26 of the slider 20 slides, is formed behind the stopper 34. In addition, at the rear end, an inner step 36 is provided against which the clamping ring 6 abuts so that when the chuck 5 and the clamping ring 6 are advanced by a knocking operation, the clamping of the chuck 5 by the clamping ring 6 is released midway through the advancement.

[0018] Figure 6 shows another embodiment of the outer pipe holder 18. In this embodiment, instead of the retaining groove 33 as shown in Figure 5, a retaining protrusion 37 is provided for contact with the retaining abutment portion 28 of the slider 20 shown in Figure 4, and a stopper portion 32 is provided at the rear end for contact with the front end of the holding tube 10.

[0019] The lead protection pipe 17 is fixed to the front side tube portion 22 of the slider 20 shown in Figure 3, and the exterior pipe 19 is fixed to the exterior pipe holder 18 shown in Figure 5. Then, the lead protection pipe 17 is inserted into the exterior pipe 19, and with the retaining claws 27 engaged in the retaining grooves 33, the slider 20 and the exterior pipe holder 18 are combined and assembled into the tapered member 16 (see Figure 7). The exterior pipe holder 18 is inserted until it hits the inner surface of the tapered member 16 and stops. At this time, the lead protection pipe 17 is formed to a length that allows its tip to protrude slightly forward beyond the tip of the exterior pipe 19. In this state, if an excessive load is applied to the tip of the lead protection pipe 17, the entire lead protection pipe 17 will enter the exterior pipe 19, and as the rear end of the slider 20 hits the stopper portion 32, the slider 20 will retract within the exterior pipe holder 18, and the exterior pipe holder 18 will also retract within the tapered member 16, as shown in Figure 8.

[0020] The wick protection pipe 17 is fixed to the slider 20 shown in Figure 4, and the exterior pipe 19 is fixed to the exterior pipe holder 18 shown in Figure 6. Then, the wick protection pipe 17 is inserted into the exterior pipe 19 so that its tip protrudes beyond the tip of the exterior pipe 19, and the slider 20 is assembled into the exterior pipe holder 18 so that it is positioned in front of the raised portion 37 provided in the exterior pipe holder 18, and this is set in the tapered member 16 (see Figure 9). In this state, if an excessive load is applied to the tip of the wick protection pipe 17, as shown in Figure 10, the entire wick protection pipe 17 will enter the exterior pipe 19, and the slider 20 will move back within the exterior pipe holder 18 until its rear end abuts the raised portion 37, and the exterior pipe holder 18 will also move back within the tapered member 16.

[0021] The lead advancement mechanism of the present invention is shown in Figure 11. Figure 11A shows the state in which the lead protection pipe 17 is sunk into the outer pipe 19 as writing begins. In this state, as shown in Figures 8 and 10, the slider 20 is retracted to a position where it abuts against the stopper portion 32 and the raised portion 37. In this state, a gap of distance L3 is left between the tip of the clamping ring 6 and the inner step 36, and this distance L3 is the lead advance distance. That is, when the lead tank 8 is knocked as shown in Figure 11B, the chuck 5 and clamping ring 6 advance, and halfway through, the clamping ring 6 abuts against the inner step 36, stopping its advance and releasing the chuck 5. In this way, the lead 9 can be advanced until the clamping ring 6 abuts against the inner step 36, and this distance is the lead advance distance. The chuck 5 moves forward further, pushing the slider 20 forward until it hits the stopper portion 34, causing the tip of the core protection pipe 17 to protrude from the tip of the outer pipe 19. At this time, the distance from the tip of the outer pipe 19 to the tip of the core protection pipe 17 is the maximum pipe protrusion distance L4.

[0022] When the click is stopped, the chuck 5 retracts due to the chuck spring 12 (see Figure 11C). As it retracts, the chuck 5 gradually enters the clamping ring 6, closing as it retracts, retracting the lead 9 backward. At this time, as shown in Figure 11D, the weak lead retaining portion 25 of the slider 20 holds the lead 9 with extremely weak retention force, so the slider 20 also retracts, creating a gap equivalent to the lead retraction distance L5 between the tip of the slider 20 and the stop portion 34. Although this gap is small, the lead 9 is held by the chuck 5, allowing for writing without support. Because the slider 20 does not have a resisting elastic piece like a conventional mechanical pencil, when the chuck 5 retracts and retracts the lead 9 backward, the slider 20 is also retracted. Therefore, to ensure proper writing, the lead advance distance L3 must be determined taking into account the retraction distance L5. Specifically, if the lead protrusion required for writing is 0.8 mm and the retraction distance is 0.7 mm, the lead feed distance L3 is 1.5 mm, which is 0.8 mm plus 0.7 mm. In this way, even if the lead is retracted and retracted 0.7 mm, 1.5 mm - 0.7 mm = 0.8 mm, and 0.8 mm is secured as the lead feed distance L3, allowing for uninterrupted writing.

[0023] In this state, writing is possible, and the lead protection pipe 17, which protects the lead, protrudes a distance L6 and contacts the paper surface 38, as shown in FIG. 12A. As the lead wears, the lead protection pipe and slider retract, resulting in a protruding distance of L7 (see FIG. 12B). During retraction, the slider 20, which has a non-resistance sliding surface 26 on its outer periphery, moves without resistance between itself and the inner periphery of the outer pipe holder 18, so there is almost no significant drag resistance. As writing continues, the slider 20 retracts until its rear end contacts the stopper portion 32, as shown in FIG. 11A. Once this state is reached, knocking the lead tank 8 as described above allows the lead 9 to be advanced with a single knock, as shown in FIGS. 11B, 11C, and 11D. At this time, since the outer periphery of the slider 20 is formed into a non-resistance sliding surface 26, the slider 20 can be advanced together with the lead 9 when the lead is fed out, and there is no risk that only the lead 9 will jump out from the tip of the lead protection pipe 17.

[0024] In conventional mechanical pencils that do not have an outer pipe 19, the outer periphery of the lead protection pipe 17 is not covered by the outer pipe 19, so almost the entire length of the lead protection pipe 17 is exposed from the tip of the tapered member 16. In contrast, in the present invention, the outer periphery of the lead protection pipe 17 is covered by the outer pipe 19 attached to the tapered member 16, so the exposed length of the lead protection pipe 17 is the length that protrudes from the tip of the outer pipe 19. This exposed length of the lead protection pipe 17 is shorter than in conventional mechanical pencils. When writing, as shown in FIG. 12A , the pencil body is held at an angle, so an oblique load due to writing pressure acts on the tip of the lead protection pipe 17. This load acts as a bending force that bends the lead protection pipe 17. This bending force is calculated as (the load acting on the tip of the lead protection pipe) x (the length that the tip of the lead protection pipe protrudes). As described above, the tip of the lead protection pipe of the present invention protrudes from the tip of the outer pipe, so the protruding length can be made shorter than in the conventional case where the lead protection pipe is exposed directly from the tapered member without providing an outer pipe. This reduces the bending force acting on the lead protection pipe 17. This also reduces the frictional resistance acting when the lead protection pipe 17 and slider 20 retract, ensuring the linear movement of the slider 20 and adequately preventing lead breakage.

[0025] Furthermore, because the lead protection pipe 17 moves while being guided by the outer pipe 19, the guide length is longer than in conventional mechanical pencils that do not have an outer pipe 19. This reduces the wobble of the lead protection pipe 17 and slider 20, allowing them to retract in a stable state, further preventing lead breakage. If the mechanical pencil is dropped, the lead protection pipe 17 retracts into the outer pipe 19, protecting the tip of the lead protection pipe 17.

[0026] In the embodiment shown in FIG. 1, a cushion spring is provided behind the retaining tube 10, providing a cushioning effect when excessive writing pressure is applied. Referring to FIG. 13, FIG. 13A shows the lead 9 being held by the chuck 5 and the clamping ring 6, as shown in FIG. 1. If an excessive load is applied to the tip of the lead 9 in this state, as shown in FIGS. 13B and 14A, the lead protection pipe 17 and the slider 20 move back via the lead 9 (see FIG. 14A). At the same time, the retaining tube 10, which houses the chuck 5 and the clamping ring 6, also moves back, compressing the cushion spring 14. At this time, the cushion spring 14 contracts to a length, or distance L8, creating a gap L9 between the outer pipe holder 18 and the retaining tube 10. When the excessive load is removed, the retaining tube 10 moves forward by the gap L9 due to the action of the cushion spring 14, and the slider 20 and the lead protection pipe 17 also move forward by the same distance, returning to the writing position (see FIGS. 13A and 14B). At this time, since no resisting elastic piece is provided on the outer periphery of the slider 20, the slider 20 advances along with the lead 9. Therefore, unlike the conventional mechanical pencil shown in Figure 17C, there is no risk of the slider getting stuck partway inside the tapered member and only the tip of the lead protruding, and the lead can be reliably protected all the way to the tip by the lead protection pipe.

[0027] Figure 15 shows the protection mechanism for the exterior pipe 19. In this embodiment, the exterior pipe holder 18 is inserted into the tapered member 16 so that it can move back and forth. First, as shown in Figures 15A and 15C, the core protection pipe 17 is stored inside the exterior pipe 19. If the main body is dropped to the floor 39 in this state, as shown in Figures 15B and 15D, the exterior pipe holder 18, which secures the exterior pipe 19, retreats a distance L10 within the tapered member 16 and hits the retaining tube 10, forcing the retaining tube 10 to retreat against the cushion spring 14. The cushion spring 14 contracts to a length L11. The cushioning effect of the cushion spring 14 prevents damage to the exterior pipe 19, and when the main body is lifted from the floor, the cushion spring 14 moves the retaining tube 10 and exterior pipe holder 18 forward, returning them to their original positions.

[0028] Although the above embodiment includes a cushioning mechanism, this can be omitted. Figure 16 shows such an embodiment, which has essentially the same configuration as the embodiment shown in Figure 1, and therefore common parts will be described using the same reference numerals. The main body 1 is cylindrical, with a rear portion 2 having a clip 3 on the outside, and a front portion 4, which has a smaller inner diameter than the rear portion 2, and a grip 15 on the outer periphery. A chuck 5 and a clamping ring 6 are housed at the tip of the front portion 4 so that they can move back and forth, and the rear portion of the chuck 5 is connected to a lead tank 8 housed in the main body 1. A chuck spring 12 is provided between the tip of the lead tank 8 and an inner step 11 provided within the front portion of the main body, biasing the chuck 5 rearward. A known eraser feeding mechanism 40 is provided at the rear end of the lead tank 8, and an eraser 7 is attached to it. The eraser may be attached to the rear end of the lead tank, as shown in Figure 1. A tapered member 16 is screwed onto the front end of the main body 1, and an exterior pipe holder 18 having an exterior pipe 19 is inserted and fixed into this tapered member 16. A slider 20 is inserted into the exterior pipe holder 18 so as to be movable back and forth, and a lead protection pipe 17 is fixed to the front end of the slider 20. The lead protection pipe 17 is inserted into the exterior pipe 19 so as to be movable back and forth, and protrudes from its front end.

[0029] A cylindrical weak lead holder 25 is provided inside the slider 20 to temporarily hold the lead 9. Like conventional mechanical pencils, the weak lead holder 25 has a longitudinal slit for elastically temporarily holding the lead. However, the weak lead holder can also be made of an elastic material such as rubber (not shown). The lead retention force provided by the weak lead holder 25 is set to be much weaker than that of conventional mechanical pencils. Specifically, the lead retention force is set to be extremely weak, for example, a few grams, so that the lead does not fall out under its own weight when the tip of the main body is pointed downward. It is also set to a load that does not interfere with writing while dragging the lead protection pipe 17. The outer surface of the slider 20 is formed with a non-resistance sliding surface 26, which slides against the inner surface of the outer pipe holder 18 with almost no resistance. A raised portion 37 is provided on the inner surface of the outer pipe holder 18 to prevent the slider 20 from slipping out.

[0030] With the above configuration, when the lead tank 8 is knocked, the chuck 5 moves forward, advancing the lead 9. When the knock is stopped and the chuck 5 moves back, the chuck 5 enters the clamping ring 6, retracting the lead 9. Therefore, the distance the lead is advanced by the knock operation is determined taking into account the retraction distance. In other words, the lead advance distance is the sum of the lead retraction distance and the amount of lead extension required for writing. In this way, even if the lead 9 is retracted backward when the chuck is retracted, the length required for writing can be secured, allowing for smooth writing.

[0031] With the above-described configuration, the mechanical pencil shown in the embodiment of Figure 16 can advance the slider 20 and lead protection pipe 17 with a single knock operation, advancing the lead 9. As writing progresses, the slider 20 and lead protection pipe 17 retract without resistance, so dragging the tip while writing feels natural and does not interfere with writing. Furthermore, because the outer periphery of the lead protection pipe 17 is covered by the outer pipe 19, it is able to withstand the bending force acting on the tip during writing, making it less likely to bend and preventing lead breakage. [Explanation of symbols]

[0032] 1 Main unit 5. Chuck 6 Clamping ring 10 Holding cylinder 14 Cushion spring 16 Tapered member 17 Core protection pipe 18 Outer pipe holder 19 Outer pipe 20 Slider 25 Weak core holding part 26 Non-resistance sliding surface

Claims

1. a main body accommodating a core feeding mechanism including a chuck and a clamping ring; a tapered member provided at the tip of the main body; a slider provided within the tapered member forward of the positions where the chuck and the clamping ring are disposed, capable of moving back and forth, and having a core protection pipe that protrudes from the tip of the tapered member when the slider moves forward; an outer pipe provided at the tip of the tapered member, which is the tip of the tapered member, to surround the core protection pipe; The slider has, on its inner surface, a lead holding portion that holds the lead sent out by the chuck, and on its outer surface, a slider outer sliding surface that slides against the inner surface of the tapered member, which is the inner surface of the tapered member, When the chuck is knocked, the lead feeding mechanism moves the chuck, which is fastened by the fastening ring, forward, and as the chuck moves forward, the fastening ring releases the fastening of the chuck, sending the lead forward and exposing at least the tip of the lead from the tip of the lead protection pipe, which is the tip of the lead, so that the mechanical pencil is ready for writing; the outer pipe is provided at the tip of the tapered member with a length such that the position of the outer pipe tip, which is the tip of the outer pipe, in the writable state is located rearward of the position of the tip of the lead protection pipe in the writable state, The relationship between the lead holding force that holds the lead by the lead holding portion of the slider and the holding force that is exerted between the inner surface of the tapered member and the outer sliding surface of the slider is as follows: the holding force exerted between the inner surface of the tapered member and the outer sliding surface of the slider is smaller than the lead holding force with which the lead holding portion holds the lead, When the lead advances, the slider advances in accordance with the advancement of the lead, and when the lead retracts, the slider retracts in accordance with the retraction of the lead. Mechanical pencil with lead breakage prevention mechanism.

2. A main body that houses a core feeding mechanism including a chuck and a clamping ring; a tapered member provided at the tip of the main body; an outer pipe holder which is provided in the tapered member forward of the position where the chuck and the clamping ring are disposed and is movable back and forth, and has at its tip a tapered outer pipe attachment part which protrudes from the tip opening of the tapered member when it moves forward, and is provided at its rear end with a shoulder part rearward of the outer pipe attachment part which abuts against the inner surface of the tapered member when it moves forward to prevent it from coming off, and a rear stopper part at its rear end which abuts against the front end of a retaining cylinder into which the chuck and the clamping ring are inserted and which is inserted in the main body and is movable back and forth; an exterior pipe fixed to the exterior pipe attachment portion of the exterior pipe holder; a slider provided in the outer pipe holder so as to be movable forward and backward, the slider having a core protection pipe whose tip protrudes from the tip of the outer pipe when the slider is moved forward; The slider has, on its inner surface, a lead holding portion for holding the lead sent out by the chuck, and on its outer surface, a slider outer sliding surface that is in sliding contact with the inner surface of the outer pipe holder, which is the inner surface of the outer pipe holder, When the chuck is knocked, the lead feeding mechanism moves the chuck, which is fastened by the fastening ring, forward, and as the chuck moves forward, the fastening ring releases the fastening of the chuck, sending the lead forward and exposing at least the tip of the lead from the tip of the lead protection pipe, which is the tip of the lead, so that the mechanical pencil is ready for writing; the outer pipe is provided in the outer pipe holder at a length such that the position of the outer pipe tip, which is the tip of the outer pipe, in the writable state is located rearward of the position of the tip of the lead protection pipe in the writable state, The relationship between the lead holding force of the lead holding portion of the slider and the holding force exerted between the inner surface of the outer pipe holder and the outer sliding surface of the slider is as follows: The holding force exerted between the inner surface of the outer pipe holder and the outer sliding surface of the slider is smaller than the lead holding force by which the lead holding part holds the lead, When the lead advances, the slider advances in accordance with the advancement of the lead, and when the lead retracts, the slider retracts in accordance with the retraction of the lead. Mechanical pencil with lead breakage prevention mechanism.

3. A mechanical pencil with a lead breakage prevention mechanism as described in claim 1, wherein the outer pipe is fixed to the tapered member.

Images