Mechanical pencil

Abstract

To provide a mechanical pencil provided with a rotational drive mechanism for rotating a writing lead, in which a retreating amount of the writing lead is further reduced.SOLUTION: A mechanical pencil 1 includes: a barrel 5; a chuck unit 10 that allows a writing lead to advance and prevents it from retreating; and a rotational drive mechanism 30 that has a rotor 40, and rotates and drives the rotor 40 in one direction by receiving a retreat operation in an axial direction by writing pressure received by the writing lead held by the chuck unit 10 and an advance operation in the axial direction by release of the writing pressure. A retreating amount m due to the retreating operation is within a range of 0.05 to 0.3 mm.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a mechanical pencil. [Background technology]

[0002] There is known a mechanical pencil which is equipped with a rotating member including a slider equipped with a chuck that allows the writing lead to move forward and prevents it from moving backward, and a rotation drive mechanism which has a rotor and drives the rotor to rotate in one direction in response to the axial backward movement caused by the writing pressure applied to the writing lead held by the chuck and the axial forward movement caused by the release of the writing pressure, and in which the chuck rotates in response to the rotational drive force of the rotor, causing the writing lead to rotate (Patent Documents 1 and 2).

[0003] In mechanical pencils equipped with a rotary drive mechanism as described in Patent Document 1, the lead usually undergoes slight forward and backward movements in order to rotate the lead. The series of forward and backward movements of the lead are collectively referred to as "cushioning movements." The mechanical pencil described in Patent Document 1 focuses on the issue that such cushioning movements, particularly the retraction of the lead, can be bothersome when, for example, writing in shorthand, and allows the user to freely switch the rotary drive mechanism on and off. The cushioning movements by the rotary drive mechanism will be described with reference to Figs. 12 and 13.

[0004] Fig. 12 is a schematic diagram for explaining the rotational drive of rotor 240 of a conventional rotational drive mechanism, and Fig. 13 is a schematic diagram for explaining the rotational drive of rotor 240 subsequent to Fig. 12. The rotational drive mechanism has rotor 240 formed in a cylindrical shape, upper cam forming member 241 formed in a cylindrical shape, and lower cam forming member 242 formed in a cylindrical shape. In Figs. 12 and 13, a first cam surface 240a that is continuously sawtoothed along the circumferential direction is formed in an annular shape on the rear end surface, which is the upper surface of rotor 240, and a second cam surface 240b that is continuously sawtoothed along the circumferential direction like the rear end surface is formed in an annular shape on the front end surface, which is the lower surface of rotor 240.

[0005] A first fixed cam surface 241a having a continuous sawtooth shape along the circumferential direction is also formed on an annular end surface of the upper cam forming member 241 facing the first cam surface 240a of the rotor 240. A second fixed cam surface 242a having a continuous sawtooth shape along the circumferential direction is also formed on an annular end surface of the lower cam forming member 242 facing the second cam surface 240b of the rotor 240. The cam surfaces of the first cam surface 240a and the second cam surface 240b formed on the rotor 240, and the cam surfaces of the first fixed cam surface 241a formed on the upper cam forming member 241 and the second fixed cam surface 242a formed on the lower cam forming member 242 are formed so that their pitches in the circumferential direction are substantially the same.

[0006] The rotation drive mechanism converts the backward and forward motions (cushion motions) of the writing lead based on the writing action transmitted to the rotation drive mechanism into the rotational motion of the rotor 240. The rotational motion of the rotor 240 is transmitted to the chuck unit gripping the writing lead, and therefore the writing lead held by the chuck unit also rotates.

[0007] 12(A) shows the relationship between rotor 240, upper cam forming member 241, and lower cam forming member 242 when no writing pressure is applied to the writing lead. In this state, second cam surface 240b formed on rotor 240 abuts against second fixed cam surface 242a of lower cam forming member 242 by the biasing force of a spring (not shown). At this time, first cam surface 240a of rotor 240 and first fixed cam surface 241a of upper cam forming member 241 are set to be shifted by half a phase with respect to one tooth of the cam in the axial direction.

[0008] 12(B) shows the initial state when writing pressure is applied to the writing lead for writing with a mechanical pencil. In this state, the rotor 240 moves backward against the biasing force of the spring as the chuck unit moves backward. As a result, the rotor 240 moves toward the upper cam forming member 241 and comes into contact with the first fixed cam surface 241a.

[0009] 12(C) shows a state in which further writing pressure is applied to the writing core, causing the rotor 240 to slide back while abutting against the first fixed cam surface 241a of the upper cam forming member 241. In other words, the rotor 240 receives a rotational drive equivalent to a half phase of one tooth of the first cam surface 240a. In this state, the first cam surface 240a of the rotor 240 meshes with the first fixed cam surface 241a of the upper cam forming member 241.

[0010] 12 and 13, a circle drawn in the center of rotor 240 indicates the amount of rotational movement of rotor 240. In the state shown in Fig. 12(C), second cam surface 240b of rotor 240 and second fixed cam surface 242a of lower cam forming member 242 are set to have a relationship of being shifted by half a phase with respect to one tooth of the cam in the axial direction.

[0011] 13(D) shows the initial state when writing with the mechanical pencil is finished and the writing pressure on the writing lead is released. In this state, the rotor 240 advances due to the biasing force of the spring. As a result, the rotor 240 moves toward the lower cam forming member 242 and abuts against the second fixed cam surface 242a.

[0012] 13(E) shows a state in which the rotor 240 advances while sliding against the second fixed cam surface 242a of the lower cam forming member 242 due to the biasing force of the spring. That is, the rotor 240 is again subjected to a rotational drive equivalent to a half phase of one tooth of the second cam surface 240b. In this state, the second cam surface 240b of the rotor 240 meshes with the second fixed cam surface 242a of the lower cam forming member 242.

[0013] Therefore, as shown by the circle drawn in the center of the rotor 240, as the rotor 240 receives writing pressure and reciprocates in the axial direction, i.e., moves back and forth, the rotor 240 is rotationally driven corresponding to one tooth of the first cam surface 240a and the second cam surface 240b, and the writing lead held by it is similarly rotated via the chuck unit. Therefore, the rotor 240 undergoes a rotational motion corresponding to one tooth of the cam by one back and forth movement in the axial direction of the rotor 240 due to writing, and by repeating this, the writing lead is sequentially rotated. Therefore, it is possible to prevent uneven wear of the writing lead as writing proceeds, and it is possible to prevent a large change in the thickness and darkness of the drawn line. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Patent Publication No. 2022-073560 [Patent Document 2] International Publication No. 2007 / 142135 Summary of the Invention [Problem to be solved by the invention]

[0015] As described above, in Patent Document 1, the problem of the deterioration of the writing feeling due to the cushioning action being felt as an annoyance at times is focused on, and the problem is solved by making it possible to turn off the rotation drive mechanism as necessary so that the cushioning action itself is not performed. However, Patent Document 1 does not discover the problem of reconsidering the cushioning action itself. The forward movement of the writing lead is performed as the writing lead moves away from the writing surface during writing, so it is hardly noticed by the user. On the other hand, the retraction movement of the writing lead may cause the user to feel a visual or tactile discomfort because the main body of the mechanical pencil moves forward, in other words, the writing lead moves backward relatively, even though the writing lead is brought into contact with the writing surface to write.

[0016] In this regard, the inventors conducted a survey to compile negative and positive opinions about mechanical pencils equipped with a rotary drive mechanism that rotates the lead, and found that of the 21.4% of negative opinions, 44.8% of users cited lead retraction as the reason for their negative opinions. On the other hand, 78.6% of users positively evaluated these mechanical pencils, so the function of rotating the lead was highly evaluated. Therefore, the inventors came up with the idea of ​​reducing the amount of cushioning action, particularly the amount of lead retraction, to the limit, even though a cushioning action is necessary to rotate the lead using a rotary drive mechanism.

[0017] The amount of cushioning action or the amount of retraction of the writing lead will be described with reference to Fig. 12(A). The height of the cam tooth is distance h, and the distance traveled until the tip of the cam tooth on first cam surface 240a abuts against first fixed cam surface 241a due to the retraction of rotor 240 is distance d. The distance s in the axial direction between the rear end of first cam surface 240a of rotor 240, i.e., the tip of the crest of the cam tooth, and the valley of the cam tooth on first fixed cam surface 241a of upper cam forming member 241, corresponds to the amount of retraction of the writing lead during the cushioning action.

[0018] In FIG. 12(A), the second cam surface 240b of the rotor 240 is engaged with the second fixed cam surface 242a of the lower cam forming member 242. To release this engagement, at least the tip of the cam tooth of the second cam surface 240b must pass the tip of the cam tooth of the second fixed cam surface 242a. In other words, the rotor 240 and the writing lead must be retracted by the distance h of the cam teeth. If the distance d is smaller than the distance h, the rotation of the rotor 240 is hindered by the first fixed cam surface 241a or the second fixed cam surface 242a, and therefore the rotor 240 does not function as a rotation drive mechanism. Therefore, if the rotor 240 further retracts beyond the distance h of the cam teeth, the distance equivalent to the distance dh indicates that there is room for reducing the amount of retraction of the writing lead.

[0019] An object of the present invention is to provide a mechanical pencil equipped with a rotary drive mechanism that rotates a writing lead, which further reduces the amount of retraction of the writing lead. [Means for solving the problem]

[0020] According to one aspect of the present invention, there is provided a mechanical pencil comprising a barrel, a chuck unit that allows the writing lead to move forward and prevents it from moving backward, and a rotation drive mechanism having a rotor, which rotates the rotor in one direction in response to an axial backward movement caused by writing pressure applied to the writing lead gripped by the chuck unit and an axial forward movement caused by the release of the writing pressure, wherein the amount of backward movement caused by the backward movement is within the range of 0.05 to 0.3 mm.

[0021] According to another embodiment, the recession amount is within a range of 0.1 to 0.2 mm.

[0022] According to another aspect, the rotational drive mechanism has a first annular cam surface formed on the rear end surface of the rotor, a second annular cam surface formed on the front end surface of the rotor, a first fixed cam surface provided on the shaft tube side and cooperating with the first cam surface to rotate the rotor, and a second fixed cam surface provided on the shaft tube side and cooperating with the second cam surface to rotate the rotor, and the first fixed cam surface and the second fixed cam surface are configured to be positioned at a minimum distance such that rotation of the rotor is not hindered.

[0023] According to another embodiment, the writing pressure causes the retraction of the chuck unit to cause the first cam surface of the rotor to come into contact with the first fixed cam surface and engage with it while rotating the rotor, and the writing pressure is released to cause the second cam surface of the rotor to come into contact with the second fixed cam surface and engage with it while rotating the rotor. When the first cam surface of the rotor is engaged with the first fixed cam surface, the second cam surface and the second fixed cam surface are set in a relationship shifted by half a phase with respect to one tooth of a cam in the axial direction, and the second cam surface of the rotor is engaged with the second fixed cam surface. In this state, the first cam surface and the first fixed cam surface are set in a relationship shifted by half a phase with respect to one tooth of the cam in the axial direction, the first cam surface has first cam teeth, the second cam surface has second cam teeth, the first fixed cam surface has first fixed cam teeth cooperating with the first cam teeth, and the second fixed cam surface has second fixed cam teeth cooperating with the second cam teeth, and the height of the second cam teeth or the second fixed cam teeth is equal to the moving distance from a state in which the second cam surface and the second fixed cam surface are engaged to a state in which the tip of the first cam tooth abuts against the first fixed cam tooth due to the backward movement of the rotor.

[0024] Also, according to another aspect, by the retracting operation of the chuck unit due to the writing pressure, the first cam surface of the rotor abuts against the first fixed cam surface and is engaged while rotating the rotor. By releasing the writing pressure, the second cam surface of the rotor abuts against the second fixed cam surface and is engaged while rotating the rotor. In a state where the first cam surface of the rotor is engaged with the first fixed cam surface, the second cam surface and the second fixed cam surface are set in a relationship shifted by half a phase with respect to one tooth of the cam in the axial direction. In a state where the second cam surface of the rotor is engaged with the second fixed cam surface, the first cam surface and the first fixed cam surface are set in a relationship shifted by half a phase with respect to one tooth of the cam in the axial direction. The first cam surface is provided with first cam teeth, the second cam surface is provided with second cam teeth, the first fixed cam surface is provided with first fixed cam teeth that cooperate with the first cam teeth, and the second fixed cam surface is provided with second fixed cam teeth that cooperate with the second cam teeth. In the first cam teeth, when the length of the bottom side on the rear side with respect to the perpendicular line drawn from the apex is X and the length of the bottom side on the front side with respect to the rotation direction of the rotor is Y, the first cam teeth are configured such that the relationship 0 < Y < X holds.

[0025] Also, according to another aspect, the chuck unit is configured to rotate the refill by rotating upon receiving the rotational driving force of the rotor.

Advantages of the Invention

[0026] According to an aspect of the present invention, there is a common effect of providing a sharp pencil having a rotational drive mechanism for rotating the refill, in which the amount of retraction of the refill is further reduced.

Brief Description of the Drawings

[0027] [Figure 1] FIG. 1 is a longitudinal sectional view of a sharp pencil according to an embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged sectional view of the first half of the sharp pencil of FIG. 1. [Diagram 3] FIG. 3 is an enlarged cross-sectional view of the central portion of the mechanical pencil of FIG. [Figure 4] FIG. 4 is a partial enlarged view of the rotation drive mechanism. [Diagram 5] FIG. 5 is a diagram for explaining the sequence of rotational driving of the rotor of the rotational driving mechanism. [Figure 6] FIG. 6 is a schematic diagram for explaining the sequence of rotational driving of the rotor of the rotational driving mechanism. [Figure 7] FIG. 7 is a schematic diagram for explaining the relationship between the cams of the rotation drive mechanism. [Figure 8] FIG. 8 is a diagram for explaining the misalignment of the rotor. [Figure 9] FIG. 9 is a diagram for explaining the rotor rotation failure. [Figure 10] FIG. 10 is a schematic diagram for explaining the relationship between the cams of another rotation drive mechanism. [Figure 11] FIG. 11 is a schematic diagram for explaining the sequence of rotational driving of the rotor of the rotational driving mechanism of FIG. [Figure 12] FIG. 12 is a schematic diagram illustrating the rotational drive of a rotor in a conventional rotational drive mechanism. [Figure 13] FIG. 13 is a schematic diagram illustrating the rotational drive of the rotor, following FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Corresponding components are designated by common reference numerals throughout the drawings.

[0029] FIG. 1 is a vertical cross-sectional view of a mechanical pencil 1 according to an embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view of the front half of the mechanical pencil 1 of FIG.

[0030] The mechanical pencil 1 has a front shaft 2, a rear shaft 3 that screws onto the outer peripheral surface of the rear end of the front shaft 2, and an inner tube 4 that fits onto the inner peripheral surface of the rear end of the rear shaft 3 and has a clip. The front shaft 2 and the rear shaft 3 form a barrel 5. The barrel 5 may also be referred to as including the inner tube 4. The mechanical pencil 1 is configured so that a writing lead protrudes from the tip of the barrel 5. The tip of the barrel 5 is covered by a tip pipe 6 that guides the writing lead. In this specification, in the axial direction of the mechanical pencil 1, the writing lead side is defined as the "front" side, and the opposite side to the writing lead side is defined as the "rear" side.

[0031] A slider 7 is disposed inside the front end of the barrel 5 so as to be slidable in the axial direction and rotatable about the axis. The slider 7 is formed in a cylindrical shape whose outer diameter tapers in stages toward the front. The tip pipe 6 described above is attached to the front end of the slider 7. In addition, a holding chuck 8 having a through hole formed in the center is disposed behind the tip pipe 6. The through hole of the holding chuck 8 comes into sliding contact with the outer circumferential surface of the writing lead and acts to temporarily hold the writing lead.

[0032] A cylindrical relay member 9 is screwed to the rear end of the slider 7. A chuck unit 10 and a lead case 13 for gripping a writing lead are disposed inside the slider 7 and the relay member 9. The chuck unit 10 has a chuck main body 11 and a fastener 12 formed in a cylindrical shape so as to surround the front end of the chuck main body 11. At least the front half of the chuck main body 11 is divided into three chuck pieces 11a along the axial direction, and a through hole for the writing lead is formed along the central axis. The chuck pieces 11a are formed so that the front ends are spaced apart from each other. The lead case 13 is formed in a cylindrical shape, and a writing lead is accommodated inside. The rear end of the chuck main body 11 is inserted into the front end of the lead case 13 and fitted therein.

[0033] The coil spring 14 is disposed so as to surround the chuck body 11. The front end of the coil spring 14 is supported by a step formed on the inner circumferential surface of the relay member 9, and the rear end of the coil spring 14 abuts against the front end surface of the lead case 13. Therefore, the coil spring 14 biases the lead case 13 and the chuck body 11 rearward. The chuck body 11 biased rearward is accommodated in the fastener 12, so that the front ends approach each other and the writing lead can be maintained in a gripped state. In addition, when writing pressure is applied to the writing lead, the chuck body 11 retreats further and is accommodated in the fastener 12, and the writing lead is gripped by the chuck body 11. This prevents the writing lead from retracting. On the other hand, when a force is applied to pull the writing lead forward, the chuck body 11 is not acted on by the fastener 12, so that the writing lead can be pulled forward without resistance. That is, the chuck unit 10 acts to allow the writing lead to move forward and prevent it from moving backward, but other chuck units, such as a ball chuck, may be used as long as they perform this function.

[0034] The outer peripheral surface of the fastener 12 fits into the inner peripheral surface of the front end portion of the relay member 9. Therefore, the slider 7, the relay member 9 and the chuck unit 10 are movable in the axial direction within the barrel 5. The rear end portion of the relay member 9 is connected to a rotation drive mechanism 30, which will be described later.

[0035] A cylindrical knock member 20 is provided at the rear end of the barrel 5, specifically at the rear end of the inner barrel 4, so as to be movable back and forth relative to the barrel 5. The knock member 20 is biased rearward by a coil spring 21. The lead case 13 is inserted inside the front end of the knock member 20. An eraser 22 is removably attached inside the rear end of the knock member 20. A knock cover 23 is removably attached to the outer circumferential surface of the rear end of the knock member 20 to protect the eraser 22 from dirt and the like.

[0036] The lead case 13 advances by performing a knock operation that presses the knock member 20 or the knock cover 23 forward. This pushes the chuck body 11 forward. Accordingly, the writing lead held by the chuck body 11 also advances, acting to feed the writing lead from the tip pipe 6. When the pressure caused by the knock operation is released, the knock member 20 retreats and returns to its original position due to the biasing force of the coil spring 21. At this time, the chuck body 11 retreats due to the biasing force of the coil spring 14. On the other hand, since the writing lead is held by the holding chuck 8 arranged in the slider 7, the writing lead is drawn out of the chuck body 11 without resistance due to the action of the chuck unit 10. As a result, the writing lead is fed out from the tip pipe 6, so that a predetermined amount of the writing lead can be fed out each time the knock operation is repeated.

[0037] Fig. 3 is an enlarged cross-sectional view of the center portion of the mechanical pencil 1 in Fig. 1, and Fig. 4 is a partial enlarged view of the rotation drive mechanism 30. The rotation drive mechanism 30 is disposed in the internal space of the rear shaft 3. The rotation drive mechanism 30 is connected to the rear end portion of the relay member 9. An axis spring 31 is disposed between the rear end surface of the front shaft 2 and the front end surface of the rotation drive mechanism 30, and the rotation drive mechanism 30 is biased rearward. The lead case 13 passes through the interior of the relay member 9 and the rotation drive mechanism 30, and is separated from the rotation drive mechanism 30.

[0038] The rotation drive mechanism 30 has a rotor 40 formed in a cylindrical shape, an upper cam forming member 41 which is a first cam forming member formed in a cylindrical shape, a lower cam forming member 42 which is a second cam forming member formed in a cylindrical shape, a cylinder member 43 which is formed in a cylindrical shape, a torque canceller 44 which is also formed in a cylindrical shape, and a coil-shaped cushion spring 45. The rotation drive mechanism 30 is a unit formed by integrating these members.

[0039] The outer peripheral surface of the rear end of the relay member 9 is fitted onto the inner peripheral surface of the front end of the rotor 40. The rotor 40 has a flange-shaped portion with a slightly larger diameter near the front end, with a first cam surface 40a formed on the rear end surface of that portion and a second cam surface 40b formed on the front end surface of that portion.

[0040] The upper cam forming member 41 rotatably surrounds the rotor 40 behind the first cam surface 40a of the rotor 40. The lower cam forming member 42 fits onto the outer peripheral surface of the front end portion of the upper cam forming member 41. A first fixed cam surface 41a is formed on the front end surface of the upper cam forming member 41 facing the first cam surface 40a of the rotor 40. A second fixed cam surface 42a is formed on the inner surface of the front end portion of the lower cam forming member 42 facing the second cam surface 40b of the rotor 40.

[0041] The first cam surface 40a includes a plurality of first cam teeth 40aa, the second cam surface 40b includes a plurality of second cam teeth 40ba, the first fixed cam surface 41a includes a plurality of first fixed cam teeth 41aa, and the second fixed cam surface 42a includes a plurality of second fixed cam teeth 42aa. The first cam teeth 40aa and the first fixed cam teeth 41aa have the same shape and the same orientation. The first cam teeth 40aa and the second cam teeth 40ba have the same shape but are line-symmetric. The first cam teeth 40aa, the second cam teeth 40ba, and the first fixed cam teeth 41aa are continuously arranged without gaps along the circumferential direction on the corresponding cam surfaces. On the other hand, the second fixed cam teeth 42aa of the second fixed cam surface 42a are similar in shape to the first cam teeth 40aa, the second cam teeth 40ba, and the first fixed cam teeth 41aa, but are larger than them. The second fixed cam teeth 42aa are arranged at equal intervals and spaced apart from one another along the circumferential direction on the second fixed cam surface 42a. The first cam surface 40a is formed in a sawtooth shape by a plurality of first cam teeth 40aa, the second cam surface 40b is formed in a sawtooth shape by a plurality of second cam teeth 40ba, and the first fixed cam surface 41a is formed in a sawtooth shape by a plurality of first fixed cam teeth 41aa.

[0042] A cylindrically shaped cylinder member 43 is fitted onto the outer peripheral surface of the rear end of the upper cam forming member 41. An insertion hole 43a through which the lead case 13 can be inserted is formed in the rear end of the cylinder member 43. A cylindrically shaped torque canceller 44 that is movable in the axial direction is disposed within the cylinder member 43. A cushion spring 45 is disposed between the inner surface of the front end of the torque canceller 44 and the inner surface of the rear end of the cylinder member 43. The cushion spring 45 urges the rotor 40 forward via the torque canceller 44.

[0043] Here, the relay member 9 transmits the backward and forward movements (cushioning movement) of the writing lead based on the writing action to the rotation drive mechanism 30, i.e., the rotor 40, and also transmits the rotational motion of the rotor 40 in the rotation drive mechanism 30 caused by the cushioning movement to the chuck unit 10 holding the writing lead. Therefore, the rotation of the relay member 9 also rotates the writing lead held by the chuck unit 10.

[0044] When the mechanical pencil 1 is not being used for writing, i.e., when no writing pressure is being applied to the writing lead, the rotor 40 is positioned forward by the urging force of the cushion spring 45 via the torque canceller 44. Therefore, the second cam surface 40b of the rotor 40 abuts against the second fixed cam surface 42a and is brought into an engaged state. When the mechanical pencil 1 is used for writing, i.e., when writing pressure is being applied to the writing lead, the chuck unit 10 moves backward against the urging force of the cushion spring 45, and the rotor 40 also moves backward accordingly. Therefore, the first cam surface 40a of the rotor 40 abuts against the first fixed cam surface 41a and is brought into an engaged state. The writing lead and the rotor 40 move forward, backward, or rotate together.

[0045] FIG. 5 is a diagram for explaining the rotational drive of the rotor 40 of the rotational drive mechanism 30 in sequence, and FIG. 6 is a schematic diagram for explaining the rotational drive of the rotor 40 of the rotational drive mechanism 30 in sequence. FIG. 6(A) to (E) are schematic diagrams corresponding to FIG. 5(A) to (E), respectively. Furthermore, FIG. 5(A) to (E) and FIG. 6(A) to (E) correspond to FIG. 12(A) to (C) and FIG. 13(D) and (E), respectively. FIG. 6 partially shows the rotor 40, the upper cam forming member 41, and the lower cam forming member 42 in a circumferentially developed state. In addition, in order to make the cushioning operation easier to understand, the cam teeth of the rotor 40 will be explained as one cam tooth unit U surrounded by the imaginary line in FIG. 4.

[0046] The second fixed cam tooth 42aa is substantially equivalent to a cam tooth of the same shape arranged continuously from the functional point of view, since it has a similar shape to the other cam teeth. Therefore, for example, in FIG. 6 and FIG. 7 described later, the second fixed cam tooth 42aa is shown in a schematic manner to approximate a cam tooth of the same shape arranged continuously as the other cam teeth, so as to be easily compared with FIG. 12 and FIG. 13. The second fixed cam tooth 42aa may be arranged continuously along the circumferential direction with the same shape as the other cam teeth. In addition, the first cam tooth 40aa, the second cam tooth 40ba, and the first fixed cam tooth 41aa are each arranged continuously along the circumferential direction, but may be arranged at intervals along the circumferential direction, and may be similar in shape to the other cam teeth from the functional point of view.

[0047] 5(A) and 6(A) show the relationship between the advanced rotor 40, the upper cam forming member 41, and the lower cam forming member 42 when no writing pressure is applied to the writing lead. In this state, the second cam surface 40b formed on the rotor 40 abuts against the second fixed cam surface 42a of the lower cam forming member 42 by the biasing force of the cushion spring 45. At this time, the first cam surface 40a of the rotor 40 and the first fixed cam surface 41a of the upper cam forming member 41 are set to be shifted by half a phase with respect to one tooth of the cam in the axial direction.

[0048] 5(B) and 6(B) show the initial state in which writing pressure is applied to the writing lead for writing with the mechanical pencil 1. In this state, the rotor 40 retracts by contracting the cushion spring 45 as the chuck unit 10 retracts. As a result, the rotor 40 moves toward the upper cam forming member 41 and comes into contact with the first fixed cam surface 41a.

[0049] 5(C) and 6(C) show a state in which further writing pressure is applied to the writing core, and the rotor 40 moves back while sliding against the first fixed cam surface 41a of the upper cam forming member 41. In other words, the rotor 40 receives a rotational drive equivalent to a half phase of one tooth of the first cam surface 40a. In this state, the first cam surface 40a of the rotor 40 meshes with the first fixed cam surface 41a of the upper cam forming member 41.

[0050] In addition, the circle drawn in the center of the rotor 40 in Fig. 5 indicates the amount of rotational movement of the rotor 40. In the state shown in Fig. 5(C), the second cam surface 40b of the rotor 40 and the second fixed cam surface 42a of the lower cam forming member 42 are set to have a relationship of being shifted by half a phase with respect to one tooth of the cam in the axial direction.

[0051] 5(D) and 6(D) show the initial state in which writing with the mechanical pencil 1 is completed and the writing pressure on the writing lead is released. In this state, the rotor 40 advances due to the biasing force of the cushion spring 45. As a result, the rotor 40 moves toward the lower cam forming member 42 and comes into contact with the second fixed cam surface 42a.

[0052] 5(E) and 6(E) show a state in which the rotor 40 advances while sliding against the second fixed cam surface 42a of the lower cam forming member 42 due to the biasing force of the cushion spring 45. That is, the rotor 40 is again subjected to a rotational drive equivalent to a half phase of one tooth of the second cam surface 40b. In this state, the second cam surface 40b of the rotor 40 is engaged with the second fixed cam surface 42a of the lower cam forming member 42.

[0053] Therefore, as shown by the circle drawn in the center of the rotor 40 in FIG. 5, the rotor 40 receives a reciprocating motion in the axial direction of the rotor 40 under writing pressure, that is, a back-and-forth motion, and the writing lead held by the rotor 40 is also rotated through the chuck unit 10. Therefore, the rotor 40 receives a rotational motion corresponding to one tooth of the cam by one back-and-forth motion in the axial direction of the rotor 40 due to writing, and by repeating this, the writing lead is sequentially rotated. Therefore, it is possible to prevent the writing lead from being worn unevenly as writing progresses, and it is possible to prevent a large change in the thickness and darkness of the drawn line. Note that the following description is also applicable to a mechanical pencil that has a rotation drive mechanism but is not configured to rotate the writing lead.

[0054] In short, the rotation drive mechanism 30 has a first cam surface 40a having an annular shape formed on the rear end surface of the rotor 40, a second cam surface 40b having an annular shape formed on the front end surface of the rotor 40, a first fixed cam surface 41a provided on the shaft cylinder 5 side and cooperating with the first cam surface 40a to rotate the rotor 40, and a second fixed cam surface 42a provided on the shaft cylinder 5 side and cooperating with the second cam surface 40b to rotate the rotor 40. When the chuck unit 10 is moved backward by writing pressure, the first cam surface 40a of the rotor 40 comes into contact with the first fixed cam surface 41a and is engaged while rotating the rotor 40, and when the writing pressure is released, the second cam surface 40b of the rotor 40 comes into contact with the second fixed cam surface 42a and is engaged while rotating the rotor 40. When the first cam surface 40a of the rotor 40 is engaged with the first fixed cam surface 41a, the second cam surface 40b and the second fixed cam surface 42a are set in a relationship in which they are shifted by half a phase with respect to one tooth of the cam in the axial direction, and when the second cam surface 40b of the rotor 40 is engaged with the second fixed cam surface 42a, the first cam surface 40a and the first fixed cam surface 41a are set in a relationship in which they are shifted by half a phase with respect to one tooth of the cam in the axial direction.

[0055] The torque canceller 44, which pushes the rotor 40 forward by receiving the biasing force of the cushion spring 45, generates a slip between its front end face and the rear end face of the rotor 40, preventing the rotational motion of the rotor 40 from being transmitted to the cushion spring 45. In other words, the torque canceller 44 prevents the rotational motion of the rotor 40 from being transmitted to the cushion spring 45, thereby preventing the cushion spring 45 from twisting back (torque) that would impede the rotational motion of the rotor 40.

[0056] As described above, the mechanical pencil 1 has a chuck unit 10 and a rotor 40, and is configured so that the chuck unit 10 moves back and forth to release and grip the writing lead, thereby allowing the writing lead to be advanced forward. The chuck unit 10 is held within the barrel 5 so that it can rotate about the central axis while gripping the writing lead, and the rotor 40 is rotated by the back and forth movement of the rotor 40 via the chuck unit 10 due to the writing pressure of the writing lead, and the rotational motion of the rotor 40 is transmitted to the writing lead via the chuck unit 10.

[0057] FIG. 7 is a schematic diagram for explaining the relationship between the cams of the rotation drive mechanism 30, and is the same as FIG. 6(A). The first cam tooth 40aa of the first cam surface 40a has a first inclined surface 40aa1 and a vertical surface 40aa2 corresponding to the second inclined surface, and the first cam surface 40aa1 and the vertical surface 40aa2 of the adjacent first cam teeth 40aa form the first cam surface 40a into a continuous sawtooth shape. The first inclined surface 40aa1 is a surface inclined at an inclination angle θ with respect to the transverse direction perpendicular to the axial direction, and the vertical surface 40aa2 is a surface parallel to the axial direction, i.e., a surface perpendicular to the transverse direction. As described above, the second cam tooth 40ba of the second cam surface 40b and the first fixed cam tooth 41aa of the first fixed cam surface 41a also have the same shape.

[0058] The heights of the first cam teeth 40aa and the second cam teeth 40ba, and the height at which the second fixed cam teeth 42aa substantially mesh with the second cam teeth 40ba, correspond to the distance h in FIG. 12A and are defined as distance H. The length of the vertical surface 40aa2 of the first cam tooth 40aa is equal to the height of the first cam tooth 40aa and is therefore equal to the distance H. The movement distance until the tip of the first cam tooth 40aa abuts against the first fixed cam tooth 41aa due to the retreat of the rotor 40 corresponds to the distance d in FIG. 12A and is defined as distance D. The length of the first cam tooth 40aa along the circumferential direction is defined as the cam tooth length L.

[0059] The first cam tooth 40aa has a radial thickness according to the member of the rotor 40 formed in a cylindrical shape. Fig. 6 and Fig. 7 show the rotor 40, the upper cam forming member 41, and the lower cam forming member 42 in a circumferentially expanded state, but strictly speaking, the angles and dimensions of the first cam tooth 40aa are slightly different depending on which part of the range of the radial thickness is expanded. Therefore, in Fig. 6 and Fig. 7 and other descriptions in this specification, the angles and distances such as θ and L and the positional relationships of other members are defined as being the circumferentially expanded outermost part that defines the outer diameter of the rotor 40.

[0060] In the rotation drive mechanism 30 of the mechanical pencil 1, the first fixed cam surface 41a and the second fixed cam surface 42a are disposed at a minimum distance that does not impede the rotation of the rotor 40. Therefore, the distance H, which is the height at which the second cam tooth 40ba and the second fixed cam tooth 42aa substantially mesh with each other, is configured to be equal to the distance D in the axial direction between the tip of the first cam tooth 40aa and the first fixed cam tooth 41aa.

[0061] In detail, in Fig. 7, which corresponds to Fig. 5(A) and Fig. 6(A), the rotation of the rotor 40 is restricted by the engagement between the second cam tooth 40ba of the second cam surface 40b and the second fixed cam tooth 42aa of the second fixed cam surface 42a. When the rotor 40 retreats by a distance H from this state due to the retreat of the writing lead, the engagement between the second cam tooth 40ba and the second fixed cam tooth 42aa is released, and the restriction on the rotation of the rotor 40 is released. When the rotor 40 retreats by a distance D, the first inclined surface 40aa1 of the rotor 40 comes into contact with the first fixed cam tooth 41aa, and the rotor 40 can be rotated.

[0062] In short, when the restriction on the rotation of the rotor 40 is released and the first cam surface 40a and the first fixed cam surface 41a come into contact with each other at the same time, that is, when the distance H and the distance D are equal (D=H), the first fixed cam surface 41a and the second fixed cam surface 42a are disposed at the minimum distance at which the rotation of the rotor 40 is not hindered. In other words, when the distance H and the distance D are equal, the retraction amount m of the writing lead is minimum. Taking into account the manufacturing tolerance, the distance D may be configured to be slightly longer than the distance H. The minimum distance is determined as long as the intention of the design not to hinder the rotation of the rotor is objectively or externally clear, and is determined while taking into account the manufacturing tolerance, and is determined without taking into account the wear caused by the use of the mechanical pencil.

[0063] As described above, the first cam surface 40a and the first fixed cam surface 41a are arranged with a half phase shift with respect to one tooth of the cam. Therefore, the rotor 40 rotates by a distance 1 / 2L and retreats by a distance 1 / 2H from the state shown in Fig. 5(B) and Fig. 6(B) to the state shown in Fig. 5(C) and Fig. 6(C). In short, in a series of cushioning operations, the writing lead retreats by a distance 3 / 2H (= 1 / 2H + H), which is the minimum retreat amount m of the writing lead as the rotation drive mechanism 30. The minimum retreat amount m thus geometrically obtained is the minimum retreat amount M. Naturally, the axial movement amount of the rotor 40 from the retreated state (Fig. 5(C) and Fig. 6(C)) to the advanced state (Fig. 5(E) and Fig. 6(E)), i.e., the advance amount, is the same distance 3 / 2H as the minimum retreat amount M.

[0064] In addition, when focusing on the movement of the tip of the crest of the second cam tooth 40ba of the second cam surface 40b, it moves along a trajectory T1 when it first retreats, and then moves along a trajectory T2 by rotating and retreating thereafter. The first cam tooth 40aa of the first cam surface 40a also moves while describing a similar trajectory.

[0065] The distance H depends on the inclination angle θ and the circumferential length L of the first cam tooth 40aa, and has the relationship H = L tan θ. Therefore, by making the cam tooth length L or the inclination angle θ smaller, the distance H can be reduced, and as a result, the minimum retraction amount M can be reduced. Next, the design of the inclination angle θ and the cam tooth length L will be described.

[0066] The inclination angle θ is one factor that determines how easily the cam teeth slide over each other, depending on its magnitude. That is, if the inclination angle θ is too small, for example if the inclination angle θ is smaller than the friction angle, the cam teeth will not slide over each other, and therefore the rotor 40 will not rotate. If the inclination angle θ is too large, the distance H will be larger, and the minimum retraction amount M will also be larger. Taking into consideration the general materials used as parts of writing instruments, it is preferable that the inclination angle θ is within the range of 8 to 25°.

[0067] Generally, many of the components of writing implements such as mechanical pencils are made of resins such as polypropylene and polyacetal. In particular, internal parts such as the cam structures of the rotor 40, the upper cam forming member 41, and the lower cam forming member 42, which have complex shapes and do not affect the appearance, are rarely made of metal materials. In order to ensure the cooperative action of the cam teeth formed on these parts, specifically, the rotor 40 abutting against the upper cam forming member 41 or the lower cam forming member 42 and rotating while sliding, especially taking into account friction resistance, each cam tooth needs to have an inclination angle θ larger than the friction angle. For example, the rotor 40, the upper cam forming member 41, and the lower cam forming member 42 are made of polyacetal, and the friction angle is set to 10.2°. In other words, if the inclination angle θ is 10.2° or less, the cam teeth do not slide against each other, and therefore the rotor 40 cannot be rotated.

[0068] The length L of the cam teeth is calculated by calculating the total circumference length from the outer diameter of the rotor 40 (outer diameter x π) and dividing it by the number of cam teeth. An example of the dimensional design of the outer diameter of the rotor 40 will be described. According to the JIS standard S6005 for mechanical pencil leads, a writing lead of 0.5 mm is allowed up to an outer diameter of 0.58 mm. If multiple writing leads are to be accommodated in the lead case 13, the inner diameter of the lead case 13 needs to be at least 1.8 mm, for example, for three writing leads. From the viewpoint of strength, the thickness of the cylindrical part of the resin member is at least 0.5 mm. Therefore, the thickness of the lead case 13, the thickness of the rotor 40 surrounding the lead case 13, and the thickness of the part where the cam teeth are formed are each 0.5 mm. Taking these thicknesses and the inner diameter of the lead case 13 into consideration, the outer diameter of the first cam surface 40a and the second cam surface 40b of the rotor 40 is 4.8 mm.

[0069] The number of cam teeth on the first cam surface 40a, i.e., the number of cam teeth on the corresponding second cam surface 40b, is preferably 20 to 90. The number of cam teeth determines the rotation angle of the writing lead rotated by one cushioning motion. For example, when the number of cam teeth is 90, 360° is divided by 90 to obtain 4°, so the rotor 40 rotates by 4° with one cushioning motion. Therefore, when writing 90 strokes, the writing lead rotates once.

[0070] If the number of cam teeth is more than 90, the rotation angle becomes smaller, and the next writing is performed in the part where the writing lead is worn. Therefore, the original purpose of a mechanical pencil equipped with a rotation drive mechanism, which is to prevent uneven wear of the writing lead, cannot be achieved. On the other hand, if the number of cams is less than 20, the length L of the cam teeth becomes larger. Therefore, from the above-mentioned relational expression of distance H=Ltanθ, the distance H, which is the height of the cam teeth, becomes larger, and the minimum retraction amount M also becomes larger. Therefore, the number of cam teeth is preferably 20 to 90.

[0071] If the outer diameter of the rotor 40 is 4.8 mm, the number of cam teeth is 90, and the inclination angle θ is 10.3°, which is larger than the friction angle 10.2°, then the length L of the cam teeth is about 0.17 mm from 4.8×π / 90. Then, the distance H, which is the height of the cam teeth, is 0.03 mm from the relational expression Ltanθ. As a result, the minimum retraction amount M is 0.05 mm from the relational expression 3 / 2H.

[0072] From the above, if the retraction amount m of the writing lead is smaller than the minimum retraction amount M of 0.05 mm, the inclination angle θ of the cam teeth becomes smaller, so there is a risk that the cam teeth will not slip against each other and rotation problems will occur, or the rotation angle of the rotor 40 becomes smaller, so there is a risk that the original purpose of a mechanical pencil equipped with a rotation drive mechanism cannot be achieved. Therefore, it is preferable that the retraction amount m is equal to or greater than the minimum retraction amount M of 0.05 mm.

[0073] On the other hand, the retraction amount m is preferably 0.3 mm or less. If the retraction amount m is greater than 0.3 mm, the user may feel uncomfortable due to the retraction of the writing lead.

[0074] The inventors conducted a survey in which 23 students were asked to write with a mechanical pencil with a retraction amount m of 0.15 mm and a mechanical pencil with a retraction amount m of 0.3 mm without being informed in advance that there was a difference in the retraction amount m. The results showed that all of the students noticed the difference. In short, it was found that users can feel a difference of only 0.15 mm. It is preferable that the retraction amount m of the writing lead is smaller, but as mentioned above, if the retraction amount m is too small, there is a risk of poor rotation. In order to reliably realize the rotation of the rotor 40 and the writing lead while preventing the user from feeling a sense of discomfort due to the retraction of the writing lead as much as possible, it is preferable that the retraction amount m is 0.3 mm or less.

[0075] In view of the above, in a mechanical pencil 1 equipped with a barrel 5, a chuck unit 10 that allows the writing lead to move forward and prevents it from moving backward, and a rotation drive mechanism 30 that has a rotor 40 and rotates the rotor 40 in one direction in response to the axial backward movement caused by the writing pressure applied to the writing lead held by the chuck unit 10 and the axial forward movement caused by the release of the writing pressure, it is preferable that the amount of retraction m of the writing lead is within the range of 0.05 to 0.3 mm.

[0076] As described above, if the number of cam teeth is 90, the rotor 40 rotates by 4° with one cushioning motion. For users who write with strong writing pressure, the amount of writing lead worn out by one writing stroke is large, so a rotation of 4° may not be sufficient. In order to increase the rotation angle of the writing lead rotated by one cushioning motion, it is more preferable that the number of cam teeth is 20 to 40. For example, if the number of cam teeth is 40, 360° is divided by 40 to get 9°, so the rotor 40 rotates by 9° with one cushioning motion. Therefore, when writing 40 strokes, the writing lead rotates once.

[0077] If the outer diameter of the rotor 40 is 4.8 mm as described above, the number of cam teeth is 40, and the inclination angle θ is 10.3°, the length L of the cam teeth is about 0.38 mm from 4.8×π / 40. Then, the distance H, which is the height of the cam teeth, is 0.07 mm from the relational expression Ltanθ. As a result, the minimum retraction amount M is 0.1 mm from the relational expression 3 / 2H.

[0078] From the above, it is more preferable that the retreat amount m is 0.1 mm or more, because sufficient rotation of the writing lead can be obtained even in the case of a user with a strong writing pressure. Furthermore, some users may write with the mechanical pencil 1 extremely tilted relative to the writing surface. In such cases, it is preferable to have a larger retreat amount m, that is, to make the length L of the cam teeth longer or the inclination angle θ larger, because this ensures that the cam teeth work together. For these reasons, it is more preferable that the retreat amount m is 0.1 mm or more.

[0079] Incidentally, when writing small characters, the tip of the writing lead is closely watched and the senses are sharpened, so it is more preferable that the retraction amount m is 0.2 mm or less. Also, even with the same cushioning amount, the feeling felt when writing with a 0.5 mm writing lead is different from the feeling felt when writing with a 0.3 mm writing lead. In other words, the feeling felt when writing with a 0.3 mm writing lead is more likely to feel strange because the distance the tip of the writing lead moves back and forth is relatively large compared to the thickness of the writing lead. For these reasons, it is more preferable that the retraction amount m is 0.2 mm or less.

[0080] In view of the above, it is more preferable that the retraction amount m of the writing lead is within the range of 0.1 to 0.2 mm.

[0081] The retraction amount m may be changed according to the lead diameter of the writing lead, and is more preferably about half or less of the outer diameter of the writing lead. For example, according to the JIS standard S6005 for mechanical pencil leads, for example, a 0.5 mm writing lead is specified as 0.55 to 0.58 mm. Therefore, for a 0.5 mm writing lead, the retraction amount m is preferably 0.3 mm or less. Similarly, a 0.3 mm writing lead is specified as 0.37 to 0.39 mm. Therefore, for a 0.3 mm writing lead, the retraction amount m is preferably 0.2 mm or less.

[0082] The cam teeth do not have to be continuous around the entire circumference. When considering the number of cam teeth, even if the cam teeth are not continuous around the entire circumference but are spaced apart, the virtual number of cam teeth may be calculated by dividing the length of the entire circumference by the circumferential length L of one representative cam tooth. For design efficiency, the number of cam teeth is preferably 20, 40, 60, or 90 per 360° circumference of the rotor 40, and 40 is most preferable from the viewpoint of reducing the retreat amount m.

[0083] In the above embodiment, the minimum retraction amount M and further the retraction amount m of the writing lead were explained based on an example of the outer diameter, number of cam teeth, and inclination angle of the rotor 40, but the above-mentioned suitable range of the retraction amount m of the writing lead can be similarly applied to mechanical pencils with other outer diameters, numbers of cam teeth, etc. In other words, according to the above embodiment, in a mechanical pencil 1 equipped with a rotation drive mechanism that rotates the writing lead, it is possible to further reduce the retraction amount of the writing lead.

[0084] By the way, shortening the length L of the first cam tooth 40aa reduces the ratio of the length of the entire circumference that one first cam tooth 40aa occupies. In other words, shortening the length L makes it possible to increase the number of cam teeth. If the length L is shortened, the relative positional relationship of the rotor 40 with respect to the upper cam forming member 41 and the lower cam forming member 42 may be shifted in the radial direction, that is, the central axes of the rotor 40 may be shifted, and the meshing of the cam teeth arranged at positions corresponding to the direction perpendicular to the shifting direction may become incomplete. As a result, the rotor 40 may rotate improperly. This will be described with reference to Figs. 8 and 9.

[0085] Fig. 8 is a diagram for explaining the misalignment of the rotor 40, and Fig. 9 is a diagram for explaining the rotation failure of the rotor 40. Fig. 8 is a schematic diagram of the rotation drive mechanism 30 as viewed from the axial direction, somewhat exaggerated and without scale. Fig. 8 shows a state in which the rotor 40 is misaligned by a distance g upward in the drawing with respect to the upper cam forming member 41 and the lower cam forming member 42. That is, since the upper cam forming member 41 and the lower cam forming member 42 are provided on the shaft cylinder 5 side, their central axes coincide, but only the central axis of the rotor 40 is misaligned by the distance g.

[0086] Fig. 9(A) shows the relationship of each cam in part P1 of Fig. 8, which is the position where rotor 40 is most displaced in the radial direction. Fig. 9(B) shows the relationship of each cam in part P2 of Fig. 8, which is the position where rotor 40 is most displaced in the circumferential direction. That is, part P1 is the part located in the direction in which rotor 40 is displaced, and part P2 is the part located in a direction perpendicular to the direction of displacement. Since each cam tooth of each cam is arranged along the circumferential direction, each cam tooth in part P1 is arranged along the left-right direction in the figure, and each cam tooth in part P2 is arranged along the up-down direction in the figure.

[0087] 9(A), the cam teeth of the rotor 40 are shifted by a distance g in the radial direction of the rotor 40, i.e., in the direction perpendicular to the paper surface in the figure, with respect to the cam teeth of the upper cam forming member 41 and the lower cam forming member 42, as compared to the state shown in FIG. 6(A). Therefore, in part P1, there is no shift in the phase of the cam teeth, and therefore there is almost no effect on the rotational drive of the rotor 40.

[0088] On the other hand, referring to Fig. 9(B), the cam teeth of the rotor 40 are shifted by a distance g in the circumferential direction of the rotor 40, i.e., to the right in the figure, with respect to the cam teeth of the upper cam forming member 41 and the lower cam forming member 42, compared to the state shown in Fig. 6(A). Normally, when the rotor 40 moves backward by writing, the first cam surface 40a of the rotor 40 abuts against the first fixed cam surface 41a of the upper cam forming member 41 over half the length of the first inclined surface 40aa1 of the rotor 40. That is, as shown in Fig. 6(B), the engagement allowance E, which is the length of the abutment portion in the circumferential direction, is 1 / 2L.

[0089] On the other hand, because the rotor 40 is shifted by the distance g, the engagement allowance E is reduced by that amount. Therefore, the first cam surface 40a and the first fixed cam surface 41a cannot cooperate reliably, and there is a risk of the rotor 40 not rotating properly. Also, as shown in FIG. 9C, if the distance g is greater than half the length L of the cam teeth of the first cam teeth 40aa, that is, if the first cam surface 40aa is shifted by more than half a phase with respect to one tooth of the cam, the first cam surface 40a cannot abut against the corresponding first fixed cam surface 41a that it should abut against. As a result, even if a rotational driving force is generated in other parts, the rotation is restricted by those parts, and the rotor 40 does not rotate properly.

[0090] In short, the smaller the cam tooth length L is relative to the radially displaced distance g of the rotor 40, the higher the possibility of rotation failure. Therefore, taking into consideration the radial displacement of the rotor 40, the cam tooth length L, and therefore the number of cam teeth, are appropriately determined within a range that allows the above-mentioned retraction amount m of the writing lead to be realized.

[0091] The radial deviation of rotor 40 depends greatly on the clearance between the outer circumferential surface of the tip of slider 7, to which rotor 40 is connected via relay member 9, and the inner circumferential surface of front shaft 2, which surrounds said outer circumferential surface. Since the clearance is caused by manufacturing tolerances, it is preferable that at least slider 7 is made of metal so that it can be processed with greater precision.

[0092] The first cam tooth 40aa of the rotor 40 in the above-mentioned embodiment has a first inclined surface 40aa1 and a vertical surface 40aa2 corresponding to the second inclined surface. Therefore, the first cam surface 40a is formed in a continuous, so-called sawtooth shape. The other cam teeth have the same shape. For example, the mechanical pencil described in Patent Document 1 has a similar shape. The cam teeth can rotate the rotor even if they are not sawtooth. Hereinafter, other cam tooth shapes will be described.

[0093] Fig. 10 is a schematic diagram for explaining the relationship between the cams of another rotation drive mechanism, and corresponds to Fig. 7. The rotation drive mechanism shown in Fig. 10 has a rotor 140, an upper cam forming member 141, and a lower cam forming member 142, and can be replaced with the rotor 40, the upper cam forming member 41, and the lower cam forming member 42 of the rotation drive mechanism 30 described above.

[0094] The first cam tooth 140aa of the first cam surface 140a has a first inclined surface 140aa1 and a second inclined surface 140aa2, and the first cam surface 40a is formed into a continuous mountain shape by the first inclined surface 140aa1 and the second inclined surface 140aa2 of the adjacent first cam tooth 140aa. The first inclined surface 140aa1 is a surface inclined at an inclination angle θ with respect to the transverse direction perpendicular to the axial direction. The second cam tooth 140ba of the second cam surface 140b, the first fixed cam tooth 141aa of the first fixed cam surface 141a, and the second fixed cam tooth 142aa of the second fixed cam surface 142a also have a shape similar to that of the first cam tooth 140aa.

[0095] Fig. 11 is a schematic diagram for sequentially explaining the rotational drive of the rotor 140 of the rotational drive mechanism of Fig. 10. Figs. 11(A) to (E) are schematic diagrams corresponding to Figs. 6(A) to (E), respectively, and the basic operation is the same. Fig. 11 partially shows the rotor 140, the upper cam forming member 141, and the lower cam forming member 142 in a circumferentially developed state. Also, to make the cushioning operation easier to understand, the cam teeth of the rotor 140 will be explained as one cam tooth unit U, as in Fig. 6.

[0096] 11(A) shows the relationship between the advanced rotor 140, the upper cam forming member 141, and the lower cam forming member 142 when no writing pressure is being applied to the writing lead. In this state, the second cam surface 140b formed on the rotor 140 is in contact with the second fixed cam surface 142a of the lower cam forming member 142 by the biasing force of the cushion spring 45. At this time, the first cam surface 140a of the rotor 140 and the first fixed cam surface 141a of the upper cam forming member 141 are set to be shifted by half a phase with respect to one tooth of the cam in the axial direction.

[0097] 11(B) shows the initial state in which writing pressure is applied to the writing lead for writing with the mechanical pencil 1. In this state, the rotor 140 retracts by contracting the cushion spring 45 as the chuck unit 10 retracts. As a result, the rotor 140 moves toward the upper cam forming member 141 and comes into contact with the first fixed cam surface 141a.

[0098] 11(C) shows a state in which further writing pressure is applied to the writing core, causing the rotor 140 to slide back while abutting against the first fixed cam surface 141a of the upper cam forming member 141. In other words, the rotor 140 receives a rotational drive equivalent to a half phase of one tooth of the first cam surface 140a. In this state, the first cam surface 140a of the rotor 140 meshes with the first fixed cam surface 141a of the upper cam forming member 141.

[0099] 11(D) shows an initial state in which writing with the mechanical pencil 1 has finished and the writing pressure on the writing lead has been released. In this state, the rotor 140 advances due to the biasing force of the cushion spring 45. As a result, the rotor 140 moves toward the lower cam forming member 142 and comes into contact with the second fixed cam surface 142a.

[0100] 11(E) shows a state in which the rotor 140 advances while sliding against the second fixed cam surface 142a of the lower cam forming member 142 due to the biasing force of the cushion spring 45. That is, the rotor 140 is again subjected to a rotational drive equivalent to a half phase of one tooth of the second cam surface 140b. In this state, the second cam surface 140b of the rotor 140 meshes with the second fixed cam surface 142a of the lower cam forming member 142.

[0101] Therefore, as rotor 140 receives writing pressure and reciprocates in the axial direction, i.e., moves back and forth, rotor 140 receives rotational drive corresponding to one tooth of first cam surface 140a and second cam surface 140b, and the writing lead held thereby is similarly rotated via chuck unit 10. In short, there is no difference in the basic rotational drive operation of the rotational drive mechanism whether the cam teeth are sawtooth-shaped or mountain-shaped.

[0102] Calculation of the minimum retreat amount M will be described with reference to FIG. 10. The height of the sawtooth cam tooth shown in FIG. 7 is distance H, whereas the height of the mountain-shaped cam tooth shown in FIG. 10 is distance H'. In FIG. 10, the sawtooth cam tooth shown in FIG. 7 is shown by virtual lines. The distance traveled until the tip of the first cam tooth 140aa abuts against the first fixed cam tooth 141aa due to the retreat of the rotor 140 is distance D. The length of the first cam tooth 140aa along the circumferential direction is length L of the cam tooth. Considering a triangle of the first cam tooth 140aa, when a perpendicular line is drawn from the apex to the base to divide the length L, the length of the rear side of the base in the rotation direction of the rotor 140 (left direction in the figure) is set to X, and the length of the front side of the base in the rotation direction of the rotor 140 is set to Y.

[0103] The distance H of the sawtooth cam teeth and the distance H' of the mountain-shaped cam teeth are geometrically related as H'=HX / (X+Y). In addition, when considering the multiple auxiliary lines J of the second cam tooth 140ba in FIG. 10, the distance D is D=H-2H(Y / (X+Y))=H(XY) / (X+Y). From these, the minimum retreat amount M is related as M=1 / 2H+D=1 / 2H+H(XY) / (X+Y)=H(3X-Y) / {2(X+Y)}=H'(3X-Y) / (2X). Therefore, the relational expression of the minimum retreat amount M=3 / 2H'-H'Y / (2X) is obtained. In the case of the sawtooth cam teeth with the height of the cam teeth shown in FIG. 7 having the distance H, Y is zero, so according to the relational expression, the minimum retreat amount M=3 / 2H as described above.

[0104] In addition, when focusing on the movement of the tip of the crest of second cam tooth 140ba of second cam surface 140b, it moves along a trajectory T3 when it first retreats, and then moves along a trajectory T4 by rotating and retreating thereafter. First cam tooth 140aa of first cam surface 140a also moves while describing a similar trajectory.

[0105] The first cam tooth 140aa forms an isosceles triangle when X=Y, and such cam teeth are disclosed in FIG. 4 of Patent Document 2. In this case, the minimum retraction amount M=H' from the relational expression of minimum retraction amount M=3 / 2H'-H'Y / (2X), and the minimum retraction amount M is minimum. However, as is clear from considering the case of X=Y with reference to FIG. 10, the apex of the first cam tooth 140aa and the apex of the first fixed cam tooth 141aa are located at opposing positions. Therefore, the engagement amount E is small or point-like, and a slight deviation in the radial direction of the rotor 140 may cause poor rotation.

[0106] Therefore, it is preferable that Y is smaller than X. Also, from the above relational expression, the minimum retraction amount M can be made smaller if the first cam teeth 140aa are not the sawtooth first cam teeth 40aa that are in the shape of a right triangle as shown in Fig. 7. Therefore, it is preferable that Y is greater than zero.

[0107] From the above, with respect to the apex of the first cam tooth 140aa or the apex of the second cam tooth 140ba, if the length of the bottom side on the rear side with respect to the rotation direction of the rotor 140 is X, and the length of the bottom side on the front side with respect to the rotation direction of the rotor 140 is Y, it is preferable that the first cam tooth 140aa and the second cam tooth 140ba are configured such that the relationship 0 < Y < X holds. And it is preferable that the first fixed cam surface 141a and the second fixed cam surface 142a are configured to be arranged at the minimum distance that does not inhibit the rotation of the rotor 140. Thereby, while reducing the minimum retraction amount M and thus the retraction amount m of the refill more, it is possible to ensure a larger required cost E.

[0108] By the way, considering the manufacturing tolerance, it is preferable that the cost E is 0.1 mm or more (E ≧ 0.1 mm). Regarding this, taking the case where the number of cam teeth is 40 and the outer diameter of the portions of the first cam surface 140a and the second cam surface 140b of the rotor 140 is 4.8 mm as described above. Also, various dimensions will be described corresponding to the rotation angle around the central axis of the mechanical pencil 1 or the rotor 140.

[0109] When the number of cam teeth is 40, the rotation angle α corresponding to half the phase of one cam tooth is 360 / 40 / 2 = 4.5°. The rotation angle β corresponding to the cost E of 0.1 mm is 2.4° from the relational expression 4.8 mm × π × β / 360 = 0.1. Referring to FIG. 10, considering an isosceles triangle with X = Y for the bottom side of the first cam tooth 140aa described above, when the apex of the first cam tooth 140aa is offset 1.2° to the left in the figure and the opposing first fixed cam tooth 141aa is offset 1.2° to the right in the figure, the relative total rotation angle becomes 2.4°, and the cost E becomes 0.1 mm. Regarding the length of the bottom side of the first cam tooth 140aa at this time, the rotation angle corresponding to X is 9.0° which is the rotation angle corresponding to one cam tooth, so 9.0 / 2 + 1.2 = 5.7°, and the rotation angle corresponding to Y is 9.0 / 2 - 1.2 = 3.3°. Therefore, in order to make E ≧ 0.1 mm, it is preferable that X / Y ≧ 5.7 / 3.3 = 1.72.

[0110] From the above, it is preferable that the first cam teeth 140aa and the second cam teeth 140ba are configured so that the relationship X / Y ≧ 1.72 is satisfied. Furthermore, in order to more reliably prevent rotation failure due to radial deviation of the rotor 140, it is more preferable that the first cam teeth 140aa and the second cam teeth 140ba are configured so that the relationship X / Y ≧ 2.0 is satisfied. Furthermore, even in the case of cam teeth having the above-mentioned relationship of X and Y, as described above, the retraction amount of the writing lead due to the retraction operation is preferably within the range of 0.05 to 0.3 mm, and more preferably within the range of 0.1 to 0.2 mm.

[0111] In the above embodiment, a suitable shape of the cam teeth, i.e., the relationship between X and Y, was described based on an example of the outer diameter, number of cam teeth, and inclination angle of the rotor 140, but the above-mentioned relationship between X and Y can be similarly applied to mechanical pencils with other outer diameters, numbers of cam teeth, etc. In other words, according to the above embodiment, in a mechanical pencil 1 equipped with a rotation drive mechanism that rotates the writing lead, the retraction amount of the writing lead can be further reduced. [Explanation of symbols]

[0112] 1 mechanical pencil 5 shaft cylinder 10 Chuck unit 20 Knock parts 31 Axle spring 40 Rotor 40a First cam surface 40aa 1st cam tooth 40b Second cam surface 40ba 2nd cam tooth 41 Upper cam forming member 41a First fixed cam surface 41aa 1st fixed cam tooth 42 Lower cam forming member 42a Second fixed cam surface 42aa Second fixed cam tooth 140 Rotor 140a First cam surface 140aa 1st cam tooth 140b Second cam surface 140ba 2nd cam tooth 141 Upper cam forming member 141a First fixed cam surface 141aa 1st fixed cam tooth 142 Lower cam forming member 142a Second fixed cam surface 142aa Second fixed cam tooth M Minimum retraction amount

Claims

1. A shaft cylinder, A chuck unit that allows the writing lead to move forward and prevents it from moving backward; a rotation drive mechanism having a rotor, which rotates the rotor in one direction in response to an axial retraction movement caused by a writing pressure applied to the writing core held by the chuck unit and an axial advancement movement caused by the release of the writing pressure; The mechanical pencil is characterized in that the retraction amount by the retraction operation is within a range of 0.05 to 0.3 mm.

2. 2. The mechanical pencil according to claim 1, wherein the recession amount is within a range of 0.1 to 0.2 mm.

3. the rotation drive mechanism includes a first annular cam surface formed on a rear end surface of the rotor, a second annular cam surface formed on a front end surface of the rotor, a first fixed cam surface provided on the shaft tube side and cooperating with the first cam surface to rotate the rotor, and a second fixed cam surface provided on the shaft tube side and cooperating with the second cam surface to rotate the rotor, 2. The mechanical pencil according to claim 1, wherein the first fixed cam surface and the second fixed cam surface are arranged at a minimum distance such that rotation of the rotor is not hindered.

4. a retraction movement of the chuck unit due to the writing pressure causes the first cam surface of the rotor to come into contact with the first fixed cam surface and engage with the rotor while rotating, and a release of the writing pressure causes the second cam surface of the rotor to come into contact with the second fixed cam surface and engage with the rotor while rotating, When the first cam surface of the rotor is engaged with the first fixed cam surface, the second cam surface and the second fixed cam surface are set in a relationship in which they are shifted by half a phase with respect to one tooth of a cam in the axial direction, and when the second cam surface of the rotor is engaged with the second fixed cam surface, the first cam surface and the first fixed cam surface are set in a relationship in which they are shifted by half a phase with respect to one tooth of a cam in the axial direction, the first cam surface includes first cam teeth, the second cam surface includes second cam teeth, the first fixed cam surface includes first fixed cam teeth cooperating with the first cam teeth, and the second fixed cam surface includes second fixed cam teeth cooperating with the second cam teeth; 4. The mechanical pencil according to claim 3, wherein the height of the second cam tooth or the second fixed cam tooth is equal to a distance traveled from a state in which the second cam surface and the second fixed cam surface are engaged to a state in which the tip of the first cam tooth abuts against the first fixed cam tooth due to the retraction movement of the rotor.

5. a retraction movement of the chuck unit due to the writing pressure causes the first cam surface of the rotor to come into contact with the first fixed cam surface and engage with the rotor while rotating, and a release of the writing pressure causes the second cam surface of the rotor to come into contact with the second fixed cam surface and engage with the rotor while rotating, When the first cam surface of the rotor is engaged with the first fixed cam surface, the second cam surface and the second fixed cam surface are set in a relationship in which they are shifted by half a phase with respect to one tooth of a cam in the axial direction, and when the second cam surface of the rotor is engaged with the second fixed cam surface, the first cam surface and the first fixed cam surface are set in a relationship in which they are shifted by half a phase with respect to one tooth of a cam in the axial direction, the first cam surface includes first cam teeth, the second cam surface includes second cam teeth, the first fixed cam surface includes first fixed cam teeth cooperating with the first cam teeth, and the second fixed cam surface includes second fixed cam teeth cooperating with the second cam teeth; 4. The mechanical pencil according to claim 3, wherein the first cam teeth are configured such that, with respect to a perpendicular line drawn from the apex, a length of a base side on a rear side in a rotation direction of the rotor is defined as X, and a length of a base side on a front side in a rotation direction of the rotor is defined as Y, such that a relationship of 0<Y<X is satisfied.

6. The mechanical pencil according to claim 1 , wherein the chuck unit is rotated by receiving a rotational driving force of the rotor, thereby rotating the writing lead.

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