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 sharp pencil.

Background Art

[0002] A rotary member including a slider having a chuck that allows the writing core to advance and prevents it from retracting, and a rotary drive mechanism that has a rotor and receives an axial retraction operation due to the writing pressure received by the writing core gripped by the chuck and an axial forward movement due to the release of the writing pressure, and rotates the rotor in one direction. The chuck is configured to rotate the writing core by receiving the rotational driving force of the rotor, and a sharp pencil is known (Patent Documents 1 and 2).

[0003] In a sharp pencil provided with a rotary drive mechanism as described in Patent Document 1, usually, in order to rotate the writing core, a forward movement and a backward movement of the writing core are performed slightly. A series of forward and backward movements of the writing core are collectively referred to as "cushion operation". In the sharp pencil described in Patent Document 1, for example, in the case of shorthand, paying attention to the problem that such a cushion operation, particularly the retraction of the writing core, is bothersome, the user can freely switch on and off the rotary drive mechanism. The cushion operation by the rotary drive mechanism will be described while referring to FIGS. 12 and 13.

[0004] FIG. 12 is a schematic diagram for explaining the rotational drive of the rotor 240 of a conventional rotary drive mechanism, and FIG. 13 is a schematic diagram for explaining the rotational drive of the rotor 240 following FIG. 12. The rotary drive mechanism has a rotor 240 formed in a cylindrical shape, an upper cam forming member 241 formed in a cylindrical shape, and a lower cam forming member 242 formed in a cylindrical shape. In FIGS. 12 and 13, on the rear end surface which is the upper surface of the rotor 240, a first cam surface 240a formed in a continuous sawtooth shape along the circumferential direction is formed in an annular shape, and on the front end surface which is the lower surface of the rotor 240, a second cam surface 240b formed in a continuous sawtooth shape along the circumferential direction is formed in an annular shape in the same manner as the rear end surface.

[0005] A first fixed cam surface 241a, which is continuously serrated along the circumferential direction, is also formed on the annular end face of the upper cam forming member 241, which faces the first cam surface 240a of the rotor 240. A second fixed cam surface 242a, which is continuously serrated along the circumferential direction, is also formed on the annular end face of the lower cam forming member 242, which faces 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 such that their circumferential pitches are substantially the same.

[0006] The rotary drive mechanism converts the retraction and advancement (cushioning) of the writing lead, based on the writing motion transmitted to the rotary drive mechanism, into rotational motion of the rotor 240. The rotational motion of the rotor 240 is transmitted to the chuck unit, which holds the writing lead, and therefore the writing lead held in the chuck unit also rotates.

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

[0008] Figure 12(B) shows the initial state when writing pressure is applied to the lead for writing with a mechanical pencil. In this state, the rotor 240 retracts against the biasing force of the spring as the chuck unit retracts. 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] Next, Figure 12(C) shows the state in which further writing pressure is applied to the writing lead, causing the rotor 240 to contact the first fixed cam surface 241a of the upper cam forming member 241 and slide backward. That is, the rotor 240 receives rotational drive equivalent to half a phase of one tooth of the first cam surface 240a. In this state, the first cam surface 240a of the rotor 240 is engaged with the first fixed cam surface 241a of the upper cam forming member 241.

[0010] The circles drawn in the center of the rotor 240 in Figures 12 and 13 indicate the amount of rotational movement of the rotor 240. In the state shown in Figure 12(C), the second cam surface 240b of the rotor 240 and the second fixed cam surface 242a of the lower cam forming member 242 are set to be half a phase offset with respect to one tooth of the cam in the axial direction.

[0011] Next, Figure 13(D) shows the initial state after writing with the mechanical pencil has finished and the writing pressure on the lead has been released. In this state, the rotor 240 moves forward due to the biasing force of the spring. As a result, the rotor 240 moves toward the lower cam forming member 242 and comes into contact with the second fixed cam surface 242a.

[0012] Next, Figure 13(E) shows the rotor 240 sliding forward while contacting 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 again receives rotational drive corresponding to half a phase of one tooth of the second cam surface 240b. In this state, 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.

[0013] Therefore, as indicated by the circle drawn in the center of the rotor 240, when the rotor 240 receives writing pressure, it reciprocates in the axial direction, i.e., moves back and forth, and the rotor 240 receives rotational drive corresponding to one tooth of the first cam surface 240a and the second cam surface 240b, and the writing lead held by it via the chuck unit is similarly driven to rotate. Thus, with each back and forth movement of the rotor 240 in the axial direction due to writing, the rotor 240 receives rotational movement corresponding to one tooth of the cam, and by repeating this, the writing lead is sequentially driven to rotate. Therefore, it is possible to prevent uneven wear of the writing lead as writing progresses, and to prevent large changes in line thickness and line darkness. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] Japanese Patent Publication No. 2022-073560 [Patent Document 2] International Publication No. 2007 / 142135 [Overview of the project] [Problems that the invention aims to solve]

[0015] As mentioned above, Patent Document 1 focuses on the problem of reduced writing feel due to the sometimes bothersome cushioning action, and solves this problem by allowing the rotation drive mechanism to be turned off as needed to prevent the cushioning action from occurring. However, Patent Document 1 does not identify the problem of rethinking the cushioning action itself. The forward movement of the writing lead occurs as the writing lead moves away from the writing surface during writing, so it is hardly noticeable to the user. On the other hand, the backward movement of the writing lead occurs because the body of the mechanical pencil moves forward even though the writing lead has been brought into contact with the writing surface to write; in other words, the writing lead moves backward relatively, which may cause the user to feel a visual or tactile discomfort.

[0016] In this regard, the inventors conducted a survey on mechanical pencils equipped with a rotational drive mechanism that rotates the writing lead, and compiled negative and positive opinions. Of the 21.4% of negative opinions, a remarkable 44.8% of users cited the retraction of the writing lead as the reason for their negative opinion. On the other hand, 78.6% of users evaluated such mechanical pencils positively, indicating that the function of rotating the writing lead is highly valued. Therefore, the inventors concluded that a cushioning action is necessary to rotate the writing lead using a rotational drive mechanism, but they came up with the idea of ​​further reducing the amount of cushioning action, in particular, reducing the amount of retraction of the writing lead to the absolute minimum.

[0017] The amount of cushioning action or the amount of retraction of the writing lead will be explained with reference to Figure 12(A). Let the height of the cam teeth be distance h, and let the distance d be the distance traveled from the tip of the cam teeth on the first cam surface 240a until it contacts the first fixed cam surface 241a due to the retraction of the rotor 240. The axial distance s between the rear end of the first cam surface 240a of the rotor 240, i.e., the tip of the peak of the cam teeth, and the valley of the cam teeth on the first fixed cam surface 241a of the upper cam forming member 241 corresponds to the amount of retraction of the writing lead in the cushioning action.

[0018] In Figure 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. Therefore, in order to disengage this engagement, at least the tip of the cam teeth on the second cam surface 240b must extend beyond the tip of the cam teeth on the second fixed cam surface 242a. In other words, the rotor 240, and consequently the writing lead, must be retracted by the distance h of the cam teeth. If the distance d is less 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 the rotor does not function as a rotational drive mechanism. Therefore, if the rotor 240 retracts further beyond the distance h of the cam teeth, the distance corresponding to the distance dh indicates that there is room to reduce the amount of retraction of the writing lead.

[0019] The present invention aims to provide a mechanical pencil equipped with a rotational drive mechanism for rotating the writing lead, which further reduces the amount the writing lead retracts. [Means for solving the problem]

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

[0021] In another embodiment, the amount of retraction is within the range of 0.1 to 0.2 mm.

[0022] In another embodiment, the rotational drive mechanism includes an annular first cam surface formed on the rear end surface of the rotor, an annular second cam surface formed on the front end surface of the rotor, a first fixed cam surface provided on the shaft side and cooperating with the first cam surface to rotate the rotor, and a second fixed cam surface provided on the shaft side and cooperating with the second cam surface to rotate the rotor, wherein the first fixed cam surface and the second fixed cam surface are arranged at the minimum distance that does not obstruct the rotation of the rotor.

[0023] In another embodiment, the retraction of the chuck unit due to the writing pressure causes the first cam surface of the rotor to contact the first fixed cam surface and engage while rotating the rotor, and when the writing pressure is released, the second cam surface of the rotor to contact the second fixed cam surface and engage while rotating the rotor, and in the 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 to be offset by half a phase with respect to one tooth of the cam in the axial direction, and the second cam surface of the rotor engages with the second fixed cam surface In this configuration, the first cam surface and the first fixed cam surface are set to be offset by half a phase with respect to one tooth of the cam in the axial direction, the first cam surface has a first cam tooth, the second cam surface has a second cam tooth, the first fixed cam surface has a first fixed cam tooth that cooperates with the first cam tooth, and the second fixed cam surface has a second fixed cam tooth that cooperates with the second cam tooth, and the height of the second cam tooth or the second fixed cam tooth is equal to the distance traveled from the state in which the second cam surface and the second fixed cam surface are engaged until the tip of the first cam tooth contacts the first fixed cam tooth due to the retraction movement of the rotor.

[0024] Also, according to another aspect, by the retraction 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, and 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. The first cam surface of the rotor and 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 when the first cam surface of the rotor is engaged with the first fixed cam surface. 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 shifted by half a phase with respect to one tooth of the 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 that cooperate with the first cam teeth, and the second fixed cam surface includes 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 rotational direction of the rotor is Y, the first cam teeth are configured such that the relationship of 0 < Y < X holds.

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

Advantages of the Invention

[0026] According to the aspect of the present invention, in a mechanical pencil provided with a rotational driving mechanism for rotating the refill, there is a common effect of providing a mechanical pencil with a further reduced retraction amount of the refill.

Brief Description of the Drawings

[0027] [Figure 1] FIG. 1 is a longitudinal sectional view of a mechanical pencil according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged sectional view of the first half of the mechanical pencil of FIG. 1. [Figure 3] Figure 3 is an enlarged cross-sectional view of the central portion of the mechanical pencil shown in Figure 1. [Figure 4] Figure 4 is a magnified view of a portion of the rotary drive mechanism. [Figure 5] Figure 5 is a diagram illustrating the rotational drive of the rotor of a rotary drive mechanism step by step. [Figure 6] Figure 6 is a schematic diagram illustrating the rotational drive of the rotor of a rotary drive mechanism step by step. [Figure 7] Figure 7 is a schematic diagram illustrating the relationship between each cam in a rotary drive mechanism. [Figure 8] Figure 8 illustrates the rotor misalignment. [Figure 9] Figure 9 illustrates a malfunction in the rotor's rotation. [Figure 10] Figure 10 is a schematic diagram illustrating the relationship between the cams in another rotary drive mechanism. [Figure 11] Figure 11 is a schematic diagram illustrating the rotational drive of the rotor of the rotary drive mechanism shown in Figure 10, step by step. [Figure 12] Figure 12 is a schematic diagram illustrating the rotational drive of a rotor in a conventional rotary drive mechanism. [Figure 13] Figure 13 is a schematic diagram illustrating the rotational drive of the rotor, following Figure 12. [Modes for carrying out the invention]

[0028] Embodiments of the present invention will be described in detail below with reference to the drawings. Throughout all drawings, corresponding components are denoted by the same reference numerals.

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

[0030] The mechanical pencil 1 has a front barrel 2, a rear barrel 3 that screws onto the outer circumferential surface of the rear end of the front barrel 2, and an inner cylinder 4 that fits onto the inner circumferential surface of the rear end of the rear barrel 3 and is equipped with a clip. The front barrel 2 and the rear barrel 3 constitute the barrel 5. The inner cylinder 4 may also be included in the term barrel 5. The mechanical pencil 1 is configured such that the writing lead protrudes from the tip of the barrel 5. The vicinity of 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 side with the writing lead is defined as the "front" side, and the side opposite to the writing lead is defined as the "rear" side.

[0031] A slider 7 is positioned inside the front end of the barrel 5 so as to be slidable in the axial direction and rotatable around the axis. The slider 7 is formed in a cylindrical shape, with its outer diameter tapering in a stepped manner towards the front. The aforementioned tip pipe 6 is attached to the front end of the slider 7. Behind the tip pipe 6 is a retaining chuck 8 with a through hole formed in the center. The through hole of the retaining chuck 8 slides against the outer surface of the writing lead and acts to temporarily hold the writing lead.

[0032] A cylindrical intermediate member 9 is screwed onto the rear end of the slider 7. Inside the slider 7 and the intermediate member 9 are a chuck unit 10 for gripping the writing lead and a lead case 13. The chuck unit 10 has a chuck body 11 and a cylindrical fastener 12 that surrounds the front end of the chuck body 11. At least the front half of the chuck 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. Each of the chuck pieces 11a is formed so that the front ends are spaced apart from each other. The lead case 13 is cylindrical and houses the writing lead inside. The rear end of the chuck body 11 is inserted into and fitted inside the front end of the lead case 13.

[0033] A coil spring 14 is positioned to surround the chuck body 11. The front end of the coil spring 14 is supported by a stepped portion 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 backward. When the chuck body 11 is biased backward, its front ends move closer together when it is housed in the clamp 12, maintaining a grip on the writing lead. Furthermore, when writing pressure is applied to the writing lead, the chuck body 11 retracts further and is housed in the clamp 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 affected by the clamp 12, so the writing lead can be pulled forward without resistance. In other words, 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 circumferential surface of the fastener 12 is fitted to the inner circumferential surface of the front end of the intermediate member 9. Therefore, the slider 7, intermediate member 9, and chuck unit 10 are movable in the axial direction within the shaft cylinder 5. The rear end of the intermediate member 9 is connected to a rotational 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 cylinder 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. A lead case 13 is inserted inside the front end of the knock member 20. An eraser 22 is detachably mounted inside the rear end of the knock member 20. A knock cover 23 is detachably attached to the outer circumferential surface of the rear end of the knock member 20 to protect the eraser 22 from dirt and other contaminants.

[0036] By performing a knock operation, which involves pressing the knock member 20 or knock cover 23 forward, the lead case 13 moves forward. This pushes the chuck body 11 forward. Consequently, the writing lead held by the chuck body 11 also moves forward, causing the writing lead to be fed out from the tip pipe 6. When the pressure from the knock operation is released, the knock member 20 retracts and returns to its original position due to the biasing force of the coil spring 21. At this time, the chuck body 11 retracts due to the biasing force of the coil spring 14. On the other hand, since the writing lead is held by the retaining chuck 8 located in the slider 7, the writing lead is pulled out from the chuck body 11 without resistance as an action of the chuck unit 10. As a result, the writing lead is fed out from the tip pipe 6, and a predetermined amount of the writing lead can be fed out each time the knock operation is repeated.

[0037] Figure 3 is an enlarged cross-sectional view of the central portion of the mechanical pencil 1 shown in Figure 1, and Figure 4 is a partially enlarged view of the rotary drive mechanism 30. The rotary drive mechanism 30 is located in the internal space of the rear shaft 3. The rotary drive mechanism 30 is connected to the rear end of the intermediate member 9. An axis spring 31 is positioned between the rear end surface of the front shaft 2 and the front end surface of the rotary drive mechanism 30, biasing the rotary drive mechanism 30 backward. The lead case 13 passes through the interior of the intermediate member 9 and the rotary drive mechanism 30, and is spaced apart from the rotary drive mechanism 30.

[0038] The rotary drive mechanism 30 includes a cylindrical rotor 40, a cylindrical upper cam forming member 41 which is a first cam forming member, a cylindrical lower cam forming member 42 which is a second cam forming member, a cylindrical cylinder member 43, a cylindrical torque canceller 44, and a coil-shaped cushion spring 45. These components are integrated into a single unit in the rotary drive mechanism 30.

[0039] The outer circumferential surface of the rear end of the intermediate member 9 is fitted to the inner circumferential surface of the front end of the rotor 40. Near the front end of the rotor 40, there is a flange-shaped portion with a slightly larger diameter, a first cam surface 40a is formed on the rear end surface of this portion, and a second cam surface 40b is formed on the front end surface of this 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 is fitted to the outer circumferential surface of the front end 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 of the lower cam forming member 42 facing the second cam surface 40b of the rotor 40.

[0041] The first cam surface 40a has a plurality of first cam teeth 40aa, the second cam surface 40b has a plurality of second cam teeth 40ba, the first fixed cam surface 41aa has a plurality of first fixed cam teeth 41aa, and the second fixed cam surface 42a has 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 orientation. The first cam teeth 40aa and the second cam teeth 40ba have the same shape but are symmetrical. The first cam teeth 40aa, the second cam teeth 40ba, and the first fixed cam teeth 41aa are arranged continuously without gaps along the circumferential direction on their respective corresponding cam surfaces. On the other hand, the second fixed cam teeth 42aa of the second fixed cam surface 42a have a similar shape that is larger than the first cam teeth 40aa, the second cam teeth 40ba, and the first fixed cam teeth 41aa. Furthermore, the second fixed cam teeth 42aa are arranged at equal intervals along the circumferential direction on the second fixed cam surface 42a, spaced apart from each other. 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 cylindrical cylinder member 43 is fitted to the outer circumferential surface of the rear end of the upper cam forming member 41. An insertion hole 43a is formed in the rear end of the cylinder member 43 through which the core case 13 can be inserted. A cylindrical torque canceller 44, which is movable in the axial direction, is arranged inside the cylinder member 43. A cushion spring 45 is arranged 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 biases the rotor 40 forward via the torque canceller 44.

[0043] Here, the intermediate member 9 transmits the retraction and advancement (cushioning) of the writing lead based on the writing motion to the rotary drive mechanism 30, i.e., the rotor 40, and also transmits the rotational motion of the rotor 40 in the rotary drive mechanism 30, which is generated by the cushioning motion, to the chuck unit 10, which is holding the writing lead. Therefore, the writing lead held in the chuck unit 10 also rotates as the intermediate member 9 rotates.

[0044] Except when writing with the mechanical pencil 1, that is, when no writing pressure is applied to the lead, the rotor 40 is positioned forward due to the biasing force of the cushion spring 45 via the torque canceller 44. Therefore, the second cam surface 40b of the rotor 40 contacts the second fixed cam surface 42a and engages with it. When writing with the mechanical pencil 1, that is, when writing pressure is applied to the lead, the chuck unit 10 retracts against the biasing force of the cushion spring 45, and the rotor 40 retracts accordingly. Therefore, the first cam surface 40a of the rotor 40 contacts the first fixed cam surface 41a and engages with it. The lead and the rotor 40 move forward, backward, or rotate as a single unit.

[0045] Figure 5 is a diagram illustrating the rotational drive of the rotor 40 of the rotary drive mechanism 30 in a step-by-step manner, and Figure 6 is a schematic diagram illustrating the rotational drive of the rotor 40 of the rotary drive mechanism 30 in a step-by-step manner. Figures 6(A) to (E) are schematic diagrams corresponding to Figures 5(A) to (E), respectively. Furthermore, Figures 5(A) to (E) and Figures 6(A) to (E) correspond to Figures 12(A) to (C) and Figures 13(D) and (E), respectively. Figure 6 partially shows the rotor 40, the upper cam forming member 41 and the lower cam forming member 42 in a circumferentially unfolded state. In addition, to make the cushioning operation easier to understand, the cam teeth of the rotor 40 are described as a single cam tooth unit U enclosed by the dashed line in Figure 4.

[0046] Since the second fixed cam tooth 42aa has a similar shape to the other cam teeth, from a functional standpoint it is substantially equivalent to a cam tooth that is continuously arranged with the same shape. Therefore, for example, in Figure 6 and Figure 7 described later, the second fixed cam tooth 42aa is schematically shown approximated as a cam tooth that is continuously arranged with the same shape as the other cam teeth, for ease of comparison with Figures 12 and 13. The second fixed cam tooth 42aa may also be arranged continuously along the circumferential direction with the same shape as the other cam teeth. Furthermore, although 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, they may also be arranged spaced apart along the circumferential direction, and from a functional standpoint they may be similar in shape to the other cam teeth.

[0047] Figures 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 is in contact with the second fixed cam surface 42a of the lower cam forming member 42 due to 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 half a phase shift with respect to one tooth of the cam in the axial direction.

[0048] Figures 5(B) and 6(B) show the initial state when writing pressure is applied to the lead for writing with the mechanical pencil 1. In this state, the rotor 40 retracts as the chuck unit 10 retracts, causing the cushion spring 45 to contract. 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] Next, Figures 5(C) and 6(C) show the state in which further writing pressure is applied to the writing lead, causing the rotor 40 to contact the first fixed cam surface 41a of the upper cam forming member 41 and slide backward. That is, the rotor 40 receives rotational drive equivalent to half a phase of one tooth of the first cam surface 40a. In this state, the first cam surface 40a of the rotor 40 is engaged with the first fixed cam surface 41a of the upper cam forming member 41.

[0050] The circle drawn in the center of the rotor 40 in Figure 5 indicates the amount of rotational movement of the rotor 40. In the state shown in Figure 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 be half a phase offset with respect to one tooth of the cam in the axial direction.

[0051] Next, Figures 5(D) and 6(D) show the initial state after writing with the mechanical pencil 1 has finished and the writing pressure on the lead has been released. In this state, the rotor 40 moves forward 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] Next, Figures 5(E) and 6(E) show the rotor 40 sliding forward while contacting 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 again receives rotational drive corresponding to half a 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 Figure 5, when the rotor 40 receives writing pressure, it reciprocates in the axial direction, i.e., moves back and forth, and the rotor 40 receives rotational drive corresponding to one tooth of the first cam surface 40a and the second cam surface 40b, and the writing lead held by it via the chuck unit 10 is similarly driven to rotate. Thus, with each back and forth movement of the rotor 40 in the axial direction due to writing, the rotor 40 receives rotational movement corresponding to one tooth of the cam, and by repeating this, the writing lead is sequentially driven to rotate. Therefore, it is possible to prevent uneven wear of the writing lead as writing progresses, and to prevent large changes in line thickness and line darkness. , below The following explanation is also applicable to mechanical pencils that have a rotational drive mechanism but are not configured to rotate the writing lead.

[0054] In short, the rotary drive mechanism 30 has an annular first cam surface 40a formed on the rear end surface of the rotor 40, an annular second cam surface 40b formed on the front end surface of the rotor 40, a first fixed cam surface 41a provided on the shaft cylinder 5 side that cooperates 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 that cooperates with the second cam surface 40b to rotate the rotor 40. The mechanism is configured such that when the chuck unit 10 retracts due to writing pressure, the first cam surface 40a of the rotor 40 comes into contact with the first fixed cam surface 41a and engages 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 engages 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 to be offset 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 to be offset by half a phase with respect to one tooth of the cam in the axial direction.

[0055] Furthermore, the torque canceller 44, which pushes the rotor 40 forward under the biasing force of the cushion spring 45, prevents the rotational motion of the rotor 40 from being transmitted to the cushion spring 45 by causing slippage between its front end surface and the rear end surface of the rotor 40. 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 generation of torsional unwinding (torque) of the cushion spring 45 that would hinder the rotational movement of the rotor 40.

[0056] In summary, the mechanical pencil 1 has a chuck unit 10 and a rotor 40, and is configured to allow the writing lead to be advanced by releasing and gripping the writing lead through the back-and-forth movement of the chuck unit 10. The chuck unit 10 is held inside the barrel 5 so as to be able to rotate around its 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] Figure 7 is a schematic diagram illustrating the relationship between each cam of the rotational drive mechanism 30, and is identical to Figure 6(A). The first cam teeth 40aa of the first cam surface 40a have a first inclined surface 40aa1 and a vertical surface 40aa2 corresponding to the second inclined surface, and the first cam surface 40aa is made into a continuous sawtooth shape by the first inclined surface 40aa1 and the vertical surface 40aa2 of adjacent first cam teeth 40aa. The first inclined surface 40aa1 is a surface inclined at an 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, that is, a surface perpendicular to the transverse direction. As described above, the second cam teeth 40ba of the second cam surface 40b and the first fixed cam teeth 41aa of the first fixed cam surface 41a have similar shapes.

[0058] The heights of the first cam tooth 40aa and the second cam tooth 40ba, and the height at which the second fixed cam tooth 42aa substantially meshes with the second cam tooth 40ba, correspond to the distance h in Figure 12(A), and are denoted 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 therefore equal to distance H. The distance traveled by the tip of the first cam tooth 40aa until it contacts the first fixed cam tooth 41aa due to the retraction of the rotor 40 corresponds to the distance d in Figure 12(A), and are denoted as distance D. The length of the first cam tooth 40aa along its circumferential direction is denoted as the length of the cam tooth L.

[0059] The first cam teeth 40aa have a radial thickness corresponding to the cylindrical rotor 40. Figures 6 and 7 schematically show the rotor 40, upper cam forming member 41, and lower cam forming member 42 in a circumferentially unfolded state. However, strictly speaking, the angles and dimensions differ slightly depending on which part of the radial thickness range of the first cam teeth 40aa is unfolded. Therefore, in Figures 6 and 7 and other descriptions in this specification, the angles and distances such as θ and L, as well as the positional relationships of other members, are defined assuming that the outermost part defining the outer diameter of the rotor 40 is unfolded in a circumferential direction.

[0060] In the rotary drive mechanism 30 of the mechanical pencil 1, the first fixed cam surface 41a and the second fixed cam surface 42a are positioned at the minimum distance that does not hinder 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, and the axial distance D between the tip of the first cam tooth 40aa and the first fixed cam tooth 41aa are configured to be equal.

[0061] More specifically, in Figure 7, which corresponds to Figures 5(A) and 6(A), the rotation of the rotor 40 is restricted by the locking of the second cam teeth 40ba on the second cam surface 40b and the second fixed cam teeth 42aa on the second fixed cam surface 42a. When the rotor 40 retracts by a distance H due to the retraction of the writing lead from this state, the locking of the second cam teeth 40ba and the second fixed cam teeth 42aa is released, thereby releasing the restriction on the rotation of the rotor 40. Furthermore, when the rotor 40 retracts by a distance D, the first inclined surface 40aa1 of the rotor 40 comes into contact with the first fixed cam teeth 41aa, thereby allowing the rotor 40 to rotate.

[0062] In short, the release of the restriction on the rotation of the rotor 40 and the contact between the first cam surface 40a and the first fixed cam surface 41a occur simultaneously, that is, the state where distance H and distance D are equal (D=H), is the state in which the first fixed cam surface 41a and the second fixed cam surface 42a are positioned at the minimum distance without hindering the rotation of the rotor 40. In other words, the amount of retraction m of the writing lead is minimized when distance H and distance D are equal. Taking into account manufacturing tolerances, etc., the distance D may be configured to be slightly longer than distance H. The minimum distance is determined by objectively or externally demonstrating the intention to not hinder the rotation of the rotor, taking manufacturing tolerances into consideration, and without considering wear due to the use of the mechanical pencil.

[0063] As described above, the first cam surface 40a and the first fixed cam surface 41a are positioned with a half-phase difference relative to one tooth of the cam. Therefore, the rotor 40 rotates by a distance of 1 / 2L and retracts by a distance of 1 / 2H from the state shown in Figures 5(B) and 6(B) to the state shown in Figures 5(C) and 6(C). In short, during the series of cushioning movements, the writing lead retracts by a distance of 3 / 2H (= 1 / 2H + H), and this is the minimum retraction amount m of the writing lead as the rotation drive mechanism 30. This geometrically determined minimum retraction amount m is defined as the minimum retraction amount M. Naturally, the amount of axial movement of the rotor 40 from the retracted state (Figures 5(C) and 6(C)) to the advanced state (Figures 5(E) and 6(E)), i.e., the amount of advance, is the same distance as the minimum retraction amount M, 3 / 2H.

[0064] Furthermore, focusing on the movement of the tips of the peaks of the second cam teeth 40ba on the second cam surface 40b, they move along trajectory T1 when they first retract, and then move along trajectory T2 due to subsequent rotation and retraction. The first cam teeth 40aa on the first cam surface 40a also move while tracing 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 the relationship H = Ltanθ holds. Therefore, by reducing the length L of the cam tooth or reducing the inclination angle θ, the distance H can be reduced, and as a result, the minimum retraction amount M can be reduced. Accordingly, the design of the inclination angle θ and the length L of the cam tooth will be explained.

[0066] The inclination angle θ is one factor that determines how easily the cam teeth slide against each other. 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 against each other, and therefore the rotor 40 will not rotate. If the inclination angle θ is too large, the distance H will become larger, and the minimum retraction amount M will also become larger. Taking into account the materials used in general for the writing instrument components, it is preferable that the inclination angle θ is within the range of 8 to 25°.

[0067] Generally, many components of writing instruments such as mechanical pencils are made of resins such as polypropylene or polyacetal. In particular, internal components with complex shapes that do not affect the appearance, such as the cam structure of the rotor 40, upper cam forming member 41, and lower cam forming member 42, are rarely made of metal. In order to ensure that the cooperative action of each cam tooth formed on these components, specifically the rotation of the rotor 40 while sliding against the upper cam forming member 41 or lower cam forming member 42, is more reliable, especially considering frictional resistance, an inclination angle θ greater than the friction angle is required for each cam tooth. For example, if the rotor 40, upper cam forming member 41, and lower cam forming member 42 are manufactured from polyacetal and their friction angle is 10.2°, then if the inclination angle θ is 10.2° or less, the cam teeth will not slide against each other, and therefore the rotor 40 cannot be rotated.

[0068] The length L of the cam teeth is calculated by determining the total circumference length from the outer diameter of the rotor 40 (outer diameter × π) and dividing it by the number of cam teeth. An example of the dimensional design of the outer diameter of the rotor 40 is described below. According to the JIS standard S6005 for mechanical pencil leads, a 0.5 mm writing lead is allowed up to an outer diameter of 0.58 mm. If multiple writing leads are to be housed in the lead case 13, the inner diameter of the lead case 13 must be at least 1.8 mm, for example, enough for three writing leads. From the standpoint of strength, the wall thickness of the cylindrical part of the resin component should be at least 0.5 mm. Therefore, the wall thickness of the lead case 13, the wall thickness of the rotor 40 surrounding the lead case 13, and the wall thickness of the part where the cam teeth are formed should each be 0.5 mm. Considering these wall thicknesses and the inner diameter of the lead case 13, the outer diameter of the first cam surface 40a and the second cam surface 40b of the rotor 40 will be 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 that rotates with one cushioning action. For example, if the number of cam teeth is 90, dividing 360° by 90 gives 4°, so the rotor 40 rotates by 4° with one cushioning action. Therefore, when writing 90 strokes, the writing lead rotates once.

[0070] If the number of cam teeth exceeds 90, the rotation angle becomes smaller, and the next writing occurs on the worn part of the lead. Therefore, the original purpose of a mechanical pencil with a rotation drive mechanism, which is to prevent uneven wear of the lead, cannot be achieved. On the other hand, if the number of cam teeth is less than 20, the length L of the cam teeth becomes larger. Therefore, from the relationship H = Ltanθ mentioned above, the distance H, which is the height of the cam teeth, becomes larger, and the minimum retraction amount M also becomes larger. For this reason, the number of cam teeth is preferably between 20 and 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 greater than the friction angle of 10.2°, then the length L of the cam teeth is approximately 0.17 mm, calculated as 4.8 × π / 90. Then, the distance H, which is the height of the cam teeth, is 0.03 mm, given by the relationship Ltanθ. As a result, the minimum retraction distance M is 0.05 mm, given by the relationship 3 / 2H.

[0072] Therefore, if the retraction distance m of the writing lead is smaller than the minimum retraction distance M of 0.05 mm, the inclination angle θ of the cam teeth becomes smaller, which may cause the cam teeth to not slide against each other and result in poor rotation, or the rotation angle of the rotor 40 becomes smaller, which may prevent the mechanical pencil equipped with a rotation drive mechanism from achieving its intended purpose. For this reason, it is preferable that the retraction distance m is 0.05 mm or more, which is the minimum retraction distance M.

[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 discomfort due to the retraction of the writing lead.

[0074] The inventors conducted a survey with 23 students, asking them to write with a mechanical pencil with a retraction distance m of 0.15 mm and a mechanical pencil with a retraction distance m of 0.3 mm without being told beforehand that there was a difference in retraction distance m. The results showed that all students noticed the difference. In short, it was found that users can perceive even a difference of just 0.15 mm. A smaller retraction distance m of the writing lead is preferable, but as mentioned above, if the retraction distance m is too small, there is a risk of rotation problems. In order to ensure reliable rotation of the rotor 40 and the writing lead while minimizing the user's discomfort from the retraction of the writing lead, it is preferable that the retraction distance m is 0.3 mm or less.

[0075] Based on the above, in a mechanical pencil 1 comprising a barrel 5, a chuck unit 10 that allows the writing lead to move forward and prevents it from moving backward, and a rotary drive mechanism 30 that rotates the rotor 40 in one direction in response to the axial backward movement caused by the writing pressure on 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 backward movement m of the writing lead is within the range of 0.05 to 0.3 mm.

[0076] As mentioned above, if the number of cam teeth is 90, the lead rotates only 4° with one cushioning action. For users with strong writing pressure, a large amount of lead is worn down with each writing stroke, so a 4° rotation may not be sufficient. To increase the rotation angle of the lead with each cushioning action, it is preferable to have 20 to 40 cam teeth. For example, if the number of cam teeth is 40, dividing 360° by 40 gives 9°, so the rotor 40 rotates 9° with one cushioning action. Therefore, when writing 40 strokes, the 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°, then the length L of the cam teeth is approximately 0.38 mm, calculated as 4.8 × π / 40. Then, the distance H, which is the height of the cam teeth, is 0.07 mm, calculated using the Ltanθ relationship. As a result, the minimum retraction distance M is 0.1 mm, calculated using the 3 / 2H relationship.

[0078] Therefore, a retraction amount m of 0.1 mm or more is preferable because it allows for sufficient lead rotation even for users with strong writing pressure. Furthermore, some users may tilt the mechanical pencil 1 extremely relative to the writing surface when writing. In such cases, a larger retraction amount m, that is, a longer cam tooth length L or a larger inclination angle θ, is preferable because it allows each cam tooth to work together reliably. For these reasons as well, a retraction amount m of 0.1 mm or more is preferable.

[0079] Incidentally, when writing small letters, the tip of the writing lead is closely observed and the sense of touch is heightened, so a retraction distance m of 0.2 mm or less is preferable. Furthermore, even with the same amount of cushioning, the sensation felt when writing with a 0.5 mm writing lead differs from the sensation felt when writing with a 0.3 mm writing lead. In other words, the sensation felt when writing with a 0.3 mm writing lead is more likely to feel unnatural because the distance the tip of the writing lead moves back and forth is relatively large relative to the thickness of the writing lead. For these reasons as well, a retraction distance m of 0.2 mm or less is preferable.

[0080] Based on the above, it is more preferable that the retraction distance m of the writing lead is within the range of 0.1 to 0.2 mm.

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

[0082] Furthermore, the cam teeth do not have to be continuous over the entire circumference. When considering the number of cam teeth, even if the cam teeth are not continuous over the entire circumference but are spaced apart, the number of virtual cam teeth can be calculated by dividing the total circumference by the circumferential length L of one representative cam tooth. For the sake of design efficiency, the number of cam teeth is preferably 20, 40, 60, and 90 for one full rotation of the rotor 40 (360°), with 40 being the most preferable from the viewpoint of reducing the retraction amount m.

[0083] In the embodiments described above, the minimum retraction amount M and the retraction amount m of the writing lead were explained based on an example of the outer diameter of the rotor 40, the number of cam teeth, and the inclination angle. However, the preferred range of the retraction amount m of the writing lead described above is similarly applicable to mechanical pencils with other outer diameters, number of cam teeth, etc. In other words, according to the embodiments described above, the retraction amount of the writing lead can be further reduced in a mechanical pencil 1 equipped with a rotational drive mechanism for rotating the writing lead.

[0084] By the way, shortening the length L of the first cam teeth 40aa means that the proportion of the total circumference accounted for by one first cam tooth 40aa is reduced. In other words, shortening the length L allows for an increase in the number of cam teeth. When 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 shifts radially, that is, their respective central axes shift, which may result in incomplete meshing of the cam teeth positioned in a direction perpendicular to the shifted direction. As a result, there is a possibility of malfunction in the rotation of the rotor 40. This will be explained with reference to Figures 8 and 9.

[0085] Figure 8 illustrates the misalignment of the rotor 40, and Figure 9 illustrates the malfunction of the rotor 40. Figure 8 schematically depicts the rotational drive mechanism 30 as viewed from the axial direction, with some exaggeration and disregard for scale. In Figure 8, the rotor 40 is shown to be misaligned upward by a distance g relative 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 located on the shaft cylinder 5 side, their central axes coincide, but only the central axis of the rotor 40 is misaligned by a distance g.

[0086] Figure 9(A) shows the relationship between the cams in section P1 of Figure 8, which is the position where the rotor 40 is most radially displaced. Figure 9(B) shows the relationship between the cams in section P2 of Figure 8, which is the position where the rotor 40 is most circumferentially displaced. In other words, section P1 is the part of the rotor 40 located in the direction of displacement, and section 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, in section P1 each cam tooth is arranged along the left-right direction in the figure, and in section P2 each cam tooth is arranged along the up-down direction in the figure.

[0087] Referring to Figure 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., perpendicular to the plane of the paper in the figure, compared to the state shown in Figure 6(A), with respect to the cam teeth of the upper cam forming member 41 and the lower cam forming member 42. Therefore, in section P1, there is no phase shift of the cam teeth, and thus there is almost no effect on the rotational drive of the rotor 40.

[0088] On the other hand, referring to Figure 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, relative to the cam teeth of the upper cam forming member 41 and the lower cam forming member 42, compared to the state shown in Figure 6(A). Normally, when the rotor 40 is retracted by writing, the first cam surface 40a of the rotor 40 contacts the first fixed cam surface 41a of the upper cam forming member 41 over a length of half the length of the first inclined surface 40aa1 of the rotor 40. That is, as shown in Figure 6(B), the engagement length E, which is the length of the contact portion in the circumferential direction, is 1 / 2L.

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

[0090] In short, the smaller the length L of the cam teeth is relative to the radial displacement g of the rotor 40, the higher the likelihood of rotational malfunction. Therefore, taking into account the radial displacement of the rotor 40, the length L of the cam teeth, and consequently the number of cam teeth, is appropriately determined within a range that allows for the aforementioned retraction amount m of the writing lead to be achieved.

[0091] Furthermore, the radial displacement of the rotor 40 largely depends on the clearance between the outer circumferential surface of the tip of the slider 7, to which the rotor 40 is connected via the intermediate member 9, and the inner circumferential surface of the front shaft 2 that surrounds the said outer circumferential surface. Since the clearance is due to manufacturing tolerances, it is preferable that at least the slider 7 be made of metal in order to enable more precise machining.

[0092] In the embodiment described above, the first cam teeth 40aa of the rotor 40 have 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 a similar shape. For example, the mechanical pencil described in Patent Document 1 has a similar shape. It is possible to rotate the rotor even if the cam teeth are not sawtooth-shaped. The shapes of other cam teeth will be described below.

[0093] Figure 10 is a schematic diagram illustrating the relationship between the cams of another rotary drive mechanism, and corresponds to Figure 7. The rotary drive mechanism shown in Figure 10 has a rotor 140, an upper cam forming member 141, and a lower cam forming member 142, and is interchangeable with the rotor 40, upper cam forming member 41, and lower cam forming member 42 of the rotary drive mechanism 30 described above.

[0094] The first cam teeth 140aa of the first cam surface 140aa have a first inclined surface 140aa1 and a second inclined surface 140aa2, and the first cam surface is formed by the first inclined surface 140aa1 and the second inclined surface 140aa2 of adjacent first cam teeth 140aaa. 1 40a is formed in a continuous mountain shape. The first inclined surface 140aa1 is a surface inclined at an angle θ with respect to the transverse direction perpendicular to the axial direction. The second cam teeth 140ba of the second cam surface 140b, the first fixed cam teeth 141aa of the first fixed cam surface 141a, and the second fixed cam teeth 142aa of the second fixed cam surface 142a also have the same shape as the first cam teeth 140aa.

[0095] Figure 11 is a schematic diagram illustrating the rotational drive of the rotor 140 of the rotational drive mechanism in Figure 10, step by step. Figures 11(A) to (E) are schematic diagrams corresponding to Figures 6(A) to (E), respectively, and the basic operation is the same. Figure 11 partially shows the rotor 140, the upper cam forming member 141, and the lower cam forming member 142 in a circumferentially unfolded state. Furthermore, to make the cushioning operation easier to understand, the cam teeth of the rotor 140 are described as a single cam tooth unit U, similar to Figure 6.

[0096] Figure 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 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 due to 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 half a phase shift with respect to one tooth of the cam in the axial direction.

[0097] Figure 11(B) shows the initial state when writing pressure is applied to the lead for writing with the mechanical pencil 1. In this state, the rotor 140 retracts as the chuck unit 10 retracts, causing the cushion spring 45 to contract. 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] Next, Figure 11(C) shows the state in which further writing pressure is applied to the writing lead, causing the rotor 140 to contact the first fixed cam surface 141a of the upper cam forming member 141 and slide backward. That is, the rotor 140 receives rotational drive equivalent to half a phase of one tooth of the first cam surface 140a. In this state, the first cam surface 140a of the rotor 140 is engaged with the first fixed cam surface 141a of the upper cam forming member 141.

[0099] Next, Figure 11(D) shows the initial state after writing with the mechanical pencil 1 has finished and the writing pressure on the lead has been released. In this state, the rotor 140 moves forward 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] Next, Figure 11(E) shows the rotor 140 sliding forward while contacting 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 again receives rotational drive corresponding to half a phase of one tooth of the second cam surface 140b. In this state, the second cam surface 140b of the rotor 140 is engaged with the second fixed cam surface 142a of the lower cam forming member 142.

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

[0102] The calculation of the minimum retraction amount M will be explained with reference to Figure 10. While the height of the sawtooth-shaped cam tooth shown in Figure 7 is distance H, the height of the mountain-shaped cam tooth shown in Figure 10 is distance H'. In Figure 10, the sawtooth-shaped cam tooth shown in Figure 7 is shown by a dashed line. The distance traveled by the tip of the first cam tooth 140aa until it contacts the first fixed cam tooth 141aa due to the retraction of the rotor 140 is denoted as distance D. The length of the first cam tooth 140aa along its circumference is denoted as the length of the cam tooth L. Considering the triangle of the first cam tooth 140aa, when a perpendicular line is drawn from the vertex to the base to divide the length L, the length of the rear base with respect to the rotation direction of the rotor 140 (left direction in the figure) is denoted as X, and the length of the front base with respect to the rotation direction of the rotor 140 is denoted as Y.

[0103] The distance H of the sawtooth-shaped cam tooth and the distance H' of the ridge-shaped cam tooth are geometrically related by H' = HX / (X+Y). Furthermore, considering the multiple auxiliary lines J of the second cam tooth 140ba in Figure 10, the distance D is D = H - 2H(Y / (X+Y)) = H(XY) / (X+Y). From these, the minimum retraction amount M is related by M = 1 / 2H + D = 1 / 2H + H(XY) / (X+Y) = H(3X-Y) / {2(X+Y)} = H'(3X-Y) / (2X). Therefore, the relationship M = 3 / 2H' - H'Y / (2X) is obtained. In the case of a sawtooth-shaped cam tooth with a height of distance H shown in Figure 7, since Y is zero, according to the above relationship, the minimum retraction amount M = 3 / 2H.

[0104] Furthermore, focusing on the movement of the tips of the peaks of the second cam teeth 140ba on the second cam surface 140b, they move along trajectory T3 when they first retract, and then move along trajectory T4 due to subsequent rotation and retraction. The first cam teeth 140aa on the first cam surface 140a also move while tracing a similar trajectory.

[0105] The first cam tooth 140aa forms an isosceles triangle when X=Y, and such a cam tooth is disclosed in Figure 4 of Patent Document 2. In this case, from the relationship minimum retraction amount M=3 / 2H'-H'Y / (2X), the minimum retraction amount M=H', and the minimum retraction amount M is minimized. However, as is clear when considering the case X=Y with reference to Figure 10, the vertex of the first cam tooth 140aa and the vertex of the first fixed cam tooth 141aa are positioned opposite each other. Therefore, the engagement amount E becomes minute or point-like, and even a slight radial misalignment of the rotor 140 may cause rotational problems.

[0106] Therefore, it is preferable that Y is smaller than X. Also, from the above relationship, the minimum retraction amount M can be made smaller if the first cam tooth 140aa is not a sawtooth-shaped first cam tooth 40aa which is a right triangle as shown in Figure 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, when 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 the first fixed cam surface 141a and the second fixed cam surface 142a are preferably configured to be arranged at the minimum distance that does not inhibit the rotation of the rotor 140. Thereby, while reducing the minimum retreat amount M, and thus the retreat amount m of the refill, it is possible to ensure a larger necessary cost E.

[0108] By the way, considering the tolerance during manufacturing, it is preferable that the cost E is 0.1 mm or more (E ≧ 0.1 mm). Regarding this, taking the number of cam teeth as 40, and as described above, considering the case where 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. Also, various dimensions will be described in correspondence with the rotation angle around the central axis of the mechanical pencil 1 or the rotor 140. <​​​​​​Based on the above, it is preferable that the first cam teeth 140aa and the second cam teeth 140ba are configured such that X / Y ≥ 1.72. Furthermore, in order to more reliably prevent rotational failure due to radial displacement of the rotor 140, it is even more preferable that the first cam teeth 140aa and the second cam teeth 140ba are configured such that X / Y ≥ 2.0. In addition, even in the case of cam teeth with the above-described X and Y relationship, as described above, it is preferable that the amount of retraction of the writing lead due to the retraction operation is in the range of 0.05 to 0.3 mm, and more preferably in the range of 0.1 to 0.2 mm.

[0111] In the embodiments described above, a suitable cam tooth shape, i.e., the relationship between X and Y, was explained based on an example of the outer diameter, number of cam teeth, and inclination angle of the rotor 140. However, the relationship between X and Y described above is similarly applicable to other mechanical pencils with different outer diameters, number of cam teeth, etc. In other words, according to the embodiments described above, the amount of retraction of the writing lead can be further reduced in a mechanical pencil 1 equipped with a rotational drive mechanism for rotating the writing lead. [Explanation of Symbols]

[0112] 1. Mechanical pencil 5 shaft cylinder 10 Chuck Units 20 Knock Member 31 Axle spring 40 rotors 40a First cam surface 40aa First cam tooth 40b Second cam surface 40ba Second cam tooth 41 Upper cam forming member 41a First fixed cam surface 41aa First fixed cam teeth 42 Lower cam forming member 42a Second fixed cam surface 42aa Second fixed cam teeth 140 rotor 140a First cam surface 140aa First cam tooth 140b Second cam surface 140ba Second cam tooth 141 Upper cam forming member 141a First fixed cam surface 141aa First fixed cam teeth 142 Lower cam forming member 142a Second fixed cam surface 142aa Second fixed cam teeth M Minimum retraction amount

Claims

1. The barrel and, A chuck unit that allows the writing lead to move forward and prevents it from moving backward, The device comprises a rotor and a rotational drive mechanism that rotates the rotor in one direction in response to the axial retraction movement caused by the writing pressure applied to the writing lead held by the chuck unit and the axial advancement movement caused by the release of the writing pressure, The amount of retraction due to the aforementioned retraction movement is within the range of 0.05 to 0.3 mm. The rotational drive mechanism includes an annular first cam surface formed on the rear end surface of the rotor, an annular second cam surface formed on the front end surface of the rotor, a first fixed cam surface provided on the shaft side that cooperates with the first cam surface to rotate the rotor, and a second fixed cam surface provided on the shaft side that cooperates with the second cam surface to rotate the rotor. A mechanical pencil characterized in that the first fixed cam surface and the second fixed cam surface are arranged at the minimum distance that does not obstruct the rotation of the rotor.

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

3. The retraction of the chuck unit due to the writing pressure causes the first cam surface of the rotor to contact the first fixed cam surface, engaging while the rotor rotates, and the release of the writing pressure causes the second cam surface of the rotor to contact the second fixed cam surface, engaging while the rotor rotates. 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 to be offset by half a phase with respect to one tooth of the 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 to be offset 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, The mechanical pencil according to claim 1, wherein the height of the second cam tooth or the second fixed cam tooth is equal to the distance traveled from the state in which the second cam surface and the second fixed cam surface are engaged until the tip of the first cam tooth contacts the first fixed cam tooth due to the retraction movement of the rotor.

4. The retraction of the chuck unit due to the writing pressure causes the first cam surface of the rotor to contact the first fixed cam surface, engaging while the rotor rotates, and the release of the writing pressure causes the second cam surface of the rotor to contact the second fixed cam surface, engaging while the rotor rotates. 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 to be offset by half a phase with respect to one tooth of the 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 to be offset 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, The mechanical pencil according to claim 1, wherein in the first cam teeth, if the length of the rear base with respect to the rotation direction of the rotor is X and the length of the front base with respect to the rotation direction of the rotor is Y with respect to a perpendicular line drawn from the vertex, the first cam teeth are configured such that 0 < Y < X.

5. The mechanical pencil according to any one of claims 1 to 4, wherein the chuck unit is configured to rotate by receiving the rotational driving force of the rotor, thereby causing the writing lead to rotate.

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