Mechanical pencil

A chuck unit (4) for grasping a writing lead (10) and a rotor (6) arranged to be movable in a direction of rotation and an axial direction within a body cylinder (1) are provided. First and second cam faces (6a) and (6b) are respectively formed at one end face and another end face of the rotor in the axial direction, and first and second fixed cam faces (13a) and (17a) are arranged on the body cylinder side to face the first and second cam faces respectively. The first cam face in the rotor is brought into abutment with and meshed with the first fixed cam face by retreat operation of the chuck unit under writing pressure, and the second cam face in the rotor is brought into abutment with and meshed with the second fixed cam face by releasing the writing pressure, so that the rotor rotates, whereby the writing lead also rotates.

TECHNICAL FIELD

The present invention relates to a mechanical pencil which can rotate a writing lead (refill lead) by writing pressure.

BACKGROUND ART

In the case of writing with a mechanical pencil, it is generally often the case that the mechanical pencil is not used in a situation where a body cylinder is perpendicular to a writing side (page), but used in a situation where the body cylinder is somewhat inclined to the writing side. In the case where the body cylinder is thus inclined, there arises a phenomenon that a drawn line becomes bold as compared with that in the beginning, since the writing lead may locally abrade as the writing proceeds. Further, not only the drawn line changes in boldness, but also there arises a phenomenon that the drawn line changes in thickness (drawn line becomes thin) as the writing proceeds, since a contact area of the writing lead changes with respect to the writing side.

In order to avoid the above-mentioned problem, when the writing is carried out with the body cylinder being rotated, then it is possible to avoid such a problem that, as described above, the drawn line becomes bold as it is drawn, since a sharper side of the writing lead is in contact with the page when writing. However, when you write down with the body cylinder being rotated, there arises a problem in that operation of re-holding the body cylinder is required while the writing proceeds, leading to considerable reduction in writing efficiency.

In that case, it is not impossible to write down by re-holding the body cylinder and rotating it in a stepwise manner, in the case where exterior of the body cylinder is formed to be cylindrical. However, in the case of the mechanical pencil whose exterior may not be cylindrical and which may be designed to have a projection in the middle or which is a side-knock-type mechanical pencil, it is difficult to write by re-holding the body cylinder to be rotated in a stepwise manner as described above.

In order to solve such a problem, as described above, patent documents 1 and 2 disclose that a main part of a mechanical pencil is provided with a small motor, reduction gears, etc., so that a writing lead is gradually rotated according to writing operation.

Patent Document 2: Japanese Utility Model Publication (KOKOKU) S52-50828

DISCLOSURE OF THE INVENTION

Object of the Invention

Incidentally, according to the mechanical pencil disclosed in the above-mentioned patent documents 1 and 2, it is necessary for the main part of the mechanical pencil to have the small motor, the reduction gears, etc. as described above, and also the necessity arises to install a battery etc. in order to rotationally drive the small motor.

Therefore, the cost of a product unavoidably increases, and the whole mechanical pencil is large in size and increases in weight, leading to very poor user-friendliness.

The present invention arises in view of the above-mentioned problems with the mechanical pencil disclosed in patent documents, and aims at providing a light-weight mechanical pencil in which a rotational drive mechanism allowing a writing lead to be rotated using writing pressure is provided, and which does not substantially have the necessity of changing an existing exterior shape.

Means for Solving the Problems

The mechanical pencil in accordance with the present invention made in order to solve the above-mentioned problem is a mechanical pencil which is arranged such that a chuck unit provided in a body cylinder reciprocates so as to grasp and release a writing lead to inch the writing lead forward, wherein the chuck unit is held within the body cylinder so as to rotate about a lead axis in a situation where the writing lead is grasped, a rotational drive mechanism is provided in which the chuck unit is retreated by writing pressure of the writing lead so as to rotationally drive a rotor, and rotational motion of the rotor is transmitted to the writing lead through the chuck unit.

In a first preferred embodiment, the rotor which constitutes the rotational drive mechanism is formed into the shape of a ring and first and second cam faces are respectively formed at one end face and another end face of the rotor in an axial direction, first and second fixed cam faces arranged on the body cylinder side are provided to face the first and second cam faces, respectively, the first cam face in the ring-shaped rotor is brought into abutment with and meshed with the first fixed cam face by retreat operation of the chuck unit by way of the writing pressure, and the second cam face in the ring-shaped rotor is brought into abutment with and meshed with the second fixed cam face by releasing the writing pressure, the second cam face on the rotor side and the second fixed cam face are arranged to have a half-phase shifted relationship with respect to one tooth of a cam in the axial direction in a situation where the first cam face on the rotor side is meshed with the first fixed cam face, and the first cam face on the rotor side and the first fixed cam face are arranged to have the half-phase shifted relationship with respect to one tooth of the cam in the axial direction in a situation where the second cam face on the rotor side is meshed with the second fixed cam face.

In this case, it is preferable that a spring member is provided which biases the second cam face in the ring-shaped rotor into abutment with the second fixed cam face and brings the second cam face and the second fixed cam face to mesh with each other in a situation where the writing pressure is released.

Further, in the first embodiment, it is possible to arrange the rotor including the chuck unit to bring, by weight of the rotor, the second cam face of the ring-shaped rotor into abutment with and to mesh with the second fixed cam face in a situation where the writing pressure is released.

In a second preferred embodiment of the mechanical pencil in accordance with the present invention, first and second legs are arranged at one end face and another end face, in an axial direction, of the rotor which constitutes the rotational drive mechanism at acute angles with respect to the faces, respectively, and first and second groove formation sides are disposed on the body cylinder side and selectively engage with tips of the first and second legs; when the rotor moves to a first position in the axial direction by retreat operation of the chuck unit under the writing pressure, the first leg engages with the first groove formation side and rotationally steps the rotor in one direction; when the rotor returns to a second position in the axial direction by release of the writing pressure, the second leg engages with the second groove formation side and rotationally steps the rotor in the same direction.

In this case, it is desirable to have a spring member for biasing the rotor so as to return to the second position in the axial direction in a situation where the writing pressure is released.

Further, in the second embodiment, it is also possible to arrange the weight of the rotor including the chuck unit to cause the rotor to return to the second position in the axial direction in a situation where the writing pressure is released.

Furthermore, in a third preferred embodiment of the mechanical pencil in accordance with the present invention, the rotor which constitutes the rotational drive mechanism is formed into the shape of a ring, a cam face is formed at an end face of the rotor in an axial direction thereof, and the ring-shaped rotor moves to a first position in the axial direction by retreat operation of the chuck unit under the writing pressure, and returns to a second position in the axial direction by release of the writing pressure; a fixed abutting member arranged on the body cylinder side which comes into abutment with a slope of the cam face, and rotationally steps the rotor in one direction by movement of the ring-shaped rotor to the first position, and a movable abutting member which moves in the axial direction in the case where the ring-shaped rotor moves to the second position, while being in contact with the slope of the cam face, and rotationally steps the rotor in the same direction.

It is preferable that the fixed abutting member and the movable abutting member in the above-mentioned structure are respectively formed at tips of first and second cylindrical members which are formed cylindrically and arranged coaxially within the body cylinder, the second cylindrical member having the movable abutting member is disposed within the first cylindrical member having the fixed abutting member, and the second cylindrical member is arranged to be movable in an axial direction within the first cylindrical member by combination of grooves and ribs mutually formed in the axial direction at the first cylindrical member and second cylindrical member.

In this case, it is desirable that a spring member which returns the ring-shaped rotor to the second position is arranged to bias the second cylindrical member forward in a situation where the writing pressure is released.

Further, in the third embodiment, the movable abutting member can be arranged to be brought into abutment with the cam face of the ring-shaped rotor by weight of the second cylindrical member in a situation where the above-mentioned writing pressure is released.

In the first to the third embodiments in which the spring member for returning the position of the rotor upon release of the writing pressure is used, it is desirable that a torque canceller which is formed cylindrically is interposed between the rotor and the spring member so as to prevent the rotational motion of the rotor from being transmitted to the spring member.

EFFECT OF THE INVENTION

According to the mechanical pencil having the above-described structure, there are advantages in that the rotational drive mechanism is provided in which the chuck unit is retreated under the writing pressure of the writing lead so as to rotationally drive the rotor. According to the first preferred embodiment, with application of the writing pressure, the rotor moves in the axial direction, and is subjected to rotational motion when the first cam face of the rotor is brought to mesh with the first fixed cam face. Further, as the writing pressure is released, the rotor returns to the original position, and then operates so as to bring the second cam face of the rotor to mesh with the second fixed cam face so as to be subjected to the rotational motion in the same direction.

Therefore, when the rotor is reciprocated in the axial direction by writing, the rotor is subjected to the rotational motion corresponding to one tooth of the cam. By repeating this operation, the writing lead is rotationally driven stepwise. Thus, it is possible to provide the rotational drive mechanism having a simple structure, in which the writing lead can be rotated by writing.

Further, according to the above-mentioned second embodiment, with application of the writing pressure, the rotor moves in the axial direction, and the first leg attached to the rotor engages with the first groove formation side arranged at the body cylinder side, so as to rotationally step the rotor in one direction. Further, when the writing pressure is released, the rotor returns to the original position, and the second leg attached to the rotor engages with the second groove formation side arranged at the body cylinder side, so as to rotationally step the rotor in the same direction.

Therefore, when the rotor is reciprocated in the axial direction by writing, the rotor is subjected to the rotational motion corresponding to bending of the leg. By repeating this operation, the writing lead is rotationally driven stepwise. Thus, it is possible to provide another rotational drive mechanism having a simple structure, in which the writing lead can be rotated with writing.

Furthermore, according to the above-mentioned third embodiment, with application of the writing pressure, the rotor moves in the axial direction, so that the fixed abutting member provided on the body cylinder side comes into abutment with the cam face formed at the rotor, so as to rotationally step the rotor in one direction. Further, when the writing pressure is released, the movable abutting member slides in the axial direction in contact with the cam face of the rotor, so as to rotationally step the rotor in the same direction.

Therefore, when the rotor is reciprocated in the axial direction by writing, the rotor is subjected to the rotational motion by the action of the fixed abutting member which abuts a cam face thereof and the movable abutting member. By repeating this operation, the writing lead is rotationally driven stepwise. Thus, it is possible to provide another rotational drive mechanism having the simple structure in which the writing lead can be rotated with writing.

According to the mechanical pencil of the above-mentioned first to third embodiments, with application of the writing pressure, the writing lead can be rotated in any of the embodiments, so that local abrasion of the writing lead can be controlled effectively even in the mechanical pencils which may be designed to have a projection in the middle of the body cylinder as described above or which may be difficult to write by re-holding and rotating the body cylinder of a “side-knock-type” mechanical pencil. Thus, it is possible to prevent the local abrasion of the writing lead according to the progress of the writing and to solve the problem that the thickness of a drawn line and the boldness of the drawn line may change badly.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a mechanical pencil in accordance with the present invention will be described with reference to the embodiments illustrated in the drawings. Firstly,FIGS. 1-3show a first preferred embodiment.FIG. 1shows a principal part of a mechanical pencil which is partly broken, and partially seen through. Reference numeral1denotes a body cylinder which constitutes the exterior, and reference numeral2indicates a base attached to a tip portion of the body cylinder1, i.e., a plastic base molded conically with a resin.

A cylindrical lead case3is accommodated coaxially within the body cylinder1, and a chuck unit4is connected with a tip portion of the lead case3. The chuck unit4is mounted so that its tip portion may be in a loose fit state in an annular clamp5, and the clamp5is attached to a ring-shaped tip portion of a rotor6.

The mechanical pencil shown inFIG. 1is arranged to have a so-called pipe slide structure where a slider8is accommodated in the tip portion of the plastic base2, and a holding chuck9made of rubber is accommodated in the slider8. Further, a linear lead inserting hole is so formed as to pass through the inside of the slider8via the chuck unit4from the above-mentioned lead case3, and a writing lead (refill lead)10is inserted into the inserting hole.

In the mechanical pencil shown inFIG. 1, when knock operation of a knock part (not shown) which is disposed at a rear end portion of the body cylinder1is carried out, the lead case3advances in the body cylinder1. The tip of the chuck unit4projects from the clamp5to cancel a grasp state of the writing lead10. With cancellation of the knock operation, the lead case3and the chuck unit4retreat in the body cylinder1by the action of a return spring12, and the tip portion of the chuck unit4is accommodated in the clamp5, thus the writing lead10again comes into the grasp state. In other words, the writing lead10is grasped and released when the chuck unit4moves back and forth by repeating the knock operation, whereby the writing lead operates to inch forward from the chuck unit4stepwise.

The rotor6shown inFIG. 1is formed into a ring shape where a central part in the axial direction is larger in diameter. A first cam face6ais formed at one end face (rear end face), and a second cam face6bis formed at the other end face (front end face) which is formed into a ring shape. On the other hand, at the rear end of the rotor6, a cylindrical upper cam formation member13is mounted in the body cylinder1so as to cover the rear end of the rotor6. At the front end of the upper cam formation member13, a fixed cam face (also referred to as “first fixed cam face”)13ais formed so as to face the first cam face6ain the rotor6.

Furthermore, although not shown inFIG. 1, a cylindrical lower cam formation member is mounted on the body cylinder1side so as to face the second cam face6bin the rotor6, and a fixed cam face (also referred to as “second fixed cam face”) is formed at the rear end in the axial direction. In addition, a relationship and mutual operation among the first and the second cam faces6aand6bwhich are formed at the rotor6, the first fixed cam face13a, and the second fixed cam face will be described in detail later with reference toFIGS. 2 and 3.

Further, a coil-like spring member14is mounted in the upper cam formation member13. The spring member14acts so as to bias forward a torque canceller15which is formed cylindrically and movable in the axial direction. Being pushed by the torque canceller15subjected to this bias force, the rotor6moves forward.

According to the above-mentioned structure, in a situation where the chuck unit4grasps the writing lead10, the rotor6together with the chuck unit4is accommodated in the body cylinder1so as to be rotatable about a lead axis. Further, in a situation where the mechanical pencil is not in use (or not in writing state), the rotor6is biased forward by the action of the spring member14through the torque canceller15, resulting in a situation shown inFIG. 1.

On the other hand, when the mechanical pencil is used, i.e., when the writing pressure is applied to the writing lead10, the chuck unit4retreats against the bias force of the spring member14. According to this operation, the rotor6also retreats in the axial direction. Therefore, the first cam face6aformed at the rotor6shown inFIG. 1engages with and meshes with the first fixed cam face13a.

FIGS. 2(A) to 2(C)andFIGS. 3(D) and 3(E)are for explaining in order the operation of a rotational drive mechanism which rotationally drives the rotor6by the above-mentioned operation. InFIGS. 2 and 3, reference numeral6indicates the above-mentioned rotor which is schematically shown, and at one end face thereof (upper face in figures) the first cam face6ahaving a continuous sawtooth shape along a circumference direction is formed into the shape of a ring. Further, similarly, the second cam face6bhaving a continuous sawtooth shape along the circumference direction is formed into the shape of a ring at the other end face (lower face in figures) of the rotor6.

On the other hand, as shown inFIGS. 2 and 3, the first fixed cam face13ahaving a continuous sawtooth shape along the circumference direction is also formed at a ring-shaped end face of the upper cam formation member13, and a second fixed cam face17ahaving a continuous sawtooth shape along the circumference direction is also formed at a ring-shaped end face of the lower cam formation member17. The cam faces formed into the sawtooth shape along the circumference direction at the first cam face6aand the second cam face6bformed at the rotor, the first fixed cam face13aformed at the upper cam formation member13, and the second fixed cam face17aformed at the lower cam formation member17are each arranged to have substantially the same pitch.

FIG. 2(A)shows a relationship among the upper cam formation member13, the rotor6, and the lower cam formation member17in the situation where the mechanical pencil is not in use (or not in writing state). In this situation, by the bias force of the spring member14shown inFIG. 1, the second cam face6bformed in the rotor6is brought into abutment with the second fixed cam face17aside of the lower cam formation member17mounted at the body cylinder1. At this time, the first cam face6aon the rotor6side and the first fixed cam face13aare arranged to have a half-phase (half-pitch) shifted relationship with respect to one tooth of the cam in the axial direction.

FIG. 2(B)shows an initial situation where the writing pressure is applied to the writing lead10by use of the mechanical pencil. In this case, as described above, the rotor6retreats in the axial direction while the chuck unit4retreats. Thus, the rotor6moves to the upper cam formation member13side mounted at the body cylinder1.

FIG. 2(C)shows a situation where the writing pressure is applied to the writing lead10by use of the mechanical pencil and the rotor6comes into abutment with the upper cam formation member13side and retreats further. In this case, the first cam face6aformed at the rotor6meshes with the first fixed cam face13aon the upper cam formation member13side. Thus, the rotor6is subjected to rotational drive corresponding to the half-phase (half-pitch) with respect to one tooth of the first cam face6a.

In addition, circle (◯) drawn in the center of the rotor6inFIGS. 2 and 3indicates the amount of rotational movement of the rotor6. In the situation shown inFIG. 2(C), the second cam face6bon the rotor6side and the second fixed cam face17aare arranged to have a half-phase (half-pitch) shifted relationship with respect to one tooth of the cam in the axial direction.

Next,FIG. 3(D)shows an initial situation where drawing with the mechanical pencil is finished and the writing pressure to the writing lead10is released. In this case, the rotor6moves forward in the axial direction by action of the spring member14. Thus, the rotor6moves to the lower cam formation member17(side) mounted at the body cylinder1.

Furthermore,FIG. 3(E)shows a situation where the rotor6comes into abutment with the lower cam formation member17side and moves forward further by action of the spring member14. In this case, the second cam face6bformed at the rotor6meshes with the second fixed cam face17aon the lower cam formation member17side. Thus, the rotor6is subjected again to the rotational drive corresponding to the half-phase (half-pitch) of one tooth of the second cam face6b.

Therefore, as shown by circle (◯) drawn in the center of the rotor6, according to reciprocating movement of the rotor6in the axial direction, the rotor6is subjected to the rotational drive corresponding to one tooth (one pitch) of the first and second cam faces6aand6b, and the writing lead10grasped by the chuck unit4is rotationally driven through the chuck unit4similarly.

As is clear from the above description, according to the mechanical pencil having the structure as illustrated inFIGS. 1 to 3, each time the writing causes the rotor6to reciprocate in the axial direction, the rotor is subjected to the rotational motion corresponding to one tooth of the cam. By repeating this operation, the writing lead10is rotationally driven stepwise. Therefore, it is possible to prevent the writing lead from locally abrading as the writing proceeds, and it is also possible to solve the problem that the boldness of the drawn line and the thickness of the drawn line may change badly.

In addition, the cylindrical torque canceller15disposed between the rotor6and the coil-like spring member14generates a slide between the end face of the torque canceller15and the end face of the rotor6, and acts so that the rotational motion of the rotor6generated by repetition of the writing action is prevented from being transmitted to the spring member14.

In other words, since the torque canceller formed cylindrically is interposed between the rotor and the spring member, the rotational motion of the rotor is prevented from being transmitted to the spring member, and it is possible to solve the problem that back torsion (spring torque) of the spring member14occurs and places an obstacle to rotation operation of the rotor6.

In the first embodiment as described above, as for the first cam face6a, the second cam face6b, the first fixed cam face13a, and the second fixed cam face17a, the cam faces are arranged to have the continuous sawtooth shape in the circumferential direction, however the rotational drive mechanism for rotating the writing lead is not limited to such a specific arrangement.

FIG. 4schematically shows another example of the above-mentioned rotational drive mechanism.FIG. 4(A)shows a state similar to the operation state as already described and shown inFIG. 2(A), andFIG. 4(B)shows a state similar to the operating state as shown inFIG. 2(C). Further, inFIG. 4, like reference signs indicate like parts which achieve like functions as shown inFIG. 2.

As shown inFIG. 4, the first cam face6ain which there are continuous undulations whose upslopes and downslopes have substantially the same inclination to the axial direction is formed into the shape of a ring at one end face (upper face in figure) of the rotor6. Further, the second cam face6bin which there are continuous undulations similarly is also formed in the shape of a ring at the other end face (lower face in figure).

Further, the cam faces in which there are continuous undulations whose upslopes and downslopes have substantially the same inclination to the axial direction are also formed at the first fixed cam face13aformed at the end face of the upper cam formation member13facing the first cam face6a, and at the second fixed cam face17aformed at the end face of the lower cam formation member17.

Except in the case where the mechanical pencil is in the writing state, as shown inFIG. 4(A), the bias force of the spring member14brings the rotor6into abutment with the second fixed cam face17aside formed at the end face of the lower cam formation member17mounted at the body cylinder1side. Therefore, the second cam face6bof the rotor6engages with and meshes with the second fixed cam face17a. At this time, the first cam face6aon the rotor side and the first fixed cam face13aare arranged to have the half-phase shifted relationship with respect to one tooth of the cam in the axial direction.

On the other hand, in the case where the mechanical pencil is used, that is, in the case of the writing state, the rotor6retreats in the axial direction as described above. As shown inFIG. 4(B), the rotor6moves towards and meshes with the first fixed cam face13aside formed at the upper cam formation member13mounted on the body cylinder1side. At this time, therefore, the rotor6is rotationally driven by an angle corresponding to the half-phase of one tooth formed at the cam.

As shown inFIG. 4(B), in the situation where the first cam face6ais brought to mesh with the first fixed cam face13a, the second cam face6bon the rotor6side and the above-mentioned second fixed cam face17aare arranged to have the half-phase shifted relationship with respect to one tooth of the cam in the axial direction. At this time, therefore, it returns to the state as shown inFIG. 4(A)in the case where the writing pressure is released, and the rotor6is again rotationally driven by an angle corresponding to the half-phase of one tooth formed at the cam.

In other words, also in the rotational drive mechanism with the structure shown inFIG. 4, it is possible to obtain the operational effect similar to that of the rotational drive mechanism shown inFIGS. 2 and 3.

Further, in the embodiment described above, the spring member14shown inFIG. 1is used. In the case where the writing pressure is released, it is arranged that the bias force of the spring member14causes the rotor6to return to the state before application of the writing pressure and to apply the rotational motion to the rotor. Thus, in the case where the spring member is used, the rotation operation of the rotor is stabilized, which is preferred. However, the return action of the rotor6in the case of the released writing pressure can be carried out by the weight of the rotor6including the above-mentioned chuck unit, without using the spring member14. Thus, in the case of using gravity, it is possible to contribute to simplifying the mechanism and reduction in cost.

FIGS. 5-7show a second embodiment of the mechanical pencil in accordance with the present invention. In addition,FIG. 5shows the principal part of the second embodiment which is partially seen through, where like reference signs indicate like parts equivalent to the respective parts in the embodiment shown inFIG. 1. Further, a basic structure for realizing the inching operation of the writing lead in the mechanical pencil etc., is similar to that shown inFIG. 1, therefore its description will not be repeated.

Also in this second embodiment, the rotor21formed in the shape of a ring is provided. This rotor21together with the chuck unit4is disposed in the body cylinder (not shown) so as to be rotatable about the lead axis and movable in the axial direction. The first and second legs21aand21bare disposed on one end face and the other end face of the rotor21in the axial direction and at acute angles to the above-mentioned faces, respectively. In addition, a plurality of the first legs21aare molded at substantially regular intervals along one annular end face at the rotor21, and a plurality of the second legs21bare similarly molded at substantially regular intervals along the other annular end face at the rotor21.

As illustrated inFIGS. 6 and 7in detail, an end face of a cylinder body22is located facing the tip of the first leg21a, and this end face constitutes a first groove formation side22a. Further, an end face of a cylinder body23is located facing the tip of the above-mentioned second leg21b, and this end face constitutes a second groove formation side23a. In addition, sawtooth-like projections are radially formed at the first and second groove formation sides22aand23aalong the circumferential direction. Further, the cylinder bodies22and23are mounted on the body cylinder side (not shown).

On the other hand, a coil-like spring member25is provided that biases forward the rotor21and the chuck unit4which move integrally. In the case where the pressure by the writing is applied, the chuck unit4retreats against the bias force of the spring member25. With this operation, the rotor21operates to retreat in the axial direction. In addition, the cylindrical lead case is disposed inside the spring member25, which is not shown.

In the above-mentioned structure, when the mechanical pencil is used or when the writing pressure is applied, the chuck unit4retreats against the bias force of the spring member25. With this operation, the rotor21also retreats in the axial direction. In other words, as shown inFIG. 6, since the rotor21moves in a direction of arrow a (moves to first position), the first leg21aengages with the first groove formation side22aand bends, so as to rotationally step the rotor21in a direction of arrow b.

Further, in the case where the writing pressure is released, the chuck unit4and the rotor21are returned in a direction of arrow c (moves to second position) as shown inFIG. 7by the action of the spring member25. Thus, the second leg21bengages with the second groove formation side23aand bends, so as to rotationally step the rotor21in the direction of arrow b.

Therefore, when the rotor21is reciprocated in the axial direction by the writing, the rotor21is subjected to the rotational motion corresponding to the bending of the leg. By repeating this operation, the writing lead10is rotationally driven stepwise. Therefore, it is possible to prevent the writing lead from locally abrading as the writing proceeds, and also possible to obtain the operational effect similar to that in the first embodiment as already described.

In addition, also in the above-mentioned second embodiment, a cylindrical torque canceller denoted by reference numeral24inFIG. 6is provided. Since the torque canceller24is interposed between the rotor21and the spring member25, the rotational motion of the rotor21is prevented from being transmitted to the spring member25, thereby making it possible to solve the problem that the back torsion (spring torque) of the spring member25occurs and places the obstacle to rotation operation of the rotor21.

Further, also in the above-mentioned second embodiment, the spring member25shown inFIGS. 5 and 6is used. In the case where the writing pressure is released, it is arranged such that the bias force of the spring member25causes the rotor21to return to the state before application of the writing pressure and to apply the rotational motion to the rotor. Thus, in the case where the spring member25is used, the rotation operation of the rotor is stabilized, which is preferred. However, the return action of the rotor21in the case of the released writing pressure may be carried out by the weight of the rotor21including the above-mentioned chuck unit, without using the spring member25. Thus, in the case of using gravity, it is possible to contribute to simplifying the mechanism and reduction in cost.

FIGS. 8-15show a third embodiment of the mechanical pencil in accordance with the present invention. In addition,FIG. 8shows the principal part of the third embodiment which is partially seen through, where like reference signs indicate like parts equivalent to the respective parts in the embodiment shown inFIG. 1. Further, a basic structure for realizing the inching operation of the writing lead in the mechanical pencil etc., is similar to that shown inFIG. 1, therefore its description will not be repeated.

Also in this third embodiment, as shown inFIG. 8, the rotor31formed in the shape of a ring is provided. This rotor31together with the chuck unit4is disposed in the body cylinder (not shown) so as to be rotatable about the lead axis and movable in the axial direction. As shown inFIG. 9andFIG. 10in which the rotor31and its circumference portion are enlarged and shown, sawtooth-like protrusions are formed radially and continuously at the rear end of the rotor31in the axial direction, to thereby form a cam face31a.

On the other hand, the first cylindrical member32is mounted inside the body cylinder (not shown). As shown inFIGS. 9 and 10, a fixed abutting member32aconstituted by two sawtooth-like protrusions is formed at a front end of the cylindrical member32so as to face the cam face31aof the rotor31. In addition, the fixed abutting member32ais enlarged and indicated by solid lines inFIG. 11et seq. as will be described later. Further, a plurality of the fixed abutting members32aare formed at the front end of the cylindrical member32at substantially regular intervals in the circumference direction.

The second cylindrical member33is accommodated coaxially inside the first cylindrical member32. The second cylindrical member33is arranged to be slidable in the axial direction inside the first cylindrical member32. In other words, as shown inFIGS. 9 and 10, it is arranged that a plurality of grooves32bare formed in the axial direction on an inner wall surface of the first cylindrical member32, a plurality of ribs33bare formed in the axial direction on an outer wall surface of the second cylindrical member33, and each rib33bis inserted into a respective one of the grooves32b, whereby the second cylindrical member33can slide in the axial direction inside the first cylindrical member32.

Isosceles triangle-like movable abutting members33aare formed at the front end of the second cylindrical member33so as to face the cam face31aof the rotor31. In addition, at the front end of the cylindrical member33, a plurality of the movable abutting members33aare formed at substantially regular intervals in the circumferential direction. The second cylindrical member33is arranged to be subjected to the bias force so as to be pushed out forward by the coil-like spring member34disposed at the rear end in the axial direction as shown inFIGS. 8 and 9. Thus, the movable abutting member33aformed at the second cylindrical member33is always in abutment with the cam face31aof the rotor31and acts so as to bias the rotor31forward.

FIGS. 11-15are for explaining in order how the cam face31aformed at the rotor31is rotationally driven by the fixed abutting member32aand the movable abutting member33adue to the reciprocation of the rotor31in the axial direction according to the writing.

First,FIG. 11shows a situation where the writing pressure is not applied. In this situation, being subjected to the action of the spring member34, the movable abutting member33acomes into abutment with the cam face31aof the rotor31, and the rotor31together with the chuck unit4moves forward (second position) inside the body cylinder. Next,FIG. 12shows a situation in the middle of operation in the case where the writing pressure is applied. By the action of writing pressure, the rotor31moves backward via the chuck unit4inside the body cylinder. Thus, the movable abutting member33amoves backward while compressing the spring member34, and further the cam face31aformed at the rotor31comes into abutment with the fixed abutting member32a.

Next,FIG. 13shows a situation where the rotor31(cam face31a) is moved back (first position) further after being subjected to the writing pressure. The cam face31ais pushed against the fixed abutting member32aas shown by arrow d and a sawtooth-like face of the cam face31arelatively moves in a direction as shown by arrow e with the result that the rotor31is subjected to the rotational drive corresponding to a horizontal component of force shown by arrow e.

Thus, the chuck unit4is also rotationally driven in the same direction, and the writing lead10grasped by the chuck unit4is rotated similarly. In addition, in this situation, although not shown inFIG. 13, the isosceles triangle-like movable abutting member33apasses over one tooth at the sawtooth-like cam face31a, and is brought into abutment with a sawtooth-like face of the next tooth in a direction of rotation.

FIG. 14shows an initial situation where the writing pressure is released. The movable abutting member33awhich is subjected to the action of the spring member34moves forward, thereby releasing the meshing of the sawtooth-like cam face31awith the fixed abutting member32a. As shown inFIG. 15, when the movable abutting member33ais still subjected to the action of the spring member34and moves forward, a slope of the movable abutting member33ais pushed against the cam face31aas shown by arrow f, so that the sawtooth-like face of the cam face31arelatively moves in a direction shown by arrow g. As a result, the rotor31is subjected to the rotational drive corresponding to a horizontal component of force as shown by arrow g.

Therefore, the chuck unit4is also rotationally driven in the same direction, and the writing lead10is rotated similarly. In other words, one operation cycle of the application and release of the writing pressure causes the rotor31to be stepped corresponding to one sawtooth of the cam face31a. By repeating this operation, the writing lead10is rotationally driven stepwise. Therefore, it is possible to prevent the writing lead from locally abrading as the writing proceeds, and also possible to obtain the operational effect similar to that in the first embodiment as already described.

In addition, in the above-mentioned third embodiment, the second cylindrical member33arranged to be slidable in the axial direction operates to play the role of the torque canceller as described in the above-mentioned first and second embodiments. In other words, the second cylindrical member33is interposed between the rotor31and the spring member34, and operates to prevent the rotational motion of the rotor31from being transmitted to the spring member34. Thus, it is possible to solve the problem that the back torsion (spring torque) of the spring member34occurs and places the obstacle to rotation operation of the rotor31.

In the above-mentioned third embodiment, the spring member34shown inFIGS. 8 and 9is used. In the case where the writing pressure is released, it is arranged that the bias force of the spring member34brings the movable abutting member33awhich is formed at the second cylindrical member33, into abutment with the cam face31aof the rotor31to apply the rotational motion to the rotor.

Thus, in the case where the spring member34is used, the rotation operation of the rotor is stabilized, which is preferred. However, the rotational operation of the rotor34in the case of the released writing pressure can be carried out by the weight of the second cylindrical member33without using the spring member34. Thus, in the case of using gravity with respect to the second cylindrical member, it is possible to contribute to simplifying the mechanism and reduction in cost.