LEAD CHUCK OF MECHANICAL PENCIL

Abstract: A lead holding part (62) is formed with several teeth (63) for use in holding the lead under four-point or six-point contacted condition. In this manner lead dust discharging regions are made. The extremity end (41) of the lead supplying cylinder is abutted against the rear raised surface (601) of the flange part (6A) from the rear end side of the lead chuck, forces applied from both directions when the front raised surface (602) of the flange part (6A) receive the rear end of the resilient member (12) installed between it and the sleeve (7) are utilized and each of the chuck members (61) generates a flexing phenomenon and then the chuck members may perform an instantaneous expanding operation under this flexing force.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a lead chuck constituting a lead feeding mechanism of a mechanical pencil, and more particularly a lead chuck of a mechanical pencil in which a relative sliding between a lead holding part of the lead chuck and an outer circumference of a lead is prevented, a biting action against the lead is positively performed, and even if an outer circumference of the lead is scraped by the lead holding part, the biting against the lead is positively performed and at the same time a clogging caused by lead dust or the like is prevented. Description of the Prior Art In general, a lead chuck of a mechanical pencil is installed between a lead pipe arranged at a rear end of a shaft and a slider arranged at an extremity end of the shaft. The lead chuck is constructed such that three-divided chuck pieces equally divided into three portions through slots in an axial direction at the extremity end are integrally formed, and these chuck pieces are merely formed by a repetitive cutting works over three times of each of the slots or by injection molding a complex mold so as to make a lead chuck. The above-mentioned lead chuck of a type of three-divided end portions shows a reduction in its productivity and a substantial cost-up due to the fact that its manufacturing and working method such as a cutting work or an injection molding or the like is complicated as described above. Since a mere forming of three-divided lead holding part with slots does not show any sufficient lead holding force, it is sometimes found that a tooth part having some lead biting teeth is formed. However, forming of such teeth causes a complex shape and structure of the lead chuck in addition to the above-mentioned structure. Thus, in such a case, after the slot forming operation is carried out, the teeth must be formed by tapping operation or the like, resulting in that an efficiency of operation is substantially deteriorated. In view of the foregoing, it is proposed by the present applicant to provide a lead chuck of two-divided full separate structure in place of the above-mentioned lead chuck of three-divided structure with slotted extremity end. The lead chuck of this two-divided full separate type is constructed such that two chuck members having small cylindrical cylinder axially divided into two separate portions and having approximate similar shape are integrally assembled in such a way as their divided surfaces are contacted to each other so as to hold a lead therein. In order to hold the lead, the divided surfaces of the above-mentioned chuck members are formed with a lead insertion hole along their axial directions at a substantial central part, and at the extremity ends of these chuck members are formed lead holding small diameter holes. Each of the outer circumferences of the chuck members is provided with a ball holding part for setting positions of balls guided by an inner circumferential tapered surface of the chuck fastening member at the extremity end to fasten and hold the chuck member, and at the rear end is formed each of the resilient means engaging flanges in a semi-circumferential form for resiliently biasing against the sleeve. The divided surfaces positioned to correspond to the semi-circumferential flanges are formed some supporting points for use in expanding or retracting each of the chuck members of the lead chucks in a forward or rearward direction. Further, at each of the rear end portions of the chuck members is formed an outer circumferential tapered surface for use in expanding an extremity end of the chuck member when the rear end of the chuck member is pushed out in a rearward direction by knocking a knock part projected and arranged at an axial rear end of th e mechanical pencil. According to the two-divided full separate type lead chuck constructed as described above, it is possible to eliminate disadvantages such as a reduction in productivity or an increased cost of manufacturing or the like, to perform a simultaneous formation of the lead holding teeth even in case of forming of the teeth when the chuck member is to be formed by using an injection molding or the like, for example, and further to assure an easiness in manufacturing process and a sufficient lead holding force at the lead holding teeth. However, even if the above-mentioned conventional type of lead chuck of a mechanical pencil is used, it shows a so-called lead diameter reducing phenomenon in which teeth formed at the lead holding part at each of the chuck portions may cut an outer circumference of the lead as the mechanical pencil is used in sequence and so irrespective of intending to make a positive holding of the lead under formation of the teeth at best, a lead holding force is gradually decreased and so the sliding of lead may occur. The above-mentioned lead chuck in the mechanical pencil of a rear end knock type, the mechanical pencil of automatic knock type receiving a foot-light in recent years in which a pressing pressure of the extremity end of the lead against the surface of a writing paper and a lead is automatically fed when a writing pressure is loosened during a writing operation, and a mechanical pencil of extremity end knock type used together with this automatic lead feeding type mechanical pencil or to be used independently and a desired amount of lead projection can be got in case of lack of projection amount of the lead, an outer circumference of the lead is cut by the teeth of the lead chuck divided surfaces and the lead is further reduced in its diameter to cause a reduction in holding force due to the reasons that a particular strong holding force is required and a writing pressure of a writer is utilized during the pressing of the pencil against the writing sheet or its releasing state or the like. Such an occurrence of a phenomenon of reducing diameter of the lead in which an outer circumference of the lead is cut by the teeth as described above causes the lead dusts cut to be accumulated in a clearance of the lead insertion hole of the lead chuck or another clearance between the lead chuck and the sleeve or the like, resulting in that various lead feeding operations such as a rear end knock, automatic lead feeding and an extremity end knock or the like is delayed due to clogging of the lead dust, an operation characteristic is deteriorated and in the worst state, the lead feeding function is not operated at all. Particular examples of prior art mechanical pencil chucks are disclosed in EP-A-146128, EP-A-88318 and US-A-4571105. EP-A-146128 describes a lead chuck comprising two juxtaposed chuck members, adjacent surfaces of which define a lead insertion hole and are provided at their forward ends with lead holding parts, the forward end of the chuck being expandable by relative pivotal movement of the chuck members, the chuck having means for receiving the rear end of a resilient biasing member and means for receiving the forward end of a receiving element of a lead supplying cylinder, the pivotal motion, in use, being effected by abutment of the forward end of the receiving element against the chuck and biasing of the chuck in a rearward direction by reception of the rear end of the biasing member. The lead holding part of the chuck comprises a continuation of the lead insertion hole, the lead holding part and the lead insertion hole forming a continuous groove of uniform, semi-circular cross section. There are also provided, at the lead holding part, a plurality of transversely disposed semi-circular teeth which span the width of the groove. EP-A-88318 describes a similar arrangement to the above but which, rather than having a plurality of teeth at the lead holding part, has a groove which is shallower than the lead insertion hole. EP-A-215584, cited as prior art under Article 54(3) EPC, discloses in Fig. 34 thereof a chuck according to claim 1 hereof for Spain, but in which the first teeth at the lead holding part span the entire width of the groove by traversing the lower surface thereof. Finally, US-A-4571105 describes a chuck having the features discussed above with reference to EP-A-146128. SUMMARY OF THE INVENTION This invention has been invented in order to resolve the above-mentioned problems and establishes the following objects. It is a first object of the present invention to provide a lead chuck of a mechanical pencil in which the structure of lead holding teeth of a lead chuck is made such that only the same portions of an outer circumferential part of the lead are not held, a cutting of the outer circumference of the lead with the teeth formed at the lead holding part at each of the extremity ends of the chuck part is not performed irrespective of a use of mechanical pencil of longer period, a so-called reduction in a diameter of lead can be prevented, a sliding of the lead is not generated and the lead holding teeth having a superior lead holding force are provided. It is a second object of the present invention to provide a lead chuck for a mechanical pencil in which the above-mentioned phenomenon of reducing diameter of a lead can be prevented even in case of a lead chuck requiring a special strong lead holding force as found in an automatic lead feeding mechanical pencil receiving a foot-light in recent years or an extremity end knock type mechanical pencil as well as in a rear end knock type mechanical pencil, and further a positive lead feeding characteristic in these automatic or semi-automatic mechanical pencil and a smooth writing caused by difficulty in breaking of the lead can be promoted. It is a third object of the present invention to provide a lead chuck for a mechanical pencil in which a phenomenon of reducing diameter of a lead of which outer circumference is cut by the teeth formed on the above-mentioned lead holding surface is prevented, thereby the lead dust cut can be prevented from being clogged in a lead insertion hole of the lead chuck or between the lead chuck and the sleeve, and so various lead feeding operations such as a rear end knock, an automatic lead feeding and an extremity end knock or the like can be smoothly performed and at the same time an occurrence of troubles in these lead feeding mechanisms can be reduced or completely eliminated. It is a fourth object of the present invention to provide a lead chuck for a mechanical pencil in which an expanding operation of the lead chuck for releasing a lead held condition is performed positively, smoothly and rapidly by the stepped projections formed at an approximate displacement of 900 at a semi-circumferential flange arranged to correspond to the supporting points positioned at the divided surfaces of the chuck and the extremity end of the stopper applying an expanding flexing force under an abutment against the projections at the rear end, thereby some disadvantages such as the above-mentioned lead diameter reducing phenomenon and the phenomenon of clogging of lead dust are resolved together with the improvement of the teeth for use in holding the lead and its operating characteristic can be improved. According to the invention, there is provided a chuck according to claim 1 hereof. Preferably, each lead holding part further comprise a plurality of second teeth, interposed between adjacent first teeth and formed on at least the bottom surface of said groove which, in combination with said first teeth, in use, hold the outer circumference of a lead in a six point contacted condition and whose biting surfaces lie substantially at right angles to the longitudinal axis of the chuck. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic section for showing a first preferred embodiment of a lead chuck of a mechanical pencil of the present invention. Fig. 2 is an enlarged development perspective view for showing a lead chuck of a first preferred embodiment of Fig. 1. Fig. 3 is also a section for showing a lead chuck of a first preferred embodiment of Fig. 1. Fig. 4 is also a top plan view for showing a lead chuck of a first preferred embodiment. Fig. 5 is a section taken along a line V-V of Fig. 4. Fig. 6 is a section taken along a line VI-VI of Fig. 4. Fig. 7 is a section taken along a line VII-VII of Fig. 3 for illustrating a lead holding condition of a lead holding part. Fig. 8 is a top plan view for showing one of the chucks in Fig. 7 in a partially enlarged state. Fig. 9 is a partial enlarged development view for showing a lead holding part of Fig. 7. Fig. 10 is an enlarged view for showing the teeth of Fig. 9. Fig. 11 illustrates a second preferred embodiment of a lead chuck for a mechanical pencil of the present invention and an enlarged section for showing a different shape of the teeth. Fig. 12 illustrates a third preferred embodiment of a lead chuck for a mechanical pencil of the present invention and is an enlarged section for showing a different shape of the teeth. Fig. 13 illustrates a fourth preferred embodiment of a lead chuck of a mechanical pencil of the present invention and is an entire section for showing an assembled condition of the lead chuck into the mechanical pencil having a stepped expanding projection at a semi-circumferential flange of the chuck member. Fig. 14 is an enlarged front elevational view partly in section for showing a state in which the lead chuck of a fourth preferred embodiment together with the sleeve and the stopper. Fig. 15 is also an enlarged development perspective view for showing a face-to-face condition of the chuck member of a fourth preferred embodiment. Fig. 16 is a section for showing the chuck member of a fourth preferred embodiment. Fig. 17 is also a top plan view for showing the chuck member. Fig. 18 is also a front elevational view for showing a chuck member. Fig. 19 is a front elevational view for showing a condition in which a lead chuck is constructed by assembling the two chuck members under their slid condition. Fig. 20 is a section taken along a line F-F of Fig. 19. Fig. 21 is also a section taken along a line G-G of Fig. 19. Fig. 22 is a top plan view for showing a shape of the teeth in a chuck member. Fig. 23 is a perspective view partly in section for showing a ball holding part for a chuck member. Fig. 24 is a top plan view for showing a fifth preferred embodiment of a lead chuck of a mechanical pencil of the present invention. Fig. 25 is a top plan view for showing a sixth preferred embodiment of a lead chuck of a mechanical pencil of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, some preferred embodiments of the lead chuck of the mechanical pencil of the present invention will be described in detail. Figs. 1 to 10 illustrate a first preferred embodiment, wherein the lead chuck of the preferred embodiment is, as illustrated in Fig. 1, arranged at an extremity end of an outer cylinder 1 of the mechanical pencil. To the extremity end of the outer cylinder 1 is engaged a tip element 2 by torsion operation, and within a part near the extremity end of the outer cylinder 1 is arranged a lead supplying cylinder 3 which can be slid in an axial forward direction. To the extremity end of the lead supplying cylinder 3 is fitted an extremity end receiving element 4, and to the extremity end of the extremity end receiving element 4 is arranged a lead feeding mechanism 5 with a spacing of an inter-contact distance (a). The extremity end receiving element 4 pushes a lead chuck 6 to be described later and has an extremity end hole 4a to be engaged with the chuck. The lead chuck is slidably stored in a substantial cylindrical sleeve 7, and a part 4b projected and formed at any location of an outer circumferential part of the extremity end hole 4a of the extremity end receiving element 4 is slidably fitted to a longitudinally extending guide groove 7a punched axially at a rear end of the sleeve 7. The lead feeding mechanism 5 is substantially composed of a two-divided full separate type lead chuck 6, a sleeve 7 having the lead chuck installed therein and its rear end slidably engaged with the extremity end of the extremity end receiving element 4, an intermediate frame 8 arranged at an outer circumference of the sleeve 7 and slidably holding the sleeve 7, a front cylinder 9 fitted to the extremity end of the intermediate frame 8, a chuck fastening element 10 for use in fastening the lead chuck 6 from an outer circumferential direction of the extremity end of the lead chuck 6, fastening balls 11 installed between an inner circumferential tapered surface 10a of the chuck fastening element 10 and the lead chuck 6, and a first resilient body 12 installed between a flange part 7b formed at an inner circumferential surface at the front end of the sleeve 7 for use in biasing the lead chuck 6 in a reward direction against the sleeve 7 and an engaging stepped part 6a as semi-circumferential flange projected and formed at an outer circumference at a rear end of the lead chuck 6. The sleeve 7 and the intermediate frame 8 are integrally formed in such a way as the sleeve 7 may slide axially within the intermediate frame 8 while the rearward movement of the sleeve 7 is being limited by the large diameter circumferential stepped part 7c of the sleeve 7 and the large diameter inner circumferential stepped part 8a of the intermediate frame 8. The outer circumferential side of the intermediate frame 8 is provided with sliding guide projections 8b, for example, at two locations of opposing outer circumferential surface, this projection 8b is slidably fitted to a guide groove la formed at a corresponding position of the inner circumferential surface of the outer cylinder 1 acting as a shaft of the mechanical pencil. Further, the front end side of the chuck fastening element 10 is provided with ball receiving portion 10b for use in preventing balls 11 from being disengaged from a space between the tapered surface 10a and the chuck member 6. The structure of the mechanical pencil at its extremity end is made such that the extremity end of the intermediate frame 8 is stored in such a way as it may be advanced or retracted from the extremity end of the outer cylinder 1 to within the tip element 2, and the slider 13 is arranged at the far extremity end of the intermediate frame 8 in such a way as the slider can be slid axially within the tip element 2. This slider 13 is provided with a lead pipe 14 which is integrally formed with the extremity end, and the rear end part has a central rear opening part and is provided within it a friction applying member 15 such as a packing or the like having a specified friction between it and the slider 13 so as to apply the specified friction force to the lead S in case of lead feeding operation. To the outer circumference of the slider 13 is fixed a second resilient member 16 for always biasing the slider 13 in a forward direction and a spring receiver 17 engaged with the rear end part of the second resilient member 16 is fixed to an inner circumferential surface of the tip element 2. The extremity end of the second resilient member 16 is engaged with a large diameter outer circumferential stepped part 13a of the slider 13, and the outer circumferential surface of the rear end of the slider 13 has a temporary engaging projection 13b temporarily causing the slider 13 to be engaged with the engaging projection 9a projected and formed at the inner circumferential surface of the front cylinder 9. Structure at a central part of the mechanical pencil, i.e. a rear end of the lead feeding mechanism 5 is made such that a third resilient member 18 is installed between a flange 4a circumferentially projected and formed at an outer circumference of the rear end of the receiving element 4 fixed to the extremity end of the lead supplying cylinder 3 and a rear end surface of the intermediate frame 8. As regards the positional relation of each of the members across an axial direction of the lead feeding mechanism 5, the following relation can be found in addition to the clearance (a) between the extremity end surface of the receiving element 4 and the desired part of the rear tapered cylindrical part 6b at the rear end of the lead chuck 6 to be described later. At first, as shown in Fig. 1, a clearance (b) is arranged between the flange 4a of the receiving element 4 and the rear end surface of the sleeve 7, a clearance (c) is arranged between the extremity end surface of the sleeve 7 and the rear end surface of the front cylinder 9 arranged at the intermediate frame 8, and a clearance (d) is arranged at a guide groove 1a of the outer cylinder 1 in such a way as the sliding guide projection 8b of the intermediate frame 8 can be axially advanced or retracted. Then, one of the most important feature of the present invention, i.e. a detailed constitution of the lead chuck in the lead feeding mechanism 5 will be described. The lead chuck 6 is made by a metallic formed product formed by a forging or pressing work, sintered alloy or die-casting work, or a synthetic resin formed product molded by an injection molding, press molding or the like. Details of the lead chuck 6 are such that as shown in Fig. 2 the chuck is composed of two chuck members 61 and 61 divided into two portions in a longitudinal direction along an axis of the lead S insertion hole 60. The chuck member 61 has the flange 6a semi-circumferentially projected and formed at its outer circumference, a rear tapered cylindrical part 6b extending rearwardly from the flange 6a and having a gradual small diameter rear end, and a ball holding part 6c for setting positions of the balls 10 held against the lead chuck fastening element 9. At the junction surfaces of the chuck members 61 and 61 is formed a lead holding part 62 at the front end of the chuck member 61 in continuous with the lead insertion hole 60, and the lead holding part 62 is formed with teeth 63 which are axially, continuously and alternatively formed. Junction surfaces of the chuck members 61 are further provided with, at the location corresponding to the flange 6a, projections 65 and 65, concave portions 66 and 66 formed at each of the connecting partners so as to cause the projections 65 and 65 to be fitted therein, and opening or closing supporting point projections 67 and 67 projected and formed in parallel with the projections 65 and 65 so as to apply a resilient force in case of releasing the lead chuck to the relative chuck members by spacing apart the relative junction surfaces by a specified distance in such a way as they are fitted to each other while each of the chuck members 61 and 61 are connected to each other. The inner circumferential rear end is in continuous with the lead insertion hole 60 to make lead guides 68 and 68 which are expanded to form a tapered part in a rearward direction, and the front ends of the lead holding parts 62 and 62 are also expanded in a forward direction to make tapered portions 69 and 69. Since the projections 65 and the concave portions 66 are arranged at each of the symmetrical positions of the junction surfaces, it is possible to prevent the positions of the chuck members 61 and 61 from being displaced from their desired positions when the divided surface of one member 61 is opposite to the divided surface of the other member 61. Although the opening or closing point projections 67 may act as a spacer for assuring a clearance K in Fig. 1, a setting of heights of both projections 65 and 65 slightly larger than a depth of both concave portions 66 and 66 results in that the projections 65 and 65 may act as the opening or closing point while acting as a spacer even if the projections 66 are eliminated. The lead holding portions 62 are a rectangular flat concave portion arranged at a front end of the lead chuck, and the teeth 63 are constructed such that the lead S is supported by four points while the chuck members 61 and 61 are being connected to each other. Detailed construction of the teeth 63 will be described in reference to Figs. 2 and 7 - 10. That is, the lead holding part 62 is formed to have a substantial U-shaped section of which part facing to the lead S may expand gradually. Both inner surfaces of the lead holding part 62 are formed in integral with a plurality of cogs of the teeth 63 with a desired spacing along an axial direction thereof. These cogs of the teeth 63, as shown in Figs. 8 to 10, are formed such that the extremity end of the raised surface 63b is tapered to show a gradual accute shape, and each of the extremity end surfaces 63a is a narrow flat surface. Each of the groove bottoms 63c of the teeth 63 is also formed as a flat shape. The teeth 63 form lead supporting portions 63g to 63j for supporting a n outer circumference of the lead S at four points while each of the chuck members 61 and 61 are being combined and assembled. These lead supporting portions 63g to 63j may support the lead S at four points under a line contacted state. A sufficient lead biting force can be attained and a proper lead holding is carried out by the lead supporting parts 63g to 63j formed by the teeth 63. As described above, the lead holding part 62 is formed to have a substantial U-shaped section and a bottom part of the lead holding part 62 is not formed with the teeth 63 so as to keep a space for the lead dust discharging part 62b. Therefore, since the lead dust or the like is discharged through the lead dust discharging part 62b, so the lead dust is not accumulated entirely and even if the lead dust begins to accumulate, the lead dust or the like is automatically discharged as the lead is moved during its feeding operation. Therefore, the present invention may provide an excellent feature that the sliding of the lead may not be occurred during writing operation even under a rough writing of longer period of time. Then, a lead feeding operation of the present invention will be described. The lead feeding operation can be classified into two categories. (1) At first, a first lead feeding operation is a normal means for performing with a rear end knock of the lead supplying cylinder 3. That is, the sleeve 7 engaged with the extremity end receiving element 4 is advanced together with the lead supplying cylinder 3 or the like under a knocking operation, feeds the lead until it may abut against the rear end of the front cylinder 9 and thereafter it is stopped. That is, (A) in case that the slider 12 is not locked with the front cylinder 9, a normal lead feeding operation is carried out by the rear end knocking operation. (B) In turn, in case that the slider 13 is locked with the front cylinder 9 under engagement between the inner wall annular projection 9a and an outward projection 13b (see Fig. 1), the lead is fed in the same manner as that of (A) until the extremity end of the sleeve 7 is abutted against the rear end of the front cylinder 9 under the above-mentioned rear end knocking operation [a spacing of a distance (c)], thereafter the slider 13 is pushed forwardly under advancement of the lead chuck 6. With this arrangement, the outward directed projection 13b of the slider 13 rides over the inner wall annular projection 9a of the front cylinder 9 and then the locked condition is released. Thereafter, it is biased and moved in a forward direction by the second resilient body 16 and the slide pipe 14 is projected out of the tip element 2. During this process, the lead S supported by a retracting frictional force of the friction applying member 15 is pulled out of the lead chuck 6 in a forward direction and is advanced together with the slider 13. Therefore, the lead S is always projected by a distance (c) from the extremity end of the slider pipe 14 which is appropriate for writing action. As described above, both a lock releasing action and a lead feeding operation can be performed simultaneously and a condition in which the lead S is projected only by a distance (c) which is appropriate for writing operation. Therefore, it becomes possible to perform a writing operation while the lead S is confirmed with bare eyes. (2) As a second lead feeding operation, an automatic lead feeding operation can be carried out after the writing action is interrupted. That is, the writing operation is normally performed while the lead S is projected from the slider pipe 4 by a desired amount. Then, the lead S is worn out in sequence as the writing action is promoted, and finally becomes in flush with an extremity end of the slider pipe 14. Even under this condition, the slider 13 may retract as much as possible against a biasing force of the second resilient body 16 to the rear end by a distance in which the inner wall annular projection 9a is engaged with the outward projection 13b. In turn, a writing of quite longer period is required in order for an amount of worn-out lead S under its writing action to become equal to a retracted distance. For example, in case of the mechanical pencil with a concentration degree of HB and a lead diameter of 0.5 mm under a normal writing pressure of adult person, an amount of worn-out lead during writing of one Chinese character on a high quality paper is merely about 0.01 mm. Therefore, a continuous writing until the slider 13 is retracted by a retracting distance may not normally be performed and it may occur that the writing is interrupted due to a rest of writing. So, for example, it is assumed that the writing action is interrupted and the extremity end of the slider pipe 14 is removed from the paper sheet. With this action, the slider 13 may advance by a resilient force of the second resilient body 16 and at the same time the lead S is also pulled in an advancing direction from the friction applying member 15 under the desired frictional force together with the slider 13. In turn, since the chuck fastening force of the lead chuck 6 biting the lead S is applied by a weaker the first resilient body 12 than the second resilient body 16, it is compressed with a pulling force in an advancing direction of the above-mentioned lead S to allow for an advancement of the entire lead chuck 6. In case of this advancement, the head part of the lead chuck 6 is operated such that as the balls 11 may rotate and contacted with the inner surface tapered wall 10a of the fastening element 10 arranged at the extremity end of the sleeve 7 and advance, a biting force of the lead chuck is gradually decreased and the feeding of the lead S is carried out. Under these series of operation, the lead chuck is returned again to its above-mentioned flush condition to perform an automatic lead feeding operation to enable a writing operation to be performed and so a continuous writing up to the maximum retracting distance can be carried out. Then, a case of non-using of the writing instrument will be described. A rear end of the lead supplying cylinder 3 is knocked from a condition in which the slider 13 is not locked with the front cylinder 9 and the slider pipe 14 is pushed against the paper sheet or the like, thereby the slider pipe 14 is completely stored in the tip element 2 and locked therein. That is, when the slider pipe 14 is pushed against the paper sheet or the like while the rear end of the lead supplying cylinder 3 is being knocked, the slider 13 is retracted together with the slider pipe 14. With this arrangement, as the slider pipe 14 is stored completely in the tip element 2, at that time, the outer projection 13b of the slider 13 rides over the inner wall annular projection 9a of the front cylinder 9 in its retracting direction, the outward projection 13b is engaged with the inner wall annular projection 9a, thereby the slider pipe 14 is stored completely in the tip element 2 and then locked therein. This clocked condition may not be released even if a certain amount of external force is applied as long as the rear end of the lead supplying cylinder 3 is not knocked. Figs. 11 and 12 illustrate second and third preferred embodiments of the chuck members 61 and 61, respectively. In the second preferred embodiment shown in Fig. 11, the teeth 63 of the lead holding part 62 in the first preferred embodiment are removed, and both released ends of the lead holding hole 62 are applied as lead holding parts 62g to 62j. Also in this preferred embodiment, the lead holding hole 62 is formed to have a substantial U-shaped section, a lead dust discharging part 62L is arranged to enable an effective discharging of the lead dust to be performed. Also in the third preferred embodiment shown in Fig. 12, the teeth 63 of the lead holding part 62 are removed and both sides of the released end of the lead holding hole 62 are applied as the lead supporting parts 62g to 62j. The lead holding hole 62 is formed as a U-shaped section and a lead dust discharging part 62L is arranged. In this way, even in case of the lead holding hole 62 shown in Figs. 11 and 12, a substantial similar effect to that of the first preferred embodiment can be got. The lead holding hole 62 described in the each of the first to third preferred embodiments may have another shape of section if the hole is supported by four points as described above. Then a fourth preferred embodiment of the present invention will be described in reference to Figs. 13 to 23. The fourth preferred embodiment corresponds to the case in which the lead S in the first to third preferred embodiments is supported by the teeth 63 or at four points at its outer circumference with the lead holding part 62 and in place of this arrangement the lead S is cut and reduced in its diameter by the teeth 63 supporting it with four points. That is, in the fourth preferred embodiment, it has some advantages that the lead S is held at its six points from its outer circumference in case that a sliding of the lead is generated with the holding force of the lead holding part 62 under the reduced state of the lead S. In the fourth preferred embodiment, the extremity end receiving element for pushing the lead chuck in a forward direction is provided with a resilient stepped part to enable an instantaneous expansion of the lead chuck at a location where it is abutted against the lead chuck. In Fig. 13, the same reference numerals as those of the first to third preferred embodiments described in reference to Figs. 1 to 12 are applied for indicating the same or similar corresponding members in this fourth preferred embodiment, so that their repetitive description will be eliminated. In the figure, the mechanical pencil according to the fourth preferred embodiment is composed of an outer cylinder 1, a tip element 2, a lead supplying cylinder 3, an extremity end receiving element 4 and a lead feeding mechanism 5. This lead feeding mechanism 5 is composed of a lead chuck 6, a sleeve 7, a front cylinder 9 fixed to the extremity end of the sleeve 7, a chuck fastening element 10 having a tapered surface 10a, balls 11 for use in fastening the chuck and a first resilient member 12 for relatively biasing the lead chuck 6 within the sleeve 7. Within the front cylinder 9 is arranged a projecting bar 20 to be described later against the slider 13 through the second resilient member 16. The slider 13 is provided with a lead pipe 14 and a friction applying member 15 in the same manner as that of the first preferred embodiment. In Fig. 14, a connected condition of the lead chuck 6 and the sleeve 7 in the lead feeding mechanism 5 is illustrated. In this preferred embodiment, an extremity end of the extremity end receiving element 4 is projected long to become a lead chuck pushing part 41 and then inserted into the sleeve 7 at the rear end of the sleeve 7. This lead chuck pushing part 41 is constructed such that it may push a semi-circumferential flange 6a of the lead chuck 6. Detailed construction of the lead chuck 6 will be described. It is different from that of the first to third preferred embodiments described above. That is, as the first feature, a stepped part 601 is projected and formed at a part near the sliding surface at the rear part of the semi-circumferential flange 6a and another stepped part 602 is projected and formed in a circular form at a front side of which position is displaced by a degree of 90° in respect to the stepped part 601. As a second feature, it shows a different constitution of the teeth 63 of the lead holding part 62. The teeth 63 is composed of two kinds of teeth, i.e. a first teeth 63a holding an outer circumference of the lead S at four points in the same manner as that of the first preferred embodiment and a second teeth 63b projected and formed across the groove bottom part of U-shape of the lead holding part 62 between the two adjoining the first teeth 63a. Action and operation of the fourth preferred embodiment will be described in reference to the above-mentioned constitution. Since the description of the operation is basically the same as that of the first to third preferred embodiments, a repetitive description is eliminated and only a feature of the fourth preferred embodiment will be described. At first, the stepped portions 601 and 602 projected and formed across the semi-circumferential flange 6a of the first feature with a displacement of 90° are abutted against only the stepped part 601 projected in a rearward direction as shown in Fig. 14 when the lead chuck pushing part 41 of the extremity end receiving element 4 is abutted from a rear part, and further since the stepped part 602 is provided with the first resilient member 12 resiliently, each of the chuck members 61 and 61 is expanded to flex outwardly in respect to the lead S. Since the expanding operation accompanying with this flexing action is carried out instantaneously, an expanding operation of the lead chuck 6 is rapidly carried out. A second feature of the action of the fourth preferred embodiment will be described. In the lead feeding mechanism for performing not only the rear end knocking but also three operations such as an automatic lead feeding and a so-called extremity end knocking or the like, since the lead holding force is stronger than that of the normal mechanical pencil, the lead chuck may cut the outer circumference of the lead S and sometimes generate a so-called lead reduction state. Application of the lead chuck in the fourth preferred embodiment causes a state in which the second teeth 63b formed across the groove bottom of the holding part 62 may hold the lead S positively and feed the lead even in case of occurrence of reduction of lead caused by cutting of the four-point supporting part. As regards the cut lead dust, since the first teeth 63a and the second teeth 63b are projected and formed alternatively, the lead dust may drop while being in a zig-zag fashion as the dust may transmit along the sliding surfaces spaced apart slightly as well as the groove bottom part of the lead holding part 62, i.e. the dusts may drop at the extremity end and so a disadvantage of clogging of the lead dust may not be generated. In Figs. 20 and 21 is indicated this lead holding condition and both of these figures show that each of the teeth 63a and 63b holds the lead S. When a so-called reduction in diameter of the lead is generated, as shown in Fig. 20, the lead holding is not positively performed only with the four-points lead holding condition of the first teeth 63a, so that as shown in Fig. 21, the second teeth 63b may hold the lead S. Fig. 23 is a perspective view for showing an enlarged state of the ball receiving portion 6c which is a basic constitution of lead holding action of the chuck member 61 of the lead chuck 6 in the fourth preferred embodiment. Although several kinds of structures of the teeth 63 are already described in the first to fourth preferred embodiments, the lead chuck of the present invention is not limited to the description of these structures and it may be constructed as shown in Figs. 24 and 25. That is, in the fifth preferred embodiment shown in Fig. 24, the stepped portions 601 and 602 for applying resilient force which are projected and formed across the semi-circumferential flange illustrated in the fourth preferred embodiment are combined with one kind of the teeth 63 illustrated and described in the first preferred embodiment. In a sixth preferred embodiment shown in Fig. 25, the stepped portions 601 and 602 are combined only with the second teeth 63b in the fourth preferred embodiment. Also in the fifth and sixth preferred embodiments having each of the above-mentioned constitutions, a basic action and operation of the present invention of a resilient expanding action of the lead chuck 6 and a positive holding of lead while discharging the lead dust without accumulating the same can be performed in the same manner as that of the fourth preferred embodiment. As described above in detail, according to the lead chuck for a mechanical pencil of the present invention, the teeth formed at the holding parts of the extremity ends at the sliding surfaces of the chuck part in the two-divided full separate type lead chuck are contacted with the outer circumference of the lead at four points or six points as desired by adding the second teeth, and they are constructed in such a positional relation as the four points at the first teeth and the two points at the second teeth are alternatively arranged and at the same time the stepped portions are projected at the roots of the extremity end and the rear end of the semi-circumferential flange arranged at an outer circumference in correspondence with the supporting points for the lead chuck expansion in a relative displacement of approximately 90° as desired, so that the present invention has the following various effects. At first, since the structure of lead holding teeth of the lead chuck is constructed such that only the same part of the outer circumference of the lead is not held, even if the mechanical pencil is used for a long period of time, it is possible to sell a lead chuck having a superior lead holding force in which a state in which the outer circumference of the lead is cut by the teeth formed at the lead holding part of each of the extremity ends of the chuck is reduced, a so-called lead reduction phenomenon can be prevented as much as possible and at the same time a sliding of the lead or the like are less occurred. Secondly, the above-mentioned phenomenon of reduction of lead diameter can be prevented even in case of an automatic lead feeding type mechanical pencil or an extremity end knock type mechanical pencil or the like having a foot-light in recent years as well as a rear end knock type mechanical pencil requiring a special strong lead holding force and a positive lead feeding operation in these automatic or semi-automatic mechanical pencil and a smooth writing of the mechanical pencil caused by a prevention of the lead breakage can be promoted. Thirdly, even if the outer circumference of the lead is cut by the teeth formed at the above-mentioned lead holding surface to generate a lead reduction phenomenon, the cut lead dust may not be clogged in the lead insertion hole of the lead chuck or in a space between the lead chuck and the sleeve, and in view of these points, various smooth feeding operations such as a rear end knock, an automatic lead feeding and an extremity end knocking or the like can be performed and at the same time an occurrence of troubles at these lead feeding mechanisms can be reduced or completely eliminated. Fourthly, the expanding operation to be performed by the lead chuck for use in releasing the lead held condition is resiliently expanded with a flexing force applied by the stepped portions formed at the semi-circumferential flange arranged at an outer circumference in a displacement of about 90° in respect to the supporting points positioned at the sliding surfaces of the chuck part and the extremity end of the receiving element abutted against the stepped portions at the rear end side, so that a positive, smooth and rapid expanding operation can be performed, some disadvantages such as the lead reduction phenomenon and a lead dust clogging phenomenon together with the improvement of the teeth at the lead holding part are entirely eliminated and further an operativity of the mechanical pencil can be improved.

Claims: Claims for the following Contracting States : DE, GB, FR, IT A chuck for a mechanical pencil comprising two juxtaposed chuck members (61), adjacent surfaces of which define a lead insertion hole (60) and are provided at their forward ends with lead holding parts (62) the forward end of said chuck being expandable by relative pivotal movement of said chuck members (61), the chuck having means for receiving the rear end of a resilient biasing member (12) and means for receiving the forward end (41) of a receiving element (4) of a lead supplying cylinder (3), the said pivotal movement, in use, being effected by abutment of the forward end (41) of the receiving element (4) against the chuck and biasing of the chuck in a rearward direction by reception of the rear end of said biasing member (12), wherein each lead holding part (62) of the chuck members (61) comprises a longitudinally extending groove (62a, 62b), which is shallower than said lead insertion hole (60), and characterised in that, in use, lead dust formed within the chuck is discharged along the bottom surface of said grooves and by a plurality of first teeth (63a) formed on at least the upper corners of said grooves (62a, 62b), but not traversing the lower surface thereof, to hold the outer circumference of a lead in a four point contacted condition and whose biting surfaces lie substantially at right angles to the longitudinal axis of the chuck. A chuck according to claim 1 wherein each lead holding part (62) further comprises a plurality of second teeth (63b), interposed between adjacent first teeth (63a) and formed on at least the bottom surface of said groove (62a, 62b) which, in combination with said first teeth (63a), in use, hold the outer circumference of a lead in a six point contacted condition and whose biting surfaces lie substantially at right angles to the longitudinal axis of the chuck. A chuck according to claim 1 or claim 2 wherein the said grooves are substantially U-shaped in cross-section. A chuck according to any preceding claim, further comprising a ball-holding concave depression (6c) in the surface of each chuck member opposite said lead holding part (62), the periphery of the concave depression (6c) being provided with an upstanding bead. A chuck according to any preceding claim wherein the said first teeth (63a) are also formed on the inner side surfaces of the grooves (62a, 62b). Claims for the following Contracting State : ES A chuck for a mechanical pencil comprising two juxtaposed chuck members (61), adjacent surfaces of which define a lead insertion hole (60) and are provided at their forward ends with lead holding parts (62) the forward end of said chuck being expandable by relative pivotal movement of said chuck members (61), the chuck having means for receiving the rear end of a resilient biasing member (12) and means for receiving the forward end (41) of a receiving element (4) of a lead supplying cylinder (3), the said pivotal movement, in use, being effected by abutment of the forward end (41) of the receiving element (4) against the chuck and biasing of the chuck in a rearward direction by reception of the rear end of said biasing member (12), wherein each lead holding part (62) of the chuck members (61) comprises a longitudinally extending groove (62a, 62b), which is shallower than said lead insertion hole (60), and characterised in that, in use, lead dust formed within the chuck is discharged along the bottom surface of said grooves and by a plurality of first teeth (63a) formed on at least the upper corners of said grooves (62a, 62b) which, in use, hold the outer circumference of a lead in a four point contacted condition and whose biting surfaces lie substantially at right angles to the longitudinal axis of the chuck. A chuck according to claim 1 wherein each lead holding part (62) further comprises a plurality of second teeth (63b), interposed between adjacent first teeth (63a) and formed on at least the bottom surface of said groove (62a, 62b) which, in combination with said first teeth (63a), in use, hold the outer circumference of a lead in a six point contacted condition and whose biting surfaces lie substantially at right angles to the longitudinal axis of the chuck. A chuck according to claim 1 or claim 2 wherein the said grooves are substantially U-shaped in cross-section. A chuck according to any preceding claim, further comprising a ball-holding concave depression (6c) in the surface of each chuck member opposite said lead holding part (62), the periphery of the concave depression (6c) being provided with an upstanding bead.

Inventors: KAGEYAMA, HIDEHEI C/O KOTOBUKI & CO. LTD., MITSUYA, YOSHIHIDE C/O KOTOBUKI & CO. LTD., NAKAZATO, YOICHI C/O KOTOBUKI & CO. LTD., Kageyama, Hidehei c/o Kotobuki &amp; Co. Ltd., Mitsuya, Yoshihide c/o Kotobuki &amp; Co. Ltd., Nakazato, Yoichi c/o Kotobuki &amp; Co. Ltd.
Applicants: KOTOBUKI & CO., LTD.
Application year: 1987
Main classification: B43K21
IPC codes: B43K21