Mechanical pencil

Abstract

 An improved propelling pencil is provided of which lead can be projected or exposed to a predetermined amount by applying writing pressure to a pencil cyclinder, when the lead is worn out or broken. According to the invention, the pencil is free from breaking of the lead due to excessive projection of the lead from the pencil body.

Description

[0001] This invention relates to an improved propelling pencil. More particularly, the invention relates to an improved propelling pencil in which the lead can be projected or exposed to a predetermined amount only by applying writing pressure to a pencil cylinder, when the lead is worn out or broken.

[0002] Consequently, an object of the preferred form of the invention is to provide an improved propelling pencil which is convenient for use and which is free from breaking of the lead due to excessive exposure of the lead from the pencil body. Further objects of the invention will be apparent from the explanation hereinafter.

[0003] According to the invention in one aspect there is provided a propelling pencil characterised in that when the writing cylinder end is pushed onto sheet or the desk, the writing end rotates, while a chuck for a lead is operated due to the rotation of the writing end and opens to allow the lead to fall freely to the end of the writing end, the chuck grasps the lead when a pencil cylinder rises, and descends due to returning rotation of the writing cylinder so as to maintain a predetermined amount of projected portion of the lead.

[0004] According to another aspect there is provided a propelling pencil including a chuck for holding the lead which is operated by downwards pushing of the body of the pencil so that the point is pushed to the paper to effect projection of a fresh length of lead from the pencil for writing.

[0005] An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein:-

Fig. I is a longitudinal sectional view of a preferred embodiment of the invention;

Fig. 2 and 3 are longitudinal sectional views explaining the operation of the pencil of the invention;

Fig. 4 is a sectional view showing the inner side of a metal piece; and,

Fig. 5 is a sectional view explaining the relationship between a writing cylinder and a chuck cylinder.

[0006] Description of Preferred Embodiments of the Invention

[0007] In Fig. 1, a pencil cylinder 1 is proviaed at its top with an eraser 2, and the cylinder is fixed by a screw 6 to a metal piece 7. At the top of the cylinder 1 a store 4 is defined, from which extends a lead guide 3. The bottom 5 of the lead guide 3 acts a stopper 5 for a chuck 25.

[0008] Cylinder surfaces 8 and 9 inside the metal piece 7 are separated by a section of oblique surfaces 10, which form helical grooves 11, and the surface 8 has part of piece 7 defining vertical grooves 12. A writing cylinder 13 fits in metal piece 7 and is provided with followers 14 which slide within said grooves 11. The cylinder 13 is provided'at its upper part with saw-set cam surfaces 15, and at its lower part with a projected taper 16 for opening the chuck, and a lead protective passage 17. The inside 18 of the cylinder 13 is slidably provided with a chuck cylinder 19.

[0009] At the upper part of the chuck cylinder 19 are provided a pair of oblique cam surfaces 20, a cylinder surface 21 which slides on the cylinder surface 8 of the metal piece 7, and a pair of keys 22 which slide in the grooves 12. A chuck taper 23 is provided at the bottom of the chuck cylinder 19, while a spring opening 24 is provided at its upper part. A chuck 25 which can be opened at two or three positions, has a recessed taper 25a at its bottom surface. The chuck 25 is urged constantly in the upward direction by a spring 27 provided between a collar 26 and chuck cylinder 19. A writing spring 28 urges the writing cylinder 13 downward via oblique surfaces 20 of the chuck cylinder 19. In the drawings, reference 29 indicates a lead and 30 is paper on which writing is to take place.

[0010] In the following, the operation of the pencil while it is used, is explained.

[0011] In the initial stage, the lead 29 is stored in lead store 4. When the pencil cylinder 1 is stood upriht, the lead 29 falls to the chuck 25 through the guide 3 due to the action of gravity.

[0012] To cause the lead to project from the pencil, the cylinder 1 is pressed strongly to the paper 30, the metal piece 7 descends, and the writing cylinder 13 is rotated by means of the action of followers 14 following the helical grooves 11. Although the saw-set cam surfaces 15 are also roated, since the oblique surfaces 20 which engage with the surfaces 15, are prevented from rotating by virtue of the engagements of keys 22 in grooves 12, the surfaces 20 and the cylinder 19 ascend upward relative to cylinder 13. The chuck cylinder 19 rises relative to the cylinder 13 to the extent of the thread of the saw-set cam surface 15.

[0013] By pushing the pencil cylinder further downwards, the stopper 5 engages the upper surface of the chuck 25 and moves the chuck downwards with the result that the chuck 25 is opened and the lead falls through the chuck and the bottom of the lead 29 reaches the sheet 30, as shown in fig. 3.

[0014] If the push-down force applied to the pencil cylinder I is now relaxed, the cylinder 1 is pushed upward due to the reactive force of the writing spring 28, but initially the lead 29 remains in contact with the sheet 30. If the force is further relaxed, the stoper 5 moves clear of the chuck 25 permitting it to rise due to the action of the chuck spring 27 until the chuck 25 chucks the lead 29, and, the lead 28 and the chuck rise together until the chucking force balances the lead weight and, thus the chuck chucks the lead firmly, and reaches the state shown in fig. 2.

[0015] With the further relaxing of the force applied to the cylinder 1 still further, the followers 14 engage the grooves 11 provided in the metal piece 7, and the writing cylinder 13 starts to rotate in a direction opposite to that in which it rotated when the cylinder 1 was pushed downwards. Consequently, the saw-set cam surfaces 15 of the cylinder 13 turn with a position permitting the oblique surfaces 2e and hence the cylinder to move downwards relative to cylinder 13, and the chuck 25 and the lead 20 descend. When the bottom of the lead 29 reaches the sheet 30, the force of the writing spring 28 is stopped by the contact between the lead 29 and the sheet 30. After that, the pencil cylinder 1 is pushed upwards, the writing cylinder 13 rises while rotating, and reaches the state shown in Fig. 1 in which the lead projects from the pencil by a predetermined amount, ready for writing.

[0016] Writing work is effected with the pencil in this state. Writing can take place as long as the force of writing is below that of the pressure of writing spring 28. If the writing pressure becomes excessive, the lead 29 enters into the lead protective passage 17, and if the writing pressure is reduced, the lead 29 returns its original position. In this way, the lead is prevented from being broken.

[0017] When the lead is worn out, writing pressure is strengthened so that the lead is caused to project from the pencil as a result of the procedure as described above. After such procedure, the pencil reaches the state shown in Fig. 3. With the reduction of the writing pressure, it reaches the state shown in Fig. 2 and then Fig. 1.

[0018] Since the state snown in Fig. 3 is independent or the projected amount of the lead prior to the application of excess writing pressure, the projected or exposed amount of the lead at the stage shown in Fig. 1, is maintained constantly at a certain value and, thus, the objective purpose of the invention is achieved.

[0019] The chuck 25 is constructed to open when stress is applied thereto. If the chuck does not to open during the normal opening described above, the pencil cylinder 1 is pushed further downwards then as shown in Fig. 3. Then the stopper 5 descends and the chuck 25 as well descends, so that the recessed taper 25a collides with the projected taper 16 and forces the chuck 25 to open to its full extent.

[0020] According to the invention, the projected amount or the lead can be selected in accordance with the user's own choice. That is, the height of respective thread pairs of the saw-set surface 15 which determines the projected amount of the lead, is varied so that the projected amount can be controlled by rotating the writing cylinder 13 to select preferably thread pair. A similar effect can be obtained if the angle of respective oblique surfaces 10 of the metal is varied. In this instance, however, a pair of oval followers 14 should be used.

[0021] According to the invention, no obstacle such as rubber packing is provided in the lead protective passage 17 so that the lead may fall freely under gravity when the chuck is opened. Accordingly, the lead remains in the chuck, and projects only by detaching the writing cylinder from the sheet.

[0022] According to the embodiment illustrated in the drawings, a predetermined amount of the lead remains projected constantly from the writing cylinder. If a two-stage knocking mechanism or a rotary entering mechanism is provided instead of an eraser at the top of the pencil cylinder, usability of the pencil is more enhanced. In this case, an outer cylinder is covered on the pencil cylinder so that the writing cylinder or the metal portion can be entered into or out from the outer cylinder.

Claims

1. A propelling pencil characterised in that when the writing cylinder end is pushed onto sheet or the desk, the writing end rotates, while a chuck for a lead is operated due to the rotation of the writing end and opens to allow the lead to fall freely to the end of the writing end, the chuck grasps the lead when a pencil cylinder rises, and descends due to returning rotation of the writing cylinder so as to maintain a predetermined amount of projected portion of the lead.

2. A propelling pencil according to claim 1, characterised in that plural pairs of oblique surfaces are provided between the writing cylinder and the chuck, for changing the rising amount of the chuck, which rises in accordance with the rotation of the writing cylinder, so that a certain pair of oblique surfaces can be selecged by previously rotating the writing cylinder so as to control the projected amount of the lead.

3. A propelling pencil according to claim 1 or 2, characterised in that plural pairs of oblique surfaces are provided between metal piece and the writing cylinder, for adjusting the rising amount of the chuck by changing the rotating angle of the oblique surfaces, so that a certain pair of oblique surfaces can be selected by previously rotating the writing cylinder so as to control the projected amount of the lead.

4. A propelling pencil according to any preceding claim, characterised in that the bottom surface of the chuck is formed as a recessed taper and that a projecting taper is provided at the inside bottom of the writing cylinder, so that the chuck can be opened to its full extent by bringing the said tapers together.

5. A propelling pencil according to claim 1, characterised in that a so called two stage knocking mechanism is provided at the upper part of the pencil, and that an outer cylinder is covered over the entire pencil so that the writing element including the metal piece and the writing cylinder can be exposed during writing.

6. A propelling pencil according to any preceding claim, characterised in that the writing cylinder defines a stopper adapted to contact the chuck to open same when the writing cylinder is pushed downwards.

7. A propelling pencil including a chuck for holding the lead which is operated by downwards pushing of the body of the pencil so that the point is pushed to the paper to effect projection of a fresh length of lead from the pencil for writing.

Drawing