EP2349737B1 - Writing implement comprising a slide-on end member - Google Patents

Description

The present invention relates to a writing instrument comprising a hollow body on which is mounted by fitting an end member. For example, it may be a mechanical pencil comprising an inner mine reservoir tube on which is fitted a rubber holder which also serves as a rear push button and to facilitate the filling of the tank tube mines.

More particularly, the invention relates to a writing instrument comprising a deformable hollow body elongated along a central axis to an end, and an end member comprising a tubular portion having an inner face provided with a plurality of first identical salient reliefs adapted to engage and deform radially the hollow body during assembly of said end member by engagement of its tubular portion around the end of said hollow body.

We know the document US 6347898 B1 describing an end member as a rubber support having a tubular portion having on its inner side such protruding projections in the form of longitudinal ribs.

The mounting of such an end member must satisfy two types of constraints resulting in sometimes contradictory solutions, namely on the one hand a simple manufacturing that reduces the overall cost of production, and on the other hand, a sufficient assembly resistant to prevent the user inadvertent detachment of the end member.

Indeed, it is desirable that the end piece can not be detached as long as no effort is exerted abnormally high traction. This is to avoid the loss of the end piece that could degrade the appearance of the instrument, and its functional characteristics, or even cause tasks in the case of a ballpoint or felt tip instrument. In the particular case of a mechanical pencil, the end member is often a support receiving an interchangeable rubber and surmounted by a protective cap. In addition, this set serves as a push button back. The mounting of the eraser holder on the mine reservoir tube must withstand the repeated pulls during removal of the rubber cap and removal of the eraser from its support.

Furthermore, for manufacture, it is advantageous that the end member has shapes corresponding to a simple mold to be machined, but especially that this member is releasable reliably at high rates. Then, it is also preferable that the assembly can be performed quickly, especially in an automated process, and taking into account the inevitable dispersions of dimensions of hollow bodies and end members manufactured. In particular, in the case of a mechanical pencil, the reservoir tube constituting the hollow member is generally an extruded polypropylene tube produced by the meter and cut to length. It can have relatively large variations in outside diameter, inside diameter and radial elasticity. Its long length makes it also relatively sensitive to buckling when pressure is exerted on the free rear end thereof.

A tubular portion having inner reliefs, particularly in the form of longitudinal ribs, can be molded easily. To obtain a compromise between the ease of assembly and the holding force required, it is known to vary the height and the number of these protruding reliefs. But it turns out that the number and height of the reliefs quickly reach a limit from which it is difficult to fully grip the end member. Moreover, it turns out that, even if a satisfactory holding force is obtained for precise given dimensions of the hollow body and the end member, this force decreases very substantially in the event of dimensional variations, even if these variations remain in usual ranges in production. industrial.

Moreover, we know of the document JP10-203076 A a solution to the problem of holding a rubber support on a mine tank which consists of providing a central protruding portion which is inserted inside the reservoir tube. But, again, the possibility of mounting and the retaining force are sensitive to variations in the inner diameter of the reservoir tube. Moreover, this type of solution makes practically impossible the recharging of the tank by introducing the mines through a hole of the rubber support.

There is therefore a need in the field of writing instruments to improve the mounting of an end piece on a hollow body, in particular to offer a compromise between the ease of manufacture and the quality of the outfit for the user, while tolerating a certain variability of the geometrical dimensions.

For this purpose, the subject of the present invention is a rubber support of the aforementioned type, characterized in that the inner face of the tubular portion has a plurality of second projecting protrusions having a height measured radially from said inner face which is lower at the height of the first protruding reliefs and is adapted so that said second reliefs exert a radial pressure on the hollow body deformed by the first reliefs.

It turns out that the presence of the second reliefs protruding does not substantially increase the force to exert to press the tubular portion on the free end of a given hollow body. The strength of the assembly is, on the other hand, increased and especially the holding force varies less substantially as a function of the undistorted outer diameter of the hollow body. It is assumed that the second reliefs can limit overall the amount of deformation of the mounted hollow body, while taking advantage of the deformations created by the first reliefs to create additional gripping zones that exert a radial pressure on the deformed hollow body. As shown schematically in figure 4 the presence of three or four relatively high reliefs creates important deformation lobes between these reliefs. By adopting the second reliefs, as it appears schematically in the figure 5 the deformation lobes of the hollow body come into contact with the second reliefs, which limits the amplitude of the deformation of the lobes between the first reliefs. It is assumed that the additional support zones thus created improve the strength by increasing friction. But it is also possible that the amplitudes of the deformations reached in a very localized way are less important, and that thus the material of the hollow body works more importantly in its zone of elastic deformation and less in its zone of plastic deformation.

In addition, it appears that the holding force after one or more unintentional disassembly, degrades less rapidly than the sets of identical first reliefs of the prior art.

• la pluralité de deuxièmes reliefs est régulièrement répartie circonférentiellement entre les premiers reliefs ; afin de bloquer chacun des lobes de déformation créés par les premiers reliefs avec un ou plusieurs deuxièmes reliefs ;
• chaque pluralité de reliefs comprend un nombre identique de premiers et de deuxièmes reliefs, de préférence égale à trois ou quatre reliefs ;
• les premiers et deuxièmes reliefs sont des nervures faisant saillie vers l'axe central et s'étendant longitudinalement sur la face intérieure de la portion tubulaire ;
• les premiers et deuxièmes reliefs sont des nervures présentant un sommet aplati ; grâce à quoi les déformations sont exercées en évitant des concentrations de contraintes trop ponctuelles, voire un endommagement de la surface extérieure du corps creux ;
• les nervures présentent une extrémité en forme de rampe à proximité du débouché de la portion tubulaire et s'étendent sur la majeure partie de cette portion ;
• l'organe d'extrémité présente un premier diamètre correspondant au cercle inscrit entre les sommets des premiers reliefs, et un deuxième diamètre correspondant au cercle inscrit entre les sommets des deuxièmes reliefs, ledit deuxième diamètre étant supérieur de 2% à 10% au premier diamètre, et de préférence supérieur d'environ 4% au premier diamètre ; en effet, il apparaît qu'une hauteur légèrement inférieure des deuxièmes reliefs suffise pour qu'ils n'augmentent pas excessivement la force nécessaire au montage ;
• le corps creux présente un diamètre extérieur nominal supérieur au premier diamètre et de préférence sensiblement égal au deuxième diamètre ; afin de limiter les déformations du corps creux ;
• l'instrument d'écriture comprend en outre un fût extérieur à l'intérieur duquel le corps creux formant un réservoir de mines est agencé, et l'organe d'extrémité est un support de gomme monté coulissant à travers l'extrémité arrière ouverte du fût, l'ensemble formé sur le corps creux et l'organe d'extrémité étant solidairement mobiles pour actionner un mécanisme d'avance de mine.

In preferred embodiments of the invention, use is also made of one or other of the following provisions:

• the plurality of second reliefs is regularly distributed circumferentially between the first reliefs; in order to block each of the deformation lobes created by the first reliefs with one or more second reliefs;
• each plurality of reliefs comprises an identical number of first and second reliefs, preferably equal to three or four reliefs;
• the first and second reliefs are ribs projecting towards the central axis and extending longitudinally on the inner face of the tubular portion;
• the first and second reliefs are ribs having a flattened top; thanks to which the deformations are exerted by avoiding stress concentrations too punctual or damage to the outer surface of the hollow body;
• the ribs have a ramp-shaped end near the outlet of the tubular portion and extend over most of this portion;
• the end member has a first diameter corresponding to the circle inscribed between the vertices of the first reliefs, and a second diameter corresponding to the circle inscribed between the vertices of the second reliefs, said second diameter being 2% to 10% greater than the first diameter; and preferably about 4% higher than the first diameter; indeed, it appears that a slightly lower height of the second reliefs is sufficient so that they do not excessively increase the force required for assembly;
• the hollow body has a nominal outside diameter greater than the first diameter and preferably substantially equal to the second diameter; in order to limit the deformations of the hollow body;
• the writing instrument further comprises an outer barrel inside which the hollow body forming a mine reservoir is arranged, and the end member is a rubber holder slidably mounted through the open rear end of the barrel, the assembly formed on the hollow body and the end member being integrally movable to actuate a mine advance mechanism.

• la figure 1 est une vue en coupe longitudinale d'un instrument d'écriture comportant un organe d'extrémité selon l'invention emmanché sur un corps creux ;
• la figure 2 est une vue agrandie de l'organe d'extrémité représenté à la figure 1 ;
• la figure 3 est une vue de gauche de l'organe d'extrémité complet représenté en coupe à la figure 2, et
• les figures 4 et 5 sont des vues schématiques en coupe transversale de l'engagement d'un corps creux dans un organe d'extrémité de l'art antérieur et dans un organe d'extrémité selon l'invention respectivement.

Other features and advantages will become apparent from the following description of an embodiment given without any limitation, with reference to the figures in which:

• the figure 1 is a longitudinal sectional view of a writing instrument comprising an end member according to the invention fitted on a hollow body;
• the figure 2 is an enlarged view of the end member shown at figure 1 ;
• the figure 3 is a left view of the complete end member shown in section at figure 2 , and
• the Figures 4 and 5 are schematic cross-sectional views of the engagement of a hollow body in an end member of the prior art and in an end member according to the invention respectively.

In the different figures, the same references designate identical or similar elements.

To the figure 1 , is shown in section a writing instrument 1 extending along a central axis between a front end 1a and a rear end 1b. More particularly in the embodiment shown by way of example, it is a mechanical pencil having a scrub assembly 2 at the rear end 1b. The mechanical pencil 1 also comprises a barrel 3 which forms the bulk of the outer body, and at the front end 1b a conical nose 4 which has a passage of mines. Inside the barrel 1 is arranged a mine advance mechanism 5 and a mine reservoir tube 6. The reservoir tube 6 is connected at its front end 6a to the mine advance mechanism 5 and secondly a rear end 6b on which is mounted the scrub assembly 2 in a manner which will be detailed below. The front end 6a of the tube 6 is preferably fixed releasably to the mine advance mechanism 5, for example by fitting on a metal rear end harpoon of the clamp.

The mine advance mechanism 5 is compressible longitudinally along the central axis X against an internal stop at the conical nose 4. This is to advance a clamp clamped to a mine by a ring and to allow the retraction of the clamp to the untightened state as is well known.

The mine reservoir tube 6 is a hollow body, here made of polypropylene (PP) extruded and cut to the desired length. This tube has cylindrical inner and outer walls in the absence of constraints. The outer diameter of the reservoir tube must be smaller than the inside diameter of most of the barrel 3 to slide freely therein. On the other hand, its inside diameter indicated by broken lines, must be large enough to contain several mines, and preferably at least three mines. The reservoir tube 6 thus constitutes a hollow body having a large elongation and a relatively thin wall. It is therefore sensitive to buckling, but must, however, have sufficient strength to transmit the pressure exerted by the user, especially with the thumb, on the scrub assembly 2 to operate the mechanism 5 and create the advance of mine.

The scrub assembly 2 comprises a gum carrier 20 visible to Figures 2 and 3 , a gum 21 and a gum cap 22. As is best seen in the figure 2 , the eraser holder 20 has a tubular portion 24 in the front portion thereof. This tubular portion 24 receives by fitting the rear end 6b of the reservoir tube 6. This tubular portion 24 makes it possible to maintain attached to the mechanical pencil 1 the end member constituted by this support, and more generally the scrub assembly 2. The characteristics of this portion and the mounting methods will be detailed below, but it should already be noted that these are not only applicable to the mounting of an eraser holder on a mine reservoir tube, but can be applied to the assembly of other pieces of mechanical pencil, or other writing instruments.

More particularly, the eraser 21 is received in a pot-shaped housing 25. To better maintain the eraser 21 and avoid its rotation, four protruding ridges 25a are angularly distributed on the inner periphery of the housing 25. The edges 25a all have an identical V-shaped profile which penetrates more or less into the material constituting the eraser 21. The rubber cap 22 is simply fitted to an outer peripheral recess of the rubber support 20. The bottom 25b of the rubber housing 25 is constituted by a wall having an opening 26 at its center. This opening 26 allows the passage of mines towards the inside of the reservoir tube 6 when the eraser 21 is removed.

The front tubular portion 24 has an inner face 24c registering in a cylinder coaxial with the central axis X. This cylindrical shape is favorable for resistance to radial forces, but not absolutely necessary. The inner face could have for example a hexagonal profile. This tubular portion 24 has an outlet 24a at its engagement end. On the other hand, it is bounded at the rear by a radial wall 24b which limits the depth of engagement of the reservoir tube 6. This wall 24b also constitutes the bottom 25b of the rubber housing 25.

In known manner, first reliefs 27 identical to each other project from the inner face 24c and constitute a first series of three first reliefs. These first reliefs 27 extend generally towards the central axis X on a first height measured radially from the inner face 24c. This first height is determined so that the circle inscribed between their apex has a diameter, called first diameter and indicated by the radius R1 on the figure 3 , which is less than the outer diameter of the reservoir tube 6. This outer diameter corresponds to the nominal diameter of the hollow body, that is to say outside of any deformation thereof. Thus, when the reservoir tube 6 is fitted into the tubular portion 24, it undergoes inward radial deformations at the contact zones with the first reliefs 27. This creates friction forces which ensure a certain maintenance of the support of rubber 20 on the rear end 6b of the reservoir tube.

The inner face 24c further has second reliefs 28 which project towards the central axis X. These second reliefs 28, preferably but not necessarily identical to each other, constitute a second series of three second reliefs. It is important to note that the second reliefs each have a second height which is less than the first height first reliefs. This second height is determined so that the reservoir tube 6 comes to bear against the second reliefs 28 at least when it is deformed by the first reliefs 27.

It is quite possible that the second reliefs 28 have a second height which necessarily entails engagement with the reservoir tube 6. In this case, the vertices of the second reliefs 28 are at a height such that the circle inscribed therebetween a diameter, said second diameter and indicated by the radius R2, is also smaller than the nominal outside diameter of the reservoir tube 6. Nevertheless, this second diameter R2 must be greater than the first diameter R1, even if it is only a few percent , to obtain a combined effect on the ease of assembly and the retention of the eraser support 20.

By way of example, satisfactory results have been obtained with first reliefs 27 having a height of 0.72 mm for a first diameter R1 of 3.08 mm. While the second reliefs 28 had a height of 0.6 mm for a second diameter R2 of 3.2 mm, and that also the reservoir tube 6 had a nominal diameter of 3.2 mm +/- 0.1 mm. It appears that a slightly lower height of the second reliefs 28 creating a second diameter R2 greater by only about 4% in the first diameter R1, has a notable influence on the holding of the eraser support 20. A range of value for the second diameter R2 greater than 2 to 10% in the first diameter R1 should give for most materials used for the reservoir tube 6 improved results.

These improved results seem to be explained by a locking effect obtained by the second reliefs 28, which block the deformations of the hollow body 6 created by the first reliefs 27. As schematically represented in figure 5 wherein the difference in height between the first and second reliefs (27, 28) is exaggerated, it appears that the deformation lobe created between the first reliefs 27 and visible on the figure 4 illustrating the prior art, is limited by the presence of the second reliefs 28. This overall less significant deformation of the hollow body 6 is supposed to limit the plastic deformations thereof while creating additional contact areas. However, the lower height of the second reliefs 28 makes the initial assembly of the end member 20 on the hollow body 6 does not require a much greater force. On the other hand, the reassembly of the end member after a voluntary removal keeps a satisfactory retention force, even by repeating the reassembly.

As it appears on the figure 3 the second reliefs 28, at the same number as the first reliefs 27, are regularly distributed on the circumference of the inner face 24c and arranged in the median position between the first reliefs 27. Thus, each lobe of deformations of the reservoir tube 6 is blocked by a second relief 28 in its largest displacement zone relative to the nominal outside diameter. However, it is conceivable to limit the number of second reliefs, or to increase this number, relative to the number of the first series of first reliefs. For example it is possible to provide two second reliefs 28 between each first relief 27.

The first and second series of first and second reliefs (27, 28) each comprise three reliefs. This number could be four, particularly in the case of a substantially larger external diameter of the hollow body 6. But although this is possible, it seems preferable not to reduce this number to two, nor to increase it beyond four.

The first reliefs 27, as well as the second reliefs 28, are in the form of ribs extending longitudinally over almost the entire extent of the tubular portion 24, except near the outlet 24a of this portion where the ribs have the shape a ramp (27a, 28a) to facilitate the introduction of the reservoir tube 6.

The ribs constituting the first and second reliefs (27, 28) have a square transverse profile, and even rectangular with a large side oriented towards the central axis X. This profile of the ribs has the advantage of creating a contact surface with the reservoir tube 6 relatively extended in the circumferential direction, in any case more extensive than with a triangular profile. This avoids damage to the outer surface of the reservoir tube 6, but it also seems that this provision limiting the locally created constraints would be favorable to the holding of the rubber support 20 after several pumping over.

As will be understood from the description of the embodiment shown by way of example, the number and shape of the first series of first projecting reliefs 27 and the second series of second projecting reliefs 28 may vary substantially. This within the scope of the present invention defined by the appended claims, which involves an action of the second reliefs 28 of the end member 20 on the hollow body 6 which is somewhat different in nature and intensity, in relation to the action of the first reliefs 27.

Claims (9)

1. Writing implement comprising a deformable hollow body (6) extended along a central axis (X) as far as one end, and an end member (20) comprising a tubular portion (24) which has an inner face (24c) equipped with a plurality of first identical projecting reliefs (27) suitable for engaging with and radially deforming the hollow body (6) during the fitting of said end member by engagement of its tubular portion around the end of said hollow body, characterized in that the inner face (24c) of the tubular portion has a plurality of second projecting reliefs (28) having a height measured radially from said inner face which is less than the height of the first projecting reliefs (27) and is adapted so that said second reliefs apply a radial pressure on the hollow body (6) deformed by the first reliefs, and in that the end member (20) has a first diameter (R1) corresponding to the circle inscribed between the apexes of the first reliefs (27), and a second diameter (R2) corresponding to the circle inscribed between the apexes of the second reliefs (28), said second diameter (R2) being greater than the first diameter (Rl).
2. Writing implement according to claim 1, in which the plurality of second reliefs (28) is regularly distributed circumferentially between the first reliefs (27).
3. Writing implement according to claim 1 or 2, in which each plurality of reliefs comprises an identical number of first and second reliefs (27, 28), preferably equal to three or four reliefs.
4. Writing implement according to any of the preceding claims, in which the first and second reliefs (27, 28) are ribs projecting towards the central axis (X) and extending longitudinally over the inner face (24c) of the tubular portion.
5. Writing implement according to any of the preceding claims, in which the first and second reliefs (27, 28) are ribs having a flattened apex.
6. Writing implement according to claim 4 or 5, in which the ribs (27, 28) have an end (27a, 28a) in form of a ramp close to the opening (24a) of the tubular portion and extend over the major part of this tubular portion (24).
7. Writing implement according to any of the preceding claims, in which the second diameter (R2) is 2% to 10% greater than the first diameter (Rl), and preferably approximately 4% greater than the first diameter.
8. Writing implement according to the preceding claim, in which the hollow body (6) has a nominal outer diameter greater than the first diameter (R1) and preferably substantially equal to the second diameter (R2).
9. Writing implement according to any of the preceding claims, also comprising an outer barrel (3), inside which the hollow body (6) forming a lead container is arranged, and in which the end member (20) is an eraser holder slidably fitted through the open rear end of the barrel (3), the assembly formed by the hollow body (6) and the end member (20) being jointly mobile in order to actuate a lead advance mechanism (5).

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