EP0151456B1

EP0151456B1 - Mechanical pencil

Info

Publication number: EP0151456B1
Application number: EP19850100907
Authority: EP
Inventors: Curtis L. Malm
Original assignee: Gillette Co LLC
Current assignee: Gillette Co LLC
Priority date: 1984-02-09
Filing date: 1985-01-29
Publication date: 1990-05-23
Anticipated expiration: 2005-01-29
Also published as: EP0151456A3; CA1219555A; JPS60233000A; EP0151456A2; DE3577825D1; JPH0557920B2

Description

Background of the invention

For many years, the lower-priced end of the pencil market has been dominated by conventional wooden pencils with mechanical pencils being unable to secure but a minor portion of the market. A number of factors have contributed to this devision of marked share, most importantly, the relative expense of the mechanical pencils which have been made available requiring that they be regarded as nondisposable items. Many attempts have been made to develop a simplified mechanical pencil which can compete with the less expensive wood pencils. Such pencil would overcome the advantages of the need to sharpen the point and the fact that the entire length of the wooden pencil is not usable. Although some of the designs for disposable mechanical pencils in the prior art would appear to be less expensive to manufacture than conventional mechanical pencils, they are still generally much more expensive than the common wooden pencil and hence have not been able to acquire a significant share of that market.
Examples of known mechanical pencils can be seen from document CH-A-266391 and document US-A-1627602.- In both of these documents there is shown a mechanical pencil including a hollow barrel, a tip rotatably mounted in said barrel, a helical spring axially within the bareel and keyed to the tip, a lead advance-retract member located within the helical spring for carrying a lead and having a radial lug passing between the turns of the helix of the spring, the lug being guided in a longitudinal guide in the inner wall of the barrel, such that relative rotational movement between the barrel and the tip is converted to a longitundinal movement of the lead advance-retract member (preamble of claim 1).
In these arrangements, the radial lug is formed from the trailing end of the advance-retract member, which is bent over at right angles, thereby passing between the turns of the helical spring. The lug serves to prevent rotation of the advance-retract member with respect to the hollow barrel but it does not provide any lateral positioning of the lead. In document US-A-1627602 the spring and advance-retract member are free to float about laterally within the housing but in document CH-A-266391 they are held by the fact that the spring is a tight fit in the housing.
In the arrangement of the present invention (characterising part of claim 1), the longitudinal guide consists of a plurality of spaced apart longitudinal grooves and the lead advance-retract member has a plurality of radially and axially spaced lugs for engaging said grooves and co-operating with the helix of the spring. With this arrangement, the lateral stability problem is solved but the provision of axially spaced lugs gives rise to assembly problems. To overcome these, the invention provides that a rearwardly disposed one of the lugs has a forwardly extending projection at its radially outermost end so that during assembly of the pencil the forward most lug and said projection align simultaneously with the longitudinal grooves. The forward end of the advance-retract member includes a lead-holding bore to retain frictionally the end portion of the lead.

Brief description of the drawings

Figure 1 is an exploded view of a complete embodiment of the operating mechanism of a mechanical pencil in accordance with the present invention.
Figure 2 is a sectional view inside elevation of the rearward portion of a mechanical pencil of this invention illustrating the operation of the lead advance-retract mechanism.
Figure 3 is a sectional view inside elevation of the forward portion of a mechanical pencil of this invention illustrating the operation of the lead advance-retract mechanism.
Figure 4 is a sectional view in enlarged scale taken on line 4-4 of Figure 2.

Description of the preferred embodiments

Referring to Figure 1, a mechanical pencil has essentially five parts, a hollow barrel 10, a rotatable tip 20, a lead advance-retract member 30, a helical metal spring 40, and an eraser or barrel plug 50.
Referring now to Figures 2-4, the hollow barrel 10 of the mechanical pen comprises a forward end 12 terminated by a bore portion of reduced inside diameter 14 and a rearward end 16 terminated by a bore portion of increased diameter 17 within which are located dimples 22 which serve to frictionally retain eraser 50. Mounted near the rearward end of barrel 10 is integrally molded clip member 18, which serves to retain the mechanical pencil in a pocket or the like when it is not in use. Located axially within the bore of barrel 10 are helical spring 40 typically of metal, lead advance-retract member 30, and lead 24. Located on the inner wall of hollow barrel 10 are longitudinal grooves 32, the purpose of which will be made clear hereinafter.
Referring to Figure 3, tip 20 comprises conical forward portion 34 bearing finger-gripping grooves 38 (best seen in Figure 1) and terminating at shoulder 36. Rearward portion 44 of tip 20 comprises skirt 46 split by slots 48 and which bears lugs 50 to form a discontinuous shoulder which during assembly abuts shoulder 15 formed by bore portion of reduced inside diameter 14.
Lead advance-retract mechanism 30 comprises forward end 54 within which is located lead holding bore 56 within which is frictionally retained lead 24. Mounted on rearward end 58 of lead advance-retract member 30 are lugs 60 and 61. The lugs are spaced radially and axially to cooperate with the helix of the spring. They also mate and are guided within barrel grooves 32 as shown best in Figure 4. Contiguous with a lug 61 is lug lead portion consisting of a forwardly extending projection 62 at its radially outermost end which serves to reduce assembly problems by insuring that both of the lugs 60 and 61 are simultaneously aligned with grooves 32 during assembly.
Located axially within the bore of hollow barrel 10 is helical spring 40 which comprises forward portion 64 which is terminated by turns of reduced pitch 66 which are keyed by frictional engagement with hollow bore of tip 20 and rearward portion 68 terminated by open turn 70.
In operating the pencil to advance or retract the lead, barrel 10 and tip 20 are rotated with respect to each other. In so doing, spring 40 is caused to rotate with tip 20 by virtue of the friction fit of spring turns of reduced pitch 66. At the same time, lead advance-retract member 30 is caused to rotate with barrel 10 by the keying action of lugs 61 and longitudinal grooves 32 on the inner wall of the barrel. As a result, the rotational movement of tip 20 and helical spring 40 is converted to longitudinal movement of lead advance-retract member 30 as the rotating turns of the spring bear upon lug 60 as shown in Figure 2.
From the foregoing, it will be seen that there has been provided a practical mechanical pencil of very simple contruction, requiring a limited number of parts and adapted for low-cost mass production.

Claims

1. A mechanical pencil including a hollow barrel (10), a tip (20) rotatably mounted in said barrel (10), a helical spring (40) axially within the barrel (10) and keyed to the tip (20), a lead advance-retract member (30) located within the helical spring (40) for carrying a lead and having a radial lug (60, 61) passing between the turns of the helix of the spring (40), the lug (60, 61) being guided in a longitudinal guide (32) in the inner wall of the barrel (10), such that relative rotational movement between the barrel (10) and the tip (20) is converted to longitudinal movement of the lead advance-retract member (30),
characterized in that the longitudinal guide (32) consists of a plurality of spaced apart longitudinal grooves (32) and the lead advance-retract member (30) has a plurality of radially and axially spaced lugs (60, 61) for engaging said grooves (32) and co-operating with the helix of the spring (40), and in that

a rearwardly disposed one (61) of said lugs has a forwardly extending projection (62) at its radially outermost end so that during assembly of the pencil the forward most lug (60) and the said projection (62) align simultaneously with the longitudinal grooves (32), and

the forward end of the advance-retract member (30) includes a lead-holding bore (56) to retain frictionally the end portion of the lead (24).

2. A mechanical pencil according to claim 1, characterized in that the helical spring (40) is keyed to the tip (20) by frictional engagement.