Slider for mechanical pencil

A slider for a mechanical pencil comprises: a slider body provided with a through bore through which a lead is passed and disposed in the tip of a barrel so as to be axially slidable in a predetermined range; a lead guide concentrically fixed to the slider body so as to let the lead slide therethrough; a sliding part concentrically connected to the outer circumference of the rear end of the slider body so as to extend forward and to be able to slide against a predetermined frictional resistance relative to the inner circumference of the tip; and a lead guiding part disposed in one end of the slider body and capable of expansion and of applying a frictional resistance smaller than that applied to the sliding part by the inner circumference of the tip to the lead.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a slider for a mechanical pencil and, more 
particularly, to a slider for a mechanical pencil provided with a lead 
guide which is forced to slide to project the lead. 
2. Description of the Related Art 
Generally, in a mechanical pencil having a tip member and a lead guide 
comprising a pipe and a chip and fixed to the front end of the tip member, 
the length of a portion of the lead projecting from the front end of the 
lead guide is limited to prevent breakage of the lead. Therefore, when 
writing for a long time, a push head provided on the rear end of a lead 
tank must be frequently pushed as the lead wears to feed the lead. Since 
one's grip on the mechanical pencil must be changed to push the push head 
for a lead feed operation, the lead feed operation reduces writing 
efficiency. 
A slide type mechanical pencil provided with a lead guide which is operated 
for sliding when the lead wears and a mechanical pencil capable of feeding 
a desired length of the lead by pressing the lead against the writing 
paper or the like without requiring the change of grip on the mechanical 
pencil have been proposed to solve such a problem. For example, the 
assignee of the present patent application proposed in U.S. Pat. No. 
4,714,365 a lead feed slider formed by concentrically arranging a larger 
tubular member and a smaller tubular member having a diameter different 
from that of the larger tubular member toward the rear, in which the 
larger tubular member is placed in sliding contact with the inner 
circumference of the tip member of a mechanical pencil so that a large 
frictional resistance acts thereon, and the smaller tubular member holds 
the lead securely so that a fixed frictional resistance acts on the lead. 
Referring to FIGS. 1 to 3 showing this prior art lead feed slider, in a 
slider for a mechanical pencil, comprising a lead guide 11 disposed within 
the tip of a barrel so as to be axially slidable in a predetermined range, 
and a sliding member 12 fixed to the rear end of the lead guide 11, having 
an inner circumference capable of applying a fixed frictional resistance 
to the lead to hold the lead and an outer circumference in sliding contact 
with the inner circumference of the tip and capable of sliding against a 
frictional resistance greater than the frictional resistance acting on the 
lead, the sliding member 12 has a smaller tubular portion 13 and a larger 
tubular portion coaxial with the smaller tubular portion 13 and having a 
diameter larger than that of the smaller tubular portion 13, a plurality 
of axial recesses 15 are formed in the smaller tubular portion 13, the 
sliding member 12 is provided with an inner sliding piece 16 tapered 
toward a lead guiding part to hold the lead that slides through the lead 
guide by a frictional resistance, a plurality of recesses 17 formed in the 
larger tubular portion 14, and an outer sliding piece in sliding contact 
with the inner circumference of the tip and capable of sliding against a 
frictional resistance greater than the aforesaid frictional resistance. 
In the prior art slider thus formed, the larger tubular portion and the 
smaller tubular portion are formed concentrically backward in a single 
body, and an annular gap opening toward the rear is formed in the rear end 
through which the lead is fed. Therefore, when inserting the lead in the 
slider, the lead is liable to enter the gap and hence it is difficult to 
guide the lead forward. Consequently, there is the possibility that the 
lead will be broken. Furthermore, particles of leads, fragments of leads 
and residual leads accumulated in the gap make the reliable action of the 
slider impossible. 
SUMMARY OF THE INVENTION 
The present invention has been made to solve the foregoing problems and it 
is therefore an object of the present invention to provide a slider for a 
mechanical pencil, capable of a) preventing breakage of the lead, of b) 
avoiding being stopped-up with particles of the lead, of c) reliably 
guiding, holding and feeding the lead, and of d) enabling writing for a 
long time without changing one's grip on the mechanical pencil. 
With the aforesaid object in view, the present invention provides a slider 
for a mechanical pencil, comprising: a slider body provided with a through 
bore through which a lead is passed and disposed in the tip of a barrel so 
as to be axially slidable in a predetermined range; a lead guide 
concentrically fixed to the slider body to let the lead slide 
therethrough; a sliding part concentrically connected to the outer 
circumference of the rear end of the slider body so as to extend forward 
and to be able to slide against a predetermined frictional resistance 
relative to the inner circumference of the tip; and a lead guiding means 
disposed in one end of the slider body and capable of expansion and of 
applying a frictional resistance smaller than that applied to the sliding 
part by the inner circumference of the tip to the lead. 
According to the present invention, the sliding part formed concentrically 
on the outer circumference of the sliding body of the slider is able to be 
held in sliding contact with the inner circumference of the tip by a 
sufficiently large frictional resistance, the slider is able to hold the 
lead securely by the lead guiding means provided on the sliding body by 
the predetermined frictional resistance, no gap is formed because the rear 
end of the slider body and the rear end of the sliding part are joined 
together and hence particles of leads, broken leads and residual leads are 
not accumulated and the lead can be smoothly guided toward the tip. Since 
the lead guiding means is flexible to facilitate the advancement of the 
lead, the lead can be reliably guided, held and advanced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 4 to 8 show a slider in a first embodiment according to the present 
invention. Referring to FIG. 4, a tip 2 is formed on the front end of a 
barrel 1 integrally with the barrel 1. A lead tank 3 is inserted in the 
barrel 1 coaxially for sliding movement, and a lead chuck 4 is fixedly 
attached to the front end of the lead tank 3. A knocking cap, not shown, 
is detachably put on the rear end of the lead tank 3 so as to slide 
relative to the barrel 1. A chuck ring 5 is put loosely on the front end 
of the lead chuck 4. The rear end of the chuck ring 5 faces an inside 
flange 6a formed on the inner surface of the front end of a cushion sleeve 
6 axially movable within the barrel 1. The cushion sleeve 6 is an 
elastically deformable member and has a generally cylindrical shape. The 
rear end of the cushion sleeve 6 is expanded to form a stopping part 6c 
having a diameter greater than the outside diameter of the body part 6b. A 
radial recess 6d is formed in the body part 6b and an axial recess 6e is 
formed in the rear end to enable the stopping part 6c to produce a 
resilient force relative to the body part 6b. The stopping part 6c is 
formed in a shape so that the stopping part 6c can be surely and smoothly 
fitted in a stopping hole 1a formed in the barrel 1 when the cushion 
sleeve 6 is inserted together with a lead feed mechanism in the barrel 1 
by a simple pushing action and the stopping part 6c will not rattle in the 
stopping hole 1a. The body part 6b moves elastically in a range 
corresponding to the axial gap G of the recess 6d relative to the stopping 
part 6c held in the stopping hole 1a. Normally, the body part 6b is biased 
forward. A chuck spring 7 is interposed between the front end of the lead 
tank 3 and the flange 6a of the cushion sleeve 6 to bias the lead tank 3 
backward. 
The front portion of the tip 2 is tapered toward the front in the shape of 
a circular cone. A tapered stopping step 8 is formed between portions of 
different diameters of the inner circumference of the front portion of the 
tip 2. A slider 9 having stopping parts 9a is axially slidably fitted in 
the front portion of the tip 2. The forward movement of the slider 9 is 
limited by the step 8. As shown in FIGS. 5 to 9, the slider 9 has a 
substantially cylindrical slider body 9b, and a sliding part 9c. The 
respective rear ends of the slider body 9b and the sliding part 9c are 
joined together in an integral piece. The slider 9 is an integral member 
formed of a synthetic resin, such as an ABS resin or a polyacetal resin. 
The front portion of the slider 9 is pressed in a lead guide 10 for 
guiding the lead, i.e., a tip member. The lead guide 10 is neither abraded 
nor damaged even if the same strikes on a paper sheet or the like during 
writing. Since the lead is held by the front portion of the slider 9 and 
only the outer surface of the slider body 9b is available for attaching, 
the lead guide 10 as shown in FIG. 4 is a suitable tip member. A lead 
guiding part 9e for holding the lead is formed in the front portion of the 
slider body 9b. More specifically, the lead guiding part 9e is provided 
with a bore tapering toward the front, a plurality of slits 9f extending 
backward from the front end, and lead holding protrusions 9g on the inner 
surface of the front end. 
The rear end of the slider body 9b and the rear ends of the sliding part 9c 
are joined concentrically in an integral piece. In this embodiment, the 
sliding part 9c has two sliding lugs extending toward the front and 
capable of being radially and elastically strained. In a free state, i.e., 
in a state before the slider 9 is inserted in the tip 2, the outside 
diameter of the rear end of the sliding part 9c is greater than the inside 
diameter of the tip 2. Protrusions 9h are formed on the outer 
circumference of the sliding part 9c. A frictional resistance that acts on 
the outer circumference of the sliding part 9c when the sliding part 9c is 
brought into contact with the inner surface of the tip 2 is far greater 
than a frictional resistance applied to the lead by the inner surfaces of 
the lead holding protrusions 9g. 
The operation of the slider in this embodiment will be described 
hereinafter with reference mainly to FIG. 4. In a state where any external 
force is not applied to the rear end of the lead tank 3, the cushion 
sleeve 6 is held at the front end of the range of its movement, and the 
lead is held firmly by the front end of the lead chuck 4 because the lead 
chuck 4 is biased backward relative to the chuck ring 5 as shown in FIG. 
4. When the knocking cap, not shown, is knocked to push the lead tank 3 
forward in this state, the lead chuck 4 is moved forward together with the 
chuck ring 5, and then the chuck ring 5 is disengaged from the lead chuck 
4 and only the lead chuck 4 advances further to release the lead after the 
chuck ring 5 has been brought into contact with a step 2a formed in the 
inner surface of the tip 2. 
When the force applied to the knocking cap is removed, the lead tank 3 is 
moved backward together with the lead chuck 4, the chuck ring 5 comes into 
contact with the front end of the cushion sleeve 6 and squeezes the front 
end of the lead chuck 4 to hold the lead, and then the lead tank 3 stops. 
This lead feed operation is repeated to feed the lead stepwise. The length 
of the lead by which the lead is fed by one cycle of the lead feed 
operation is approximately equal to the distance between the front end of 
the chuck ring 5 and the step 2a. When the lead feed operation is 
performed to advance the lead, the lead advances through the lead guide 10 
because the frictional resistance applied to the lead by the protrusions 
9g of the lead guiding part 9e is smaller than the frictional resistance 
applied to the protrusions 9h of the sliding part 9c by the inner 
circumference of the tip 2. Then, the mechanical pencil, similarly to the 
ordinary mechanical pencil, is used for writing. 
When the tip of the lead is abraded or broken during writing, the remaining 
part of the lead is pressed against the paper sheet or the like without 
changing one's hold on the barrel 1. Then, a backward force acts on the 
lead chuck 4 holding the lead and the lead tank 3 to move the lead chuck 4 
and the lead tank 3 together with the chuck ring 5 and the cushion sleeve 
6 backward against the resilience of the stopping part 6c. The range of 
backward movement is about 0.5 to about 1.0 mm. Since the stopping parts 
9a formed at the front end of the sliding part 9c are in contact with the 
step 8 of the barrel 1, the size of the range for the backward movement of 
those components is G at the maximum. When the lead is moved backward to 
the front end of the lead guide 10, the paper sheet applies a pressure to 
the lead guide 10 and the lead guide 10 moves backward together with the 
slider 9. When the lead is moved to the rear end of the range of its 
movement, the position of the lead coincides with that of the lead guide 
10. 
When one removes the pressure pressing the barrel 1 against the paper 
sheet, the resilience of the flexed stopping part 6c moves the body part 
6b of the cushion sleeve 6 forward to the front end of the moving range 
and, consequently, the chuck ring 5 advances together with the lead chuck 
4 and the lead held by the lead chuck 4 to its original position. However, 
the lead guide 10 is restrained from advancement by the large frictional 
resistance applied by the inner circumference of the tip 2 to the 
protrusions 9h of the sliding part 9c and hence the front end of the lead 
projects from the tip of the lead guide 10 by a length corresponding to 
the distance by which the lead guide 10 has been moved backward. The same 
operation can be repeated until the lead guide 10 reaches the rear end of 
its moving range. 
If it is desired to further project the lead from the lead guide 10 after 
the point at which the lead guide 10 has reached the rear end of its 
moving range, the lead tank 3 is pushed axially for lead feed operation. 
When the lead tank 3 is pushed axially, the lead chuck 4 advances 
releasing the lead, the lead chuck 4 comes into contact with the rear end 
of the slider 9 and moves the slider 9 to the front end of its moving 
range. Then, the lead advances together with the slider 9 and hence the 
front end of the lead remains at the tip of the lead guide 10. When the 
force applied to the lead tank 3 is removed, the lead chuck 4 moves 
backward leaving the lead and the lead guide 10 at the same position, and 
stops after engaging with the chuck ring 5. The lead can be advanced 
gradually by a predetermined distance at a time by repeating the lead feed 
operation. 
In the slider in the first embodiment, the lead guiding part 9e is located 
at the front end of the slider body 9b, no projections are formed in the 
surface of the through bore 9d formed in the slider body 9b, and the 
through bore 9d is a straight bore extending from the rear end of the 
slider body 9b to the lead guiding part 9e. Therefore, the lead, dropping 
by gravity, can readily advance and can be readily guided through the 
through bore 9d. 
FIGS. 10 to 15 show a slider 9 in a second embodiment according to the 
present invention. While the slider 9 in the first embodiment holds the 
lead at its front end, the slider 9 in the second embodiment holds the 
lead at its rear end. A slider 9b is provided with a through bore 9d 
through which the lead moves. The slider 9 is fitted in the tip 2 of a 
barrel 1 so as to be axially movable in a predetermined range. A lead 
guide 10 is fixed concentrically to the front end of the slider body 9b, 
and the lead slides through the lead guide 10. The slider 9 has a sliding 
part 9c concentrically joined to the outer circumference of the rear end 
of the slider body 9b so as to extend forward, provided with a plurality 
of axial slits 9f and in sliding contact with the inner circumference of 
the tip 2 and held in place by a frictional resistance, and lead holding 
pieces 9i for applying a frictional resistance smaller than the frictional 
resistance applied to the sliding part 9c by the inner circumference of 
the tip 2 to the lead. The rear end of a lead guiding part 9e formed on 
the inner circumference of the rear end of the slider body 9b is joined to 
the rear end of the sliding part 9c, and has a plurality of connecting 
pieces 9k (FIG. 13), and a plurality of lead holding pieces 9i (FIG. 14) 
tapered backward, separated from the connecting pieces 9k by a plurality 
of slits 9f extending from the rear toward the front and having rear ends 
not connected to the sliding part 9c. The connecting pieces 9k and the 
lead holding pieces 9i are separated from each other by the slits 9f and 
are arranged alternately on a circle. An arcuate lead holding protrusion 
9g protrudes inward from the rear end of each lead holding piece 9i. 
The lead holding pieces 9i are formed so that the diameter of a circle 
circumscribed about the lead holding pieces 9i is equal to or greater than 
the diameter of a lead guiding opening 9j formed in the rear end of the 
lead guiding part 9e to prevent the lead being stopped when inserting the 
lead into the slider 9 from the rear end of the slider 9; that is, the 
outer surfaces of the lead holding pieces 9i are on the circumference of a 
circular cylinder corresponding to the inner circumference of the lead 
guiding opening 9j or on the circumference of a circular cylinder greater 
than the inner circumference of the lead guiding opening 9j. Since the 
lead can be easily guided into the lead guiding opening 9j without being 
caught and the rear ends of the lead holding pieces 9i are free, the lead 
holding pieces 9i can be easily bent radially outward and the lead can be 
automatically held. 
The operation of the slider 9 in the second embodiment having the lead 
guiding part 9e at its rear end is substantially similar to that of the 
slider 9 in the first embodiment having the lead guiding part 9e at its 
front end. In this embodiment, the lead guide 10 may be a chip or a pipe. 
The slider body 9b and the lead guide 10 may be separate members or may be 
formed integrally. Naturally, the number of the slits 9f formed in the 
lead guiding part 9e of the slider body 9b need not be limited to three or 
four as shown in the drawings, and the number of the sliding pieces of the 
sliding part 9c need not be limited to two. 
Although the invention has been described in its preferred embodiments with 
a certain degree of particularity, obviously many changes and variations 
are possible therein. It is therefore to be understood that the present 
invention may be practiced otherwise than as specifically described herein 
without departing from the scope and spirit thereof.