Projection-retraction mechanism for a writing instrument

A two-part barrel sleeve includes an internal spring finger which rides in a spiral groove in the combined ink reservoir and barrel of a ball pen, the spiral groove having a detent at its rear end to provide a snap-action as the barrel sleeve is retracted to its rearmost position exposing the writing tip for normal use.

The present invention relates in general to writing instruments of the type 
in which a tubular shroud may be moved between a forward storage postion 
wherein it covers and protects the writing tip of the instrument, and a 
rearward retracted position wherein the writing tip is exposed for normal 
use. 
BACKGROUND OF THE INVENTION 
It is known in the prior art to threadedly mount a tubular barrel to a 
writing cartridge located within the barrel so that relative rotation 
between the writing cartridge and the barrel results in axial displacement 
of the barrel relative to the cartridge. In that construction the writing 
tip may be shrouded by the barrel when the writing instrument is not being 
used. See, for example, U.S. Pat. Nos. 2,441,280 and 2,603,186 for a 
description of that type of writing instrument. Similarly, it is known to 
threadedly attach a short, tubular shroud sleeve to the barrel of a 
writing instrument for the same purpose. 
Although these prior art systems have functioned as intended, they have 
exhibited several characteristics which leave room for improvement. For 
example, in some cases the threadedly connected parts have not been 
sufficiently tight to prevent a noticeable amount of axial play between 
the two parts. In other designs, the parts were complex and expensive to 
manufacturer while in other cases they were not conducive to use in 
attractively styled writing instruments. 
It would be desirable, therefore, to provide a novel writing instrument of 
the heretofor mentioned type wherein the projection/retraction mechanism 
is durable, yet simple in construction and easy to assemble with automated 
assembly techniques. 
SUMMARY OF THE INVENTION 
Briefly, there is provided in accordance with the present invention a new 
and improved writing instrument having a construction which is 
particularly suited to automated assembly techniques. This instrument 
includes a ball pen cartridge constituting the barrel of the pen and 
having a spiral groove near its forward end into which a follower lug on a 
spring finger carried internally by a two-part tubular shroud assembly is 
resiliently pressed. The spring finger provides uniform resistance to 
relative rotation between the barrel and the shroud as the shroud is 
rotated between the writing and storage positions. A detent step is 
provided at the rearmost end of the spiral groove so that the shroud snaps 
into its rearmost position fully exposing the writing tip for normal use. 
In the rearmost position of the shroud the annular rear end of the shroud 
abuts a forwardly facing annular stop shoulder on the barrel whereby the 
shroud is trapped between the stop shoulder and the step in the spiral 
groove whereby any substantial spurious movement relative to the cartridge 
is prevented. 
Preferably, the shroud consist of two axially aligned sleeves which are 
snap-fitted together during assembly to the barrel. The rear sleeve 
includes the spring finger which extends under the front sleeve and is 
held in operative engagement with the spiral groove by means of a collar 
on the front sleeve. 
In accordance with another feature of a preferred embodiment of the present 
invention, the annular portion of the barrel disposed just in front of the 
stop shoulder and which is exposed when the shroud is in its forwardmost 
position shrouding the writing tip carries visible indicia corresponding 
to a writing characteristic of the writing instrument such as the size of 
the ball and the color or type of ink. 
The barrel and shroud may be injection molded plastic parts thereby 
reducing the weight of the writing instrument and enabling the use of 
attractively styled designs.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
Referring to the drawing, a writing instrument 10 of the ball pen type 
comprises as its principal elements a tubular barrel 12 having a 
conventional writing tip 14 fitted into the front and in communication 
with a supply of liquid ink 16 contained within the barrel 12; a pocket 
clip member 18 affixed over the rear end of the barrel 12; and a shroud 
assembly made up of front and rear tubular shroud pieces 20 and 22 
snap-fitted together over the forward portion of the barrel 12. As more 
fully described hereinafter, rotation of the shroud assembly in one 
direction relative to the barrel 12 causes the shroud assembly to move 
forward and to shroud or cover the writing tip 14 as shown in FIG. 1. 
Rotation of the shroud assembly in the opposite direction causes the 
shroud assembly to move rearwardly on the barrel 12 to the writing 
position shown in FIG. 3 exposing the writing tip 14. A detent is provided 
to prevent spurious movement of the shroud from its rearwardmost writing 
postion during use of the instrument. 
Considering the writing instrument 10 in greater detail, the barrel 12 is 
preferably a molded plastic part which functions as the main body member 
and also as the ink reservoir. It includes a forwardly facing annular 
shoulder 26 against which the rear, annular edge 28 at the rear of the 
shroud piece 22 abuts when the shroud assembly is in its rearwardmost 
position exposing the tip 14 for normal use. When the shroud assembly is 
in its forward, shrouding position, a narrow annular band 30 on the barrel 
12 is exposed. Preferably the band 30 is color coded or imprinted with 
some other code identifying the type of ink, the color of the ink and the 
size or type of writing tip, such for example, as fine, medium or board. 
The barrel 12 is provided with a spiral camming groove 34, and the rear 
shroud piece 22 includes a forwardly extending spring finger 36 having 
near its distal end a cam follower projection in the form of a button 38 
extending into the groove 34. The cam follower projection 38 is held in 
the groove 34 by means of the front shroud piece which extends over the 
collar 40 at the front of the rear shroud piece 22. The two shroud pieces 
20 and 22 are held in mutually assembled relationship by a narrow, 
internal annular rib 42 on the piece 20 which, as best shown in FIG. 3 
fits into a complimentary annular groove 44 in the collar 40 of the rear 
shroud piece 22. In addition, a plurality of longitudinally extending ribs 
47 are provided on the collar 40 to assure that there is no noticeable 
relative movement between the shroud pieces. 
A plurality of equally spaced annular grooves 48 are provided in the 
external surface of the front shroud piece 20 to facilitate gripping of 
the instrument 10 during writing. The rearwardmost groove 48 is bounded on 
its rear side by a forwardly facing annular shoulder 50 of the rear shroud 
piece 22. Consequently, the demarcation line between the two shroud pieces 
is not visually apparent in the assembled writing instrument. 
With particular reference to FIG. 4, it may be seen that the rear portion 
of the groove 34 identified at 34A lies in a plane perpendicular to the 
longitudinal axis of the barrel 12, and a detent ridge 52 is located 
between the portion 34A and the spiral portion of the groove 34 to prevent 
spurious movement of the shroud down over the writing tip during normal 
use of the instrument. The forward end portion 34B of the groove 34 also 
lies in a plane perpendicular to the longitudinal axis of the instrument 
so that a torque must be applied between the barrel 12 and the shroud 
assembly to unshroud the writing tip. 
It may thus be seen that the writing instrument is readily adaptable to 
automated assembly techniques. After the barrel 12 has been filled with 
ink and the tip 14 fitted in place, the rear shroud piece may be pushed 
over the front end of the barrel until the cam follower projection 38 
snaps into the groove 34. Then the front shroud piece may be pushed over 
the front end of the barrel and over the collar until the rib 42 thereon 
snaps into the groove 44 in the rear shroud piece. The rib is sufficiently 
thin, and the plastic of which the piece 20 is molded is sufficiently 
resilient to permit the rib 42 to slide over the forward portion of the 
collar 40. It may be seen that the front end 40A of the collar 40 is 
tapered to facilitate movement of the collar 40 into the rear end of the 
front shroud piece 20 during the assembly operation. Once assembled, the 
shroud pieces cannot be readily disassembled from one another or from the 
barrel. 
While the present invention has been described in connection with a 
particular embodiment thereof, it will be understood by those skilled in 
the art that many changes and modifications may be made without departing 
from the true spirit and scope of the present invention. Therefore, it is 
intended by the appended claims to cover all such changes and 
modifications which come within the true spirit and scope of this 
invention.