Printing medium detecting mechanism of printer

A printing medium detecting mechanism of a printer having a plurality of printing medium traveling paths includes a detecting groove provided in a circumferential portion of a platen other than a printing region thereof, a first printing medium detecting lever disposed on one of the plurality of the traveling paths to freely fit in the detecting lever, and a medium detecting sensor provided on a printer control circuit board. The printing medium detecting mechanism further includes a second printing medium detecting lever provided on any other medium traveling path of the plurality of the medium traveling paths. The first printing medium detecting lever is adapted to be interlocked with the second printing medium detecting lever, thereby enabling to provide a simplified printing medium detecting mechanism.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a printing medium detecting mechanism of a 
printer. 
2. Description of the Prior Art 
There is generally known heretofore, as a detecting sensor of a continuous 
printing medium detecting mechanism in a printer, a mechanism comprising a 
micro-switch, a Hall device, a photointerrupter, a lead switch, and a 
detecting lever. 
A printing medium is generally inserted from the rear of a platen, wound 
around the platen from the lower part thereof, and wound in front of a 
printing head. To so wind the printing medium around the platen, a paper 
chute is provided for guiding the printing medium, serving as a traveling 
path for a printing medium detecting mechanism provided therein. 
By contrast, a printer of a certain kind has a traveling path other than 
that described above. This traveling path is provided such that the 
printing medium is inserted from the bottom of the printer, and fed 
through the front thereof toward a printing head. For that, a paper guide 
is provided below the platen. The other traveling path described above is 
formed by this paper guide. The other printing medium detecting mehanism 
is provided also in the other traveling path described above. 
A printing medium detecting mechansim in a printer having a plurality of 
printing medium traveling paths as described above requires a plurality of 
medium detecting mechanisms and detecting circuits of the same kind. The 
printing medium detecting mechanism has drawbacks of allowing wirings 
thereof to connectors to be increased and a plurality of structures and 
assembling processes to be needed. 
SUMMARY OF THE INVENTION 
In view of the drawbacks with the conventional printing medium detecting 
mechanism, it is an object of the present invention to provide an improved 
printing medium detecting mechanism of a printer. 
Another object of the present invention is to provide an improved printing 
medium detecting mechanism in a printer including a plurality of printing 
medium traveling paths. 
Still another object of the present invention is to provide printing medium 
detecting mechanisms and detecting circuits minimized in the numbers 
thereof and simplified in the structures thereof in a printer including a 
plurality of printing medium traveling paths. 
A still further object of the present invention is to provide a printing 
medium detecting mechanism limited in wirings thereof to a connector to 
the minimum and facilitated in assembling thereof. 
According to the present invention, a first printing medium traveling path 
can serve to permit a first printing medium detecting lever to pivot due 
to the passage of a printing medium to operate a medium detecting sensor 
provided on a printer substrate, whereby the sensor detects the presence 
of the printing medium, while a second printing medium traveling path 
serves to permit the medium detecting sensor to be operated for detecting 
the presence of the printing medium with the first printing medium 
detecting lever by pivotal movement of a second printing medium detecting 
lever contacting the first lever by a cam.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1 through 3 show a first embodiment of a printing medium detecting 
mechanism of a printer according to the present invention. 
The printing medium detecting mechanism of a printer includes a platen 1 
having a detecting groove 1a provided in a circumferential portion thereof 
other than a printing region 20 of the platen, a printing medium 2 wound 
around the platen 1 and having final ends 2a, 2b each for their insertions 
into the printer in the directions of arrows A and C, a horizontally 
extending paper chute 3 below the platen 1 for guiding the printing medium 
2 to provide a travelling path of the medium and having a slit 3a provided 
therein for allowing the tip of a printing medium detecting lever to pass 
through the chute. The mechanism further includes a pin tractor unit 9 
which may be separated from the platen 1 for feeding the printing medium 
2, a printer control circuit board 10 provided on a frame of a printer 
body (not shown) for supporting a medium detecting sensor 26 disposed 
thereon, and a printing head 12 of the printer. Designated at 13, 14 are 
generally vertically extending front and rear paper guides supported on a 
frame of the printer body (not shown) for guiding the printing medium 2 
coming from the lower part in the figures, both guides having slits 13a, 
14a for allowing a bottom medium detecting lever 24 to pass therethrough. 
Designated at 21 is a printing medium detecting lever supported on a 
support bracket 22, whose tip end 21a is freely fitted in the detection 
groove 1a and whose weight is distributed such that a rear end 21b of the 
printing medium detecting lever is slightly heavier than the tip end 21a 
with respect to support point 23 of rotation so as to bias the tip end 21a 
toward the detection groove 1a. 
Designated at 24 is a bottom medium detecting lever is supported on the 
support bracket 22, whose weight is distributed such that the tip end 24a 
of the bottom medium detecting lever is slightly heavier than an opposite 
end thereof with respect to a support point 25 of rotation so as to bias 
the tip end 24a in a direction through the gap between guides 13 and 14 
into the slit 14a. 
Designated at 26 is a medium detecting sensor such as a photointerrupter 
directly disposed on the printer control base plate 10, and designated at 
21c is a projection part provided on a part of the printing medium 
detecting lever 21 and adapted to form a cam together with a projection 
part 24b of the bottom medium detecting lever. Both the projection parts 
are disposed to contact each other. 
Operation of the embodiment with the arrangement described above will be 
discribed below. 
First, with the printing medium 2 inserted from a direction of an arrow A 
in the figure, the tip end 21a of the printing medium detecting lever in 
contact with the bottom surface of the detecting froove 1a in the platen 1 
rises to the surface of the platen 1 due to reigidity of the printing 
medium 2, while the rear end 21b thereof is separated from the medium 
detecting sensor 26 and held in a state shown in FIG. 1, thus allowing the 
printer to be ready for opertion. 
Then, when the printing medium 2 is fed by the pin tractor unit 9 and the 
final end 2a of the printing medium 2 passes through the tip end 21a of 
the printing medium detecting lever, the printing medium detecting lever 
21 is rotated in a direction of an arrow B of FIG. 1 around the support 
point 23 of rotation, and the tip end 21a of the printing medium detecting 
lever is brough into contact with the bottom surface of the detecting 
groove 1a of the platen 1 passing through the slit 3a. With this, the rear 
end 21b of the printing medium detecting lever goes across the medium 
detecting sensor 26 mounted on the printer control circuit board 10, 
whereby the printer immediately stops printing operation thereof. 
In addition, in case of insertion of the printing medium 2 from a direction 
of an arrow C of FIG. 1, with the tip end 24a of the bottom medium 
detecting lever rotated around the rotation support point 25 of rotation, 
the projection part 24b pushes the projection part 21c of the printing 
medium detecting lever is separated from the medium detecting sensor 26 to 
be kept in a state shown in FIG. 1, thereby allowing the printer to be 
ready for printing operation. 
Successively, when the final end 2b of the printing medium 2 passes through 
the tip end 24a of the bottom medium detecting lever, the bottom medium 
detecting lever 24 is rotated in a direction of an arrow D of FIG. 1 
around the rotation support point 25 and passes through the slits 13a, 
14a. The rear end 21b of the medium detecting lever traverses the medium 
detecting sensor 26, whereby the printer is immediately stopped in 
printing operation thereof. 
FIG. 4 is a second embodiment of a printing medium detecting mechanism of a 
printer according to the present invention. Only the different parts from 
the first embodiment will be described. Designated at 27 is a printing 
medium detecting lever, which has a printing medium detecting lever tip 
end 27a, and designated at 28 is a reset spring fixed at opposite ends to 
lever 27 and a stationary portion of the printer for serving to urge the 
printing medium detecting lever 27 always toward a prescribed equilibrium 
postion in which rear end 21b crosses the sensor 26. This position is 
located between respective positions shown in phantom line in FIG. 4 in 
which tip end 27a is obstructed by the printing medium 2 to pivot the rear 
end above or below sensor 26 depending on the location of printing medium 
2 along chute 3 or between guides 13 and 14. Here, the printing medium 
detecting lever 21 and the bottom medium detecting lever 24, both shown in 
the first embodiment, are replaced by the present one printing medium 
detecting lever 27, which is rotatable around a support point 29 of 
rotation in a direction of an arrow shown in FIG. 4. The printing medium 2 
can be detected by the one printing medium detecting lever 27 regardless 
of a traveling path of the printing medium 1. 
Although certain preferred embodiments have been shown and described, it 
should be understood that many changes and modifications may be made 
therein without departing from the scope of the appended claims.