Film-engaging sprocket drive

Details Film-engaging sprocket drive Film-engaging sprocket drive

2000-01-06

2001-08-07

Perkey, W. B. (Department: 2851)

Photography

With film drive

Mechanical detail

C226S076000, C242S354000

Reexamination Certificate

active

06270265

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to the field of photography, and in particular to a film engaging sprocket drive preferably for use in a camera.
BACKGROUND OF THE INVENTION
As shown in
FIG. 12
(Prior Art), a typical edge-perforated 35 mm filmstrip
10
has successive evenly-spaced film perforations
12
a
,
12
b
,
12
c
, etc. The pitch
14
of the film perforations
12
a
,
12
b
,
12
c
. . . from one perforation to the next perforation is uniform (the same) as indicated in
FIG. 12
, and as is commonly understood it is the distance between one point on a film perforation and a corresponding point on the next perforation.
A typical film-engaging sprocket drive includes a single sprocket wheel
16
having a series of eight successive uniform-pitch film-engaging teeth
18
a
,
18
b
,
18
c
,
18
d
,
18
e
,
18
f
,
18
g
,
18
h
that are similarly shaped to engage the filmstrip
12
within the film perforations
12
a
,
12
b
,
12
c
, etc. The teeth
18
a
,
18
b
,
18
c
,
18
d
,
18
e
,
18
f
,
18
g
,
18
h
are spaced 45° apart, and the pitch
20
of the teeth is substantially the same as the pitch
14
of the film perforations
12
a
,
12
b
,
12
c
. . . to permit the teeth to enter the film perforations.
Problems
If the leading or forward edge
22
of an integral film leader
24
of the filmstrip
10
has a relieved edge portion
26
that is directly forward of the film perforations
12
a
,
12
b
,
12
c
. . . as shown in
FIG. 12
, then when the film leader
24
is longitudinally advanced to the right in FIG.
12
and against the tooth
18
a
of the sprocket wheel
16
, the sprocket wheel will be rotated clockwise in
FIG. 12
to swing the immediately preceding tooth
18
h
against an underside section
28
of the film leader
24
between the first available (initial) perforation
12
a
and the second available perforation
12
b
. The tooth
18
h
is swung against the underside section
28
of the filmstrip
10
because the distance
30
between the relieved edge portion
26
and the first available perforation
12
a
is less than the pitch
14
of the film perforations
12
a
,
12
b
,
12
c
. . . , i.e. it is less than the pitch
20
of the teeth
18
a
,
18
b
,
18
c
,
18
d
,
18
e
,
18
f
,
18
g
,
18
h
. Thus, the tooth
18
h
may not be able to enter the first or second available perforations
12
a
and
12
b
in order to engage the film leader
24
, which would result in a film loading failure.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a film-engaging sprocket drive for use with an edge-perforated filmstrip having successive uniform-pitch film perforations comprises:
a set of two coaxial sprocket wheels each having a series of uniform-pitch film-engaging teeth that are similarly shaped to engage the filmstrip within the film perforations and that are arranged in successive pairs of one tooth from one sprocket wheel and another tooth from the other sprocket wheel, and the sprocket wheels each are rotatable relative to the other to similarly increase the pitch of the two teeth in the respective pairs of teeth to greater than the pitch of the film perforations; and
a return spring arranged to rotate one sprocket wheel relative to the other sprocket wheel to decrease the pitch of the two teeth in the respective pairs of teeth substantially to the pitch of the film perforations. A film-engaging sprocket drive that has two coaxial sprocket wheels which can be rotated relative to one another in the manner described solves the previously discussed problem that occurs with a single sprocket wheel.
According to another aspect of the invention, a method of engaging a sprocket drive with an edge-perforated filmstrip comprises:
rotating one of two identical multi-tooth sprocket wheels relative to the other sprocket wheel to position one tooth of the one sprocket wheel in a second available perforation in the filmstrip; and
rotating the other sprocket wheel relative to the one sprocket wheel to position one tooth of the other sprocket wheel in a first available perforation in the filmstrip which precedes the second available perforation.


REFERENCES:
patent: 649563 (1900-05-01), Willson
patent: 717976 (1903-01-01), Dodge
patent: 742812 (1903-10-01), Winton
patent: 1744576 (1930-01-01), Rhett
patent: 2161913 (1939-06-01), Doyle
patent: 2351999 (1944-06-01), Nerwin
patent: 4087165 (1978-05-01), Pasturczak et al.
patent: 4437749 (1984-03-01), Ehgartner et al.
patent: 6137962 (2000-10-01), Namai

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