Film drive for motion picture apparatus

A film drive for a motion-picture camera or projector has a film drive wheel which is rotatable about a first axis and has a plurality of angularly equi-spaced and radially extending teeth. A function cam rotatable about a second axis spaced from and perpendicular to the film axis has a generally helical peripheral formation which engages with the teeth of the wheel. This helical formation includes an intermittent-drive section having a holding portion constituting almost a complete turn of the formation of zero degree pitch and a switching portion at each end of the holding portion of predetermined pitch greater than zero degrees, and a constant-drive section of constant pitch greater than zero degrees and axially offset from the intermittent-drive section. A shifter is provided for displacing the function cam along its axis relative to the drive wheel so that the teeth on the drive wheel either engage the intermittent-drive section or one of the constant-drive sections axially flanking the intermittent-drive section. A motor is connected to the function cam and rotates it at a relatively slow speed in a forward direction when the teeth of the drive wheel are engaged with the intermittent drive section so as to rotationally step this drive wheel. When engaged with one of the constant-drive sections the motor rotates the function cam at a relatively elevated forward speed for fast-forward motion of the film, and when teeth are engaged with the other constant-drive section the motor rotates the function cam in the opposite direction for fast rewind of the film.

BACKGROUND OF THE INVENTION 
This invention relates to a film drive for a motion-picture apparatus. More 
particularly this invention concerns a film advance for a motion-picture 
camera or projector. 
In both a motion-picture camera and a motion-picture projector it is 
necessary to drive the film in at least two separate manners: it must be 
able to move intermittently during exposure or projection in synchronism 
with appropriate shutter arrangements, and it must be able to move 
continuously for loading and/or rewinding. Typically the displacement rate 
during continuous displacement can be no greater than two to three times 
the normal advance speed during intermittent displacement. 
In most movie projectors and cameras the complicatd intermittent-drive 
arrangement is simply disconnected and an auxiliary continuous drive is 
connected up for rewinding or loading the film. Such provision of two 
separate drives considerably increases the cost of the unit as well as its 
size. Furthermore, after the film has been rewound or advanced 
continuously it is necessary to orient it again properly behind the 
shutter, as the sprocket wheel which serves intermittently to drive the 
film and to synchronize the frames with the shutter action has been 
disengaged. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
film drive for a motion-picture apparatus. 
Another object is the provision of film advance for movie camera or 
projector which is relatively simple and inexpensive but which has two 
functions, an intermittent-advance function and a continuous-advance 
function. 
Another object is the provision of such a drive for 35 mm film or the like 
which does not de-synchronize the frames with the shutter when the film is 
switched from intermittent to continuous drive or back. 
These objects are attained according to the present invention in a film 
drive having a film drive wheel rotatable about a first axis and having 
relative to this first axis a plurality of angularly equispaced radial 
projections. A function cam rotatable about a second axis transverse to 
the first axis has a generally helical formation thereon engaging the 
projections of the drive wheel and including an intermittent-drive section 
constituting almost a complete turn of the helical formation and of 
substantially 0.degree. pitch and having an end portion of predetermined 
pitch greater than 0.degree., and a constant-drive section of constant 
pitch greater than 0.degree. and offset axially from this 
intermittent-drive section. Shift means is provided for displacing the 
axes relative to each other for engagement of the projections of the drive 
wheel with the intermittent-drive section or with the constant-drive 
section. A drive motor is provided for continuously rotating the cam about 
its second axis, so that the drive wheel is advanced intermittently when 
engaged with the intermittent-drive section and continuously when engaged 
with the continuous-drive section. 
According to further features of this invention the cam is formed as a drum 
having a generally helically extending ridge. Slightly less than one turn 
of this ridge constitutes the holding portion of the intermittent-drive 
section and the rest of the ridge to either side of the holding portion is 
of generally constant pitch. Two constant drive sections are, therefore, 
provided, one to each side of the central intermittent-drive section, and 
the switching portions of the intermittent-drive section are continuations 
of the constant-drive sections. 
The shift means in accordance with further features of this invention can 
displace the cam between three different positions. In a central position 
the formations on the drive wheel are only engageable with the 
intermittent-drive section so that this wheel is only stepped when the 
switching portions of the intermittent-drive section come into engagement 
with the formations on the drive wheel. When the shifter moves the cam 
axially in one direction and increases the speed of the motor, the film is 
then advanced through the camera/projector in a forward direction at an 
elevated rate of speed, approximately twice the normal advance rate. When 
the shifter moves the cam axially in the opposite direction so as to 
engage the formations on the drive wheel with the other constant-drive 
section, it also reverses the motor direction so that the film is caused 
to advance backwardly at an elevated rate of speed which, once again, is 
approximately twice the normal rate of advance. 
According to another feature of the invention the axial distance between 
axially adjacent regions of the ridge on the cam is smaller than twice the 
angular space in between the formation on the drive wheel. This insures 
that the two will always remain in synchronism and that even after a 
fast-forward or rewind operation the shutter and frame synchronization is 
maintained. 
With the system according to the present invention it is possible very 
easily to switch the motion-picture apparatus from a normal forward 
function with intermittent drive of the film to either a fast-forward 
function in which the film is moved at a constant and high rate of speed 
in the forward direction or to a rewind function in which the film is 
moved at a constant and high rate of speed in the reverse direction. The 
mechanism for carrying this out is relatively simple and can fit in even 
the smallest hand-held movie camera. In addition, such functions can be 
added to a camera/projector with only a minor increase in production cost 
of the camera or projector so that normally deluxe features can be 
provided even in amateur or home-movie equipment. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself 
however, both as to its construction and its method of operation, together 
with additional features and advantages thereof will be best understood 
from the following description of specific embodiment when read in 
connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The drive system 1 shown in the drawing has a pair of fixed bearings 2 and 
3, defining an axis A' about which is rotatable a shaft 4 carrying a cam 
5. This cam 5 is subdivided into a central region A and a pair of end 
regions B and C over which extends a generally helical ridge 6-9. In the 
central region A almost one turn 6 of the ridge constitutes a holding 
portion of a central intermittent drive section. This holding portion 6 is 
of 0.degree. pitch and terminates at each end in a switching or end 
portion 7 and 8 of predetermined pitch. In each of the sections B and C 
the ridge 9 is of constant pitch, corresponding generally to the pitch of 
the sections 7 and 8 and forming continuations thereof. Thus the sections 
B and C can act as simple constant-speed drive worms. 
A drive wheel 10 carrying eight angularly equispaced and radially extending 
projections 28 is carried on a shaft 11 defining an axis A" spaced from 
and perpendicular to the axis A' and carrying a sprocket wheel 12 for 
engaging the film in the motion-picture apparatus embodying the drive 
system 1. 
The one end of the shaft 4 is connected to a reversible two-speed electric 
drive motor 27 and the other end is formed with a circumferential groove 
13 in which engages a roller 14 rotatable about an axis 15 on the end of a 
lever 16 pivoted on the motion-picture apparatus at 17. The other end of 
the lever 16 has an operating knob 18 and a pointer 19 engageable in a 
central position 20 with indicia indicating operation of the 
camera/projector at normal forward speed, with indicia 21 indicating 
operation of the camera/projector at fast forward speed, and with indicia 
22 indicating operation of the camera/projector at a fast reverse speed 
for rewind. 
During normal-forward operation of the camera/projector, the lever 16 is in 
the solid-line position and the motor 27 connected to this lever 16 
operates at a relatively slow speed to rotate the shaft 4 about the axis 
A' in a direction indicated by arrow 23. Since the center section A of the 
cam 5 only engages the wheel 10 this wheel 10 will not rotate at all about 
its axis A' so long as the 0.degree. pitch section 6 is between the 
projections 28, but will step one increment in the direction of arrow 25 
when the sections 7 and 8 engage the projections 28. Thus for each 
revolution of the shaft 4 about the axis A' in the direction of arrow 23 
the shaft 11 of the wheel 10 will be moved one increment in the direction 
of arrow 25. When not engaging the switching portions 7 and 8 of the 
section A the wheel 10 does not rotate at all. 
In order to switch from intermittent-forward drive to fast-forward drive 
the lever 18 is moved to the left until the pointer 19 is in line with the 
indicia 21. This causes the cam 5 to act as a rack for the wheel 10 so as 
to turn it in the direction of arrow 26 until section C of the cam 5 is 
aligned with the wheel 10. In this position the drive system, with the 
shaft 4 now rotating at a relatively high speed about the axis A' in the 
direction of arrow 23 to rotate the wheel in the direction of arrow 25. 
During such fast-forward drive the rotation in the direction of arrow 25 
will be considerably faster than the average advance speed during normal 
running of the device as the motor speed is increased. 
Swinging of the lever 16 to the right so that the pointer 19 is aligned 
with the indicia 22 for rewind or fast reverse of the apparatus causes 
opposite rotation of the shaft. During the switch-over operation the cam 5 
again acts as a rack to rotate the wheel 10 in the direction of arrow 25. 
Once the section C is aligned with the wheel 10, however, the reversed 
rotation of the shaft 4 in the direction of arrow 24 at a relatively high 
speed causes the wheel to rotate at a constant speed in the direction of 
arrow 26. Thus, it is seen that in the central position the motor 27 
rotates the shaft 4 in the direction of arrow 23 at a relatively slow 
speed, whereas in the fast-forward position, the motor 27 rotates this 
shaft 4 in the direction of arrow 23 at a higher rate of speed, and in the 
rewind position it rotates it in the direction of arrow 24 at a similarly 
high speed. 
The lever 16 can be provided with a detent to hold it in the two end 
positions, or can simply be provided with torque springs to return it to 
the central position so that it has to be held in these end positions 
during fast-forward operation or rewind. 
The shutter of the camera or projector is operated by the rotation of the 
shaft 4. Since with this system the same sprocket wheel 12 is used for 
fast-forward advance and rewind advance proper synchronization of the 
shutter and the frames of the film is insured even after a fast-forward or 
rewind operation. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
apparatus differing from the types described above. 
While the invention has been illustrated and described as embodied in a 
film drive for motion-picture apparatus, it is not intended to be limited 
to the details shown, since various modifications and structural changes 
may be made without departing in any way from the spirit of the present 
invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.