Automatic lower loop restorer mechanism

A lower loop restorer for automatically resetting the lower loop of a motion picture projector when the loop is lost. A loop restoring roller, located in the film path, is provided at one end of a pivotable control arm assembly. When the lower loop is lost, the control arm is triggered to cause drive means to pivot the control arm assembly downward and then upward to pull film from the film gate and reset the lower loop. Means are provided to disable or inhibit the operation of the lower loop restoring mechanism when the projector is operated in the reverse projection mode, the in path fast forward mode, or the inpath rewind mode. Means are also provided to protect the film from damage if the lower loop restorer is triggered and film is jammed in the film gate.

FIELD OF THE INVENTION 
The present invention relates to mechanisms for use with motion picture 
projectors. More specifically, the present invention relates to mechanisms 
for automatically resetting or restoring a lost film loop. 
PRIOR ART 
Conventional sound motion picture projectors provide a film gate thru which 
the film is incremented by film driving means on a frame by frame basis 
for projection, and a sound drum around which the film is continuously 
transported for sound signal reproduction. In order to isolate the 
intermittent motion of the film thru the film gate from the sound drum, 
and the continuous motion of the film around the sound drum from the film 
gate, it is customary to provide a slack loop in the film between the film 
gate and the sound drum. This slack loop is known as a lower loop. For 16 
MM film projection, the length of the lower loop is established by an 
industry wide standard as 26 frames. With this loop length, 
synchronization is achieved between the visual presentation and the sound 
presentation. 
Occasionally, the film drive means may not be able to increment the film 
thru the film gate because of damage to or irregularities in the film. 
Such damage or irregularities may include splice repairs, torn, worn, or 
missing sprocket holes, heat damage, and the like. When the film is not 
incremented thru the film gate, the sound drum will continue to transport 
the film and thereby takeup or shorten the slack lower loop. In time the 
film between the sound drum and the film gate becomes taut and the lower 
loop is lost causing the loss of the visual sound synchronization. 
The present invention provides a lower loop restorer mechanism to 
automatically restore the lower loop when it is lost. The mechanism is 
inexpensive to manufacture, and operates reliably without the need for 
critical adjustment. A loop setting roller is provided at a location in 
the film path and means are provided to cause the loop setting roller to 
move downward and then upward to reset the loop. Means are provided to 
protect the film from damage when the loop is jammed in the film gate and 
the lower loop restorer triggered. Means are also provided to disable or 
inhibit the lower loop restorer mechanism during the reverse projection 
mode, the in path fast forward mode, or the in path rewind mode.

SUMMARY OF THE INVENTION 
A lower loop restorer for automatically resetting the lower loop of a 
motion picture projector when the lower loop is lost includes a pivotably 
mounted control arm having a film engaging element at its distal end. The 
control arm is pivotably from an initial park position to an extended 
position to cause the film engaging element to reset the lower loop. A 
crank pin, extending from a rotatably mounted loop set gear, is 
selectively engageable with the control arm to cause the control arm to 
pivot. Trigger means are provided to cause drive means to engage the loop 
set gear when the lower loop is lost. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
A movie film projector 20 suitable for use with the present invention is 
illustrated in schematic fashion in FIG. 1. The projector 20 includes a 
side wall 22 with a conventional projection lens 24, a film gate 26, and a 
sound drum 28 with cooperating rollers 30 and 32 supported on the side 
wall 22. A film supply reel 34 supplies film 36 along a path leading from 
the supply reel 34 thru the film gate 26, to and around the sound drum 28, 
and to a take-up reel 38. A lower loop, generally designated by the 
reference character 40, is formed in the film 36 between the film gate 26 
and the sound drum 28 to isolate the motion imparted to the film 36 as it 
is incremented thru the film gate 26 from the sound drum 28. A lower loop 
restorer 42, not shown in FIG. 1, is located on the projector side wall 22 
in the area enclosed by the broken line 43. Rollers, sprockets, and other 
projector elements not essential to an understanding of the present 
invention have been omitted from FIG. 1. 
The principle elements of applicant's lower loop restorer 42 mechanism are 
illustrated in exploded perspective in FIG. 2. As shown therein, the lower 
loop restorer 42 includes a control arm assembly 44, a swing arm assembly 
46, and a loop set gear 48. The control arm assembly 44 is assembled from 
an outer control arm 50 and an inner control arm 52, and the swing arm 
assembly 46 is assembled from a swing arm plate 54, a pinion gear 56, and 
an idler gear 58. 
The outer control arm 50, which is preferably fabricated from a sheet metal 
stamping, includes a vertical plate portion 60 with a lateral surface 62 
extending outward from the upper edge of the plate 60. The lateral surface 
62 includes a triggering edge 64, the function of which is described in 
detail below. A tab 66, which extends laterally outward from the upper 
edge of the outer control arm 50 in the same direction as the lateral 
surface 62, is also provided. A shaft 68 having one end secured to the 
plate portion 60 of the outer control arm 50 extends laterally outward 
from the outer control arm 50 in the direction opposite that of the 
lateral surface 62 and the tab 66. A conventional diploconical film 
engaging roller 70 is rotatably mounted on the shaft 68 and restrained 
from axial translation thereon by a "C" ring 72 located in a groove 74 
formed at the distal end of the shaft 68. Two shafts 76 and 78 extend 
laterally outward from the side of the outer control arm 50 in the same 
direction as the tab 66 and the lateral surface 62. The function of the 
shaft 76 and the shaft 78 are described below. 
The inner control arm 52, which is preferably fabricated from a sheet metal 
stamping, includes a vertical plate portion 80 with a lateral surface 82 
extending outward from the lower edge of the plate portion 80. A tab 84 
also extends outward from the lower edge of the inner control arm 52 in 
the same direction as the lateral surface 82. The left side of the inner 
control arm 52 has a mounting bore 86 formed therein and the right side of 
the inner control arm 52 is turned to define a stop surface 88 as 
illustrated in FIG. 2. 
FIG. 3 illustrates the outer control arm 50 assembled to the inner control 
arm 52 from the side opposite that illustrated in FIG. 2. The outer 
control arm 50 is assembled to the inner control arm 52 by mounting the 
inner control arm on the shaft 76 and restraining it from axial 
translation thereon by a "C" ring 90 disposed in a groove 92 formed in the 
shaft 76. When the outer control arm 50 and the inner control arm 52 are 
assembled, the tab 66 and the tab 84 are in vertical registration with one 
another. One end of a coil spring 94 in tension is anchored to the tab 66 
and the other end of the spring 94 is anchored to the tab 84 to cause the 
stop 88 at the distal end of the inner control arm 52 to be resiliently 
biased against the under side of the lateral surface 62 of the outer 
control arm 50. The inner control arm 52 may be pivoted relative the outer 
control arm 50 to the position shown by the broken line illustration of 
FIG. 3. 
A cylindrical lock-out pin 96, shown in FIG. 2 and FIG. 3, having an 
eccentric axially aligned bore 98 there thru, is rotatably mounted on the 
shaft 78 and restrained from axial translation thereon by any suitable 
means. The function of the lock-out pin 96 is described below. 
The loop set gear 48, shown in perspective in FIG. 2 and in side elevation 
views in FIGS. 4 and 5, includes a body portion 100 having a central 
mounting bore 102 there thru. The peripheral surface of the loop set gear 
48 is divided into a cylindrical surface portion 104 and a portion having 
a plurality of uniformly spaced gear teeth 106 formed thereon. A space or 
gap 108 is provided in the gear teeth 106 as shown in FIGS. 2, 4, and 5. A 
cam 110, (FIGS. 4 and 5) having a ramp 112 and a ramp 114, is formed on 
the cylindrical surface 104. The cam 110 is so located that it is in 
registration with the gap 108, and axially offset or spaced from the gear 
teeth 106. 
As shown in FIGS. 2 and 4, a crank pin 116 extends laterally outward from 
the side of the loop set gear 48. The peripheral surface of the crank pin, 
when viewed from the end as in FIG. 4, has a spiral form with a trigger 
surface 118 or step formed therein. The opposite side of the loop set gear 
48, shown in FIG. 5, includes a hub 120 surrounding the mounting bore 102. 
The hub 120 has a portion cut away to define a flat surface 122. 
The swing arm assembly 46, shown in perspective view in FIG. 2, carries 
both the input pinion gear 56 and the idler gear 58. A swing arm plate 54, 
preferably fabricated from a metal stamping, includes a shaft 124 secured 
to and extending laterally outward from the plate 54. The idler gear 58 is 
rotatably mounted on the shaft 124 and restrained from axial translation 
thereon by a "C" ring 126 disposed in a groove 128 formed at the distal 
end of the shaft 124. A bowed spring washer 130 is mounted on the shaft 
124 between the idler gear 58 and the swing arm plate 54. The spring 
washer 130 applies a preload force, in the axial direction, to the idler 
gear 58 to provide a rotary friction drag between the idler gear 58 and 
the shaft 124. The pinion gear 56 is secured to one end of an input shaft 
132 for rotation therewith. The shaft 132 is rotatably mounted in a 
bearing 134 in the swing arm plate 54 for rotation relative thereto and 
also rotatably mounted in a support bearing (not shown) in the projector 
side wall 22. The end of the input shaft 132 remote from the pinion gear 
56 is connected to suitable drive means, such as a pulley and elastomer 
drive means, (not shown), which provides input rotation to the pinion gear 
56. When the idler gear 58 and the pinion gear 56 are assembled to the 
swing arm plate 54, the idler gear 58 and the pinion gear 56 are in 
constant mesh. Rotation of the pinion gear 56 will cause rotation of the 
idler gear 58. The swing arm plate 54 is so formed to include a cam 
follower surface 134 which extends outward beyond the addendum circle of 
the idler gear 58. The function of the follower surface 134 is described 
below. 
FIG. 6 represents the assembled lower loop restorer 42 when the movie 
projector is in the forward projection mode. The position of the various 
elements shown in FIG. 6 is defined herein as the park position. As shown 
therein, the swing arm assembly 46 is rotatably supported in the projector 
side wall 22 by the input shaft 132 which extends thru a bearing (not 
shown) in the projector side wall 22, the loop set gear 48 is rotatably 
mounted on a shaft 134 which is secured to and extends laterally outward 
from the projector side wall 22, and the control arm assembly 44 is 
rotatably supported in the projector sidewall 22 by the shaft 76 which is 
secured to the outer control arm 50 and extends thru a bearing (not shown) 
in the projector sidewall 22. A lock-out lever 136, whose function is 
described below, is shown below the lower loop restorer 42. 
In the forward projection mode, the projector drive means rotates the input 
pinion 56 in the counter-clockwise direction as indicated by the arrow 
138. The rotary drag on the idler gear 58 provided by the spring washer 
130 (FIG. 2) causes the swing arm assembly 46 to rotate in the 
counter-clockwise direction as indicated by the arrow 142 to cause the cam 
follower 134 to contact the ramp 112 of the cam 110 located on the loop 
set gear 48. Since the cam folower 134 extends beyond the addendum circle 
of the idler gear 58, the idler gear 58 is prevented from engaging with 
and causing rotation of the loop set gear 48. 
The conrol arm assembly 43 is so located relative the loop set gear 48 that 
the triggering edge 64 (FIGS. 2 and 3) formed on the lateral surface 62 is 
engageable with the triggering surface 118, the loop set gear 48 is 
prevented from rotating in the counter-clockwise direction as indicated by 
the arrow 144. 
A flat spring 146, acting on the hub 120 of the loop set gear 48, is 
provided to resiliently bias the loop set gear 48 for an incremental 
rotation in the counter-clockwise direction as indicated by the arrow 144. 
The spring 146, which is preferably fabricated from a section of flat 
spring steel, has both ends turned around pins 148 which are secured to 
and extend laterally outward from the projector sidewall 22. Rotation of 
the loop set gear 48 in the clockwise direction as indicated by the arrow 
150 will cause the edge 152 of the flat 122 on the hub 120 to deflect the 
center region of the spring 146 in the direction of the arrow 154 and 
store potential energy in the spring 146 sufficient to bias the loop set 
gear 48 for rotation in the counter-clockwise direction of the arrow 144, 
and thereby bias the triggering surface 118 (FIG. 4) against the 
triggering edge 64 (FIG. 2). 
Thus, when the lower loop restorer 42, is in the park position and the 
projector 20 is in the forward projection mode as shown in FIG. 6, the 
pinion gear 56 is rotating in the counter-clockwise direction as indicated 
by the arrow 138 and thereby biasing the swing arm assembly 46 in the 
direction of the arrow 142. The rotating idler gear 58 is poised near the 
gap 108 for engagement with the gear teeth 106 of the loop set gear 48. 
The cam follower 134, in contact with the ramp 112 of the cam 110 
positions the swing arm assembly 46 away from the loop set gear 48 and 
thereby prevents engagement between the idler gear 58 and the loop set 
gear 48. The loop set gear 48 is rotatably biased by the spring 146 for 
incremental rotation in the direction indicated by the arrow 144 but is 
prevented from such incremental rotation by the engagement of the 
triggering surface 118 with the triggering edge 64. With the lower loop 
restorer 42 elements configured in the park position as described above, 
the lower loop restorer 42 is ready to trigger should the lower loop 40 be 
lost. 
When the film 36 fails to be advanced out of the film gate 26 by the film 
advancing means, the sound drum 28 will continue to transport the film 36 
and thereby cause the film path between the film gate 26 and the sound 
drum 28 to shorten. The film 36 will be drawn into the path represented by 
the dotted line 156 in FIG. 6. The film 36 will engage the film roller 70 
at the distal end of the control arm assembly 44 and cause the control arm 
assembly 44 to pivot in the counter clockwise direction as indicated by 
the arrow 158. This rotation of the control arm assembly 44 will cause the 
triggering edge 64 to disengage from the triggering surface 118. The 
potential energy stored in the spring 146 acting against the hub edge 152 
will cause the loop set gear 48 to incremently rotate in the 
counter-clockwise direction of the arrow 144. As the loop set gear 48 is 
rotated, the gear teeth 106 will be presented to the idler gear 58 and the 
cam follower 134 of the swing arm assembly 46 will move along the ramp 
surface 112 (FIG. 4) of the cam 110 and then down the ramp 114 to cause 
the swing arm assembly 46 to pivot in the counter-clockwise direction of 
the arrow 142. The rotating idler gear 58 will move into engagement with 
the gear teeth 106 on the loop set gear 48 and cause the loop set gear 48 
to rotate in the direction of the arrow 144. The cam 110 cooperates with 
the cam follower 134 to insure that engagement between the idler gear 58 
and the gear teeth 106 takes place without gear lockup or jamming between 
the two gears. As the loop set gear 48 rotates, the crank pin 116 will 
bear against the lateral surface 82 of the inner control arm 52 to pivot 
the control arm assembly 44 clockwise to an extended position as shown in 
FIG. 7 and then against the lateral surface 62 of the outer control arm 50 
to pivot the control arm assembly 44 counter-clockwise to return the 
control arm assembly 44 to park position of FIG. 6. As the control arm 
assembly 44 is pivoted downward, the film roller 70 will pull film 36 down 
from the film gate 26 to restore the lower loop 40. As the crank pin 116 
moves the control arm assembly 44 upward the triggering surface 118 will 
contact the triggering edge 64 to stop both the control arm assembly 44 
movement and the loop set gear 48 rotation. The cam follower 134 will move 
up the ramp 112 of the cam 110 to cause the idler gear 58 to disengage 
from the loop set gear 48, and the edge 152 of the flat 122 on the hub 120 
will deflect the center region of the spring 146 in the direction of the 
arrow 154 and thereby bias the loop set gear 48 for rotation in a 
counterclockwise direction. The lower loop 40 is restored and the lower 
loop restorer 42 elements are reset to their initial park position. 
During the reverse projection mode the projector motor is operated in 
reverse and the film 36 is drawn up to the film gate 26 in a direction 
opposite that from the forward projection mode. During the reverse 
projection mode the maintainence of a lower loop 40 is not required. A 
feature of the present lower loop restorer 42 is that it is disabled or 
inhibited from operation during the reverse projection mode. As shown in 
FIG. 8, the reverse projection mode causes the input pinion gear 56 to 
rotate in the direction of the arrow 162. The rotary drag placed on the 
idler gear 58 by the spring washer 130 causes the swing arm assembly 46 to 
rotate in the clockwise direction as indicated by the arrow 162. The swing 
arm assembly 46 is then rotatably biased against a stop pin 164 which is 
secured to and extends laterally outward from the projector sidewall 22. 
During reverse operation of the projector, the film path between the film 
gate 26 and the sound drum 28 is somewhat shortened. The film 36 is drawn 
up into the path represented by the dotted line 156 in FIG. 8. The film 36 
will engage the film roller 70 at the distal end of the control arm 
assembly 44 and cause the control arm assembly 44 to rotate in the 
direction of the arrow 158. This rotation of the control arm assembly 44 
will cause the triggering edge 64 to disengage from the triggering surface 
118. The potential energy stored in the spring 146 will cause the loop set 
gear 48 to incremently rotate in the direction of the arrow 144. Since the 
swing arm assembly 46 is rotatably biased in the direction of the arrow 
162 against the stop pin 164 by the reverse input rotation of the input 
gear 56, the idler gear 58 cannot engage the loop set gear 48 to cause 
loop set gear 48 rotation and consequent movement of the control arm 
assembly 46. Thus during reverse projection operation, the lower loop 
restorer 42 is disabled or inhibited from operation. If the projection 
mode is changed from the reverse direction mode to the forward projection 
mode, the swing arm assembly 46 will be rotatably biased in the direction 
of arrow 142 and the idler gear 58 will engage the gear teeth 106 of the 
loop set gear 48 to cause the loop set gear 48 to restore the lower loop 
40 as described above. 
When the movie projector 20 is operated in either the in path fast forward 
mode or the in path rewind mode it is necessary that the film roller 70 be 
in a fixed location for in path film transport. The lock out lever 136 is 
provided to prevent the operation of the lower loop restorer 42 mechanism 
during these modes. As shown in FIG. 8, the lock-out lever 136 is secured 
on its left side to one end of a shaft 166 which is rotatably mounted in a 
bearing (not shown) carried by the projector sidewall 22. The lock-out 
lever 136, which is connected by connecting means to the projector mode 
selection switch (not shown), is pivotable from a first position shown in 
FIGS. 6, 7, and 8 to a second position shown in FIG. 9. The right side of 
the lock-out lever 136 has a slot 168 formed therein adapted to receive 
the lock-out pin 96 when the lock-out lever 136 is in the second position 
as shown in FIG. 9. During the in path fast forward mode the lock-out 
lever 136 is caused to engage the lock-out pin 96 and prevent rotation of 
the outer control arm 50. Should the lower loop restorer 42 be triggered, 
the idler gear 58 will engage the loop set gear 48 and cause rotation of 
the loop set gear 48 in the direction of the arrow 144. Since the outer 
control arm 50 is locked against movement by the lock-out lever 136, the 
crank pin 116 will pivot the inner control arm 52 only by engaging the 
lateral surface 82 of the inner control arm 52 and drive the inner control 
arm 52 in the direction of the arrow 170 against the resilient biasing 
force of the coil spring 94 as illustrated in FIG. 9. Thus during the in 
path fast forward mode, the outer control arm 50 and the film engaging 
roller 70 connected thereto are inhibited from resetting the loop 40 by 
the lock out lever 136 engaging the lock out pin 96. During the in path 
rewind mode the lock-out lever 136 is also caused to engage the lock-out 
pin 96 and prevent rotation of the outer control arm 50. 
The use of the outer control arm 50 pivoted to the inner control arm 52 
prevents damage to the film 36 should an attempt be made to reset the 
lower loop 40 and the film 36 be so jammed, obstructed, or otherwise 
immobilized in the film gate 26 that it cannot be pulled down by the outer 
control arm 52 without damaging the film 36. Thus, should the film 36 be 
jammed in the film gate 26 and the lower loop restorer 42 triggers, the 
control arm assembly 44 will attempt to pivot and pull film from the film 
gate 26 to reset the lower loop 40. If the force required to pull the film 
36 from the film gate 26 is greater than the force provided by the coil 
spring 94 which biases the inner control arm 52 to the outer control arm 
50, the inner control arm 52 will pivot relative the outer control arm 50 
as illustrated in FIG. 9 and thereby limit the force applied to the film 
36. In this way film 36 which is tightly jammed in the film gate 26 is 
protected from damage during an attempted restoring of the lower loop. 
As is apparent to those skilled in the art, various changes and 
modifications may be made to the mechanism described herein without 
departing from the spirit and the scope of the present invention as 
defined by the appended claims and their legal equivalent.