US3719418A

US3719418A - Reset control particularly for optical compensators

Info

Publication number: US3719418A
Application number: US00175482A
Authority: US
Inventors: R Johnston; K Hendrickson
Original assignee: Bell and Howell Co
Current assignee: Bell and Howell Co
Priority date: 1971-08-27
Filing date: 1971-08-27
Publication date: 1973-03-06
Anticipated expiration: 1990-03-06

Abstract

A repeatedly advanced device, such as an optical compensator or rectifier in continuous film feed motion picture apparatus, is reset between successive advancements with the aid of resetting energy. Errors in the resetting of the device are sensed and an error signal is controlled with the error signal to correct errors in the resetting of the device.

Description

United States Patent 1191 1111 3,719,418 Johnston et al. 1 March 6, 1973 [5 RESET CONTROL PARTICULARLY [56] References Cited FOR OPTICAL COMPENSATORS UNITED STATES PATENTS W'ld d; [75] Imam g 1 f r s" i gg 3,181,403 5/1965 Stems =1 al ..3l8/85 x c 3,584,203 6/1971 Patzelt et al ..3l8/60l 0f 3,539,250 11/1970 Johnston ..352/92 x [73] Assignee: Be" & Howe" p y Chicago, 3,459,471 8/1969 Johnston ..352/l05 Primary Examiner-Robert P. Greiner [22] Filed: Aug. 27, 1971 Attorney-Luc P. Benoit [21] Appl. No.: 175,482 ABSTRACT A repeatedly advanced device, such as an optical 52 US. c1. ..3s2/109, 95/38, 318/640 compensator or rectifier in continuous film feed 51 1111. c1. ..G03b 41/10 on pictm apparatus, is reset between successive Field of Search "352/109, 105, 1 10, 92, 38; vancements with the aid of resetting energy. Errors in the resetting of the device are sensed and an error signal is controlled with the error signal to correct errors in the resetting of the device.

29 Claitns, 24 Drawing Figures PATENTED R 6 75 SHEET 10F 7 N who WWW W A QQWQQU HL/ In INHNQ NQM N w .Y/r a ,m W $3 JL. 0 r W m 8 am Q g MW N hm, .mw w hm m II II I PATENTED 61973 SHEET 3 I]? 7 PATENTEUMAR 61975 SHEET 5 OF 7 y A m A98 PATENTEUMAR 6 1075 I SHEET 7 OF 7 RESET CONTROL PARTICULARLY FOR OPTICAL COMPENSATORS CROSS-REFERENCE TO RELATED APPLICATIONS Subject matter disclosed in the present patent application is disclosed and claimed in the following patent applications which are assigned to the subject assignee and which are herewith incorporated by reference herein:

Patent Application Ser. No. 89,323, filed Nov. 13,

BACKGROUND OF THE INVENTION 1 Field of the Invention The subject invention relates to the operation of repeatedly advanceable and resettable devices, such as optical compensators or rectifiers in continuous film feed motion picture apparatus.

2. Description of the Prior Art While the prior art and the subject invention are primarily described with reference to non-intermittent or continuous motion picture apparatus, it should be understood that no limitation of the utility or applicability of the subject invention to that field is intended. Also, it should be understood that the subject invention is not limited in its utility to the operation of optical compensators or rectifiers, but may be employed to control the operation of other repeatedly advanceable and resettable devices.

There exist many proposals for compensating the continuous film motion in continuous film feed motion picture apparatus, such as motion picture projectors or television scanners, with the aid of continuously advanced optical compensators or rectifiers that track successive portions of the film. In systems of this type the optical compensator has to be reset between successive advancements thereof.

These resetting operations have to be carried out very accurately to prepare the compensator for the display of a succeeding image in a very short period of time which typically is on the order of l millisecond or less. lnaccuracies at this stage of the operation manifest themselves mainly by smearing of the projected or scanned images.

A proposal for a fast resetting of a scanning element has in a different context been made by C.E. Baker and H.W. Parker in their LASER DISPLAY STUDY, Technical Report No. RADCTR-65-l69, July 1965, Rome Air Development Center, Research and Technology Division, Air Force Systems Command, Griffiss Air Force Base, New York, July 1965, pp.3l to 36. According to the proposal, pulse doublets composed of 65- oppositely poled pulses are generated and are employed for resetting a scanner element. The initial pulse in each doublet serves to accelerate the scanner element in the resetting direction, and the second pulse in each doublet serves to decelerate the resetting scanner element, the objective being to have the scanner element stop its resetting operation exactly at the point from which a subsequent scanning operation is to commence.

An application of the concept behind the latter proposal to continuous film feed motion picture systems has been fraught with difficulties. Most of these have been solved in the manner disclosed in the crossreferenced related applications or patents listed above.

Nevertheless, it has been found in practice that pulse width variations in the reset pulses of as little as i 1 percent caused by bearing friction variations or other factors may provoke degradations of the image display.

SUMMARY OF THE INVENTION The subject invention overcomes the above mentioned disadvantages and provides methods and apparatus for operating a repeatedly advanceable and resettable device in general, and methods and apparatus for displaying images from a motion picture film with the aid of a repeatedly advanceable and resettable compensator device in particular.

From one aspect thereof, the subject invention is concerned with a method of operating a repeatedly advanceable and resettable device, and resides in the improvement comprising in combination the steps of repeatedly advancing the device through arange of motion, providing energy for resetting the device between successive advancements, resetting the device through said range of motion with the resetting energy after essentially each advancement, sensing errors in the resetting of the device, providingan error signal indicative of the sensed errors, and controlling the resetting energy with the error signal to correct the errors.

In this manner, a closed-loop servo system is provided for controlling the resetting operation of the repeatedly advanced device.

From another aspect thereof, the subject invention is concerned with a method of displaying images from a motion picture film, and resides in the improvement comprising in combination the steps of substantially continuously advancing the motion picture film,

providing an optical compensator including a repeatedly advanceable and resettable compensator device for compensating the continuous film advance, displaying the images by way of the compensator device, repeatedly advancing the compensator device to maintain each displayed image substantially stationary during its display, providing energy for resetting the compensator device between successive advancements, resetting the compensator device between successive advancements with the resetting energy, sensing errors in the resetting of the compensator device, providing an error signal indicative of the sensed errors in the resetting of the compensator device, and controlling the resetting energy with the error signal to correct the errors.

In accordance with the preferred embodiment of the subject invention, the resulting closed-loop servo system for controlling the resetting operation of the compensator device may be supplemented by, or combined with, a closed-loop servo system for controlling the advancement of the compensator device.

The subject invention is also concerned with apparatus for operating a repeatedly advanceable and resettable device, and resides in the improvement comprising, in combination, means coupled to the device for repeatedly advancing the device through a range of motion, means for providing energy for resetting the device between successive advancements, means connected to the energy providing means and coupled to the device for resetting the device through said range of motion with the resetting energy after essentially each advancement means for sensing errors in the resetting of the device, means coupled to the error sensing means for providing an error signal indicative of the sensed errors, and means connected to the error signal providing means and the energy providing means for controlling the resetting energy with the error signal whereby to correct the errors.

From yet another aspect thereof, the subject invention is concerned with apparatus for displaying images from a motion picture film, and resides in the improvement comprising, in combination, means for substantially continuously advancing the motion picture film, means including a repeatedly advanceable and resettable optical compensator device for compensating the continuous film advance, means operatively associated with the motion picture film and the compensator device for displaying the images by way of the compensator device, means coupled to the compensating means for repeatedly advancing the compensator device whereby to maintain each displayed image substantially stationary during its display, means for providing energy for resetting the compensator device between successive advancements, means connected to the energy providing means and coupled to the compensating means for resetting the compensator device between successive advancements with the resetting energy, means for sensing errors in the resetting of the compensator device, means connected to the sensing means for providing an error signal indicative of the sensed errors in the resetting of the compensator device, and means connected to the error signal providing means and the resetting energy providing means for controlling the resetting energy with the error signal whereby to correct the errors.

BRIEF DESCRIPTION OF THE DRAWINGS The subject invention will become more readily apparent from the following detailed description of preferred embodiments thereof, illustrated by way of example in the accompanying drawings, in which:

FIG. 1 is a diagrammatic illustration of a non-intermittent or continuous film feed motion picture projector implementing a preferred embodiment of the subject invention;

FIG. 2 is a view substantially along the lines II II of FIG. 1;

FIG. 3 is a view similar to FIG. 2 but illustrating a film with opaque film base or margin;

FIGS. 4a to 40 are diagrammatic illustrations of different phases of operation of the projector accdrding to FIG. 1;

FIG. 5 is a circuit diagram of an apparatus in accordance with a preferred embodiment of the subject invention for use in the motion picture projector of FIG. 1;

FIG. 6 is a circuit diagram of a preferred operational amplifier or servo amplifier for use in the apparatus of FIGS. 5 and FIGS. 7a to 7h are amplitude-versus-displacement plots illustrating different phases of operation of the illustrated embodiment according to FIG. 5;

FIG. 8 is a side view, partially in section, of a compensator for use in the projector of FIG. 1;

FIG. 9 is a section along line IX IX in FIG. 8;

FIG. 10 is a circuit diagram of a retrace sensing control in accordance with a preferred embodiment of the subject invention, for use in the apparatus of FIG. 5 or the projector of FIG. 1;

FIGS. 11a to 11d are amplitude-versus-time plots illustrating phases of operation of the illustrated embodiments;

FIG. 12 is a circuit diagram of a modification of the apparatus of FIG. 5.

DESCRIPTION OF PREFERRED EMBODIMENTS By way of example, and not by way of limitation, the preferred embodiments are herein disclosed and illustrated with reference to the systems disclosed in the above mentioned cross-referenced patent applications or patents.

The non-intermittent or continuous motion picture projector 10 shown in FIGS. 1, 2, and 3 has a film gate 12 which may be curved in accordance with the wellknown principles rendering the angular rate of film advance equal for different points of the film gate.

A conventional variable speed drive 15 has a capstan 16 which may have a rubber lining 17 that engages the film with the aid of a nip roller 18. The drive 15, which may comprise a variable-speed electric motor with reduction gear (not shown), is set at any practical speed to advance a motion picture film 13 through the film gate 12 in the direction of an arrow 19 at a substantially continuous or uniform rate (as distinguished from an intermittent film advance): Two guide rollers 20 and 21 assist the movement of the film into and out of the film gate.

In principle, a sprocket drive can be used for advancing the film 13. Where film sprocket holes are employed as control marks, it is, however, preferred that a capstan which does not wear out the sprocket hole areas be used as the power-transmitting device.

The film l3 bears a succession of optically reproducible recordings in the form of transparent images 23 located in image frames 24 and typically representing a filmed scene. The film further has sprocket holes 25 along a margin 26 thereof. In accordance with known principles, the film gate has a projection aperture 28 whose length is at least equal to twice the height of each image frame 24 plus the height of an interframe space 29, so that the continuous motion compensator 30 is able to handle two full image frames in succession. The width of the projection aperture is sufficient for a projection of the sprocket hole that pertains to each projected image.

The film 13 at the projection aperture 28 is illuminated by a projector lamp 32 and condensor lens system 33. The lamp 32, which may have a conventional reflector (not shown), is energized from an electric power source 34 upon closure of a switch 35. A projector lens system 38 projects the illuminated images and sprocket holes by way of the continuous motion compensator 30 onto a conventional backlighted screen 39. The back-lighted screen is shown by way of example, and a conventional front-lighted screen may be used instead.

The compensator 30 has a first-surface mirror 40 which is repeatedly advanceable by motive power applied to a coil 41 through a range of angular motion so as to compensate for the continuous movement of the film 13. The objective of the compensator mirror 40 is to maintain eachprojected image substantially stationary. Since the projection aperture 28 in the film gate 12 is larger than an image, the screen 39 is pro vided with an opaque frame 43 which blocks from the view of the observer the projected sprocket holes and also part of images other than the one image that is being projected for viewing at the particular time.

A device 45 is located at the screen for sensing relative movements of each displayed image in a first direction corresponding to the direction 19 of movement of the film 13. The device 45 also senses relative movements of displayed images in a second direction opposite the first direction just mentioned. These movements in a second direction occur, for instance, if the compensator mirror 40 overshoots in its forward motion the advance of the film.

By way of example and as shown in FIGS. 40 to 40 and 5, the motion sensing device 45 may include two conventional

photovoltaic cells

47 and 48 located near each other. The luminous sprocket hole is projected by way of the compensator mirror 40 onto the light-sensitive parts of the

photocells

47 and 48. Each of the

photocells

47 and 48 produces a signal which varies as a function of the area of cell illumination.

It may be helpful to note at this juncture that the sensor 45 need not necessarily be located at the screen 39. Rather, the sensor 45 may be positioned closer to the compensator mirror 40 (such as within the projector housing), with a lens (not shown) being provided for imaging the illuminated sprocket hole onto the sensing device 45 after projection thereof by way of mirror 40.

The projected luminous sprocket hole images are shown in FIGS. 40 to 40 at 160 within an outline 161 and in relation to the

photocells

47 and 48 of the sensor 45. In accordance with the teachings of the above mentioned Johnston and Lichodziejewski patent application or patent, at least two

borderline element images

162 and 163 are projected along with the sprocket hole image 160.

As disclosed in that Johnston and Lichodziejewski patent application or patent, the sprocket hole image, the borderline images and luminous areas 166 adjacent the borderline images are preferably produced by transmitting light through the sprocket hole and adjacent film margin and projecting such transmitted light.

While Johnston and Lichodziejewski did not subscribe to any particular theory, it is believed that the occurrence of the subject borderline images is due to diffraction or refraction, or to a combination of these phenomena. For instance, it appears that light proceeding through the film sprocket hole experiences a diffraction at the sprocket hole edges, resulting in a diffraction pattern including the subject borderline images. Alternatively or additionally, light which angularly enters the sprocket hole is reflected at an inside wall of the sprocket hole in a direction away from that sprocket hole. Furthermore, light which angularly enters the transparent film margin adjacent the sprocket hole in a direction toward the sprocket hole is deflected at a refractive angle toward the sprocket hole. That deflected light is thereupon reflected by the film-to-air interface at the sprocket hole. As a result, the light under consideration leaves the transparent film at an angle which carries it beyond the pull-in range of the projection lens. Similarly, light which angularly enters the film margin adjacent the sprocket hole in a direction away from the sprocket hole is deflected further away from the sprocket hole thereby providing for a'dearth of transmitted light at sprocket hole edges.

Moreover, if the film is not exactly perpendicular to the optical axis of the projection lens, an image of the film thickness at the sprocket hole will be projected along with the sprocket hole image, further emphasizing the observed dark borderline. It will thus be appreciated that the dark borderline images may be due to anyone or more of the above mentioned optical effects.

The expression borderline image herein employed refers to a dark line which extends along at least one edge of the sprocket hole image. In practice, this borderline image may extend along two or more edges of the sprocket hole image. Since the expression borderline is broad enough to cover also a dark outline around the entire sprocket hole image, the somewhat more qualified expression borderline element image is herein employed to refer to a borderline portion that extends along a sprocket hole edge, and that may or may not be part of a borderline.

It should be understood at this juncture that the subject invention is broadly applicable to sensing systems for sprocket holes or other fiducial markings and is not limited in its application to the projection and utilization of the above mentioned borderline images. However, we have found that the use of these borderline images provides a particularly advantageous embodiment of the subject invention.

For the purpose of the subject disclosure it is assumed that the film 13 shown in FIG. 2 has a transparent base or film margin 26. By way of contrast, the film 13 shown in FIG. 3 has a filmbase or margin 26' of an opaque type. As is well known in the art, motion picture films developed by a reversal process typically have an opaque base or margin, and films produced in a negative-to-positive printing process typically have a transparent base or margin. In practice, borderline images of the above mentioned type are observed in transparent-margin and in opaque-margin film, inasmuch as the opacity of opaque-margin film is not absolute, but allows for a reduced transmission of light through the film margin.

As shown in FIGS. 4a to 4c, a first borderline element image 162 appears at one side of the sprocket hole image due to any one or more of the above mentioned diffraction, refraction, reflection or projection effects. Similarly, a second borderline element image 163 appears at the opposite side of the sprocket hole image. Some of the light which penetrates the film margin 26 or 26' adjacent the particular sprocket hole 25 provides luminous areas 166 adjacent the

borderline element images

162 and 163. In FIG. 40, these luminous areas are shown consolidated into a halo 167. To avoid crowding the luminous areas 166 have not been shown again in FIGS. 4b and 40. It is, however, to be noted that the borderline element images are darker than both the sprocket hole image 160 and the adjacent luminous area 166.

As also shown in FIGS. 4a to 40, the

photocells

47 and 48 are long and narrow, extending with their long axes parallel to the

borderline elements

162 and 163. For maximum sensitivity, the long axes of the light-sensitive areas of the

photocells

47 and 48 may be substantially equal to the lengths of the

borderline element images

162 and 163. It is, however, preferable in practice that the long axes of the photocells be somewhat shorter than the lengths of the borderline element image to avoid normal tolerances of the sprocket hole image sizes and positions from taking effect.

The short axes of the light-sensitive areas of the

photocells

47 and 48 should be larger than the widths of the

borderline element images

162 and 163 to avoid disturbances from dirt particles and normal irregularities in the sprocket hole edges. By way of example, the short axis of each photocell may be about 4 to 5 times the width of the corresponding borderline element image.

Photocells of the type shown at 47 and 48 are commercially available. Examples include the Hoffman silicon photocell type 58C and the type SS-12-LC photocell manufactured by the Solar Systems Division of Tyco Corporation.

Two nodes 180 and 181 are shown in FIG. 5 at the

photocells

47 and 48, respectively, of the sensor 45. Signal voltages versus displacement provided by the photocell 47 at node 180 are shown in FIGS. 7a and e for opaque-margin film and transparent-margin film, respectively. Similarly, signal voltages versus displacement provided by the photocell 48 at the node 181 are shown in FIGS. 7b and f for opaque-margin film and transparent-margin film, respectively. It will be recalled in this connection that FIG. 3 shows an example of a film 13' with an opaque margin 26', and that an example of a film 13 with a transparent margin 26 is shown in FIG. 2. As seen from the base level 183 in FIG. 7a and the base level 184 in FIG. 7b, the

photocells

47 and 48, respectively, produce a relatively low voltage level at the nodes 180 and 181, respectively, in response to illumination by way of the opaque film margin 26' shown in FIG. 3. In contrast thereto, and as seen from the higher base level 185 in FIG. 7e and from the higher base level 186 in FIG. 7f, the

photocells

47 and 48, respectively, produce at the nodes 180 and 181 a higher signal level in response to illumination through the transparent margin 26 of the film 13 shown in FIG. 2.

In the embodiment shown in FIG. 1, images are introduced onto the screen 39 from the bottom thereof. Accordingly, the lower photocell 48 first produces at the node 181 a signal having an amplitude 188 as shown in FIG. 7b in response to illumination by a new sprocket hole image 160. Thereafter, the upper photocell 47 produces at the node 180 a signal of an amplitude 189 as shown in FIG. 7a in response to illumination by the new sprocket hole 160. Undesignated signal spikes throughout FIG. 7 represent signal variations which occur when

borderline element images

162 and 163 pass onto or over the

photocells

47 and 48, respectively.

Since the transparency of the sprocket holes 25 is, of course, the same whether transparent or opaque film bases are used, it follows that the amplitude 188 provided according to FIG. 7 at the node 181 in response to illumination of the photocell 48 through a sprocket hole in a transparent film margin is the same as the above mentioned amplitude 188 shown in FIG. 7b and produced by the photocell 48 at the node 181 in response to illumination through a sprocket hole in an opaque film margin. Similarly, the amplitude 189 produced at the node in response to illumination of the photocell 47 through a sprocket hole in a transparent film margin is, of course, the same as the above mentioned amplitude 189 produced at the node 180 by the photocell 47 in response to illumination through a sprocket hole in an opaque film margin. While the latter statement seems obvious, it should, however, be qualified in that it only holds true for signal amplitudes as considered with respect to the .x-axis (e.g., absolute amplitude values).

What the sensing equipment is capable of distinguishing, however, are not absolute amplitude values, but rather relative or effective amplitudes which are the difference between the levels 183 and 189 in FIG. 7a, the

levels

184 and 188 in FIG. 7b, the levels 185 and 189 in FIG. 7e, and the

levels

186 and 188 in FIG. 7f. In this connection it is noted that the difference between the levels 183 and 189 is much larger than the difference between the levels 185 and 189. Similarly, the difference between the

levels

184 and 188 is much larger than the difference between the

levels

186 and 188. These differences reflect themselves in the respective sensing signals as will presently be shown.

More specifically, FIGS. 70 and g show output voltage variations occurring at an output 191 of an operational amplifier 192 having an inverting input 193 and a non-inverting input 194, as shown in FIG. 5.

A circuit diagram of a suitable operational amplifier 192 is shown in FIG. 6. Those skilled in the art of integrated circuits will recognize that the operational amplifier 192 is available in monolithic form from several manufacturers as standardized circuit 1709 (for instance MOTOROLA OPAMP MC1709CL, or MICROSYSTEMS INTERNATIONAL OPAMP ML709C). In the type ML709C, NPN transistors having interconnected base and emitter circuits are substituted for the diodes shown in FIG. 6.

As shown at 196 in FIGS. 5 and 6, and input frequency compensation network is provided by a series connected capacitor and resistor. An output frequency compensation 197 is provided by a capacitor 198, also as shown in FIGS. 5 and 6. This combination with the values indicated in FIGS. 5 and 6 provides a flat response out to approximately 200 kHz at 40 db gain. The remaining parts of the amplifier 192 are standard and this type of amplifier is that widely manufactured and employed that a specific description of its components beyond the showing thereof made in FIG. 6 is unnecessary.

Reverting to the sensor 45 as shown in FIG. 5, it is seen that the photocell 47 has a resistor 200 connected in parallel thereto, and that the photocell 48 has a resistor 201 connected in parallel thereto. The resistance values of the resistors 200 and 201 are preferably on the order of one-tenth or less of the source resistance of the photocells under full light level conditions. These resistors 200 and 201 force the

photocells

47 and 48 to operate in the preferred short circuit mode, wherein the current is linearly related to illumination. Moreover, the resistors 200 and 201 increase the stability of the signal conditioner by shunting out the photocell capacitances.

The photosensor 45 is of a differential type since the

photosensors

47 and 48 are, respectively, connected to the inverting and

non-inverting inputs

193 and 194 of the amplifier 192. In consequence, the signal characteristics shown in FIGS. 7a and b provide at the output 191 of the amplifier 192 a signal characteristic of the type shown at 203 in FIG. 70. It will be noted that the base levels 183 and 184 are mutually compensated in the characteristic 203 of FIG. 70. Similarly, the high base levels 185 and 186 of FIGS. 7e andf are compensated in the signal characteristic 205 shown in FIG. 7g. In consequence, the amplitudes of the signal voltage characteristic 205, which occurs at the amplifier output 191 in response to the combined signal characteristics shown in FIGS. 7e and f, is much smaller than the amplitude of the signal characteristic 203.

A comparison of the characteristics or wave

forms

203 and 205 indicates why attempts to design fiducial marking sensing systems that would interchangeably accept transparent-base film and opaque-base film have been fraught with difficulties prior to the above mentioned Johnston invention (i.e., the invention disclosed in the above mentioned Johnston application or patent). In particular, practical tests have verified that important factors, such as system damping and servo pull-in after retrace of the compensator mirror 40, are functions of the amplitude of the fiducial marking sensing signal. This being the case, transparent-margin film and opaque-margin film could not be interchanged without considerable adjustment work.

In accordance with the above mentioned Johnston invention, a bidirectional limiter 207 is provided and is connected to the amplifier output 191 by way of a resistor 108 and a node 210. The limiter 207 is composed of a resistor 209 connected to the node 210, and a pair of oppositely poled and parallel-connected diodes 212 and 213; each diode being connected between the node 210 and ground. By way of example, the diodes 212 and 213 may be of the type IN4002.

FIG. 7d shows the wave shape characteristic 215 occurring at the node 210 by operation of the limiter 207 in the case of film with opaque margin 26' as shown in FIG. 3. FIG. 7h shows the wave shape characteristic 216 occurring at the node 210 by operation of the limiter 207 in the case of film with the transparent margin 26 shown in FIG. 2. It is seen from a comparison of FIGS. 7d and h that the positive amplitudes 218 and 219 of the wave shapes 215 and 216 are equal and that the negative amplitudes 220 and 221 of the wave shapes 215 and 216 are also equal. In other words, the wave shapes 215 and 216 present fiducial marking sensing signals which are indicative of the sensed fiducial markings substantially independently of the different relative contrasts between the sprocket holes 25 and the

film margins

26 and 26 Reviewing FIGS. 7a to h it may be stated that the photosensor 45 generates in response to the fiducial markings 25 different first electric signals corresponding, respectively, to the different relative contrasts between the markings 25 and the bases 26 and 26' (see FIGS. 2, 3, and 7a, b, e, andf).

The operational amplifier 192 and the limiter 207 cooperate in, producing the contrast-independent signals illustrated in FIGS. 7d and h by converting the different first electric signals provided by the sensor 45 into corresponding second electric signals having at least one common characteristic. According to FIGS. 7d and 12, this common characteristic in the illustrated system is manifested by equal amplitude values.

In the system shown in FIG. 5, the latter conversion is effected by having the amplifier 192 increase the amplitudes of the signals provided by the sensor 45 to values which provide for a sufficient leeway for amplitude limitation, and by having the limiter 207 effect such amplitude limitation to equal amplitude values for all kinds of film base or margin transparency or opacity.

A feedback path 223 extends from the amplifier output 191 by way of the resistor 208 and a feedback resistor 224 to the inverting input 193 of the amplifier 192. The feedback resistor 224 is adjustable to permit adjustments of the amplifier gain. A zero adjustment potentiometer 226 is connected between the positive terminal 227 of a power supply (not shown) and ground. The wiper arm of the potentiometer 226 is connected by a resistor 229 and by a lead 230 (see FIGS. 5 and 6) to one side of the inputfrequency compensation of the amplifier 192. As its name implies, the zero adjustment potentiometer 226 provides for the application of an adjustable bias to one side of the input frequency compensation ofthe amplifier 192 to permit adjustment of the amplifier output to zero voltage level when both

photocells

47 and 48 are initially exposed to equal illumination for adjustment purposes.

In a prototype of the illustrated embodiment, the resistor 208 had a value of 47 ohms and the resistor209 ahead of the limiter node 210 had a value of l kilohm.

Considering the wave shapes 215 and 216 shown in FIGS. 7d and h, the amplifier 192 and limiter 207 may jointly be considered a signal conditioning circuit. The output signal of this conditioning circuit, which appears at the node 210 is next fed to a lead network 232 composed of a resistor 233 and a capacitor 234 connected in parallel to that resistor, and of a variable resistor 236. This lead network corrects the phasing of the system to compensate for the inertial lag in the drive transducer 41 of the compensator mirror 40.

The variable resistor 236 has its wiper arm connected to the non-inverting input 237 of a feedback amplifier 238. In a prototype of the illustrated system, the feedback amplifier 238 is identical in design to the feedback amplifier 192 so that reference may be hadto the previously described FIG. 6 of the drawings. Also, the input frequency compensation 240 of the amplifier 238 was identical to the input frequency compensation 196 of the amplifier 192, and the output frequency compensation 241 of this amplifier 238 was identical to the output frequency compensation 197 of the amplifier 192.

The gain of the amplifier 238 is set by means, of a feedback voltage divider between the amplifier output 243 and the inverting input 244. This feedback voltage divider includes. a feedback resistor 245. and a resistor 246 connected, between the inverting input 244. andground. For optimum stability, the, feedback ratio is made as low as possible consistent with ample system gain. The amplifier output at 243 is zeroed by means of an. offset adjustment potentiometer 248. which. corresponds to the above mentioned zero adjustment potentiometer 226. g

The amplified sprocket hole sensing signal is applied by way of an adjustable potentiometer 250 to an output amplifier 251. This output amplifier is composed of a pair of complementary drivers 252 and a complementary output stage 253. The driver and the output stages 252 and 253 are of a conventional design and a conventional chain of diodes 255 is employed at the driver stage 253 to obtain proper bias for class B operation. The compensator mirror coil drive 41 is connected to and energized by the output stage 253.

The power supply (not shown) for energizing the circuits and components shown in FIG. may also be of a conventional design providing high output voltage stability.

In the diagrammatic view of FIG. 1, the signal conditioning circuit composed of the operational amplifier 192, the limiter 207, the lead network 232 and the amplifier 238 are represented by a block 257. The amplifier 251, on the other hand, is represented by a triangular block 55.

Further details of the operation of the circuits so far discussed may now be considered with the aid of FIGS. 1, 4 and 7. In the illustrated preferred embodiment, no routine sawtooth motion is imposed on the compensator mirror 40 as was the case with some prior-art proposals. Rather, the mirror is only advanced in accordance with the then prevailing demands of the system aiming at a stabilization of displayed images in a substantially stationary condition.

To illustrate this principle, a dotted line a in FIG. 1 approximately designates a ray of light emanating from the center of an image 23 initially appearing in the aperture 28 of the film gate 12 for projection by the objective 38 and via the compensator mirror 40 onto the screen 39. A dotted line b, on the other hand, approximately designates a ray of light emanating from the center of the same image, after that image has traveled along the film gate 12 to its extreme position in the aperture 28, just before the compensator mirror 40 is reset onto the next succeeding image. The stop plane of the lens 38 is preferably in front of the lens near the mirror 40. 1

The letter 0 in FIG. 1 designates a ray of light leading from the compensator mirror 40 to the center of the projected image on the screen 39. To maintain each projected image stationary during the movement of the image center lines from'a to b, the mirror has to advance during such movement by an angle of a magnitude substantially equal to one-half of the magnitude of the angle between the lines a and b.

To provide for such a mirror advance, the mirror 40 is wide enough to receive and project images of the sprocket holes 25 which are illuminated by the projector lamp 32. Where the mirror 40 operates in substantially collimated light, as is preferably the case, reduction of the mirror size reduces the total light level, but does not as such suppress passage of the sprocket hole image. As indicated above, borderline element images and adjacent luminous areas are projected to the sensing device 45 along with the sprocket hole images (see FIGS. 4a to c). The relationship between the

photocells

47 and 48 and the projected

elements

160, 162, 163 and 166 is as shown in FIG. 40 when the mirror 40 tracks the film 13 perfectly (assuming no offset is introduced by the servo system).

If the mirror advance leads the film, the sprocket hole image moves downwardly as seen in FIG. 4b, placing the borderline 162 onto the photocell 47, as shown in FIG. 4b. This provides an error signal of the first polarity. If the mirror advance lags the film, the borderline 163 moves onto the photocell 48 as shown in FIG. 4c, providing an error signal of the opposite polarity.

These error signals are applied to the servo amplifier 55 which drives the compensator mirror correspondingly.

As has been disclosed in the above mentioned Lancor and Ferrari patent application or patent, a substantially constant tracking error may be provided between the angular advance of the mirror 40 and the continuously moving film 13. This tracing error is preferably realized by frictional and other damping of the driven compensator part including the mirror 40. Bias or suspension springs at the driven compensator part are preferably avoided. Nevertheless, the practice of the subject invention is not limited to systems without spring bias at the compensator.

The

photocells

47 and 48 translate the above mentioned tracking error into a corresponding error signal which acts on the servo amplifier 55. That amplifier, in turn, produces a corresponding drive current for the compensator coil 41 which develops an advance torque for the mirror in accordance with the mirror tracking error. In this manner, the projected image is displayed in a substantially steady manner, without undue jitter.

As has been further disclosed in the above mentioned Lancor and Ferrari patent application or patent, and as will be fully mentioned below, a direct-current level may be applied to the servo amplifier 55 in lieu of or in addition to the drive current provided by the tracking error, in order to provide for biasing of the mirror 40 in a direction opposite to the direction of mirror advance during the display of each image. This further helps eliminate the need for the traditional bias spring at the mirror 40 or at least permitting the use of only a weak mirror suspension or bias spring. If no mirror bias spring is used, the amplifier 55 does not have to provide a mirror drive current that increases in a sawtooth fashion to overcome the force of a mirror bias spring as the display of the image progresses. Similarly, if a spring of low spring constant is used for mirror suspension or other purposes, the servo amplifier 55 still does not have to provide a mirror drive current that rises to as high a magnitude as would be required if the spring had a sufficiently high spring constant to effect.

an automatic resetting of the mirror 40 between image displays or to act as the sole agency for precluding overshooting of the mirror 40 during image display.

In addition, the amplifier 55 is constructed in a double-ended fashion to develop and apply to the mirror drive coil 41 a decelerating current when a large excursion of the error signal developed by the sensing device 45 indicates the danger of ringing of the servo system. These features are more fully disclosed in the above mentioned copending Lancor and Ferrari patent application or patent.

The requisite direct-current level for biasing the mirror 40 in a direction opposite to the direction of mirror .advance during image display may be provided by developing adirect current potential with the aid of a potentiometer248 shown in FIG. 5..ln this manner, an adjustable current is provided in the drive coil 41 for biasing the compensator mirror 40 in a directionopposite to or againstthe direction of mirror advanceduring image display.

During image display, undesired image movements areeasily reduced'by increasing the. gain of the amplifier 55. This gain is preferably higher than .100 (onehundredland may be in the thousands.

Upon completion of the display of an image, the compensator mirror 40 is angularly reset preparatory to the display of the next image. As disclosed in the above mentioned copending Lancor andFerrari patent applicationor patent, timed electric pulse doublets are applied to the compensator coil 41 for resetting the mirror 40 betweenimage displays.

In FIG. .1, a block '84 symbolically shows a pulse doublet generator which provides .an electric doublet '260forresetting the compensator mirror 40. The pulse doublet 260 is composed of an initial pulse 261 'for accelerating the mirror40backwardly and a subsequent pulse 262 for decelerating or braking the backward movement of the compensator mirror so that thismirvror will be reset to an initial position preparatory to the display of the next image.

Pursuantto the above mentionedWoodier.patentapplication or patent, a commutator or rotary switch at the compensator mirror is employed for 'timing the doublet generator 84.01" course, other'timing' devices, such as photosensorsbeyond the mirror 40 as seen from the film gate may be employed,'if desired. However, utilization of a mirror-driven commutator or rotary switch has been preferred for aprototype of the illustrated embodiment. This rotary switch is symbolically indicated at 85 in FIG. 1 where a dottedline 86 depicts a coupling betweenthe compensator mirror 40 and-the switch 85. The switch85'initiatesoperationof the doublet generator 84 each time the extreme addicates a need fora mirror resetting operation.

For a practicaldesign of thecompensator 'with switch 85, reference may behad to- FIGS.-8 and9-ofthe drawings.

In the compensator embodimentshown in FIGS. 8 and9 thecompensator mirror 40is mounted by means of cement 1 10'on a short tube ll2iof non-magnetic material. The mirror-drivecoil 41 is wound-on 'the tube 1131.2. The tube 112 with drive coil '41'partially extends between pole pieces of a magneticarmature whichrmay be of a conventional permanent-magnettype, hav'inga central core of soft magnetic material and permanentmagnetic .pole pieces 115 and 1 16. The central core 114 is mounted on a'post 1170f non-magnetic material. Suitable 'fasteners( not shown) retain 'thepole pieces :l 'lsand 116, the central core 114 and the post 117 in :position relative to-the main body of thearmature 113. Mechanical stops 150 and 151 may be provided to -avoid-contact ot the coil 41 or tube l'l2

with'the pole pieces

115 and 116 and the'core 1 14. .In contrast to .prior-art stops, these stops are so ipositioned asto be not regularly contacted by the driven compensator part. Rather, these stops are placed beyond the regular range.of-motionof-thedrivencompensator part.

Two bearings 1:18 and 119are coupled to the mirror 40 and tube 112 by cement bonds 120 and mount the compensator mirror 40 for pivotal or angular movement about an axis 122. A mounting blade 123 is fixedly held atone end as shown at 124 and carriesat the other end apivot member 125 which frictionally engages the bearing member 126.

The signal generating device or rotary switch 85 is combined with the bearing 1 19 and includes a core .of electrically conducting material. The core 130 has an integral radial projection 131 which forms an electricalswitch contact. A sleeve 132 of electrically insulating material circumferentially covers the conducting core 130, except for the switch contact 131.

An electrical contact blade 134 has one of its ends 135 fixedly mounted as shown at 136. The other end 1380f thecontact blade 135 is in engagement with the insulating sleeve 132 of the rotary switch 85.

Therotary switch 85is coupled to and actuated by the compensator advancing coil 41. In the illustrated embodiment, the rotaryswitch 85 is also coupledto the compensator mirror 40 by a cement bond 120. In this manner,the moving portion of the rotary switch 85, in-

cluding the

elements

130, 131 and l32, follows the angularmovement of the mirror 40. The angular position 'of'the switch contact 131 relative to the reflecting surface of the mirror 40 is such that the movable switch contact 131 engages the contact tip of the blade 134 upon attainment of'the angular position 40' by the compensator mirror'40. It may be said that the switch contact 131 is at the beginning of a compensating operationdisplaced from the contact tip of the blade 134 by an angle which corresponds to the angle by which the compensator mirror has to be displaced for a complete display ofa projected image.

The conductive core 130 of the rotary switch 85 is grounded by way of an electrically conducting mirror mounting blade 142 and an electrically conducting pivot member 143 connectedto the blade 142 andcontacting the core 130, as shown inFlG. 9, or altemative' vly-bya flexible lead.(not shown) connecting the core 130 to ground.

The rotary switch 85 initiates operation of the doublet generator 84 upon engagement of the rotary contact 131*with the contact blade 138 (see FIG. 8). In ithe preferredembodiment shown in FIG.5 the doublet generator comprises a pairof monostable multivibrators-300and301.

In the preferred embodiment shown in FIG. 5, the doublet generator also includes a further monostable multivibrator302 which may be considered part of the rotary switch-85, ifdesired. The multivibrator 302 is of a-conventional transistordesign and has an input 303 .connected-tothe switch85 andan output 304 coupled to aninput 3050f the multivibrator 300.

Upon-engagement of the rotarycontact 131 andcontact Made '138 (see FIG. 8) the switch 85 applies voltageffromthe positive supply voltage terminal 307-to'the mnltivibrator'input 303. The'time constant ofthe'multivibrator 302 isapproximately 4 milliseconds so that an output pulse of about 4 milliseconds duration is igenerated at the-multivibrator output 304. In practical termsthe multivibrator302 operates as a-device for protecting the mirror compensator 30 since it effectively-disarms the switch 85 for 4 milliseconds and prevents the high frequency electromechanical oscillations that otherwise tend to occur at the compensator 30 when bias circuits are improperly adjusted and override the input signal so that the movable compensator part is rotated in the direction of closure of the switch 85. The protective multivibrator 302 may also be considered a pulse shaper in that it generates a unitary pulse in response to each closure of the switch 85, free from contact noise or contact bouncing effects.

The leading edge of the output pulse of the multivibrator 302 causes the multivibrator 300 to generate at its output 310 a pulse of the type shown at 261 in FIG. 1. That pulse, it will be recalled, is part of the pulse doublet 260 and serves to accelerate and actuate the compensator mirror 40 in the resetting direction. In the preferred embodiment shown in FIG. 5, the multivibrator 300 generates a positive pulse at its output 320 since that is the polarity which, after amplification of the pulse at 251, will in the particular illustrated embodiment drive the compensator mirror 40 from its advanced position 40' to its initial position preparatory to the display of the next image.

The multivibrator 300 includes a pair of series-connected variable resistors 312 and 313 with which the width of the pulse generated at the output 310 may be manually adjusted. By way of example, the resistor 312 may have a maximum value of, say, 50 kilohms for effecting rough adjustments and the resistor 312 may have a maximum value of, say, 10 kilohms for effecting fine adjustments of the pulse width. A practical range of adjustment for motion picture display purposes has been found to be from 0.25 to 1.0 milliseconds.

The output 310 of the multivibrator 300 is coupled by way of a resistor 315 to the driver stage 252 of the power amplifier 251 and, by way, of a diode 316 to a variable potentiometer 318. The potentiometer 318 serves the adjustment of the height of the pulse generated by the multivibrator 300 and applied to the amplifier 251. The diode 316 serves as a diode limiter and the variable potentiometer 318 applies an adjustable back bias to the diode 316.

The power amplifier 251 amplifies the pulse generated by the multivibrator 300 and applies the amplified pulse to the drive coil 41 of the compensator 30 for a resetting of the mirror 40. In practice, such a resetting operation is very delicate, since an excess of resetting energy will cause the mirror 40 to overshoot in its resetting direction, while a deficiency in the resetting energy will provoke an incomplete resetting operation.

These deficiencies are countered by generating and utilizing the second pulse 262 subsequent to the pulse 261 (see FIG. 1). To this end, the output 310 of the multivibrator 300 is coupled by way of a capacitor 320 to theinput 321 of the multivibrator 301. The trailing edge of the pulse generated by the multivibrator 300 triggers the multivibrator 301 whereby a pulse is generated at the output 323 of the multivibrator 301. That pulse is of a polarity opposite to the polarity generated by the multivibrator 300 at the output 310. For instance, if the pulse generated at 310 is positive, then the pulse generated at 323 is negative, assuming that a positive pulse will cause resetting of the mirror 40 while a negative pulse will cause deceleration of the mirror resetting operation.

The multivibrator 301, which is also of a conventional design, includes a variable resistor 324 for adjusting the width of the pulses generated at 323. The width of the pulse generated at 323 may be adjustable over substantially the same range as the width of the pulse generated at 310.

The output 323 of the multivibrator 301 is connected by way of a resistor 326 to the amplifier 251 and also to a diode 327 which, in turn, is connected to a variable potentiometer 328. The diode 327 serves as a diode limiter and the potentiometer 328 provides an adjustable back bias for that limiter whereby the height of the pulse generated by the multivibrator 301 is adjustable. The power amplifier 251 amplifies the pulse generated by the multivibrator 301 and applies the amplified pulse to the mirror drive coil 41 for deceleration of the mirror resetting operation. No electronic switch means are in the illustrated embodiment required for deactivating the photoelectric servo during resetting operations, since the

multivibrators

300 and 301 and the amplifier 251 are so designed that the amplifier 251 is driven into saturation by the pulse doublet generated by the

multivibrators

300 and 301 so that the photoelectric servo is effectively decoupled from the mirror drive coil 41 during resetting operations.

The mirror reset control according to the subject invention, as implemented in the illustrated preferred embodiments, will now be explained. To this end, FIG. 11a again depicts a diagrammatic illustration of the above mentioned reset pulse doublet 260 composed of the oppositely poled reset acceleration pulse 261 and reset deceleration pulse 262. This pulse doublet is generated in the above mentioned manner by the

multivibrators

300 and 301 shown in FIG. 5. The

variable potentiometers

318 and 328 in that figure are adjusted to provide a desired height of the

pulses

261 and 262, while the

variable resistors

312, 313, and 324 are adjusted to provide pulse widths considered adequate for resetting of the compensator mirror 40 between successive image displays.

By way of example and with reference to FIG. 11a, the reset acceleration pulse 261 may be provided with a certain initial pulse width 345. The reset deceleration pulse 262 may have the same or a similar pulse width.

A negative pulse 346 in FIG. 11b depicts the signal occurring at the node 210 of FIG. 5 when a sprocket hole image leaves the photosensor 45 at the beginning of a resetting operation initiated by the reset acceleration pulse 261. The pulse 346 stems from the fact that the illumination of the lower photocell 48 is cut off before the illumination of the upper photocell 47 when a sprocket hole image is moved away from the photosensor 45 during a resetting operation. Accordingly, the pulse 346 in FIG. 11b (and also in FIGS. 11c and d) corresponds to the pulse 220 shown in FIG. 7d for opaque-margin film or the pulse 221 shown in FIG. 7h for transparent-margin film.

A pulse 347 in FIG. 11b depicts the signal occurring at the node 210 of FIG. 5 when a new sprocket hole image is brought onto the photosensor 45 at the end of a mirror resetting operation. In that case the lower photocell 48 is illuminated prior to the illumination of the upper photocell 47. Accordingly, the pulse 347 corresponds to the pulse 218 in FIG. 7d for opaque-margin film or the pulse 219 in FIG. 7h for transparent-margin film. No signal spikes due to

borderline image elements

162 and 163 have been shown in FIGS. 11b to d because of the considerably smaller time displacement scale of these figures as compared to FIGS. 7a through h.

If the resetting operation is perfect, the mirror will move right to the point where the mirror advancement for the next image display is to commence. Taking practical realities of friction and inertia into account, some tolerable damping-in effect will be observed in actual operation, even under practically ideal conditions. Thus, FIG. 11b shows a slight damping-in waveform 348 occurring at the beginning of a subsequent image display and having no noticeable adverse effect on the displayed image unless one of the conditions depicted in FIGS. 1 1c and d should prevail.

It may be noted at this juncture that the time axes 1 shown in FIG. 1 1 do not necessarily indicate zero signal amplitude. As has been mentioned above, it may be advantageous to operate the system at a constant tracking error so that the absolute time axes may be somewhat offset from the time axes tin FIG. 11.

If the reset movement of the compensator mirror 40 is excessive, then a negative pulse349 will occur at the node 210 in FIG. 5 subsequent to the pulse 347, as shown in FIG. 11c.

The negative pulse 349 is due to the fact that an overshooting of the mirror reset will move the sprocket holeimage past the lower photo-cell 48 and exclusively onto the upper photocell 47. The photoservo responds to this excessive reset condition but is by itself only capable of correcting it at the expense of an excessively long damping-in period which is indicated by the waveform 350 in FIG.- 11c, and which results in intolerable smearing of displayed images.

If the mirror resetting motion is insufficient, the

previously mentioned pulse 347 is extended into a prolonged pulse 347' since the sprocket hole image will not be able to move onto the upper photocell 47 within an adequately short period of time. Again, the photoelectric servo will attempt to correct this condition, but will only be able to do so at the expense of a long damping-in period depicted by the waveform 351 in FIG. 11d, and leading again to severe image smearing, A resetcontrol'353 in accordance with a preferred embodiment of the subject invention will now first be explained with the aid of the block diagram shown in FIG. 1.

The reset control 353 samples the signal occurring at the signal conditioner 257 upon cessation of the reset deceleration pulse 262. To this end, the reset control 353 has a first input 354 connected to the signal conditioner 257. The reset control 353 further has a second input 357 connected by a lead 358 to the doublet generator 48. The lead 358 applies the trailing edge of the reset deceleration pulse 262 to the reset control. The reset control responds to the signal received at 357 by sampling the signal received at 354, so that either the pulse 349 shown in FIG. 1 1c or the prolonged pulse 347' shown in FIG. 11d is discerned by the reset control 353, depending on whether the mirror reset motion is excessive or insufficient.

In response to this discernment, the reset control 353 provides at an output 360 an error signal which is indicative of the resetting error occurring at the mirror 40. The resetting error signal is applied by a lead 362 to the doublet generator 84 where it controls the resetting energies represented by the

pulses

261 and 262.

By way of example, it is within the scope of the subject invention that one or more of the following parameters of the resetting pulse doublet be controlled: the height of the reset acceleration pulse 261, the width of the reset acceleration pulse 261, the height of the reset deceleration pulse 262, and the width of the reset deceleration pulse 262.

While the subject invention is not limited to any of these parameters, control of the width of the reset acceleration pulse 261 is presently considered the best single factor in obtaining proper retrace action since it determines the ultimate speed at which the compensator mirror rotates. This speed is preferably controlled by the acceleration pulse width so that it is matched to the braking power of the deceleration pulse 262 which brings the mirror 40 to rest at the proper place and time. According to the preferred embodiment of the invention shown in FIG. 5, the lead 356 preferably connects the input 354 of the reset control 353 to the node 210 at the limiter 207 of the signal conditioner 257. The lead 358 preferably connects the reset control input 357 to the output 3230f the deceleration pulse multivibrator 301, so that the reset control 353 will, in response to the trailing edge of the reset deceleration pulse 262, sample the signal occurring at the node 210.

In the illustrated preferred embodiment, the reset control 353 responds to the negative pulse 349 shown in FIG. 11c by applying through its output 360 and by way of the lead 362 a positive bias to the base of the transistor 365 in the acceleration pulse multivibrator. That positive bias has the effect of reducing the width of the reset acceleration pulse 261 from the value 345 to a value 366. As indicated in FIG. 11 by the

phantom lines

367 and 368, this shifts the timing of the reset deceleration pulse 262 so that the pulse commences and terminates earlier than when the width of the pulse 261 has the value 345.

Conversely, the prolonged positive pulse 347 shown in FIG. 11d causes the reset control 353 to apply through its output 360 and by way of the lead 362 a relatively negative bias to the base of the transistor 365 so that the width of the reset acceleration pulse 261 is extended to a value 370. As indicated by the dotted

lines

371 and 372 in FIG. 11a, this retards the leading and trailing edges of the reset deceleration pulse 262. The width of the reset deceleration pulse 262 is neither altered by a positive bias nor by a negative bias at the transistor base 365.

A circuit diagram of the reset control in accordance with a preferred embodiment of the subject invention is shown in FIG. 10 where like reference numerals as among FIGS. 1, 5,'and 10 indicate like or functionally equivalent parts.

The reset control 353 has the above mentioned

inputs

354 and 357 and the output 360, which are connected to the signal conditioner, the reset deceleration pulse multivibrator 301 and the reset acceleration multivibrator 300as shown in FIG. 5. The reset control 353 comprises a gate pulse generator 375, a sampler 376, and an integrator 377.

The gate signal generator 375 comprises a monostable multivibrator 379 which has an input 380 and a pair of

outputs

381 and 382. A resistor 383 and coupling capacitor 384 couple the reset control input 357 to the multivibrator input 380. The multivibrator output 381 is coupled by a diode 386 and a variable resistor 387 to an input 388 of the sampler 376. Similarly, a diode 390 and a variable resistor 391 couple the multivibrator output 382 to an input 392 of the sampler 376.

When triggered by the trailing edge of a reset deceleration pulse entering through the input terminal 357, the multivibrator 379 provides at the sampler inputs 388 and 392 a pair of opposite gate pulses. The gate pulse at the input 388 is negative while the gate pulse at the input 392 is positive. The width of each of these gate pulses is sufficiently long for a sampling of the pulses 349 and 347' shown in FIGS. 11c and d. In a prototype of the illustrated embodiment, the gate pulse width was 250 microseconds.

The sampler 376 comprises a first sampling circuit 394 with a PNP transistor 395, and a second sampling circuit 396 with an NPN transistor 397. The

sampling circuits

394 and 396 are so designed in a conventional manner that the gate pulses received at the

terminals

388 and 392 are'of themselves incapable of switching on the

transistors

395 and 397, respectively.

Sprocket hole image sensing signals occurring at the node 210 in FIG. are received through the input 354 as mentioned above and are applied to the base of the transistor 395 by way of a coupling capacitor 398 and a resistor 399, and are simultaneously applied to the base of the transistor 397 by way of a coupling capacitor 400 and a resistor 401. No signal amplitude occurring at the node 210 in FIG. 5 and being applied to the latter transistor bases is of itself capable of turning on either

transistor

395 or 397. Also, since the amplitude of the damping-in waveform 348 in FIG. 11b is insignificant, no corrective control function is instituted by the sampler 376 when the mirror reset operation conforms to the desired standard.

The negative pulse 349 of FIG. 1 Is also has no effect on the operation of the transistor 397 whose base simultaneously receives a positive sampling pulse through the sampler input 392. However, the negative pulse 349 is additive with the negative sampling pulse received through the sampler input 388 so that the transistor 395 is turned on and acts through a diode 403 to provide a positive pulse at an input 404 of the integrator 377.

The integrator 377 comprises an integrating capacitor 406 which may, for instance, be on the order of about 50 microfarad, and

resistors

407 and 408. The resistor 407 which couples to the sampler output 404 may have a value on the order of 45 to 50 kilohms. The integrator 377 includes an operational amplifier 409 which may be of the same design as the

amplifiers

192 and 238 shown in FIGS. 5 and 6.

The amplifier 409 has an inverting input 410 and a non-inverting input 411, as well as an output 412. The amplifier 409 is provided with an offset adjustment potentiometer 413 which corresponds to the offset

adjustment potentiometers

226 and 248 shown in FIG. 5, as well as with an input frequency compensation network 415 that corresponds to the

networks

196 and 240, and an output frequency compensation 416 that corresponds to the

compensation

197 and 241 in FIG. 5. The amplifier 409 further has a negative feedback circuit 418 extending between the amplifier output 412 and the inverting input 410. The feedback circuit includes a unilaterally grounded

potentiometer comprising resistors

420 and 421, and a capacitor 422 connected in parallel to the resistor 421.

In principle, it would be possible to view only the capacitor 406 and

resistors

407 and 408 as parts of the integrator 377. In the present disclosure, the amplifier 409 has, however, been included with the capacitor 406 and

resistors

407 and 408 in the integrator 377 mainly because of the fact that an integrating function may be performed by the amplifier 409 with the aid of the feedback capacitor 422 which is then provided with a larger capacitance.

The integrator 377 integrates positive pulses received through the input terminal 404 from the sampler 376 (note transistor 395). In response to these integrated positive pulses, the integrator 377 provides at the output 360 a positive direct-current bias. The relative level of that bias is adjustable by means of a potentiometer 424. As mentioned above, the bias occurring at the terminal 360 is applied to the base of the transistor 365 in the multivibrator 300 shown in FIG. 5 and has the effect of decreasing the width of the reset acceleration pulse 261 as shown in FIG. 11a (compare the reduced pulse width 366 with the initially provided pulse width 345). This reduces the net energy content of the reset pulse doublet 260 so that the compensator mirror, during the next resetting operation or operations, is reset to a lesser extent than during the previous resetting operation which gave rise to the pulse 349 and the excessive damping in operation 350 illustrated in FIG. 11c, thereby bringing about the ideal condition shown in FIG. 7b.

As has been mentioned above, the prolonged positive pulse 247' occurs at the node 210 of FIG. 5 when the compensator mirror 40 is insufficiently reset. The prolonged positive pulse 347' has no effect on the operation of the transistor 395, since that transistor simultaneously receives a negative gate pulse through the sampler input terminal 388. The prolonged positive pulse 347', however, combines with the positive gate pulse received through the sampler input terminal 392 to turn on the transistor 397. The turned-on transistor 397, provides by way of a diode 426 a negative pulse at the integrator input 404. It will be noted at this juncture that the

diodes

403 and 426 servo to isolate the

sampling circuits

394 and 396 from each other.

The integrator 377 integrates the negative pulses received at the input 404. This integration of negative pulses may, for instance, be effected by a diminution of the charges of the

capacitors

406 and 422 or other integrated elements which have been chargedby positive pulses received at the integrator input 404. In response to the negative pulses received at the input 404, the integrator 377 provides a negative bias at the output 360.

. It will be recalled that a negative bias at the base of the transistor 365 has been designated above as increasing the width of the reset acceleration pulse 261.

The term negative" in this connection has to be understood in its relative implication. of course, it is possible and within the scope of the subject invention to apply to the doublet generator bias voltages or currents which are positive or negative relative to a zero level. It will, however, in practice be found more convenient to apply to the base of the transistor 365 a positive direct-current level that increases its amplitude in response to positive pulses provided at the input 404, and that decreases its amplitude in response to negative pulses received by the input terminal 404. In that case, the negative bias provided at the output 360 and applied to the base of the transistor 365 in FIG. is negative not relative to a zero voltage axis, but rather relative to the amplitude of the direct current level that will provide the median pulse width 345 shown in FIG. 1 1a.

In consequence, the width of the reset acceleration pulse 261 is increased, such as from a

value

366 or 345 to a value 370 shown in FIG. 11a, whereupon the insufficiency of the mirror resetting operation will be corrected until the practically ideal condition depicted in FIG. 1 lb is realized.

It will now be recognized that the subject invention provides an automatic closed-loop control for the compensator resetting operation, thereby automatically correcting resetting errors and greatly improving the display of the motion picture images, particularly at the beginning of each image display. In the illustrated preferred embodiments, successive errors in the resetting of the compensator mirror are sensed (sensor 45, etc.), and successive error signals indicative of the successive errors are provided (sampler 376). These successive error signals are combined or integrated (integrator 377) to provide at the reset pulse generator 84 an error signal for controlling the resetting energy and thereby correcting the resetting errors.

A modification of the apparatus of FIG. 5 is shown by the circuit diagram of FIG. 12. The previously described photocells 4'7 and 48 of the sensor 45 are connected in parallel with opposite polarities. The parallel-connected

photocells

47 and 48 are connected between the inverting and non-inverting inputs 193 and 19 4 of the amplifier 192. The feedback resistor 224 is connected between the amplifier output 191 and the inverting input 193 as before. The non-inverting input 194 is grounded.

A shunt resistor 700, which is similar to the above mentioned resistors 200 and 201, is connected in parallel to the photocells 47'and 48 in order to shunt out the photocell capacitances and to force the photocells to operate in the preferred short circuit mode. The resistance of the resistor 700 is small compared to that of the illuminated photocells.

We claim:

1. In a method of operating a repeatedly advanceable and resettable device, the improvement comprising in combination the steps of:

repeatedly advancing said device through a range of motion;

providing energy for resetting said device between successive advancements;

resetting said device through said range of motion with said resetting energy after essentially each advancement;

sensing errors in the resetting of said device;

providing an error signal indicative of said sensed errors; and controlling said resetting energy with said error signal to correct said errors.

2. A method as claimed in claim 1, wherein:

said resetting energy is provided by generating for each resetting operation a pair of oppositely poled electric pulses;

said electric pulses are employed to reset said device;

and

one of said pulses is controlled with said error signal to correct said errors.

3. A method as claimed in claim I, wherein:

said error signal is provided by sensing successive errors in the resetting of said device, providing successive error signals indicative of said successive errors, and

combining said successive error signals to provide said error signal indicative of said sensed errors.

4. A method as claimed in claim 1, wherein:

said resetting energy is provided by generating for each resetting operation a reset acceleration pulse and a reset deceleration pulse;

said device is reset with said reset acceleration and deceleration pulses; and

said reset acceleration pulse is controlled with said error signal to correct said errors.

5. A method as claimed in claim 4, wherein:

said reset acceleration pulse is controlled by varying the, width of said reset acceleration pulse in response to said error signal.

6. A method as claimed in claim 1, wherein:

said device is advanced by providing driving energy for advancing said device, advancing said device with said driving energy, sensing errors in the advancement of said device, providing an advancement error signal indicative of said sensed errors in the advancement of said device, and controlling said driving energy with said advancement error signal to correct said errors in the advancement of said device.

7. A method as claimed in claim 6, wherein:

said error signal indicative of errors in the resetting of said device is provided by sampling said advancement error signal.

8. A method as claimed in claim 1, wherein:

said device is an optical compensator element ina continuous film feed motion picture apparatus.

9. In a method of displaying images from a motion picture film, the improvement comprising in combination the steps of: Y

substantially continuously advancing said motion picture film;

providing an optical compensator including a repeatedly advanccable and resettable compensator device for compensating the continuous film advance;

displaying said images by way of said compensator device;

repeatedly advancing said compensator device to maintain each displayed image substantially stationary during its display;

providing energy for resetting said compensator device between successive advancements;

resetting said compensator device between successive advancements with said resetting energy;

sensing error in the resetting of said compensator device;

providing an error signal indicative of said sensed errors in the resetting of said compensator device; and

controlling said resetting energy with said error signal to correct said errors.

10. A method as claimed in claim 9, wherein:

1 1. A method as claimed in claim 9, wherein:

said electric pulses are employed to reset said device;

and

one of said pulses is controlled with said error signal to correct said errors.

12. A method as claimed in claim 9, wherein:

said compensator device is advanced by providing driving energy for advancing said device, advancing said device with said driving energy, sensing errorsin the advancement of said device, providing an advancement error signal indicative of said sensed errors in the advancement of said device, and controlling said driving energy with said advancement error signal to correct said errors in the advancement of said device.

13. A method as claimed in claim 12, wherein:

said error signal indicative of errors in the resetting of said device 1 is provided by sampling said advancement error signal.

14. In apparatus for operating a repeatedly advanceable and resettable device, the improvement comprising in combination:

means coupled to said device for repeatedly advancing said device through a range of motion;

means for providing energy for resetting said device between successive advancements;

means connected to said energy providing means and coupled to said device for resetting said device through said range of motion with said resetting energy after essentially each advancement;

means for sensing error in the resetting of said device;

means coupled to said error sensing means for providing an error signal indicative of said sensed errors; and

means connected to said error signal providing means and said energy providing means for controlling said resetting energy with said error signal whereby to correct said errors.

15. An apparatus as claimed in claim 14, wherein:

said means for providing said error signal include means for providing successive error signals indicative of sensed successive errors' in the resetting of said device, and means for combining said successive error signals to provide said error signal indicative of said sensed errors.

16. An apparatus as claimed in claim 14, wherein:

said energy providing means include means for providing for each resetting operation a pair of opposite poled pulses;

said resetting means include means for resetting said device with ,said pair of oppositely poled pulses; and

said means for controlling said resetting energy include means for controlling one of said pulses with said error signal whereby to correct said errors.

17. An apparatus as claimed in claim 14, wherein:

said energy providing means include means for providing for each resetting operation a reset acceleration pulse and a reset deceleration pulse;

said resetting means include means for resetting said device with said reset acceleration and reset deceleration pulses; and

said means for controlling said resetting energy include means for controlling said reset acceleration pulse with said error signal whereby to correct said errors.

18. An apparatus as claimed in claim 14, wherein:

said means for advancing said device include means for providing driving energy for advancing said device, means connected to said driving energy providing means and coupled to said device for advancing said device with said driving energy, means for sensing errors in the advancement of said device, means connected to said advancement error sensing means for providing an advancement error signal indicative of said sensed errors in the advancement of said device, and means connected between said advancement error sensing means and said driving energy providing means for controlling said driving energy with said advancement error signal whereby to correct said errors in the advancement of said device.

19. An apparatus as claimed in claim 18, wherein:

said means for sensing errors in the resetting of said device include means coupled to said advancement error sensing means for sampling said advancement error signal.

20. An apparatus as claimed in claim 14, wherein:

said device is an advanceable and resettable optical compensator of a continuous film feed motion picture apparatus.

21. In apparatus for displaying images from a motion picture film, the improvement comprising in combination:

means for substantially continuously advancing said motion picture film;

means including a repeatedly advanceable and resettable optical compensator device for compensating the continuous film advance;

means operatively associated with said motion picture film and said compensator device for displaying said images by way of said compensator device;

means coupled to said compensating means for repeatedly advancing said compensator device whereby to maintain each displayed image substantially stationary during its display;

means for providing energy for resetting said compensator device between successive advancements;

means connected to said energy providing means and coupled to said compensating means for resetting said compensator device between successive advancements with said resetting energy;

means for sensing errors in the resetting of said compensator device;

means connected to said sensing means for providing an error signal indicative of said sensed errors in the resetting of said compensator device; and

Claims

1. In a method of operating a repeatedly advanceable and resettable device, the improvement comprising in combination the steps of: repeatedly advancing said device through a range of motion; providing energy for resetting said device between successive advancements; resetting said device through said range of motion with said resetting energy after essentially each advancement; sensing errors in the resetting of said device; providing an error signal indicative of said sensed errors; and controlling said resetting energy with said error signal to correct said errors.

2. A method as claimed in claim 1, wherein: said resetting energy is provided by generating for each resetting operation a pair of oppositely poled electric pulses; said electric pulses are employed to reset said device; and one of said pulses is controlled with said error signal to correct said errors.

3. A method as claimed in claim 1, wherein: said error signal is provided by sensing successive errors in the resetting of said device, providing successive error signals indicative of said successive errors, and combining said successive error signals to provide said error signal indicative of said sensed errors.

4. A method as claimed in claim 1, wherein: said resetting energy is provided by generating for each resetting operation a reset acceleration pulse and a reset deceleration pulse; said device is reset with said reset acceleration and deceleration pulses; and said reset acceleration pulse is controlled with said error signal to correct said errors.

5. A method as claimed in claim 4, wherein: said reset acceleration pulse is controlled by varying the width of said reset acceleration pulse in response to said error signal.

6. A method as claimed in claim 1, wherein: said device is advanced by providing driving energy for advancing said device, advancing said device with said driving energy, sensing errors in the advancement of said device, providing an advancement error signal indicative of said sensed errors in the advancement of said device, and controlling said driving energy with said advancement error signal to correct said errors in the advancement of said device.

7. A method as claimed in claim 6, wherein: said error signal indicative of errors in the resetting of said device is provided by sampling said advancement error signal.

8. A method as claimed in claim 1, wherein: said device is an optical compensator element in a continuous film feed motion picture apparatus.

9. In a method of displaying images from a motion picture film, the improvement comprising in combination the steps of: substantially continuously advancing said motion picture film; providing an optical compensator including a repeatedly advanceable and resettable compensator device for compensating the continuous film advance; displaying said images by way of said compensator device; repeatedly advancing said compensator device to maintain each displayed image substantially stationary during its display; providing energy for resetting said compensator device between successive advancements; resetting said compensator device between successive advancements with said resetting energy; sensing error in the resetting of said compensator device; providing an error signal indicative of said sensed errors in the resetting of said compensator device; and controlling said resetting energy with said error signal to correct said errors.

10. A method as claimed in claim 9, wherein: said error signal is provided by sensing successive errors in the resetting of said device, providing successive error signals indicative of said successive errors, and combining said successive error signals to provide said error signal indicative of said sensed errors.

11. A method as claimed in claim 9, wherein: said resetting energy is provided by generating for each resetting operation a pair of oppositely poled electric pulses; said electric pulses are employed to reset said device; and one of said pulses is controlled with said error signal to correct said errors.

12. A method as claimed in claim 9, wherein: said compensator device is advanced by providing driving energy for advancing said device, advancing said device with said driving energy, sensing errors in the advancement of said device, providing an advancement error signal indicative of said sensed errors in the advancement of said device, and controlling said driving energy with said advancement error signal to correct said errors in the advancement of said device.

13. A method as claimEd in claim 12, wherein: said error signal indicative of errors in the resetting of said device is provided by sampling said advancement error signal.

14. In apparatus for operating a repeatedly advanceable and resettable device, the improvement comprising in combination: means coupled to said device for repeatedly advancing said device through a range of motion; means for providing energy for resetting said device between successive advancements; means connected to said energy providing means and coupled to said device for resetting said device through said range of motion with said resetting energy after essentially each advancement; means for sensing error in the resetting of said device; means coupled to said error sensing means for providing an error signal indicative of said sensed errors; and means connected to said error signal providing means and said energy providing means for controlling said resetting energy with said error signal whereby to correct said errors.

15. An apparatus as claimed in claim 14, wherein: said means for providing said error signal include means for providing successive error signals indicative of sensed successive errors in the resetting of said device, and means for combining said successive error signals to provide said error signal indicative of said sensed errors.

16. An apparatus as claimed in claim 14, wherein: said energy providing means include means for providing for each resetting operation a pair of opposite poled pulses; said resetting means include means for resetting said device with said pair of oppositely poled pulses; and said means for controlling said resetting energy include means for controlling one of said pulses with said error signal whereby to correct said errors.

17. An apparatus as claimed in claim 14, wherein: said energy providing means include means for providing for each resetting operation a reset acceleration pulse and a reset deceleration pulse; said resetting means include means for resetting said device with said reset acceleration and reset deceleration pulses; and said means for controlling said resetting energy include means for controlling said reset acceleration pulse with said error signal whereby to correct said errors.

18. An apparatus as claimed in claim 14, wherein: said means for advancing said device include means for providing driving energy for advancing said device, means connected to said driving energy providing means and coupled to said device for advancing said device with said driving energy, means for sensing errors in the advancement of said device, means connected to said advancement error sensing means for providing an advancement error signal indicative of said sensed errors in the advancement of said device, and means connected between said advancement error sensing means and said driving energy providing means for controlling said driving energy with said advancement error signal whereby to correct said errors in the advancement of said device.

19. An apparatus as claimed in claim 18, wherein: said means for sensing errors in the resetting of said device include means coupled to said advancement error sensing means for sampling said advancement error signal.

20. An apparatus as claimed in claim 14, wherein: said device is an advanceable and resettable optical compensator of a continuous film feed motion picture apparatus.

21. In apparatus for displaying images from a motion picture film, the improvement comprising in combination: means for substantially continuously advancing said motion picture film; means including a repeatedly advanceable and resettable optical compensator device for compensating the continuous film advance; means operatively associated with said motion picture film and said compensator device for displaying said images by way of said compensator device; means coupled to said compensating means for repeatedly advancing said compensaTor device whereby to maintain each displayed image substantially stationary during its display; means for providing energy for resetting said compensator device between successive advancements; means connected to said energy providing means and coupled to said compensating means for resetting said compensator device between successive advancements with said resetting energy; means for sensing errors in the resetting of said compensator device; means connected to said sensing means for providing an error signal indicative of said sensed errors in the resetting of said compensator device; and means connected to said error signal providing means and said resetting energy providing means for controlling said resetting energy with said error signal whereby to correct said errors.

22. An apparatus as claimed in claim 21, wherein: said means for providing said error signal include means for providing successive error signals indicative of sensed successive errors in the resetting of said device, and means for combining said successive error signals to provide said error signal indicative of said sensed errors.

23. An apparatus as claimed in claim 21, wherein: said energy providing means include means for providing for each resetting operation a pair of oppositely poled pulses; said resetting means include means for resetting said device with said pair of oppositely poled pulses; and said means for controlling said resetting energy include means for controlling one of said pulses with said error signal whereby to correct said errors.

24. An apparatus as claimed in claim 21, wherein: said means for advancing said device include means for providing driving energy for advancing said device, means connected to said driving energy providing means and coupled to said device for advancing said device with said driving energy, means for sensing errors in the advancement of said device, means connected to said advancement error sensing means for providing an advancement error signal indicative of said sensed errors in the advancement of said device, and means connected between said advancement error sensing means and said driving energy providing means for controlling said driving energy with said advancement error signal whereby to correct said errors in the advancement of said device.

25. An apparatus as claimed in claim 24, wherein: said means for sensing errors in the resetting of said device include means coupled to said advancement error sensing means for sampling said advancement error signal.

26. An apparatus as claimed in claim 21, wherein: said means for advancing said compensator device include means for providing driving energy for advancing said compensator device, means connected to said driving energy providing means and coupled to aid compensator device for advancing said compensator device with said driving energy, means connected to said resetting error sensing means for sensing errors in the advancement of said compensator device, means connected to said advancement error sensing means for providing an advancement error signal indicative of said sensed errors in the advancement of said device, and means connected between said advancement error sensing means and said driving energy providing means for controlling said driving energy with said advancement error signal whereby to correct said errors in the advancement of said device.

27. An apparatus as claimed in claim 26, wherein: said resetting error sensing means and said advancement error sensing means include means for sensing the position of substantially each displayed image at the beginning of a display operation and means for sensing movement of substantially each displayed image during display.

28. An apparatus as claimed in claim 26, wherein: said resetting error sensing means and said advancement error sensing means include differential photocell image movement sensing means, means connected to said differential photocell Sensing means for sampling the output of said differential photocell sensing means, and means connected to said sampling means for activating said sampling means substantially immediately after each resetting of said compensator device.