US3603495A

US3603495A - Film feeding equipment

Info

Publication number: US3603495A
Application number: US790044A
Authority: US
Inventors: Bretislav Stejskal; Vladimir Stepan; Petr Vlach
Original assignee: Tesla AS
Current assignee: Tesla AS
Priority date: 1968-01-12
Filing date: 1969-01-09
Publication date: 1971-09-07
Anticipated expiration: 1988-09-07
Also published as: DE1901026A1; NL6900485A; SE335673B; FR2000209A1; CH490685A; AT288865B; GB1198040A

Abstract

The invention relates to a film-feeding device for advancing a perforated or unperforated film strip of any width by any number of frames in either direction. The feeding of the film strip is effected by means of friction drive powered by two reversing motors. The advancement and braking of the film strip is carried out by variously supplying power to the two reversing motors. The displacement as well as the required positioning of the film strip are determined by sensing synchronizing indicia on the film strip by photoelectric sensors. The two reversing motors are switched from a rest condition to working and braking conditions by a special motor control device which is actuated either by starting signals from a primary source effecting the forward or reverse movement of the film strip or by stopping signals set up by the photoelectric sensors sensing the synchronizing marks.

Description

United States Patent [54] FILM FEEDING EQUIPMENT 9 Claims, 7 Drawing Figs.

[52] US. Cl 226/33, 226/50 [51] lnt.Cl ....Gllb 15/20 [50] Field of Search 226/32, 34, 27, 43, 50, 33, 9; 179/1002 S, 100.3 D

[56] References Cited UNlTED STATES PATENTS 3,248,029 4/1966 Money 226/33 X Primary Examiner-Allen N. Knowles Attorney-Richard Low TRACT: The invention relates to a film-feeding device for advancing a perforated or unperfo'rated film strip of any width by any number of frames in either direction. The feeding of the film strip is effected by means of friction drive powered by two reversing motors. The advancement and braking of the film strip is carried out by variously supplying power to the two reversing motors. The displacement as well as the required positioning of the film strip are determined by sensing synchronizing indicia on the film strip by photoelectric sensors. The two reversing motors are switched from a rest condition to working and braking conditions by a special motor control device which is actuated either by starting signals from a primary source effecting the forward or reverse movement of the film strip or by stopping signals set up by the photoelectric sensors sensing the synchronizing marks.

PATENTEUsEP (19H 3.608%95 SHEET 2 W 5 l lllLMl FEEDING EQUHIPMIENT The present invention relates to apparatus for feeding film and for advancing a perforated or unperforated film strip of any width by any required number of frames in either direction.

In conventional perforated film-feeding mechanisms the film perforation is used to determine the position, as well as to provide the means for moving the film strip. If, however, the film perforation is damaged, the feeding of the strip is im paired or even rendered impossible. With film-feeding mechanisms for unperforated film strips, a friction drive has been employed for the same purpose. However, due to slippage of the film strip and other integrating errors, such mechanisms are not reversible and the stopping of the strip at the desired or required frame cannot be always made with ac curacy. These mechanism are therefore useful only for unidirection film shooting and copying but are unsuitable for projection purposes. It has been attempted to utilize a synchronizing mark or detent for the identification of the required position of the film strip, the advancing of the film being effected by the cooperation therewith of a rotating friction drive. This mechanism, also has to be equipped with a complex braking device which unfortunately increases the transition period during starting and stopping of the film strip while simultaneously limiting the film-feeding speed.

It is the object of the present invention to eliminate the disadvantages noted above and to provide an improved filmfeeding apparatus.

According to the present invention there is provided apparatus for feeding a film strip through a gate. The film strip is provided with optical indicia indicative of the predetermined location of particular film frames. The film is moved by a pair of frictional drive means associated respectively to a pair of reversible motors. The motors are controlled by a control device responsive to one of a pair of signals derived from a primary control system so as to be operable to move the film forwardly or backwardly. The control device is further selectively responsive to one of a pair of signals obtained by a photoelectric sensor reading" the indicia on the film, to effect the stopping of the movement of the film. Preferably two sensors are used, each being respectively located to be operative in response to the direction of movement of the film.

in the preferred form the sensors are located to either side of the gate but in an alternate form the sensors may be mounted on the display screen. It is also preferred that the reversible motors be operated so that the pulling" motor (i.e. the one in the direction of movement of the film) be provided with a greater voltage so as to keep the film taut.

A control device is also provided for integrating the drive and stop signals and to control the movement of the film. The control device includes means for reversing the polarity and level of voltage to the motors to effect braking, it being advantageous to provide a greater braking effect on the pushing motor to prevent the film from becoming loose.

The specific details of the present invention, together with its objects and advantages, will be seen from the following description.

The invention will be better understood from the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of film-feeding device embodying the invention,

FIGS. 2a, b, show the location and the types of synchronizing marks or triggering codes on the film strip,

FIG. 3 is a block diagram of the motor control mechanisms employed in the device of FIG. 11,

H6. 42 is a block diagram of the switching device, and

FIG. 5 is a circuit diagram of the switching device, used in the device of FIG. i.

As is shown in H6. 1 the film strip ll is moved within a gate between the light source 2 and the objective 2% and is wound off from or taken up on either the film reel 7 or the film reel 8, as the case may be. The reels are located on the exterior side of the film-feeding equipment so that the film strip can freely be taken from or returned to a storage magazine. A first friction drive is located above the light source and, consisting of a driving pulley l3 and pressure pulley I5 is connected to the shaft of a first reversible motor 4 to transmit its torque on to the film strip. A second friction drive is located below the light source, and it too consists ofa driving pulley I l and a pressure pulley l6, transmitting torque to the film strip from the shaft of a second reversible motor 5 to which it is connected. The motors 4i and 5 are normally driven in opposite directions to each other.

A primary control system, of wellknown and conventional nature requiring it to be neither described in detail in this disclosure nor indicated in the drawings produces starting signals which are applied to a motor control system to cause the forward or reverse advancement of the film strip. The primary control system can be, e.g., the logic circuit center of a teaching machine or a keyboard control system permitting the control of a film projector, etc.

A first forward-movement stopping photoelectric sensor 9 and a first backward-movement stopping photoelectric sensor it) are located to either side of and near the film gate. Alternatingly, a second forward-movement stopping photoelectric sensor Ill and a second backward-movement stopping photoelectric sensor 12, is located to either side of and near display screen. The photoelectric sensors are arranged to sense and produce a signal indicative of prearranged and located indicia or synchronizing marks on the film strip and to produce a resultant electric signal.

The synchronizing marks (or triggering codes) can be transparent code fields formed by nontransparent longitudinal stripe marked on the film strip (see FIG. 2a), nontransparent transverse stripes located between the frames together with a transparent longitudinal stripe (indicated by dashed lines) (see FIG. 2b), or transparent transverse stripes between the frames together with a nontransparent longitudinal stripe (indicated by dashed lines on a negative film in FIG. 20).

A motor control device 6 is provided to switch the rotational direction of the two reversible motors Al and 5, in a controlled manner so that selected forward and backward movement can be obtained by the opposite drive of the motors. To prevent the forming of a loop on the film strip, the pulling motor (to which a higher voltage is applied) is controlled to produce a higher torque than the pushing motor. Since the motors are driven in opposite directions, by simultaneously switching their direction of rotation, the function of the two reversible motors is exchanged and the direction of film movement is reversed. When the advancement of the film strip is to be stopped, the motor control device 6 provides a first stage in which the effect of the inertia of the rotors of the reversible motors is decreased by simultaneously connecting the two electric motors to a reverse voltage, at the moment of an incoming stopping signal. During this procedure the pushing motor is more intensively braked than the pulling motor and prevented from loosening or winding the film. The braking efficiency is further increased, in a second stage, by shorting the terminals of the two motors, at the end of the application of reverse voltage, so that a braking effect similar to that of a shorted dynamo is utilized.

The motor control device 6, whose block diagram is shown in H0. 3, includes a forward-movement bistable circuit l7 and a backward-movement bistable circuit 118. These bistable or flip-flop circuits are triggered from their quiescent stable state, by the starting signal described earlier which is, applied through a forward-movement start signalling path 22 or a backward-movement start signalling path 23. When triggered the circuits switch to an operating stable state a signal l appears on their first outputs connected to the forward-movement action signalling path 216 and the backward-movement signalling path 2?, respectively. The bistable circuits l7 and i8 can be triggered to return to their quiescent stable state by the application of a stopping signal applied through the forwardmovement stop signalling path 24 or the backwardmovement stop signalling path 25 connected to the

photoelectric sensors

9 and 10, respectively (or 11 and 12, respectively). The motor control device 6 further includes a forward movement monostable timing circuit 19 and the backwardmovement monostable timing circuit 20 which are each operable for a predetermined period t. The

timing circuits

19 and 20 are triggered instantaneously with the return of the forwardfmovement bistable circuit 17 or the backward-movement bistable circuit 18 to their quiescent stable state by a signal appearing on the second outputs of each of the

bistable circuits

17 and 18 respectively. The

reversing motors

4 and 5 can be thus switched to carry out their working functions as required, by means of a switching device 21 deriving signals from either the bistable circuits l7 and 18, or the timing circuits l9 and 20.

The forward-movement of the film strip is effected by the starting signal applied through path 22 which triggers the bistable circuit 17. A signal l appears on the first output of this bistable circuit which is further applied through path 26 to the switching device 21 which operates to connect the first reversing motor 4, which in this case will be the pulling motor to a power supply at full voltage. The switching device operates simultaneously to connect the other reversing motor 5, which in this case becomes the pushing motor, to the power supply at a reduced voltage of the same polarity. With the switching device 21 three different potential levels of a DC power supply are utilized, i.e., positive voltage, zero voltage, and negative voltage. For the forward rotation the reversing motors can be connected, e.g., to the positive terminal and the neutral terminal of the DC power supply (and for reverse rotation, to the negative terminal and neutral terminal, as seen in FIG. 4).

The forward-movement of the film strip is stopped as soon as the first photoelectric sensor 9 or the alternate photoelectric sensor 11 senses the predetermined synchronizing mark. A signal is produced which is applied through path 24 to trigger the bistable circuit 17 to return to the quiescent stable state. As a result, a signal is applied through path 26 to the switching device 21 causing it, as a first stage, to disconnect the two reversing

motors

4 and 5 from the positive voltage of the power supply. Simultaneously a signal appears on the second output of the bistable circuit 17, which is a logic negation of the first output of the bistable circuit 17, and causes the forward-movement monostable timing circuit 19 to trigger for the predetermined period 1.

During this period t the two reversing

motors

4 and 5 are connected to the reverse voltage of the power supply due to the signal applied through path 28, from a connection with the positive

terminal reversing motors

4 and 5 are shifted to the negative voltage of the power supply in such a manner that the second reversing motor 5 is connected to the full negative voltage while the first reversing motor 4 is connected to the reduced negative voltage. The pushing motor is always braked more intensively than the pulling motor preventing crimpage of the film strip and keeping it always taut. After the elapse of the period t, i.e., during the second stage of the braking period, the timing circuits return to stable condition and the switching device 21 shorts the terminals of the two reversing

motors

4 and 5 thus utilizing the braking effect of a short-circuited dynamo.

The backward movement of the film strip is caused by the reverse operation of the motors and of the control system. it is The first reversing motor 4, which in this case becomes the pushing motor, is simultaneously connected to the reduced voltage of the same polarity as the second reversing motor 5.

The backward-movement of the film strip is stopped as soon as the first photoelectric sensor 10 or the alternate photoelec tric sensor 12 senses the predetermined synchronizing mark and produces a stopping signal applied through path 25 to the bistable circuit 18. The circuit 18 produces a signal applied through the path 27 which operates the switching device 21, causing it to disconnect the two reversing

motors

4 and 5 from the negative voltage of the power supply. Simultaneously a signal appears on the second output of the bistable circuit 18 triggering the monostable timing circuit 20 for a predetermined period t. As a result, a signal passes along path 29 to the switching device 21, causing it to connect reversing

motors

4 and 5 to the reverse voltage for a period t, i.e., in this case to the positive voltage of the power supply. Here the first reversing motor 4 is connected to the full positive voltage while the second reversing motor 5 is connected to the reduced positive voltage of the power supply. Subsequently, in the course of the second stage of the braking operation, the switching device 21 shorts the terminals of the two reversing

motors

4 and 5.

The switching device 21, whose block diagram is shown in FIG. 4, consists of a forward and backward control system. The forward system comprises an input decoder 30, a forward-movement control switch 33, a forward-movement auxiliary switch 34, a forward-movement brake switch 35, a forward-movement main switch 36, and a forward-movement brake main switch 37. The backward system comprises a backward-movement control switch 38, a backward-movement auxiliary switch 39, a backward-movement brake switch 40, a backward-movement main switch 41, and a backwardmovement brake main switch 42. A Gratz rectifier 43, and a series resistor 44 for the pushing motor are employed jointly. In the switching device 21 three different potential levels of the DC power supply are utilized as follows: The maximum potential level is formed by the positive voltage, (+U terminal) the medium potential level is formed by the neutral voltage (zero terminal) and the minimum potential level is formed by the negative voltage of the DC power supply (U terminal).

All the elements of the switching device 21 are provided with control inputs by which a predetermined signal causes the selective and synchronous operation of their output, i.e., the first output to be switched on is selectively connected to the second or the third output which may then be closed. These switches are designed so that they are closed when their control inputs are connected to the positive, zero or negative voltage as follows: The forward-movement control switch 33, the forward-movement auxiliary switch 34 and the backwardmovement control switch 38 are closed when their control inputs are connected to the positive voltage. The forward-movement main switch 36 and the backward-movement main switch 41 are closed when their control inputs are connected to the zero voltage. The backward-movement auxiliary switch 39, and the backward-movement brake main switch 42 are closed when their control inputs are connected to the negative voltage of the power supply.

The outputs of the forward-movement brake switch 35 are closed during the quiescent condition but as soon as its control input is connected to the positive voltage, its outputs are immediately opened. Similarly the outputs of the backwardmovement brake switch 41) are closed during the quiescent condition but as soon as its control input is connected to the negative voltage, its outputs are immediately opened.

The input decoder 30 carries out a logic function as follows:

al zo+ z9)' :1'{ zs s-z z1+ zs)' ze' z9 Where Y is the forward-movement output of the input decoder 30,

Y is the backward-movement output of the input decoder X is the signal applied through the forward-movement action signalling path 26,

X is the signal applied through the backward-movement action signalling path 27 X is the signal applied through the forward-movement brake signalling path 28,

X is the signal applied through the backward-movement brake signalling path 29.

The formulae mentioned above can be explained as follows:

The forward movement output 31 of the input decoder is placed into operation as soon as a signal 1 is applied through the forwardmovement action signalling path 26 or the backwardmovement brake signalling path 29. At the same time no signal I is applied through the backwardmovement action signalling path 27 and the forward-movement brake-signalling path 28. Similarly the backward-movement output 32 of the input decoder 30 is placed into operation as soon as the signal l is applied through the backwardmovement action signalling path 27 or the forward-movement brake signalling path 28 while no signal l is applied through the forward-movement action signalling path as or the backward-movement brake signalling path 29.

A signal in the forward-movement output 31 causes the closing of the forward-movement control switch 33 which in turn causes the forward-movement auxiliary switch 34 to close which again in turn causes the closing of the forwardmovement main switch 36. The first reversing motor l is consequently connected to the full positive voltage (+U terminal) of the power supply through the forward-movement main switch 36 while the second reversing motor 5 is connected through the pushing motor series resistor id and also to the power supply but at a reduced positive voltage developed by the drop across the series resistor 44. Simultaneously the forward-movement brake switch 35, which was closed during the quiescent condition, is opened and in turn causes the forward movement brake main switch 37 to be opened.

A signal in the backward-movement output 32 causes the closing of the backward-movement control switch 38 which in turn causes the backward-movement auxiliary switch 39 to be closed resulting in the closing of the backward-movement main switch ll. The second reversing motor 5 is consequently connected to the full negative voltage of the power supply through the backward-movement main switch 4i while the first reversing motor 4 is connected through the pushing motor series resistor Ml and the backward-movement main switch 411 to the negative terminal of the power supply (U) but at a voltage reduced by the drop across the series resistor 44. Simultaneously the backward-movement brake switch 44), which was closed during the quiescent condition, is opened and in turn causes the backward-movement brake rnain switch 42 to be opened.

The braking of the forward-movement of the film strip is effected as soon as a signal is removed from the forward-movement output 311 of the input decoder 3i). This causes the forward-movement control switch 33, the forward-movement auxiliary switch 34 and the forward-movement main switch as to be successively opened. Simultaneously the backwardmovement output 32 of the input decoder 3% is put into operation for the predetermined period t which results in connecting each of the reversing motors 4i and 5 to the negative voltage terminal, as during the backward-movement of the film strip. After the elapse of the period I all the switches are returned to the quiescent state. The forward-movement brake switch and the backward-movement brake switch d ll are thus closed which results in the closing of the forward-movement brake main switch 37 and the backward-movement brake main switch 42. The two reversing motors 4i and 5, under the effect of inertia continue to run in the forward direction, even afiter power has been removed and operate as dynamos generating positive voltage which is then applied both to the forward-movement nodal point id and the backwardmovement nodal point do. The positive voltage is thereafter further applied through the Grate rectifier d3 to the forward-movement brake main switch 37 which then becomes short-circuited.

The braking of the backward movement of the film strip is carried out in a similar way as the braking of the forward movement. As soon as the signal is removed from the backward-movement output 32 of the input decoder 30, the backwardmovement control switch 33, the backwardmovement auxiliary switch 39 and the backwardmovement main switch llll are successively opened and the forward-movement output 31 is simultaneously placed into operation for a predetermined period t resulting in the connection of the two reversing motors d and 5 positive voltage terminal (+U After the elapse of the period 1, these switches are opened and the forward-movement brake breaker 35 and the backwardmovement brake breaker 40 are closed resulting in the closing forward-movement brake main switch. 37 and the backwardmovement brake main switch 4L2. The two reversing motors 4i and 5, again due to inertia continue to run out in the reverse direction, operating as dynamos to generate negative voltage which is applied both to the forward-movement node 4-5 and the backward-movement node 46. The negative voltage being applied through the Gratz rectifier 43 to the bacltward movement brake main switch 42 which is then also short circuited.

Semiconductor diodes and transistors are used throughout in the switching circuits of the switch device 211 as is apparent from the circuit diagram shown in H6. 5. The input decoder 36 consists of transistors Tl and T2, diodes D1, D2, D3, D4, D3, Dill, Dlll and DH, and their relevant circuits. The forward-movement control switch 33 is formed by the circuit of the transistor T3. The forward-movement auxiliary switch 34 is formed by the circuit of the transistor T4, the forwardmovement brake switch 35 is formed by the circuit of the transistor T6, the forward-movement main switch as is formed by the circuit of the transistor Tll, the forward-movement brake main switch 37 is formed by the circuit of the transistor Tll2, the backwardmovement control switch 38 is formed by the circuit of the transistor T5, the backwardmovement auxiliary switch 39 is formed by the circuit of the transistor T8, the backward-movement brake switch dll is formed by the circuit of the transistor T7, the backwardmovement main switch 431'. is formed by the circuit of the transistor TM, and the backward-movement brake main switch 472 is formed by the circuit of the transistor Till. The Gratz rectifier 43 includes the diodes D5, D6, D7 and Dtl. The pushing motor series resistance M is formed by the resistor R31.

The operation of the switching device 21 is as follows:

When a signal (e.g., a positive pulse) obtained from the forward-movernent bistable circuit l7 employing NlN transistors, is applied through the forward-movement action signalling path 26, the transistor "fl is turned on and the voltage applied to its collector drops almost to zero. if simultaneously a zero voltage is applied to the input of the backward movement action signalling path 27, the transistor T3 is turned off and substantially the full. positive voltage of the power supply is applied to its collector. This causes the transistor T4 to be turned on, driving the base of transistor T9 which is of the PNlP type. As a result, current starts flowing through the diode D9, the transistor T9 and the node 45 to the first reversing motor d which is thus connected to the full positive voltage of the power supply. From the node electric current also flows through the resistor R3ll and the second node 36 to the second reversing motor 5 which is thus connected to the reduced positive voltage across the resistor R311 producing a smaller torque in the reversing motor 5.

The backward or reverse movement of the reels is started as soon as a signal, e.g., of positive polarity, is received from the bistable circuit R8. The signal is applied through path 27 to turn on transistor T2 whose voltage at its collector drops almost to zero. W hen a zero voltage is applied simultaneously to the input of path 261, the transistor T5 is turned ofi which results in the applying of negative voltage to the emitter of the transistor T5. The base of the transistor T8 is driven through the resistor R19 which causes the transistor T8 to be turned on permitting passage of electric current from the zero conductor through the resistor R27 to the base of the transistor T10. From the zero conductor of the power supply electric current flows through the reversing motor and the node 46, Le, in the reverse direction than in the forward driving of the reels, and further through the transistor T10, the diode D to the negative terminal (-U) of the power supply so that thus the reversing motor 5 is connected to the full negative voltage of the power supply. Simultaneously from the zero conductor current flows through the reversing motor 4, the node 15, the resistor R31, the backward movement node 46, the conducting transistor T10 and the diode D10 to the negative terminal of the power supply to thus feed the first reversing motor 4 with a negative voltage reduced by the voltage drop developed across the resistor R31 to produce a lower torque. As soon as the signal is removed from path 27, the transistor T2 is turned off and the transistor T5 is turned on. The voltage divider, consisting of the resistors R10 and R19, is adjusted so that with the transistor T5 conducting its emitter is of positive voltage which causes the transistor T8 and simultaneously the transistor T10 to be turned off. This results in the stopping of the two reversing

motors

4 and 5 to be fed from the power supply.

The operation of the switching device 21 during braking is as follows:

During the forward movement of the film strip, for example, the transistor T9 is turned on and the two reversing

motors

4 and 5 are connected to the positive voltage of the power supply. On triggering the forward-movement bistable circuit 17 to the quiescent stable state, the voltage applied to the in puts of the switching device 21 drops to zero due to which the transistor T1 and as a result, also the transistor T9 are turned off which causes the two reversing

motors

4 and 5 to be disconnected from the positive voltage of the power supply. When the second output of the forward-movement bistable circuit 17 becomes positive, the forward-movement monostable circuit 19 is triggered for a period t during which a positive pulse is applied to the input of the switching device 21 causing the diode D12 and the transistor T2 to be turned on. As a result, the transistor T10 is turned on and the two reversing

motors

4 and 5 are connected to the reverse voltage, i.e., the pulling motor 5 is connected direct while the pushing motor 4 is connected through the series resistor R31 to the power supply. As soon as the forward-movement monostable circuit 19 is triggered to the quiescent stable state, zero voltage is applied to all the inputs of the switching circuits, the transistors T9 and T10 are turned off, and the two reversing

motors

4 and 5 are disconnected from the power supply. When no voltage is applied to the inputs of the switching device 21, the transistor T1 is turned off and the transistor T5 is turned on. As a result, the transistor T6 is also turned off and through the resistors R11 and R24 the base of the transistor T12 is driven, causing the transistor T12 to be turned on. The two reversing

motors

4 and 5 which run out, due to inertia operate as dynamos so that positive voltage appearing across the forward-movement nodal point 45 and the backward-movement nodal point 46 is short-circuited through the diodes D5 and D6 by the transistor T12. The shorting transistor T12 is turned off as soon as the transistor T9 connects the two reversing motors 4 and S to positive voltage of the power supply because during this operation the transistor T3 is turned off which results in the transistor T6 to be turned on and the transistor T12 to be turned off.

During the reverse movement the braking is effected in a similar way as follows:

On triggering the backward-movement bistable circuit 18 to the quiescent stable state, the backward-movement monostable circuit 20 is triggered and the signal, then applied through the backward-movement brake-signalling path 29, causes the transistor T1 to be turned on. By means of the transistor T9 the reversing

motors

4 and 5 are connected to reverse voltage for a period 1. During the final braking stage the two reversing

motors

4 and 5 are short-circuited by means of the transistor T11 which is controlled by the transistor T7.

During the final braking stage the bases of the shorting transistors T11 and T12 are driven and these transistors are thus prepared to short the voltage applied to their collectors. Even if the reverse voltage, creating the braking effect, causes the reverse rotation of the two reversing

motors

4 and 5 and produces reverse voltage appearing on the nodal point 45 and the nodal point 46, the reverse voltage will nevertheless be shorted by either the transistor T11 or the transistor T12.

The Zcner diodes Z1, Z2, Z3 and Z4 protect the switching transistors T9 and T10 against peak voltage occurring when switching off the reversing

motors

4 and 5.

The diode D9, driven through the resistor R32, and the diode D10, driven through the resistor R33 shifts the voltage applied to the emitters of the transistors T9 and T10 so that turning off of these transistors is ensured during the quiescent condition.

The transistors T1 and T2 together with the diodes D1, D2, D3 and D4 ensure that no short circuit occurs if simu|taneously a forward-movement signal and a backward-movement signal are set up. In this case both forward and backward movement signalling paths are switched off and neither the transistor T9 nor the transistor T10 can be turned on.

The film feeding equipment according to the present invention permits the advancement of the film strip in either direction by any number of film frames. The film strip is in constant contact with the two reversing motors by means of the friction gearing. The identification of the position of the film strip is effected optically by sensing the synchronizing marks on the film strip. The braking effect of the reversing motors can be utilized when braking the advancing film strip.

The filmfeeding equipment according to the present invention ensures high-speed feeding of the film frames, considerable stopping accuracy of the film strip, absolute independence from the film perforation, and reliable operation in spite of simple mechanical structure and design.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

We claim:

1. Apparatus for feeding a film strip having a plurality of frames through a gate, said film strip having optical indicia thereon indicative of the location of predetermined frames, comprising a pair of reversible motors respectively located to either side of said gate, frictional drive means associated with each of said motors and engaging the surface of said film strip, and control means for activating said motors to move the film in a predetermined forward or backward direction, said control means being responsive to one of a pair of power signals derived from a primary control system, and a selected one of a pair of stop signals derived from photoelectric sensing means responsive to the optical indicia on said film to provide a signal to stop the movement of said film at a predetermined frame, said control means comprising a switching device having an output connected to each of said respective reversible motors, a pair of inputs connected to said primary control system, and means responsive to the signals of said primary control system for selectively supplying unidirectional current to said motors including means for providing to the motor in the direction of movement of said film a voltage greater than that provided to the other motor.

2. The apparatus according to claim 1, wherein said photoelectric sensing means comprises a pair of sensors respectively operable in response to the forward and backward movement of said film strip, to provide a respective signal effecting the corresponding movement of said motors.

3. The apparatus according to claim 2, wherein said sensors are located on either side of said gate.

4. The apparatus according to claim 2, wherein said sensors are located on the usual display means for projection of the 5. The apparatus according to claim 2, wherein said switching device includes a pair of input means from said respective photoelectric sensors, and means for reversing the direction and voltage level of said current to said motors on receipt of a selected signal from said sensors to thereby brake said motors.

6. The apparatus according to claim 5, including a timing switch, for deactivating the signal derived from said photoelectric sensor at the end of a predetermined interval.

'7. The apparatus according to claim 6, wherein said motors are permitted to freely run after the predetermined interval, and the switch device includes means for shorting said motors to thereby provide a dynomatic braking.

8. The apparatus according to claim 11, wherein the control means comprises a first and second bistable control circuit, each having a pair of inputs and a pair of outputs, a first and second monostable timing circuit having an input and an out put and a switching device having a pair of outputs and four inputs,

The inputs of said switching device being connected respectively to the reversible motors,

the first input of said switching device being connected to the first output of the first bistable control circuit, the second input of said switching device being connected to the first output of the second bistable control device,

the third input of said switching device being connected to the output of the first monostable timing circuit, the input of said first monostable timing circuit being connected to the second output of the first bistable control circuit,

the fourth input of said switching device being connected to the output of the second monostable timing circuit, the input of said second monostable timing circuit being connected to the second output of said second bistable con trol circuit,

one input of each of said bistable control circuits being connected to the primary control system to respectively receive one of the power signals, the second input of each of said bistable control circuits being connected respec tively to one of said photoelectric sensors to receive the signal therefrom, whereby said signals may be applied to lltl selectively operate said reversible motors and to control the braking thereof.

9. The apparatus according to claim 8, wherein said switching device includes positive, negative and neutral power terminals, an input decoder incorporating said four switching device inputs and having a first and second output, a pair of control switches, a pair of auxiliary control switches, a pair of braking switches, a pair of main switches and a pair of main braking switches, each of said control switches having an input and three outputs, each of the auxiliary, braking, main, and main braking switches having a single input and two outputs, the output in each of said switches being selectively operable to pass a signal therethrough alternatively with at least one of the other outputs, one of each of said switches being arranged in sequential order associated with one of said decoder outputs, said control switches having their respective inputs connected to one of said decoder outputs, one of the three outputs to the positive or negative power terminal, the second of their outputs to the input of the associated auxiliary control switch and the third of the outputs to input of the associated brake switch,

the auxiliary control switches having one of their outputs commonly joined to the neutral power terminal and the other of the outputs respectively connected to said main switch,

the braking control switch having one output connected to the respective positive and negative power terminal and the other of the outputs to the input of the main braking switch,

the main switches having one output connected to the respective positive and negative power terminals and the other output to the first input of each of the respective reversible motors, the main braking switch having one output connected in common to the neutral power terminal and the other output respectively to the terminal of a Gratz rectifier circuit bridging the outputs of said main switches and the first of the inputs of said reversible motors,

the second inputs of said reversible motors being connected to the neutral terminal.

Claims

4. The apparatus according to claim 2, wherein said sensors are located on the usual display means for projection of the film.

5. The apparatus according to claim 2, wherein said switching device includes a pair of input means from said respective photoelectric sensors, and means for reversing the direction and voltage level of said currEnt to said motors on receipt of a selected signal from said sensors to thereby brake said motors.

7. The apparatus according to claim 6, wherein said motors are permitted to freely run after the predetermined interval, and the switch device includes means for shorting said motors to thereby provide a dynomatic braking.

8. The apparatus according to claim 1, wherein the control means comprises a first and second bistable control circuit, each having a pair of inputs and a pair of outputs, a first and second monostable timing circuit having an input and an output and a switching device having a pair of outputs and four inputs, The inputs of said switching device being connected respectively to the reversible motors, the first input of said switching device being connected to the first output of the first bistable control circuit, the second input of said switching device being connected to the first output of the second bistable control device, the third input of said switching device being connected to the output of the first monostable timing circuit, the input of said first monostable timing circuit being connected to the second output of the first bistable control circuit, the fourth input of said switching device being connected to the output of the second monostable timing circuit, the input of said second monostable timing circuit being connected to the second output of said second bistable control circuit, one input of each of said bistable control circuits being connected to the primary control system to respectively receive one of the power signals, the second input of each of said bistable control circuits being connected respectively to one of said photoelectric sensors to receive the signal therefrom, whereby said signals may be applied to selectively operate said reversible motors and to control the braking thereof.

9. The apparatus according to claim 8, wherein said switching device includes positive, negative and neutral power terminals, an input decoder incorporating said four switching device inputs and having a first and second output, a pair of control switches, a pair of auxiliary control switches, a pair of braking switches, a pair of main switches and a pair of main braking switches, each of said control switches having an input and three outputs, each of the auxiliary, braking, main, and main braking switches having a single input and two outputs, the output in each of said switches being selectively operable to pass a signal therethrough alternatively with at least one of the other outputs, one of each of said switches being arranged in sequential order associated with one of said decoder outputs, said control switches having their respective inputs connected to one of said decoder outputs, one of the three outputs to the positive or negative power terminal, the second of their outputs to the input of the associated auxiliary control switch and the third of the outputs to input of the associated brake switch, the auxiliary control switches having one of their outputs commonly joined to the neutral power terminal and the other of the outputs respectively connected to said main switch, the braking control switch having one output connected to the respective positive and negative power terminal and the other of the outputs to the input of the main braking switch, the main switches having one output connected to the respective positive and negative power terminals and the other output to the first input of each of the respective reversible motors, the main braking switch having one output connected in common to the neutral power terminal and the other output respectively to the terminal of a Gratz rectifier circuit bridging the outputs of said main switches and the first of the inputs of said reversible motors, the Second inputs of said reversible motors being connected to the neutral terminal.