GB2190518A - Telecine synchronization - Google Patents

Abstract

To reduce synchronization errors caused by travel fluctuations of a motion picture film (1) moved continuously through a picture scanning station (6) by a capstan (7) via a sprocket (4), both when the film (1) is stationary and when it is moving a constant film pull acting counter to the film travel direction is applied by a motor (13) to the sprocket (4), and during film movement an additional, variable film pull acting in opposition to travel fluctuations is applied by the motor (13) to the sprocket (4). The variable film pull is varied according to a frequency or phase comparison of the output of a tacho disc (16) on the shaft of motor (13) with the output of a tacho disc (12) on the shaft of a motor (11) driving the capstan (7). <IMAGE>

Description

SPECIFICATION method for reducing synchronization errors in a motion picture film This invention concerns a method for reducing synchronization errors in a motion picture film moved continuously through a picture scanning station.

As a result oftransport movementfluctuations and also splices in the film, during the television scanning of motion picture films synchronization errorscanoccurand become disturbingly noticeable, e.g. through a slowvertical drift orjump ofthe picture. To avoid these problems the transport speed of the film in the vicinity of the picture scanning station should be constant and any superimposed speed fluctuations (synchronization errors) very small. These synchronization errors are mainly caused by dynamic changes to the film pull duetotheelasticityofthefilm material. Film pull fluctuations are e.g. produced by errors orfaults in the rotary components of the transport mechanism and non-periodic irregularities in the drive and in the film.

Thus, it is conventional in the case of sound picture projectors to arrange mechanical filters in the film travel path for eliminating disturbing synchronization errors by adequately reducing the amplitudes ofthese interfering frequencies not adequately suppressed by the capstan. However, these filter elements, e.g. in the form of flywheels, are extremely large and heavy.

The problem of the invention is therefore to provide a method of the aforementioned type, in orderto achieve a stable vertical picture position and also permit a rapid change in operating modes (start, stop, rewind).

Accordingly, the invention provides a method for reducing synchronization errors caused by film pull fluctuations of a motion picture film moved continuously through a picture scanning station by a uniformly rotating capstan located downstream of the picture scanning station and engaging a sprocket located upstream of the station, wherein both when the film is stationary and when it is moving a constantfilm pull moment acting countertothefilm travel direction is coupled to the sprocket, and wherein during film movement an additional, variable film pull moment acting in opposition to film speed fluctuations is coupled to the sprocket.

The invention has the advantage that during different operating modes synchronization errors are substantially reduced or eliminated at the picture scanning station.

It is particularly advantageousthat no heavy mechanical filters are required, which lead to a disturbing inertia of the system in the case of desired filmtransportspeed changes.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein: Figure lisa schematic view of an apparatus for performing the inventive method and showing the film travel path; Figure2 is a block circuit diagram of a firstvariant of the regulating circuit of Figure 1; and Figure 3 is a block circuit diagram of a second variant of the regulating circuit.

In the apparatus shown in Figure 1,a motion picture film 1 is fed from a feed spool 2 over a plurality of guide pulleys 3 to a sprocket 4 and from there past a scanning station 6, in which television scanning of the film takes place, to a film-driving capstan 7 and subsequently via further guide pulleys 8to atake-up spool 9.

The capstan 7 is uniformly driven by a motor 11 which is supplied across terminal 10, with a current produced by a speed control circuit (not shown). A pulse-generating tacho-disk 12 is mounted on the shaft of the motor 11. The sprocket 4 is mounted on the shaft of an electric motor 13 acting as an electronically controllable brake. The motor 13 is supplied with a continuous constant current 1const across terminal 14, and also with a variable regulating current IR. When the film is moving. The current IR is formed in a regulating circuit 17 asa function of the pulses derived both from tacho-disk 12 and from a tacho-disk 16 coupled to the sprocket 4.

The constant current supplied across terminal 14 produces a torque in motor 13 whIch, transmitted to sprocket 4, produces a constantfilm pull moment (-MConst) acting counter to the film travel direction.

This leads to form locking ofthe flanks oftheteeth of sprocket 4with the edges of the film sprocket holes remote from the scanning station 6. The regulating circuit 17 also influences thetorque ofthe motor 13 in such a way that during film transport a variable film pull moment (-MfUt) acting against film pull (and hence speed) fluctuations (KflUct) is also produced at sprocket 4. The film pull (KConst) acting counter to the constant film pull moment ( Mconst) must consequently be greater than the change for eliminating film pull fluctuations (Kfluct), so thatthe form locking between the tooth flanks and the edges of the sprocket holes is always maintained (Mconst > Mfluct or Kconst > Kfluct).

Figure 2 shows a blockcircuitdiagramofafirst variant of the regulating circuit 17 comprising a frequency comparison circuit 21, a film size divider 22 and a PID network 23. All that is shown ofthefilm travel mechanism are those parts necessaryforthe explanation of the invention, namelythe sprocket 4, the tacho-disk 16 and the motor 13'. In the frequency comparison circuit 21 a comparison takes place between pulses taken from the tacho-disk 16 and pulses taken from the capstan tacho-disk 12 which are passed across the size divider 22 and are supplied thereto at a terminal 24. The film size divider22controlsthecapstan pulses in accordance with the film size to be scanned (e.g. 16 or35mm), which is indicated by a microprocessor 26.The PID network 23 connected to the outputofthefrequency comparison circuit 21 supplies a current IRwhich varies in accordance with the interfering frequencies and such current is supplied across a switch 27 to a summing circuit 28. The constant current 1const is applied across the terminal 1 4to the other input of the summing circuit 28. The output current ofthe summing circuit28consequently influences the torqueofthe motor 13' so that a reduction in synchronization errors orfluctuations can be achieved. Switch 27 is only closed when the capstan 7 has reached its rated speed.

In the second variant ofthe regulating circuit 17 shown in Figure 3, the already described components are given the same references. A phase comparison takes place in a circuit 31 of the pulses derived from thetacho-disk 16 and thecapstan pulses supplied to the terminal 24. Here again the capstan pulses are influenced (modified) in accordance with the film size as indicated by microprocessor 26. The output signal of the phase comparison circuit 31 is then supplied across a filter 32 to an amplifier 33.Filter 32 has an amplitude characteristic which rises to the frequency fro where the maximum interfering power occurs and then drops above the said frequencyfO. The amplified regulating current IR from the output of the amplifier 33 is supplied across the switch 27 to one input ofthe summing circuit 28 and at whose other input (terminal 14) there is the constant current 1coast From the output of the summing circuit 28 it is once again in synchronization errors and which is supplied to the motor 13'.

CLAI MS 1. A method for reducing synchronization errors caused byfilm pull fluctuations of a motion picture film moved continuouslythrough a picture scanning station by a uniformly rotating capstan located downstream ofthe picture scanning station and engaging a sprocket located upstream ofthestation, wherein both when the film is stationary and when it is moving a constant film pull moment acting counterto the film travel direction is coupled to the sprocket, and wherein during film movement an additional, variable film pull moment acting in opposition to film speed fluctuations is coupled to the sprocket.

2. A method according to Claim 1, wherein the sprocket is arranged on the shaft of an electronically controllable brake and wherein the brake is supplied continuously with a constant current producing the constantfilm pull moment, and during film movement with an additional currentwhich varies as a function offilm speed fluctuations.

3. A method according to Claim 2, wherein the electronically controllable brake is an electric motor.

4. A method according to Claim 2 or 3, wherein the additional current is only supplied after capstan has attained its desired speed.

5. A method according to Claim 2,3 or 4 wherein the additional current is varied by a frequency comparison between first pulses derived from a tacho-disk coupled to the sprocket and second pulses derived from a tacho-disk coupled to the capstan and corresponding to the film size.

6. A method according to Claim 2,3 or 4, wherein the additional current is varied buy a phase comparison between the first pulses derived from a tacho-disk coupled to the sprocket and second pulses derived from atacho-diskcoupledtothe capstan and corresponding to the film size.

7. A method according to Claim 5, wherein the additional current is suppled across a PID networkto the electronically controllable brake.

8. Amethod according to Claim 6, wherein the additional current is supplied across a filter to the electronically controllable brake.

9. A method according to Claim 8, wherein the filter has an amplitude characteristic which rises to the frequency at which the maximum interference occurs and then falls above the said frequency.

10. A method according to Claim 1, substantially as described with reference to Figures 1 and 2 orto Figures 1 and 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. summing circuit28consequently influences the torqueofthe motor 13' so that a reduction in synchronization errors orfluctuations can be achieved. Switch 27 is only closed when the capstan 7 has reached its rated speed. In the second variant ofthe regulating circuit 17 shown in Figure 3, the already described components are given the same references. A phase comparison takes place in a circuit 31 of the pulses derived from thetacho-disk 16 and thecapstan pulses supplied to the terminal 24. Here again the capstan pulses are influenced (modified) in accordance with the film size as indicated by microprocessor 26. The output signal of the phase comparison circuit 31 is then supplied across a filter 32 to an amplifier 33.Filter 32 has an amplitude characteristic which rises to the frequency fro where the maximum interfering power occurs and then drops above the said frequencyfO. The amplified regulating current IR from the output of the amplifier 33 is supplied across the switch 27 to one input ofthe summing circuit 28 and at whose other input (terminal 14) there is the constant current 1coast From the output of the summing circuit 28 it is once again in synchronization errors and which is supplied to the motor 13'. CLAI MS

1. A method for reducing synchronization errors caused byfilm pull fluctuations of a motion picture film moved continuouslythrough a picture scanning station by a uniformly rotating capstan located downstream ofthe picture scanning station and engaging a sprocket located upstream ofthestation, wherein both when the film is stationary and when it is moving a constant film pull moment acting counterto the film travel direction is coupled to the sprocket, and wherein during film movement an additional, variable film pull moment acting in opposition to film speed fluctuations is coupled to the sprocket.

2. A method according to Claim 1, wherein the sprocket is arranged on the shaft of an electronically controllable brake and wherein the brake is supplied continuously with a constant current producing the constantfilm pull moment, and during film movement with an additional currentwhich varies as a function offilm speed fluctuations.

3. A method according to Claim 2, wherein the electronically controllable brake is an electric motor.

4. A method according to Claim 2 or 3, wherein the additional current is only supplied after capstan has attained its desired speed.

5. A method according to Claim 2,3 or 4 wherein the additional current is varied by a frequency comparison between first pulses derived from a tacho-disk coupled to the sprocket and second pulses derived from a tacho-disk coupled to the capstan and corresponding to the film size.

6. A method according to Claim 2,3 or 4, wherein the additional current is varied buy a phase comparison between the first pulses derived from a tacho-disk coupled to the sprocket and second pulses derived from atacho-diskcoupledtothe capstan and corresponding to the film size.

7. A method according to Claim 5, wherein the additional current is suppled across a PID networkto the electronically controllable brake.

8. Amethod according to Claim 6, wherein the additional current is supplied across a filter to the electronically controllable brake.

9. A method according to Claim 8, wherein the filter has an amplitude characteristic which rises to the frequency at which the maximum interference occurs and then falls above the said frequency.

10. A method according to Claim 1, substantially as described with reference to Figures 1 and 2 orto Figures 1 and 3 of the accompanying drawings.