FR2487600A1 - APPARATUS FOR QUICKLY STOPPING THE ROTATION OF AN ELECTRIC MOTOR, IN PARTICULAR A CAPSTAN MOTOR OF A MAGNETIC BAND DEVICE - Google Patents

Abstract

THE APPARATUS FOR STOPPING AN ELECTRIC MOTOR 20 INCLUDES A CURRENT SOURCE 67 PROVIDING THE EXCITATION VOLTAGE AND MEANS 55-58 TO GENERATE AND APPLY A REVERSE VOLTAGE TO THE MOTOR AND TO STOP IT AFTER A DETERMINED TIME INTERVAL. DETECTION MEANS 65 DETERMINE THAT THE ENGINE IS STOPPED. IT IS THUS POSSIBLE TO USE THE MOTOR 20 TO DRIVE THE CAPSTAN OF A VIDEO RECORDER TO OPERATE VIEW BY VIEW.

Description

The present invention relates generally

  general to devices that allow you to quickly stop

  rotation of a motor and it concerns, more particularly-

  ment, such a device which is suitable when it is applied to a capstan motor in a device intermittently ensuring the movements and stops of a magnetic tape in order to ensure slow motion reproduction by reproducing a video signal recorded on the magnetic strip. Conventionally, the reproduction of the images in slow motion was carried out by a reduction in the speed of advance of the tape until a speed of advance slower than that of a normal reproduction. However, it was difficult to obtain an image reproduced by an arbitrary slow motion with low noise and at a

  arbitrary slow speed. The downside was the introduction-

  inevitable noise in the reproduced image.

  Consequently, to eliminate the above drawback

  above, an installation has been proposed enabling

  nir an image reproduced at low noise, in patent application FR 79 19813, filed August 1, 1979 in the name of the same Applicant. In this installation, the magnetic strip moves and is stopped intermittently and the stop positions of the rotary heads are adjusted so that the rotary head stops at a location on the magnetic strip where this head can explore a track on the magnetic tape in a state in which the

noise introduced is minimal.

  The proposed reproductive system includes a tape on which video signals are recorded on tracks

  video with an oblique orientation to the di-

  longitudinal rection of the strip, practically without space

  cement between them. A control signal is recorded

  on a control track extending in the longitudinal direction

  tudinal, the video tracks being recorded by several video rotating heads having intervals whose azimuth angles are mutually different. The signal from

  command is recorded on the command track in inter-

  relation to the recording of video tracks by video heads. A motor drives the belt in its path

  or stops the tape. Several rotating video heads re-

  producers successively trace the video tracks to capture and reproduce the recorded video signals. The video rotary heads have intervals of which the azimuth angles are mutually different, namely substantially the same azimuth angles as in the previously mentioned case, the vertical positions also being different above the plane of rotation of the

  runway centers in their width direction. The if-

  Control signals are reproduced from the control track of the moving tape. A circuit differs the control signal reproduced by a specific time in order to obtain a delayed signal and the latter stops the motor and then stops the progression of the strip. The tape is stopped in a position, with respect to the reproducing video heads in which the reproduction is carried out, so that the precise instant at which the level of the reproduced video signal becomes minimum is in the neutral period

  vertical or in the immediate vicinity of this period.

  In the installation proposed and described above,

  the rotation of the cab engine must be stopped quickly

  tan when the magnetic strip stops.

  The technique to quickly stop rotation

  an engine is essential in various industrial fields

  triels and is in no way limited to the application to a

  video signal reproduction system, as above.

  Conventionally, as a general method for stopping the rotation of an engine, there are known methods such as (1) a mechanical stopping method which uses a brake

  mechanical or similar mechanism and (2) an electrical process

  stick which obtains the stopping torque by a shortening

  motor terminal circuit, a process which applies reverse torque to the motor by applying reverse voltage, etc. However in the mechanical shutdown process

  above, we are obliged to use a brake mechanism

  which constitutes a separate device and there is a

  limit for reducing the size of the repro-

  conductor. Consequently, when such a braking mechanism is used frequently, the reliability of the installation is deteriorated due to breaks in the mechanism.

  and phenomena of the same type. On the other hand, in the pro-

  electric shutdown mentioned, it is impossible to ob-

  maintain sufficient stopping torque by a technique of short-circuiting the motor terminals. Furthermore, it

  Another disadvantage is that the setting is different.

  difficult to execute in a process comprising the applica-

  reverse voltage to the motor.

  As a result, the proposed video signal reproducing apparatus just described is highly advantageous for obtaining a slow motion image in which the noise is very low. However, for intermittent starting and stopping of the magnetic strip, it is difficult to quickly stop the rotation of the motor.

  capstan. Thus the creation of a device capable of

  quickly turning the rotation of a motor is highly desirable when implementing the installation described

upper.

  The main object of the present invention is therefore to

  create a new and efficient device allowing

  stop the rotation of an engine and a type capable of stopping

  quickly turn the engine rotation.

  More particularly, the invention relates to an apparatus for stopping the rotation of a motor, constructed so as to stop the rotation of the motor by repeated operations in which an opposite voltage is applied to a motor in rotation in view to apply

  rotation in a direction opposite to that of rota-

  tion of the motor for a predetermined period of time and then the application of the reverse voltage is interrupted for a predetermined period of time and a counter-electromotive force voltage of the motor is detected within the period of time during which the reverse voltage East

  applied to the motor until the voltage counter

  electromotive motor detected becomes zero or becomes

  opposite polarity to the rotating motor.

  With the device which is the subject of the invention, the rotation of the motor can be stopped quickly. In addition, the motor is prevented from turning in the opposite direction since the information, for example of the type concerning the stopping of the rotation of the motor and the direction of rotation of the motor, is detected by detection.

  of the counter electromotive voltage of the motor. In use

  being a predetermined device such as a microcomputer

  and a motor excitation circuit, you can stop po-

  sitatively and in a highly reliable way the rotation of the

  motor and, in addition, the dimension of the ap-

  like himself. In particular, this is valid when the apparatus is applied to a capstan motor within a recording and / or reproducing apparatus which ensures slow motion reproduction by displacements and

  intermittent magnetic strip stops with preci-

  at the desired stop position. In addition, since the magnetic tape can be stopped quickly, it is possible to perform slow-motion reproduction by which the introduction of image instability, noise is avoided.

and similar phenomena.

  Various other features of the invention

  moreover emerge from the detailed description which follows.

  Embodiments of the subject of the invention are shown, by way of nonlimiting examples, in

attached drawing.

  Fig. 1 is a block diagram showing a reproduction in slow motion and a reproduction in stop of the video signals, within the framework of an embodiment of the apparatus for stopping the rotation of a motor according to the

present invention.

  Figs. 2 (A) to 2 (F) are diagrams respectively showing the waveforms of signals in various

  parts of the block diagram of fig. 1.

  Fig. 3 is a diagram showing the configuration

  tion of tracks when recording.

  Fig. 4 is a diagram showing the configuration of the exploration tracks during reproduction in

freeze frame.

  Fig. 5 is a diagram showing the level of the signal reproduced at the time of playback while stopped

on the image.

  Fig. 6 is a diagram allowing the description

  of the position where the tape must be stopped during reproduction while stopped on the image according to the concepts of the invention.

  Fig. 7 is a block diagram of the circuit

  trant an embodiment of a concrete circuit in an essential part of the engine rotation stopping device according to the invention

  Figs. 8 (A) to 8 (I) are diagrams showing res-

  pectively the waveforms of signals in various parts of the block diagram of FIG. 1 and all

of circuit in fig. 7.

  Referring first to FIG. 1, an emptied signal to be recorded is introduced into the installation through an input terminal 11 and passes through a recording and reproduction circuit 12 and this signal is then sent to two recording and reproduction video heads 13a and 13b and also to a vertical synchronization signal separation circuit 14. The heads emptied

  13a and 13b have opposite azimuths and piss widths

  you. different, as will be described later, and they are mounted on diametrically opposite sides of a rotary drum 16 driven in rotation by a motor 15

  at a speed of 30 revolutions per second. A magnetic strip

  tick 18 is wound obliquely around the rotary drum 16 and a fixed drum 17 and is driven in the direction of arrow X by a capstan 19 itself driven by a

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  motor 20 by means of a belt 21 and a flywheel 22, and by a pinch roller 23. A video signal is recorded by the heads 13a and 13b alternately along tracks of the strip 18, at the rate of a frame per track, the tracks being consequently contiguous

  between them and oblique to the long direction

gitudinal of the band.

  On the other hand, a vertical synchronization signal

  wedge a (fig. 2 (A) of 60 Hz, which has been separated from the signal

  video in the sync signal separation circuit

  verticalization 14, is supplied to a mono-multivibrator

  stable 24 o its frequency is halved and reduced to 30 Hz. The outgoing signal is sent to a monostable multivibrator 25 to adjust the phase of the signal and, at the same time, via a switch 26 whose mobile contact is connected to a contact point R in a recording mode, at a control head 27 by which the signal is recorded as a control signal

  on the lower edge of the strip 18.

  The outgoing signal resulting from the mono- multivibrator

  stable 25 is supplied via a switch

  tor 28 whose mobile contact is connected to a contact

  R, to a sampling and holding circuit 29.

  The rotary drum 16 mentioned above is mounted

  coaxially on a rotary shaft 31 driven by the mo-

  tor 15 and rotating integrally with the drum 16. Two magnets 33a and 33b of opposite polarity are mounted on a rotating disc 32 coaxially fixed to the rotary shaft

  31. Simultaneously with the rotation of the drum 16, im-

  pulses b of positive polarity and negative polarity,

  as shown in fig. 2 (B), are provided alternati-

  by a read head 34 and are applied to a flip-flop 35. The outgoing signal c of flip-flop 35, having the waveform indicated in FIG. 2 (C), is applied via a switch 36 whose movable contact is connected to a contact R, to a trapezoidal waveform circuit 37, and converted into a wave signal

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  trapezoidal, which is then supplied to the sample circuit

lonnage and maintenance 29.

  The embodiment described is designed in such a way that, when the outgoing signal c from flip-flop 35 is at its low level, the video head 13a explores the band and, when the outgoing signal c is at its high level,

  the other video head 13b explores the tape.

  In the sampling and holding circuit 29, the trapezoidal wave signal is sampled in its inclined part by the sampling pulse and a sloping part. So the sampled pulse is

  detention. The outgoing signal thus obtained from the exchange circuit

  filling and holding 29 is sent through an amplifier

  motor exciter 30 to motor 15 for

  thus controlling its rotation. The rotation phase of the mo-

  15 is controlled so that the sample position

  lonnage on the trapezoidal wave in circuit 29 becomes

  a determined position, for example the middle of the par-

  tilted tie of the trapezoidal wave signal.

  According to the control operation described above, the video heads 13a and 13b are rotated, their phase of rotation retaining a determined relationship with the phase of the vertical synchronization signal of the input video signal. To set this phase ratio, set the time constant of the monostable multivibrator

  using a variable resistor 38.

  On the other hand, as the capstan 19 rotates, a read head 39 detects the rotation of the capstan 19 in cooperation with magnets (not shown) mounted on the steering wheel 22. The signal thus detected is applied to a control device. 55, the output signal of which is transmitted to a motor 20 by means of a motor excitation circuit 58 in order to regulate the rotation of the motor 20. Consequently, the capstan 19 forces the magnetic strip 18 to progress at a constant speed of such

  so that the tape is moved a distance that cor-

  responds to a step of the track during the period during

  which the video heads 13e and 13b perform respectively

  half a full rotation.

  When reproducing at normal speed, the con-

  mobile tacts of switches 26, 28 and 36 are respected

  switched to their contact points P, the switch 41 and the switch circuit 43 being maintained

  in a position where their movable contacts are connected

  tees at contact points N. The control head 27 shows

  duit the control signal d with the indicated waveform

  in fig. 2 (D), this signal being sent1 through

  diary of the switch 26 and of an amplifier 44, to a

  monostable multivibrator 45 having a delay time tl.

  The outgoing signal thus obtained e from the mono- multivibrator

  stable 45 / having the waveform shown in fig. 2 (z),

  is supplied by switch 28 to the sample circuit-

  swimming and holding 29. On the other hand, the signal leaving the flip-flop 35 is reversed in phase by a phase inverter 46 and this signal is then brought by the switch 36 to the circuit 37 trapezoidal waveformer. From the trapezoidal waveformer circuit 37, a trapezoidal wave signal f is obtained as shown in fig. 2 F),

  having a polarity opposite to that of the traf- fic wave signal

  pezoidal at the time of registration. The trapezoidal wave signal f is supplied to the sampling and holding circuit 29 where it is subjected to sampling by the above-mentioned signal e delayed by a time tl. In response to

  output signal from the sampling and maintenance circuit

  tien 29, the rotation of the motor 15 is controlled.

  The video signal read or reproduced by heads 13a and 13b passes through the recording circuit 12 and exits

by a terminal 54.

  It goes without saying that when the trapezoidal wave signal is used as the signal to be sampled also at the time of reproduction, a signal having the same waveform as at the time of its recording, the operation of advancing the phase of rotation is subject to

some limitation.

  For this reason, the adaptation is such that at the time of reproduction, the part inclined towards the

  bottom of the trapezoidal wave signal f having undergone an invert-

  phase sion, is subject to sampling by the ascending part of the signal delayed by the time tl.

  Since the video head intervals 13.

  and 13b have mutually opposite azimuths, no signal is reproduced as a result of losses of azimuth in the case where the video heads 13b and 13a respectively explore the tracks recorded by the video heads 13a and 13l (i.e. say when doing what is called a reverse scan). Thus, during reproduction at normal speed, the rotation phase of the motor 15 is controlled so that the sampling signal e, which has been formed by the monostable multivibrator 45 in response to the pulses of positive polarity in each set of two frames coming from the control head 27, as indicated above, samples the middle part of the

  slope of the trapezoidal wave signal f formed during pulse

  sions of positive polarity from the com- puter head

  command 27. In such cases, the polarity pulses posi-

  tive from the control head 27 are adjusted so as to be formed in coincidence with the rotational position, for example, of the head 13a. For this reason, in such a normal mode of reproduction, the phases of rotation of the video heads 13a and 13b are adjusted so that these heads always explore (positive exploration) the tracks recorded respectively by the heads 13a and 13b, so that the reverse exploration mentioned

higher does not happen.

  As seen in fig. 3, video heads

  13a and 13b have respective intervals 60a and 60b do

  sant an angle in direction opposite to the perpendicular direction of the exploration, that is to say that the azimuths have an angle a. These video heads 13a and 13b have different track widths W1 and W2 and are arranged so that their respective end faces 61a and 61b are on the same face

  of the rotary drum 16. In the reset mode

  lization chosen, the width Wl is substantially understood

between 1.5 and 1.6 W2.

  As can be seen in fig. 3, the tracks tl, t2, t3, ... are in contiguous contact with intervals between them, so that the efficiency of use

  bandwidth is high. Each track receives the record-

  part of the video signal which corresponds sensi-

wholly to a frame.

  The angle between the video heads 13a and 13b and the magnets 33a and 33b as well as the time constant of the monostable multivibrator 25 for adjusting the phases are adjusted so that a vertical synchronization signal is placed near the track. A signal

  is recorded on the lower side edges

  laughing strip 18 following a control track 62

  in the longitudinal direction of the strip.

  We will now describe the operation relating to

  nant the freeze frame reproduction, with reference

for this in fig. 4.

  For freeze frame reproduction, the movement

  the magnetic tape 18 is stopped while the video heads 13a and 13b are rotated at a speed which is the same as during recording or

of normal reproduction.

  In fig. 4, when for example the head 13b begins its course from an overlapping position of the tracks t6 and t7, it follows the path indicated in lines

  full and ends its course in a riding position

  Track 5 and T6 tracks. Since the band 18

  is stopped, the head 13a, with its end face 61a followed

  vant the same path as the end face 61b of the head 13b1 also begins its path starting from a position in which it straddles the tracks t6, t7 and t8 and ends its path in an overlapping position of the tracks t5, t6 and t7. Then the above operation is repeated. 11 Heads 13b and 13a have a normal relation of course pespectively with tracks t6 and t7. For this reason, the level of the signal reproduced by the heads

  13b and 13a is that shown in fig. 5.

  It will be assumed that the relative travel positions of the heads 13a and 13b with respect to the strip are offset, for example, with a shift to the left from the positions indicated in this figure. In such a case, the level of reproduction L1 at the time when the head 13b begins to travel the track t6 increases, but the level of reproduction L2 at the time of the completion of the course decreases. In addition, the reproduction time of the maximum level L3 of the head 13a relative to the track t7 becomes short and the proportion of the course of the track t5 at the time of the completion of the course relative to the track t7 increases. For this reason, there is a beat interference in the area near the L4 level. On the other hand, when the relative positions of travel of the heads 13a and 13b are shifted to the right with respect to the positions shown in the figure, the reproduction level L1 decreases starting from the track t6 of the head 13b and the signal ratio / noise of this

  reproductive part is greatly deteriorated. Therefore

  quence, the most advantageous state of the path of the heads 13a and 13b compared to the tracks during reproduction in

  freeze frame is the one shown in fig. 4.

  When the control signal is recorded by the head 27, the recording of the tracks t2 (t4, t6, ...) by the head 13b begins. Therefore, if we stop

  arbitrarily the progression of the tape at a time

  reproduction freeze frame, while the magnetic tape 18 recorded in this way is set in motion and is reproduced, the stop position of

  the band 18 relative to the video heads is undefined.

  Thus if the progression of the tape is stopped immediately at the instant of the reproduction of the control signal, the head 13b assumes the state in which it

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  begins its journey starting from track t6, for example, while the head 13a takes the state in which it begins its journey from tracks t6 and t7,

  as shown in fig. 6. In this case, while the ni-

  calf reproduction of track t6 is maximum at the start of the course of the head 13b, it becomes almost zero at the end of the course and the noise becomes very large. In addition, the reproduced signal from tracks t7 and t5 gives rise to beats during a certain period after the start of the course of the head 13a, and the quality of the reproduced image is greatly deteriorated. On the contrary, the optimal positions of the paths relative to the tracks for the reproduction in freeze frame, as seen in FIG. 4, are the positions o the end faces 61a and 61b of the heads 13a and 13b

  cover the path indicated in fig. 6 in phantom.

  Consequently, according to the invention the magnetic strip 18

  must travel a distance Il and stops after the

  detection of the control signal; band progression

  is stopped when the heads 13a and 13b are in the posi-

  allow to move according to the optimal state that we see in fig. 4, i.e. with a minimum of

  beat noise or interference.

  We will now describe the reproduction operation.

  idling by applying the optimal concepts of a

freeze frame reproduction.

  When carrying out the control manipulation for the slow-motion reproduction mode, the switches 26, 28 and 36 (FIG. 1) are connected to their respective points of contact P while the switch 53 is closed. Furthermore, the frequency division ratio of the frequency divider 51, which is obtained with the signal coming out of the flip-flop 35, is adjusted in accordance with the slow movement of the

  slow motion reproduction. For example, for a reproduc-

  half idle, adjust the division ratio

frequency at 1/2.

  The square wave output signal c of the scale

  is sent to the frequency divider 51 when the frequency

  signal frequency is divided at half the initial frequency. Consequently, the outgoing signal f having the waveform indicated in FIG. 8 (A) is sent to a monostable multivibrator 52. This multivibrator 52 gives an outgoing signal h whose waveform is indicated in fig. 8 (B), increasing in response to an elevation

  the signal from the frequency divider 51 and dimi-

  after a particular time Tl which is determined according to the time constant of the monostable multivibrator 52. The reason why the delay Tl is essential relates to the timing concordance in order to eliminate the noise generated when the system is started up

  reproductive by varying the time Tl.

  The outgoing signal h of the monostable multivibrator 62 is sent to a flip-flop 49 and the control device / which is constructed from a microcomputer, to

  through switch 53 which is in the closed state.

  On the other hand, a control signal i reproduced by the control unit 27, as indicated in FIG. 8 (C), signal which is the same as the signal d in fig. 2 (D), except that in fig. 8 (C) we have not shown

  the negative polarity pulse is supplied to a multi-

  monostable vibrator 47 via the switch 26 and the amplifier 44. Consequently, a signal having a waveform indicated in FIG. 8 (D) is

  supplied to the scale 49 and the control device 55.

  This signal 1 increases in response to the rise in the positive polarity signal i and decreases after a specific time T2 determined as a function of the time constant of the monostable multivibrator 47. The delay T2 is related to the time required for the motor 20 of the capstan to stop after detection of the reproduced control signal i. More precisely, the capstan motor 20 stops rotating after a duration which represents the total of the aforementioned delay T2 and the inertia rotation time of the capstan motor 20. The delay T2 can be modified by varying the time constant of the monostable multivibrator 47, that is to say by varying the value of the variable resistor 48. Consequently, the variable resistor 48 is adjusted in this way and the delay T2 is adjusted

  of the monostable multivibrator 47 so that the

  tance between the detection of the control signal and the complete stopping point of the magnetic strip 18 is the desired distance described above which has been studied with reference to FIG. 6 As a practical example, the distance t1 is of the order of 0.4 mm and the delay T2 represents a few milliseconds. The flip-flop 49 gives an outgoing signal k which, as indicated in FIG. 8 (E)} goes up in response to an increase in the signal from the monostable multivibrator 52 and goes down in response to the rise in the signal from the multivibrator 47. As will be explained below, the period during which the signal k remains at its high level coincides with the period of rotation of the

vabestan engine 20.

  When the capstan motor 20 is running, the capstan 19 is rotated together with the motor

  20. The magnetic strip 18 which is pinched between the cabes-

  tan 19 and the pinch roller 23 moves in the direction

  tion of arrow X in fig. 1. The direction of rota-

  tion of the capstan motor 20 in the indicated condition will

  hereinafter called "positive direction". The signal goes out

  as long as flip-flop 49 is supplied to a NO / OR circuit 57, the drive circuit 58 of the motor and a circuit of

detection 66.

  In fig. 7, an embodiment has been represented.

* tion showing a concrete circuit of the excitation circuit of the motor 58 and the peripheral circuits. A high level signal is continuously produced on an output terminal of the control device 55 and it is applied to a terminal of an AND circuit 56. On the other hand, a signal n having the waveform indicated in fig . 8 (H) is obtained

  from the other output terminal of the device

  signal 55 and this signal n is applied to the NO / OR circuit 57 and to the detection circuit 66. Normally the signal n is of low level and comprises a train of pulses which is of a high level for a predetermined width of im - pulses T4 which is obtained intermittently, after a predetermined time T3 indicated in fig. 8 (F) 1 since the elevation of the output pulse j of the monostable multivibrator 47 applied to the control device 55. The signal n is reset to zero in response to a drop in the signal o indicated in FIG. 8 (I) supplying the circuit

  66, and this signal becomes low.

  During the period of high signal level

  as long k of the flip-flop 49 between the times ta and tb, the signal n obtained through the other output terminal of the control device 55 is of a low level as can be seen in FIG. 8 (H). Consequently, the signal leaving circuit 57 NO / OR with two inputs to which one applies

  signals n and k respectively become low level.

  This low level output signal from the NO / OR circuit 57 is applied to an input terminal 64a of a logic circuit 64 in the motor excitation circuit 58. Furthermore, the detection circuit 66 is constructed from a microcomputer and it supplies the signal o indicated in FIG. 8 (I) which rises in response to an elevation of the outgoing signal k of the flip-flop 49, to the control circuit 55 and to the AND circuit 56. Thus the output signal of the circuit

  AND 56 becomes of a high level during the indi-

  high level of signal k (between times ta and tb).

  This high level outgoing signal from the ET 56 circuit is

  applied to an input terminal 64b of logic circuit 64.

  In addition, another input terminal 64c of the logic circuit 64 is connected to the output terminal of the flip-flop 49, and the high level signal k is applied to this terminal.

entry 64c.

  As seen in fig. 7, the logic circuit 64 comprises a NOR / OR circuit 59 with two inputs whose input terminals are connected respectively to the input terminals 64a and 64c, a NON / OR circuit 60 with two inputs whose input terminals are connected respectively

  at the input terminal 64c and at the output terminal of the circuit

  cooked NO / OR 59, a NOT / OR 61 circuit with two inputs whose input terminals are respectively connected to the input terminal 64a and to the output terminal of the NON / OR 59 circuit, and of the NON / AND circuits 62 and 63 with two inputs whose input terminals are, respectively connected to the output terminal of the ON / OR circuit 61 and to the input terminal 64b. The output signals of the NO / OR circuit 60, the NON / AND circuits 62 and 63 and the NON / OR circuit 61 are obtained respectively through the output terminals

  64d, 64e, 64f and 64g of logic circuit 64.

  Each of the output signals obtained by the

  these terminals 64d, 64e, 64f and 64g are applied

  respectively to electronic switches S4, S1, S3 and S2, which are constructed from transistors

  bipolar or unipolar, as communication signals

  tation. Switches S1 and S3 are closed in response to a low level switching signal while switches S2 and S4 are closed in response to a signal

  high level switching. A series circuit comprising

  taking switches S1 and S2 and a series circuit

  including switches S3 and S4 are connected res-

  pectively between a current source 67 and the earth.

  In addition, a connection point between the switches S1 and S2 is connected to a terminal of the capstan motor 20, while a connection point between the switches S3

  and S4 is connected to the other terminal of the motor 20.

  More precisely, the switches S1 to S4 cons-

  are a bridge circuit. In addition, the two terminals of the capstan motor 20 are respectively connected to the

  input terminals of a comparator 65 comprising an amplifier

operational ficitor.

  The relationships between the signal levels on the input terminals 64a to 65c and the output terminals 64d to 64g of logic circuit 64 and the state of the switches S1

  to S4 are indicated respectively in the following table

  boast. In this table, "H" and "L" respectively denote

  the high and low level of a signal while "CL" indicates that the switch is closed. On the other hand, the spaces left blank correspond to the state

opening the switch.

BOARD

  TERMINAL DIENTREEj [OUTPUT TERMINAL jCUTTER SWITCH S1 64a 64b 64c 64d 64e 64f 64 "fi Si S2

S3 J S4

  i) HHHLHHL (ii) HLHLHHL (iii LHHLHLH CL CL (iv) LLHLHHH CL yv) HHLHLHL CL CL vi) HLLHHHL CL vii LHLLHHL (viii) LLLLHHL Consequently, in the outgoing signal k of the flip-flop tb, the levels of the signals in trée 64a, 64b and 64c of the circui high level period of 49, between times ta and troduits on logic t 64

the terminals of

are respecti-

  "L", "H" and "H". Thus from (iii) on this table, signals having levels "L", "H", "L" and "H" are obtained respectively by the output terminals 64d,

  64e, 64f and 64g of logic circuit 64. Thus the switches

  tors S2 and S3 close while switches S1 and S4 open. During this period between times ta and tb, the current coming from the source 67 thus passes through the switch S3, the capstan motor 20 and the switch S2 to turn the motor 20 in the positive direction.

  The output voltage of source 67 is relative-

  high at time ta, and its waveform decreases pro-

  gradually towards time tb. Thus} during the aforementioned period between ta and tb, an inclined wave voltage PI; as shown in fig. 8 (F), is applied to the motor terminal 20. An inclined wave voltage of this kind is used in order to obtain a rapid rise when the motor is started and to minimize the downtime necessary to stop the engine. This inclined wave is obtained using a discharge voltage wave

of a capacitor.

  After that, the outgoing signal k from flip-flop 49 falls at time tb. When the outgoing signal k becomes low level, it is applied to the input terminals 64c and

  a high level signal is applied to the input terminal

  input 64a of logic circuit 64. On the other hand, a high level signal is continuously applied to the input terminal 64b of logic circuit 64. Consequently, the

  output levels at output terminals 64d to 64g become

  respectively "H", "L", "H" and "L" as can be seen in (y) on the table. Thus the switches S1 and S4 are closed while the switches S2 and S3 are open. The current from source 67 thus passes

  through the switch S1, the motor 20 and the switch

  tor S4 to apply reverse voltage to motor 20 of the capstan and thus rotate this motor in the direction

  opposite to that in which said motor 20 was rotating.

  As explained, the controller 55 is adjusted in response to a drop in the output pulse j from the monostable multivibrator 47 to provide the signal n, shown in FIG. 8 (H), to the ON / OR circuit 57 and to the detection circuit 66. The signal n takes a high level during the short duration T4 after the duration T3 has passed since the time tb. Thus the input level at terminal 64a of logic circuit 64 changes to a low value during the aforementioned brief period of signal n from its high value to its low value. At this time, the levels

  on the other input terminals 64b and 64c remain respected

  tively at a high level and at a low level. During this brief period T4, the levels of the output signals at terminals 64d to 64g of logic circuit 64 become low high, high and low, as can be seen in (vii) on the table. All the switches S1 to S4 are thus opened and the supply of a reverse voltage to the capstan motor

is interrupted.

  During this period T4, the motor 20 continues its rotation in the positive direction under the effect of the inertia acting in the direction of the positive rotation, although the reverse voltage is applied to the motor 20 during the

  predetermined time TV. As a result, a tension counter

  electromotive in relation to the rotation due to the inertia in the direction of positive rotation, can be detected on the terminals of the capstan motor 20. This back-electromotive voltage is detected to ensure that the capstan motor is running or is stopped depending on the existence

  or the absence of the counter electromotive voltage. We are-

  performs detections alternately for a predetermined interval to detect the application of voltage

  reverse and producing the counter-electro voltage

  motor, as will be explained later.

  The input terminals of comparator 65 are connected

  ted respectively at the terminals of the capstan motor 20, but since the resistance at the input of the comparator 65 is high, no undesirable effect is introduced into the motor of the capstan. Comparator 65 gives a high level signal when the voltage at the terminals of the motor on the side of switch S3 is higher than on the side of switch S1. On the other hand, when the voltage at the terminals of the motor on the side of the switch S3 is greater than on the side of the switch Sl, the

  comparator 65 produces a low level signal. The compa-

  rator 65 is constructed so as to produce a low level signal even when the counterelectromotive voltage of the capstan motor 20 is zero. Thus, during the period between times ta and t, a voltage is applied to rotate the capstan motor 20 in the positive direction. Thus the comparator 65 produces a high level signal m which is indicated in fig. 8 (G)

  and the signal thus produced is sent to the detection circuit.

tection 66.

  This detection circuit 66 mounts in response to a

  elevation of the output pulse k of the flip-flop 49.

  On the other hand, the detection circuit 66 is brought to zero

  in response to a drop in impulse k. When the ni-

  Calves of the output signal n of the control device 55 and of the output signal of the comparator 65 are at the same logic level (ie when both are low level or high level), the detection circuit 66 produces a high level signal. On the other hand, when the levels of the signal n and of the setting of the comparator 65 are at different logic levels (i.e. if

  one is low level and the other high level), the

  cooked detection 66 produces a sîns! low level. In addition, the detector circuit 66 maintains the low level output until the rise of the pulse D. The detection circuit 66 having the construction described produces a high level signal o as indicated in FIG. 8 (T), during the aforementioned time interval between ta and tb during which the voltage is applied to the motor 20 to rotate this capstan motor in the positive direction. During the next time interval indicated by T3 after time tb, the output level of comparator 65 becomes low since the reverse voltage is applied to the motor of the capstan. In addition, the signal n is also of low level as can be seen in FIG. 8 (H) during this time interval T3. The output level of the detection circuit 66 remains high. during

  the short time interval T4 following the inter-

  valle T3, the application of a reverse voltage to the motor 20

  of the capstan is interrupted and the counter-electro-

  drive of motor 20 is detected. Thus the output level of comparator 65 becomes high. In addition, the signal n is also of high level during the interval T4 as can be seen in FIG. 8 (H) and, as a result, the output level of detection circuit 66 persists

to a high value.

  Similarly, after the time interval T4, there is an alternation of the intervals during which the reverse voltage is applied to the capstan motor 20 and the application of the reverse voltage is interrupted (time intervals T5 and T6) as can be see it in fig. 8 (F); a fourth interruption of the reverse voltage takes place at time tc. At this time, if it is assumed that the rotation of the motor 20 is completely stopped or about to start a slight rotation in the opposite direction, the output signal m of the comparator 65 becomes low as seen in FIG. . 8 (G). Else

  part, the signal indicated n again becomes high ni-

  veal. Thus the output signal o of the detection circuit 66 becomes low level at time tc as seen in FIG. 8 (I) and this low level state of the outgoing signal

  o is maintained until the next period td when the im-

drive k rises again.

  We can therefore make a discrimination as to whether the motor 20 of the capstan rotates or does not rotate at

  time tc at least in the positive direction. The exit signal

  tie of the AND circuit 56 becomes low level as a result of the low level output of the detection circuit 66. Furthermore,

  since the signal n is of high level the output signal

  part of the circuit NO / OR 57 becomes low level. Since the output levels at terminals 64d to 64g of logic circuit 64 become values indicated on line (viii) in the previous table, that is to say that the

  levels at output terminals 64d to 64g become respec-

  tively "L", "l", "R" and "L" and the switches SI, S2, S3 and S4 are open. The application of the reverse voltage to the motor 20 is thus interrupted This operation

  interruption continues until time td which * orres-

  pond to the rise of impulse k. The state indicated by (vi) in the table above is established when the signal n takes a low level and the output of the ON / OR circuit 57 becomes high level. In this state the application of the reverse voltage to the motor 20 remains interrupted since the

switches S1 to S3 are open.

  As described, the time required to reach

  missing the rotation of the motor 20 is reduced by the applica-

  tion of a reverse voltage to the capstan motor 20. In addition, since the operations are repeated to detect the possible rotation of the motor 20 or even the direction of this rotation by an interruption of the application of the

  reverse voltage and reverse voltage is again ap-

  stuck to motor 20 if its rotation has not

  been stopped, the motor 20 does not rotate in the opposite direction

  pours. The time interval T3 during which the tension

  reverse voltage is applied to motor 20 is set to-

  about 6 ms and the time intervals indicated by T4,

  T5 and T6 during which the application of the voltage

  pours to motor 20 is interrupted are set to approximately

  2 me. It has been experimentally confirmed that the time required

  from the start of engine 20 until it stops (the time interval between ta and te indicated in fig. 8 (F) for example) must be approximately 60 mu to ensure stable reproduction at idle . According to this embodiment, the rotation of the motor 20 can be stopped

  well within the 60 ma range.

  This embodiment is applied to a slow motion reproduction system, for example in VTR. Consequently, by repeatedly starting and stopping the rotation of the motor 20 (see FIG. 1), one obtains alternately and repeatedly a normal reproduction image for a predetermined frame interval during which

  the magnetic strip moves and one image per reproduc-

  when stopped for a predetermined frame interval during which the tape is stopped, so that in

  the whole obtained an image by slow motion reproduction.

  When recording, on the magnetic device

  as recording and reproducing according to fig. 1,

  switches 26, 28 and 36 are respectively commu-

  tees and are connected to their respective contact points

  tifs P. Thus the incoming video signal or an analog signal

  which is admitted on the input terminal 11 is recorded by the

  video heads 13A and 13B. So the signal coming out of the multi-

  monostable vibrator 24 is registered as a

  general control by the control head 27, and the signal leaving the monostable multivibrator 25 is supplied to the sampling and holding circuit 29 as a sampling signal. However, since these operations are not directly related to the objects

  of the invention, no detailed description will be given.

  We apply a pulse having a frequency of

  repetition as a function of the speed of rotation of the mo-

  20 to the control device 55, because the

  lant 22 comprising alternating magnets of South peel and North peel on its peripheral surface, and the read head 39 are fixed to one end of the shaft

  rotary motor 20. However, this impulse is only-

  ment used in a procedure comprising a rotation

  tion at constant speed of the capstan motor 20.

  Furthermore, the invention can be applied to stop

  ter the rotation of a motor other than according to the mode of

  described embodiment according to which one starts and stops

  te the rotation of a capstan motor to get a

image by slow motion reproduction.

  The invention is not limited to the examples of

  reading, shown and described in detail, because various modifications can be made without departing from its scope.

Claims (5)

  1 - Device for stopping the rotation of a   motor, comprising a current source (67) for furnace   supply an excitation voltage to a motor (20), characteristic   in that it includes reverse voltage urn application means (55-58) so as to apply reverse voltage to this motor and interrupt application   of this reverse voltage, by applying the reverse voltage   get to this engine for a first predetermined interval   when stopping the engine rotation and stopping it   the application of the reverse voltage to this motor during a second predetermined interval which follows   at the first predeterx interval; and means of   tection (65, 66) to detect the rotation of the motor during   during the interval during which the application of the reverse voltage to this motor is interrupted by said means of applying the reverse voltage, to stop   the operation of applying the reverse voltage by the-   so-called means of applying reverse voltage when   detects that the rotation of the moter is stopped.   2 - Apparatus according to claim 1, character-   se in that the detection means comprise means   (65) to detect the back EMF voltage in-   gendré during engine rotation.   3 - Apparatus according to Claim 1, character-   in that the current source (67) produces a voltage   sloping slope (fig. 8 (F) which is of high value when   starting the engine and which then decreases   gressively. 4 - Apparatus according to claim 1, characterized in that the means for applying the reverse voltage comprises a control device (55) for generating a train of pulses having a pulse width equal to the second predetermined interval, with a period which is equal to the total period between the first and second predetermined intervals, and a motor excitation circuit (58) for switching the connection between the current 2487dOO source and the motor according to the train of output pulses of the device control when rotating the motor, to rotate the motor in one direction   opposite to the one in which he was filming.   5 - Apparatus according to claim 4, characterized in that the motor excitation circuit comprises four electronic switches (Si-S4) respectively defining each side of a bridge, said bridge being   connected with the motor terminals on their res-   opposite players, and a logic circuit (64) for regulating   the opening and closing states of each switch   electronic generator according to the output pulse train of the control device (55).