PatentDe  


Dokumentenidentifikation EP1174997 09.11.2006
EP-Veröffentlichungsnummer 0001174997
Titel STEUERUNG FÜR MOTOR MIT UNTERBRECHENDER ANSTEUERUNG
Anmelder KABUSHIKI KAISHA TOSHIBA, Tokyo, JP
Erfinder AZUMA, Kazuki, Fukaya-shi, Saitama 366-0824, JP
Vertreter derzeit kein Vertreter bestellt
DE-Aktenzeichen 60123339
Vertragsstaaten DE, FR, GB
Sprache des Dokument EN
EP-Anmeldetag 16.01.2001
EP-Aktenzeichen 019007756
WO-Anmeldetag 16.01.2001
PCT-Aktenzeichen PCT/JP01/00211
WO-Veröffentlichungsnummer 2001054264
WO-Veröffentlichungsdatum 26.07.2001
EP-Offenlegungsdatum 23.01.2002
EP date of grant 27.09.2006
Veröffentlichungstag im Patentblatt 09.11.2006
IPC-Hauptklasse H02P 5/00(2000.01)A, F, I, 20011207, B, H, EP
IPC-Nebenklasse G11B 15/48(2006.01)A, L, I, 20011207, B, H, EP   G11B 15/54(2006.01)A, L, I, 20011207, B, H, EP   

Beschreibung[en]
BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an intermittent drive control apparatus of motor suitable for intermittent drive of a capstan motor of a video tape recorder (VTR).

Related Art Statement

In the conventional VTR of helical scanning scheme, there is sometimes adopted a slow motion playback system using such an intermittent slow scheme that tape stop and tape drive are alternately repeated. In this scheme, the capstan motor is rotated intermittently and tape is fed intermittently. Slow motion playback with noise occurrence suppressed is possible in this scheme.

Intermittent feed for such slow motion playback will now be described.

For intermittent feed of tape, a forward/reverse rotation command is supplied to a motor drive circuit of the capstan motor. In addition, since the motor is started until a predetermined rotational speed is attained, a current limit command is given so as to raise the rotational speed rectilinearly. Next when the motor attains a predetermined rotational speed, to maintain the speed, a speed control is performed by an error command. If a reproduced control pulse is obtained in the middle of an interval of this fixed speed, a reverse rotation command is given after a preset tracking adjustment time interval and a braking current is supplied. The braking current is also kept at a fixed value by a current limit command so as to lower the rotational speed of the motor at a fixed ratio. The rotational speed of the motor gradually lowers, and the rotation becomes zero. If rotation in the reverse rotation direction is subsequently detected, then a forward rotation command is given. As a result, continuation of reversal caused by inertia of the motor is prevented. (This is called re-acceleration.) Complete stop is thus obtained.

The intermittent drive of the capstan is implemented by the above described system. Slow motion playback is conducted so as not to generate noise. In the above described system, however, it is necessary to finish the braking and conduct re-acceleration operation at a time point when the rotation becomes zero. When an accuracy in detection of this zero point is low, tape is damaged at a time of tape travelling. Therefore, zero point detection is conducted by detecting a phase relation by means of two capstan rotational speed detection signals differing in phase as means for improving the zero point detection accuracy.

FIG. 3 shows a related technique of a VTR which makes intermittent feed possible. FIG. 3 is a block diagram showing invention disclosed in Japanese Patent Application Laid-Open 7-59389.

A capstan shaft 11 of the VTR is capable of pressing magnetic tape 13 against a pinch roller 12 and driving the magnetic tape 13 to make it travel. The capstan shaft 11 is integral with a rotary shaft of the capstan motor 15. Rotation of the capstan motor 15 is detected by bi-phase frequency detectors (FGa, FGb).

The frequency detectors FGa and FGb are coils disposed at such a distance as to generate a phase difference of 90 degrees between them. Detected outputs of the frequency detectors FGa and FGb are supplied to waveform shaping circuits 16 and 17, respectively. For a control track of tape 13, a control head 18 is disposed. Thereby, a control signal can be recorded and reproduced. A reproduced control signal is inputted to a waveform shaping circuit 19.

The detection signal FGa shaped in waveform to a rectangular wave by the waveform shaping circuit 16 is supplied to a speed detector 21, and used to detect the rotational speed of the capstan motor 15. The detection signals FGa and FGb of rectangular waves outputted from the waveform shaping circuits 16 and 17 are supplied to a rotational direction detector 22, and used to detect the rotational direction of the capstan motor 15.

A speed error signal fed from the speed detector 21 and a reverse rotation detection signal fed from the rotational direction detector 22 are supplied to a capstan controller 23. In addition, a control signal fed from the waveform shaping circuit 19 and tracking information fed from an external memory or the like are also inputted to the capstan controller 23.

By using these kinds of input information, the capstan controller 23 controls a motor current of a motor drive circuit 24 and drives the capstan motor 15 intermittently. Control information supplied to the motor drive circuit 24 includes forward/reverse rotation command information, current limit value command information, and error information.

FIG. 4 shows signal waveforms of various locations at the time of intermittent drive.

It is now assumed that start of the motor is begun at time t0. At this time, a motor current (F) is supplied with a fixed value (Is in FIG. 4) by current limit value command information (E) so as to increase the rotation at desired acceleration. A motor speed (G) increases at fixed acceleration as shown in FIG. 4. When the motor speed (G) arrives at a desired value W0 (time t1), rotational speed control is applied in order to keep the fixed speed.

An interval between time t0 and t1 is called start interval (a start time interval is Ts). Shift to the fixed speed state is conducted on the basis of the speed information fed from the speed detector 21, and error command information (A) is supplied to the motor drive circuit 24. As a result, the motor current changes, resulting in a fixed speed state.

Maintenance of the constant speed state is achieved by conducting speed control so as to make the frequency of the rotation detection output (FGa) constant. This interval (interval between the time t1 and time t2) is called fixed speed interval (where a fixed speed time interval is TF).

When the control signal (B) is detected in the fixed speed interval (at, for example, t5), the speed W0 is kept further for a time interval (TD) on the basis of tracking information, and then shift to braking operation is conducted (time t2). The braking operation is conducted by supplying forward/reverse rotation command information (D) to the motor drive circuit 24 and switching the motor current over to an opposite direction. At this time, the motor current (F) is prescribed (to become IB in FIG. 4) by the current limit value command information (E) so as to decrease the rotational speed of the motor at a fixed rate. If braking operation were kept, the motor would conduct reverse rotation operation after stop. The moment an opposite direction rotation detection output (reverse rotation detection signal (C)) is obtained from the rotation direction detector 22 (at time t3), therefore, the forward/reverse rotation command (D) is changed so as to order a forward rotation. At the same time, a current is applied in the forward rotation direction again for a short time in order to cancel the rotational inertia of the motor. As a result, rotatory power of the forward rotation direction is generated. The reverse rotation energy is thus absorbed completely, and complete stop is obtained. This is so-called re-acceleration. A re-acceleration time interval is TR, which is an interval between t3 and t4. (As a matter of fact, the motor is in the stop state.)

For implementing such accurate intermittent drive as not to generate noise on the screen, as above-described, it is necessary to conduct detection of timing for execution of re-acceleration, i.e., detection such timing that the rotation becomes zero (zero point detection) at high accuracy. For this reason, two capstan rotation detection signals having a phase difference of 90 degrees are used in an example of the aforementioned Japanese Patent Application Laid-Open 7-59389.

In other words, in the forward rotation, FGb is detected 90 degrees behind the rotation detection signal FGa. On the other hand, in the reverse rotation direction, FGb is detected 90 degrees before the rotation detection signal FGa. By detecting s phase relation between FGa and FGb, therefore, it becomes possible to determine whether the motor is conducting the forward rotation or the reverse rotation at the present time. It thus becomes possible to detect a zero point at high accuracy.

In this case, however, two rotation detection systems, i.e., two motor speed detectors, two detection signal amplifiers and two wave form shaping circuits are needed, resulting in a remarkably increased cost.

In this way, in an intermittent drive control apparatus of motor adopted in an intermittent slow playback system, it is necessary to improve the zero point detection accuracy. Therefore, zero point detection is conducted by using two capstan rotational speed detection signals differing in phase. Accordingly, two motor speed detectors, two detection signal amplifiers and two wave form shaping circuits are needed. This results in a problem that the apparatus scale is large and the cost is increased.

Therefore, an object of the present invention is to provide an intermittent drive control apparatus of motor capable of reducing an apparatus scale and suppressing a cost increase by making possible high accuracy zero point detection using only one capstan rotation detection signal.

Patent Abstracts of Japan, vol. 018, no. 290, 2 June 1994, and JP 06 054569 A, 25 February 1994; Patent Abstracts of Japan, vol. 012, no. 118 (E-600) 13 April 1988 and JP 62 247777 A, 28 October 1987; and WO 94 15337 A disclose apparatus as defined in the pre-characterising portion of Claim 1.

The invention provides an intermittent drive control apparatus as defined in Claim 1.

Brief Description of the Drawings

  • FIG. 1 is a block diagram showing an embodiment of an intermittent drive control apparatus of a motor according to the present invention;
  • FIG. 2 is a timing chart showing operation of the embodiment of FIG. 1;
  • FIG. 3 is a block diagram showing a related technique; and
  • FIG. 4 is a timing chart showing operation of the related technique of FIG. 3.

Best Mode for Carrying Out the Invention

Hereafter, an embodiment of the present invention will be described in detail by referring to drawing. FIG. 1 is a block diagram showing an embodiment of an intermittent drive control apparatus of a motor according to the present invention. In FIG. 1, the same components as those of FIG. 3 are denoted by like characters.

A capstan shaft 11 of the VTR is formed so as to be capable of pressing magnetic tape 13 against a pinch roller 12 and driving the magnetic tape 13 to make it travel. The capstan shaft 11 is integral with a rotary shaft of the capstan motor 15.

In the present embodiment, only a frequency detector CFG of one system is used in order to detect the rotation of the capstan motor 15. The frequency detector CFG is a coil disposed, for example, near the capstan motor 15. The frequency detector CFG is configured so as to detect the rotation of the capstan motor 15 and output detection outputs at a frequency which is proportionate to the rotation speed to a waveform shaping circuit 16. The waveform shaping circuit 16 conducts waveform shaping on the inputted detection output to yield a rectangular wave. The rectangular wave is outputted to a CPU 31 and a latch 32 as a rotation detection signal CFG.

On the other hand, a control head 18 is disposed in such a position as to be opposed to a control track of the tape 13. The control head 18 conducts recording and playback of a control signal on the control track of the tape 13. A reproduced control signal fed from the control head 18 is supplied to a waveform shaping circuit 19. The waveform shaping circuit 19 conducts waveform shaping on the control signal to yield a rectangular wave. The rectangular wave is outputted to the CPU 31 and the latch 32.

The latch 32 latches a count value of a counter 33 at timing of a rising edge and/or a falling edge of the signals fed from the waveform shaping circuits 16 and 19, and outputs to the CPU 31. The counter 33 is controlled by the CPU 31 and counts clock pulses at a predetermined frequency. The CPU 31 derives the rotational speed of the capstan motor 15 on the basis of various inputted signals, and derives the start time interval, fixed speed time interval, braking time interval, re-acceleration time interval, and so on in intermittent drive control. A program to be used by the CPU 31 to conduct processing is stored in a ROM 34. The CPU 31 functions on the basis of this program, and conducts various processing by using a RAM 35 as a memory for working. A capstan controller 23, the CPU 31, the latch 32, the counter 33, the ROM 34, and the RAM 35 form a microcomputer.

Every time the rotation detection signal CFG arrives, the CPU 31 makes the latch 32 latch the count value of the counter 33 and makes the RAM 35 store the latched value. By deriving a difference between count values corresponding to two measured rotation detection signals CFG, the CPU 31 calculates a period of the rotation detection signal CFG. As a result, the CPU 31 can acquire the rotation speed of the motor 15.

A reference value of the period of the rotation detection signal CFG at the time of ordinary operation is stored in the ROM 34. At the time of ordinary operation, the CPU 31 compares the period of the calculated rotation detection signal CFG with the reference value read out from the ROM 34, and derives an error signal. The CPU 31 is formed so as to output motor control information for conducting rotation control of the motor to the capstan controller 23, on the basis of the error signal.

The CPU 31 is formed so as to obtain the count value corresponding to the period of the rotation detection signal CFG at the time of ordinary operation, from the counter 33 and store the count value in the RAM 35.

Furthermore, in the present embodiment, the CPU 31 is formed so as to conduct computation of the braking time interval required at the time of intermittent drive, by using only the detection signal CFG of one system. For example, the CPU 31 is formed so as to derive the period of the rotation detection signal CFG on the basis of the count value each time at least three rotation detection signals CFG arrive, calculate an average rotational speed of the capstan motor 15 on the basis of the derived period, derive an attenuation value of the rotation speed (a speed deceleration rate) on the basis of the calculated average speed, and thereby set the braking time.

Furthermore, for example, the CPU 31 reads out the count value indicating the rotation detection signal period at the time of ordinary operation from the ROM 35, regards this value as the speed of the capstan motor 15 at the time of braking start, derives a difference between the speed of the capstan motor 15 at the time of braking start and the period of the rotation detection signal CFG measured after the braking start, derives the attenuation value of the rotational speed therefrom, and sets a braking interval.

By using various computation results and the control signal fed from the waveform shaping circuit 19, the CPU 31 generates the motor control information for controlling the capstan motor 15.

Tracking information pieces fed from an external memory, an adjustment circuit, and so on (not shown) are also inputted to the capstan controller 23. On the basis of the motor control information fed from the CPU 31, the capstan controller 23 generates a forward/reverse rotation command (D) from the capstan motor 15, a current limit value command (E), and an error command (A), and outputs them to a motor drive circuit 24. The motor drive circuit 24 is formed so as to generate a motor current (F) for driving the capstan motor 15 on the basis of various commands inputted thereto.

Operation of the embodiment having the configuration heretofore described will now be described by referring to a timing chart of FIG. 2. The top of FIG. 2 shows a change of the rotational speed of the motor in the braking interval and re-acceleration interval. The axis of abscissas indicates time. The axis of ordinates indicates the rotational speed of the motor. In association with therewith, a motor control voltage, a forward/reverse rotation command (motor F/R), and the rotation detection signal CFG (FG-1 to FG-4) are shown.

It is now assumed that intermittent drive is conducted for slow playback. In the present embodiment as well, operation in the start interval, fixed speed interval, and re-acceleration interval is the same as the example of the related technique of FIG. 3. In other words, in the start interval, the CPU 31 controls the capstan controller 23 to make the motor current (F) a fixed value so as to raise the rotation of the capstan motor 15 at desired acceleration. As a result, the motor speed (G) of the capstan motor 15 rises at fixed acceleration.

Rotation of the capstan motor 15 is detected by the frequency detector CFG. The detection signal CFG is inputted to the CPU 31 via the waveform shaping circuit 16. The latch 32 latches the count value of the counter 33 at timing of each detection signal (FG(1) to (5)) and supplies the latched value to the CPU 31. When the detection signal CFG fed from the waveform shaping circuit 16 is supplied, the CPU 31 enters an interrupt processing routine, acquires a count value latched so as to correspond to each detection signal (FG(1) to (5)), and calculates the rotation speed of the capstan motor 15 from a difference between count values.

Upon detecting that the rotation speed of the capstan motor 15 has arrived at a desired value WO, the CPU 31 conducts rotational speed control in order to keep the fixed speed. As a result, the capstan controller 23 supplies the error command information (A) to the motor drive circuit 24, changes the motor current, and shifts the motor into a fixed speed state.

The CPU 31 detects the frequency of the detection signal CFG, and conducts speed control so as to make the detected frequency fixed. If the reproduced control signal (B) is inputted from the waveform shaping circuit 19 in the fixed speed interval, the CPU 31 makes the speed W0 kept further for a time interval (TD) on the basis of the tracking information, and then sends an order to the capstan controller 23 so as to cause a shift to braking operation.

Upon reaching start timing (timing T0 of FIG. 2) of the braking interval, the capstan controller 23 inverts the forward/reverse rotation command (MOTOR F/R in FIG. 2) supplied to the motor drive circuit 24 and thereby switches the motor current over to the opposite direction. In this case, the capstan controller 23 prescribes the motor current (F) so as to decrease the rotational speed of the motor at a fixed rate, on the basis of the output of the CPU 31.

As shown in FIG. 2, the rotational speed of the capstan motor 15 decreases at fixed rate and stops when a predetermined time interval has elapsed. If braking operation were kept after the stop timing, the motor 15 would conduct reverse rotation. At the same time that the rotation of the motor 15 stops, the CPU 31 inverts the motor F/R (see FIG. 2) to order the forward rotation. In order to cancel the rotational inertia of the motor 15, the CPU 31 thus supplies the motor current for a minute interval (re-acceleration interval).

In the example of the related technique of FIG. 3, stop timing of the motor 15 is detected by start of the reverse operation of the capstan motor 15, as described above. On the other hand, in the present embodiment, the CPU 31 calculates the time interval (braking time interval) between the start of the braking interval and stop of the motor 15. Thereby, the stop timing of the motor 15 is derived.

Calculation of the braking time interval in the present embodiment will now be described.

The CPU 31 computes the speed deceleration rate of the rotational speed of the motor 15 by using the detection signal CFG in the braking interval and thereby obtains the braking time interval.

First, the speed deceleration rate in the braking interval will be described. In the braking interval, the motor current is fixed as described above.

An equilibrium equation of the motor torque is represented by the following equation (1), J ( d &ohgr; / d t ) + D &ohgr; + T L = K T i where

  • &ohgr; = angular speed of motor rotation
  • J = motor inertia
  • D = coefficient of viscosity of motor
  • KT = motor torque constant
  • TL = motor load torque
  • i = motor current

In the braking interval, the motor current is fixed. Letting i = I (fixed) and solving the equation (1), therefore, we get &ohgr; ( t ) = [ &ohgr; ( 0 ) B A ] e A T + B A where

  • &ohgr;(0) = initial value of the number of rotations of motor
  • A = D/J
  • B = (KT · I-TL) / J

In general, the motor time constant is longer than the braking time interval of the VTR at the time of slow motion (At << 1). Therefore, e-AT can be approximated as (1 - At). In the equation (2), &ohgr;(t) is approximated by the following equation (3). &ohgr; ( t ) = &ohgr; ( 0 ) + [ B A &ohgr; ( 0 ) ] t

The equation (3) represents that the number of rotations of the motor is proportionate to time. In other words, in the case where the motor current (braking current) is fixed and the load from the traveling system is fixed (the same load), the speed decreases at a fixed rate. In other words, the speed deceleration rate is fixed in the braking interval.

In the present embodiment, the braking time interval is computed by utilizing the fact that the speed deceleration rate is fixed. The CPU 31 calculates the speed deceleration rate by measuring the input period of the rotation detection signal CFG of the capstan motor 15 in the braking interval.

By the way, in the above described related technique of FIG. 3, the braking time interval is made fixed by controlling the value of a current supplied to the motor, in order to make the tape feed fixed in the braking interval. However, the influence of dispersion of the load or the like on screen noise is comparatively slight. In the present embodiment, therefore, the current supplied to the motor is made fixed irrespective of the dispersion of the load or the like. Even in the case where the braking interval differs from load to load, the braking time interval is derived certainly by utilizing the fact that the speed deceleration rate is fixed.

A concrete calculation method of the speed deceleration rate will now be described. The CPU 31 replaces the rotational speed of the motor 15 by the frequency of the rotation detection signal CFG, and conducts computation.

It is now assumed that, for example, three rotation detection signals CFG (FG(1), FG(2) and FG(3)) are detected in the braking interval as represented by FG-1 of FIG. 2.

The CPU 31 calculates an average frequency S(1-2) of the detection signal CFG between time T1 when the detection signal FG(1) occurs and time T2 when the detection signal FG(2) occurs, by measuring the period of the detection signals FG(1) and FG(2). The average frequency S(1-2) is given by the following equation (4), S ( 1 2 ) = { 1 / T ( 1 2 ) } ( Hz ) where T(1-2) indicates a time interval between the time T1 and the time T2.

In the same way,, the CPU 31 calculates an average frequency S(2-3) between the time T2 and time T3, by measuring the period of the detection signals FG(2) and FG(3). The average frequency S(2-3) is given by the following equation (5), S ( 2 3 ) = { 1 / T ( 2 3 ) } ( Hz ) where T(2-3) indicates a time interval between the time T2 and the time T3.

Subsequently, the CPU 31 derives a frequency decrease rate ka by the following equation (6). k a = { S ( 1 2 ) S - ( 2 3 ) } / [ { T ( 1 2 ) / 2 + T ( 2 3 ) / 2 } ] ( Hz / second )

The CPU 31 derives the braking time interval between the braking start and the motor stop, by using the calculated frequency decrease rate (speed deceleration rate). In other words, letting the rotation detection signal frequency at the time of braking start be S(0), the CPU 31 calculates such a braking time interval Ba that the frequency S(0) becomes 0, by using the following equation (7). B a = S ( 0 ) / k a ( seconds )

By the way, until a predetermined number of detection signals of CFG have been inputted, the CPU 31 cannot execute the above described computations for calculating the speed deceleration rate. Before the predetermined number of detection signals of CFG have been inputted, therefore, the CPU 31 makes the braking interval start, by using the braking time interval derived by the preceding braking processing as a temporary time interval.

For example, in the example of FG-1 of FIG. 2, the CPU 31 makes braking started on the basis of the braking time interval calculated the last time, before three signals of CFG are inputted. After three detection signals of CFG have been inputted, the CPU 31 calculates the braking time interval by using the above described computations, subtracts an elapsed time interval after start of the braking interval from the calculated braking time interval, and resets a resultant time interval as the braking time interval.

If the braking time interval is finished, the CPU 31 conducts re-acceleration for a fixed time interval in order to reduce the aftershock of the rotation of the motor 15. In order to conduct this re-acceleration processing, the CPU 31 makes the braking time interval longer than the value derived from the speed deceleration rate by a fixed time interval.

In the above described computation of the speed deceleration rate, the example in which three detection signals of CFG are generated in the braking interval. The number of the detection signals of CFG detected in the braking interval varies according to setting of the playback speed. In the present embodiment, computation of the speed deceleration rate is possible irrespective of the number of detected signals of CFG.

For example, FG-2 of FIG. 2 shows an example in which a large number of signals (FG(1) to FG(5)) of CFG are inputted in the braking interval. In this case as well, the CPU 31 calculates an average frequency S ( 1 3 ) = { 1 / T ( 1 3 ) } ( Hz ) between time T1 and time T3, by measuring a period of the detection signals FG(1), FG(2), FG(3), FG(4) and FG(5) in the same way as the case of FG-1.

T(1-3) is a time interval between the time T1 and the time T3.

In addition, the CPU 31 calculates an average frequency S (3-5) between the time T3 and time T5 according to the following equation (9), by measuring a period of FG(3), FG(4) and FG(5). S ( 3 5 ) = { 1 / T ( 3 5 ) } ( Hz )

T(3-5) is a time interval between the time T3 and the time T5.

A frequency decrease rate kb is calculated by the following equation (10). k b = { S ( 1 3 ) S - ( 3 5 ) } / [ { T ( 1 3 ) / 2 + T ( 3 5 ) / 2 } ] ( Hz / second )

Assuming that a rotation detection signal frequency at the time of braking start is S(0), such a braking time interval Bb that the frequency S(0) becomes 0 is given by the following equation (11). B b = S ( 0 ) / k b ( seconds )

FG-3 of FIG. 2 represents an example of the case where the number of detection signals of CFG used in computation of the speed deceleration rate is increased in the case where the number of inputted rotation detection signals of CFG is insufficient. In the braking interval, four rotation detection signals of CFG (FG(1) to FG(4)) are inputted to the CPU 31.

First, the CPU 31 calculates an average frequency S ( 1 3 ) = { 1 / T ( 1 3 ) } ( Hz ) between time T1 and time T3, by measuring a period of the detection signals FG(1), FG(2) and FG(3).

Subsequently, the CPU 31 calculates an average frequency S(3-5) between time T2 and time T4 according to the following equation (13), by measuring a period of detection signals FG(2), FG(3) and FG(4). S ( 2 4 ) = { 1 / T ( 2 4 ) } ( Hz )

T(2-4) is a time interval between the time T2 and the time T4.

A frequency decrease rate kc is calculated by the following equation (14). k c = { S ( 1 3 ) S - ( 2 4 ) } / [ { T ( 1 3 ) / 2 + T ( 2 4 ) / 2 } ] ( Hz / second )

Assuming that a rotation detection signal frequency at the time of braking start is S(0), such a braking time interval Bc that the frequency S(0) becomes 0 is given by the following equation (15). B c = S ( 0 ) / k c ( seconds )

FG-4 of FIG. 2 represents an example of the case where the frequency of the rotation detection signal CFG at the time of start of the braking interval is low (i.e., the rotational speed of the motor 15 is slow) and only two rotation detection signals of CFG are inputted to the CPU 31 in the braking interval. In this case, the CPU 31 can measure the speed only at one point. Therefore, the CPU 31 substitutes the rotation detection signal frequency at the time of start of the braking interval for another point.

In the braking interval, two rotation detection signals of CFG (FG(1) and FG(2)) are inputted to the CPU 31. The CPU 31 calculates an average frequency S ( 1 2 ) = { 1 / T ( 1 2 ) } ( Hz ) between time T1 and time T2, by measuring a period of the detection signals FG(1), FG(2) and FG(3).

For calculating the frequency decrease rate, it is necessary to derive an average speed at another point. Therefore, the CPU 31 utilizes the rotation detection signal frequency S(0) at the time of start of the braking interval. As a result, calculation of the braking time interval becomes possible even in the case where the number of detection signals of CFG is two.

In other words, the CPU 31 calculates the frequency decrease rate kd by using the following equation (17), k d = { S ( 0 ) S - ( 1 2 ) } / [ { T ( 0 1 ) + T ( 1 2 ) / 2 } ] ( Hz / second ) where T(0-1) is a time interval between the time T0 and the time T1.

A braking time interval Bd is calculated by using the following equation (18). B d = S ( 0 ) / k d ( seconds )

Furthermore, considering the tension of a reel drive belt included in the traveling system of tape and inertial of the reel, more reliable tape drive becomes possible by slightly prolonging the time interval of the reverse rotation in the braking time interval. In other words, a braking time interval longer than each of the above described computation results of the braking time interval by, for example, approximately 2 ms may be set.

In the case where only two rotation detection signals of CFG are inputted to the CPU 31 in the braking interval (as in the example of FG-4 of FIG. 2), the CPU 31 utilizes the rotation detection signal frequency at the time of start of the braking interval for computation of the braking time interval, as described above. In this case, the speed in the fixed speed interval is already known. As a matter of fact, therefore, it is not necessary to measure the rotation detection signal frequency at the time of start of the braking interval, but a preset value of speed in the fixed speed interval can be used.

In the case where the playback speed is extremely slow (for example, at the time of playback of tape recorded in the VHS-VP mode (five-times-recording mode)), however, speed control becomes difficult sometimes. A stable speed is not always obtained in the fixed speed interval. In this case, further higher accuracy can be obtained by measuring the rotational detection signal frequency at the time of start of the braking interval, instead of using the preset value of the speed in the fixed speed interval.

In other words, in this case, the rotation detection signal frequency is measured at arbitrary timing immediately before the start of the braking interval. The measured rotation detection signal frequency can be used as the rotation detection signal frequency at the time of start of the braking interval.

In the present embodiment, the braking time interval is thus derived by calculating the speed deceleration rate in the braking interval on the basis of the frequency of the rotation detection signal. Even in the case where one rotation detection signal is used, reliable intermittent drive control is possible. It is not necessary to conduct zero point detection using two rotation detection signals differing in phase. The rotation of the capstan motor can be detected by using a rotation detector of one system. As a result, the apparatus scale can be reduced and the cost can be lowered.

In the present embodiment, various computations for controlling the rotation of the capstan motor including the computation of the braking time interval are executed by software processing using a microcomputer. It is apparent that these computations may be implemented by using hardware such as a braking time interval computing device.

Industrial Applicability

As heretofore described, an intermittent drive control apparatus of motor according to the present invention is useful for intermittent drive of a capstan motor of a VTR. For example, it is suitable for intermittent feed control of tape for slow motion playback.


Anspruch[de]
Vorrichtung zur Steuerung eines intermittierenden Antriebs eines Motors, umfassend: ein Motorantriebsmittel (24), das imstande ist, einen Motor dadurch anzutreiben, daß dem Motor Strom einer Vorwärtsdrehrichtung und Strom einer Rückwärtsdrehrichtung intermittierend zugeführt wird; ein Drehbewegungsermittlungsmittel (CFG), das dafür eingerichtet ist, Drehbewegungsermittlungssignale mit einer Frequenz, die der Drehgeschwindigkeit des Motors proportional ist, zu erzeugen; und ein Bremszeitberechnungsmittel (31-35), das so eingerichtet ist, daß, wenn das Motorantriebsmittel so gesteuert wird, daß der Strom der Rückwärtsrichtung dem Motor zugeführt wird, wobei gebremst und die Drehbewegung des Motors beendet wird, die Zeitdauer der Drehbewegungsermittlungssignale gemessen wird, um die Verzögerungsgeschwindigkeit des Motors zu berechnen, und daß die Bremszeit zwischen dem Beginn des Bremsens und der Beendigung der Drehbewegung des Motors auf der Grundlage der Drehgeschwindigkeit des Motors zur Zeit des Bremsbeginns und der berechneten Verzögerungsgeschwindigkeit berechnet wird, so daß das Motorantriebsmittel auf der Grundlage der berechneten Bremszeit gesteuert wird; dadurch gekennzeichnet, daß das Bremszeitberechnungsmittel dafür eingerichtet ist, die Verzögerungsgeschwindigkeit dadurch zu gewinnen, daß eine mittlere Geschwindigkeit jedes Paares unter einer Vielzahl von Paaren der Drehbewegungsermittlungssignale auf der Grundlage der Zeitdauer jedes Paares unter der Vielzahl von Paaren der Drehbewegungsermittlungssignale berechnet wird, und

bis die Vielzahl von Drehbewegungsermittlungssignalen gewonnen ist, die Vorrichtung zur Steuerung des intermittierenden Antriebs dafür eingerichtet ist, das Motorantriebsmittel auf der Grundlage des Bremszeitintervalls zu steuern, das berechnet worden ist, als der Motor das letzte Mal gebremst wurde.
Vorrichtung zur Steuerung eines intermittierenden Antriebs eines Motors nach Anspruch 1, wobei das Bremszeitberechnungsmittel eine erste Zeitdauer auf der Grundlage eines ersten Drehbewegungsermittlungssignals, das in den Drehbewegungsermittlungssignalen enthalten ist, und eines zweiten Drehbewegungsermittlungssignals, das im Anschluss an das erste Drehbewegungsermittlungssignal ankommt, mißt, eine zweite Zeitdauer auf der Grundlage des zweiten Drehbewegungsermittlungssignals und eines dritten Drehbewegungsermittlungssignals, das im Anschluss an das zweite Drehbewegungsermittlungssignal ankommt, mißt und die Verzögerungsgeschwindigkeit auf der Grundlage der ersten Zeitdauer und der zweiten Zeitdauer berechnet. Vorrichtung zur Steuerung eines intermittierenden Antriebs eines Motors nach Anspruch 1, wobei das Bremszeitberechnungsmittel eine Drehbewegungsgeschwindigkeit des Motors zur Zeit eines Bremsbeginns als eine der mittleren Geschwindigkeiten verwendet, die zur Berechnung der Verzögerungsgeschwindigkeit verwendet wird. Vorrichtung zur Steuerung eines intermittierenden Antriebs eines Motors nach Anspruch 2, wobei das Bremszeitberechnungsmittel eine erste und eine zweite mittlere Geschwindigkeit auf der Grundlage eines ersten und eines zweiten Ermittlungssignalpaares berechnet, die in einer Folge der Drehbewegungsermittlungssignale nicht aufeinanderfolgen, die Verzögerungsgeschwindigkeit auf der Grundlage der ersten und der zweiten mittleren Geschwindigkeit berechnet und eine Vielzahl von mittleren Geschwindigkeiten dadurch berechnet, daß ein Drehbewegungsermittlungssignal, das zwischen Drehbewegungsermittlungssignalen auftritt, die das erste Drehbewegungsermittlungssignalpaar bilden, als eines der Drehbewegungsermittlungssignale des zweiten Drehbewegungsermittlungssignalpaares verwendet wird. Vorrichtung zur Steuerung eines intermittierenden Antriebs eines Motors nach Anspruch 2, wobei das Bremszeitberechnungsmittel eine Drehbewegungsgeschwindigkeit des Motors zur Zeit eines Bremsbeginns als eine der mittleren Geschwindigkeiten verwendet, die zur Berechnung der Verzögerungsgeschwindigkeit verwendet wird. Vorrichtung zur Steuerung eines intermittierenden Antriebs eines Motors nach einem der vorhergehenden Ansprüche, ferner umfassend: ein Bremszeitkorrekturmittel zum Gleichsetzen des Bremszeitintervalls mit einem Wert, der um ein vorbestimmtes Zeitintervall länger ist als die vom Bremszeitberechnungsmittel berechnete Zeit, wenn ein Strom der gleichen Drehrichtung wie die vor Bremsbeginn erneut zugeführt wird, nachdem der Motor angehalten hat.
Anspruch[en]
An intermittent drive control apparatus of a motor comprising: motor drive means (24) capable of driving a motor intermittently by selectively supplying current of a forward rotation direction and current of a reverse rotation direction to the motor; rotation detection means (CFG) arranged to generate rotation detection signals at a frequency proportional to the speed of rotation of the motor; and braking time calculation means (31-35) arranged, when the motor drive means is controlled to supply the current of the reverse direction to the motor, thereby braking, and stopping the rotation of the motor, to measure the period of the rotation detection signals to calculate the speed deceleration rate of the motor, and to calculate the braking time between the start of braking and the stopping of the rotation of the motor based on the rotational speed of the motor at the time of braking start and the calculated speed deceleration rate, so that the motor drive means is controlled based on the calculated braking time, characterized in that the braking time calculation means is arranged to obtain the speed deceleration rate by calculating an average speed of each pair among a plurality of pairs of the rotation detection signals based on the period of each pair among the plurality of pairs of the rotation detection signals, and

until the plurality of rotation detection signals are obtained, the intermittent drive control apparatus is arranged to control the motor drive means based on the braking time interval calculated the last time the motor was braked.
An intermittent drive control apparatus of a motor according to Claim 1, wherein the braking time calculation means measures a first period based on a first rotation detection signal included in the rotation detection signals and a second rotation detection signal arriving subsequently to the first rotation detection signal, measures a second period based on the second rotation detection signal and a third rotation detection signal arriving subsequently to the second rotation detection signal, and calculates the speed deceleration rate based on the first period and the second period. An intermittent drive control apparatus of a motor according to Claim 1, wherein the braking time calculation means uses a rotational speed of the motor at the time of braking start as one of average speeds used for calculation of the speed deceleration rate. An intermittent drive control apparatus of a motor according to Claim 2, wherein the braking time calculation means calculates first and second average speeds based on first and second detection signal pairs which are not consecutive in a sequence of the rotation detection signals, calculates the speed deceleration rate based on the first and second average speeds, and calculates a plurality of average speeds by using one rotation detection signal occurring between rotation detection signals forming the first rotation detection signal pair as one of rotation detection signals of the second rotation detection signal pair. An intermittent drive control apparatus of a motor according to Claim 2, wherein the braking time calculation means uses a rotational speed of the motor at the time of braking start as one of average speeds used for calculation of the speed deceleration rate. An intermittent drive control apparatus of a motor according to any preceding claim, further comprising: braking time correction means for setting the braking time interval equal to a value which is longer than the time calculated by the braking time calculation means by a predetermined time interval, when re-supplying a current of the same rotation direction as that before braking start, after the motor has stopped.
Anspruch[fr]
Dispositif de commande d'entraînement intermittent d'un moteur comprenant: un moyen d'entraînement de moteur (24) capable d'entraîner un moteur par intermittence en fournissant sélectivement un courant d'une direction de rotation avant et un courant d'une direction de rotation arrière au moteur; un moyen de détection de rotation (CFG) disposé pour générer des signaux de détection de rotation à une fréquence proportionnelle à la vitesse de rotation du moteur; et un moyen de calcul de temps de freinage (31 à 35) disposé, lorsque le moyen d'entraînement de moteur est commandé pour fournir le courant de la direction inverse au moteur, freinant ainsi, et arrêtant la rotation du moteur, pour mesurer la période des signaux de détection de rotation et pour calculer la vitesse de décélération de vitesse du moteur, et pour calculer le temps de freinage entre le début de freinage et l'arrêt de la rotation du moteur sur la base de la vitesse rotationnelle du moteur au moment du début de freinage et la vitesse de décélération de vitesse calculée, pour que le moyen d'entraînement de moteur soit commandé sur la base du temps de freinage calculé, caractérisé en ce que le moyen de calcul de temps de freinage est disposé pour obtenir la vitesse de décélération de vitesse en calculant une vitesse moyenne de chaque paire parmi une pluralité de paires de signaux de détection de rotation sur la base de la période de chaque paire parmi une pluralité de paires de signaux de détection de rotation, et

jusqu'à ce que la pluralité des signaux de détection de rotation soient obtenus, le dispositif de commande d'entraînement intermittent est disposé pour commander le moyen d'entraînement de moteur sur la base de l'intervalle de temps de freinage calculé la dernière fois que le moteur avait freiné.
Dispositif de commande d'entraînement intermittent d'un moteur selon la revendication 1, dans lequel le moyen de calcul de temps de freinage mesure une première période sur la base d'un premier signal de détection de rotation compris dans les signaux de détection de rotation et un second signal de détection de rotation arrivant postérieurement au premier signal de détection de rotation, mesure une seconde période sur la base du second signal de détection de rotation et un troisième signal de détection de rotation arrivant postérieurement au second signal de détection de rotation, et calcule la vitesse de décélération de vitesse sur la base de la première période et de la seconde période. Dispositif de commande d'entraînement intermittent d'un moteur selon la revendication 1, dans lequel le moyen de calcul de temps de freinage utilise une vitesse rotationnelle du moteur au moment du début de freinage comme une des vitesses moyennes utilisées pour calculer la vitesse de décélération de vitesse. Dispositif de commande d'entraînement intermittent d'un moteur selon la revendication 2, dans lequel le moyen de calcul de temps de freinage calcule des première et seconde vitesses moyennes sur la base des première et seconde paires de signal de détection qui ne sont pas consécutives en séquence des signaux de détection de rotation, calcule la vitesse de décélération de vitesse sur la base des première et seconde vitesses moyennes, et calcule une pluralité de vitesses moyennes en utilisant un signal de détection de rotation se produisant entre les signaux de détection de rotation formant la première paire de signal de détection de rotation comme un des signaux de détection de rotation de la seconde paire de signal de détection de rotation. Dispositif de commande d'entraînement intermittent d'un moteur selon la revendication 2, dans lequel le moyen de calcul de temps de freinage utilise une vitesse rotationnelle du moteur au moment du début de freinage comme une des vitesses moyennes utilisées pour le calcul dé la vitesse de décélération de vitesse. Dispositif de commande d'entraînement intermittent d'un moteur selon l'une quelconque des revendications précédentes, comprenant en outre: un moyen de correction de temps de freinage pour régler l'intervalle de temps de freinage égal à une valeur qui est plus longue que le temps calculé par le moyen de calcul de temps de freinage d'un intervalle de temps prédéterminé, lors de la refourniture d'un courant de la même direction de rotation que celle avant le début de freinage, après que le moteur a été arrêté.






IPC
A Täglicher Lebensbedarf
B Arbeitsverfahren; Transportieren
C Chemie; Hüttenwesen
D Textilien; Papier
E Bauwesen; Erdbohren; Bergbau
F Maschinenbau; Beleuchtung; Heizung; Waffen; Sprengen
G Physik
H Elektrotechnik

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