Magnetic record reproducing apparatus

Abstract: A magnetic record reproducing apparatus capable of effecting higher tape transferring operation without causing the tape damages, and may provide the stable tape running operation even in the tape high speed transfer. The magnetic record reproducing apparatus is adapted to properly fetch the output signals from the head even at the high speed running operation so as to reproduce the normal images on the picture face of a television image receiving machine.

Description: The present invention relates to a tape driving apparatus comprising a capstan, a capstan motor, a capstan speed comparing circuit, a first rotational speed detector detecting the rotational speed of the capstan, and a reference signal generator for driving the capstan at a constant speed during recording and reproducing operation, a supply side reel, a winding side reel and coupling means for selectively coupling the supply side reel or the winding side reel with the capstan motor for fast rewind or fast forward operation. A tape driving apparatus of this kind and as defined in the preamble of claim 1 is known from JP-A-57062426. In recent years, in the field of video recorders efforts have been made to shorten the fast forwarding and fast unwinding time by higher winding speeds, and also efforts have been made to shorten the image producing time when switching between play, fast forward, rewind and stop positions. The present invention is particularly related to a capstan control which makes it possible to transfer the tape at high speed. Hereinafter, the operation of a capstan control as disclosed in JP-A-57062426 will be described. Fig. 1 is a block diagram showing the construction of the conventional rotary head type magnetic record reproducing apparatus such as servo mechanism of a VTR. In Fig. 1, a cylinder control apparatus is composed of a cylinder motor 1 having a rotary head (not shown), a first frequency detector 14 for detecting the rotation speed of the cylinder motor 1, a phase detector 15 for detecting the rotation phase of the cylinder motor 1, a cylinder speed comparing circuit 20 for detecting the errors with respect to the reference period of the output signal of the first frequency detector 14, a reference signal generator 24, a cylinder phase comparing circuit 21 for detecting the phase errors between the rotation phase signals to be obtained by the phase detector 15 and the reproducing reference signals to be obtained from the reference signal generator 24, a first adder 22 for mixing the phase error output of the cylinder phase comparing circuit 21 and the speed error output of the cylinder speed comparing circuit 20, a cylinder driving circuit 23 which is controlled by the output of the first adder 22 so as to drive the cylinder motor 1. A capstan control apparatus is composed of a capstan 3 which comes into pressure contact against the pinch roller 4 with a magnetic tape 7 being grasped to transfer the magnetic tape 7, a capstan motor 2 for driving the capstan 3 a second frequency detector 16 for detecting the rotation speed of the capstan motor 2, a control head 8 for recording, reproducing the control signals on the lower end of the magnetic tape 7, a capstan speed comparing circuit 25' for detecting the error with respect to the reference period of the output signal of the second frequency detector 16, a tracking shifting circuit 29 to be triggered by the output signals of the reference signal generator 24, a capstan phase comparing circuit 26 for detecting the phase errors between the reproducing control signal to be obtained from the control head 8 and the output signal of the tracking shifting circuit 29, a second adder for mixing the phase error output of the capstan phase comparing circuit 26 with the speed error output of the capstan speed comparing circuit 25', a capstan driving circuit 28 which is controlled by the output of the second adder 27 so as to drive the capstan motor 2. A magnetic tape driving apparatus is composed of a center pulley 9 to be rotated, driven through a belting 10 by the capstan motor 2, a supply side reel 5 and a winding side reel 6 with the magnetic tape 7 being wound around them, a supply side reel gear 12 and a winding side reel gear 13 for driving the respective reels, an idler 11 for transferring to either the supply side reel gear 12 or the winding side reel gear 13 the rotation of the center pulley 9 in accordance with the running direction of the magnetic tape 7. The VTR constructed hereinabove will be described in the operation at the normal reproducing time by the block diagram of Fig. 1 and the timing chart of the major portion shown in the Fig. 2. Reference character S1 of Fig. 2 is the output wave-forms of a reference signal generator 24 of Fig. 1. The signal is fed into the cylinder phase comparing circuit 21 and a tracking shifting circuit 29 as the reference signal at the reproduction time of the VTR. The trapezoidal wave signal of the S2 of Fig. 2 is of an internal wave form of the cylinder phase comparing circuit 21, is a phase reference signal of the cylinder motor 1 triggered by the rising edge of the reference signal of the S1 of Fig. 2, is sampled by the falling edge of the rotation phase signal to be obtained from the phase detector 15, namely, by the falling edge of the S3 of Fig. 2, is fed to the cylinder driving circuit 23 with the phase error signal (not shown) of the held cylinder motor 1 and the speed error signal to be obtained from the cylinder speed comparing circuit 20 being mixed by a first adder 22. Accordingly, the cylinder motor 1 is rotated in the phase synchronous relation with the reference signal of the S1 of Fig. 2. The S4 of Fig. 2 is of the output wave form of the tracking shifting circuit 29. The trapezoidal wave signal of the S5 of Fig. 2 is of an internal wave-form of the capstan phase comparing circuit 26, is a phase reference signal of the capstan motor triggered by the falling edge of the output signal of the tracking shifting circuit 29 of the S4 of Fig. 2, is sampled by the rising edge of the reproducing control signal to be obtained from the control head 8, namely, by the rising edge of the S6 of Fig. 2, is fed into the capstan driving circuit 28 with the phase error signal (not shown) of the held cylinder motor 2 being mixed by the second adder 27 with the speed error signal to be obtained from the capstan speed comparing circuit 25'. The capstan motor 2 is rotated in the phase synchronous relation with the output signal of the tracking shifting circuit 29 of the S4 of Fig. 2 with the reference signal of the S1 of Fig. 2 being shifted in phase. The capstan motor 2 is rotated in the phase synchronous relation with the output signal of the tracking shifting circuit 29 of the S4 of Fig. 2 with the reference signal of the S1 of Fig. 2 being shifted in phase. At the normal reproducing time of the VTR, the rotation head (not shown) mounted on the cylinder motor 1 and the reproduction control signal (Fig. 2, S6) are put into the phase synchronous relation, so that the rotation head is adapted to optimally follow the track recorded on the magnetic tape 7. The rotation of the capstan motor 2 is transferred into the center pulley 9 through the belt 10, is transferred into the winding side reel gear 13 at the normal reproducing time by an idler 11 to clockwise rotate the winding side reel 6 for winding up the magnetic tape 7, retaining the proper tension. At the time of the reverse reproduction of the review reproduction, the idler 11 falls onto the lefthand side to counterclockwise rotate the supply side reel 5, and winds up the tape with the tension of the magnetic tape 7 being retained so that the magnetic head (not shown) may properly trace the track recorded on the magnetic tape 7. In order to wind up the magnetic tape 7 at high speeds (hereinafter referred to as FF mode) or to unwind (hereinafter referred to as REW mode) it, the pinch roller 4 of Fig. 1 is isolated from the capstan 3 and winds up the magnetic tape 7 with the constant speed rotation of the capstan motor 2 at high speeds. In this case, the capstan phase comparing circuit 26 is made ineffective, the capstan motor 2 is controlled in speed with the capstan speed comparing circuit 25' only. The block diagram showing the inner construction of the capstan speed comparing circuit 25' in the conventional VTR of Fig. 1 is shown in Fig. 3. In Fig. 3, it is composed of a first counter 31 for counting the clock pulses (which are represented in CLK in Fig. 3), a first register 30 for fetching the digital outputs, a first timing generator 34 for outputting the various types of timing pulses in synchronous relation with the above described clock pulses in accordance with the rotation detecting signal (which is represented as CAFG in Fig. 3) which changes in period in accordance with the rotation speed of the capstan motor 2, an AND gate circuit 35 for masking the above described clock pulses, a first data register 33 for feeding the digital initial value with respect to the first counter 31. A capstan speed comparing circuit 25' constructed hereinabove will be described easily in its operation by the block diagram of Fig. 3 and the timing chart of the major essential portions shown in Fig. 4. The reference character A of Fig. 4 is a clock pulse to be inputted from the terminal 50 of Fig. 3, is a basic unit of a clock signal of the first counter 31, namely, the reference speed, is also a synchronizing signals of the above described various types of timing pulses. The reference character B of Fig. 4 is a rotation detecting signal to be inputted from the terminal 51 of Fig. 3, is inputted into the first timing generator 34 so as to compose the clock gate pulses of the C of Fig. 4, the latch pulses of the D of Fig. 4, the preset pulses of the E of Fig. 4. The digital initial value accommodated in the first data register 33 is preset in the first counter 31 with the preset pulse E. Immediately after it, the clock pulse A cut off in the AND gate circuit 35 by the clock gate pulse C is fed into the first counter 31. The first counter 31 starts its counting operation. The data showing the counting operation in analog are F' of Fig. 4 so as to fetch the digital values of the first counter 31 into the first register 30 by the latch pulse D to be generated by the arriving of the next rotation detecting signal B. The clock gate pulse C is adapted to stop the digital operation of the first counter 31 to retain the stable operation when the digital initial value is preset in the first counter 31 and when the digital value of the first counter 31 is fetched into the first register 30. The data F' fetched into the first register 30 are converted from the digital into analog, and are outputted. In order to make the operation point in the steady condition constant, the digital initial value (which is assumed to be NP0) to be accommodated in the first data register 33 so that the digital value to be fetched into the first register 30 may become a given value (which is assumed to be NF) when the capstan motor 2 is rotating at a set speed. Assume that the reference period of the rotation detecting signal B of the capstan motor 2 is To and the frequency of the clock pulse A is fck, and the digital initial value NP0 is obtained in the follow formula. NP0 = NF - fck X To In order to switch the set speed of the rotating member, the digital initial value NPO accommodated in the first data register 33 is changed or the rotation detecting signal B to be inputted into the timing generator 34 is divided in frequency to effect the inputting operation. The problem in the above described construction is that the tape speed changes in accordance with the tape winding diameter of the reel as the capstan motor 2 is controlled at speed in the capstan speed comparing circuit 25' only in the FF / REW mode for winding, unwinding the magnetic tape at high speeds. As the rotation speed of the capstan motor 2 is constant, the rotation speed of the winding side reel 6 in, for example, FF mode becomes constant. The more the tape is wound, the bigger the winding diameter becomes. The peripheral speed, namely, the tape speed increases, so that the speed of the tape trailing end become maximum. In order to prevent the tape damage at the stop time of the tape trailing end, a certain limit value is provided in the maximum speed. It cannot be set in the tape speed beyond it, namely, the capstan speed. Therefore, there is a problem in that the FF / REW time cannot be shortened. In the field of tape drives, particularly tape drives for video recorders with rotating heads, it is already known to drive the tape for recording and reproduction not by a capstan drive but by directly driving the take-up and supply reels. From JP-A-63247946 a magnetic recording and reproducing apparatus is known in which a reel motor is provided exclusively for driving each of the supply reel and the winding reel. Both reels are provided with speed detectors, and the sum of the squared values of the periods of the signals from the speed detectors are compared with a reference period provided by a reference generator. A control circuit controls the speeds of the supply reel and the winding reel in such a way that the tape speed is substantially constant. From EP-A-0 254 511 an apparatus for reproducing signals recorded on tape is known which works in a similar way as that of JP-A-63247946, i.e. there is no capstan drive for the tape but the tape speed is controlled to a substantially constant value by controlling the speed of a reel motor driving the supply and winding reels. However, in this known apparatus, the sum of the periods of the output signals of speed detectors at the supply and winding reels is compared with a reference value. It is an object of the present invention to provide a tape driving apparatus of the kind in which the tape is driven by a capstan drive during recording and reproduction, and which is capable of effecting a higher speed tape transferring operation without causing tape damage, and which provides a stable tape running operation even during high speed transfer. In accordance with the invention, a tape driving apparatus as defined in the preamble of claim 1 is characterized by a second rotational speed detector for detecting the rotational speed of the supply side reel and a third rotational speed detector for detecting the rotational speed of the winding side reel, the second and third rotational speed detectors being connected to the capstan speed comparing circuit to control the tape speed during fast rewind and fast forward operation to a constant value by modifying the period of the reference signal of the reference signal generator to such a value that the period sum, or the square sum, of the periods of the output signals of the second and third rotational speed detectors becomes a constant value. In a preferable embodiment of such a tape driving apparatus, the reference period total or the reference period square total of the speed signals from the supply side reel and the winding side reel is changed by the type (or length) of the tape. These and other features of the present invention will become apparent from the following description taken in conjunction with preferred embodiment thereof with reference to the accompanying drawings, in which; Fig. 1 is a block diagram showing the construction of the conventional VTR servo mechanism; Fig. 2 is a timing chart for illustrating the operation of the conventional VRT servo mechanism of Fig. 1; Fig. 3 is a block diagram showing the inner construction of a capstan speed comparing circuit in the conventional VTR servo mechanism of Fig. 2; Fig. 4 is a timing chart for illustrating the circuit operation of the conventional capstan speed comparing circuit; Fig. 5 is a block diagram showing the construction of the VTR servo mechanism using the capstan control apparatus in a first embodiment of the present invention; Fig. 6 is a block diagram showing the inner construction of a capstan speed comparing circuit in the capstan control apparatus of Fig. 5; Fig. 7 is a timing chart for illustrating the circuit operation of the capstan speed comparing circuit of Fig. 6; Fig. 8 is a model for illustrating the relation between the tape speed and the reel hub diameter; Fig. 9 is a block diagram showing the construction in a case where the capstan control apparatus of another embodiment of the present invention is realized by the use of a microcomputer; Fig. 10 is a timing chart for illustrating the circuit operation of the capstan control apparatus of Fig. 10; Fig. 11 (a), (b) are flow charts of the software mounted on the microcomputer in the capstan control apparatus of Fig. 9; Fig. 12 is a characteristic view showing the relationship between the tape winding diameter and the tape speed in the FF / REW mode of the capstan control apparatus of the present invention and the conventional embodiment; Fig. 13 is a characteristic view showing the relationship between the tape speed and the winding time in the FF / REW; and Fig. 14 is a flow chart showing the software essential portions in a case where the capstan control apparatus of the other embodiment of the present invention is realized by the use of the microcomputer. Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. Fig. 5 is a block diagram showing the construction of the VTR servo mechanism using the capstan control apparatus in a first embodiment of the present invention. In Fig. 5, in addition to the construction of the conventional example of Fig. 1, a third frequency detector 17 and a fourth frequency detector 18 for detecting the respective rotating speeds of the supply side reel 5 and the winding side reel 6 are added. The respective outputs are adapted to be inputted into a capstan speed comparing circuit 25 and a tape type discriminating circuit 89. Fig. 6 is a block diagram showing the inner construction of a capstan speed comparing circuit 25 of Fig. 5. In Fig. 6, in addition to the inner construction of the conventional capstan speed comparing circuit 25, it is composed of a second counter 32 which is adapted to set the output data of the first data register 33 by the preset pulse (in Fig. 6, it is represented by PR) to be inputted from the terminal 53, to count second clock pulses (in Fig. 6, they are represented as CLK2) to be inputted from the terminal 52, and to feed the digital output into a first counter 31, a third counter 40 for counting the clock pulses (in Fig. 6, they are represented as CLK) to be inputted from the terminal 47, a second register 39 for fetching the digital output thereof, a second timing generator 42 which is inputted from a terminal 48, and is adapted to output in synchronous relation with the above described clock pulses the various types of timing pulses in accordance with a rotation detecting signal (in Fig. 6, it is represented as SREL) where the period changes in accordance with the rotation speed of the supply side reel 5, an AND gate circuit 41 for masking the above described clock pulses, a fourth counter 44 for counting the above described clock pulses, a third register 43 for fetching the digital output, a third timing generator 46 which is inputted from a terminal 49, and is adapted to output in the synchronous relation with the above described clock pulse the various types timing pulses in accordance with the rotation detecting signal (in Fig. 6, it is represented as TREL) where the period changes in accordance with the rotation speed of the winding side reel 6, an AND gate circuit 45 for masking the above described clock pulses, an adder 38 for adding the data of a second register 39 and a third register 43, a comparator 37 for comparing the size between the adding output and the output data of the second data register 36 so as to instruct the counting direction (UP/DOWN) of the second counter 32 in accordance with the results thereof. The capstan speed comparing circuit constructed as hereinabove will be described in its operation with reference to a block diagram shown in Fig. 6 and a timing chart of the major portions shown in Fig. 7. Signals K and P of Fig. 7 are rotation detecting signals of the supply side reel 5 and the winding side reel 6 to be inputted from the terminal 48 and the terminal 49 of Fig. 6, are inputted respectively into the second, third timing generators 42, 46 to generate clock gate pulses L and Q, latch pulses M and R, reset pulses N and S as shown in Fig. 7. Third, fourth counters 40, 44 are reset by reset pulses N, S. Immediately after it, a clock pulse A from a terminal 47 cut off in the AND gate circuits 41, 45 are fed into third, fourth counters 40, 44 with the clock gate pulses L, Q, so that the third, fourth counters 40, 44 start their counting operation. Signals O and T of Fig. 7 show the period data which has fetched the digital values of the third, fourth counters 40, 44 into the second, third registers 39, 43 respectively by the latch pulses M, R to be caused by the arriving of the next rotation detecting signals K, P. Here the clock gates pulses L, Q are to stop the digital operation of the counter when the counter is reset and when the digital values of the counter is fetched into the register so as to retain the safe action. Signal J of Fig. 7 is a period total data where the period data O, T of the rotation detecting signals of the supply side reel 5 and the winding side reel 6 measured in the above described manner. Signal I of Fig. 7 is a control signal for instructing a counting direction, namely, count up / down / stop with respect to the second counter 32 in accordance with the results of the size comparison between the period total data and the reference period total data accommodated in the second data resister 36. Signal G of Fig. 7 is a clock pulse of the second counter 32 to be inputted from the terminal 52. Signal H of Fig. 7 is a counter output representing the count operation of the second counter 32 in analog. When the above described period total data is smaller than the reference period total by the given value or more, the tape speed is higher than the set speed. Therefore, an instruction of the count down is fed with respect to the second counter 32 so that the second counter 32 counts down the second clock pulse G to be inputted from the terminal 52. When the above described period total data is larger than the reference period total by a given value or more, the tape speed is lower than the set speed. Thereafter, the instruction of the count up is sent with respect to the second counter, so that the second counter 32 counts up the second clock pulse G to be inputted from the terminal 52. When the above described period total data stays within a certain given value of the reference period total, the tape speed is near the set speed. Therefore, the instruction of the count stop is set with respect to the second counter 32. the second counter 32, and does not count the second clock pulse G to be inputted from the terminal 52. Signals A through E of Fig. 7 are the same in the timing chart as signals A through E of Fig. 4 described in the conventional embodiment of Fig. 3. The clock gate pulse C, the latch pulse D and the preset pulse E are composed by the circuit detecting signal B of the above described capstan motor 2 to be inputted from the terminal 51. Signal F of Fig. 7 is a counter output showing in analog the count operation of the counter 31 of Fig. 1. The difference between it and F' of Fig. 4 is in that the counting initial value to be preset into a first counter 31 becomes the counting value of the second counter 32 each time the rotation detecting signal b of the capstan motor 2 arrives, and is converted into NP0→NP1→NP2→NP3 in the case of the present embodiment. As a result, the rotation speed of the capstan motor 2 is reduced smoothly as shown as signal B of Fig. 7, so that the rotation detecting signal period total of the reels on the supply side and the winding side are retained almost constant, and thus, the tape speed is also controlled constantly. Since the period period is constant, Ts + Tt = K wherein Ts is a rotation detecting signal period of the supply side reel 5, Tt is a rotation detecting signal period of the winding side reel 6, K is a period total constant. In the case of, for example, FF mode, the winding side reel 6 is driven by the capstan motor 2. Assume that the capstan motor 2 is rotating at a certain constant speed, and the rotation detecting signal period Tt of the winding side reel 6 becomes also constant, the supply side reel 5 is accelerated as the tape is wound, the rotation detecting signal period Ts of the supply side reel 6 is reduced. Accordingly, in order to satisfy the relation of the above described (2) formula, the rotation detecting signal period Tt of the winding side reel 6 is increased larger. Namely, the speed of capstan motor 2 is decreased. The output data of the above described second data register 36, namely, the reference period total is required to be switched in accordance with the discrimination results by the tape type discriminating circuit 89 of Fig. 5. This is because the tape speed becomes different in accordance with the type of the tape unless the reference period total is varied by the length of the wound tape. The above described tape type discriminating circuit 89 obtains the tape area by the rotation detecting signal period of both the reels in the tape speed constant condition, such as at the recording time or the normal reproducing time. Fig. 8 is a model view for illustrating the relation between the tape speed and the reel hub diameter. In the drawing, Vt is a tape speed (m/s), r is a hub diameter (m) of a reel, Rs and Rt show respectively a radius (m) up to the tape outer periphery wound around a S reel and a T reel, Ss and St show the area (m 2 ) including the tape wound around the S reel and the T reel, and the reel hub, Ws and Wt show respectively the rotation angle speed (rad/sec) of the S reel and the T reel. The angle speeds Ws and Wt may be obtained by the rotation detecting signal periods Ts and Tt of both the reels. Rs and Rt are expressed by the following formula. Rs = Vt / Ws, Rt = Vt / Wt Thus, the tape overall area S of the reel hub including the reel hub equivalent to the length of the tape is shown in the following formula. S = Ss + St = π (Rs 2 + Rt 2 ) There are several types in the length of the tape. If the overall area S of the various types of tape is obtained in advance, it can be discriminated how many minutes this tape, which is being wound at present, can be used. In recent years, speed control apparatus for rotating members by software servo technique using the microcomputers have been proposed. Fig. 9 is another embodiment of the present invention showing a construction where the input capturing circuit of the above described various types of rotation detecting signal is added to a microcomputer. Fig. 9 shows a microcomputer 61, a free run counter 54 for counting clock pulses to be inputted from a terminal 50, a first flag 56, a second flag 57, a third flag 58, ..., a fourth flag 59 showing that the various types of rotation detecting signals to be inputted from the terminals 51, 48, 49, ..., 60 have been inputted, a first register 30, a second register 39, a third register 43, ..., a fourth register 55 for fetching the count values of the free run counter 54 when the above described respective types of rotation detecting signals have been inputted. The first register 30, the second register 39, the third register 43 are respectively the same as the registers in the embodiment of Fig. 6. What are inputted from the terminal 60 are, for example, the rotation speed detecting signals of the above described cylinder motor 1, the rotation phase signals or the above described reproduction control signals, and are required in a case reproduction control signals, and are required in a case where the servo function of the whole VTR is realized by the microcomputer 61 although the description is omitted in the present embodiment. Fig. 10 is a timing chart of the major portions of Fig. 9. The operation of Fig. 9 will be described with the use of Fig. 10. Signal A of Fig. 10 is inputted from the terminal 50, and is clock pulses to be counted by the free run counter 54. Signal U of Fig. 10 shows the counting operation of the free run counter 54, and is represented in analog form. Signals B, K, P of Fig. 10 are respectively the rotation detecting signals of the capstan motor 2, the supply side reel 5, the winding side reel 6 to be inputted from the terminals 51, 48, 49. Signals V, X, Y of Fig. 10 are the output signals of the first flag 56, the second flag 57, the third flag 58. They are set by the rising edges of the above described each rotation detecting signal B, K, P and are reset by the software program ( to be described later) of the microcomputer 61. Signals W, O, T of Fig. 10 are the period data to be outputted from the first register 30, the second register 39, the third register 43 which have fetched the digital values of the freerun counter 54 when the rising edges of the respective rotation detecting signals B, K, P have been inputted. In order to measure the rotation detecting signal period, it can be obtained by the calculation of the difference through the comparison with respect to the period data at the previous edge arriving time by the software program (to be described later) of the microcomputer 61. Fig. 11 (a), (b) are flow charts in a case where the present invention has been realized by the software program of the microcomputer 61. Three starts of the flow charts of Fig. 11 (a), (b) are sub-routine processing starts by the flag sense in the interrupt processing by the set of the first flag 56, the second flag 57, the third flag 58 of Fig. 9 or in the main processing. The branch 62 of Fig. 11 (a) discriminates whether or not the rotation detecting signal B of the capstan motor 2 has reached by the output condition of the first flag 56 of Fig. 9. If it has reached, it moves to the processing block 63 so as to effect the speed error computing operation. The speed error computing operation obtains the difference between the first register value which is the arriving time of the rotation detecting signal B and the expectation value computed in advance in accordance with the the previous arriving time and the reference period. The above described expectation value will be described later in detail. Then, it is judged whether or not the speed error obtained in the branch 64 is within the measuring range. If it stays within the measuring range in the processing block 65 or 66, it is outputted as it is. If it stays beyond the measuring range, the maximum or minimum output is outputted. In the processing block 67, the arriving expectation value of the next rotation detecting signal B is computed. It is obtained by the addition of the calculation value equivalent to the reference period and the speed modulating value into the first register value which is the arriving time of the present rotation detecting signal B. If it does not stay in the branch 62, it moves to the branch 68 so as to check whether the rotation detecting signal B does not arrive for the given time or more by the timer (not shown) built in in the microcomputer 61. If the signal does not arrive, the acceleration instructions are outputted in the processing block 69 so as to solve the problem at the starting time of the capstan motor 2. It is judged whether or not the mode is the FF / REW mode in the branch 70. If the mode is not the FF / REW mode, the above described modulation value is cleared to zero by the processing block 71. The branch 72 of Fig. 11 (b) discriminates whether or not the rotation detecting signal K of the supply side reel 5 has arrived by the output condition of the second flag 57 of Fig. 9. If the signal has arrived, it moves into the processing block 73 so as to effect the period computing operation of the rotation detecting signal K. Namely, the difference between the second register value which is the arriving time of the rotation detecting signal K and the previous arriving time is obtained. The branch 74 discriminates whether or not the rotation detecting signal P of the winding side reel 6 has arrived by the output condition of the third flag 58 of Fig. 9. If the signal has arrived, it moves to the processing block 75 so as to effect the period computing operation of the rotation detecting signal P is effected. Namely, the difference between the third register value which is the arriving time of the rotation detecting signal P and the previous arriving time is obtained. The period total of the rotation detecting signals K and P of the supply side reel 5 and the winding side reel 6 is obtained by the processing block 76 so as to effect the size comparison with the reference period total in the branch 77. When the measured period total is larger by a or more than the reference period total, it moves to the processing block 78 so as to subtract the A only from the present modulation value for having it as the new modulation value. When the measured period total is smaller by a or more than the reference period total, it moves to the processing block 79 so as to add the a only from the present modulation value for having it as the new modulation value. When the measured period total is within the a of the reference period total, the present modulation value is retained. The same operation as in the capstan control apparatus in the embodiment of the above described Fig. 6 is realized by the above described flow. Although the number of the pulses of the rotation detecting signals per rotation of both the reels is the same in the present embodiment, the correction thereof is required in accordance with the pulse number ratio when the pulse number is different in the period total computation of the adder 38 of Fig. 2 and the processing block 76 in the flow chart of Fig. 11 (b). Assume that the above described pulse number ratio of the supply side reel 5 and the winding side reel 6 is (m : n), and the above described period total calculation is to become as follows. m · Ts + n · Tt = K Fig. 12 shows the relationship between the tape winding diameter and the tape speed in the FF / REW mode. line b of Fig. 12 is that in the conventional capstan control apparatus, where the tape speed increases steadily through the tape winding diameter. In the capstan control apparatus of the present invention dotted line a of Fig. 12 shows that the tape speed becomes constant independently of the tape winding diameter. Fig. 13 shows the time changes of the tape speed in the FF / REW. The winding time may be considerably shortened as compared with the conventional embodiment. Fig. 14 is a flow chart showing the essential portions in the other embodiment realized by software program in the microcomputer 61. The starting shows the sub-routine processing starting by the flag sense in the interrupt processing by the sets of the second flag 57, the third flag 58 of Fig. 9 or in the main processing. In Fig. 14, the branch 81 discriminates whether or not the rotation detecting signal K of the supply side reel 5 has arrived by the output condition of the second flag 57 of Fig. 9. If the signal has arrived, it moves into the processing block 82 so as to effect the period computing operation of the rotation detecting signal K. Namely, the difference between the second register value which is the arriving time of the rotation detecting signal K and the previous arriving time is obtained. The branch 83 discriminates whether or not the rotation detecting signal P of the winding side reel 6 has arrived by the output condition of the third flag 58 of Fig. 9. If the signal has arrived, it moves to the processing block 84 so as to effect the period computing operation of the rotation detecting signal P. Namely, the difference between the third register value which is the arriving time of the rotation detecting signal P and the previous arriving time is obtained. The period square total of the rotation detecting signals K and P of the supply side reel 5 and the winding side reel 6 is obtained by the processing block 85 so as to effect the size comparison with the reference value in the branch 86. When the measured period square total is larger by a or more than the reference value, it moves to the processing block 87 to subtract the A only from the present modulation value for having it as the new modulation value. When the measured period square total is smaller by a or more than the reference value, it moves to the processing block 88 so as to add A only to the present modulation value for having it as the new modulation value. When the measured period square total is within a of the reference value, the present modulation value is retained. The above described capstan motor 2 is controlled in speed by the above described software processing so that the square total of the rotation detecting signal period of both the reels may become constant. Namely, since the period square total is constant, Ts 2 + Tt 2 = K wherein the rotating detecting signal period of the supply side reel is Ts (1/s), the rotation detecting signal period of the winding side reel is Tt (1/s), the K is a constant. Rs = V · N · Ts / (2π) Rt = V · N · Tt / (2π) wherein the tape speed is V (m/s), the supply side tape winding diameter is Rs (m), the winding side tape winding diameter is Rt (m), the pulse number of the rotation detecting signal per rotation in the supply side reel and the winding side reel. When they are respectively substituted into the (4) formula, (4π / V 2 N 2 ) · (πRs 2 + πRt 2 ) = K The second parenthesized passage on the left side of the (7) formula shows the whole tape area (which is assumed to be S (m 2 )) including both the reels, and is constant independently of the tape winding diameter. Accordingly, the tape speed V becomes a constant speed to be obtained by V = (4π · S/N 2 · K ) 1/2 In the present embodiment, the pulse number of the rotation detecting signal per rotation of both the reels is the necessary. If it is different, the correction is necessary in the period square calculation of the processing block 85 in the flow chart of Fig. 14 in accordance with the pulse number ratio. For example, if the above described pulse number ratio between the supply side reel 5 and the winding side reel 6 is (m : n), the above described period square total computing operation becomes as follows. m · Ts 2 + n · Tt 2 = K

Claims: A tape driving apparatus comprising a capstan (3), a capstan motor (2), a capstan speed comparing circuit (25), a first rotational speed detector (16) detecting the rotational speed of the capstan (3), and a reference signal generator (24) for driving the capstan (3) at a constant speed during recording and reproducing operation, a supply side reel (5), a winding side reel (6) and coupling means (9-13) for selectively coupling the supply side reel (5) or the winding side reel (6) with the capstan motor (2) for fast rewind or fast forward operation, characterized by a second rotational speed detector (17) for detecting the rotational speed of the supply side reel (5) and a third rotational speed detector (18) for detecting the rotational speed of the winding side reel (6), the second and third rotational speed detectors (17,18) being connected to the capstan speed comparing circuit (25) to control the tape speed during fast rewind and fast forward operation to a constant value by modifying the period of the reference signal of the reference signal generator (24) to such a value that the period sum, or the square sum, of the periods of the output signals of the second and third rotational speed detectors (17,18) becomes a constant value. A tape driving apparatus in accordance with claim 1, wherein the reference period total or the reference period square total is changed by the type (length) of the tape (7).

Inventors: KASHIRO TAKAO, NAKAMURA KENJIRO, OHTA YUTAKA, KASHIRO, TAKAO, NAKAMURA, KENJIRO, OHTA, YUTAKA
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: G11B15
IPC codes: H04N5, G11B15