Method for controlling the tape speed of a tape recorder without capstan and pinch roller

Abstract: A recording and/or reproducing apparatus which includes no pinch roller and no capstan and wherein the converging time to a rated speed upon starting of feeding of a tape can be reduced and the tape can be fed stably at the rated speed during recording and/or reproduction of the tape is disclosed. A rotary encoder for detecting a period of rotation is disposed between a recording and/or reproducing head and a take-up side reel, and a deviation from a predetermined reference value is calculated from the period of rotation detected by the rotary encoder. The reel motor is controlled on the basis of the average of stored deviation values once a certain number of deviation values have been calculated.

Description: This invention relates to a method of controlling a recording and/or reproducing apparatus for a recording medium in the form of a tape, and more particularly to a recording and/or reproducing apparatus of the reel drive type wherein the speed of rotation of a reel is controlled to feed a recording medium in the form of a tape at a fixed speed. Recording and/or reproducing apparatus wherein, for example, a magnetic tape accommodated in a tape cassette housing or an open reel tape is employed as a recording medium are spread widely. In the recording and/or reproducing apparatus, normally a capstan and a pinch roller are contacted with a magnetic tape and the speed of rotation of the capstan is controlled to rotate at a fixed speed to feed the magnetic tape at a fixed speed. In order to realize feeding of the tape at a fixed speed in a recording and/or reproducing apparatus of the reel drive type, it is one of possible measures to detect the speed of feeding of the tape and perform velocity servo control of a reel motor in response to the detected speed. A suitable one of means to detect the tape feeding speed involves employment of a rotary encoder having a roller which contacts with and is rotated by the tape when the tape is fed. By the way, in a recording and/reproducing apparatus of the reel drive type, when the take-up side reel (reel spindle meshed with the take-up side reel) is driven to rotate at a fixed speed, the diameter of the tape wound on the reel varies gradually, and consequently, the load to the tape varies and the tape feeding speed varies. While depending upon the length of the tape, the tape feeding speed immediately before the tape is taken up completely sometimes varies, for example, by two times or more comparing with that immediately after feeding of the tape is started from its starting end. Accordingly, even where a same recording medium is used, it is not compatible both with recording and/or reproducing apparatus of the reel drive type and recording and/or reproducing apparatus of the capstan type, which are spread widely at present. Further, a recording and/or reproducing apparatus of the reel drive type is not suitable as a recording and/reproducing apparatus for which fidelity in sound quality is required since the frequency characteristic and the S/N (signal to noise) ratio are varied from the starting end to the last end of the tape by the variation of the tape feeding speed. From those reasons, recording and/or reproducing apparatus of the reel drive type have a problem in that they are not suitable for practical use while they have an advantage in that they are simplified in construction due to absence of a capstan. For example, a recording and/or reproducing apparatus is disclosed in JP-A-3-134848 wherein a rotating roller is contacted with a magnetic tape and a reel is driven in response to the difference between a period of rotation of the rotating roller and a reference period of rotation for the rotating roller without using a capstan and a pinch roller. Two controllers are used depending whether the tape is slow or fast moving. This document is used for the delimitation of appended claims 1 and 2. When the tape stops, naturally a reel must stop, and therefore, in order to realize fixed speed feeding of the tape with a recording and/reproducing apparatus of the reel drive type, upon starting feeding of the tape, rotation of the reel must be raised rapidly to the speed for fixed speed rotation. However, it is not possible for the reel to continue, also when the recording and/or reproducing apparatus is in a stopping condition, its rotation at a fixed speed like a capstan, and from the necessity for the rising operation, much time is required until feeding of the tape reaches the predetermined speed. This gives rise to such serious problems as failure in recording at a starting end and a variation in musical interval upon reproduction. Further, even during recording or reproduction, when the tape feeding speed is displaced by a significant amount from the predetermined speed, much time is required for recovery, resulting in such problems as failure in recording at a starting end and a variation in musical interval upon reproduction. Further, when it is tried to realize fixed speed feeding of the tape with a recording and/or reproducing apparatus of the reel drive type, it is one of available measures to detect the tape feeding speed and control the speed of rotation of the reel motor by servoing control. However, the tape feeding speed is not always detected precisely due to vibrations applied to the apparatus from the outside, a momentary variation of the operating voltage or an influence of irregularity in thickness, wrinkles and so forth of the magnetic tape. Thus, it is a problem that rotation of the reel motor is liable to be placed out of control by an error in detection of the tape feeding speed arising from some of the factors just described. Accordingly, it is difficult to realize fixed speed feeding making use of a rotational servo mechanism. One of possible means for detecting the tape feeding speed involves a rotary encoder having roller which contacts with and is rotated by the tape so that pulses are generated from the rotary encoder. In this instance, where the rotary encoder is constructed so as to generate a large number of pulses during one rotation of the roller, a high resolution is obtained so that information of the tape feeding speed is obtained at a short interval of time and servoing control of a high responsibility is obtained. However, the construction requires a large size for the tape feeding speed detecting means and particularly for the roller and the pulse generating means, which is not preferable. On the other hand, where the rotary encoder is constructed so as to generate one pulse or a small number of pulses for one rotation of the roller, reduction in size of the tape feeding speed detecting means can be achieved, but since information of the tape feeding speed can be obtained only at a comparatively long interval of time, servoing control of a high responsibility cannot be achieved and a delay in servoing control may be resulted. Further, even during recording or reproduction, when the tape feeding speed is displaced by a significant amount from the predetermined speed, much time is required for recovery, resulting in such problems as failure in recording at a starting end and a variation in musical interval upon reproduction. Furthermore, when the speed is detected by means of the rotary encoder, a slip between the tape and the roller makes it difficult to detect the speed accurately. Accordingly, there is a problem in that it is difficult to achieve accurate servoing control. For example, if the back tension of the supply side reel is insufficient, the contacting pressure or the contacting area between the roller and the tape is rendered unstable so that a slip may be produced between the roller and the tape. On the other hand, when it is tried to obtain sufficient back tension of the supply side reel to eliminate such a possible slip as described just above, then complication of the structure, increase of the torque of the take-up side reel and employment of a motor of a large size and a high power for such increase, increase of the power dissipation and so forth are involved. Further, a rise of the slip torque may result in damage to the tape. European patent application EP-A-0 538 959 and the abstract of JP-A-59-124 054 both disclose a method where a capstan is controlled. US patent US-A-5 012 989 discloses a method where tape velocity is controlled in a closed loop fashion and tape tension is controlled in an open loop fashion to provide an improved system. It is an object of the present invention to provide a recording and/or reproducing apparatus of the reel drive type which is high in responsiveness upon starting and high in accuracy in speed of feeding of a tape. It is another object of the present invention to provide a recording and/or reproducing apparatus of the reel drive type which assures stabilized feeding of a tape at a fixed speed. It is a further object of the present invention to provide a recording and/or reproducing apparatus of the reel drive type wherein a rise to a predetermined speed upon starting of feeding of a tape is performed rapidly. It is a still further object of the present invention to provide a recording and/or reproducing apparatus of the reel drive type which eliminates a reel motor from being placed out of servoing control in rotation by an error in detection of a feeding speed of a tape. According to the present invention, there is provided a controlling method for a reel motor of a recording and/or reproducing apparatus which includes no capstan and no pinch roller and wherein a rotatable member is contacted with a recording medium in the form of a tape to measure a period of rotation of said member and a reel is driven to rotate by a reel motor in accordance with the period of rotation thus measured, comprising the steps of: measuring a one rotation period of said member by rotation detection means; calculating a deviation of the one rotation period obtained at the measuring step from a predetermined rated period ; characterised by : successively storing the last n deviations obtained by the deviation calculating step, n being a natural number equal to or greater than 3; determining whether or not the number of stored deviations is smaller than n-1; either adding, if it is determined that the number of stored deviations is equal or greater than n-1, the values of the stored deviations except a maximum value and a minimum value of them and dividing the sum value obtained by the addition by n-2 to obtain an average value; or adding, if it is determined that the number of stored deviations is smaller than n-1, all of the stored deviations and dividing the sum value obtained by the addition by the number of stored deviations to obtain an average value; calculating a servo control value in accordance with the average value thus obtained; storing the thus calculated servo control value; converting the stored servo control value into a PWM signal; and controlling driving of said reel motor in response to the PWM signal obtained by the conversion step. With the method of the invention since a servo control value is calculated in accordance with part or all of the last n deviations, an error caused by an influence of a disturbance or the like which may be had on the deviation can be cancelled. The present invention will be further described by way of example in the following description, taken in conjunction with the accompanying drawings in which like parts or elements are denoted by like reference characters, and in which:- Fig. 1 is a block diagram of a recording and/or reproducing apparatus showing the principles of the present invention; Fig. 2 is a flow chart illustrating operation of the recording and/or reproducing apparatus of Fig. 1; Figs. 3(a) and 3(b) are time charts showing output signals of a rotary encoder and a waveform shaping circuit of the recording and/or reproducing apparatus of Fig. 1; Fig. 4 is a block diagram of a recording and/or reproducing apparatus which operates according to a first preferred embodiment of the present invention; Fig. 5 is a flow chart illustrating operation of the recording and/or reproducing apparatus of Fig. 4; Fig. 6 is a block diagram of a recording and/or reproducing apparatus which operates according to a second preferred embodiment of the present invention; Fig. 7 is a flow chart illustrating operation of the recording and/or reproducing apparatus of Fig. 6; Fig. 8 is a schematic view of a reel drive structure of a recording and/or reproducing apparatus to which the present invention is applied; Fig. 9(a) is a perspective view showing a mounted condition of a rotary encoder in a recording and/or reproducing apparatus to which the present invention is applied, Fig. 9(b) is a partial perspective view of a roller of the rotary encoder, and Fig. 9(c) is a diagrammatic view schematically showing an electric construction of the rotary encoder; Figs. 10(a) and 10(b) are schematic sectional views illustrating a detecting operation of the rotary encoder shown in Figs. 9(a) to 9(c); Figs. 11 to 27 are perspective views showing different mechanical arrangements of a magnetic head or heads and a rotary encoder in a recording and/or reproducing apparatus to which the present invention can be applied; Fig. 28 is a schematic plan view of a compact cassette tape; and Fig. 29 is a schematic plan view of a micro cassette tape. Referring first to Fig. 1, there is shown, for reference, in block diagram a recording and/or reproducing apparatus. A magnetic tape 1 is wound on a supply reel 2 and a take-up reel 3 and accommodated in a body of a tape cassette not shown. The magnetic tape 1 is loaded in position and fed in the recording and/reproducing apparatus when a recording and/or reproducing operation for audio information or the like is performed by a magnetic head 10. The magnetic tape 1 is fed when the take-up reel 3 is driven to rotate by a reel motor 11. Referring also to Fig. 8, rotation of the reel motor 11 is transmitted to a flywheel 13 by way of a belt 19 so that a drive shaft 14 provided on the flywheel 13 is rotated. A take-up reel receiver 15 is held in contact with the drive shaft 14 by way of a rubber belt 16 provided on a circumferential face of the take-up reel receiver 15. Consequently, when the drive shaft 14 rotates, the take-up reel receiver 15 is rotated by the drive shaft 14 to rotate a reel driving shaft 17 mounted on the take-up reel receiver 15. Then, when the tape cassette 4 is loaded in position as indicated by a broken line in Fig. 8, a hub of the take-up reel 3 is engaged with the reel driving shaft 17, and consequently, the take-up reel 3 is rotated by the reel driving shaft 17 to feed the magnetic tape 1. The supply reel 2 has a reel shaft 18 thereon. A rotary encoder 12 is provided in order to detect the feeding speed of the magnetic tape 1 and includes a roller 12a, a shutter plate 12b provided on the roller 12a, a photo-diode 12c serving as a light outputting element, and a phototransistor 12d for detecting an optical output of the photo-diode 12c and converting it into an electric signal. Referring now to Figs. 9(a) to 9(c), the roller 12a is mounted for rotation on a frame 12e, and a photo-reflector 12f in the form of a single chip element including the photo-diode 12c and the phototransistor 12d is mounted on a base plate 12g below the roller 12a. The photo-reflector 12f has a window 12f 1 and another window 12f 2 formed therein so that light from the photo-diode 12 is outputted through the window 12f 1 while light to be detected by the photo-transistor 12d is admitted through the window 12f 2 . The shutter plate 12b is formed on a lower face of the roller 12a opposing to the photo-reflector 12f such that, when the angular position of the shutter plate 12b with respect to the photo-reflector 12f is varied by rotation of the roller 12a, light emitted from the photodiode 12c is admitted into the photo-transistor 12d or intercepted from entering the photo-transistor 12d. In particular, referring also to Figs. 10(a) and 10(b), the roller 12a and the shutter plate 12b are mounted for rotation around a shaft 12a 1 relative to the frame 12e, and accordingly, when the roller 12a is contacted with the magnetic tape 1 as shown in FIG. 1, as the magnetic tape 1 is fed, the roller 12a is rotated by the magnetic tape 1 and rotates the shutter plate 12b. Here, when the shutter plate 12b is at such a rotational position as shown in Fig. 10(a) relative to the photo-reflector 12f, light emitted from the photo-diode 12c and outputted through the window 12f 1 is intercepted by the shutter plate 12b, and consequently, it is not detected by the photo-transistor 12d. On the other hand, when the shutter plate 12b is at another rotational position as shown in Fig. 10(b) relative to the photo-reflector 12f, light emitted from the photo-diode 12c and outputted through the window 12f 1 is not intercepted by the shutter plate 12 and is introduced into the phototransistor 12d through the window 12f 2 . Accordingly, admission or non-admission of light into the photo-transistor 12d is repeated each time the roller 12a rotates 1/4 rotation. Consequently, such a detection waveform as indicated, for example, by Fig. 3(a) is output from the phototransistor 12d. It is to be noted that the roller 12a has such a diameter that it rotates four rotations for one second when the magnetic tape 1 is fed at a rated speed (4.76 cm/sec with a compact cassette tape). Referring back to FIG. 1, a waveform shaping circuit 20 shapes the waveform of an output of the photo-transistor 12d, which may have some distortion, into a rectangular waveform. In particular, the waveform shaping circuit 20 has a predetermined threshold level having a hysteresis for the output Sa of the rotary encoder 12 of FIG. 3(a) and produces such a waveform shaped output Sb as seen from FIG. 3(b). A rotation time measurement section 21 calculates a time required for one rotation of the roller 12a. One rotation of the roller 12a corresponds to a period T in FIG. 3(b), that is, a period from the rising edge (or the falling edge) of a pulse to the rising edge (or the falling edge) of a second pulse next to the first pulse. A deviation calculation section 22 holds in advance therein information (hereinafter referred to as rated period information T ⊘25 ) of the period of one rotation of the roller 12a at a rated speed in feeding of the magnetic tape 1. It is to be noted that, since the roller 12a is rotated four rotations for one second when the magnetic tape 1 is fed at the rated speed, the rated period information T ⊘25 is 0.25 seconds. The deviation calculation section 22 calculates a deviation d using the rated period information T ⊘25 and the period T of an actual one rotation inputted thereto. In particular. the deviation d is calculated in accordance with the following equation: d = T - T ⊘25 T ⊘25 A gain coefficient generation section 23 outputs a coefficient K to be used for setting of a servo gain. It is to be noted that, when the coefficient K should always be kept equal to K = 1, the gain coefficient generation section 23 need not be provided. However, by setting the coefficient K to a predetermined value, the servo gain can be set to a desired value and the responsiveness of a servoing operation which will be hereinafter described can be set arbitrarily. A control constant generation section 24 generates a control constant A calculated in accordance with a functional expression between a range of speed of rotation of the reel motor 11 and a servo control value L which will be hereinafter described. The control constant A is used to obtain a servo control value L which appropriately coincides with the range of variation of rotation of the reel motor 11, and accordingly, the control constant A is a fixed value peculiar to the apparatus. The control constant A is calculated in accordance with the following equation: A = (L MAX - L MIN ) * N MIN N MAX - N MIN where N MAX is a speed of rotation of the reel motor 11 at the starting end of the magnetic tape 1. N MIN is a speed of rotation of the reel motor 11 at the last end of the magnetic tape 1. L MAX is a servo control value at the starting end of the magnetic tape 1, and L MIN is a servo control value at the last end of the magnetic tape 1. The recording and/or reproducing apparatus further includes a control output calculation section 25 for calculating and outputting a servo control value L N , and an output storage section 26 for storing the servo control value L N output from the control output calculation section 25 and supplying the servo control value L N to a data conversion section 27 which will be hereinafter described. The servo control value L N supplied to the output storage section 26 is stored as a servo control value L in the output storage section 26, and the servo control value L is fed back as a servo control value in a preceding control cycle to the control output calculation section 25 and used for calculation of a servo control value L N . The control output calculation section 25 calculates, using the deviation d, the gain coefficient K, the control constant A and the servo control value L thus fed back, a servo control value L N for a current control cycle in accordance with the following expression: L N = L + d * A * K The data conversion section 27 converts the servo control value L supplied thereto from the output storage section 26 into a reference value for a servoing operation. For example, the data conversion section 27 converts the servo control value L into a resistance value, a voltage value, a pulse width or a pulse period corresponding to the servo control value L. In the present embodiment, the servo control value L is converted into a PWM (pulse width modulation) signal having a corresponding "L period" (period of a low level) with respect to a fixed "H period" (period of a high level). Accordingly, the servo control values L MAX and L MIN used for calculation of the control constant A described above represent the pulse widths of an "L period" of the PWM signal at the starting end and the last end of the magnetic tape 1. A motor servo circuit 28 converts the PWM signal supplied thereto, for example, into a voltage value or a resistance value and supplies a servo output EM to the reel motor 11 so that the voltage value or resistance value obtained by the conversion may coincide with a drive voltage value (or resistance value) fed back thereto from the reel motor 11 to control driving of the reel motor 11 so as to minimize the deviation d. In the recording and/or reproducing apparatus of the present embodiment having such a construction as described above, servoing control is performed so that the speed of rotation of the reel motor 11 may be kept substantially constant while the magnetic tape 1 is fed from the starting end to the last end thereof. A servoing operation for the speed of rotation of the reel motor 11 is illustrated in the flow chart of FIG. 2. Referring to FIGS. 1 and 2, when the magnetic tape 1 is fed, the roller 12a is rotated by the magnetic tape 1, and thereupon, rotational speed information Sa is outputted from the rotary encoder 12 to the waveform shaping circuit 20 and a waveform shaped output Sb is outputted from the waveform shaping circuit 20. In response to the waveform shaped output Sb, a one rotation period T of the roller 12a is measured by the rotation time measurement section 21 (step F101). Then, using the one rotation period T, a deviation d is calculated in the deviation calculation section 22 as described above, and the deviation d is supplied to the control output calculation section 25 (step F102). The control output calculation section 25 calculates a servo control value L N for a current control cycle from the deviation d, a gain coefficient K, a control constant A and another servo control value L in a preceding control cycle (step F103), and supplies the servo control value LN to the output storage section 26 so that it may be stored into the output storage section 26 (step F104). The servo control value L thus stored is converted into a PWM signal by the data conversion section 27 (step F105), and in response to the PWM signal, the motor servoing circuit 28 develops a servo output EM to control driving of the reel motor 11 (step F106). The sequence of operations described above is repeated, and as the operations proceed, the speed of rotation of the reel motor 11 decreases gradually in accordance with the diameter of the magnetic tape 1 wound on the take-up reel 3 while the feeding speed of the magnetic tape 1 is kept substantially constant. Referring now to Fig. 4, there is shown in block diagram a recording and/or reproducing apparatus according to a first preferred embodiment of the present invention. In the recording and/or reproducing apparatus of the present embodiment, the control output calculation section 25 calculates a servo control value L N for a current control cycle using a deviation d AV , a gain coefficient K, a control contact A and a servo control value L fed back thereto. The servo control value L N is calculated in accordance with a modified equation to the equation (3) given hereinabove wherein the deviation d is replaced by d AB . The recording and/reproducing apparatus includes a deviation storage section 32 for storing last five deviations calculated by the deviation calculation section 22. In particular, the deviation storage section 32 holds a deviation d for a current control cycle as d 1 and holds deviations d calculated in last four control cycles as deviations d 2 to d 5 . The holding operation can be realized, for example, by means of data control based on an address shift of a memory area or by constituting the deviation storage section 32 from a shift register. An output selection section 33 selects three of the deviations d 1 to d 5 stored in the deviation storage section 32 except those which have the highest and lowest values among them, and outputs the selected three deviations. It is to be noted that, when a total of five deviations are not stored in the deviation storage section 32 as yet upon starting of feeding of the magnetic tape 1, the discrimination for the highest and lowest values is not performed, but the output selection section 33 outputs three or less deviations stored in the deviation storage section 32. An average value calculation section 34 calculates an average value d AV among three deviations supplied thereto from the output selection section 33. A controller 35 controls operation of the deviation storage section 32, the output selection section 33 and the average value calculation section 34. Particularly, the controller 35 controls the write/read address of the deviation storage section 32 so that a deviation d calculated newly is stored as a deviation d 1 into the deviation storage section 32, and thereupon, deviations held as deviations d 1 to d 4 are shifted so that they are thereafter held as deviations d 2 to d 5 . The controller 35 normally controls the output selection section 33 so that three deviations except two deviations which exhibit the highest and lowest values are outputted, but effects output selection control when the number of deviations stored in the deviation storage section 32 is smaller than 5. Further, the controller 35 controls the average value calculation section 34 so that the dominator for calculation of an average value is normally set to 5, but when the number of deviations stored in the deviation storage section 32 is smaller than 5, the denominator is set to 1 or 2 in accordance with the number of outputs of the output selection section 33. In the recording and reproducing apparatus of the present embodiment having such a construction as described above, the speed of rotation of the reel motor 11 is controlled by servoing control so that the feeding speed of the magnetic tape 1 may be kept substantially constant from the starting end to the last end of the magnetic tape 1. Then, since the average value d AV calculated by the average value calculation section 34 is used as the deviation d for calculation of a servo control value L N by the control output calculation section 25, even if a great error in detection of feeding of the tape is temporarily caused by a disturbance or the like, possible influence is cancelled or minimized. A servoing operation for the speed of rotation of the reel motor 11 is illustrated in Fig. 5. Referring to Fig. 5, when the magnetic tape 1 is fed to rotate the roller 12a so that rotational speed information Sa is output from the rotary encoder 12 to the waveform shaping circuit 20 and a waveform shaped output Sb is output from the waveform shaping circuit 20, a one rotation period T of the roller 12a is measured by the rotation time measurement section 21 (step F901). Then, a deviation d is calculated using the one rotation period T by the deviation calculation section 22 as described above (step F902). Here, deviations stored in the deviation storage section 32 are shifted under the control of the controller 35. In particular, the deviation d 4 is shifted to the deviation d 5 ; the deviation d 3 is shifted to the deviation d 4 ; the deviation d 2 is shifted to the deviation d 3 ; and the deviation d 1 is shifted to the deviation d 2 . Then, the deviation d newly calculated is fetched as the deviation d 1 into the deviation storage section 32 (steps F903 to F907). Accordingly, the last five deviations including the newly calculated deviation d are thereafter held in the deviation storage section 32. The controller 35 discriminates the number of stored deviations in the deviation storage section 32 (step F908), and if it discriminates that a total of five deviations are stored in the deviation storage section 32, then it sets the denominator of the calculation equation of the average value calculation section 34 to 3 (step F909) so that those three of the deviations d 1 to d 5 except those which exhibit the highest and lowest values among them are outputted from the output selection section 33. On the other hand, when the number of stored deviations is smaller than 5 as upon starting of feeding of the magnetic tape 1, the controller 35 sets the denominator for calculation of an average value in response to the number of stored deviations (step F911) so that a suitable deviation is outputted from the output selection section 33. For example, if the number of stored deviations is 1, then the denominator is set to 1 so that the deviation d 1 is outputted; if the number of stored deviations is 2, then the denominator is set to 2 so that the the deviations d 1 and d 2 are outputted; if the number of stored deviations is 3, then the denominator is set to 3 so that the deviations d 1 , d 2 and d 3 are output and if the number of stored deviations is 4, then the denominator is set to 3 so that the deviations d 2 , d 3 and d 4 are output. The average value calculation section 34 thus calculates an average value d AV of the deviations supplied thereto from the output selection sections 33 (step F913) and supplies it to the control output calculation section 25. The control output calculation section 25 calculates a servo control value L N for a current control cycle from the average value d AV of the relevant deviations, the gain coefficient K, the control constant A and the servo control value L in a preceding control cycle (step F914) and supplies and stores the servo control value L N to and into the output storage section 26 (step F915). The thus stored servo control value L is converted into a PWM signal by the data conversion section 27 (step F916), and the motor servo circuit 28 develops a servo output EM in response to the PWM signal to effect driving control of the reel motor 11 (step F917). The sequence of operations described above is repeated, and as the operations proceed, the speed of rotation of the reel motor 11 decreases gradually in accordance with the feeding position of the magnetic tape 1, that is, the diameter of the magnetic tape 1 wound on the take-up reel 3. Accordingly, the feeding speed of the magnetic tape 1 is kept substantially constant. Accordingly, a recording medium such as, for example, a compact cassette tape which is used with the recording and/or reproducing apparatus of the present embodiment is compatible with a recording and/or reproducing apparatus of the capstan type, and besides, the frequency characteristic and the signal to noise ratio are not fluctuated from the starting end to the last end of the magnetic tape and a recording or reproducing operation is achieved with fidelity. Furthermore, since a servo control value L N is calculated from an average value of the last five deviations except those which exhibit the highest and lowest values among them, even if a temporary error in detection of a speed (period) or the like is caused by some irregularity of the period of the roller 12 which is caused by an irregular thickness or a wrinkle of the magnetic tape so that the deviation d is increased to an excessively high value, this will not have an influence upon calculation of the servo control value L N . Consequently, the servoing control is stabilized and the stability in fixed speed feeding of the magnetic tape is improved. Referring now to Fig. 6, there is shown in block diagram a recording and/or reproducing apparatus according to a second preferred embodiment of the present invention. The recording and/or reproducing apparatus of the present embodiment is a modification to the recording and/or reproducing apparatus of the first embodiment shown in Fig. 4 in that a deviation d outputted from the deviation output section 22 and an average value d AV outputted from the average value calculation section 34 are selectively used to calculate a servo control value L N . To this end, a switching circuit 36 is provided additionally. The switching circuit 36 has a contact SW1 to which the output of the average value calculation section 34 is supplied, and another contact SW2 to which the output of the deviation output section 22 is supplied. The switching control of the switching circuit 36 is effected by the controller 35. Further, the denominator of the average value calculation equation of the average value calculation section 34 is fixed to 3. In short, the recording and/or reproducing apparatus of the present embodiment uses the deviation d as it is when the number of stored deviations in the deviation storage section 32 is smaller than 5. Accordingly, the servoing operation of the recording and/or reproducing apparatus is such as illustrated in the flow chart of Fig. 7. In the flow chart of Fig. 7, the processing at steps F1001 to F1007 is similar to the processing at steps F901 to F907 of Fig. 5 while the processing at steps F1013 to F1016 is similar to the processing at steps F914 to F917 of Fig. 5. respectively, and overlapping description of them will be omitted herein to avoid redundancy. Referring to Figs. 6 and 7 the controller 35 discriminates, at step F1008, the number of deviations stored in the deviation storage section 35, and if a total of five deviations are stored in the deviation storage section 35, then the controller 35 connects the switching circuit 36 to the contact SW1 (step F1009). Then, the output selection section 33 outputs three of the deviations d 1 to d 5 except those which exhibit the highest and lowest values among them (step F1010). Consequently, the average value calculation section 34 calculates an average value d AV (step F1012) and supplies it to the control output calculation section 25. In this instance, the control output calculation section 25 calculates a servo control value L N for a current control cycle from the average value d AV of the relevant deviations, the gain coefficient K, the control constant A and the servo control value L in a preceding control cycle (step F1013). On the other hand, when the number of stored deviations is smaller than 5 as at starting of feeding of the magnetic tape, the controller 35 connects the switching circuit 36 to the other contact SW2 (step F1011). Consequently, the deviation d outputted from the deviation calculation section 22 is supplied as it is to the control output calculation section 25. In this instance, the control output calculation section 25 calculates a servo control value L N for a current control cycle from the deviation d, the gain coefficient K, the control constant A and the servo control value L in a preceding control cycle (step F1013). The recording and/or reproducing apparatus of the present embodiment is advantageous, in addition to advantages similar to those of the recording and/or reproducing apparatus of the first embodiment, in that the averaging processing of deviations can be simplified. It is to be noted that the number of stored deviations of the deviation storage section is not limited to 5 in the first or second embodiment, and the number of deviations to be selected is not limited to the number of deviations except those which exhibit the highest and lowest values. Particularly where the number of stored deviations is sufficiently great, an average of all of stored deviations can cancel an influence of a temporary error in detection of a speed. The servo control system for a reel motor which employs the rotary encoder 12 as tape feeding speed detection means as described above will be described subsequently with reference to Figs. 11 to 27 which show different mechanical arrangements of the servo control system. As seen from Figs. 11 to 27, the magnetic head 10 (10a, 10b, 10c, 10a(F), 10a(R), 10b(F), 10b(R), 10c(F) and 10c(R)) and the rotary encoder 12 (12(F), 12(R)) are secured to a head base 19 mounted on a mechanism chassis 19a so that, when the head base 19 is slidably moved, they are inserted into the tape cassette through a window in a front wall of the tape cassette until they are contacted with the magnetic tape. It is to be noted that the recording medium to be used in any of the mechanical arrangements may be either a compact cassette tape or a micro cassette tape, whose structure is shown in Fig. 28 and 29. Referring first to Fig. 28 which shows a compact cassette tape, a magnetic tape 1 is wound around a supply reel 2 and a take-up reel 3 and accommodated in a housing 4, and a tape path is set by a pair of guide rollers so that the magnetic tape 1 is fed while it is exposed to the outside through windows 8a to 8e formed in a front wall of the housing 4. In the window 8c, a pad 6 for contacting with the rear face of the magnetic tape 1 is secured to a leaf spring 6a and disposed in front of the front face of a shield plate 7. Referring now to Fig. 29 which shows a micro cassette tape, a magnetic tape 1 is wound around a supply reel 2 and a take-up reel 3 and accommodated in a housing 4, and a tape path is set by a pair of guide rollers so that the magnetic tape 1 is fed while it is exposed to the outside through windows 9a to 9e formed in a front wall of the housing 4. A pair of pads 6 for contacting with the rear face of the magnetic tape 1 are secured to a leaf spring 6a in the windows 9b and 9d, respectively. The head 10 and the rotary encoder 12 are disposed in the following manner in the mechanical arrangements of the recording and/or reproducing apparatus of the present invention which uses a compact cassette tape or a micro cassette tape of the construction described above. <Arrangement 1 (Fig. 11)> Recording medium: compact cassette tape Tape feeding: one-directional feeding Magnetic head: erasing/recording/reproducing head 10a ... inserted through window 8c Rotary encoder: rotary encoder 12 ... inserted through window 8e Accordingly, the rotary encoder 12 is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 and the take-up reel 3. <Arrangement 2 (Fig. 12)> Recording medium: compact cassette tape Tape feeding: one-directional feeding Magnetic head: erasing/recording/reproducing head 10b ... inserted through window 8e Rotary encoder: rotary encoder 12 ... inserted through window 8c Accordingly. the rotary encoder 12 is contacted with the magnetic tape 1 with the magnetic tape 1 held between the rotary encoder 12 and the pad 6 (refer to 28). <Arrangement 3 (Fig. 13)> Recording medium: compact cassette tape Tape feeding: one-directional feeding Magnetic head: recording/reproducing head 10b ... inserted through window 8c erasing head 10c ... inserted through window 8b Rotary encoder: rotary encoder 12 ... inserted through window 8e Accordingly, the rotary encoder 12 is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 and the take-up reel 3. <Arrangement 4 (Fig. 14)> Recording medium: compact cassette tape Tape feeding: one-directional feeding Magnetic head: recording/reproducing head 10b ... inserted through window 8c erasing head 10c ... inserted through window 8a Rotary encoder: rotary encoder 12 ... inserted through window 8e Accordingly, the rotary encoder 12 is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 and the take-up reel 3. <Arrangement 5 (Fig. 15)> Recording medium: compact cassette tape Tape feeding: normal/reverse bi-directional feeding Magnetic head: recording/reproducing head 10b ... inserted through window 8c normal direction erasing head 10c(F) ... inserted through window 8b reverse direction erasing head 10c(R) ... inserted through window 8d Rotary encoder: normal direction rotary encoder 12(F) ... inserted through window 8e reverse direction rotary encoder 12(R) ... inserted through window 8a Accordingly, when the magnetic tape 1 is fed in the normal direction, the normal direction rotary encoder 12(F) is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 and the take-up reel 3, but when the magnetic tape 1 is fed in the reverse direction. the reverse direction rotary encoder 12(R) is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 and the supply reel 2 which functions as a take-up reel when the magnetic tape 1 is fed in the reverse direction. <Arrangement 6 (Fig. 16)> Recording medium: compact cassette tape Tape feeding: normal/reverse bi-directional feeding Magnetic head: normal direction erasing/recording/ reproducing head 10a(F) ... inserted through window 8e reverse direction erasing/recording/reproducing head 10a(R) ... inserted through window 8a Rotary encoder: normal/reverse bi-directional rotary encoder 12 ... inserted through window 8c Accordingly, the normal/reverse bi-directional rotary encoder 12 is contacted with the magnetic tape 1 with the magnetic tape 1 held between the rotary encoder 12 and the pad 6 (refer to Fig. 28). <Arrangement 7 (Fig. 17)> Recording medium: micro cassette tape Tape feeding: one-directional feeding Magnetic head: recording/reproducing head 10b ... inserted through window 9d erasing head 10c ... inserted through window 9e Rotary encoder: rotary encoder 12 ... inserted through window 9c Accordingly, the rotary encoder 12 is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 and the take-up reel 3. <Arrangement 8 (Fig. 18)> Recording medium: micro cassette tape Tape feeding: one-directional feeding Magnetic head: recording/reproducing head 10b ... inserted through window 9d erasing head 10c ... inserted through window 9e Rotary encoder: rotary encoder 12 ... inserted through window 9b Accordingly, the rotary encoder 12 is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 and the take-up reel 3 with the magnetic tape 1 held between the rotary encoder 12 and the pad 6 (refer to Fig. 27). <Arrangement 9 (Fig. 17)> Recording medium: micro cassette tape Tape feeding: one-directional feeding Magnetic head: erasing/recording/reproducing head 10a ... inserted through window 9d Rotary encoder: rotary encoder 12 ... inserted through window 9c Accordingly, the rotary encoder 12 is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 and the take-up reel 3. <Arrangement 10 (Fig. 20)> Recording medium: micro cassette tape Tape feeding: one-directional feeding Magnetic head: erasing/recording/reproducing head 10a ... inserted through window 9d Rotary encoder: rotary encoder 12 ... inserted through window 9b Accordingly, the rotary encoder 12 is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 and the take-up reel 3 with the magnetic tape 1 held between the rotary encoder 12 and the pad 6 (refer to Fig. 27). <Arrangement 11 (Fig. 21)> Recording medium: micro cassette tape Tape feeding: one-directional feeding Magnetic head: erasing/recording/reproducing head 10a ... inserted through window 9d Rotary encoder: rotary encoder 12 ... inserted through window 9a Accordingly, the rotary encoder 12 is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 and the take-up reel 3. Further, in this instance, the location of contact is in the proximity of one of the guide rollers 5 (refer to Fig. 29). <Arrangement 12 (Fig. 22)> Recording medium: micro cassette tape Tape feeding: one-directional feeding Magnetic head: recording/reproducing head 10b ... inserted through window 9d erasing head 10c ... inserted through window 9e Rotary encoder: rotary encoder 12 ... inserted through window 9a Accordingly, the rotary encoder 12 is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 and the take-up reel 3. Further, in this instance, the location of contact is in the proximity of one of the guide rollers 5 (refer to Fig. 29). <Arrangement 13 (Fig. 23)> Recording medium: micro cassette tape Tape feeding: normal/reverse bi-directional feeding Magnetic head: normal direction recording/reproducing head 10b(F) ... inserted through window 9d reverse direction recording/reproducing head 10b(R) ... inserted through window 9b normal direction erasing head 10c(F) ... inserted through window 9e reverse direction erasing head 10c(R) ... inserted through window 9a Rotary encoder: normal/reverse bi-directional rotary encoder 12 ... inserted through window 9c Accordingly, when the magnetic tape 1 is fed in the normal direction, the normal/reverse bi-directional rotary encoder 12 is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 (10b(F)) and the take-up reel 3, but when the magnetic tape 1 is fed in the reverse direction, the normal/reverse bi-directional rotary encoder 12 is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 (10b(R)) and the supply reel 2 which functions as a take-up reel when the magnetic tape 1 is fed in the reverse direction. <Arrangement 14 (Fig. 24)> Recording medium: micro cassette tape Tape feeding: normal/reverse bi-directional feeding Magnetic head: normal direction erasing/recording/ reproducing head 10a(F) ... inserted through window 9d reverse direction erasing/recording/reproducing head 10a(R) ... inserted through window 9b Rotary encoder: normal/reverse bi-directional rotary encoder 12 ... inserted through window 9c Accordingly, when the magnetic tape 1 is fed in the normal direction, the normal/reverse bi-directional rotary encoder 12 is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 (10a(F)) and the take-up reel 3, but when the magnetic tape 1 is fed in the reverse direction, the normal/reverse bi-directional rotary encoder 12 is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 (10a(R)) and the supply reel 2 which functions as a take-up reel when the magnetic tape 1 is fed in the reverse direction. <Arrangement 15 (Fig. 25)> Recording medium: micro cassette tape Tape feeding: one-directional feeding Magnetic head: erasing/recording/reproducing head 10a ... inserted through window 9b Rotary encoder: rotary encoder 12 ... inserted through window 9a Accordingly, the rotary encoder 12 is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 and the take-up reel 3. Further, in this instance, the location of contact is in the proximity of one of the guide rollers 5 (refer to Fig. 29). <Arrangement 16 (Fig. 26) > Recording medium: micro cassette tape Tape feeding: one-directional feeding Magnetic head: recording/reproducing head 10b ... inserted through window 9b erasing head 10c ... inserted through window 9d Rotary encoder: rotary encoder 12 ... inserted through window 9a Accordingly, the rotary encoder 12 is contacted with the magnetic tape 1 in the tape path between the magnetic head 10 and the take-up reel 3. Further, in this instance, the location of contact is in the proximity of one of the guide rollers 5 (refer to Fig. 29). <Arrangement 17 (Fig. 27)> Recording medium: micro cassette tape Tape feeding: one-directional feeding Magnetic head: recording/reproducing head 10b ... inserted through window 9b erasing head 10c ... inserted through window 9d Rotary encoder: rotary encoder 12 ... inserted through window 9c. It is to be noted that naturally the present invention can be applied not only to the arrangements described above but also to various arrangements and can be applied widely to recording apparatus constructed only for recording, reproducing apparatus constructed only for reproduction, recording and reproducing apparatus and so forth which use a recording medium such a compact cassette tape, a micro cassette tape, an open reel tape, a digital audio tape or the like. Further, a recording and/or reproducing apparatus which uses an open reel tape may be constructed such that a pad for contacting with the rear face of a tape is provided therein so as to cooperate with the roller of the rotary encoder to hold the tape between them. As apparent from the foregoing description, a recording medium such as, for example, a compact cassette tape which is used in a recording and/or reproducing apparatus having no pinch roller and no capstan according to the present invention is compatible with a recording and/or reproducing apparatus of the capstan type and allows recording and reproducing operations with fidelity without any variation in frequency characteristic and signal to noise ratio from the starting end to the last end thereof. It is to be noted that the present invention can be applied widely to recording apparatus constructed only for recording, reproducing apparatus constructed only for reproduction, recording and reproducing apparatus and so forth which conform to such recording media as a compact cassette tape, a micro cassette tape, an open reel tape and a digital audio tape.

Claims: A controlling method for a reel motor (11) of a recording and/or reproducing apparatus which includes no capstan and no pinch roller and wherein a rotatable member (12a) is contacted with a recording medium in the form of a tape to measure a period of rotation of said member and a reel (3) is driven to rotate by a reel motor (12) in accordance with the period of rotation thus measured, comprising the steps of: measuring (F901) a one rotation period (T) of said member by rotation detection means; calculating (F902) a deviation (d) of the one rotation period (T) obtained at the measuring step from a predetermined rated period (T⊘25); characterised by : successively storing (F903-F907) the last n deviations obtained by the deviation calculating step, n being a natural number equal to or greater than 3; determining (F908) whether or not the number of stored deviations is smaller than n-1; either adding, (F910, F913) if it is determined that the number of stored deviations is equal or greater than n-1, the values of the stored deviations except a maximum value and a minimum value of them and dividing the sum value obtained by the addition by n-2 to obtain an average value; or adding (F912, F913), if it is determined that the number of stored deviations is smaller than n-1, all of the stored deviations and dividing the sum value obtained by the addition by the number of stored deviations to obtain an average value; calculating (F914) a servo control value in accordance with the average value thus obtained; storing (F915) the thus calculated servo control value; converting (F916) the stored servo control value into a PWM signal; and controlling (F917) driving of said reel motor in response to the PWM signal obtained by the conversion step. A controlling method for a reel motor of a recording and/or reproducing apparatus which includes no capstan and no pinch roller and wherein a rotatable member (12a) is contacted with a recording medium in the form of a tape (1) to measure a period of rotation of said member and a reel (2) is driven to rotate by a reel motor (11) in accordance with the period of rotation thus measured, comprising the steps of: measuring (F1001) a one rotation period (T) of said member by rotation detection means; calculating (F1002) a deviation (d) of the one rotation period (T) obtained at the measuring step from a predetermined rated period T025; characterised by: successively storing (F1003-F1007) the last n deviations obtained by the deviation calculating step, n being a natural number equal to or greater than 3; determining (F1008) whether or not the number of stored deviations is smaller than n-1; either adding (F1010, F1012), if it is determined that the number of stored deviations is equal or greater than n-1, the values of the stored deviations except a maximum value and a minimum value of them and dividing the sum value obtained by the addition by n-2 to obtain an average value; calculating (F1013) a servo control value in accordance with the average value thus obtained; or calculating (F1011, F1013) if it is determined that the number of stored deviations is smaller than n-1, a servo control value in accordance with the deviation; storing (F1014) the servo control value calculated in accordance with the deviation; converting (F1015) the stored servo control value into a PWM signal; and controlling (F1016) driving of said reel motor in response to the PWM signal obtained by the conversion step.

Inventors: NAKANO YOSHITOMO, SHIMIZU KUNIO, NAKANO, YOSHITOMO, SHIMIZU, KUNIO
Applicants: SONY CORP, SONY CORPORATION
Application year: 1993
Main classification: G11B15
IPC codes: G11B15