Method of and system for driving magnetic tape

Abstract: A method of regulating the transverse position of a running magnetic tape (4) comprising steps of generating a unidirectional travelling-surface-wave by ultrasonic oscillation on a surface of an oscillator (62A,62B;65;66A,66B), and pressing the surface of the oscillator against a surface of the magnetic tape (4) so that the travelling direction (B,D) of the surface wave on the oscillator (62A,62B;65;66A,66B), has a component directed in transverse direction of the magnetic tape (4).

Description: The invention relates to a method of and a system for regulating the transverse position of a running magnetic tape. As is well known, in a videotape recorder, or an audiotape recorder the magnetic tape is conventionally run by a capstan and a pinch roller rotated at constant speed. However, when a thin magnetic tape such as a long-playing tape is driven by such a driving system, the magnetic tape is apt to twist or meander to adversely affect running of the tape, or is sometimes stretched by tension, thereby making it impossible to effect accurate tracking. SU-A-670 974 discloses a magnetic tape piezo-electric driving system using two types of piezo elements. A transverse movement element with a slot operates at the center with two alternately operating tape pressure elements on both side of a housing. Control pulses operate pressure element first pressing the tape against the slot side. The transverse element pulls the tape. Second pressure element removes the slack moving the tape forward. This driving system offers relative high speed and uniformity of tape movement. JP-A-58-196653 discloses a magnetic tape guide device in which a piezo electric element vibrates in the width direction of the tape so that the protrusions at the upper and lower edges thereof abut to the tape edges and thereby the tape is guided to a predetermined position in the width direction. From FR-A-2 522216 a motor device using an ultrasonic device for driving a tape in its running direction is known. This device generates an ultrasonic surface wave at the surface of an oscillator for driving the tape. It is the object of the invention to provide an improved method and an improved system for regulating the transverse position of the running magnetic tape. This object is solved according to the invention by a method as claimed in claim 1 and by a system as claimed in claim 2. In accordance with the present invention, a unidirectional travelling-surface-wave by ultrasonic oscillation is generated on a surface of an oscillator, and a magnetic tape position is regulated in the direction transverse to the travelling direction of the tape by pressing the surface of the oscillator against a surface of the magnetic tape. As the oscillator, an electrostrictor or a magnetostrictor is used. That is, in the present invention, the principle of an ultrasonic motor which generates a surface wave (flexure vibration) by ultrasonic oscillation by the use of an electrostrictor or a magnetostrictor is applied. As for the ultrasonic motor, see, for instance, "Applied Physics", pp.65 - 66, No. 6, Vol. 54, 1985, "Nikkei Mechanical", p. 40, No. 24, March, 1986, "Nikkei Electronics", pp. 90 - 92, No. 24, March, 1986, and "Nikkei Electronics", pp. 86 - 87, No. 9, March, 1987. In accordance with the principle, numbers of wave peaks of the surface wave generated on the surface of the oscillator make ultrasonic oscillation while generating ellipsoidal loci and moves a movable member on the surface in the direction opposite to the traveling direction of the surface wave by friction. In the present invention, the magnetic tape is driven by bringing the oscillator having such a surface wave into surface-to-surface contact with the magnetic tape. In the tape driving system of the present invention, the oscillator to be brought into contact with the magnetic tape may be caused to oscillate by transmitting vibration from a plurality of oscillating elements which are applied with high frequency voltages with phases different from each other by 90° or 120°, or may be directly formed of a plurality of contiguously arranged piezo-electric elements which are arranged so that traveling waves are generatea on the surface of the piezo-electric elements when alternating voltages with different phases are applied to alternate piezo-electric elements. Thus, according to the present invention, the transverse position of the magnetic tape is regulated by generating a unidirectional traveling-surface-wave by ultrasonic oscillation on a surface of an oscillator, and pressing the surface of the oscillator against a surface of the magnetic tape so that the traveling direction of the surface wave has a component directed in the transverse direction of the magnetic tape. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view showing a tape running system for a videotape recording and reproducing system provided with a tape driving system; Figure 2A is a schematic plan view showing a tape driving system using ultrasonic oszillation for driving a tape in its running direction, Figure 2B is a side view of the tape driving system of Figure 2A, Figure 3 is a schematic perspective view showing another tape driving system in accordance with the above principle, Figure 4 is a schematic side view showing another tape driving system in accordance with still the above principle, Figure 5 is a schematic perspective view for illustrating another tape driving system, Figure 6 is a schematic side view for illustrating a modification of the system shown in Figure 5, Figure 7 is a schematic plan view showing an audiotape recording and reproducing system provided with such a tape driving system, Figures 8, 9 10 and 11A are schematic views for illustrating various embodiments of a system for regulating the transverse position of the magnetic tape according to the present invention, Figure 11B is a side view of Figure 11A, and Figure 12 is a schematic view showing an example of the tape driving system which can employed in the systems shown in Figures 8 to 11A. DESCRIPTION OF THE PREFERRED EMBODIMENT In Figure 1, a videotape 4 is unrolled from a supply reel 6 and taken up by a take-up reel 5. The videotape 4 is driven by first and second tape driving systems 1 and 2, respectively disposed downstream and upstream of a rotary drum 3 having a magnetic head (not shown). The first tape driving system 1 downstream of the rotary drum 3 is for accurately running the magnetic tape 4 with respect to the rotary drum 3, and the second tape driving system 2 upstream of the rotary drum 3 is for applying back tension to the magnetic tape 4. As in the conventional videotape recording system, the take-up reel 5 is driven to take up the magnetic tape 4, while the supply reel 6 is arranged to apply light back tension to the magnetic tape 4. Each of the first and second tape driving systems 1 and 2 comprises, as shown in Figures 2A and 23, a piezo-electric element row formed of a plurality of piezo-electric element pairs, each pair comprising first and second piezo-electric elements 11 and 12, arranged on a support 10 contiguously with each other. The piezo-electric element pairs are arranged so that the first and second piezo-electric elements 11 and 12 alternate with each other. The first and second piezo-electric elements 11 and 12 are respectively connected to first and second alternating electric sources Ea and Eb to be applied with alternating voltages with different phases. When the first and second piezo-electric elements 11 and 12 are applied with alternating voltages with different phases, traveling waves (surface waves) are generated on the surfaces of the piezo-electric element row and by pressing the magnetic tape 4 against the surface of the piezo-electric element row, the magnetic tape 4 is run in the direction opposite to the traveling direction of the surface waves as described above. Figure 3 shows another tape driving system comprising piezo-electric elements 21 fixed on one side of an elastic body 20. In this system, by causing the elastic body 20 to make high frequency oscillation by the piezo-electric elements 21, thereby generating unidirectional traveling waves on the other side of the elastic body 20, and pressing the magnetic tape 4 against said the other side of the elastic body 20, the magnetic tape 4 is run. Figure 4 shows still another tape driving system comprising a pair of oscillators 31 and 32 in contact with an elastic body 30 at opposite ends of the elastic body 30. The oscillators 31 and 32 cause the elastic body 30 to make high frequency oscillations which differ from each other in phase by 90°. Further, a vibration absorber 33 is connected to one end of the elastic body 30 to prevent generation of reflected waves at one end of the elastic body 30 which can cause the oscillation of the elastic body 30 to act as stationary wave as a whole. In still another system shown in Figure 5, the tape driving systems are directly provided on a pair of cylinders 7 and 8 of the rotary drum of a videotape recording system. Between the cylinders 7 and 8 is provided a rotary magnetic head 9. The rotary magnetic head 9 is mounted on the cylinder 7 and the cylinder 8 is stationary. In this case, a piezo-electric element row like that described above is provided at least a part of the surface of the stationary cylinder 8 along which the magnetic tape 4 is run. In the case that both the cylinders 7' and 8' are stationary with the rotary magnetic head 9 intervening therebetween as shown in Figure 6, piezo-electric element groups 40 and 41 are provided on the cylinders 7' and 8', respectively. Each of the piezo-electric element groups 40 and 41 comprises a plurality of piezo-electric element rows 42 contiguously arranged in the direction perpendicular to the running direction of the magnetic tape 4. Each of the piezo-electric element rows 42 comprises a plurality of piezo-electric element pairs which are like those described above in conjunction with Figures 2A and 2B and arranged in the running direction of the magnetic tape 4 to generate surface waves in the longitudinal direction of the row, though the individual piezo-electric elements are not shown. Figure 7 shows a system in which the above tape driving systems are applied to an audiotape cassette 50. A pair of tape driving systems 51 and 52 are provided on opposite sides of the part at which the magnetic head of a tape recording and reproducing system is given access to the magnetic tape 4. The tape driving forces of the tape driving systems 51 and 52 differ from each other so that a desired back tension is applied to the tape 4 by virtue of the difference in the driving force. In the case that the one of the above tape driving systems is applied to a videotape recording and reproducing system, the frequency of the oscillation of the tape driving system is preferably a multiple of a frequency corresponding to the number of horizontal scanning lines of a TV system. The term "multiple" should be interpreted to include "one-fold". That is, the frequency of the oscillation of the tape driving system may be equal to a frequency corresponding to the number of horizontal scanning lines of the TV system. That is, an oscillator such as an electrostrictor or a magnetostrictor is generally oscillated at a resonance frequency which depends on the material of the element, the size of the element and the like. However, such a frequency can adversely affect the recording signal or the reproducing signal of the videotape recording and reproducing system to generate noise and/or fricker in a reproduced image. As will be apparent to those skilled in the art, when the frequency of the oscillation of the tape driving system is a multiple of a frequency corresponding to the number of horizontal scanning lines of the TV system used in the videotape recording and reproducing system, influence of the oscillation of the tape driving system on the image signals can be easily removed, and at the same time, the frequency of the driving power of the tape driving system can be easily obtained from the frequency used in the videotape recording and reproducing system. For example, in the case of a NTSC TV system, the frequency of the oscillation of the tape driving system is preferred to be a multiple of 15.75KHz, i.e., 262.5 x 2(fields) x 30(frames). The aforesaid principle can be applied in order to regulate position of the magnetic tape in the transverse direction. That is, conventionally, position of the magnetic tape is transversely regulated by a mechanical guiding member such as a flanged roller, a drum like pole or the like. However, as the thickness of the magnetic tape becomes smaller, it becomes more difficult to mechanically regulate position of the tape in the transverse direction by means of such a conventional guiding member. That is, by generating a unidirectional traveling-surface-wave by ultrasonic oscillation on a surface of an oscillator, and pressing the surface of the oscillator against a surface of the magnetic tape so that the traveling direction of the surface wave has a component directed in the transverse direction of the magnetic tape, position of the magnetic tape can be regulated in the transverse direction. For example, by providing a pair of oscillators so that the traveling directions of the surface waves generated on the surfaces of the respective oscillators have components which are directed in the transverse direction of the magnetic tape and are opposite to each other, and selectively driving one of the oscillators, transverse position of the magnetic tape can be regulated. Otherwise, transverse position of the magnetic tape may be regulated in one direction by an oscillator while the magnetic tape is normally urged in the other direction by other suitable means such as an inclined surface. In Figure 8, a tape guide 63 is provided with a pair of tape driving systems 62A and 62B so that the magnetic tape 4 is pressed against the tape driving systems 62A and 62B. The tape driving systems 62A and 62B may be like those described above in conjunction with Figures 2 to 4 or may be as shown in Figure 12 which will be described later. The tape driving systems 62A 62B are respectively oriented to move the tape 4 obliquely upwardly and downwardly as shown by arrows B with respect to the running direction of the magnetic tape shown by arrow A. The tape driving systems 62A and 62B are selectively energized to move upward or downward the magnetic tape 4 under the control of an output signal of a tape position detecting means (not shown) which detects the transverse position of the magnetic tape 4. The tape driving system 62A and 62B may be oriented to move the magnetic tape 4 upward and downward in perpendicular to the running direction of the magnetic tape 4 as shown in Figure 9. Though, in the embodiment shown in Figure 9, the tape driving system 62A is positioned on the upper portion of the tape guide 3 while the tape driving system 62B is positioned on the lower portion of the tape guide 3, the tape driving systems 62A and 62B may be alternately arranged as shown in Figure 10. In the embodiments shown in Figures 8 to 10, when both the driving systems 62A and 62B are simultaneously energized to exert the same driving forces, the magnetic tape 4 is not moved in the transverse direction thereof. On the other hand, when only one of the driving systems 62A and 62B is energized with the other being de-energized, or when both the driving systems 62A and 62B are simultaneously energized so that one of them exerts driving force stronger than the other, the magnetic tape 4 is moved in the direction in which the driving force of said one of the driving systems 62A and 62B acts. In another embodiment shown in Figures 11A and 11B, a single tape driving system 65 is supported on an inclined surface of a tape guide 64 so that the magnetic tape 4 is urged in the direction shown by arrow C in Figure 11A by virtue of the inclined surface of the tape guide 64. The tape driving system 65 is energized to exert a driving force in the direction shown by arrow D which is equally balanced with the urging force provided in the direction of the arrow C by the inclined surface of the tape guide 64. The driving force of the driving system 65 is adjusted under the control of an output signal of a tape position detecting means (not shown) which detects the transverse position of the magnetic tape 4. The tape driving system shown in Figure 12 comprises a plurality of electrostrictors 66A and 66B alternately arranged side by side. The electrostrictors 66A and 66B are connected to a single long electrode 68 at respective one ends and are respectively opposed to separate electrodes 67 67B at respective the other ends. The electrodes 67 connected to an alternating electric source 69 and the electrodes 67B are connected to another alternating electric source 70. When the electrodes 67A and 67B are imparted with alternating voltages with difference phases, the electrostrictors 66A and 66B make longitudinal oscillations, thereby generating laterally (in the direction of the row of the electrostrictors) traveling-surface-wave as a whole. As can be understood from the description above, in the tape driving system using an ultrasonic oscillation, the magnetic tape is not subjected to strong local tension since the magnetic tape is run by way of surface-to-surface contact of the oscillater and the magnetic tape, and accordingly, the magnetic tape cannot be stretched or twisted to adversely affect running of the tape even if the magnetic tape is very thin. Further, since the motor for driving the capstan required in the conventional tape driving system can be eliminated and the position of the tape driving system can be freely selected, the overall tape driving system can be further reduced in size and weight. Further, the tape position regulating system in accordance with the present invention is advantageous over the conventional tape position regulating systems in that the magnetic tape can be run with a high accuracy better than 1µm and with an excellent response.

Claims: A method for regulating the transverse position of a magnetic tape (4) running in a tape feeding system and being driven by a tape driving means in its longitudinal direction, characterized by the steps of generating a unidirectional traveling surface wave by ultrasonic oscillation on a surface of an oscillator (62A, 62B; 65, 66A, 66B) traveling in a direction having a component in a direction perpendicular to said longitudinal direction and parallel to the surface of the magnetic tape, and pressing the surface of the oscillator against the surface of said magnetic tape (4) to thereby regulate the transverse position of the magnetic tape (4) by controlling said surface wave. A magnetic tape feeding system comprising: a tape driving means (1, 2, 10, 20, 30, 42, 51, 52, 63) for driving a magnetic tape (4) in the longitudinal direction of the tape, and a tape edge position regulating means characterized in that said tape edge position regulating means comprises an oscillator (62A, 62B, 63, 64, 65, 68) which is adapted to be pressed on a surface of the magnetic tape (4), and means for generating on the surface of the oscillator (62A, 62B, 63, 64, 65, 68) which is to be brought into contact with the magnetic tape (4) a surface wave traveling in a direction having a component (B, D) in a direction perpendicular to said longitudinal direction and parallel to the surface of the magnetic tape (4), thereby regulating the lateral position of the magnetic tape (4) by controlling the said surface wave.

Inventors: KITAMOTO TATSUJI, SEKIGUCHI TAKUJI, YOKOYAMA KATSUYA, KITAMOTO, TATSUJI, SEKIGUCHI, TAKUJI, YOKOYAMA, KATSUYA, KITAMOTO, TATSUJI, C/O FUJI PHOTO FILM CO. LTD., SEKIGUCHI, TAKUJI, C/O NIPPON HOSO KYOKAI, YOKOYAMA, KATSUYA, C/O NIPPON HOSO KYOKAI
Applicants: FUJI PHOTO FILM CO LTD, JAPAN BROADCASTING CORP, FUJI PHOTO FILM CO., LTD., NIPPON HOSO KYOKAI
Application year: 1988
Main classification: G11B15
IPC codes: G11B15