GB2160348A

GB2160348A - Recording/reproducing apparatus of the rotary head type

Info

Publication number: GB2160348A
Application number: GB08511182A
Authority: GB
Inventors: Shigekazu Wada
Original assignee: Pioneer Electronic Corp
Current assignee: Pioneer Corp
Priority date: 1984-05-02
Filing date: 1985-05-02
Publication date: 1985-12-18
Also published as: DE3515806A1; GB8511182D0; JPH0426972Y2; JPS60180321U

Abstract

A recording/reproducing apparatus of the rotary head type has means for correcting tilting and bending type tracking errors. Errors in, for instance, a guide surface of the head and in the rotary locus transcribed by the head are measured (14) and stored (22,23). The stored information is later applied through a pattern generated (21) to correct the positions of rotary magnetic heads (12a, 12b) so that the heads track linearly and without tilting. <IMAGE>

Description

SPECIFICATION Recording/reproducing apparatus of the rotary head type The present invention relates to recording/reproducing apparatuses such as a VTR (Video Tape Recorder) or the like, and particularly to a recording/reproducing apparatus of the rotary head type in which a recording medium such as a video tape or the like is moved past a rotary head to perform signal recording/reproducing.

A recording/reproducing apparatus such as a VTR or the like generally employs a rotary head drum device in which a magnetic head is mounted on a rotary drum which can rotate at a high speed. This is done in order to increase the relative speed between the tape and the magnetic head. An example of such a rotary head drum is shown in Figure 1. In this example, a fixed drum 1 is provided at its outer periphery with a groove-like guide surface 3 for spirally guiding a tape 2. A housing portion 4 is formed integrally with the fixed drum 1 at the central lower portion thereof. A rotary shaft 6 passes through the housing portion 4, supported thereon hy a pair of upper and lower bearings 5. Movement of the rotary shaft 6 passes through the housing portion 4, supported thereon by a pair of upper and lower bearings 5.Movement of the rotary shaft 6 in the axial direction is restricted by a flange 7 and a stop 8. A pair of drum 1 in opposition to the magnets 9.

The flange 7 is fitted into the central hole of a rotary drum 11 to which a pair of magnetic heads 1 2a and 1 2b for performing recording/reproducing of a video signal are attached by means of supports, specifically, bias elements 1 3a and 1 3b such as bimorphic ceramic piezoelectric elements. Ceramic piezoelectric elements are used so that the magnetic heads may be biased in the axial direction of the rotary shaft 6, that is, a direction perpendicular to the longitudinal direction of the video track. The supply of drive current to the bias elements 1 3a and 1 3b is achieved between the rotary drum 13 and the stationary side via a slip ring or the like. The rotational driving force of a drive motor (not shown) is transmitted to the rotary shaft 6 directly or through a belt or like drive.

Figure 2 shows a block diagram of a conventional apparatus employing a rotary head drum device having an arrangement such as that described above. The vertical positions of the respective magnetic heads 1 2a and 1 2b are detected at predetermined scanning positions by a head height detecting unit 14, the detection outputs of which are converted by a switching circuit 15 into height signals corresponding to the respective magnetic heads 1 2a and 1 2b in response to drum pulses obtained from the outputs of the Hall element 10 (Figure 1 ) as the magnetic heads 1 2a and 1 2b are rotated. The height signals are applied to respective sample-and-hold circuits 16 and 17.The level difference between the outputs of the sample-and-hold circuits 16 and 17 is detected by a comparator 18, and an error voltage-thus produced at the output of the comparator 18 is applied to the bias elements 1 3a and 1 3b after being amplified by an amplifier 19.

It sometimes occurs that, as illustrated in Figure 3, a recording track pattern becomes tilted with respect to a standard angle due, for instance, to dimensional inaccuracies of the guide surface 3 on the fixed drum 1. This results in a loss of tracking accuracy. Further, depending on the accuracy of the bearing mechanism for the rotary shaft 6, etc., the locus of rotations of the magnetic heads 1 2a and 1 2b may become sinusoidal of a period corresponding to one revolution, as shown in Figure 4, thereby further adversely affecting the linearity and tracking accuracy of the magnetic heads 1 2a and 1 2b.

To reduce such errors, the dimensional accuracy of various components of the head and the accuracy in assembling the head can be increased. Doing so, however, is costly. Moreover, if the track width is made narrower, it becomes difficult to maintain interchangeability of tapes.

A specific object of the invention is to provide a recording/reproducing apparatus of the rotary head type in which the linearity of a recording track is improved by biasing magnetic heads so as to correct the tilting or bending of the tracking pattern of the magnetic heads due to errors in mechanical components.

According to the present invention, a recording/reproducing apparatus of the rotary head type comprises a fixed drum having at its outer periphery a guide surface for guiding a tape; a rotary drum means rotatably supported by the fixed drum; means for biasing magnetic heads relative to the rotary drum means substantially in the direction of the rotational axis of the rotary drum; and means for controlling the biasing means so as to bias the magnetic heads in accordance with errors in tracking accuracy in the fixed drum and/or rotary drum means.

Thus the magnetic heads are supported in such a manner that they can be biased relative to a rotary drum in the direction of the rotational axis of the rotary drum in accordance with errors in mechanical accuracy in each of the fixed and rotary drums caused, for example, by inaccuracies in the guide surface in the assembling of the respective parts of the drum so as to record a standard track.

Due to the elimination of such error, tapes can be easily interchanged and a clear picture always obtained. Further, it is possible to perform reproducing with less error, even in the case where the track width is made narrow.

Moreover, good interchangeability is assured, even if the dimensional accuracy and assembling accuracy are not improved; therefore, it is possible to make the cost of the apparatus low. Further, it is possible to make the height equal along the longitudinal direction of tracks in performing recording by using an F; system in an 8 mm video tape recorder.

In the drawings: Figure 1 is a cross-sectional view showing an example of a conventional rotary head drum; Figure 2 is a block diagram showing an example of a conventional tracking control circuit; Figure 3 is a diagram showing a tilting-type tracking pattern error; Figure 4 is a diagram showing a bending type tracking pattern error; Figure 5 is a block diagram of a tracking control circuit of the present invention; Figure 6 is a diagram showing the arrangement of a head height detecting device; and Figures 7A, 78 and 7C show an example of a head level detector used in the system in accordance of the invention.

A preferred embodiment of the present invention will be described with reference to the block diagram of Figure 5, in which elements corresponding to those of Figure 2 are designated by like reference numerals.

In Figure 5, in addition to the elements employed in the apparatus of Figure 2, there are provided a switching circuit 20 for performing a switching operation in response to a drum pulse signal, a pattern generator 21, and an adder 24 for adding the output of the switching circuit 20 to the output of the pattern generator 21. In use, example, the accuracy of the guide surface 3 of the fixed drum 1 is measured and stored in a guide surface accuracy detecting and storing unit 22, and the deviation between an ideal and the actual rotary locus measured and stored in a rotary locus detecting and storing unit 23.

From this information, supplied at the outputs of the units 22 and 23, the pattern generator 21 supplies a control signal to the adder 24 which effects correction for the measured errors. That is, the control signal, which is in phase with the drum pulse signal, is added to the output of the switching circuit 20 by the adder 24 so as to maintain the head position constant with respect to the recorded track.

The operation of the apparatus according to the present invention will now be described.

During recording, the vertical positions of the magnetic heads 12a and 1 2b (Figure 1) are detected at predetermined scanning positions by the head height detecting unit 14.

The head height detecting unit 14 is constituted by, for example, a light-emitting element 14a emitting light at a certain angle relative to the Y direction along the axis of each of the magnetic heads 12a and 12b, and a lightdetecting element 14b receiving light emitted by the light-emitting element 14a reflected from the magnetic head 12a or 12b. The light-detecting element 14b may be, for example, an image sensor capable of detecting a light reception point. The vertical position Y of the magnetic head 12a and 12b is detected by the displacement in the direction perpendicular to the rotary shaft 6 by the reflecting position of the magnetic head 12a or 12b. The head height detecting unit 14 is fixed to the rotary drum 11 at a position where the tape does not contact and at the side of the fixed head 1.

The output of the head height detecting unit 14 is switched between magnetic heads by the switching circuit 15 in response to a drum pulse signal so as to route the output of the unit 14 for each of the magnetic heads to a corresponding one of the sample-and-hold circuits 16 and 17. An error signal obtained at the output of the comparator 18 is selectively applied to the adder 24 through the switching circuit 20, which also performs its switching operation in response to the drum pulse signal.That is, by the switching operation of the switching circuit 20, only the output from the pattern generator 21 is amplified by the amplifier 19 with respect to one of the magnetic heads 12a and 12b (namely, the head regarded as the reference head), while a composite signal of the above-mentioned error signal and the output from the pattern generator 21 is amplified by the amplifier 19 with respect to the other one of the magnetic heads 12a and 12b (that is the head to be adjusted), the amplified signals being applied to the bias element 13b or 13a.

Thus, the magnetic head 12a or 12b is driven while correcting the deviation of its tracking pattern relative to a standard pattern so that the actual tracking pattern is made linear and accurate. Specifically, for recording, the magnetic heads 12a and 12b are made to track a linear pattern due to the corrections imposed by the pattern generator 21. Thus, a recorded pattern is provided without bending in the recorded tracks.

The head height level detecting means may be constructed as follows. Referring to Figures 7A to C, bias element 13a (13b) such as a bimorphic piezoelectric element is fixed at one end to the rotary drum 11 and is provided at the other end with a magnetic head 12a (12b). A head position determining head 33 is provided close to the head 12a at the position where the magnetic tape is not provided, to generate a magnetic field 34. Then, the head 12a is mechanically vibrated and is held stationary at a detection output amplitude maximum position. The head 12a is held at the constant position at least during a time period from the contact between the tape and the head to the separation therebetween. Figure 7C shows a block diagram of a control system for the head height level detecting means.

The head 12a is being used for detecting its position and the other head 12b is being used for recording information onto the tape. To the head 12a for detection, there is applied a signal from a signal generator 36 such as an oscillator through a drive amplifier 37. Thus, a predetermined electric field is obtained.

Then, another oscillator 38 applies its signal to the bias element 13a through an adder 39, a first switch SW1, and a bias element drive circuit 40B to thereby mechanically vibrate the head 13a. A change component alone, of the output signal of the head 12a, in correspondence with the vibration of the head is separated through a second switch SW2 by a band pass filter 41. A polarity and an amplitude thereof are separated on the basis of the output of the oscillator 38 to which a signal is applied through a phase shifter 44 from a synchronization detector 42. The obtained signal is supplied to the drive circuit 408 through a smoothening circuit 43 and an adder 39, so that the position of the head 12a is determined. Thereafter the first switch SW, is turned off and the displacement of the head is held at a capicitor C,.

Although the description has been made with regard to a recording operation, the same effects are obtained during reproduction. Further, although in the above-described embodiment the magnetic heads are arranged such that they are registered in height and one of them is regarded as a reference and the other adjusted to agree with the reference head, the two heads may be arranged such that the height of each of them is made to agree with a reference height. Further, although in this embodiment tracking error due to both tilting and bending is corrected, it may be sufficient to correct only for bending. Moreover, although in the above-described embodiment correction is performed with respect to both tilting and bending for both heads, substantially the same effect may be obtained if the correction for bending is effected with respect to only one head.Furthermore, the head height detector 14 may be an F5 system in an 8 mm video recorder. Still further, although each of the magnetic heads is arranged to be movable, one of them may be fixed.

Moreover, although in the described arrangement the units 22 and 23 have been described as performing their measuring operations under the condition that the drum has been assembled, these measurements can be made by detecting an error voltage, etc., upon running a reference tape. The pattern generator 21 may be constituted by executing a program in a microcomputer. In using the guide surface accuracy detecting and storing unit 22, a hole acting as a positional reference in the direction of rotations may be formed in the fixed drum 1. It is preferable, however, to utilize a reference hole formed in working a guide surface. It is convenient to perform correction control by making the reference hole in phase with the position of the Hall element 10 (Figure 1) for generating the drum pulse signal. Although the upper drum is of a movable type in the embodiment described above, the upper drum may be of the fixed type. Although the drum pulse signal is generated by the Hall element, other detecting methods may be employed.

Claims

1. A recording/reproducing apparatus of the rotary head type, comprising a fixed drum having at its outer periphery a guide surface for guiding a tape; a rotary drum means rotatably supported by the fixed drum; means for biasing magnetic heads relative to the rotary drum means substantially in the direction of the rotational axis of the rotary drum; and means for controlling the biasing means so as to bias the magnetic heads in accordance with errors in tracking accuracy in the fixed drum and/or rotary drum means.

2. A recording/reproducing apparatus according to claim 1, wherein the controlling means comprises means for detecting and storing values representing tilting and bending errors; and means for generating signals which, when applied to the biasing means, eliminate such errors.

3. A recording/reproducing apparatus according to claim 2, wherein the controlling means further comprises means for adding outputs of the detecting and storing means with head height indicating signals.

4. A recording/reproducing apparatus of the rotary head type substantially as described with reference to any of Figures 5 to 7 of the accompanying drawings.