Rotary head adjuster

Abstract: A rotary head adjuster for a rotary head (18) having plural head chips adjusts the position of each head chip by making use of partial plastic deformation of a head base (27) caused by laser irradiation. The adjuster comprises stage means (17) for fixing the rotary head (18) composed of plural head chips on a movable stage part, and for moving the stage together with the rotary head; measuring means (13,11) for measuring relative positions across the plural head chips; laser means (14,15,25) for emitting a laser beam and applying the laser beam to the head base (27) and control means (11) for comparing a desired relative position with a result of measurement of positions of individual head chips received from the measuring means, calculating a necessary adjustment amount of each head chip, and setting appropriate laser irradiation conditions to realize deformation of the head base depending on the necessary adjustment amount, and for controlling the stage means and the laser means on the basis of the set laser irradiation conditions.

Description: This invention relates to an apparatus for adjusting a position of a rotary head in a magnetic recording/reproducing apparatus such as a video cassette recorder (VCR). As shown in Figs. 1A and 1B, recent high quality consumer VCRs have several rotary heads 1 on a rotary drum 2 for recording video signals, high fidelity audio signals and for erasing recorded tracks. All heads are bonded on small metal plates 3a, called head base, and the rotary drum 2 is mounted on a fixed drum 4. See EP-A-0185844. Another form of rotary head is also shown in EP-A-0185844 which discloses a rotary head in which the head itself is attached to a head base which is in turn attached to the rotary drum by laser welding. The head base in the area where the head is attached has two arcuate slots cut into it from the edge of the head base to form a head attachment portion attached to the head base by a narrow neck, permitting adjustment of the position of the head. All heads should be precisely positioned on a rotary drum 2 in order to satisfy the desired recording format on the tape, because the arrangement of recorded tracks are mainly determined by the head positions on the rotary drum. The head position includes absolute head height Ha which is the distance between a datum plane 5 of the fixed drum 4 and a track edge 6 of the head 1, relative head height Hr which is the relative head height among the track edges of different heads, and gap azimuth angle 31 of the head 1. The conventional manner of adjusting the head position is as follows: Consumer VTRs are not provided with a mechanism for adjusting the azimuth angle, and the angle is adjusted in the manufacturing process of the head when cutting out the chip from the gapped bar. Therefore, the precision of azimuth angle depends on the machining precision and the precision of adhering the head 1 to the head base 3a with an adhesive 8. On the other hand, to adjust the head height, first the height H0 of each head from the surface (the head adhesion surface) of the head base 3a of the track edge 6 is measured, and the absolute height Ha of each head is roughly adjusted by placing a metal plate 9 called shim in a thickness corresponding to a required adjusting amount on the basis of the measured H0 value between the head base 3a and the rotary drum 2, and each head is fixed to the rotary drum with screws. Consequently, the rotary drum 2 on which the heads are mounted is fixed on the fixed drum 4, and the relative height of the heads is precisely adjusted using a screw 10 of which tip is contacting with a part of the head base as shown in Fig. 1b. More specifically, by tightening or loosening the screw 10, the head base is elastically deformed, and the head chip adhered to the tip of the head base is moved vertically in the head height direction (the direction parallel to the rotary shaft A of the rotary drum) as indicated by arrow B in the drawing, and Ha and Hr are adjusted precisely. However, since the fluctuations of the tip shape of the screw 10 are significant and the height is changed as much as 500 microns by turning the screw 10 by a revolution, the precise adjustment of the height in the sub-micron order was not realized. The basis of the above conventional manner is the mechanical deformation of the head base by pushing a small screw within its elastic limits. Accordingly, when the drum unit is subjected to vibratory or temperature changing circumstances, the small screw pushing the head base may be loosened and the head height may be fluctuated. In our experiments, on ambient temperature cycle test of -40 degrees and +80 degrees and vibration test, it was found that the fluctuations of the relative head height were about 2 microns. The influence of the above fluctuations on the reproduced picture qualities is very severe, especially in the long play mode, for example, the six-hour mode in the VHS system of narrow track recording, because the above fluctuations will cause tracking errors and decrease of reproducing voltage and increase of cross talk interference from adjacent tracks. Furthermore, if a fluid bearing is adopted as the bearing of the rotary head drum, the yawing of the rotary head drum during rotating depends on the rotation of the rotary drum. It indicates that the absolute head height, relative head height and azimuth angle also depend on the rotation of the rotary head drum. Consequently, by the conventional head adjusting method, in which the head position should be adjusted without rotating the drum, it is very difficult to guarantee the high accuracy of adjusting. It is hence a primary object of the invention to present an apparatus and an appropriate rotary head for adjusting the head position without being influenced by vibrations and ambient temperature changes. The present invention provides a rotary head adjuster for adjusting a position of a head chip of a rotary head which comprises a head base and at least one said head chip fixed to said head base, characterized by comprising: a stage for mounting thereon said rotary head; a position measuring means for measuring a position of said head chip of said rotary head mounted on said stage; a laser means for emitting a laser beam and applying the laser beam to a specified area on said head base of said rotary head mounted on said stage so as to cause a plastic deformation of said head base at said specified area; and control means for comparing the position of said head chip measured by said position measuring means with a predetermined position, calculating a necessary position adjusting amount, setting appropriate laser irradiation conditions depending on said necessary position adjusting amount, and controlling said laser means according to said laser irradiation conditions so as to cause a change of the position of said head chip by the plastic deformation of said head base to be the predetermined position. The measuring means is connected to the control means, and it possesses a function of measuring relative positions of plural head chips, and a function of transmitting results of measurement to the control means. Since the rotary head is adjusted by means of plastic deformation, which is not susceptible to influence of vibrations and ambient temperature changes, high accuracy head positioning is realized. No screws are required for adjusting the head positions, and hence it has advantages in production costs. Furthermore, according to this invention, enabling to apply a laser beam to a head base while rotating the head drum, the rotary head can be adjusted precisely even if a fluid bearing is adopted as a bearing of a rotary drum. The present invention also provides a rotary head comprising a head base and at least one head chip fixed to said head base, characterized in that said head base has at a specified area thereon a thermally caused plastic deformation area and is bent at a boundary of said plastic deformation area, and that said at least one head chip is fixed to said head base at a position defined by a bent amount of said head base. The present invention also provides a method of adjusting a position of a head chip of a rotary head according to claim 12 In order that the present invention be more readily understood embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:- Figs. 1A and 1B are diagrams for explaining the prior art, Fig. 1A being a bottom view of a rotary drum mounting a rotary head and a magnified view of the head from its gap side direction, and Fig. 1B being a side view of a drum unit having the rotary drum of Fig. 1A fixed on the fixed drum. Fig. 2 is a functional block diagram of an apparatus for adjusting the head position in the drum unit state fixing the rotary head on the rotary drum in a preferred embodiment of the invention. Figs. 3A and 3B are diagrams for explaining the principle of head position adjusting method by irradiation with laser beam of the invention. Fig. 4 is a diagram showing the dependence of the head position changes on the plate thickness of the groove part when emitting laser beam to the concave groove part of the head base. Fig. 5 is a diagram showing the relation between the irradiation position of laser beam and the position changes of the head. Fig. 6 is a partially magnified view around the rotary head of the head position adjusting apparatus of the invention. Fig. 7 is a functional diagram of an apparatus for adjusting the head position by a rotary head in another embodiment of the invention. Fig. 8 is a functional constitutional diagram of an apparatus for adjusting the head position by a rotary head only in another preferred embodiment of the invention. Fig. 9 is a perspective view of a rotary head composed of plural head chips possessing concave grooves suited to the adjusting method of the invention. Fig. 10 is a diagram showing a flat sectional shape of laser beam of the invention. As shown in Fig. 2, an apparatus for adjusting a position of a rotary head comprises a microcomputer 11, an image processor 12, a CCD camera 13 for taking an image of a head gap surface, a laser unit 14 for lasing a YAG laser beam 15 which is excited and reflected by a mirror 25 and focused to illuminate a head base 27 of the rotary head by a focusing lens 26, a CCD camera 16 for monitoring the head base where a laser beam is applied, and a stage 17 fixing the rotary head drum unit 18. Meanwhile, the drum unit 18 employs a fluid bearing, and the rotary drum is designed to be rotated by a driver circuit 19. From the driver circuit, a signal synchronized with the rotation is generated, and this synchronous signal is sent to the microcomputer 11. The stage 17 comprises two stepping motor stages for moving the rotary head drum with heads in order to apply a laser beam to a proper point on the head base. The movement of the stage 17 is controlled by the microcomputer 11. The microcomputer 11 is connected to the laser unit 14 for lasing the YAG pulse laser; beam wavelength being 1.06 µm, by sending a laser ON signal synchronized with the rotation of the drum. Also the lasing conditions are sent to the laser unit 14 from the microcomputer 11. The image of a gap surface during rotation of the drum is observed as a still picture by the CCD camera 13 using the synchronous signal synchronized with rotation sent from the microcomputer 11, and the video signal of the still picture is sent to the image processor 12. Then, the image is stored in the image processor 12. The head positions such as absolute head height, relative head height and azimuth angle are obtained by processing the brightness of the image divided into some gray levels. The precision of the above measurement is about 0.06 µm. The measured data are sent to the microcomputer 11, and compared with data indicative of desired head positions to get required amount of adjustment. The proper lasing conditions corresponding to the required adjustment are obtained by using a preprogrammed algorithm in the microcomputer 11. The algorithm is based on some experimental result described below. Referring first to Fig. 3, the principle of head position adjustment by irradiation of a laser beam is explained below. As shown in Fig. 3, in the head bases 3a, 3b, grooves 21a, 21b are formed between penetration holes 20a, 20b for fixing the rotary heads and head chips 1a, 1b. In Fig. 3A, the laser beam is emitted on a line of wave line AA′ other than the groove part 21a, and the illuminated part 22a rises in temperature by energy of the laser beam, thereby causing plastic deformation. This plastic deformation part 22a induces a concave deformation of the head base 3 on the irradiation side on the boundary of the wave line AA′ when restrained from the surroundings in the cooling process and cooled to room temperature. In Fig. 3B, the laser beam is emitted to the bottom of the groove part 21b, and the illuminated part 22b is raised in temperature by the energy of the laser beam, thereby causing plastic deformation. This plastic deformation part 22b is restrained from the surroundings in the cooling process in same way as in the case in Fig. 3A. This plastic deformation part, however, induces a convex deformation of the head base 3b on the irradiation side, contrary to the case above, on the boundary of the wave line BB′ when cooled to room temperature because the plate thickness is less than half. Fig. 4 shows the relation between the groove part plate thickness and the head base deformation. The energy of the emitted laser beam is an Nd YAG pulse laser of wavelength of 1.06 microns with 1 joule per pulse. The rotary heads No. 1, No. 2, No. 3 have a groove part plate thickness of 70%, 50%, 30% as compared with the thickness of the head base itself. The axis of ordinates in the diagram denotes the results of measurement of position changes in the z-axis direction in the diagram of the points 1A′, 1B′, 1C′ of the head gap surface, and the axis of abscissas represents the number of irradiations of the laser beam to the groove part 21b. As understood from this diagram, the deformation direction of the head base varies depending on the plate thickness of the groove part. When the plate thickness of the groove part is less than half the plate thickness of the head base itself, a convex deformation is induced on the irradiation side by the irradiation to the groove part bottom surface. Besides, since all points on the head gap surface show change in position by a same amount, it is known that the azimuth angle is not changed by irradiation on the groove part bottom surface, and that only the z-axis, that is, the head height direction is changed. Fig. 5 shows the changes of head positions when applying YAG laser pulses to the points 2A or 2B on the head base 9b with the power of 1 joule per pulse for several times. The thickness at the pit portion 2B was less than a half of the head base 9b. As shown in Fig. 5, by applying the laser pulses to the point 2A, the points 2A′ and 2B′ move into the "plus" direction in z-axis about 0.2 µm and 0.1 µm per a laser pulse respectively, but the position change of the point 2C′ was small enough to be ignored as compared with the others. Similarly, when applying laser pulses to the point 2C, the points 2C' and 2B' move into the "plus" direction in the z-axis about 0.2 µm and 0.1 µm per a laser pulse respectively, but the position change of the point 2A′ was small enough to be ignored as compared with the others. As mentioned above, the changes at both side edges of a head, such as 2A′ and 2C′, are not the same, but stable. As a head 9a having a width of 2 mm, the different change at side edges of about 0.2 µm per a laser pulse causes a head rotating corresponding to the change of 20 seconds in azimuth angle. It indicates that, by applying a laser pulse to the point 2A or 2C, about 0.1 µm in head height and 20 seconds in azimuth angle can be adjusted. Furthermore, by applying a laser pulse to both points 2A and 2C, it was found that about 0.2 µm in head height can be adjusted without varying the azimuth angle. On the other hand, as shown in Fig. 5, by applying laser pulses to the point 2B, each of three points in a head, 2A′, 2B′ and 2C′, moves into the "minus" direction in z-axis about 0.2 µm per pulse. Accordingly, it is possible to compensate the over-adjustment into the "plus" direction in z-axis without any changes in azimuth angle. Here, the important fact obtained through the above results is that the changes in head positions per a laser pulse are dependent not only on the point where a laser pulse is applied to and the number of the laser pulse applying times but also the power of the laser pulse. As mentioned above, the adjusting algorithm adopted in the preferred embodiment includes calculating the proper lasing conditions and determining the point to which the laser pulse is applied, corresponding to the required adjustment in head height and azimuth angle of head. As shown in Fig. 6, with the rotary head possessing the groove part actually fixed on the rotary drum, the laser irradiation is conducted through a penetration hole 61 opened in the rotary drum. Anyway, the head position adjusting process in the preferred embodiment comprises: 1. inputting the desired head position data to the microcomputer; 2. measuring all of the head positions fixed on the rotary head drum by processing the images of all head gap surfaces taken with the drum rotating; 3. determining the proper lasing conditions and the point to which the laser pulse is applied on the head base by the microcomputer according to the preset algorithm; 4. moving the stage for adjusting the head drum in order to apply the laser pulse to an appropriate point on the head base; 5. applying the laser pulses to the head base with the drum rotating; and repeating the operations 3 through 5 until all rotary heads are adjusted to the desired head positions. ALTERNATIVE EMBODIMENTS In the apparatus for adjusting the head position in the foregoing preferred embodiment, it is intended to adjust the head position in the drum unit using a fluid bearing in the rotary drum, and therefore measurement of head position and irradiation of laser beam are conducted while the drum is rotating. In other apparatus for adjusting the position of a head by emitting a laser beam while the drum is rotating, for example as shown in Fig. 7, two mirrors 28, 29 are disposed between a focusing lens 26 and the rotary head, and the mirrors 28, 29 are rotated in synchronism with the rotation of the drum so that the optical axis of the laser beam may always come right on the head base to be irradiated. Or in adjustment of head position in a drum unit using a ball bearing, instead of a fluid bearing, in the rotary drum, the measurement and irradiation may be done while the rotary drum is stopped still, and the apparatus for adjustment is only the constitution shown in Fig. 8 excluding the driver block enclosed by broken line in the constitution in Fig. 2. Moreover, instead of the hitherto explained case of adjusting the head position by laser beam irradiation in the state of being installed in the rotary drum, it is also possible to adjust the position by the rotary head alone before fixing the rotary head on the drum. For example, in the multi-head for multi-channel recording as shown in Fig. 9, at least two heads 71, 72 may be bonded on each one of head bases 73, 74. In such a case, in respect to the production cost, it is preferable that the adjustment of relative head height among all heads bonded on one head should be carried out before the head bases are fixed on the rotary head drum. Here, in order to adjust the relative head height in one head base, the head base should have the pits (at least) as many as the number of heads bonded as shown in Fig. 9. Besides, as clear from the relation between the irradiation position and head position mentioned so far, when a cylindrical lens 91 is put before a head base 100 and the sectional shape 92 of the laser beam is an elliptical shape 93 as shown in Fig. 10, the head height can be adjusted without varying the azimuth angle. The invention has been described in detail with reference to the preferred embodiments, but it is understood that variations and modifications can be effected within the scope of the invention.

Claims: A rotary head adjuster for adjusting a position of a head chip (1a, 1b, 71, 72) of a rotary head (1) which comprises a head base (3a, 3b, 73, 74) and at least one said head chip fixed to said head base, characterized by comprising: a stage (17) for mounting thereon said rotary head; a position measuring means (12, 13, 16) for measuring a position of said head chip of said rotary head mounted on said stage; a laser means (14, 25, 26) for emitting a laser beam and applying the laser beam to a specified area on said head base of said rotary head mounted on said stage so as to cause a plastic deformation of said head base at said specified area; and control means (11) for comparing the position of said head chip measured by said position measuring means with a predetermined position, calculating a necessary position adjusting amount, setting appropriate laser irradiation conditions depending on said necessary position adjusting amount, and controlling said laser means according to said laser irradiation conditions so as to cause a change of the position of said head chip by the plastic deformation of said head base to be the predetermined position. A rotary head adjuster according to claim 1, wherein said stage (17) is a movable stage, and wherein said control means (11) controls at least one of said movable stage and said laser means (14) to adjust a position of said specified area on said head base to which the laser beam is applied. A rotary head adjuster according to claim 1, wherein said rotary head (1) is mounted on a rotary drum (2, 18), and said stage (17) mounts thereon said rotary drum. A rotary head adjuster according to claim 3, wherein said stage (17) mounts thereon said rotary drum 2, 18) rotatably, and wherein said rotary head adjuster further comprises a drive means (19) which is responsive to a control signal from said control means (11) for rotating said rotary drum mounted on said stage at a specific speed. A rotary head adjuster according to claim 4, wherein said position measuring means (12, 13, 16) measures the position of said head chip (1a) of said rotary head (1) on said rotary drum (2, 18) rotating on said stage, and wherein said control means (11) controls said laser means (14) for applying the laser beam to said specific area on said head base (3a) mounted on said rotary drum rotating on said stage. A rotary head adjuster according to any of claims 3, 4 and 5, wherein said rotary drum is provided with a hole for passing therethrough said laser beam. A rotary head adjuster according to any of claims 1, 2, 3, 4, 5 and 6, wherein said head base (3a) has a groove (21b, 75, 76) having a bottom surface, and wherein said laser means (14, 25, 26) applies the laser beam to an area on said bottom surface of said groove. A rotary head adjuster according to any of claims 1, 2, 3, 4, 5, 6 and 7, wherein rotary head (1) comprises a single head base (73, 74) and a plurality of head chips (71, 72) fixed to said single head base, and wherein said control means (11) and said position measuring means (12, 13, 16) are cooperative to control said laser means (14, 25, 26) to apply said laser beam to a plurality of different predetermined areas on said single head base so as to adjust relative positions of said plurality of head chips to one another. A rotary head adjuster according to any of claims 1, 2, 3, 4, 5, 6, 7 and 8, wherein the laser beam applied to said base by said laser means has a sectional shape which is elliptical. A rotary head comprising a head base (3a, 73, 74), and at least one head chip (1a, 1b, 71, 72) fixed to said head base, characterized in that said head base (3a, 73, 74) has at a specified area thereon a thermally caused plastic deformation area and is bent at a boundary of said plastic deformation area, and that said at least one head chip (1a, 1b, 71, 72) is fixed to said head base at an adjusted position defined by a bent amount of said head base. A rotary head according to claim 10, wherein said head base (3a, 73, 74) has formed at said specified area a groove (21b, 75, 76) which has a bottom surface, said bottom surface having said thermally caused plastic deformation area. A method of adjusting a position of a head chip (1a, 1b, 71, 72) of a rotary head (1) which comprises a head base (3a, 73, 74) and at least one said head chip fixed to said head base, characterized by comprising the steps of: positioning said head base; and applying a laser beam to a specified area on said head base for causing a plastic deformation of said head base at said specified area to bent said head base by said plastic deformation so that the position of said head chip becomes a predetermined position. A method according to claim 12, further comprising a step of forming a groove (21b, 75, 76) having a bottom surface on a surface of said head base prior to said positioning step, wherein said laser beam applying step applies said laser beam to a specified area on said bottom surface of said groove for causing said plastic deformation of said head base at said specified area on said bottom surface of said groove to bent said head base by said plastic deformation in a direction opposite to a laser beam applying direction so that the position of said head chip becomes said predetermined position.

Inventors: HIGASHIONJI MASARU, MAEGAWA TAKAAKI, MUKAE HIDEAKI, MURATA AKIO, OKADA TOSHIHARU, HIGASHIONJI, MASARU, MAEGAWA, TAKAAKI, MUKAE, HIDEAKI, MURATA, AKIO, OKADA, TOSHIHARU
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: G11B5
IPC codes: G11B5