JPS61246911A - Rotary head operating device - Google Patents

Abstract

PURPOSE:To control axial displacement of a magnetic head surely by applying control current to two driving coils provided at the center of rotation of a rotary body and concentric cylindrical part of a stator. CONSTITUTION:When control current iR is applied only to the first driving coil 8a in the direction of arrow mark F, an upward thrust F is generated in the first magnets 6a, 7a fixed to needles 4, 5, and needles 4, 5 displace upward parallel to the rotation shaft. When control current is large enough, needles 4, 5 displace until they strike against stoppers 18, 19 respectively. That is, magnetic heads 2, 3 can be fixed at prescribed positions adjusted respectively by stoppers 18, 19. As these stoppers 18, 19 are formed utilizing adjusting screws, final positions of displacement of magnetic heads 2, 3 can be fine adjusted by turning the adjusting screws.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a rotary head actuating device used in a helical scan video tape recorder, and more particularly, it is capable of correctly scanning signal tracks recorded on a magnetic tape. The present invention relates to a rotary head operating device that can displace a rotary magnetic head in the direction of a rotation axis.

(Prior art) Conventionally, as a method for displacing a rotating magnetic head in the axial direction, 1
For example, there is a method in which a magnetic head is mounted on a rectangular bimorph piezoelectric element and the position of the magnetic head is changed using the electro-mechanical conversion characteristics of the piezoelectric element. (Nation
al Technical Report Vol. 28, No. 3, pages 39-47).

(Problems to be Solved by the Invention) However, due to the nature of the material, the bimorph piezoelectric element constituting this type of rotary head actuating device has hysteresis, does not have sufficient mechanical strength, and has large amplitude displacement. There was a problem in that it was difficult to construct a durable and stable rotary head actuating device because it could be destroyed if you tried to make it work, and its characteristics change over time.Furthermore, this method In order to transmit electrical signals containing positional change information for driving the piezoelectric element from the fixed part to the rotating part, conductive slip rings and brushes are required, resulting in a complicated structure. Furthermore, in order to obtain the required pit displacement using the piezoelectric element described above, a high voltage of several hundred volts is required, so a high voltage generation circuit must be provided to drive the piezoelectric element, making the system expensive. There was also the problem of becoming

Also, the video tape recorder during its playback.

If the magnetic head is displaced under the operation of the tracking control system and is correctly scanning the recording track of the magnetic tape, the reproduced image will not change even in any tape speed play state such as still playback or slow motion playback. Although it has the advantage of not producing noise bars, it requires two magnetic heads to be fixed in place during recording, so two magnetic heads are used for variable speed playback and two magnetic heads are used exclusively for recording. It was attached to a rotating cylinder.

That is, a video tape recorder capable of variable speed playback requires two magnetic heads, one for variable speed playback and one for recording, making the system extremely expensive and lacking in practicality.

The present invention solves the above-mentioned problems. During playback of a video tape recorder, no noise bars are generated in the playback image in any tape speed play state, and the magnetic head is fixed at a predetermined position during recording. By doing so, it is possible to record and play with the same magnetic head used for playback without having to install a special magnetic head for recording.It is durable, operates stably, and has no slip ring or brush for power supply. It is intended to provide an actuating device.

(Means for Solving the Problems) In order to solve the above problems, the rotary head actuating device of the present invention is provided with a magnetic head and two magnets, which can be displaced in the direction of the rotation axis. A rotating body provided with two movable pieces and two stoppers that regulate the amount of displacement of each of these movable pieces.

So that there is an air gap between it and the pole face of the above magnet.

and a fixed part having a stator wound with at least two drive coils disposed at the center of rotation of the rotating body or on a concentric circle thereof, and supplies a control current to the two drive coils during playback. By this, the magnetic head is operated to correctly scan the signal track recorded on the magnetic tape in the axial direction of the rotating body, and during recording, a control current is supplied to only one of the drive coils, and the two drive coils are controlled. The movable pieces are moved to their respective stopper positions, and the magnetic heads are fixed at respective predetermined positions.

(Function) With this configuration, when the video tape recorder is playing, the magnetic head on the tape is moved by displacing the magnetic head in the direction of the rotation axis in accordance with the tape speed for still playback or slow motion playback. This makes it possible to scan recording correctly, and by fixing the position using a stopper during recording, it is possible to perform variable speed reproduction and recording using the same magnetic head.

(Example) Embodiments of the present invention will be explained with reference to FIGS. 1 to 6.

Fig. 1 is a sectional view of a rotary head cylinder incorporating a rotary head actuating device according to the present invention, Fig. 2 is a plan view of the rotary head cylinder shown in Fig. 1 with the rotating body removed, and Fig. 3 is an exploded perspective view thereof. be.

In FIG. 1, a rotating body 1, which forms a normal rotating drum 1a around which a magnetic tape is wound, has magnetic heads 2 and 3 disposed at both ends of the lower diameter line, respectively.
It is driven by a motor (not shown) and rotates around a center line S.

These magnetic heads 2 and 3 are attached to the lower ends of movable pieces 4 and 5 that can be displaced in the direction of the rotation axis, that is, in the directions indicated by arrows A and B.

The inner walls of these movable pieces 4 and 5 have first and second
two magnets each called 6a, +5b and 7a
, 7b are fixed and each magnetized in the radial direction.

Two drive coils 8a and 8b called first and second
The cylindrical stator 9, which is wrapped with Fixed.

Further, the movable pieces 4 and 5 are attached to the rotating body 1 via two annular leaf springs 11 and 12 constituting a parallel rectangular spring, and are attached to the rotating body 1 as indicated by the arrows A and B as described above.
is supported so as to be displaced parallel to the axis of rotation. Furthermore, first and second magnets 6a, 7a and 6b attached to movable pieces 4 and 5, respectively,
The magnetic pole surfaces of the coils 7b are configured to face the outer circumferential surfaces of the first and second drive coils 8a and 8b wound around the stator 9, respectively, with a predetermined gap maintained therebetween.

A rotating shaft 13 fixed to the rotating body 1 is supported at a boss portion of the fixed portion 10 by two bearings 14a and 14b.

The lower end of the boss of the rotating body 1 and the fixed part IO opposite thereto
A rotor 15a and a stator 15b of a rotary transformer are respectively attached to the annular bottom surface of the magnetic head 1, so that signals can be sent and received to and from the magnetic heads 2 and 3 in a good manner.

Head position detection coils 16a and 16b for detecting the amount of displacement of the magnetic heads 2 and 3 with respect to the rotating body 1 are mounted on a conductive head mounting plate 1 to which the magnetic heads 2 and 3 are fixed.
They are attached to the rotating body 1 so as to face each other with a constant gap between them 7a and 17b.

In this type of position detection method, a high-frequency current is passed through the position detection coil to generate an alternating magnetic field around it, and when a conductive plate approaches this, an eddy current is generated inside this plate, increasing the impedance of the detection coil. It is an application of the principle of change.

The rotary head operating device of the present invention detects the positions of the magnetic heads 2 and 3 using head position detection coils 16a and 16b, and performs position control based on appropriate damping.

The rotating body 1 is provided with a stopper 18 that functions to fix the magnetic heads 2 and 3 at predetermined positions during recording.
and 19 are provided. These stoppers 18 and 19 have adjustment screws, so by rotating these stoppers 18 and 19,
The fixing positions of the corresponding magnetic heads 2 and 3 can be precisely and finely adjusted.

Note that connection lines from the magnetic heads 2 and 3 to the rotor 15a of the rotary transformer, lead wires from the stator 15b, and lead wires for supplying control current to the drive coils 8a and 8b are not shown.

2 is a plan view of the rotary head cylinder of FIG. 1 with only the rotating body 1 removed, and FIG. 3 is a perspective view of the main components of FIG. 1.

In FIG. 3, annular leaf springs 11 and 12, which constitute parallel rectangular springs and support movable pieces 4 and 5, are attached to rotating body 1 with mounting screws 21a and 21b with spacers 20a and 20b sandwiched between them. .

Other components are given the same numbers as in FIG. 1, and redundant explanation will be omitted.

Regarding the operation of the rotary head actuator with such a configuration,
This will be explained with reference to FIGS. 4 to 6.

FIG. 4 is a diagram showing the operating principle of the rotary head actuating device of the present invention shown in FIGS. 1 to 3, and the component parts are given the same numbers as in FIGS. 1 to 3, and duplicate explanations are omitted. Omitted.

In FIG. 4, the first and second
Control currents are supplied to drive coils 8a and 8b from first and second drive circuits 22 and 23, respectively. An adder 24 and a subtracter 25 are connected to these drive circuits 22 and 23, respectively, and input commands eA and elI are input to both of them.

Further, a third drive circuit 26 that supplies a control current during recording is connected to the first drive coil 8a. An input command eR is input to this.

The two annular leaf springs 11 and 12 that support the movable pieces 4 and 5 to which the magnetic heads 2 and 3 are attached are supported by fulcrums 28 and 29 at their central portions, which are supported by the spacer in FIG. 20a, 20b and mounting screw 21
The attachments attached to the rotating body 1 (not shown in FIG. 4) by means of a, 21b indicate points.

Now, the direction of magnetization of the first magnets 6a, 7a and the second magnets 6b, 7b, which face each other to the outer peripheral surfaces of the first drive coil 8a and the second drive coil 8b, is set as follows for the left movable piece 4:
Regarding the operation when both the second magnets 6a and 6b are configured so that the facing surfaces are N poles, and in the right movable piece 5, the first magnet 7a is the N pole, and the second magnet 7b is the S pole. explain.

First, when the first and second drive coils 8a and 8b are energized with control currents 1 and 12 in the direction of arrow C, the first magnet 6a and the second magnet 6b fixed to the movable piece 4 Both generate upward propulsive force. If these propulsive forces are fl and f2, respectively, the movable piece 4 moves upward by the propulsive force of deyo+f3.

On the other hand, an upward propulsive force f□ acts on the first magnet 7a fixed to the movable piece 5, and a downward propulsive force f2 acts on the second magnet 7b. It will move due to propulsion.

Assuming that the magnitudes of the propulsive forces f1 and f2 are equal and the relational expression f=f holds true, the movable piece 4 has a force of 2f.
1 acts on the movable piece 5, and no propulsive force acts on the movable piece 5. That is, the first and second drive coils 8
Control currents i and 12 are applied to a and 8b in the direction of arrow C in FIG.
If the sizes of the two parts are made equal, only the movable piece 4 moves upward, and the movable piece 5 remains stationary.

Next, without changing the energization direction of the first drive coil 8a, the second
A case will be described in which only the direction of energization of the drive coil 8b is switched as shown by arrow E, and control currents i' and iz' are applied to each of them.

An upward propulsive force f is generated in the first magnet 6a fixed to the movable piece 4, and a downward propulsive force f2 is generated in the second magnet 6b.
1 occurs. Therefore, the movable piece 4 is subjected to a propulsive force f'-f2''. On the other hand, the first magnet 7a and the second magnet 7b fixed to the movable piece 5 are both subjected to an upward propulsive force f' and f'. f and I are generated, and therefore, a driving force of f□'+f2' acts upward on the movable piece 5.

Suppose that the magnitudes of the propulsive forces fi', f, and I are equal,
If the relational expression fi' = f2' holds true, no propulsive force acts on the movable piece 4, and the movable piece 5 moves upward by 2f.
The driving force of the engineering works. That is, the first drive coil 8
a in the direction of the arrow, and the second drive coil 8b in the direction of the arrow E.
When the control currents j□'' and 12' are applied in the directions respectively, the movable piece 4 remains stationary and only the movable piece 5 moves upward.

Next, the operations of the adder 24 and the subtracter 25 will be explained using mathematical formulas.

The forces acting on movable pieces 4 and 5 are FA and F, respectively.
, then the force FA acting on the movable piece 4 is expressed by the following formula (%). However, n is the first and second drive coils 8a and 8b.
B is the number of turns per unit height of the first magnet 6a, 7a and the second magnet 6b, 7b and the stator 9.
The magnetic flux density between the first magnets 6a, 7a and the second magnet
This is the area where the magnets 6b and 7b face the first drive coil 8a and the second drive coil 8b, respectively.

Similarly, the force F acting on the movable piece 5 is expressed by the following equation.

Fl = n-i, ・tlS-n-i, ・B-S=n-
B−S(i, −i,)−(2) Furthermore, the following relational expression holds between the displacement inputs eA and e and the control currents 11 and 12.

ii= g+m CeA+ em ) ”・
”' (a)i, =g+*(eA-am)
(4) where g is the mutual conductance of the first and second drive circuits 22 and 23.

Transforming equations (1) and (2) using equations (3) and (4) above, FA=n'B''S(g, (eA+am) +g, , (
eAe++) ) = 2n fist B-3・g=jeA++・
+++ +++ (5) Fm=n-B-3(gm(eA
+am) -gjeA-ei) )= 2n+B+S
・g,'em---(6).

As is clear from equations (5) and (6), command input e
The propulsive force FA of the movable piece 4 is controlled by A, and the movable piece 5 is controlled by inputting 8 commands.
The propulsive force Fl of each can be controlled independently.

Therefore, during reproduction, it is possible to control the pair of magnetic heads 2 and 3 independently under the operation of the tracking control system, and it is possible to make each magnetic head 2 and 3 correctly scan the recording track of the magnetic tape. It becomes possible.

FIGS. 5(a), 5(b), and 5(c) are detailed views of essential parts for explaining the displacement operation of the magnetic head of the rotary head actuating device shown in FIG. 1. FIGS. Note that the component parts include the first
The same numbers as those in the figures to FIG. 3 are given, and redundant explanations will be omitted. FIG. 5(a) shows a state in which no control current is supplied to the first and second drive coils 8a and 8b. The gap surface of the magnetic head 2.

It is in perpendicular contact with the surface of the magnetic tape 29.

FIGS. 5(b) and 5(c) show control currents 11 and 12 in the first and second drive coils 8a and 8b, respectively.
shows the state in which the magnetic head 2 is displaced when electricity is applied in the direction shown.

In FIG. 5(a), the first magnet 6a and the second magnet 6
The propulsive force generated at b is in the downward direction.

The combined propulsive force F displaces the movable piece 4 to which the magnetic head 2 is attached downward to a position where it balances the restoring force of the two annular leaf springs 11 and 12 forming the parallel rectangular spring.

Similarly, in FIG. 5(c), the propulsive forces generated in the first magnet 6a and the second magnet 6b are both in the upward direction,
The combined propulsive force F displaces the movable piece 4 upward to a position where it balances the restoring forces of the two annular leaf springs 11 and 12.

Such vertical displacement is made parallel to the rotation center axis by the parallel rectangular spring made up of the two annular leaf springs If and 12, so that the magnetic head 2 is always perpendicular to the tape surface of the magnetic tape 29. Therefore, the gap surface of the magnetic head 2 is in good contact with the tape surface, and the contact pressure is always constant. Therefore, even if the magnetic head 2 is displaced in the direction of the rotation axis, no tilting occurs.

There is no attenuation of the reproduced output voltage.

Although the magnetic head 2 attached to the movable piece 4 has been described in FIG. 5, the same applies to the magnetic head 3 attached to the movable piece 5.

FIG. 6 is an operational principle diagram for explaining the operation of the magnetic head during recording. Note that the numbers assigned to the component parts are the same as in FIGS. 1, 3, and 4, so redundant explanation will be omitted.

This figure shows a state in which the control current iR is applied only to the first drive coil 8a in the direction of arrow F, and the first magnets 6a and 7a fixed to the movable pieces 4 and 5 both exert an upward propulsive force. F occurs, and both movable pieces 4 and 5 are displaced upward in parallel to the rotation axis. When the control current ill is sufficiently large, movable pieces 4 and 5 are displaced until they hit stoppers 18 and 19, respectively. That is, the magnetic head 2
and 3 can be fixed at predetermined positions adjusted by stoppers 18 and 19, respectively.

These stoppers 18 and 19 are constructed using adjustment screws as described above, so by turning the adjustment screws, the final displacement positions of the respective magnetic heads 2 and 3 can be finely adjusted. can.

(Effects of the Invention) According to the present invention, electromagnetic force is utilized by applying control current to each of the first and second drive coils disposed in the stator cylindrical portion concentric with the rotation center of the rotating body. Thus, the axial displacement of the magnetic head attached to the movable piece can be reliably controlled.

In particular, since the magnetic head is displaced using an electromagnetic conversion system consisting of a magnet fixed to a movable piece and a drive coil arranged on a stator, slip rings and brushes are no longer required, and the conventional slip ring and brush can be used. Compared to things,
No electrical noise is generated, no extra burden is placed on the rotation of the magnetic head, and the service life can be extended.

Furthermore, the high voltage generation circuit required in a rotary head actuating device that utilizes the electromechanical conversion characteristics of a piezoelectric element is no longer necessary.

Furthermore, since the pair of magnetic heads can be controlled independently, each magnetic head can correctly scan the recording track of the magnetic tape during reproduction. On the other hand, during recording, by supplying a control current to only one of the two drive coils (in the above embodiment, the first drive coil), the movable pieces to which the pair of magnetic heads are attached are moved to the respective adjusted stopper positions. The pair of magnetic heads can be fixed at predetermined positions. Therefore, reproduction and recording can be performed with the same magnetic head, and there is no need to provide a pair of magnetic heads exclusively for recording, making it possible to configure the system at low cost.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a rotary head cylinder incorporating a rotary head actuating device according to the present invention, FIG. 2 is a plan view with only the rotating body removed from FIG. 1, and FIG. 3 is a perspective view of its main components. Figures 4 and 6 are operation principle diagrams for explaining operations during playback and recording, respectively, and Figure 5 (a)
), (b) and (C) are enlarged views of main parts for explaining the operation of the magnetic head. 1... Rotating body, 1a... Rotating drum, 2, 3
... Magnetic head, 4, 5 ... Movable piece, 6a, 7
a...first magnet, 6b, 7b...second magnet, 8
a...first drive coil, 8b...second drive coil,
9... Stator, 10... Fixed part, 10a... Fixed drum, 11.12... Annular leaf spring, 13... Rotating shaft, 14a, 14b... Bearing, 15a...
Rotor of rotary transformer, 15b... Stator of rotary transformer, 16a, 16b... Head position detection coil, 17a, 17b... Head mounting plate, 18.19-... Stopper, 20a, 20b- Spacer , 21a. 21b...Mounting screw, 22...First drive circuit, 2
3... Second drive circuit, 24... Adder, 25...
Subtractor, 26...Third drive circuit, 27.28...
-Fixed point, 29...magnetic tape. Patent applicant: Matsushita Electric Industrial Co., Ltd. Figure 1 Figure 3 Figure 4 Figure 5 (a) (C)

Claims (2)

[Claims] (1) A rotating body equipped with a magnetic head and two magnets, two movable pieces that can be displaced in the direction of the rotation axis, and a stopper that regulates the amount of displacement of each of these movable pieces. , a fixed part having a stator wound with at least two driving coils disposed at the center of rotation of the rotary body or on a concentric circle so as to create a gap between the stator and the pole face of the magnet; During reproduction, the magnetic head is operated in the axial direction of the rotating body by supplying a control current to the two drive coils, and during recording, a control current is supplied to only one of the two drive coils. to respectively displace the two movable pieces to the positions of the two stoppers,
A rotating head actuating device, characterized in that a magnetic head attached to the rotating head is fixed at a predetermined position. (2) The two stoppers are each constructed with a position adjustment screw, so that the final displacement position of the magnetic head can be finely adjusted from the outside of the rotating body. ) The rotary head actuating device described in item 2.