GB2179407A

GB2179407A - Rotary head mechanism

Info

Publication number: GB2179407A
Application number: GB08616860A
Authority: GB
Inventors: Tatsumaro Yasmashita
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 1985-07-22
Filing date: 1986-07-10
Publication date: 1987-03-04
Anticipated expiration: 2006-07-10
Also published as: GB8616860D0; DE3624576A1; GB2179407B

Abstract

A rotary head mechanism (30) is for use with a magnetic recording/reproducing apparatus such as a video tape recorder or a PCM tape recorder. In the rotary has mechanism (30), a rotary drum (32) carrying a magnetic head (38) is borne rotatably with respect to a stationary drum (33) by a shift (21) and a pair of bearings (22, 34). One of these bearings (22) is held on the shaft (21) whereas the other bearing (34) is made separately of and fitted on the shaft (21). A preload spring (36) applies a preload in an axial direction to the bearing (34) made separately of the shaft. <IMAGE>

Description

SPECIFICATION Rotary head mechanism The present invention relates to a rotary head mechanism to be used with a magnetic recording/reproducing apparatus such as a video tape recorder (which will be shortly referred to as "VTR") or a POM tape recorder and, more particularly, to a rotary head mechanism of the type in which is improved a bearing mechanism supporting a rotary drum rotatably.

Before entering into the detailed description of the present invention, the prior art will be discussed with reference to Figures 6 and 7.

Figure 7 is a half section showing a rotary head mechanism according to the prior art.

In this rotary head mechanism, a pair of radial bearings 2 and 3 are fixed on the internal diameter portion of a stationary drum (or stationary member) by means of the press-fit or shrinkage fit and have their outer races positioned at their opposed end faces by stepped grooves A of the stationary drum 1.

Moreover, a shaft 4 is fixed in the inner races of the bearings 2 and 3 by means of the press-fit such that it is made rotatable by the bearings 2 and 3. On the upper end of the shaft 4, there is fixed a sleeve 5 on which in turn a rotary drum 6 is fixed. A magnetic head 8 is supported by the internal lower face of the rotary drum 6 through a head base 7.

On a lower portion of the shaft 4, there is fixed a magnet support 9 on which a rotor magnet 11 is fixed through a yoke 10. On the other hand, a stator coil 12 is fixed on the lower face of the stationary drum 1. When an electric current is fed to the stator coil 12, the rotor magnet 11 is rotationally driven so that the shaft 4 and the rotary drum 6 are rotated together. A magnetic tape is guided on the outer circumferences of the stationary drum 1 and the rotary drum 6 so that its recorded surface is scanned by the magnetic head 8 carried on the rotary drum 6. Moreover, the signals read out by the magnetic head 8 are transmitted from a rotor transformer 13 to a stator transformer 14 until they are extracted to the outside.

The assemblage of the rotary head mechanism thus composed is made by fixing the bearings 2 and 3 in the stationary drum 1, by subsequently inserting the shaft 4, by fitting a preload collar 15 and a preload ring 16 from below the stationary drum 1 on the shaft 4, and by fixing a preload bush 17 by means of a set-screw 18. When this set-screw 18 is to be fastened, the inner race of the radial bearing 3 is pressed upward by a proper pressure through the preload collar 15 and the preload ring 16 so that a preload is applied in a thrusting direction to the radial bearings 2 and 3.

However, the rotary head mechanism of the prior art shown in Figure 7 is accompanied by the promblems, as enumerated in the following.

(1) Since the preload collar 15, the preload ring 16 and the preload bush are provided as means for preloading the individual bearings 2 and 3, the number of parts consituting the lower portion than the bearing 3 is increased to raise a defect that the vertical size is enlarged. The span between the individual bearings 2 and 3 has to be enlarged to some extent because it will adversely affect the deviation of the outer circumference of the rotary drum 6. As a result, the axial length of the rotary head mechanism is naturally increased if the length of the mechanism lower than the lower bearing 3 is added to that span. Here, the VTR or the PCM tape recorder of recent years is required to have its size and thickness reduced. Especially in the case of use as a tape player to be mounted on an automobile, the reduction in thickness is a very important factor.As a result, the increase in the size, if any, of the rotary head mechanism or the thickest unit in the apparatus will obstruct the reduction in the aforementioned thickness the size of the apparatus.

If the vertical size of the rotary head mechanism is to be reduced unreasonably, the span between the bearings 2 and 3 has to be shortened to cause the aforementioned problem of the deviation of the outer circumference of the rotary drum 6 thereby to make the high precision difficult.

(2) In the assembling works, the proper preload is applied at an ambient temperature to the inner races of the bearings 2 and 3 by the members including the preload bush 17. Here, the stationary drum 1, the shaft 4 and the bearings 2 and 3 are made of different materials: the stationary drum 1 is made of an aluminum alloy; the shaft 4 of stainless steel; and the bearings 2 and 3 of an Fe alloy so that those individual members have different coefficients of thermal expansion. As a result of a change in the ambient temperature, therefore, the extensions in the axial direction become different not only between the stationary drum 1 and the shaft 4 but also between the bearings 2 and 3 and the shaft 4.Especially in case the rotary head mechanism is used with the tape recorder mounted on the automobile, it is subjected to a wide range of temperature change because the temperature of the automotive compartment may drop to a level lower than the freezing point in winter and rise to a level as high as 800C to 90 C in summer. Under these circumstances, the difference between the extensions of the individual members in the axial direction will increase so much as to change the preload to be applied to the inner races of the bearings 2 and 3.In case the axial size of the stationary drum 1 is made smaller than that of the shaft 4 by the change in the ambient temperature, more specifically, the pressure applied to the inner race of the bearing 3 by the preload collar 15 fixed on the shaft 4 drops to reduce the preload acting upon the bearings 2 and 3.

In case the axial size of the stationary drum 1 becomes larger than that of the shaft 4, on the contrary, the outer races of the bearings 2 and 3 are vertically pressed by the stepped grooves A of the stationary drum 1 so that the preload to be applied to the bearings 2 and 3 become excessive. An example of the relationship between the preload upon the bearings 2 and 3 and the change in the ambient temperature is depicted by a broken line in the diagram of Figure 6. Under the circumstances of the wide temperature change, as depicted in this diagram, the bearing mechanism of the rotary head mechanism of the prior art is encountered by the large change in the preload to be applied to the inner races of the bearings 2 and 3.At a higher ambient temperature, the bearing preload will gradually rise until this rise becomes gentle at 700C to 80 C. At this high temperature of 700C to 80 C, the balls of the bearings 2 and 3 are indented to generate vibration noises while they are rotating. If the ambient temperature becomes excessively low, on the contrary, a radial clearance is established between the bearings 2 and 3 as a result of the drop in the preload so that the shaft 4 cannot rotate highly precisely anymore due its rollings.

It is, therefore, an object of the present invention to provide an improved rotary head mechanism. The head mechanism embodying the invention and as hereinafter described is enabled to apply a proper preload to the inner races of a pair of bearings bearing a shaft and to prevent the preload from fluctuating even with large changes in the ambient temperature so that the bearings can be prevented from having their balls indented or their radial clearance excessively enlarged thereby to enhance the rotational precision of a rotary drum.

According to the present invention, there is provided a rotary head mechanism comprising: a stationary member; a shaft; a pair of integral and separate bearings the former of which is held on said shaft and the latter of which is made separately of said shaft and fitted on the same; a rotary drum carrying a magnetic head and borne rotatably with respect to said stationary member through said shaft and said paired bearings; and a preload spring for preloading said separate bearing in a thrusting direction.

According to the present invention, one bearing is held on the shaft whereas the other bearing is made separately of and fitted on the shaft and is preloaded by the preload spring so that the preload spring can apply a proper thrusting load to the inner races of the bearings to set the preload at the most proper level. As a result, even if the shaft and the rotary drum are made of materials having different coefficients of thermal expansion so that they are caused to differently extend in the axial direction by a change in the ambient temperature, this extension difference is absorbed by the extension change of the preload spring so that the preload to be applied to the inner races of the bearings can always be maintained at a constant level.

A rotary head mechanism embodying the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a half section showing the first embodiment of the rotary head mechanism according to the present invention; Figure 2 is a half section showing both the shaft to be used in the rotary head mechanism and the bearing integrated with the shaft; Figure 3 is a sectional view showing the second embodiment of the rotary head mechanism according to the present invention; Figure 4 is a top plan view showing the magnetic reproducing apparatus mounted on the automobile and equipped with the rotary head mechanism; Figure 5 is a side elevation showing the same; Figure 6 is a diagram depicting the changes in the preload upon the bearings due to the temperature change; and Figure 7 is a half section showing the rotary head mechanism of the prior art.

The embodiments of the present invention will be described in the following with reference to Figures 1 to 5.

Figure 1 is a half section showing the first embodiment of the rotary head mechanism according to the present invention, and Figure 2 is a half section showing both a shaft used in the rotary head mechanism of Figure 1 and a bearing integrated with the shaft.

As shown in Figure 2, a radial bearing 22 made integral with an upper portion of a shaft 21 used in the rotary head mechanism 30.

The radial bearing 22 is constructed of balls 22a contacting with a groove 21a formed in the upper portion of the shaft 21, and an outer race 22b disposed in contact with the outer circumferences of the balls 22a. On the other hand, a spring stop ring 23 is fixed on the shaft 21 slightly below the bearing 22.

On an upper portion of the shaft 21, as shown in Figure 1, there is fixed a sleeve 31 on which in turn a rotary drum 32 is fixed. On the other hand, a stationary drum (or a stationary member) 33 located below the rotary drum 32 is formed with stepped grooves B and C in upper and lower positions of the internal diameter portion thereof. The bearing 22 integrated with the shaft 21 is fitted from above in the stationary drum 33 by means of the press-fit or shrinkage fit so that is outer race 22a is positioned in the upper stepped groove B. On a central portion of the shaft 21, there is fitted a preload spring 36 which has its upper end abutting against the spring stop ring 23 fixed on the shaft 21. On a lower portion of the shaft 21, there is fixed a preload collar 35 which recieves the lower end of the preload spring 36.On a lower portion of the shaft 21, on the other hand, there is fitted another radial bearing 34. This bearing 34 is made separately of the shaft 21.

The fitting condition of that bearing 34 is made such that the bearing 34 can slide with respect to the shaft 21. However, the bearing 34 is fixed in the stationary drum 33 by means of the press-fit or shrinkage fit and has its outer race positioned by lower stepped groove C.

The aforementioned preload spring 36 is sandwiched in its shrinkage state between the spring stop ring 23 and the preload collar 35 so that its elastic force applies a predetermined inner ring preload to the upper bearing 22 and the lower bearing 34. And, this bearing preload is set at a properlevel by the preload spring 36.

On the lower face of the rotary drum 32, on the other hand, there is fixed a head base 37 on which in turn a magnetic head 38 is fixed.

Moreover, a rotor transformer 41 is fixed in the rotary drum 32 whereas a stator transformer 42 is fixed in the stationary drum 33 such that the two transformers 41 and 42 are opposed to each other at a minute gap. While the rotary drum 32 is rotating, the signals read out by the magnetic head 38 are guided through the two transformers 41 and 42 to the outside.

On a lower portion of the shaft 21, there is fixed a magnet support 43 on which in turn a rotor magnet 45 is fixed through a yoke 44.

To the lower end of the stationary drum 33, on the other hand, there is fixed a base plate 46 on which in turn a stator coil 47 is fixed.

When an electric current is fed to the stator coil 47, the rotor magnet 45 is rotationally driven so that the shaft 21 and the rotary drum 32 are rotated together.

In the rotary head mechanism thus constructed, the shaft 21 and the stationary drum 33 are usually made of different materials. For example, the shaft 21 is made of stainless steel whereas the stationary drum 33 is made of an aluminum alloy. If, in this case, the ambient temperature changes, the axial extensions of the shaft 21 and the stationary drum 33 become different as a result of the difference in the coefficients of thermal expansion between the individual materials. Since the bearings 22 and 34 are firmly fixed with respect to the stationary drum 33 while being positioned by the stepped grooves B and C, the span between the individual bearings 22 and 34 follows the change in the size of the stationary drum 33 in case the axial size of the stationary drum 33 is changed by the temperature change.Since the bearing 22 is integrated with the shaft 21, moreover, the difference between the axial extensions of the shaft 21 and the stationary drum 33 is absorbed by the slight sliding motions between the inner race of thedower bearing 34 and the shaft 21. As has been described above, the preload to be applied to the individual bearings 22 and 34 is preset at a suitable level by the elastic force of the preload spring 36. In case the stationary drum 33 extends or contracts as a result of the temperature change, moreover, the span between the bearings 22 and 34 changes so that the deflection of the preload spring 36 accordingly changes. Since this change in the deflection is minute, however, the change in the elastic force of the preload spring 36 according to the spring constant of the same is also minute.As a result, the elastic force of the preload spring 36 is hardly changed even with the change in the ambient temperature so that the preload to be applied to the bearings 22 and 34 is hardly influenced.

A solid curve appearing in the graph of Figure 6 plots the change in the preload upon the individual bearings 22 and 34 of the rotary head mechanism shown in Figure 1 against the change in the ambient temperature. As depicted in the graph, there arises little change in the preload upon the individual bearing 22 and 34 irrespective of the change in the ambient temperature. This makes it possible to prevent the balls in the bearings from being indented by any excessively high preload and the bearings 22 and 34 from being formed with any radial clearance due to shortage of the preload.

Since the upper bearing 22 is made to have the construction integrated with the shaft 21, moreover, the concentricity between the shaft 21 and the outer race 22b of the bearing 22 can be maintained at a high level. As a result, the deviation of the axis of the rotary drum 32 after the assemblage can be reduced to ensure the rotations in high precision.

Next, Figure 3 is a sectional view showing a second embodiment of the rotary head mechanism 30 according to the present invention. In the first embodiment shown in Figure 1, the shaft 21 is integrated with the rotary drum 32 and is rotatably borne on the stationary drum 33. In the second embodiment, on the contrary, the shaft 21 is fixed by a stationary member 33a so that the rotary drum 32 is rotatably borne on that shaft 21.

The shaft 21 and the bearing 22 used in the rotary head mechanism of this second embodiment are made so identical to those shown in Figure 2 that the bearing 22 is integrated with the shaft 21.

In this embodiment, the shaft 21 is fixed by the stationary member 33a. This stationary member 33a is made of a thin material in Figure 3 but may be identical to the stationary drum 33 shown in Figure 1. Moreover, the bearing 22 integrated with the shaft 21 is fitted in a lower end portion of the sleeve 31 by means of the press-fit or shrinkage fit and is positioned by a stepped groove E. On the other hand, the bearing 34 made separately of the shaft 21 is fitted in an upper portion of the sleeve 31 by means of the press-fit and shrinkage fit and is positioned by a stepped groove D. Moreover, the bearing 34 and the shaft 21 are made slid blue relative to each other. Still moreover, the rotary drum 32 is fixed in the sleeve 31.This sleeve 31 and rotary drum 32 are rotatably borne on the shaft 21 so that the sleeve 31 carrying the rotor magnet 45 is driven by feeding an electric current to the stator coil 47.

In this embodiment, too, there is sandwiched between the preload collar 35 and the spring stop ring 23 the preload spring 36 by which the preload to be applied to the individual bearings 22 and 34 is set at a proper level. Even if, moreover, the shaft 21 and the sleeve 31 are caused to extend differently in the axial direction by the change in the ambient temperature, no influence is exerted upon the preload upon the individual bearings 22 and 34 like the embodiment shown in Figure 1.

Next, one example of a magnetic reproducing apparatus equipped with the rotary head mechanism so that it may be mounted on an automobile will be described with reference to Figures 4 and 5. Indicated at reference numeral 51 is a chassis on which is mounted the rotary head mechanism 30 exemplified by each of the aforementioned embodiments. On the other hand, numeral 54 indicates a loading mechanism for laoding a cassette 60 onto the chassis 51. The tape T in the cassette 60 thus loaded is drawn by tape drawing members 52 and 53 mounted on the chassis 51 and is wound at an inclination on the outer circumferences of the rotary drum 32 and the stationary drum 33 (or the stationary member 33a) of the rotary head mechanism 30. And, the rotary drum 32 is rotationally driven so that the recorded surfaceof the tape T is scanned by the magnetic head 38.Moreover, the signals read out by the magnetic head 38 are transmitted from the rotor transformer 41 to the stator transformer 42 until they are outputted to the outside.

As has been described hereinbefore, there can be attained the effects which will be enumerated in the following: (1) Since the preload upon the bearings is set by the preload spring, it will not change so much, even if the extension of the stationary drum is changed by the change in the ambient temperature, so that the bearings can be prevented from being damaged or formed with their radial clearance. As a result, the rotary head mechanism can be effectively mounted on the apparatus which is subjected to large changes in the ambient temperature, especially the magnetic reporducing apparatus to be mounted on the automobile.

(2) Since it is unnecessary to ixe the preload collar 15, the preload ring 16 and the preload bush 17 on the below the lower bearing, as is different from the example of the prior art of Figure 7, the total thickness size of the rotary head mechanism can be reduced to contribute to the reduction of the thickness of the apparatus. Moreover, the span between the individual bearings 22 and 34 can be elongated to an extent corresponding to the elimination of the preload collar 15 and so on so that the rotational deviations of the shaft and the rotary drum in the radial direction can be reduced to enhance the rotational precision.

(3) If the bearing at one side is integrated with the shaft, the parts shown in Figure 2 can be used as one component so that the number of the parts to be administered can be reduced while their assemblage being simplified. Since the shaft and the bearing are integrated, moreover, their concentricity can be set highly precisely. This makes it possible to maintain the rotational precision of the rotary drum after assemblage at a high level.

(4) Especially if the bearing at one side is integrated with the shaft whereas the bearing at the other side is made separately of the shaft, the separate bearing and the shaft can be simple assembled by the pressing work, and the preload spring 36 and the preload collar 35 can be freely fitted on the remaining portion of the shaft. In other words, the construction described here is advantageous for the two means for integrating the parts and assembling the parts for the preload so that the assembling work can be performed highly efficiently.

Claims

1. A rotary head mechanism comprising: a stationary member; a shaft; a pair of integral and separate bearings the former of which is held on said shaft and the latter of which is made separately of said shaft and fitted on the same; a rotary drum carrying a magnetic head and borne rotatably with respect to said stationary member through said shaft and said paired bearings; and a preload spring or preloading said separate bearing in a thrusting direction.

2. A rotary head mechanism according to Claim 1, wherein said integral bearing is made integral with said shaft and includes: a plurality of balls abutting on the circumference of said shaft; and an outer race disposed outside of said balls and guiding said balls in a rolling manner between itself and said shaft.

3. A rotary head mechanism according to Claim 1, or to Claim 2, wherein said preload spring is sandwiched between said paired bearings.

4. A rotary head mechanism according to Claim 3, wherein said integral bearing is made integral with said shaft and includes: a plural ity of balls abutting on the circumference of said shaft, and an outer race disposed outside of said balls and guiding said balls in a rolling manner between itself and said shaft, further comprising a ring fitted on said shaft and abutting against the end portion of said preload spring at the side of said integral spring.

5. A rotary head mechanism according to any preceding Claim, wherein said rotary drum is fixed on said shaft, and wherein said paired bearings are fixed in said stationary member in a manner to bear said shaft rotatably.

6. A rotary head mechanism according to any one of Claims 1 to 4, wherein said shaft is fixed in said stationary member, and wherein said rotary drum is rotatably borne on said shaft through said paired bearings.

7. A rotary head mechanism according to any preceding Claim, wherein said stationary member is a stationary drum.

8. A rotary head mechanism substantially as hereinbefore described with reference to Figures 1 to 6 of the accompanying drawings.