GB2147728A - Magnetic head feed mechanism - Google Patents

Abstract

A magnetic head feed mechanism includes a shaft (1) having a helical groove (6) defined in an outer peripheral surface thereof, a carriage (7) having an engaging member (8) engaging the helical groove (6) and supporting a magnetic head thereon, a stepping motor (20) having an outer shell (26) and a rotor (22) to which one end of the shaft (1) is secured for co-rotation, and an adjustment screw (27) threaded in the outer shell (26) and supporting the one end of the shaft (1) through a bearing (B), whereby the position of the shaft (1) can be adjusted slightly by turning the adjustment screw (27) from outside of the stepping motor (20). <IMAGE>

Description

SPECIFICATION Magnetic head feed mechanism Background of the invention The present invention relates to a feed mechanism for intermittently feeding a carriage supporting a magnetic head in a magnetic disk drive or the like.

One known type of intermittent feed mechanism for feeding a carriage supporting a magnetic head radially across an information storage disk uses a steel belt connected between the carriage and a drive pulley or the like. Such a steel belt, however, tends to stretch and slackened with time. Accordingly, there has been developed a feed mechanism comprising a shaft supported by bearings for rotation about its own axis and having a helical groove defined on an outer peripheral surface thereof, and the carriage carrying the magnetic head has a member engaging the helical groove so that the carriage can be reciprocated a desired distance by rotating the shaft about its own axis.

Figure 1 of the accompanying drawings illustrates in plan such a conventional intermittent feed mechanism employing a screw shaft. The illustrated feed mechanism includes a shaft 1, bearings 2, 3, a gear train 4, a reversible motor 5, a helical groove 6 defined on an outer peripheral surface of the shaft 1, a carriage 7, an engaging member 8 having a pointed end, and guide bars 9.

The shaft 1 is rotatably supported at its opposite ends by the bearings 2, 3. The reversible motor 5 is operatively coupled through the gear train 4 to the left hand end of the shaft 1. The carriage 7 supports a magnetic head H thereon and is slidably fitted over the guide bars 9 extending parallel to the shaft 1. The engaging member 8 is fixed to the carriage 7 and has its pointed end slidably fitted in the helical groove 6 on the shaft 1.

When the shaft 1 is rotated about is own axis in one direction or the other by the motor 5, the engaging member 8 engaging in the helical groove 6 moves horizontally, and as a result the carriage 7 moves along the guide bars 9 a distance commensurate with the extent of rotation of the shaft 1.

With the prior feed mechanism of the above construction, however, a reference position for the carriage 7 is varied to cause the magnetic head H to read and write data inaccurately unless the ends of the shaft 1 are accurately supported by the bearings 2, 3. To ensure such accurate positioning of the shaft 1 with respect to the bearings 2, 3 after they have been assembled, the position of the shaft 1 is adjusted in an axial direction thereof with a jig or the like so as to be properly positioned in the axial direction. The adjusting process is however complicated since the bearings 2, 3 have to be moved in a complex arrangement of surrounding mechanical parts.

Various devices employing magnetic disks such as word processors have recently found widespread use. For recording and reproducing data in and from a magnetic disk in these devices, the position of a read/write head with respect to the tracks on the magnetic disk is determined by moving the head a desired distance based on a count from a zero track or an outermost reference track on the magnetic disk. Therefore, the zero reference track and the magnetic head have to be in a proper positional relationship to each other; otherwise, the head tends to deviate from a desired track during a recording or reproducing mode, and correct tracking control is impossible to achieve.

One known feed mechanism for use in the positioning of the magnetic disk includes a screw shaft having a helical groove defined in an outer peripheral surface thereof and rotatable by a stepping motor for moving a carriage supporting the magnetic head in a radial direction of the magnetic head. When positioning the magnetic head into alignment with the zero track in the conventional feed mechanism, the screw shaft is moved slightly in the axial direction thereof to adjust the position of the carriage. The adjusting operation requires much skill on the part of the operator since trackto-track intervals on the disk are extremely small, and is also complex as the stepping motor must be changed in position at the time the screw shaft is axially moved.

Summary of the invention It is an object of the present invention to provide magnetic head feed mechanism including a bearing device capable of supporting a screw shaft without wobbling movement or backlash, and allowing easy positional adjustment of the screw shaft.

Another object of the present invention is to provide a magnetic head position adjusting mechanism for simply adjusting the position of a magnetic head with respect to a zero track on a magnetic disk in a highly accurate manner without having to change the position of a stepping motor.

According to the present invention, there is provided a magnetic head feed mechanism including a shaft having a helical groove defined in an outer peripheral surface thereof, a carriage having an engaging member engaged in the helical groove and supporting a magnetic head thereon, a stepping motor having an outer shell and a rotor to which one end of the shaft is secured for co-rotation, and an adjustment screw threaded in the outer shell and supporting the one end of the shaft through a bearing, whereby the position of the shaft can be adjusted slightly by turning the adjustment screw from outside of the stepping motor.

The screw shaft and the rotatable shaft of the stepping motor may jointly constitute a single shaft, and a head position adjusting device includes spring means acting on one end of the single shaft for urging the latter in an axial direction thereof, and an-adjustment screw acts on an opposite end of the single shaft for moving the latter in the axial direction thereof.

The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example.

Brief description of the drawings Figure 1 is a fragmentary plan view of a conventional intermittent feed mechanism; Figure 2 is an enlarged cross-sectional view of a bearing according to the present invention; Figure 3 is a cross-sectional view, partly in plan, of an intermittent carriage feed mechanism of the present invention; and Figure 4 is a cross-sectional view, partly in plan, of an intermittent carriage feed mechanism according to another embodiment of the present invention.

Description of the preferred embodiments Figure 2 illustrates a bearing A according to the present invention, the bearing A supporting one end of a shaft 1. The end of the shaft 1 has a conically tapered projection 10A extending into the bearing A. The bearing A has balls 11, a retainer 12, a ball housing 13, a spring 14, a frame 15, and a retaining element 16.

The frame 15 serves as an outer shell A of the bearing A and has a bottomed recess 17 opening at one end of the frame 15. The ball housing 13 is slidably fitted in the recess 17 with the spring 14 interposed between the bottom of the recess 17 and the ball housing 13. The ball housing 13 is prevented from being dislodged from the frame 15 by the retaining element 16 which is annular in shape and force-fitted in the open end of the recess 17. The ball housing 13 has a semi-spherical cavity 18 therein having an open end, with the balls 11 placed on the semi-spherical cavity 18. The balls 11 are retained in the semi-spherical cavity 18 by the retainer 12 which is also annular in shape and force-fitted in the open end of the semi-spherical cavity 18.

The frame 15 is made of a metal such as brass, zinc, for example, or a hard synthetic resin material and is secured to a base plate 28 of a chassis at a given position thereon by being force-fitted, bonded, or any other suitable fastening means.

The conical projection 10A on the end of the shaft 1 extends through the retainer 12 into abutment against the balls 11. The shaft 1 is held under an axial or thrust load by the spring 14 so that the shaft 1 will not be dismounted from the bearing A.

The shaft 1 under the axial spring load allows the bearing A to serve as a wobble-free bearing capable of supporting the shaft 1 rotatably through rolling frictional engagement therewith at a high efficiency and having an automatic centering capability.

Figure 3 shows an intermittent carriage or magnetic head feed mechanism including a stepping motor 20. Corresponding parts in Figure 3 are designated by corresponding reference characters in Figure 2.

The stepping motor 20 is generally composed of annular permanent magnets 22, bobbins 23, and coils 24 wound around the bobbins 23. The stepping motor 20 is mounted by screws 21 onto a base plate 25 of a chassis of a floppy disk drive. A support body 26 serving as a portion of an outer shell is attached to the stepping motor 20. An adjustment screw 27 is threaded in the support body 26 and has a bearing B secured thereto. The bearing B comprises a pivot ball bearing supporting a conical projection 20B on the other end of the shaft 1.

The shaft 1 extends through and is attached to the permanent magnets 22 which serve as the rotor of the stepping motor 20. The shaft 1 thus functions as a rotatable output shaft of the stepping motor 20. The shaft 2 is supported at its opposite ends on the bearings A, B, and is placed under axial load by the spring 14 in the bearing A.

When the shaft 1 or other members are subjected to assembling errors, the adjustment screw 27 can be turned from outside of the stepping motor 20 to positionally adjust the shaft 1 easily in the axial or thrust direction, thereby increasing the accuracy with which the carriage 7 is fed. After the magnetic head has been positioned with respect to the reference track on an adjustment disk, an adhesive is applied to the head of the adjustment screw 27 to prevent the latter from being accidentally turned, thus completing the adjusting operation.

Figure 4 illustrates a magnetic head feed mechanism according to another embodiment of the present invention. Corresponding parts in Figure 4 are denoted by corresponding reference characters in Figures 2 and 3.

A shaft 1 is composed of a screw shaft C and a rotatable shaft D which are coupled coaxially. The shaft 1 is axially loaded by a leaf spring 29 attached to a chassis 28. The shaft 1 is rotatably supported at its opposite ends by bearings A, B. A conical projection 30 on the shaft 1 extends through the bearing A and is held against the leaf spring 29 in a manner to form a pivot contact.

The magnetic head can positionally be adjusted with respect to a reference track on a magnetic disk by turning the adjustment screw 27 to move the shaft 1 slightly in an axial direction thereof.

After the positional adjustment, the adjustment screw 27 is secured in position against rotation by an adhesive applied thereto.

In the embodiment of Figure 4, since the screw shaft C and the rotatable shaft D are separate members, an ordinary stepping motor can be used for rotating the shaft 1. The other construction of Figure 4 is the same as shown Figures 2 and 3, and will not be described in detail.

The present invention is applicable to an optical information reading and writing apparatus of the same arrangement as that described above. The stepping motor and the bearings are illustrative, but not restrictive.

With the arrangement of the present invention, the position of the shaft can be adjusted in the axial or thrust direction easily and reliably by the adjustment screw mounted in the outer shell of the stepping motor, a procedure which is highly efficient as it can be effected after the parts have been assembled. Since the shaft and the motor rotor are integral, the accuracy of power transmission be tween the motor and the shaft will not be impaired by the positional adjustment of the shaft. Because the shaft can be moved slightly in the axial direction by rotating the adjustment screw after the shaft and the stepping motor have been assembled in position, the position of the magnetic head with respect to the reference track on a magnetic head can simply and highly accurately be adjusted without having to displace the stepping motor.

Although certain preferred embodiments have been shown and described, it should be understood that many changes and modifications may be made therein without departing from the scope of the appended claims.

Claims (3)

1. A magnetic head feed mechanism comprising: (a) a shaft having a helical groove defined in an outer peripheral surface thereof; (b) a carriage having an engaging member engaging in said helical groove and supporting a magnetic head thereon; (c) a stepping motor having an outer shell and a rotor to which one end of said shaft is secured for co-rotation; and (d) an adjustment screw threaded in said outer shell and supporting said one end of the shaft through a bearing, whereby the position of said shaft can be adjusted slightly by turning said adjustment screw from outside of said stepping motor.

2. A magnetic head feed mechanism comprising: (a) a guide shaft; (b) a screw shaft having a helical groove defined in an outer peripheral surface thereof; (c) a carriage supporting a magnetic head and slidably fitted over said guide shaft, said carriage having an engaging member engaging in said helical groove; (d) a stepping motor for rotating said screw shaft about its own axis, said stepping motor having a rotatable shaft, said screw shaft and said rotatable shaft jointly constituting a singe shaft; and (e) a head position adjusting device including spring means acting in one end of said single shaft for urging the latter in an axial direction thereof and an adjustment screw acting on an opposite end of said single shaft for moving the latter in the axial direction thereof.

3. A magnetic head feed mechanism substantially as hereinbefore described, with reference to Figures 2 to 4 of the accompanying drawings.