1. Field of the Invention
The present invention relates to a capstan motor for a magnetic recording and reproducing apparatus, and particularly, to a capstan motor which is able to maintain driving height of a tape by preventing a capstan shaft from being vibrated in length direction.
2. Description of the Background Art
Generally, in a magnetic recording and reproducing apparatus, a magnetic tape drives at a constant speed by being inserted between a capstan shaft and a pinch roller which is cohered with the capstan shaft in recording mode and reproducing mode. The capstan shaft is driven by a capstan motor having it as a rotating shaft. The capstan motor is a motor which can be rotated forward and backward, and it can change it""s speed from a normal speed for recording and reproducing modes, that is, general function, to a low speed for a long time recording and reproducing or for a slow mode for reproducing slow motion, that is, for special functions.
Principal parts of the magnetic recording and reproducing apparatus will be described with reference to FIG. 1 as follows.
FIG. 1 is a block diagram showing a tape drive of a general magnetic recording and reproducing apparatus.
In the tape drive of the magnetic recording and reproducing apparatus, a tape 1 which is wound off from a feed reel (not shown) of a tape cassette contacts to a full width erase head 5 for erasing all video and voice control signals recorded on the tape 1 when the tape 1 is in the recording mode, to a video head drum 6 for recording/reproducing video signals, to an audio head 7 for recording/reproducing voice signals, to a control head 8 for recording/reproducing control signal on the tape so that the tape 1 can be driven in a constant speed, and then, wound on a take-up reel (not shown) of the tape cassette.
Herein, a feed reel driving unit 3 and a take-up reel driving unit 4 are installed on one side of a main chassis 2 so as to drive the feed reel and the take-up reel.
Also, a plurality of guide posts 12, 14, 16 and 18 for guiding the driving of the tape 1, and guide rollers of feed side and of take-up side 20 and 22 for supporting the tape 1 and for making the tape draw a natural trajectory are installed on the main chassis 2.
In addition, a tension post 26 for controlling tensile force in driving the tape 1 is installed on a tension arm 24. The tension arm 24 is elastically supported by a spring 29 so as to be rotated as a predetermined angle centering around a shaft pin 28 according to the tensile force of the tape 1.
In addition, a tension brake 27 having both ends fixed on the tension arm 24 respectively is wound on the feed reel driving unit 3, and the tension brake 27 controls the tension of the tape 1 by controlling the rotating speed of the feed reel driving unit 3 according to operations of the tension arm 24.
On the other hand, slant bases for feed side and for take-up side 36 and 38 are installed on both sides of the video head 6 so as to wind the tape 1 on the video head 6, and slant posts for feed side and for take-up side 42 and 44 for guiding the tape 1 toward the video head surface are installed on the slant bases for feed side and for take-up side 36 and 38.
Also, loading paths 32 and 34 for guiding the slant bases for feed side and for take-up side 36 and 38 when the slant bases are moved are formed on both sides of the video head 6.
That is, the tape 1 is guided by the slant posts 42 and 44, then pulled toward the video head 6 when the slant bases 36 and 38 are moved along with the loading paths 32 and 34, and wound on the video head 6.
In the magnetic recording and reproducing apparatus constructed as above, the capstan motor 50 and the pinch roller 54 for making the tape 1 drive are disposed, and the capstan motor 50 will be described with reference to FIGS. 2A and 2B as follows.
The capstan motor 50 comprises a rotor 47 and a stator 48, and the rotor 47 comprises a rotor case 58, a magnet 60 fixedly attached on a periphery of the rotor case 58 for forming a magnetic field required to rotate the capstan motor 50, a pulley 72 fixed on lower center of the rotor case 58 and rotated integrally with the rotor case 58 for driving reel rotation of the magnetic tape, and a capstan shaft 52 fixedly press-fitted on a center of the pulley 72 and cohered with the pinch roller 54 taking the tape 1 therebetween.
Herein, the capstan shaft 52 is an output shaft of the capstan motor 50, and the proceeding direction of the tape 1 is decided by the rotating direction of the capstan shaft 52.
The stator 48 comprises a frame 66 having bearings 64 installed respectively on inner upper and inner lower sides thereof for supporting the rotation of the capstan shaft 52 and a substrate 70 fixed thereon with a coupling bolt 68, and an armature coil 62 fixed to face the magnet 60 of the rotor 47 on the periphery of the frame 66 for rotating the rotor 47 by electromagnetic interaction with the magnet 60.
Operation of the capstan motor 50 of the conventional magnet recording and reproducing apparatus constructed as above will be described as follows.
When electric power is applied to the coil 62, electric force is generated on the coil 62, and the rotor 47 is rotated by the electromagnetic interaction between the electric force and the magnet 60.
That is, the rotor 58 is rotated according to that the direction of the magnetic force (fm) of the magnet 60 and the direction of the electromagnetic force (fc) of the coil 62 function vertically to the shaft direction of the capstan shaft 52.
At that time, the magnetic force (fm) of the magnet 60 and the electromagnetic force (fc) of the coil 62 are not functioned toward the shaft direction of the capstan shaft 52, and therefore, there is no component of the capstan shaft direction in a resultant force of the magnetic force (fm) and of the electromagnetic force (fc).
In addition, the capstan shaft 52 and the pinch roller 54 are cohered with each other taking the tape 1 therebetween to compress the tape 1, and these are rotated by the rotating force of the capstan motor 52 to make the tape 1 drive at a constant speed with a constant tensile force.
The capstan motor 50 constructed and operated as above is vibrated in up-and-down direction by outer elements such as mechanical vibration due to the rotation of the rotor 58 and run-out of the pinch roller generated when the capstan shaft 52 is selectively cohered to the pinch roller 54.
That is, thrust F1, F2 and F3 are functioned to the capstan shaft 52, to the tape 1, and to the pinch roller 54 respectively in the shaft direction of the capstan shaft 52, and therefore, the capstan shaft 52 is changed toward the shaft direction due to the thrusts, and accordingly, the tape 1 is vibrated in up-and-down direction and traveling height is changed.
In detail, since a frictional force between the pinch roller 54 and the tape 1 is greater than that between the capstan shaft 52 and the tape 1, the tape 1 is a lot affected by the thrust F2 of the pinch roller 54, and the thrust F2 of the pinch roller 54 is applied forward an opposite direction of the thrust F1 of the capstan shaft 52. Therefore, in case that the capstan shaft 52 vibrates by a mechanical vibration according to rotation of the rotor 58 or the pinch roller 54 vibrates by exterior factors such as the run out of the pinch roller 54, the tape 1 vibrates in the same direction of the pinch roller 54, thereby changing the traveling height of the tape 1.
Therefore, when the tape 1 contacts to the video head 6, to the audio head 7, and to the control head 8, etc., the contacting status becomes bad, and therefore, the signal recording and reproducing on the tape 1 are not made precisely.
Therefore, an object of the present invention is to provide a capstan motor for a magnetic recording and reproducing apparatus which is able to drive a tape stably by applying a predetermined thrust to a shaft direction of a capstan shaft to restrain vibrations of the capstan shaft in length direction.
To achieve the object of the present invention, as embodied and broadly described herein, there is provided a capstan motor for a magnetic recording and reproducing apparatus comprising: a stator including a coil on outer peripheral direction; a rotor having a magnet so as to correspond to the coil and rotated by an electromagnetic interaction between the coil and the magnet; and a capstan shaft fixed on the rotor to be rotated integrally with the rotor and having one side installed so as to cohere with a pinch roller taking a tape therebetween to drive the tape with the pinch roller, wherein the magnet of a predetermined shape is provided to apply a magnetic force eccentrically for electromagnetic force generated on the coil so that a predetermined thrust can be functioned to one direction of the capstan shaft between upper and lower directions of the shaft.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.