JPH0614777B2 - Voice coil motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voice coil motor (hereinafter abbreviated as VCM) of a disk drive, and more particularly to providing a magnetic circuit suitable for a high-power actuator for a plurality of carriages.

[Background of the Invention]

FIG. 1 shows a conventional example of a du actuator. The dual actuator has two carriages 2 with respect to a set of disk groups 1 and thereby improves the throughput of the disk.

The VCM motor has a magnet 3, two pole pieces 4,
It is composed of a front yoke 5 and a rear yoke 6. A magnetic flux is concentrated on the gap portion of the front yoke 5 and an electric current is caused to flow through a coil 7 attached to the rear portion of the carriage to generate a force, so that the carriage can be moved back and forth.

FIG. 2 shows an explanatory view of the VGM motor. Pole piece 4
A short coil 8 is wound around to improve the coil current characteristics. Also, the flow of magnetic flux is shown by arrows. In this motor, the critical point when trying to maximize the amount of magnetic flux entangled with the coil 7 is the magnetic saturation of the pole piece 4 or the magnetic saturation of the portion A of the front yoke 5.

Since the carriage gap L _S is determined by the array of disks and the number of heads per actuator, the gap dimension L _g ,
The dimension L of the pole piece 4 (the other dimension is RL) and the yoke dimension L _C between the pole pieces 4 are L _S = L _C +
There is a relationship of 2L _g + L, and L and L _C cannot both be large at one time. This is because the yoke A portion is saturated immediately when L _C is small, and the pole piece is saturated when L is small.
When the yoke is saturated, unbalanced magnetic flux is generated on the gaps B side and C side, and as a result, an unbalanced force is generated on the carriage, which causes vibration and abnormal mamou.

Therefore, when the magnetic flux density B _a at the A portion of the front yoke 5 and the hourly speed density B _p at the pole piece 4 are both equal and the maximum is B _max , k is a parameter (k is the aspect ratio of the pole piece), and the maximum is calculated. Value exists, L _s = 45 mm, T _sr = 1 mm,
Maximum magnetic flux Φ of pole piece 4 when B _max = 19KG
_p is about 160 KM _axwell . Although Φ _{p of} this degree is not sufficient for improving the average access time, it depends on the weight of the carriage and a larger Φ _p is desired. (Curve with α = 0 in FIG. 4) As an improvement measure for this, there is an example described in JP-A-55-163813, but it is difficult to dispose the magnet and a large magnet for attaching the magnet to the pole piece. Is impossible, and it is difficult to obtain a large magnetic flux density as a result.

[Object of the Invention]

An object of the present invention is to provide a VCM motor having a large gap part speed per hour by changing the magnetic circuit of the front yoke in an actuator having a plurality of pole pieces.

[Outline of Invention]

As described above, the magnetic circuit critical path of this motor is the front yoke and the pole piece. In the present invention, Φ _p can be greatly improved by providing a magnetic bypass between the pole pieces of the front yoke, and it is also expected that the output variation (abbreviated as linearity) depending on the coil position can be improved. .

Example of Invention

FIG. 3 shows an embodiment of the present invention. The difference from the conventional example is that the auxiliary magnetic circuit 9 is attached to the front yoke 5. The auxiliary magnetic circuit 9 is a block of a magnetic material having a higher magnetic permeability than the yoke material that is the surrounding magnetic circuit, and a material used as a normal yoke material is sufficient for normal use. Since the magnetic flux also passes through this portion by attaching the main block 9, the amount of magnetic flux in the center yoke portion of the pole piece 4 can be increased. As a result, the pole piece 4 can be made large, and the amount of magnetic flux in the gap can be increased.

FIG. 4 shows the relationship between the value of the amount of magnetic flux in the pole piece 4 and k when this block is provided. The parameter α is the ratio of the cross-sectional areas of the auxiliary block and the portion B of the front yoke 5, and when α = 0 indicates that there is no block.

As shown in this figure, when α = 1 to 2, Φ _p can be secured as large as 250 to 300 KM _x even when k is about 3.

Next, let us consider linearity.

The flow of magnetic flux around the conventional gap is as shown in FIG. 2, and the magnetic resistance at the front of the VCM motor is larger than that at the inside of the motor. Therefore, the linearity of the output depending on the position of the coil becomes worse when the coil is located on the inner circumference side of the disk as shown by the solid line in FIG. In contrast to this, in the present embodiment, since the front portion of the magnet is provided with a block, the leakage magnetic flux at the front portion becomes large, and as a result, the output at the coil inner peripheral position becomes large and the linearity is improved. (Dashed line in FIG. 5) In the gaps D and E, the output of the coil is different due to the influence of this magnetic circuit, and an unbalanced force is generated in the carriage. In order to avoid this, the size of the gap is changed to make the force generated in the coil uniform in the D / E section.

So far, I have described the case of two pole pieces,
It is clear that the same thing can be said for a plurality of five or more.

〔The invention's effect〕

As described above, according to the present invention, even if the amount of magnetic flux in the left and right gap portions changes depending on the shape of the front yoke of the VCM motor, it is possible to obtain a uniform left and right force by changing the dimensions of the gap portions. The amount of dimensional change varies depending on the shape of the block, but once determined, it does not change, so it can be easily determined by actual matching.

[Brief description of drawings]

Figure 1 is a side view of the disk, carriage and magnet.
2 (a) and 2 (b) are a front view and a side sectional view of a conventional motor, FIGS. 3 (a) to 3 (c) are a front view and left and right side sectional views of the motor of the present invention, and FIG. FIG. 5 is a diagram showing a relation between (aspect ratio of pole pieces) and the amount of magnetic flux of pole pieces, and FIG. 5 is a diagram showing a relation between coil position and linearity of output. 1 ... Disc, 2 ... Carriage, 3 ... Magnet, 4 ...
... Pole piece, 5 ... Front yoke, 6 ... Rear yoke, 7 ... Coil, 8 ... Short coil, 9 ... Auxiliary magnetic circuit.

Claims (1)

[Claims] 1. A magnetic circuit is formed by a magnet, a front yoke arranged in front of the magnet, a rear yoke arranged in the rear surface of the magnet, and at least two ball pieces arranged in the rear yoke. A voice coil motor for driving a plurality of carriages for positioning a magnetic head on a magnetic disk by a coil movably arranged in a gap between a pole piece and the front yoke, wherein a voice coil motor is provided on the front yoke and outside the magnetic circuit. There
A magnetic material piece is arranged at a position corresponding between the at least two ball pieces, and the gap on the side close to the magnetic material piece and the gap on the side far from the magnetic material piece are made different from each other. Characteristic voice coil motor.