Magnet/block assembly for disc drive systems

A magnet/block assembly is provided for creating and distributing a magnetic field that interacts with a magnetic field produced by an actuator coil in a disc drive system. The magnet/block includes permanent magnets and a block comprised of a back iron separated from a front iron by a gap space. A loop is integrally formed with the back iron and the front iron at an end of the gap space to provide a path for flux to be conducted between the front iron and the back iron.

BACKGROUND OF THE INVENTION 
The present invention relates to track accessing arm movement in disc drive 
systems. More specifically, the present invention relates to a 
magnet/block assembly that creates and distributes a permanent magnetic 
field which interacts with a transient magnetic field produced by an 
actuator coil that is connected to a track accessing arm in a disc drive 
system. 
In a disc drive system, transducer head assemblies write and retrieve data 
from concentric tracks of magnetic media discs. A transducer head assembly 
is typically connected to a resilient member, such as a gimbal spring, 
which in turn is connected to an end of a track accessing arm. 
An actuator coil is connected to an end of the track accessing arm opposite 
the end that carries the transducer head assembly. The actuator coil is 
placed within a gap space of a magnet/block assembly. The magnet/block 
assembly includes permanent magnets, which create a permanent magnetic 
field, and a block, typically formed of materials having ferromagnetic 
properties. Between the two ends of the track accessing arm is an actuator 
spindle that forms an axis of rotation intermediate the actuator coil and 
the transducer head assembly. 
Applying a current to the actuator coil positions and holds the transducer 
head assembly over various concentric tracks of the magnetic media disc. 
The current applied to the actuator coil produces a transient magnetic 
field that interacts with the permanent magnetic field in the gap space of 
the magnet/block assembly. The interaction between the two magnetic fields 
rotates the track accessing arm along the axis of rotation. The rotation 
of the track accessing arm moves the transducer head assembly between 
various concentric tracks of the magnetic media disc. 
In one embodiment of the prior art, a magnet/block assembly comprises 
permanent magnets and a two piece block that includes a back iron 
separated from a front iron by a gap space. The permanent magnets produce 
a magnetic field that is distributed in the gap space. A magnet/block 
assembly of this type may have two or four magnets placed in the gap 
space. One example of this type of magnet/block assembly is disclosed in 
Levy et al. U.S. Pat. No. 4,796,122. 
In another embodiment found in the prior art, a magnet/block assembly has 
three prongs that form two gap spaces between the prongs. An actuator coil 
having a hollow center surrounds the center prong with part of the coil in 
the first gap space and another part of the coil in the second gap space. 
The magnet/block assembly is formed with an open end and a closed end. A 
plate, or loop, is attached to the open end after the actuator coil is 
placed around the center prong. The plate, or loop, connects the three 
prongs and forms a flux conduction path. While this type of block can be 
formed integrally, the block has two gap spaces, and therefore requires 
more permanent magnets than does a block that has a single gap space. 
Examples of this type of magnet/block assembly are disclosed in Brand et 
al. U.S. Pat. No. 4,710,834, Wright U.S. Pat. No. 4,805,055, Chalmers et 
al. U.S. Pat. No. 4,890,174 and Yoshioka U.S. Pat. No. 4,941,062. 
SUMMARY OF THE INVENTION 
It has been found that an integrally formed magnet/block assembly having a 
single gap space minimizes the number of permanent magnets required and 
reduces manufacturing costs and tolerances by reducing the number of 
components requiring assembly. 
The present invention provides such a magnet/block assembly for use in disc 
drive systems. The magnet/block assembly creates and distributes a 
permanent magnetic field which interacts with a transient magnetic field 
produced by an actuator coil in a disc drive system. The interaction 
between the two magnetic fields moves a track accessing arm and thereby 
positions and holds a transducer head assembly over various concentric 
tracks of a magnetic media disc. The magnet/block assembly includes 
permanent magnets and a block comprised of a back iron separated from a 
front iron by a gap space. A loop formed integrally with the back iron and 
the front iron connects the back iron to the front iron at an end of the 
gap space. Compared to magnet/block assemblies of the prior art, the 
magnet/block assembly of the present invention requires fewer individual 
elements to be assembled and minimizes the number of permanent magnets 
required by employing a single gap space.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows part of a disc drive system 10 that employs an integrally 
formed magnet/block assembly 12 of the present invention. Disc drive 
system 10 includes a number of magnetic media discs 14 and a number of 
transducer head assemblies 16. Each transducer head assembly 16 is coupled 
to a track accessing arm 18. Track accessing arms 18 are assembled into a 
configuration known in the art as an "E" block. "E" block 20 is rotatably 
connected to spindle 22. Connected to an end of "E" block 20 opposite the 
end that carries transducer head assemblies 16 is actuator coil 24. 
Actuator coil 24 is positioned within gap space 26 of magnet/block 
assembly 12. As shown in FIG. 2, actuator coil 24 is a vertical flat voice 
coil, such as that disclosed in U.S. application Ser. No. 07/634,975 to 
Goss (now U.S. Pat. No. 5,050,026) and U.S. application Ser. No. 
07/685,189 to Eliason (now U.S. Pat. No. 5,233,493). While coil 94 is a 
continuous winding, it is conveniently considered to include a pair of 
opposed vertical or longitudinal segments 25a and 25b (shown in FIG. 2). 
Magnet/block assembly 12 is comprised of permanent magnets 28a and 28b and 
block 30. Block 30 is comprised of back iron 32 and front iron 34. The 
word "iron," which is used in reference to back iron 32 and front iron 34, 
is a term of the art and should not be interpreted as a limitation of the 
materials that may be used to form block 30. In the preferred embodiment, 
block 30 is formed of 10/10 steel. However, any material having desirable 
ferromagnetic properties may be used. 
In block 30, back iron 32 has gap surface 36 and front iron 34 has gap 
surface 38. Gap space 26 separates gap surface 36 from gap surface 38. End 
loop 40 is formed integrally with back iron 32 and front iron 34 and 
connects the irons at one end of the gap space. End loop 40 provides a 
means for flux to be conducted between back iron 32 and front iron 34. In 
the preferred embodiment, magnets 28a and 28b are positioned within gap 
space 26 on gap surface 36 by adhesive means having visco-elastic 
properties. However, in alternative embodiments, permanent magnets may be 
placed anywhere in the gap space. Magnets 28a and 28b have opposite 
magnetic orientations in gap space 29 to create a permanent magnetic field 
that block 30 distributes throughout gap space 26. 
Transducer head assemblies 16 read and write data to concentric tracks of a 
plurality of magnetic media discs 14. Transducer head assemblies 16 are 
moved between various concentric tracks of magnetic media discs 14 as "E" 
block 20 is rotated about an axis of rotation formed by spindle 22. 
The vertical segments 25a and 25b (shown in FIG. 2) of coil 24 generate a 
magnetic field that interacts with the field of permanent magnets 28a and 
28b to selectively rotated "E" block 20 about the axis of rotation. 
FIG. 2 is a top sectional view of disc drive system 10 taken along line 
2--2 of FIG. 1. Besides the elements shown in FIG. 1, FIG. 2 includes 
attached end loop 42 fastened to magnet/block assembly 12 by screws 44. 
Attached end loop 42 is attached to magnet/block assembly 12 after 
actuator coil 24 is placed within gap space 26. Attached end loop 42 
serves a function similar to that of integrally formed end loop 40; it 
provides a path for flux to be conducted between back iron 32 and front 
iron 34. 
In this embodiment, gap surfaces 36 and 38 have a shape substantially that 
of a curved surface of a quarter section of a right cylinder 1.560 inches 
tall. Gap surface 36 of back iron 32 has a radius of 1.750 inches. Gap 
surface 38 of front iron 34 has a radius of 1.389 inches as measured from 
a center point common to both gap surface 36 and gap surface 38. This 
forms a gap space 26 between the two gap surfaces of 0.352 inches, 
measured radially and exclusive of magnets 28a and 28b. 
In alternative embodiments, the dimensions of block 30 can be altered to 
meet the requirements of particular disc drive systems. For example, gap 
surfaces 36 and 38 (shown in FIGS. 1 and 2) could have a larger or smaller 
arc to provide a corresponding larger or smaller range of movement for 
head transducer assemblies 16, as would be required for magnetic media 
discs of different radii. If gap surfaces 36 and 38 had larger or smaller 
radii, that would require coil 22 to be correspondingly farther from or 
closer to spindle 22. This would alter the angular leverage with which 
actuator coil 24 moves "E" block 20. Also, the height of block 30 can be 
varied to accommodate varying sizes of actuator coils. 
FIG. 3 is an exploded perspective view of block 30 of the present invention 
showing end loop 42 and screws 44 removed and to the left of block 30. 
In an alternative embodiment, attached end loop 42 could be replaced by a 
second integrally formed end loop similar to integrally formed end loop 
40. This would distribute the magnetic field more evenly than the 
embodiment shown in FIG. 3. However, assembly and manufacturing 
requirements favor the invention as shown in FIGS. 2 and 3, with attached 
end loop 42, as the preferred embodiment. 
FIG. 4 is a graph of a finite element analysis of a magnet/block assembly 
of the prior art having separately formed front and back irons. The 
ferromagnetic material in this magnetic/block assembly is saturated, which 
limits gap flux density. As shown in this figure, the distribution of the 
magnetic field is biased toward one end of the gap space. 
In contrast, FIG. 5 is a graph of a finite element analysis of the magnetic 
field within gap space 26 of magnet/block assembly 12 of the present 
invention. The ferromagnetic material in magnet/block assembly 12 is not 
saturated because end loop 40 provides a path that limits saturation. The 
magnetic field is distributed much more symmetrically than is the magnetic 
field in the gap space of the magnet/block assembly of the prior art shown 
in FIG. 4. This produces a more linear interaction between actuator coil 
24 of FIGS. 1 and 2 and the magnetic field in gap space 26. 
FIG. 6 is a magnetic circuit comparison between a magnet/block assembly of 
the prior art, having separately formed front and back irons, and the 
magnet/block assembly of the present invention. In this graph, the 
abscissa represents an actuator position with reference to the 
magnet/block assembly of the present invention, with the left end of the 
abscissa representing the integral loop end of the gap space and the right 
end of the abscissa representing the attached loop end of the gap space. 
The ordinate of this graph represents a relative magnetic force constant. 
Line 46 shows the relationship between actuator coil position and relative 
magnetic force for magnet/block assembly 12 of the present invention. Line 
48 shows the relationship between actuator coil position and relative 
magnetic force constant for a two piece magnet/block assembly of the prior 
art. 
This graph indicates that for any given actuator coil position, the present 
invention provides a higher magnetic force constant than does a two piece 
magnet/block assembly of the prior art. A higher magnetic force constant 
allows a track accessing arm to respond more quickly while supplying the 
same amount of power to the actuator coil. Alternatively, a disc drive 
using the magnet/block assembly of the present invention can maintain the 
same level of track accessing arm performance as a disc drive using a 
prior art magnet/block assembly while supplying less power to the actuator 
coil, or can have more track accessing arms while supplying the same 
amount of current to the actuator coil. 
Although the present invention has been described with reference to 
preferred embodiments, workers skilled in the art will recognize that 
changes may be made in form and detail without departing from the spirit 
and scope of the invention.