Device for the automatic loading/unloading of magnetic disks

A load/unload mechanism for magnetic disks is described which allows the magnetic heads of a disk drive to be loaded and unloaded at highest possible speed in a secure manner and without collision with the surface of the disk. The slider is lifted off directly in the vicinity of the flexure without causing abrasion between the suspension of the slider and the load/unload element.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to magnetic disk drives and, in particular, to a 
method and apparatus for automatic loading/unloading of a magnetic head in 
such a magnetic disk drive. 
2. Description of the Prior Art 
In computer systems, information is frequently stored on a magnetic film on 
the surface of a magnetic disk (hard disk). Magnetic hard disk storage 
devices, that is to say assemblies of several such magnetic disks, either 
have permanently fixed disks or removable cartridges which can be removed 
from a disk storage device and inserted into the next device of the same 
type. These disks are not perfectly flat; but due to the manufacturing 
process, the disks have fine curvatures. Information is read and written 
by means of magnetic heads (sliders) which are connected to the housing of 
the disk storage device by means of a carrier structure. The magnetic 
heads, together with their suspensions, are mounted on the arms of the 
carrier structure, the actuator. 
FIG. 1 shows a part of such an assembly according to the state of the art. 
The magnetic head suspensions themselves consist of the loadbeam, the 
flexure, and the mounting block, collectively referred to as the 
suspension. The mounting block serves as a connecting element between the 
actuator arm (not shown) and the magnetic head suspension. The loadbeam is 
the backbone of this suspension. It has a relatively high rigidity against 
the slider. Toward the rear, it has a controlled flexibility defined in 
production. In this area, bending of the loadbeam in z direction furnishes 
the cross-sectional profile with a defined rigidity. When the actuator is 
subsequently fitted in the disk storage device, this controlled rigidity 
of the bend zone in the fitting position produces a pressure load 
(gramload) of the slider on the surface of the disk. 
The flexure is welded onto the loadbeam. The slider is then bonded onto a 
lug of the flexure. Due to its shape, the flexure has a very high lateral 
rigidity to prevent the slider from oscillating uncontrolledly in the 
event of rapid actuator movements. The rigidity around the transverse 
axis, on the other hand, is very low, to allow the slider to flex in 
response to the minutest unevenness on the disk. The entire assembly is 
referred to as the Head Suspension Assembly (HSA). 
During read and write operations, the slider floats on a cushion of air at 
a very low height above the disk, which rotates very fast. The bearing 
surface onto the disk is termed the Air Bearing Surface (ABS). In this 
way, direct contact between the slider and the disk is avoided. If, for 
example, the rotational speed of the disk is too low to create an adequate 
air cushion between the head and the disk, the two may touch, resulting in 
a "head crash", which may cause irreparable damage to the disk and head 
and may lead to loss of data. 
Especially in replaceable cartridge systems in which the magnetic disk is 
inserted into and withdrawn from the storage device housing inside a 
cartridge system, a mechanism is required to lift the magnetic heads off 
of the disk surface and set them to a rest position when the drive is not 
in operation. Otherwise, there would be very great danger of damage, in 
transit for example. However, a mechanism of this kind is also necessary 
in fixed systems, to prevent the head sticking to the disk at rest 
position. 
In earlier times, it was usual to start and stop a magnetic disk, or 
magnetic disk storage device, by means of a Contact Start/Stop System 
(CSS). In this process, the drive is started and stopped while the 
magnetic disk and head are in contact with each other. To prevent the head 
and disk sticking together as already mentioned when the drive is at rest, 
the surface of the disk had to be appropriately roughened. Due to the 
increasing miniaturization of hard disks and hard disk storage devices, 
however, the gap between the actuator and the surface of the disk is 
becoming ever smaller, so that this solution no longer corresponds to the 
state of the art. As a result, it is becoming more and more problematic to 
unload the magnetic heads with mechanisms of sufficient strength. Also, 
reducing the size of gap means that the influence of production and 
assembly tolerances is becoming ever greater. 
For this reason, load/unload mechanisms have been developed which lift the 
head from the disk using a load/unload element (from now on, for the sake 
of simplicity, termed an unload element) when the disk is not rotating. 
When the disk is started again, i.e., the slider is brought back onto the 
disk surface, the appropriate air cushion must be reestablished fast 
enough to prevent contact between the disk and the head, dependent on the 
lifting speed of the head, the position of the ABS relative to the disk, 
and the defined height of flight of the head. Because users of such drives 
wish to read and write data very shortly after it starts operating, a 
mechanism of this kind must be furnished with the highest possible 
load/unload speed. 
WO87/01853 discloses a load/unload mechanism for magnetic heads which has a 
comb-like structure as the unload element. The fingers of the element 
interact with the suspension of the magnetic heads to hold the heads at 
sufficient distance from the disk in the unloaded position. This device 
has the disadvantage that, due to its size, it can no longer be used for 
today's much more miniaturized magnetic disk drives. 
U.S. Pat. No. 5,296,986 describes a device to hold the actuator of a disk 
drive in a secure position when the drive is at rest. For this, the slider 
is conveyed with the aid of a driver mechanism onto a ramp outside the 
magnetic disk, where it rests. The disadvantage of this device is that 
additional means such as cam followers are required to convey the head 
onto the ramp. Another disadvantage is that abrasion occurs in the contact 
zone between the ramp surface and the slider suspension. The abrasions 
very often take on magnetic properties due to changes in the grid 
structure. At the point at which such magnetic particles touch the disk 
surface, the data already written to it would be destroyed. 
U.S. Pat. No. 5,394,281 describes a magnetic load/unload mechanism with a 
ramp as the unload element, having a piezoelectric element. In this 
mechanism, the static frictional force at the start of loading is replaced 
by a dynamic force. A magnetic solution of this kind has the disadvantage 
that the slider may drop out of control onto the surface of the disk, for 
example, if the power fails. Furthermore, this arrangement is not suitable 
for loading and unloading several magnetic heads simultaneously. In this 
case, coupling of several different transducers is not possible; and the 
available space for attachment of several such transducers is inadequate 
with today's low design heights. 
A further disadvantage of the general state of the art is that when the 
suspension conveyed runs onto the unload element mounted outside the disk, 
the risk of collision between the magnetic head and disk is very great, 
for the following reason. 
In production, the magnetic disk cannot be fully tested, i.e., the magnetic 
and mechanical properties are not precisely defined on the entire disk. 
Thus, due to technical factors, the outermost zone of the disk remains 
undefined. The consequence is the outer edge of the disk is much less flat 
than the zones further in. When the suspension is then moved onto the 
unload element with the disk rotating, the relative movement of the disk 
and the suspension causes the magnetic head to skew. This leads to a loss 
of flying height of the magnetic head and so to the risk of solid body 
contact between the head and the disk at the outermost, uneven, edge of 
the disk. For this reason, the suspension is normally unloaded in the 
outermost defined data field of the disk. 
Accordingly, it can be seen that there is a need for a method and device 
for automatic loading and unloading of a magnet head over a disk surface 
in a magnetic disk drive which allows the magnetic heads of the drive to 
be loaded at the highest possible speed in a secure manner and without 
collision with the surface of the disk. 
SUMMARY OF THE INVENTION 
The object of the invention is, therefore, to furnish a load/unload 
mechanism which ensures fast and reliable loading/unloading of the 
magnetic head by means of a mechanical unload element, without need for 
additional means. 
A further object of the invention is to provide a load/unload device which 
permits the slider to be raised directly on a level with the flexure. 
A further object of the invention is to prevent abrasion between the 
suspension of the slider and the unload element. 
These and other objects are accomplished by the device and the method in 
accordance with the present invention. 
The device in accordance with the invention permits the slider to be raised 
and lowered at high speed, while the magnetic disk is rotating at nominal 
speed, without contact occurring between the slider and the surface of the 
disk. In this, the magnetic head is raised at the level of the flexure, 
i.e., directly at the head itself. The advantage of this is that the 
effective lift of the magnetic head at the level of the slider can be 
increased significantly, with a maximum permissible gramload loss in the 
same amount, in relation to an intervention positioned closer to the 
mounting block. 
A further advantage is that no abrasion whatever occurs during 
loading/unloading. As a result, no particles can enter the air cushion 
between the slider and the disk and disturb the flight of the head, or 
even cause break-outs on the slider. The prevention of abrasion means that 
stainless steel can be used as the material for the unload element. 
The device in accordance with the invention furthermore allows the 
distance, or thickness, of the unload element to be selected such that the 
unload element can still intervene cleanly between the suspension and the 
disk surface when the production and assembly tolerances of all components 
involved in the process add together in a worst-case scenario. 
The possible vertical speed at which a magnetic head can be loaded onto the 
surface of the disk at nominal rotational speed is limited and must never 
be exceeded. Otherwise, the head will contact the disk surface. Since the 
surfaces of most disks are coated with a Carbon Overcoat (COC) to increase 
their intrinsic resistance to solid body abrasion, ensuring that the 
magnetic carrier layers underneath are not damaged in starting and 
stopping and in nominal operation, such contact would damage the COC 
layer. In the worst case, the magnetic layer underneath the overcoat may 
be damaged. 
For this reason, it is highly advisable to load and unload the magnetic 
head using a mechanical force control. This can prevent the slider from 
dropping out of control onto the surface of the disk, for example, if the 
power fails to the disk storage device. Another lifting mechanism, such as 
a magnetic one, is possible but is not beneficial for the reasons cited.

DETAILED DESCRIPTION OF THE INVENTION 
As can be seen from FIG. 2, in normal operation, the magnetic head 8 is 
loaded on the disk 10 and flies at nominal height with the disk rotating 
at nominal rotational speed. The unload element 12 is completely outside 
the surface of the disk at this point in time. FIG. 2 shows a wedge-shaped 
unload element 12 having a horizontal 20 and a sloped 16 portion. This 
shape has proved particularly advantageous, among other reasons, due to 
the severely restricted access area of the mechanism in z direction (see 
FIG. 1). It should be pointed out that the invention is not limited to 
unload elements 12 which contact both sides of the magnetic disk 
simultaneously. The mechanism presented can, of course, also function when 
the magnetic head 8 is only arranged on one side of the disk. 
When the magnetic head 8 is to be raised from the disk surface, the 
wedge-shaped unload elements 12 are conveyed transversely at high speed 
into the gap 14 between the magnetic head suspension 24 and the surface of 
the disk 10, for example, with the normal current of the actuator drive 
motor. This causes the wedges to raise the magnetic head suspension 24 
with their sloped portion areas 16 when they contact the loadbeam edges 2. 
At this moment, the magnetic head 8 is forced also to begin lifting from 
the disk surface. As it moves further in under the suspension 24, the 
wedge reaches the convex edges of the flexure 4, the transition zone 18 
between the sloped portion 16 and the horizontal section 20. Once more, 
this raises the head 8 on a level with the intervention zone by the amount 
of flexure 4 thickness. 
As already set out above, bending of the loadbeam in positive z direction 
(see FIG. 1) furnishes the cross-sectional profile with a defined 
rigidity, resulting in a defined gramload which, in nominal operation, 
presses the magnetic head 8 onto the air cushion and thus holds it at a 
nominal height of flight. 
If, when the magnetic head 8 is lifted by means of unload elements 12, the 
suspension 24 is subsequently bent in negative z direction, a gramload 
loss occurs once, dependent on the force action on the loadbeam 2 and on 
the amount of deflection. As can be seen from FIG. 5, this gramload loss, 
with equal deflection, is lower when the load is applied close to the 
magnetic head 8, while becoming almost uncontrollably high when force is 
applied closer to the mounting block 6. However, any loss of gramload 
brings about an increase in height of flight, and, thus, a weakening of 
the read/write signal. Therefore, to achieve the lowest possible loss of 
gramload in a load/unload process, intervention of the unload element 12 
should be as close as possible to the level of the flexure 4. 
In this unload operation, the wedge moves under the suspension 24 until its 
horizontal level reaches the axis of symmetry 22 of the suspension. This 
ensures that the magnetic head is not rotated around its own axis when 
raised. This means that no permanent deformation of the loadbeam around 
its longitudinal axis of symmetry occurs, and, thus, no change in height 
of flight. Then, the magnetic head suspension lying on the horizontal 
portion of the load element is pivoted out of the plane of the magnetic 
disk with the load element. 
In the load operation, the interaction between the movement of the wedge 
and that of the magnetic head 8 is the reverse of the interaction which 
occurs in the unload operation. The only difference is the lower amount of 
work consumed by friction when the ramp 16 of the wedge contacts the edge 
of the flexure 4 during loading. 
In the load/unload operation, the intervention of the wedge outside the 
suspension axis of symmetry rotates the HSA relative to ideal zero by a 
certain amount, i.e., for a fraction of the load/unload time the slider 
makes contact with only one side. For this reason, the load/unload speed 
can only be increased to the extent that the air cushion under the slider 
ABS can still be built up within fractions of a second even when, 
temporarily, contact is provided by only a part of the overall contact 
area. 
In most common suspensions 24, for cost reasons, the flexure 4 is welded 
onto the loadbeam 2 such that it lies on it in a convex form. It should be 
pointed out here that the present invention is not restricted to such 
suspensions 24. Since the flexures 4 are produced by a metal-etching 
process, the edges are extremely sharp. Also, the flexure material is by 
nature very hard. 
If an attempt is now made, as shown in the present invention, to unload the 
magnetic head 8 directly in front of the slider on a level with the 
flexure 4 using a wedge element, the said sharp edges of the ramp area of 
the wedge are automatically positioned in the way. As a result, with 
purely solid body friction, severe abrasion occurs in the contact zone of 
the flexure edge. Depending on the roughness of the surface and on the 
structure and hardness of the suspension and wedge element, abrasion may 
even occur in the contact zone of the loadbeam. 
In an especially advantageous embodiment of the invention, an additional 
hydrodynamic sliding film is therefore built up on the load/unload element 
12 using a lubricant, such as perfluoropolyether. 
The device described here permits the magnetic head 8 of a magnetic disk 
drive to be unloaded at the highest possible speed, without solid body 
contact between the head and the surface of the disk. 
By the use of a lubricant, in spite of these properties, suspensions 24 can 
still be unloaded on a level with the flexure 4, even where the flexures 
of said suspensions 24 have been welded onto a flat bearing surface of the 
loadbeam 2 and consequently protrude from the loadbeam 2 with their sharp 
edges, without the unload operation causing abrasion in the contact zone 
between the unload element 12 and the suspension 24. Avoiding abrasion 
also means that no particles caused by the load/unload process can enter 
the air cushion between the slider ABS and the surface of the disk 10 and 
disturb the flight of the head 8, or even cause break-outs on the slider. 
Due to the fact that no such abrasion occurs, stainless steel can be used 
as the material for the unload element 12. This means the unload element 
12 can be of such strength and elasticity that even very thin structures 
and, possibly, structures tapering toward the magnetic disk 10 can 
withstand the high loads with very early intervention. The use of steel 
also increases rigidity, especially of a wedge-shaped unload element 12. 
As a result, the deflection values are kept low, even with high vertical 
loads, and the wedge is never deflected so severely that, at a short 
distance from the disk surface, it would touch the surface under the loads 
of the load/unload process. 
The fact that the magnetic head 8 can be raised on a level with the flexure 
4 directly in front of the slider means that the effective lift of the 
head 8 can be increased significantly, with a constant maximum permissible 
gramload loss, in relation to an intervention positioned closer to the 
mounting block. The mechanism presented also serves as a locking mechanism 
for the magnetic heads 8 when the disk 10 is at rest and the heads 8 are 
raised. 
A further advantage is that, as a result of the avoidance of abrasion 
between the magnetic head suspension 24 and the load/unload element 12, 
thermal asperities can be avoided which occur when the slider comes into 
frictional contact with solid bodies on a level with the read/write 
element.