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.