DIRECT ACCESS STORAGE DEVICE
HAVING A DISK MOTION LIMTTER FOR
PREVENTING DISK DATA ZONE AND
SPINDLE BEARING DAMAGE
This application is a continuation, of application Ser. No. 08/324300. filed Oct. 17. 1994. now abandoned.
BACKGROUND OF THE INVENTION
1. Field of the Invention 10 The present invention relates to motion limiters in a
Direct Access Storage Device (DASD) and, in particular, motion limiters for preventing data zone and spindle bearing damage.
2. Description of the Related Art
Personal Computer Memory Card International Association (PCMCIA) standard Direct Access Storage Devices (DASDs) are inseitable into slots in computers, particularly laptop and notebook computers, where component size is a 20 very significant design factor.
PCMCIA standard handling specifications require that products (including disk drives) be able to withstand drops onto very hard surfaces. For example, the PCMCIA specification requires that a disk drive be able to survive a 30-inch 25 drop without data loss. This drop converts a significant amount of potential energy into kinetic energy. The abrupt stop upon impact converts the kinetic energy into very high deceleration forces which may exceed the forces which the PCMCIA DASD components may accommodate. Experiments indicate that a 30-inch drop onto hard vinyl can 30 transmit acceleration forces of over 1,200 g to the internal structures of a PCMCIA DASD. Accordingly, due to the reduced size of the disk drive, the PCMCIA DASD is more delicate and may be more susceptible to damage upon impact. 35
The rigid structure of the PCMCIA DASD necessary to meet the bending and twisting requirements of the PCMCIA specifications in combination with the relatively hard surface of a vinyl clad cement floor results in a very short duration acceleration pulse—on the order of 0.5 ms. The 40 high deceleration forces and short duration impact can excite the internal components in a PCMCIA DASD and put great mechanical stress on these internal components.
Of particular concern is the motion of the data storage disk normal to its plane. Though relatively rigid, the data 45 storage disk is nonetheless a flexible structure whose first two natural frequencies are each under about 2 kHz for a standard 48 mm disk, and each under about 1 kHz for a standard 65 mm disk. Structures with these natural frequencies will be strongly excited by 0.5 ms acceleration pulses. 50
As a DASD is dropped, energy is transferred from the base to the data storage disk through the spindle bearings. The energy is roughly proportional to the amplitude of resultant motion of the data storage disk, and also related to the stresses at the ball/race interface of the spindle bearings. Large amplitude deflections of the data storage disk cause 55 large stresses between the balls and races, and can lead to premature spindle bearing failure.
The use of the PCMCIA DASD in laptop and notebook size computers suggests a high probability of DASD impacts as a result of being dropped. The impacts can partially result 60 from any rough handling of the computer device itself. Additionally, the impact forces could come from dropping the disk drive itself at a time when the DASD is not installed in the computer housing. The problem becomes worse as data storage disks and actuator arms become thinner. If an 65 actuator arm is allowed to hit the data storage disk in a data zone, hard errors can occur.
U.S. Pat. No. 4.939.611. issued Jul. 3. 1990 to Connolly, proposes the use of vertical displacement limit stops on work function members in a disk drive for preventing disk surface damage. The vertical displacement limit stops are provided on work function members, such as air vanes and actuator arms. When the actuator is in a locked position, the vertical displacement limit stops prevent contact of the work function members with adjacent track surfaces of the data storage disks in the presence of shock forces as high as 105 g, acting over a time interval of 3 ms. The vertical displacement limit stops disclosed in the Connolly patent are inadequate to prevent data zone, actuator arm and spindle bearing damage during the 30-inch drop required by the PCMCIA specification, however. Because vertical displacement limit stops are mounted on the actuator arms, the actuator arms can be damaged by the 30-inch drop required by the PCMCIA specification, resulting in data loss due to track misregistration. Additionally, because vertical displacement limit stops are mounted on the actuator arms, contact between the data storage disk and the actuator arms is only prevented when the actuator arm is in the locked position. This is disadvantageous because impacts also can occur when the actuator is in an unlocked position. Further, vertical displacement limit stops are only disposed on work function members, and thus do not prevent spindle bearing damage from occurring during the 30-inch drop required by the PCMCIA specification.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an enhanced DASD for shock protection.
It is another object of the present invention to provide a DASD that protects the data zone and actuator arm from damage when subjected to acceleration forces over 1,200 g, acting over a time interval of 0.5 ms.
It is a further object of the present invention to provide a DASD that protects spindle bearings from damage when subjected to acceleration forces over 1.200 g. acting over a time interval of 0.5 ms.
It is a still further object of the present invention to provide a DASD that protects a data zone, actuator arm and spindle bearings from damage when subjected to acceleration forces, without requiring the actuator to be in a locked position.
These and other objects are achieved by the present invention.
In a first embodiment of the present invention, a DASD comprises a data storage disk rotatably mounted about an axis and having first and second opposite surfaces, a data zone on at least one of the first and second surfaces, and a peripheral portion outside the data zone; an actuator for moving a transducer head relative to the data storage disk; a housing enclosing the data storage disk and the actuator, the housing including a base and a cover; a plurality of motion limiters projecting from at least one of the base and cover, each morion limiter having a first face disposed in close proximity to and confronting the first surface of the data storage disk adjacent the peripheral portion and having a second face disposed in close proximity to and confronting the second surface of the data storage disk adjacent the peripheral portion; the first and second faces of one of the motion limiters being disposed on a first side of the actuator, and the first and second faces of another of the motion limiters being disposed on a second side of the actuator opposite the first side; and the first and second faces of the motion limiters being disposed relative to the data storage disk so that when the DASD is subjected to an acceleration the data storage disk contacts at least one of the first and second faces of the motion limiters only at the peripheral