Bearingless pivot cartridge

Details Bearingless pivot cartridge Bearingless pivot cartridge

1999-12-10

2002-07-23

Miller, Brian E. (Department: 2652)

Dynamic magnetic information storage or retrieval

Head mounting

For shifting head between tracks

Reexamination Certificate

active

06424503

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to rotary actuators for tape and disk drives and, in particular, to a combined actuator mount and pivot member having no moving contact points that provides precise rotational movement of an actuator arm about an axis within an axial region and within a limited angular arc range.
2. Description of the Prior Art
Contemporary hard disk drives employ a rotary actuator arm within a hard disk support structure. Transducers or read/write heads are located at the end of the rotary actuator arm. During use, the arm is rotated to precisely position the read/write heads relative to data tracks located on the surface of storage/retrieval disks. Repeatability, that is, the ability of the heads to return to exactly the same location relative to the disks on every cycle, is absolutely essential. The storage/retrieval disks are rotatably mounted within the same hard disk support structure. The hard disk support structure includes a base, a cover, and a seal to protect the contents from environmental contamination. Often the actuator arm has a plurality of extended fingers supporting a plurality of transducer heads that track a plurality of storage/retrieval disks co-axially mounted in a single hard disk assembly.
The movement of the transducers must be controlled with great precision in order for the hard disk assembly to function properly. Thus, the rotational movement of the actuator arm must be controlled with great precision. The rotation must be free of looseness or backlash. The precise angular movement of the actuator arm is electro-magnetically controlled by regulating current travelling through a coil mounted on the actuator arm which is positioned between two permanent magnets. For a specific current value moving through the coil, the actuator arm is precisely rotated to a specific position. However, if there is too much rotational friction in the pivot structure, the actuator arm, in response to a specific current value, can be incorrectly positioned. Thus, conventional expedients had attempted to effect the rotation of the actuator arm with as little rotational friction resistance as possible since it had been believed that such undesirable friction can cause read/write errors.
Previous expedients generally provided precision roller bearings in the assembly to precisely control the rotational movement and positioning of the actuator arm. Precision roller bearings incorporate a plurality of ball bearings positioned between annular races. The ball bearings are often lubricated to further reduce friction. The lubricants within the sealed hard disk support structure had presented serious problems because of the potential that any lubricants that escaped from the bearings can undesirably contaminate the surfaces of the storage/retrieval disks in the assembly. An example of a roller bearing assembly utilized in a hard disk drive assembly is disclosed, for example, in U.S. Pat. No. 5,510,940 to Tacklind et al.
There are numerous drawbacks to the previous expedient of using precision roller bearings. One drawback is that they are relatively expensive components because each part in the bearing must be manufactured to exacting tolerances, which, in turn, increases their costs. Another drawback is that they must be assembled in a clean room to prevent the possibility of contamination. This also increases assembly costs. Still another drawback is that the rotational frictional resistance of a precision roller bearing changes responsive to temperature changes, minute irregularities in its components, changes in the characteristics of the lubricant, contaminants, and the like. These changes have resulted in read/write errors on the storage/retrieval disks, because the transducers do not return to exactly the same locations on the disks on every cycle. Attempts to solve this problem have undesirably increased the cost and complexity of the assembly. For example, in U.S. Pat. No. 5,628,571 to Ohta et al an additional preload spring is included to act against bearing races made from dissimilar metals in order to counter the effects of temperature variation. Other friction problems result from contaminants which, when present, must be overcome by the electromagnetic forces of the actuator. Such contaminants, when present, create a resistance that is inconsistent and non-repeatable. For example, an actuator arm could rotate 2 to 4 degrees with little or no frictional resistance until a contaminant particle, which happens to reside on a ball bearing, impacts a contact point in one of the races in the bearing. This contact creates an instantaneous increase in frictional resistance. This instantaneous increase in frictional resistance is not repeatable, predictable or consistent since contaminant particles can move or be crushed into multiple particles when inside a roller bearing. The problem can further be complicated when the particles cause wear or pitting of the ball bearing surfaces or races. Thus, generally the problem is not rotational friction per se, but rather intermittent, unpredictable and non-repeatable rotational resistance. When roller bearings are used, this problem is generally unsolvable because thermal variation, particulate contaminants, as manufactured irregularities, lubricant changes, wear and pitting, and the like are unavoidable.
There are other drawbacks as well in utilizing precision roller ball bearings. They are susceptible to damage when improperly handled. For instance, when subjected to drive and shock vibration tests, damage to the bearings had been observed. Such damage can cause the loss of designed preload, which causes backlash in the actuator arm assembly. Such backlash can result in catastrophic read/write errors. In addition, as technological advances in storage/retrieval disks continue, the number of data storage tracks per inch on the disks continues to increase. This requires even closer tolerances for the roller ball bearings. Achieving these greater roller bearing tolerances, even if physically possible, would undesirably further increase the cost of the assemblies. Thus, as more data tracks are placed on read/write disks, the problems that are inherent in the use of precision roller bearings in hard disk actuator arm assemblies are becoming very serious.
Due to the continued growth and competition in the computer industry, the need has arisen for mass-produced, inexpensive hard disk drive assemblies having improved performance and reliability characteristics. Thus, there is a need to reduce the cost of the hard disk drive assemblies by eliminating the use of precision roller bearings in the actuator arm pivot.
There have been some prior expedients proposed for the elimination of precision roller bearings in actuator arm pivot assemblies. In U.S. Pat. No. 5,355,268 to Schulze, a pin/cup pivot is disclosed establishing either rolling or sliding contact between the pin and cup. The pin is fixedly attached to the actuator arm and the cup is fixedly attached to the support structure. The pin/cup pivot configuration is not mount stable by itself, that is, it requires additional components to maintain the pin against the cup. For example, a magnetic system is disclosed to maintain the pin against the cup and thereby provide the required mount stability. Another attempt to eliminate the use of precision roller bearings is disclosed in U.S. Pat. No. 5,757,588 to Larson. A plurality of resilient fingers snappedly and slideably engage a pivot shaft fixed to the support structure. However, the mount stability of the pivot structure to shock loads is inherently limited by the elasticity of the resilient fingers on the pivot shaft.
All the prior art expedients rely on rolling and/or sliding contact points in the pivot area. Undesirably, some form of lubrication and/or protection from contaminants is required. Temperature variations also pose problems for these rolling or sliding contact based expedients. Temperature variations can alter the rotational frictional resistance of the p

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