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Disk Drive Disk Stack Assembly for Reduced Disk Vibration Disclosure Number: IPCOM000014720D
Original Publication Date: 2000-Dec-01
Included in the Prior Art Database: 2003-Jun-20

Publishing Venue



Disclosed is a disk stack assembly design technique to achieve reduced disk vibration. The disclosed design significantly reduces disk flutter vibration in disk drives which is particularly problematic in high performance high RPM disk drives. The disclosed design approach achieves the reduced disk vibration without any development effort in new disk substrate materials. The approach does not require investment in new disk processing tooling which would be requied by new disk geometry (increased thickness or reduced diameter) which is a method that has been used previously in reducing disk flutter vibration. The design approach consists of using two existing standard thickness and standard diameter disks paired back to back where such paired disks become the functional disks in the new disk stack assembly which gives reduced disk vibration. The resulting functional disk thickness is twice that of the original disk thickness. Such singular disks which make up the disk pair can be single sided in terms of disk finishing and thus would be of lower cost than standard disks. When the paired disks are properly aligned using a mandrill on the disks' inner diameters, or some other means, measurements have shown no degradation in disk pair flatness or curvature when clamped in a spindle disk pack assembly. The improvement in disk drive track following servo performance with this method of reduced disk vibration is better than if a single double thickness disk were used. The latter does not have the benefit of damping effects that are realized by the disk pair. Furthermore, the double disk pair gives a frequency response that does not give disk modal frequencies as high as a single solid disk of comparable double thickness. Instead the disk frequencies are somewhat similar but only slightly increased and with reduced amplitude compared to a single original disk. (See measured frequency response in Figure 1.) This is advantageous in disk drive servo systems since at higher frequencies, common to disk higher order disk modal frequencies, the servo system amplifies position errors. The total out of plane vibrations near the disk outer diameter when spinning at 20,000 RPM is given in Figure 1 for a single disk of glass substrate and two disks sets of paired disks (one pair glass, the other pair aluminum). Note that the total vibration of the disk pairs approaches one half that of the original single disk. 1 AKH 12/20/99