Composite Ramp Structure with Suspension Lift Tab Limiter Features
Original Publication Date: 1999-Dec-01
Included in the Prior Art Database: 2003-Jun-20
Disclosed is a disk drive load/unload ramp of composite construction, consisting of a metal support plate and injection molded polymer. The primary function of the metal plate is to mechanically isolate individual ramps, limiting the thermal gage length of the higher CTE (coefficient of thermal expansion) polymer material. Unlike current art designs, a new ramp is disclosed wherein the ramps are interconnected to one another in order to accommodate mechanical limiters for the suspension lift tabs, which provide greater shock protection to the disk drive without compromising the thermal-mechanical performance necessary for tolerance control. As disk drive aerial densities continue to increase, the corresponding decrease in fly height necessary for adequate signal-to-noise response begins to exceed the capability of CSS (contact start stop) designs due to the relatively large magnetic spacing between the disk and head. As a result, many disk drive manufactures are incorporating load/unoad technology as a means of improving magnetic performance without sacrificing reliability. A simplified ramp load/unload system is illustrated in Fig. 1. One of the more challenging aspects of implementing load/unload is in managing the vertical height budget and clearance between the fixed ramp surfaces and the rotating disks. Mechanical tolerances of the various components in the system are of paramount importance. To that end, even thermally induced misalignment due to CTE mismatch between the ramp and the disk stack can be a significant variable which must be minimized. Load/unload ramps are generally fabricated from injection molded polymer materials chosen for their superior tribological properties. Unfortunately, most such materials generally have a significant CTE mismatch relative to the components of the rotating disk stack. This is especially problematic for tall ramps accommodating a large number of disks due to the large thermal gage lengths of the ramp and disk stack. In current art designs this is solved by molding the necessary ramp geometry onto a support structure with a CTE chosen to match that of the disk stack. The result is individual “islands” of plastic connected together only via the support structure, which dominates the thermal expansion of the ramp. Such a design is shown in Fig. 2, with a simple metal plate serving as the support structure. Note that the ramp is produced by conventional insert molding technology, and that the holes in the plate allow the polymer material to flow through the plate and form features on each side as defined by the mold. One of the negative consequences of such a ramp design is the elimination of ramp features called suspension limiters, which limit the axial motion of the suspension lift tab off the ramp, and therefore limit the possible load beam flexure separation during an external shock event which might otherwise damage the suspension. These features are impossible to fabricate without interconnecting the individual ramps. In all-plastic ramp designs suspension limiters are easily incorporated , as shown in Fig. 3, and help load/unload disk drives achieve relatively high shock specifications as compared to CSS designs.