BRIEF DESCRIPTION OF THE DRAWINGS
The exact nature of this invention, as well as the objects and advantages thereof, will become readily apparent from consideration of the following specification in conjunction with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:
FIG. 1 is an exploded view of a prior art disc drive actuator arm assembly and tolerance ring design.
FIG. 2 is a perspective view of a prior art tolerance ring design.
FIG. 3 is a cross-sectional view of the tolerance ring along line 3-3 of FIG. 2.
FIG. 4 is a top view of a prior art pivot bearing and tolerance ring.
FIG. 5 illustrates a force distribution on the bearing outer sleeve of FIG. 4.
FIG. 6 is a perspective view of a tolerance ring according to one embodiment of the present invention.
FIG. 7 illustrates a force distribution between the tolerance ring of FIG. 6 and the bearing outer sleeve of FIG. 4.
FIG. 8 is a perspective view of a tolerance ring according to another embodiment of the present invention.
FIG. 9 is a perspective view of a tolerance ring according to another embodiment of the present invention.
FIG. 10 illustrates a force distribution between the tolerance rings of FIGS. 9 and 10 and the bearing outer sleeve of FIG. 4.
FIG. 11 is a cross-sectional view of the tolerance ring along line 11-11 of FIG. 8.
FIG. 12 is a cross-sectional view of the tolerance ring along line 12-12 of FIG. 9.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is an exploded view of an-actuator arm assembly 13 which includes a pivot bearing cartridge 23. The pivot bearing cartridge 23 is cylindrical in shape and includes a shaft 24 about which the actuator arm assembly 13 rotates. The actuator arm assembly 13 has an opening or bore 27 therein. The pivot bearing cartridge 23 fits within the bore 27 of actuator arm assembly 13. The tolerance ring 25 fits within the space between the bore 27 and the outside diameter of the pivot bearing cartridge 23.
Actuator arm assembly 13 has a plurality of arms 15 in the head-stack assembly 17. Each arm 15 typically carries at least one suspension 19. Attached to the suspension 19 are recording heads (sliders) 21 which include magnetic transducers that magnetize the surface of the disc (not shown) to represent and store the desired data.
The tolerance ring 25 can be installed first into the bore 27 of actuator arm assembly 13 so that later a generally cylindrical inner part, such as the pivot bearing cartridge 23, can be forcibly pushed into the interior of the tolerance ring 25 to create a radial compressive preload that retains the parts by frictional engagement. Alternatively, the tolerance ring 25 can be installed first around the pivot bearing cartridge 23. The pivot bearing cartridge 23, together with the tolerance ring 25, is then forcibly pushed into the bore 27 of actuator arm assembly 13 to create a radial compressive preload that retains the parts by frictional engagement.
FIG. 2 illustrates a perspective view of a prior art tolerance ring design 29. The tolerance ring 29 is formed from a substantially planar base portion, preferably a 300 Series stainless steel, which is curved to form a cylinder 31. One end of the cylinder 31 has a first edge 33 along the length of the ring. The other end of the cylinder 31 has a second edge 35. The cylinder 31 has a first radius about a central axis and extends for a fixed length parallel to the central axis. Radial expansion and contraction of cylindrical opening 37 is facilitated by a gap 39 along the length of tolerance ring 29 created by the opposite spaced edges 33 and 35.
The tolerance ring 29 has a plurality of contacting portions 41 arranged in one or more rows. The contacting portions 41 generally have a rhomboidal cross-sectional shape extending axially along the cylinder 31. As shown in FIGS. 2 and 3, the contacting portions 41 project radially outward in a direction away from the interior of the tolerance ring 29. It is recognized that alternative configurations known in the art include tolerance rings with contacting portions 41 that project radially inward or project inward and outward in an alternating fashion.
FIG. 3 is a cross-sectional view of the tolerance ring 29 along line 3-3 of FIG. 2. The tolerance ring 29 has two rows of contacting portions 41 that equally project a predetermined radial distance from the base portion 31. These contacting portions 41 withstand forces exerted from the pivot bearing cartridge 23 and the surface walls of the bore 27, when restraining the actuator arm assembly 13 in the hard disk drive. Due to the configuration of the pivot bearing 23, the forces exerted on the contacting portions 41 cause torque “ripple.”
FIG. 4 is a top view of a prior art pivot bearing 23 and tolerance ring 29. The pivot bearing 23 has an inner bearing sleeve 43 and an outer bearing sleeve 45. Between sleeves 43 and 45 are balls or pins 47 that allow one sleeve to rotate with respect to the other. For example, if the outer bearing sleeve 45 is fixed, the inner bearing sleeve 43 can rotate about the same central axis 49 via the balls 47. Due to the configuration of the pivot bearing 23, discrete forces from the balls 47 are transferred to the outer bearing sleeve 45 and the inner bearing sleeve 43 at the contact points. These forces cause torque ripple, which consequently affects the rotational performance of the pivot bearing 23.
FIG. 5 illustrates a force distribution on the outer bearing sleeve 45 of FIG. 4. The outer bearing sleeve 45 is subjected to discrete forces 51 from the balls 47 and discrete forces 53 from the contacting portions 41 of the tolerance ring 29. When the forces 51 and 53 align, as shown in FIG. 5, the pivot bearing 23 experiences high torque ripple. Meanwhile, when the forces 51 and 53 do not align (not shown), the pivot bearing 23 experiences less torque ripple. Consequently, using the pivot bearing 23 with the prior art tolerance ring 29 will subject the pivot bearing 23 to fluctuating high and low torque ripple that affects the rotational performance of the pivot bearing 23.
To reduce torque “ripple,” it is desirable to have as many contacting portions 41 as possible, such that each contacting portion 41 bears little contact force. However, manufacturing limitations prevent more than fifty contacting portions 41. Consequently, to minimize torque “ripple,” it is preferable to evenly space or stagger the contacting portions 41, as shown in FIGS. 6-8. Furthermore, it is preferable to position the contacting portions 41 close to the central region of the cylinder 31, which corresponds to the stiff reinforced central portion of the pivot bearing 23.
FIG. 6 is a perspective view of a tolerance ring 55 with a staggered configuration for contacting portions, according to one embodiment of the present invention. The tolerance ring 55 has a first row 57 of contacting portions 41 and a second row 59 of contacting portions 41. In one embodiment, the second row 59 has contacting portions 41 relatively displaced by a distance less than the width of the contacting portions 41 of the first row 57. For example, if the width of the contacting portions is 1.5 mm, then the second row 59 can have contacting portions 41 displaced by a distance of 1 mm relative to the first row 57. In another embodiment, the second row 59 has contacting portions 41 located underneath the spacing 61 between the contacting portions 41 of the first row 57. In yet another embodiment, the second row 59 has contacting portions 41 circumferentially displaced with respect to the first row 57 by a distance greater than zero but less than or equal to half the pitch between adjacent contacting portions 41 in the first row 57. The pitch is the center-to-center distance between adjacent contacting portions 41. The resulting staggered configuration of the tolerance ring 55 minimizes torque ripple, as illustrated in FIG. 7.
FIG. 7 shows a force distribution between the tolerance ring of FIG. 6 and the bearing outer sleeve of FIG. 4. As shown in FIG. 5, the outer bearing sleeve 45 is subjected to discrete forces 51 from the balls 47. The outer bearing sleeve 45 is also subjected to discrete forces 63 from the contacting portions 41 of the tolerance ring 55. Because the forces 51 and 63 do not align together, the pivot bearing 23 experiences less torque ripple. By staggering the contacting portions 41, the forces 63 are distributed evenly around the pivot bearing 23. Consequently, the configuration of the tolerance ring 55 will subject the pivot bearing 23 to less torque ripple and improves the rotational performance of the pivot bearing 23.
FIG. 8 is a perspective view of a tolerance ring 65 with a staggered configuration for contacting portions 41, according to one embodiment of the present invention. The tolerance ring 65 has contacting portions 41 arranged in a first, a second and a third row, shown generally as 67, 69 and 71 respectively. In one embodiment, the second row 69 has contacting portions 41 circumferentially displaced with respect to the first row 67 by a distance greater than zero but less than or equal to half the pitch between adjacent contacting portions 41 in the first row 67. Similarly, the third row 71 has contacting portions 41 circumferentially displaced with respect to the second row 69 by a distance greater than zero but less than or equal to half the pitch between adjacent contacting portions 41 in the first row 69. For example, if the width of the contacting portions is 1.5 mm, then the second row 69 can have contacting portions 41 displaced by a distance of 0.75 mm relative to the first row 67, and the third row 71 can have contacting portions 41 displaced by a distance of 0.75 mm relative to the second row 69 (1.5 mm relative to the first row 65). In another embodiment, the second row 69 has contacting portions 41 located underneath the spacing 73 between the contacting portions 41 of the first row 67, while the third row 71 has contacting portions 41 located underneath the contacting portions 41 of the first row 67. Like tolerance ring 55, the staggered configuration of tolerance ring 65 reduces torque ripple.
In one embodiment, the contacting portions 41 can have a varying height or other geometry to achieve optimal distribution of load for reducing torque ripple. FIG. 9 is a perspective view of a tolerance ring 75 with a staggered configuration for contacting portions, according to one embodiment of the present invention. The tolerance ring 75 has contacting portions 77 in the second row 69. These contacting portions 77 project radially outward by a distance greater than contacting portions 41. In another embodiment, the contacting portions 77 can have a different width or a different geometry from contacting portions 41. The contacting portions 77 are preferably positioned opposite to the stiff reinforced central portion of the pivot bearing 23. By increasing the radial projection of the contacting portions 77 in the middle row 69, the contacting portions 77 will sustain a greater radial compressive preload than the contacting portions 41. The contacting portions 77 will be crushed during assembly to provide better frictional engagement with the pivot bearing 23 and the bore 27. Like tolerance ring 65, the staggered configuration of tolerance ring 75 reduces torque ripple.
FIG. 10 illustrates a force distribution between the tolerance rings of FIGS. 9 and 10 and the bearing outer sleeve of FIG. 4. As shown in FIG. 5, the outer bearing sleeve 45 is subjected to discrete forces 51 from the balls 47. The outer bearing sleeve 45 is also subjected to discrete forces 79 from the contacting portions 41 and 77. Because the forces 51 and 79 do not align together, the pivot bearing 23 experiences less torque ripple. By staggering the contacting portions 41 and/or 77, the forces 79 are distributed evenly around the pivot bearing 23. Consequently, the configuration of tolerance rings 65 and/or 75 will subject the pivot bearing 23 to less torque ripple and improves the rotational performance of the pivot bearing 23.
FIGS. 11 and 12 are cross-sectional views of tolerance rings along lines 11-11 of FIG. 8 and 12-12 of FIG. 9, respectively. FIG. 11 shows three rows of contacting portions 41 that equally project a predetermined radial distance from the cylinder 31. FIG. 12 shows two rows of contacting portions 41 that equally project a predetermined radial distance from the cylinder 31 and one middle row of contacting portions 77 that projects radially outward by a distance greater than contacting portions 41.
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of a tolerance ring having a cylinder with a predetermined length, and a plurality of contacting portions staggered over at least two rows around the cylinder.
Patent Application
20080043375
