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Four-Bar Linkage Radial Head Movement

IP.com Disclosure Number: IPCOM000047144D
Original Publication Date: 1983-Oct-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Fairchild, PT: AUTHOR

Abstract

Head alignment on a rotary actuator disk system is not possible at the extreme ends because of the angle between the head and the track on the disk. Rotary actuators or arms have a relatively simple ball bearing or spindle arrangement at the end opposite the head when compared to the complex linear bearing system used in linear actuators. Also, the effective mass at the head of a rotary actuator is the sum of all the moving parts multiplied by the square of the ratio of the mass/head radius. In a linear actuator system the effective mass at the head is the sum of all moving parts. Thus, the resulting effective mass of a rotary actuator is generally lower, and the size and power of the motor is lower. This makes rotary actuators less expensive and more reliable than linear actuators.

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Four-Bar Linkage Radial Head Movement

Head alignment on a rotary actuator disk system is not possible at the extreme ends because of the angle between the head and the track on the disk. Rotary actuators or arms have a relatively simple ball bearing or spindle arrangement at the end opposite the head when compared to the complex linear bearing system used in linear actuators. Also, the effective mass at the head of a rotary actuator is the sum of all the moving parts multiplied by the square of the ratio of the mass/head radius. In a linear actuator system the effective mass at the head is the sum of all moving parts. Thus, the resulting effective mass of a rotary actuator is generally lower, and the size and power of the motor is lower. This makes rotary actuators less expensive and more reliable than linear actuators.

One of the disadvantages of a rotary actuator is that the head moves in an arc which changes the angular relation between the head and the track below it, as shown in Fig. 2. The ideal situation is to have the head parallel to the track or moving in a radial fashion along a radius of the disk, as shown in Fig. 1. The improvement applies the principle of the four-bar linkage to the unique application of the extension of one of the bars radially through the center of the disk.

This bar whose extension is always through the center of the disk supports the head and maintains perfect head/track alignment throughout the full range of movement. See Figs....