Vision-assisted profile inspection system of inhomogeneous flex circuits in hard disk drives

Abstract

Previous contributors have identified flex circuit or cable vibrations to be problematic sources for decreasing operation accuracy of read/write head in hard disk drives. To reduce the vibrations from the flex cable, damper layer or piezo-electric (PZT) layer have been reported to be effective in controlling the cable’s dynamics. However, due to complexity in the largely deformed circuit with additional layer, it is quite difficult to come up with proper analytical model to depict cable’s profile. In this work, a vision system and detection method are proposed and examined with mock flex cables by sandwiching additional PZT film layer between two plastic laminates, causing the cable to be inhomogeneous along its free length direction. From the present investigation, close-to-real 2D geometry or say the profile of inhomogeneous flex cable can be obtained by image processing filters including standard deviation threshold of the captured flex cable image. To ensure reliability in obtaining the correct profile of the cable, three types of evaluation techniques were implemented on the flex cable’s image contour. The profile was used in constructing finite element mode from which natural frequencies were validated by experimental measurements. Study on the flex cable’s non-uniformity reveals that the PZT film near J-block joint stiffens and straightens the cable contour. Without bending the cable contour too much and destroying the mechanical design of flex cable, it was suggested by this work that PZT layer would be an appropriate control medium to eliminate the cable vibrations.