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Optical Pick Ups

FERROFLUID IN OPTICAL DISC PICKUP ACTUATORS

Ferrofluidics are becoming increasingly popular for use for actuator damping in a variety of devices including CD players, Laser Disc players, CD-ROM drives and, DVD-ROM drives.

INTRODUCTION

The actuator in such a device is an electro-mechanical device comprised of two magnetic circuits and two discreet coils, oriented perpendicular to each other. The coils and objective lens are mounted on an integral bobbin/carrier assembly which, in turn, is suspended in the magnetic air gaps by four strands of Beryllium Copper wire. The suspension is damped by the presence of silicone rubber at its termination.

In spite of the presence of the silicone rubber "damper bond", the actuator still exhibits a strong mechanical resonance which affects its settling time and vibrational characteristics. This resonance can cause errors in reading information from the disk, particularly in high speed CD-ROM and DVD-ROM drives.

FERROFLUID SOLUTION
Ferrofluid is used to dampen vibration in various commercial dampers as well as in consumer audio loudspeakers and CD/DVD-ROM devices. Ferrofluid damping is very reliable as the viscosity and retention capability of the fluid can be easily controlled to meet device requirements. In addition to the damping benefits in audio loudspeakers, ferrofluid also provides an efficient heat transfer medium to conduct heat away from the coil.

In the actuator design, ferrofluid is applied to the surface of the magnets until the quantity is sufficient to maintain intimate contact with the bobbin/carrier assembly. The fluid is retained in the magnetic field and its viscosity provides the desired mechanical resistance (damping) to the moving assembly. This improves the actuator's settling time and vibrational characteristics. Access time is also improved, particularly on warped or eccentric discs.

Developed specifically for optical pickup actuators, the CF Series of ferrofluids posses the necessary wide temperature range, colloid stability and low volatility required for long term performance in these applications. Please call for full specifications for the CF Series of fluids.

 


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