Keywords: Hardware , Electronics , Hard disk actuators, voice coil

ABSTRACT - Hard disk drives have evolved rapidly with computer miniaturization into highly compact and integrated electromechanical systems. Hard drives contain many precision mechanical parts which may prove useful in the design of small precision robots. The advantages of parts taken from hard disks include low cost, miniaturization, high quality, and for some applications, cleanliness. We report the results of engineering tests on flat coil head positioning actuators taken from hard drives of sizes ranging from 5.25? to 1.8? media diameter. We also perform a simple analysis which suggests that requirements for torque per unit mass are lower for small robot arms. The results suggest ways that hard disk actuators can be utilized in mini robotic designs and points the way towards improved versions of these designs for robotic purposes.

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Maximum Torque:

For these motors, the torque produced is linearly proportional to coil current. The ?maximum? torque is really a thermal limit determined by the temperature at which the insulation will fail. A usual standard is to measure torque with a current sufficient to raise the temperature of the coil to a specified value. We measured coil temperature as a function of coil current twice; once with the actuator coil in free air and once with the actuator installed in the drive.


Discussion

This study has measured some basic engineering parameters for actuators from hard disk drives of various sizes (physical media diameters). We suggest that devices of this sort provide a rich source of components for robotic prototyping and experimentation at low cost.

Adding ferrofluid to the magnetic gap appears to be a promising way to get increased torque capability, better thermal properties, and some well behaved damping from these devices. Problems related to non-uniform displacement of fluid can be easily solved with slight modifications.

By analysis of a simple planar direct drive arm under the acceleration of gravity, we showed that smaller direct drive arms should have better dynamic performance than larger ones. This suggests that the benefits of direct drive arms such as better force control and precision should be highly relevant to small robot designs.