A normal hard drive has two electric motors, one to spin the disks and one to position the read/write head assembly. The disk motor has an external rotor that come with the platters; the stator windings are fixed into position. The actuator incorporates a read-write head under the tip of its very end (near center); a thin printed-circuit cable connects the read-write go to the hub from the actuator. A flexible, somewhat ‘U’-shaped, ribbon cable, seen edge-on below and also to the left on the actuator arm in the first image and much more clearly while in the second, continues the web link within the visit the controller board around the opposite side.

The pinnacle support arm is incredibly light, but in addition rigid; in modern drives, acceleration in the head reaches 550 Gs.

Opening the Hard Disk drive

The silver-colored structure is a top plate with the permanent-magnet and moving coil motor that swings the heads on the desired position. The plate supports a thin neodymium-iron-boron (NIB) high-flux magnet. Beneath this plate may be the moving coil, known as the voice coil by analogy for the coil in loudspeakers, that is mounted on the actuator hub, and beneath that’s a second NIB magnet, attached to the underside plate in the motor (some drives just have one magnet).

The voice coil, itself, is shaped rather like an arrowhead, and made from doubly-coated coppmagnet wire. The inner layer is insulation, as well as the outer is thermoplastic, which bonds the coil together after it’s wound on the form, rendering it self-supporting. The portions from the coil over the two sides with the arrowhead (which point towards the actuator bearing center) interact with the magnetic field, developing a tangential force that rotates the actuator. Current flowing radially outward along one side from the arrowhead, and radially inward on the other produces the tangential force.. If your magnetic field were uniform, each side would generate opposing forces that will cancel each other out. Therefore the surface with the magnet is half N pole, half S pole, with all the radial dividing line in the middle, causing the 2 sides with the coil to discover opposite magnetic fields and produce forces that add rather than canceling. Currents over the top and bottom with the coil produce radial forces that do not rotate the top.

Tags: neodymium iron boron, permanent magnet, ribbon cable, stator windings, tangential force