hard disk
A typical hard drive has two electric motors, to spin the disks and one to position the read/write head assembly. The disk motor has an external rotor attached to the platters; the stator windings are fixed set. The actuator has a read-write head under the tip of its very end (near center); a thin printed-circuit cable connects the read-write visit the hub in the actuator. A flexible, somewhat ‘U’-shaped, ribbon cable, seen edge-on below also to the left in the actuator arm in the first image and others clearly inside second, continues the hyper link within the visit the controller board on the opposite side.
The top support arm is quite light, and also rigid; in modern drives, acceleration in the head reaches 550 Gs.
Opening the Hard Disk drive
The silver-colored structure is the top plate with the permanent-magnet and moving coil motor that swings the heads for the desired position. The plate supports a thin neodymium-iron-boron (NIB) high-flux magnet. Beneath this plate will be moving coil, known as the voice coil by analogy to the coil in loudspeakers, which is mounted on the actuator hub, and beneath that is the second NIB magnet, installed on the bottom plate of the motor (some drives have only one magnet).
The voice coil, itself, is shaped rather like an arrowhead, and created 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 along the two sides from the arrowhead (which point towards the actuator bearing center) interact using the magnetic field, possessing a tangential force that rotates the actuator. Current flowing radially outward along one side from the arrowhead, and radially inward on the other half produces the tangential force.. That the magnetic field were uniform, each side would generate opposing forces that may cancel one another out. Which means surface with the magnet is half N pole, half S pole, with all the radial dividing line in the middle, causing both sides from the coil to determine opposite magnetic fields and produce forces that add as opposed to canceling. Currents along side top and bottom with the coil produce radial forces that do not rotate the pinnacle.