HDD VCM control method at power shut down
Original Publication Date: 2000-Dec-01
Included in the Prior Art Database: 2003-Jun-18
Disclosed is the efficient brake of HDD (Hard Disk Drive) actuator movement before retract. HDD can retract its actuator more safely by this scheme. If using current retract method, read write head can possibly crash to crash stop block or ramp block when actuator is moving fast and when power is shut down. Then, read/write head or disk surface can get serious damage. In order to prevent such troubles, actuator moving speed should be reduced at the moment of power off. This invention includes applying electric voltage to VCM (Voice Coil Motor) coil to reduce the actuator moving speed. Actuator movement can provide BEMF (Back ElectroMotive Force) even after power off. The amplitude of BEMF is proportional to actuator speed and the direction of BEMF depends on the actuator moving direction. Spindle/VCM driver has the electric circuit which can detect the amplitude and direction of VCM BEMF (Figure 1). Capacitor 1 in Figure 1 is provided with VCM BEMF through the BEMF amplifier; so, Capacitor 1 can store proper electricity which is relative to actuator speed and its direction. SW 1-2 connects Capacitor 1 to VCM BEMF amplifier or to "FET switching driver" which can drive SW 2-1 and SW 2-2 in Figure 1. SW 2-1 and SW 2-2 can control FET A, B, C and D so that VCM coil current can create braking power for actuator movement as shown in Table 2. "FET switching driver" is active only when the electric charge in Capacitor 1 exists. Moreover, the charge is proportional to actuator BEMF, namely actuator speed when power off. So, "FET switching driver" can apply braking current to VCM coil for the period which is proportional to the actuator speed.