Study On The Dynamic Lubrication Characteristics Of The Ultra-thin Gas Film In Hard Disk Drive

With the development of computer technology and increase of the need for large amounts of information and data, hard drives are being upgraded continually. There are two important aspects to consider during the development process of the hard disk driver. One is that the reduction of clearance between head and disk can increase the recording density, and the other is that in order to obtain stable signal voltages and better capacities of resisting disturbance the clearance between the head and disk must keep stable. Flight characteristics of head become important factors that can affect memory property of the hard disk driver. This dissertation analyzes dynamic characteristics of the head by using time domain analysis and frequency domain analysis based on the time dependent FK-Boltzmann modified Reynolds equation and the three degree freedom dynamic equations.Firstly, the method of solving ultra-thin lubricating control equation was analyzed. In this dissertation, upwind scheme was adopted. The destabilization in calculating caused by a large bearing number was overcome by taking shear flow and time item as the principal iterative terms. Moreover, the harmonic flow factor was imported in the whole lubricating region to alter the variation of flow rate at the big steps in order to diminish calculated deviation. Compared the results of present scheme with the results of mean algorithm and one dimensional approximate analytic solution, it was showed that the results of the present scheme is more approximate to the analytic solution. Then this method was used to calculate the pressure distribution of several dissymmetry disk heads. All calculations have good convergence. The results confirmed the convergence and the accuracy of this scheme.Then the simultaneous control equations were built up. The dynamic characteristics of the ultra-thin gas film in time domain and frequency domain were analyzed by using finite difference method to solve the control equations. Based on the work, analysis software with the autonomous copyright was produced. In the time domain analysis, the rules for variation of flying pose of the magnetic head and lubricant performance of the gas-film with time was obtained through solving the equations. The results show that the magnetic head can recover to equilibrium in a certain time after undergoing a slight disturbance from outside and that the vibration in the height direction and fluctuation in the pitch direction have strong impact on dynamic lubricant property of the head. In addition, the obstacle-passing capacity of the head was analyzed. The results indicate that the head can surpass small obstacles successfully and then get back to equilibrium after a period of decaying oscillation at a certain frequency.In the frequency domain analysis, the calculated analysis on the stiffness coefficient and damping coefficient of the gas-film was conducted using perturbation method. Rules for variation of the stiffness coefficient and damping coefficient with frequency were gained. The rules show that the gas-film stiffness relies heavily upon the gas-film thickness along the height direction and the angle in pitch direction, and it is somewhat dependent on the rolling angle and the rotation velocity of the headAt last, the dynamic experiments on real hard disks were carried out in the present dissertation. A vibration experiment table for the hard disk was set up by connecting the hard drive with a vibration exciter. The values of the flight height and the output voltage of signal on different rotate speeds were tested by using the dynamic flying height tester and dynamic electric tester provided by the disk manufactory. The relational curves between output voltage differences and vibration amplitudes of heads were gained. Then hard disks of same type were tested under different vibrating frequencies. Magnetic signals were acquired via the lead wires. The influence of vibrating frequency on signal was discussed in addition. Fluctuation ranges were quantitatively judged by utilizing the flight height curve varying with voltage. After comparing the results of impact experiment and simple harmonic vibration experiment with the theoretical results respectively, we may safely draw the conclusion that the experimental results are consistent with the theoretical results.