Optimal strain gauge placement for an instrumented disk drive suspension

The magnetic disk drive industry exhibits a continuing technological trend of ever increasing storage capacity requiring track densities of 25,000 tracks per inch by early in the next century. Successful operation at these track densities will require an increase of between 2.5 and 9 times in the closed-loop bandwidth of the head positioning servo-system. Resonance modes in the suspension of hard disk drives limit the closed-loop bandwidth. The bandwidth of the servo can be increased by state feedback of the vibration modes for active vibration control. The paper considers the optimal placement of strain gauge sensors on a suspension to observe the vibration states of the suspension. Using a finite element simulation of an actual suspension, a state space model is identified for the two normal strains and the shear strain at each finite element. The state space model includes the dynamics of the three primary resonance modes. A numerical search algorithm is used to determine the sensor location and orientation which maximizes the minimum singular value of the observability grammian. Results suggest that use of an instrumented suspension is a viable candidate method for improve disk drive servo performance