Analytical dynamic model for suspension with PZT actuators

Modern hard disk drive uses voice coil motor to move its actuator across spinning disk to access data stored on disk surfaces. To achieve higher area density with narrow tracks, piezoelectric (PZT) ceramics are deployed as secondary actuator in many high capacity drives to increase servo control bandwidth for better positioning accuracy. Piezoelectric secondary stage actuators, often called dual stage actuator or DSA, integrated on suspensions are discussed in this paper. An analytic model is presented to derive a secondary order equation of motion relating suspension dynamics to key suspension and PZT geometric parameters, material properties and voltage applied to PZT. DSA DC gain is then obtained from the equation of motion. By introducing a suspension configuration without PZT installed, the DSA DC gain is then further linked to suspension dynamics parameters. With the equation of motion and DSA DC gain model, design directions for higher stroke and tradeoffs for dynamics and robustness are discussed.