Z-height control for disc drive using servo wedge timing

A data storage device comprising:

• a data storage disc comprising:
• a data track;
• a top surface and a bottom surface, each of the top and bottom surfaces being parallel to an x-y plane;
• and
• a servo wedge comprising:
• a top surface boundary of the servo wedge;
• and
• a bottom surface boundary of the servo wedge;
• wherein the top surface boundary and the bottom surface boundary are spaced apart by a distance along the data track;
• an actuator arm assembly comprising:
• a first actuator arm supporting a first head configured for interaction with the top surface, the first actuator arm spaced at a Z-height from the top surface;
• a second actuator arm supporting a second head configured for interaction with the bottom surface;
• and
• a feedback and control system configured to:
• employ a transfer function relating the Z-height to the distance;
• and
• change the Z-height based on the transfer function.

A method comprising:

• writing a servo wedge onto a data storage disc having a top surface and a bottom surface, each of the top and bottom surfaces being parallel to an x-y plane;
• the writing resulting in a top surface boundary of the servo wedge and a bottom surface boundary of the servo wedge;
• during a disc certification event:
• supporting a head pair on an actuator arm assembly while the disc rotates at a spin speed measurable in revolutions per minute (rpm);
• flying the head pair at a data track located at radius R from a disc center, wherein the head pair encounters the top surface boundary of the servo wedge at a first time and wherein the head pair encounters the bottom surface boundary of the servo wedge at a second time, thereby defining a certification time difference (ΔTc) between the first and second times;
• and
• determining a target Z-height (d1) between a first actuator arm of the actuator arm assembly and the top surface at the data track;
• during a disc read/write interaction:
• flying the head pair at the data track while the disc rotates at the spin speed, wherein the head pair encounters the top surface boundary of the servo wedge at a third time, and wherein the head pair encounters the bottom surface boundary of the servo wedge at a fourth time, thereby defining an operation time difference (ΔT) between the third and fourth times;
• determining an amount (ΔTZ) by which the operation time difference (ΔT) is changed from the certification time difference (ΔTc);
• and
• employing ΔTZ to move the first actuator arm toward the target Z-height (d1).