Abstract: A digital servo control system for disk drives is an “embedded” system—one in which servo control information is embedded on the same disk surface as the user data. In contrast to known embedded-servo systems in which a space-consuming series of many dibit pairs is present, the present system provides only a single dibit pair in a fractional positional error (PESF) area. Thus, the disk drive's read head encounters only a single dibit pair per sample period (or per data sector), thus saving valuable disk space that may be used for user data. Various pre-processing methods may be provided so as to pre-process the measurement derived from the single dibit pair per sample period (or data sector), so as to compensate for non-ideal characteristics of the dibit measurement. The system thus provides an accurate and robust servo control system, while sacrificing a minimum amount of valuable disk space to the servo information field.

Abstract: In a digital servo control system especially suitable for use in disk drives, a sample integrity tester is provided. Sample measurements, indicating the position of a disk drive's read/write head relative to tracks of information on a recording medium, are subject to error due to noise. The sample integrity tester 2410, 2420, 2430 effectively filters out noise-corrupted measurements and thus prevents clearly erroneous measurements from contaminating calculations performed within the servo controller's control loop. If a measured position signal falls outside a given window (indicating a possible spurious position value has been read), an observer's predicted value is used rather than the spurious value. Using the predicted value allows the loop to operate in a "freewheel" (open-loop) mode. A preferred implementation of the sample integrity tester involves a coarse window that is static, and a fine window that changes dynamically based on an effort signal.

Abstract: A servo control system provides adaptive compensation for a variety of tracking and seek problems found in disk drives. The servo control system is ideally implemented in digital form for accuracy, speed and compactness. A first embodiment includes two modes, a tracking (or position) mode and a seek (or velocity) mode, each mode employing a variety of compensation functions. A second embodiment includes a single comprehensive control system which functions during both tracking and seek operations.

Abstract: A servo control system provides adaptive compensation for a variety of tracking and seek problems found in disk drives. The servo control system is ideally implemented in digital form for accuracy, speed and compactness. A first embodiment includes two modes, a tracking (or position) mode and a seek (or velocity) mode, each mode employing a variety of compensation functions. A second embodiment includes a single comprehensive control system which functions during both tracking and seek operations.