Abstract: Methods, systems, and apparatus, including computer program products, are described for calibrating servos, and in some implementations for calibrating spiral servos for use in self servo write processes. In one aspect, a method is provided that includes measuring a slope of a spiral written to a machine readable medium, and adjusting a parameter in accordance with the measured slope to calibrate spacing of servo tracks, with respect to variation between a target slope and the measured slope for the spiral, for writing the servo tracks to the machine readable medium using the spiral as a reference and the adjusted parameter to generate a same radial spacing between servo tracks from spirals with different slopes.

Abstract: Embodiments of the present disclosure provide a method including recording time stamps for a repeating characteristic of a spindle back electromotive force (BEMF) signal and comparing one or more of the recorded time stamps for the repeating characteristic of the spindle BEMF signal with an expected value for the one or more recorded time stamps to detect a timing error associated with writing a servo pattern on a machine readable medium of a self-servo write (SSW) system. Other embodiments may be described and/or claimed.

Abstract: Methods, systems, and apparatus, including computer program products, are described for calibrating voice coil motors. In one aspect, a method is provided that includes seeking toward an outer diameter of a machine readable medium from a target servo track to a blank portion of the machine readable medium. A radial velocity of an actuator is determined after accelerating the actuator to a target radial velocity. The radial velocity is compared to the target radial velocity, and a current, that is used to controllably modify the radial velocity of the actuator if the radial velocity is different from the target radial velocity, is calibrated.

Abstract: Apparatus, methods, and systems can be employed for calibrating servos, and in some implementations, spiral servos are calibrated for use in self-servo-write (SSW) processes. In an aspect, an apparatus includes a timing reference detector configured to determine timing reference information from a back electromotive force signal associated with a rotating machine readable medium, and a servo track window period generator configured to determine a relative location of a spiral on the rotating machine readable medium based on the timing reference information.

Abstract: Embodiments of the present disclosure provide a method including recording time stamps for a repeating characteristic of a spindle back electromotive force (BEMF) signal and comparing one or more of the recorded time stamps for the repeating characteristic of the spindle BEMF signal with an expected value for the one or more recorded time stamps to detect a timing error associated with writing a servo pattern on a machine readable medium of a self-servo write (SSW) system. Other embodiments may be described and/or claimed.

Abstract: Systems, methods, and apparatuses, including computer program products, are described for, in at least one implementation, determining a measured slope of a spiral, calibrating radial spacing between servo tracks according to a relationship between a target slope and the measured slope, wherein an amount of calibration for the radial spacing varies directly with the relationship between the target slope and the measured slope, and generating servo tracks according to the calibrated radial spacing.

Abstract: Methods, systems, and apparatus, including computer program products are described for calibrating servos, and in some implementations, calibrating spiral servos for use in self-servo-write (SSW) processes. In one aspect, a method is provided that includes determining timing reference information on a machine readable medium, locking a clock signal to the timing reference information, detecting a spiral on the machine readable medium, determining a location of the spiral using the clock signal, and calibrating a spiral servo according to the location of the spiral.

Abstract: The present disclosure includes systems and techniques relating to magnetic recording devices, such as disk drives. A recording medium of a magnetic recording device can include multiple helicoid patterns arranged in multiple helicoid groups. A described technique includes receiving a waveform produced by a head operated with respect to the medium; determining, based on the waveform, first phase difference(s) corresponding to a first helicoid group; affecting an alignment of the head with respect to the medium based on the first helicoid group by compensating for the first phase difference(s) to maintain the alignment; determining, while compensating for the first phase differences, second phase difference(s) corresponding to a second helicoid group; and affecting, responsive to a switch from the first helicoid group to the second helicoid group, the alignment of the head with respect to the medium by compensating for the second phase difference(s) to maintain the alignment.

Abstract: Methods, systems, and apparatus, including computer program products are described for calibrating servos, and in some implementations, calibrating spiral servos for use in self-servo-write (SSW) processes. In one aspect, a method is provided that includes determining timing reference information on a machine readable medium, locking a clock signal to the timing reference information, detecting a spiral on the machine readable medium, determining a location of the spiral using the clock signal, and calibrating a spiral servo according to the location of the spiral.

Abstract: A self-servo-write system including a timing control module and a position control module. The timing control module is configured to generate (i) timing information of a first set of servo spirals and (ii) timing control signals for writing a second set of final servo wedges based on the timing information. The position control module is configured to generate (i) position information of the first set of servo spirals and (ii) positioning control signals for writing the second set of final servo wedges based on the timing information. Less than half of the servo spirals in the first set of servo spirals are over-written while writing the second set of final servo wedges. A ratio of a first number of final servo wedges in the second set of final servo wedges to a second number of servo spirals in the first set of servo spirals is a non-integer greater than one.

Abstract: Methods, systems, and apparatus, including computer program products are described for calibrating servos, and in some implementations, calibrating spiral servos for use in self-servo-write SSW processes. In one aspect, a method is provide that includes rotating a machine readable medium, and detecting a spiral on the machine readable medium. Detecting a spiral on the machine readable medium includes detecting magnitudes of the spiral and a timing mark, storing a timestamp from a clock signal that corresponds to the timing mark of the spiral, determining a peak of the spiral from the magnitudes, and locking the clock signal to the peak of the spiral using the timestamp.

Abstract: Methods, systems, and apparatus, including computer program products, are described for calibrating voice coil motors. In one aspect, a method is provided that includes seeking toward an outer diameter of a machine readable medium from a target servo track to a blank portion of the machine readable medium. A radial velocity of an actuator is determined after accelerating the actuator to a target radial velocity. The radial velocity is compared to the target radial velocity, and a current, that is used to controllably modify the radial velocity of the actuator if the radial velocity is different from the target radial velocity, is calibrated.

Abstract: An illumination apparatus for use in examining a body of living tissues, the apparatus comprising a head for contacting the body of living tissues, a light source mounted in the head for illuminating the tissues, and an annular switch disposed around the light source, the annular switch being adapted automatically to permit illumination of the light source at an examination intensity when the head contacts the body at least around an annular contact area on the head corresponding to the annular switch.

Abstract: Systems and techniques to calibrate a control loop include, in at least one implementation, a system including the control loop configured to generate a clock signal and lock the clock signal to timing marks detected on a machine readable medium, a repetitive error correction module configured to receive a predicted phase and a corrected phase error for the clock signal, generate a predicted repetitive phase disturbance using the predicted phase and the corrected phase error for the clock signal, and calibrate a phase error to compensate for variations in repetitive phase errors in the clock signal using the predicted repetitive phase disturbance; and a servo track generator configured to generate servo tracks using the clock signal.

Abstract: A recording medium can include multiple helicoid patterns arranged in multiple helicoid groups, e.g., first and second helicoid groups. Operating a disk drive can include switching between helicoid groups to maintain the alignment of the head with respect to a target track of the rotating recording medium. Enabling a switch can include receiving a waveform produced by a head operated with respect to a rotating recording medium, generating first information from one or more portions of the waveform corresponding to the helicoid patterns of the first helicoid group; generating second information from one or more portions of the waveform corresponding to the helicoid patterns of the second helicoid group; and analyzing the second information with respect to the first information to generate calibration information. The calibration information can compensate for operational differences between using the helicoid patterns of the first helicoid group and the helicoid patterns of the second helicoid group.

Abstract: A system includes a first current generator and a second current generator. The first current generator generates a first current to bias an actuator arm against a spring when a control signal is received. The first current generator discontinues the first current to release the spring and accelerate the actuator arm when servo signals are generated. The second current generator generates a second current that biases the actuator arm away from the spring when the first current is discontinued.

Abstract: A self-servo-write (SSW) system of a hard disk drive (HDD) includes a timing control module and a position control module. The timing control module generates timing information of S servo spirals and generates timing control signals for writing F final servo wedges in a circle based on the timing information, where F and S are integers, and where F is greater than S. The position control module generates position information of the S servo spirals and generates positioning control signals for writing the F final servo wedges in the circle based on the timing information.

Abstract: Methods, systems, and apparatus, including computer program products, are described for calibrating servos, and in some implementations for calibrating spiral servos for use in self-servo-write processes. In one aspect, a method is provided that includes determining a measured slope of a spiral, and calibrating radial spacing between servo tracks using the measured slope and a target slope.

Abstract: Methods, systems, and apparatus, including computer program products, are described for calibrating control loops, specifically phase-locked loops. In one aspect, an apparatus is provided that includes an oscillator model that generates a predicted phase based on an input, a first averaging submodule that generates an average predicted phase over a predetermined number of samples, and a first summing submodule that receives a first corrected phase error and generates a predicted repetitive phase disturbance using the first corrected phase error, the predicted phase, and the average predicted phase.

Abstract: A system comprises a positioning module that positions an actuator arm to read spirals that are prewritten. A frequency measuring module measures a first frequency of sync marks of said spirals. An estimation module calculates a second frequency of said sync marks when said actuator arm moves at a predetermined actuator velocity. A control module calculates an actuator velocity at which said spirals are prewritten based on said first frequency, said second frequency, and said predetermined actuator velocity.