Yoshiho Yanagita

Head positioning control for low sampling rate systems based on two degree-of-freedom control

To enhance formatting efficiency in high density hard disk drives, it is desirable to decrease the number of embedded servo signals. As a consequence, the sampling rate of servo systems has been becoming lower. In this situation, it is difficult to attain fast track seeking by using only a feedback controller. This paper presents a high-speed track seek technique, based on two degree-of-freedom control. A new reference model is developed by focusing on the attainment of fast track seeking through the effective use of a voice coil motor, which functions as a disk head actuator. The model generates reference trajectories, allowing high-speed movement. Also, in order to quickly settle the disk head to a target track under various disturbances, an initial value compensation (IVC) method to minimize a quadratic performance index is developed. Experimental results, using a 3-1/2 inch hard disk drive, confirm the validity of the proposed method.

Wide-range fine pointing mechanism for free-space laser communications

A breadboard model of a Wide-range Fine Pointing Mechanism (WFPM) designed for free-space laser communications and composed of electromagnetic actuators and a flexible support system has been developed. The WFPM is compact (45 x 45 x 39 mm3) and light in weight (160 grams). Its actuators, which consist of four moving-coil-type motors with long strokes, ensure a wide optical scan range, +/-4 degrees. The support system, which consists of a center torsion bar and four preformed thin springs, allows the mechanisms 20 mm-diameter mirror to be rotated freely about a vertically constant point; the mirror can be rotated about its x- and y-axes simultaneously. The breadboard model has passed a launch vibration test under conditions of 20 G rms overall. With its coarse and fine quadrant detectors, the WFPM is able to provide stable acquisition and tracking without any need for built-in sensors. The digital control system of the WFPM has a 1 kHz control bandwidth and -90-dB disturbance suppression at 1 Hz. Use of the WFPM by an acquisition and tracking terminal significantly shortens acquisition time and ensures accurate tracking. Acquisition and tracking simulations have shown fast acquisition time (58.7 ms for 3.5-milli-radian initial error) and high tracking precision (+/-1 micro-radian, 3 sigma). To maintain high tracking precision, we employ a tradeoff between noise reduction and disturbance suppression. The WFPM has the potential to play an essential role in helping to provide high-data-rate free-space laser communications.

Development status of a new small airborne SAR based on Pi-SAR2

This paper shows the development status of a new small airborne SAR based on Pi-SAR2. We had designed its advanced small type high resolution full polarimetric airborne SAR with the real-time processor. Its flight test will be planned in this fiscal year.

Inertial stabilization system for small airborne SAR

An inertial stabilization system for small airborne synthetic aperture radar (SAR), which consists of an active damping mechanism and a two-axis gimbal, has been developed. Both high-frequency vibration isolation by the active damping and high stability of antenna direction under low-frequency angular disturbance have been successfully demonstrated. Also, a small airborne SAR prototype for disaster monitoring has been produced and prepared for flight tests.

High-precision scanner control system using online learning

We have developed a high-precision scanner control system, which is used on earth observation satellites. This control system keeps high angular precision with ultra smooth rotation. We designed a feedback controller consists of a rate loop for rotation-speed control and a position loop for angular control. Adding a feedforward controller using cyclic memory, 1st order rotational synchronizing disturbance caused by eccentric load has been compressed over 50 dB. An online learning controller sustains long-time robustness by suppressing undesired addition to a cyclic memory. The proposed control system maintains high pointing accuracy with a standard deviation of 0.003 degree at 80 rpm.

High-precision scanner control system

A high-precision whiskbroom scanner control system, which is used on earth observation satellites, is discussed. This control system is required to keep high angular precision with ultra-smooth rotation. We designed a feedback control system consisting of a rate loop for rotation-speed control and a position loop for angular control. Adding a feedforward control system using cyclic memory, 1st order rotational synchronizing disturbance caused by eccentric load has been compressed over 50 dB. As a result, high pointing accuracy with a standard deviation of 0.003 degree or less has been achieved in rotating with a constant speed of 79.4 rpm.