A method of designing H∞ controllers based on the allowable magnitude of the perturbation is presented. The design concept is explained with first order scalar systems, and numerical examples are given to examine validity of the method. As an application, an active flutter control system is synthesized for a two-dimensional aeroelastic system. The resultant controllers with a frequency dependent weighting function are compared in view of accomplishment of the frequency loop shaping.
The behavior of the wake behind a stationary circular cylinder and behind a rotating one near the critical Reynolds number was investigated in a low speed wind tunnel. In the case of a stationary cylinder, the critical Reynolds number was easily defined by the variation of the pressure coefficients on the upper and the lower surfaces of a cylinder. The periodicity of velocity fluctuation in the wake was suppressed by the appearance of the lift force acting on a cylinder at the critical Reynolds number. In the case of a rotating cylinder, as the spin parameter was increased, the peak frequency of spectrum of the velocity fluctuation in the wake was increased in the subcritical region, while it was decreased in the supercritical region. The variation of peak frequency in terms of the spin parameter shows the drastic changes with sudden decrease of lift coefficients. The intensity of the spectral peak was decreased as the absolute value of lift was increased. For the larger lift, the peak frequency did not appear in the spectral distribution. The relation between the intensity of the spectral peak and the variation of lift was similar to that of a stationary cylinder which experienced the lift at the critical Reynolds number.
Time-delay of flight control systems has great influence on stability and manuverbility of flying vehicles, and it is of practical importance to design a control law with consideration to the estimated time-delay. H∞ control theory is one of the powerful methodologies for designing a robust control law against disturbances and parameter variations. In this paper, a H∞ optimal controller considering time-delay is solved explicitly for roll angle dynamics using aileron control surface. “Explicit” means that the time-delay is treated as it is without using approximation in frequency domain. A robust stabilization problem for multiplicative uncertainties is chosen as a formulation and an explicit H∞ optimal controller for this problem is solved analytically. Stability and performance of the controller are examined for parameter variations.
On-orbit attitude and vibration control experiment of flexible spacecraft ETS-VI has been successfully performed. The purpose is to demonstrate the H∞ robust control capability in the precise attitude control technology of the future large spacecraft or Large Space Structures. This paper reports the experimental results. The modeling method and the controller synthesis procedures employed are detailed and discussed.
This paper describes an architecture of “precise space telerobotics” and its key technologies for performing high-precision extravehicular tasks in-orbit. First, a dual-loop structure consisting of dexterous task execution and remote environment recognition is proposed for the precise space telerobotic architecture. Secondly a semidexterous end effector providing remote skill is presented. A three-finger hand with a four-DOF compliance mechanism and a fingertip fitting mechanism is devised for remote skill without increasing the load of an onboard computer. Moreover, telesensing techniques using multisensors installed in the hand are described for measuring uncertain remote environments in orbit. The concept of a virtual hypercamera generated using telemetry data from the multisensors is also proposed, and its usefulness to space applications is suggested. Finally, the development of a precise space telerobotic system utilizing the above technologies is presented, and the high-precision capability is demonstrated.