1. Field of the Invention
The invention relates to a duplicate type servo actuator apparatus which causes an operation unit to be displaced on the basis of an input signal, and also to an aircraft control apparatus which uses such a duplicate type servo actuator apparatus.
2. Description of the Related Art
In an aircraft such as a helicopter, a servo actuation system of a hydraulic, electric or electrohydraulic type is used in a control system, a stability augmentation system (SAS), and an automatic flight control system (AFCS).
Such a servo actuation system is provided with various countermeasures against hardover. In a system of the mechanical hydraulic type, duplicate spools of a hydraulic control valve and the like are used to realize multiplication of the mechanical and hydraulic systems. In a system of the electric or electrohydraulic type are employed the following countermeasures: 1) the maximum operation amount is restricted so as to exist within such a range that the flight safety is not critically affected even when a hardover occurs; and 2) the system is multiplied to be redundantly managed so that the probability of occurrence of hardover is suppressed to an allowable value or less.
As the performance and function of aircraft such as a helicopter are made higher, mechatronics systems are more frequently used. Therefore, it has been studied that a system is highly multiplied to expand an operable range while the maximum operation amount is not limited too much. In particular, triple or quadruple multiplication of a Fly-By-Wire control system, SAS, AFCS or the like realizes the following: a) the probability of function loss (including hardover) suppressed to 10.sup.-9 times/hour in commercial planes or 10.sup.-7 times/hour in military planes; b) specification of the probability of function loss (including hardover) corresponding to the failure influence request level (e.g., 10.sup.-5 times/hour); and c) a failure influence suppression (fail passive, fail soft, fail safe) and separation from a failure system.
As higher redundancy is made by multiplication of a system, higher the flight safety is improved. However, such multiplication causes the system to be complicated and increased in size, and cost.