Servo-hydraulic actuator

Aeroelastic and vibration control technology allows flight vehicles to operate beyond the traditional flutter boundaries, improves ride qualities, and minimizes vibration fatigue damage. Conventional active flutter and vibration control technology relies on the use of aerodynamic control surfaces operated by servo-hydraulic actuators. In this conventional configuration, the... 

The pseudodynamic test is carried out on a reaction-wall-based system using servo-hydraulic actuators under displacement control. The test structure under study is modeled as... 

FIGURE 26.7 The EndoLab knee simulator. This four-station machine is servo-hydraulically actuated for full force-control testing with soft tissue simulation. One of the test stations can be optionally used as a loaded soak control station. 

The interface with the process at the other end of the control loop is made by the final control element. In a vast majority of chemical engineering processes the final control element is an automatic control valve that throttles the flow of a manipulated variable. In mechanical engineering systems the final control element is a hydraulic actuator or an electric servo motor. 

Lateral loads were applied to the specimen with three servo-cmitrolled hydraulic actuators, mounted on the laboratory rigid wall at each stoiy level (Fig. 10.3c). The actuators directly pushed the test frame at each story level and pulled it with rods tied to both ends of the frame. 

Conventional test equipment like servo-hydraulics or servo-electrics are limited to driving frequencies of typically 50 Hz with respect to working with arbitrary drive signals. Thus, one approach to extending the frequency range can be to combine low and high frequency actuator devices within one test facility whereas the high frequency actuation could be done by piezoceramic interface structures similar to those described before. 

An active tendon system has been examined by using a six-story steel structure [187]. Figure 8.57 shows that a control force is transmitted to the structure through diagonal braces connected to the first floor by servo-controlled hydraulic actuators. The 600 ton symmetric building, as shown, has been erected in Tokyo, Japan. In fact, two control systems has been tested on the structure (a biaxial active tendon system and a biaxial active mass damper system). 

Many people have the motor control necessary to operate a motor vehicle, but they do not have the strength required to operate manual hand-controls. Automatic or Fly-By-Wire hand-controls use external actuators (e.g., air motors, servo mechanisms, hydraulic motors) to reduce the force required to operate various vehicle primary controls. Power steering, power brakes, six-way power seats, and power adjustable steering columns can be purchased as factory options on many vehicles. 

A variety of devices are used to implement the power stage, depending on the actuator used to move the servo system. These range from small DC motors to larger AC motors and even more powerful hydraulic systems. This section will briefly discuss the power stage options for the smaller, electric driven servo systems. 

These systems behave similarly to passive ones but, instead of inert devices, there are highly powered mechanisms (actuators) that are able to push the structure to counteract the input effect. Hydraulic cylinders driven by servo-valves are examples of actuators. An active control system is composed of a set of sensors to measure on-line the response of the structure (mostly displacements and accelerations), the actuators, a source or reservoir of eneigy to power the actuators and a controller (typically a computer) that decides the amounts of forces to be exerted by the actuators. 

It is for these reasons that - already many years ago - the controls were installed underground (Fig. 180), that the hand-levers were arranged closely to each other and that these were connected to the control shafts via a mechanical or hydraulic linkage. This development and the demand for automation of the working operations soon led to electric remote drives (Fig. 181) being actuated by pushbuttons or small control levers from a central desk. These drives operate directly or via a servo-motor, as already described, the control shaft. 

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