External Actuators

Explosion isolation can also be effected by rapid action barrier valves. At present, they can be arranged only in horizontal pipehnes and are suitable, in general, only for streams with a small amount of dust. Such valves are thus frequently used to protect ventilation lines. As a certain explosion overpressure is necessaiy to close such valves, a distinction is made between self-actuated and externally actuated barrier valves (Fig. 26-46). 

FIG. 26-46 Rapid-action barrier valves a) self-actuated (b ) externally actuated. 

Qieck Valve - A check valve is acceptable in a process pressure reheving path, provided that (1) the valve opens in the pressure reheving direction, (2) the valve is of the swing-check or wafer type with no external actuation or dampen mechanism, and (3) the pressure drop is included in the system analysis. 

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. 

The majority of microfluidic methods produce droplet using passive devices generating a uniform, evenly spaced, continuous stream of droplet, whose volume ranges from femtoliters to nanoliters. Their operational modes take advantage of the characteristics of the flow field to deform the interface and promote the natural growth of interfacial instabilities, avoiding in this way the necessity of any local external actuation. Droplet polydispersity, defined as the ratio between the standard deviation of the size distribution and the mean droplet size, can be as small as l%-3%. 

The first microvalve was introduced by Terry [1], in 1979, which was the first magnetic MEMS microvalve. After that, microvalves were improved in several ways. Around the year 2000 a revolution in fabrication of microvalves happened [2—4] which solved the problems of the various MEMS-based microvalves. However, many problems (such as (i) using moving parts that causes additional problems and difficulties, (ii) external actuation means, (iii) complex fabrication and installation processes, (iv) resistible flow and pressure, (v) considerable dead volume, (vi) long respmise time, (vii) leakage, and (viii) stability) remain unsolved when classical electrokinetic theory is used to design a microvalve. 

This chapter has been structured into four sections firstly, the principles governing the centrifugal hydrodynamics on rotational platforms are briefly discussed. Next, externally actuated (active) and rotationally controlled ( passive ) valving schemes are outlined. To form fully integrated centrifugal LoaD platforms that can operate in a sample-to-answer fashion with low-complexity instrumentation, we finally present process automation of networked LUOs through novel, rotationally, and/ or event-triggered flow control schemes as well as common detection techniques. 

In general, active valving permits execution of complex, multistep assays on disc far beyond the capabilities of passive, rotationally controlled valves. This enhanced process control comes at the expense of more complex instmmentation and manufacturing. Additionally, the heat exposure and direct contact of liquid reagents with the valves (in both a solid and melted state) may present a significant limitation of externally actuated active valves for specific applications. 

A micropump or active microvalve is said to use external actuators when the component responsible for opening or closing the valve or moving the fluid is added to the device after fabrication. Examples would be a separate miniature solenoid valve used to pressurize or depressurize air chambers in a pneumatic actuator or piezoelectric patches glued to a micromachined silicon or glass membrane. 

The characteristics of these various safety features enable the reactor to stabilize itself in the event of a transient or LOCA without the need for open- or closed-loop control equipment or external actuation (e g by emergency power or compressed air) Existing active systems required for normal plant operation supplement the passive features provided for accident control... 

Many mechanically tunable microlenses are designed as circular chambers covered by thin flexible membranes. The membrane deforms when pressure is applied to the lens liquid through external actuation. In addihon, some microlenses are formed through air-liquid or liquid-liquid interfaces (immiscible, with different refractive indices). These interfaces may also be varied by applying pressure that adjusts the radii of curvatures of the spherical membranes in air-liquid devices and the focal lengths of the microlenses formed via liquid-liquid interfaces. 

In this article we refer to an actuator as closed when the associated chamber or channel volume is minimized, and as open when that volume is maximized. The volume in the closed position is called the dead volume, and the difference between the volume in the open position and the dead volume is the stroke volume. The stroke volume divided hy the dead volume is the compression ratio. Compression ratio is particularly important when purrping gases, since the amount of gas ejected from the actuator is reduced hy the compressihility of the fluid. In pure liquids this effect is much less, hut compression ratio plays an important role in determining how severely bubbles impact a particular purrp. In classifying micro-pumps, a distinction is sometimes made between integrated actuators - fabricated along with the other components of the microfluidic system - and external actuators - fabricated separately and attached later. It is common to see peristaltic micropumps of either kind. 

This concept takes advantage of measured real-time feedback of AP and IE rotation from sensors on board the knee simulator. Based on those instantaneous AP and IE implant positions/motions, a real-time (or strictly, semi-real-time) computation is made of the influence/contribution of the desired soft tissue springs or any virtual mathematical restraint models. The computed AP force and IE torque contributions are added (vectorially, mathematically) to the electronic command signals for the externally actuated AP and IE torques of the simulator. 

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