Positional servomechanism

In position control the position of the prosthetic joint is proportional to the input amount/intensity. The input amount/intensity might be the position of another physiological joint or a force level. If the position of another joint is used as the input then the system is known as a position actuated, position servomechanism. If the amount of force applied by some body part is the input, then the system is a force actuated, position servomechanism. An example is die power steering of a car. Here, the position of the steering wheel is related directly (proportional) to the position of the front wheels. Such a system is an example of a position follower (the position of the wheels follows the position of the steering wheel) or a position servomechanism. 

If a further constraint is added whereby the input and output are physically (mechanically) linked such that change in position of the output cannot occur without a change in position of the input and vice versa, then as is the case in the power steering example, the system becomes what Simpson (1974) called an unbeatable position servomechanism or a system that has inherent extended physiological proprioception (EPP). Unbeatable servomechanisms are a subset of position servomechanisms as a whole where the input and output must move together. One cannot beat the other. 

World-scale, single-train units, coupled with advances in automation, led to the use of servomechanisms for valve plug positioning. 

Throttling of the suction of centrifugal and axial compressors wastes less power than throttling the discharge. Even less power is wasted by adjustment of built-in inlet guide vanes with a servomechanism which is a feedback control system in which the controlled variable is mechanical position. Speed control is a particularly effective control mode, applicable to large units that can utilize turbine or internal combustion drives control is by throttling of the supply of motive fluids, steam or fuel. 

Figure 3.24. Control of positive displacement compressors, rotary and reciprocating, (a) Flow control with variable speed drives, (b) Pressure control with bypass to the suction of the compressor, (c) Reciprocating compressor. SC is a servomechanism that opens some of suction valves during discharge, thus permitting stepwise internal bypass. The clearance unloader is controllable similarly. These built-in devices may be supplemented with external bypass to smooth out pressure fluctuations.

The servomechanism incorporates a radioactive isotope feedback transducer system for detecting the position of the burning surface. 

At present, there is no standard definition of a servomechanism. Some engineers prefer to classify any system with a feedback loop as a servomechanism. According to this interpretation, an electronic amplifier with negative feedback is a servo. More frequently, however, the term servomechanism is reserved for a feedback control system containing a mechanical quantity. Thus, the IRE defines a servomechanism as "a feedback control system in which one or more of the system signals represents mechanical motion . Some would restrict the definition further by applying the term only to a special class of feedback control system in which the output is a mechanical position... 

Servomechanisms are an important part of nearly every pieee of modem mechanized Army equipment. They are used to automatically position gun mounts, missile launchers, and radar antennas. They aid in the control of the flight paths of jet-propelled rockets and ballistic... 

There are five basic types of synchros which are designated according to their function. The basic types are transmitters, differential transmitters, receivers, differential receivers, and control transformers. Figure 1 illustrates schematic diagrams used to show external connections and the relative positions of synchro windings. If the power required to operate a device is higher than the power available from a synchro, power amplification is required. Servomechanism is a term which refers to a variety of power-amplifiers. These devices are incorporated into synchro systems for automatic control rod positioning in some reactor facilities. 

Where there are large pressure drops across the valve, double-seated valves are used to balance the pressures on the plug and ensure easy operation. To avoid erratic control action due to valve sticking the controller output may be applied to a valve positioner, which is a servomechanism (position controller) designed to fix the valve position as required by the controller. 

One limitation on using control theory in process control problems has been a lack of data on process characteristics, but now an increasing volume of effort is being applied to the dynamic characterization of processes. The fact that many typical processes of importance in chemical engineering are much harder to describe dynamically than the simple positioning operations in servomechanisms, may have been a deterrent to any earlier development of this area. Up to now most process characterization has focused on heat transfer processes, but every other type of process or operation has been studied to at least some extent. A number of process companies, particularly certain petroleum companies, have conducted extensive frequency response studies of their process units. Also a few process companies have undertaken dynamic studies of various kinds of instruments. 

Finally, we mention the respiratory control studies of Priban and co-workers (50, 51, 52, 53). In the models presented above, respiratory control is represented as a position control servomechanism, and as such the control variables are maintained near certain reference values (or set... 

The stepper motor is another example of a servomechanism. Given a specific voltz e input, the stepper motor turns to an angular position that exactly corresponds to that voltage. Stepper motors are essential components of disk drives in computers, moving the read and write heads to precise data locations on the disk surfece. 

Two of the most important applications of servomechanisms in industrial operations are control of position and control of rotational speed. Both commonly employ digital measurement. Positional... 

Servomechanisms. Automated processes controlled by digital logic require other devices by which the function of the machine can be measured. Typically, a measurement of some output property is automatically fed back into the controlling system and used to adjust functions so that desired output parameters are maintained. The adjustment is carried out through the action of a servomechanism, a mechanical device that performs a specific action in the operation of the machine. Positions and rotational speeds are the principal properties used to gauge machine function. 

In addition to tracking and seeking, the laser spot in an optical drive must be kept in perfect focus on the disk regardless of the motion of the disk (there can be quite a lot of vertical motion if the disk has tilt or is slightly warped). To do this, the objective lens must be constantly adjusted to correct for the axial motion of the disk surface as the media spins. The lens position is controlled by a focus servomechanism. 

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