Actuators

An actuator is a functional element which connects the information processing part of an electronic control system with a technical or nontechnical, e.g. biological, process. Actuators can be used to control the flow of energy, mass or volume. The output quantity of an actuator is energy or power, often in the form of a mechanical working potential “force times displacement” ¹. The actuator control is always achieved using very low electrical power, ideally without any power consumption, with currents and voltages which are, if possible, microelectronically (e.g. TTL) compatible.

This chapter deals with power circuits and their use for actuator control. Figure 2.1 shows the general structure of such a power circuit, where one or several power devices are turned on and off by a driving stage. Protection circuits are used to prevent the power devices from failure due to overload conditions.

Electromagnetic actuators transform electrical and mechanical energy into one another using the electromagnetic-mechanical principle. In the following small electric machines, especially motors, are described with a nominal power in the range about up to 1 kW, so-called fractional-horsepower motors [8]. In the simplest case a mechanical switch serves as a controller. For open-loop and closed-loop control of motors more and more electronic components are used, mechanically switched or triggered by hardware or software. In this chapter the combination of motor and electronic control is called an actuator or drive.

In fluidpower actuators, the power of a liquid or gas flow is adjusted by means of suitable devices. These devices are controlled by an electric input signal, and transform the applied power into a specified mechanical variable such as stroke (angle of rotation), speed (rotatory speed), or force (torque) of a longitudinal or rotatory motion. The thermal energy of the pressure medium is not utilized in any of these cases.

Unconventional actuator is a rather pragmatic label for an energy controller/energy converter combinations whose functions are based on other physical effects than described so far. According to this definition one would have to consider a large number of actuator principles, including those which are not really relevant in practice. A selection is therefore made under the following two criteria: The first says that the actuators presented here are based on special properties of new or improved materials, the second says that they must have passed the laboratory stage of development and/or they must be on the verge of a large-scale application in the industry.