Actuators named instruments which are operated directly by supervisory systems outgoings. Follow we’ll try to describe small set of used actuators but we’ll try to cover main ones.
One of the most used kind in automation (we have in mind mostly controlled) are electrical motors – drives. We can divide them into linear and rotating. Characteristic for these equipment today is possibility of higher type communication, e.g. by analog output, by serial link (RS-232C, RS-485), which can be used for control rotation speed, position etc.
These motors consist of stator (fixed part) with main poles with excitation coil and helping coil, placed between main poles for improving commutating properties. Moving part - rotor rotating in magnetic field, which consists of metal plates.
Biggest current flows into rotor coils in quiet = motor make big starting torque. On the other hand, in speedy rotating rotor there is inducting tension reductive current flowing into rotor coils and torque with increasing revolutions is lowering. Motor with these torque speed-torque characteristic easily overcomes varying load.
Main characteristic of these motors is equality of rotor speed with magnetical stator field. Alternate current in stator winding (1 or 3 phases) generates stator rotating magnetic field. Rotor can be made from permanent magnet with alternative designed poles around circumstance or has winding powered from DC power source (excitor) and making electromagnet. Excited synchronous motor after direct connection to AC link isn’t rotating by itself. Three-phase AC in stator makes rotating magnetic field which is rotating by rotating speed given by frequency of power source and number of poles in motor. Rotor, which is stopped, is powered by direct current and it excites stationary magnetic field. There is an action of force stator and rotor field by interaction these two fields. Direction of this force is changed with stator rotation speed.
Stepper motors with respect to growth of digital control systems and working with digital information it’s enlarging of usage so-called stepper motors, where steering angle of shaft is given by number of impulses on control winding. Characteristic is discontinuous shaft movement done by angle jumps = steps, which are done by response to one control impulse.
Principle of function is based on mutual electromagnetic influence of rotated magnetic field of rotors and stators and currents generated in rotors winding by this magnetic field.
Asynchronous motor is based on induction tensions and currents in rotor and this is the reason, why we call it also inductive motor. Rotated magnetic field is in asynchronous motor generated in stator (stable non-rotated part) winding, which is made as three-phase, where winding is turned 120° in space.
Awe recognize: Single-phase asynchronous motors, Two-phase asynchronous motors, Three-phase asynchronous motors
These types are used mostly.
By design are pneumatic drives dividing into piston and membrane types. Membrane drives are mostly used for linear control in valve technique. Rotating types are designed for control regulation rotation armatures or clack valves.
Control force of pneumatic drives is between 0.5 kN and 90 kN. These drives are only single acting function, which means that pressure of control medium forcing contra spring. Described design is able to apply these action elements as emergency drives too, because in case of losing press of control media it’s able to shift closing part by function to set position. According to springs design in driver hat function for pneumatic drives is: