3 Actuators
3.1 Hydraulic Actuators

Hydraulic actuators are suited especially for high-force applications. Produced force is 25 times greater than pneumatic cylinders of equal size. Also have high horsepower-to-weight ratio by 1 to 2 hp/lb greater than a pneumatic motor. What is also important is that can hold force and torque constant without the pump supplying more fluid or pressure due to the incompressibility of fluids. These type of actuators can have their press sources (pumps and motors) located a considerable distance away with minimal loss of power. But exists some disadvantages too like leaking fluid. Like pneumatic actuators, loss of fluid leads to less efficiency. Requires many companion parts, including a fluid reservoir, motors, pumps, release valves, and heat exchangers, along with noise-reduction equipment.

Frequency Converters

Used for smooth control of asynchronous motors with squirrel cage - means rotation speed, torque, starting and after running. Control is implementing by changed power supply frequency combined with control voltage per semiconductor frequency converter – it´s compound from indirect voltage frequency converter (rectifier, DC link, transistor inverter). DC link is mostly noncontrolled - diode. In DC link is filtration condenser for current filtering rectified voltage and suppressor for suppressing current shocks when uncharged condenser is connected and for improving network current – restriction harmonic and improve efficiency. From DC link is powered transistor inverter, which by pulse-width modulation shaped sinus output tension and control its effective value. Control of rotation speed is made by frequency changing optimally according to voltage motor. Frequency range is from 0 to nominal frequency supply network or to the higher frequencies. Frequency changes have program adjustable curve incl. current limits what can be used for control starting and after-running motor. With use frequency converter can be realized braking in modes: braking DC, resistor braking, regenerative braking.

Softstarters

Is also equipment for smooth starting asynchronous motors – starting with limits with restriction current and moment shocks, what is achieved by control voltage at motor clamps with unchanged network frequency by semiconductor changer of AC. They are used for motors with power from kilowatts to megawatts. Softstarters are able for one phase motors too. Softstarter for three phases motor is compound from three twins tyristors phase controlled and connected in antiparallel for power input. For Y-connected motors we can connect softstarters in triangle, so that softstarted will control only current in winding and in comparison for control phase current can be less dimensioned for current – it is used in particular for bigger powers. It is possible to use so-called bypass which provides after start by clamper overbridge connection and softstarter can be used for starting other motors. Softstarter has no possibility to control rotation speed of motor what is compensated by design control and power function and lower price. It is used especially for starting fans, pumps, compressors and there where is big inertial mass starting e.g. in conveyors, centrifuges etc. Softstarter is not suitable for drive with big starting torque.