The electric linear actuator is controlled by the relay which at the same times controls the direction of the movement of the linear actuator. The role of the linear actuator is simple to provide the necessary mechanical linear movement, however, the relay’s role is of a switch. And there are more than just one reason to use relays instead of the mechanical switches.
For the control of the linear actuators are also used switches but they are less popular than relays because of their comparatively large scales, and the need to be manually turned on and off. That is why relays which can be turned on and off by the application of a low voltage across the relay terminals are more convenient to be used in most cases.
First of all, what is actuator? It is a mechanical device which is made of two distinct modules, one of which is the signal amplifier and the second one is the transducer. The amplifier functions as the converter of the low power control signal into the high one. The transducer in its turn transforms this amplified signal into the needed form of energy and to a necessary scale.
According to the number of stable states, there are two types of actuators: Binary and Continuous. Due to two stable states, the relay actuators are classified as the binary devices. They can be or energized or de-energized, which influences their position – latched or unlatched respectively.
Relays use the input source energy which via the magnet pulls the switch allowing the higher current to flow from the other side of the relay. These automation devices are used in the automatic control applications and they function by means of controlling the actuator with the help of electric signals. Specifically for the linear actuators are used relays with the high current capacity, which are also called the contractors. And there are two types of such contractors due to their mode of operation: normally open and normally closed relays. The contacts in normally open relays are only connected when the actuation terminals and on contrary are energized as in normally closed relays when the actuation terminals contacts are not connected.
There are also different relays according to the number of their poles and throws:
- SPST: Single Pole – Single Throw
- DPST: Double Pole – Single Throw
- SPDT: Single Pole – Double Throw
- DPDT: Double Pole – Double Throw
Another example of implementation the relay technology for the construction of the electric linear actuators is the usage of electromechanical relays and the solid state relays, although, the second one was chosen to be used a bit later than the first one due to several drawbacks electromechanical relays have.
Electromechanical relays have three contact terminals most widely known among electromechanical devices as COM – Common, NC – Normally Closed, NO – Normally Opened. To control the electric circuit electromechanical relays close and open the above-mentioned types of contacts. In addition, electromechanical relays are capable to work on both Alternative Current (AC), and Direct Current (DC) as despite several construction peculiarities both work thanks to the principle of the electromagnetic induction. Most of these electromechanical relays can only be or of the attracted type or the induction type. The first, use the electromagnetism to work, the second one can only work with AC sources of energy.
The use of the electric relays for the construction of electric linear actuators simplified this technology and enabled engineers to improve it. This made a significant push forward towards the modern machine-building industry and provided more creative control options and allows to use actuators in the wider range of the engineering spheres.