Transmission (Converting) Type Electric Linear Actuators.
The majority of the electric linear actuators used in today’s industry are of the transmission (converting) type. The rotational motion of an electric motor is converted into linear. The fact that the primary motion is rotary and has to be converted into linear seems, at first glance appears as a disadvantage. Electric motors are generally designed for high power density by having high speeds and low or moderate torques. Their “torque density is fairly low. The torque and rotational speed can be easily “conditioned” to the appropriate level by using suitable gearboxes (torque boosting speed reducing mechanical devices). The conditioned torque and speed is then converted to the desired speed and force linear motion. For conversion of the rotational motion into linear motion the following mechanical devices are the most suitable:
• Screw and Nut mechanism (acme-, ball-, roller-screw)
• Rack and Pinion mechanism
• Belt and Pulley, Chain and Sprocket, Rope and Wheel etc. type mechanisms
There are two basic electric linear actuator designs widely used, namely the “ROD-TYPE” electric linear actuator and the “ROD-LESS” design. The rod-type have a rod which performs the linear motion, in the rodless actuators a carriage or slide moves back and forth within a supporting structure.