For most assembly operations that do not require complex motion systems, up-down movements could be sufficient for some of the simple application systems. Some of the motion systems require belt-driven electric linear actuators that provide high motion speed and long strokes. A linear actuator in a motion system could be used to extend/retract a valve or screw-driving components, move a pallet in and out of a semiautomatic assembly cell, move a robotic component from a processing cell to another, clamp some parts in one place or separate items when the motion system is active. In most assembly operations, linear actuators are used to extend and retract along a simple path.
Simplicity of the motion system does not solve all the problems for engineers as they face options and many other factors when choosing a linear actuator. Some of the options include speed of the system, distance to be travelled, load and accuracy of the system among other factors. An engineer evaluates the possibility of using an electric or pneumatic actuator, ball screw or lead-screws. Frank Langro, director of Festo Corp, which supplies pneumatic and electric actuators, says that one needs to consider the amount of load being moved and the speed at which they should be moved. Other factors include the nature of motion; repetitive or constant and flexibility.
Pneumatic Actuators
Pneumatic actuators are fast, simply built, lightweight and less costly, making them a crucial component of the modern linear motion technology. A small set of pneumatics can produce more end-stroke force compared to the electro-mechanical actuators. Ruberti, a team leader at Pneumatic actuators are preferred to electric actuators when the application moves along two points, producing simple motion. While pneumatic actuators remain a key component of linear motions, modern technology has advanced various components such as seals, drives, valves and control sensors to improve their performance. Maintenance and lubrication which pose problems in linear motion and play a critical efficiency role in pneumatic actuators have been advanced such that a pneumatic actuator could be given a lifetime lubrication thereby minimizing maintenance costs. However, pneumatic actuators have less flexibility and relatively low precision compared to electric actuators.
Electric Actuators
Electric actuators are highly flexible and easily controlled. With electric actuators, one controls velocity and acceleration of the different moving components of the system. This allows optimization for improved efficiency which in turn reduces the amount of energy consumed. When connected with belt drives, electric actuators can move heavy loads at high speeds. However, engineers are faced with several options regarding the use of drives depending on the application. Belt drives move over a long interval at high speed compared to screw drives but cannot handle heavy loads.
Specifications
Detailed information regarding the application should be provided by the engineer to determine the position of the linear actuator, the manner in which it will be mounted, functionality of the actuator, stoppage points, repeatability of the motion, payload size, amount of thrust required and speed of movement required. In addition, engineers have to consider precision levels specified by the client, since modern technology demands high precision levels and speed. The best way to determine the specifications of the actuator is to evaluate various application scenarios to arrive at the most effective linear actuator for the given application.
