Disadvantages of Each
Pneumatics are subject to encountering pressure loss and air compressibility, which can make this actuator less efficient in comparison to others. These limitations may translate into lower forces and slower speeds during operation at a lower pressure. In order to work to its full potential, pneumatics must be sized specifically for its application so it may not be available as an easy “drop-in” system. In order to perform under accurate and efficient control, it requires proportional regulators and valves, which can raise the cost and complexity of a pneumatic actuator significantly. Additionally, the air has the potential to be contaminated by oils and other lubricants, which can lead to downtime and maintenance issues. Many companies still purchase compressed air in order to avoid this particular issue, but the compressor and lines provide other maintenance issues.
Hydraulics can leak hazardous fluids, leading to inefficiency and other contamination issues and potentially damaging other parts of the overall application. However, the largest disadvantage to using hydraulic actuators is the incredible amount of operator support needed to maintain, monitor, program, and use these mechanisms. Mid-stroke positioning requires additional components as well as a decision from the operator about where the positioning is acceptable; speed settings for the application require the operator to set the exact speed; and the operator must dial in on the desired force. In addition, it is often times difficult to achieve correct settings the first time.
Once everything is set up with the hydraulic actuator, the operator must still monitor for maintenance concerns, temperature changes (in fear of overheating or not reaching key performance due to the cold changing the consistency of the oil), and leakage. Also, many hydraulics require additional parts in order to perform various necessary tasks. These can include motors, pumps, release valves, heat exchangers, noise-reduction equipment, fluid reservoirs, and data collection sensors and servo systems. In addition, hydraulic actuators generally only perform in the 40% to 55% efficiency range, and are noisy.
There are still applications in which electric linear actuators cannot compete due to the required load ratings, force, or speed. There are some environments in which electric actuation is not suitable, and will have a velocity maximum that cannot be exceeded. Although it is not common, electric actuators can overheat if there are extreme changes in duty cycle or if they are being used outside of the warranty.
Shock loads on an electromechanical actuator can affect its lead screw or bearing, possibly affecting the entire system's performance. Some electric actuators have difficulty holding a locked position or have issues with backlash, usually dependent on the screw pitch. And the initial cost of an electric motion system may be higher than other actuator options. However, the increased efficiency of the total operation coupled with the little to no maintenance required over its life span can make the total cost lower in comparison with other types of actuators.
Each of these actuators exhibit both good and bad characteristics that one must weigh when determining the right component for their application. By determining what characteristics are non-negotiable from the start, you will begin to rule out certain actuators based off of these needs. If it comes down to two specific actuators that are both able to efficiently do the job, you may want to consider the entire cost of the system. This cost includes the initial investment, maintenance and repair fees, as well as the cost of potential risks you could take with each motion component system.
This article was written by Samantha Rosenfeld, Senior Marketing Associate for TiMOTION, Charlotte, NC. For more information, Click Here .