SOLUTIONS MOTION CONTROL
By Chad Carlberg and Chris Diak
Eight selection criteria for actuation components Electromechanical systems offer advantages over hydraulic and pneumatic actuators
W
hen deciding between fluid-driven and electromechanical linear actuators, close consideration of long-term benefits to the intended end user can help original equipment manufacturer (OEM) system designers maximize both product value and return on investment (ROI). Fluid-driven actuators translate electric energy motion through a column of air, gas, oil or other media. While the motion they provide is simpler than with other type actuators, the infrastructure required to support them is not. Hydraulic actuators require an external system of pumps and valves; Pneumatic actuators require complex air delivery systems. For both, stroke length is defined by a mechanical hard stop. Electromechanical systems can handle more complex operations with a much simpler design. Figure 1: Packaging lines benefit from the increased controllability of electromechanical actuators as they often eliminate the need for changeover when switching from one product to another. All images courtesy: Thomson Industries Inc.
An electric motor — through a belt gear, a worm gear, a planetary gear or via a direct coupling — rotates a ball screw, which translates the torque into axial force through an extension tube. All key motion components are, or can be, self-contained. Motion is controlled by a programmable electronic signal. System designers should consider the following eight criteria when choosing between fluid-driven and electromechanical actuators.
1. Motion profile control
As business volatility and complexity increase, users of actuator-driven machinery and equipment demand greater control over position, velocity or force throughout the range of motion. Fluid-driven actuators cannot provide this easily. It is difficult for them to achieve the slow, controlled speeds that may be needed in many applications. To some extent, fluid-based actuators can gain control using external systems such as proportional regulators, valves and encoders, but this adds cost and further complexity. Because electromechanical motion is controlled electronically, the device can be programmed to stop at any point along the stroke. Force and motion profiles can be changed in software without having to shut down and reconfigure the machine. The increased controllability of electromechanical actuators often can eliminate the need for changeover when switching from one product to another. In applications such as packaging lines, where numerous package sizes may run in a single shift, this can result in significant savings (see Figure 1). Electromechanical actuators also can be networked, enabling functionality such as synchronization, making it easier for end users to work with unbalanced loads.
2. Impact on cleanliness and safety
In addition to limiting control over the motion profile, fluids make for a grimier, potentially dangerous work environment. For example, hydraulic fluids must be transported and stored. Ever-present leaks www.plantengineering.com
PLANT ENGINEERING
November 2019
•
13
