Designing Motion-Control Systems With Electric Cylinders

Electric cylinders are relatively inexpensive and easy to program. New options are also shortening design cycles. Improvements in dynamic response, force, and environmental parameters let electric cylinders fit applications previously dominated by leak-prone hydraulic and pneumatic linear actuators. Electric cylinders are easy to install, offer longer service life and higher accuracy, and work effectively in a wide variety of sophisticated control systems. Fast, powerful, and reliable electric cylinders consist of electric motors, belts, and leadscrews that are matched for optimum performance. Electric cylinders come in a variety of load and speed ratings, lengths, motor types, and load attachments. Their modular design lets them fit a wide range of machines. Internal construction of a belt-drive electric cylinder Electric cylinders are often used in simple bang-bang motion control systems where limit switches placed at each end of travel comprise the simplest type of control. Analog control systems employ a feedback sensor to determine the actual position of the load. This more accurate, absolute closed-loop positioning system easily interfaces with a variety of sensors, PLCs, and PCs. Speed-thrust curves help select a best-fit electric cylinder. Motion-control systems that require linear movement can be built around a variety of different actuators. The most common types fall into linear actuators, linear motors, and precision positioning tables. Linear actuators, generally the lowest cost approach, can be hydraulic, pneumatic, or electromechanical. Each comes with advantages and drawbacks, so their use depends on the specific application. Hydraulic cylinders, for example, can handle high loads and generate forces up to several tons. But they're not so good at accurate load positioning. This task requires relatively expensive position sensors and electrohydraulic servovalve controls. Hydraulic systems also tend to leak which contaminates the work area. By comparison, pneumatic cylinders are primarily used when light loads must be repeatedly moved between fixed positions. Pneumatics have high-speed capabilities, reaching speeds to 200 in./sec. Because of these qualities, they