Blog: Electric cylinders

A large majority of the electric cylinder actuators have a screw/nut type mechanism to convert the linear motion into rotary motion. The screw is driven directly by an electric motor or via a gearbox, the nut is connected to a guided rod. Since the nut is guided and cannot rotate, the rod is moving back and forth when the motor rotates the screw. Most of the industrial type actuators feature this design.   There are also designs where the nut is rotating and the screw is moving in the linear direction. This design is more common in small actuators with hollow rotors, frequently used in high volume consumer products such as actuators for automobile power seat adjustment. The rod is usually guided in bushings, which gives the rod some side load capacity, but generally, the rod type actuators are not designed for side loads. They are made to generate a certain linear force (thrust), move with a certain speed and a limited travel distance (stroke). The positioning accuracy, repeatability, backlash, the control performance depends on the selected components. A   preloaded zero backlash ball screw with a backlash-free coupling and gearbox, combined with a servo motor with high-resolution feedback and a motion controller can perform a speedy, high accuracy motion suitable for precision motion and positioning in a machine tool system. On the other hand, a rugged properly sized acme screw, driven by a simple motor via a high reduction ratio industrial gearbox can develop tons of thrust, move large loads, open/close gates, etc.  It is obvious that with the right selection and combination of commercially available power transmission and motion control components and subsystems a suitable cost effective linear electric actuator can be created. It is generally the OEM's choice whether he wants to design an actuator for his application on his own,  or select one from the available pre-engineered optimized modular designs from specialized actuator manufacturers. In most cases it is possible for the user to find a suitable unit from actuator vendors for a much lower overall expense than design and manufacturing his own special unit. There are actuators on the market based on a modular principle, allowing virtually unlimited combinations and a quasi-custom design carried out within weeks instead of months.