Understanding Linear Actuator Technology

Pneumatic and hydraulic actuators create linear force through controlled fluid/air pressure. Screw driven actuators use mechanical leverage to create a linear force. Screw actuators are driven by an electric motor to rotate a screw. The linear force is created by connecting a nut to the screw and translating the rotary motion of the motor and screw into a linear motion as the nut moves back and forth along the fixed screw.

Screw actuators are excellent for load carrying applications that require high levels of position and speed control; such as machine tools, packaging machinery, converting machinery, and many factory automation and hydraulic applications. Screw actuators are available from extremely small to quite large to handle a wide range of loads. Screw actuators perform comparably to hydraulics at high loads but cannot achieve the highest forces of hydraulics. Their modular design minimizes installation time since no air compressors, pumps, hoses, tubing, or valves are required. The minimal maintenance, since it is limited to the actuator itself, just requires occasional lubrication and inspection for wear and tear. The electric motors used to drive the screws, along with the efficient translation of rotary torque into linear force, provide an overall efficient system.

Belt actuators, like screw actuators, are driven using an electric motor. A belt actuator, however, incorporates a belt and pully system instead of a screw. The linear force is created by connecting the belt and pully system to the rotary motion of the motor. The belt then translates to a linear motion as the belt rotates back and forth around the pulleys.

Belt actuators are excellent choices for high-speed indexing applications that require position and speed control, such as multi-axis cartesian and long span gantry systems, but are not recommended for pressing applications. Belt actuators can operate at very high speeds and offer very quick accelerations. The electric motors used to drive the belts, along with the efficient translation of rotary torque into linear force, provides an overall efficient system. While certain types of belts tend to stretch over time, material improvements and new belt technologies have mitigated this issue. Many belt actuators are supplied with pretensioned belts. With proper maintenance, belt actuators can operate over a long-life span.

Linear motor actuators are direct drive solutions that contain no mechanical transmission elements. The load is connected directly to the carriage assembly and is moved by the linear motor itself. Linear motors are available in a variety of types, including iron core platen style, ironless T- or U-channel style, or tubular style. Linear actuators are typically based on a BLDC servo motor and utilize linear encoders for position and commutation control.

Depending on the application requirements, the more compact and efficient linear motors are potential alternatives for belt or screw driven actuators and pneumatic or hydraulics systems. They are particularly excellent choices for multi axis cartesian or gantry systems where fast move and settle times and precision is important. Linear motors are capable of very high speeds and quick accelerations and are typically only limited by the available current and capabilities of the linear rails to which they are mounted. Linear motor systems are inherently compact, as many transmission elements are eliminated, and can be constructed with very low profiles for space saving requirements. With reduced energy consumption, efficient linear motors, and the elimination of hydraulic fluids, linear motor actuators are an environmentally friendly approach.

Telescoping actuators are similar to the rod style actuator but are designed to expand to two to three times their collapsed length through imbedded segments within the actuator body. These actuators are typically used in vertical lifting applications to extend or retract a load. They can be screw or belt driven with servo or stepper motors. Pneumatic and hydraulic systems are also a possibility with telescoping actuators.

Typical applications are to raise and lower various loads or to insert or retract parts into another machine process. Depending on the actuation technology, the telescoping actuator can handle mid-load ratings and may use screw or belt actuators to provide rugged designs and extended life. The telescoping actuator is not ideal for horizontal applications due to potential moment load deflection when fully extended.