Linear actuators are machine tool elements that are used in many sophisticated machine tools. The actuator is designed to transfer lines to provide a linear motion to the slides. Power and motion are obtained from a motor-driven ball screw or an acme screw assembly. Some linear actuators have rods while others are rod less. Depending on the application, linear actuators can be designed to operate in tight tolerances. The load being moved is attached to the end of the screw or rod and it is unsupported. The screw can be either direct, belt or gear driven.
When looking for a linear actuator, drive screw specifications that you should consider include drive screw type and screw lead. Features include self-locking, limit switches, motor encoder feedback, and linear position feedback. You can either use acme screws or ball screws. Acme screws can generally hold loads without power but they are usually less efficient than the ball screws. In addition, acme screws also usually have a shorter life span, but they are more robust to shock loads. If backlash is a concern for you then it is probably better to use a ball screw as they have lower friction and therefore higher efficiency than lead screws. The screw lead refers to the distance the rod advances with one full turn of the screw.
When looking for a linear actuator the dimensions you should consider include retracted length, width, height, and weight. The unit’s housing can have flanges, rear clevis, side angle brackets, side lugs, tapped holes, trunnion, and spherical bearings. The rod ends can be clevis, female eye, female thread, male thread, and spherical bearing.
While selecting the linear actuator, there are several other important features that you should take into consideration.
- The total weight or load that it can move
- Holding brakes
- The stroke (the maximum length between completely retracted and extended positions)
- The maximum speed of travel and the backlash error that occurs when the direction of travel is reversed.
Motors for linear actuators can be DC, DC Servo, brushless, AC, AC Servo, stepper etc. Input power can be specified for AC, DC and stepper motors. Other industrial devices such as hydraulic or pneumatic cylinders can also be used to produce the motion and power a linear actuator. Holding brakes can be used to hold the actuator in position while machining or other types of processes are being performed.
Other devices that should be used with a linear actuator include: torque limiters; overload slip clutches, thermal overload protection, protective boost and cushions at the ends to absorb the impact, etc. Water and fluid resistant actuators are also available.