Find out how the spindle (also called a ‘lead screw’) pitch is connected to an actuator’s efficiency and self-locking ability, and why an actuator will always provide the same efficiency output, regardless of the load applied. Our expert Hunter Stephenson explains the essentials in this video.
How do spindles influence/impact actuator efficiency?
The efficiency of an actuator is directly related to the motor, the gears, and the spindle, and how these components work together.
Because of the spindle and its shape, an electric actuator will always provide the same output power, regardless of the load applied, whereas a hydraulic or pneumatic system will provide a varied efficiency between push or pull. Even though the pressure in such a system is the same, the inside area through which the oil or air travels will be smaller when running inwards in pull, and the efficiency relatively lower than in push.
Regardless of the load, an electric actuator can run at the same speed both in push and pull.
With the actuator output power available, you can choose to move a high load at a low speed, or the other way around. If you multiply the load with the speed, you will get the output power required for the right movement – this will give you a good indication which actuator model you need. With a LINAK® actuator you can choose between different gears and spindle pitches to get the ideal solution.
There are many different types of spindles and spindle nuts for electric linear actuators, and they are always selected based on the required load and performance of an actuator. For example, for lifting heavier loads, the nut must be longer to better distribute the load between the threads in the nut.
Spindle geometry must be considered to obtain an optimal efficiency output of a spindle. Trapezodial, high profile and low profile are examples of spindle geometry used for LINAK industrial actuators.
What is a spindle pitch?
The spindle pitch is the distance that a nut travels when rotating 360 degrees on a spindle. So, if the spindle pitch is 12 mm, it means that the nut travels 12 mm on one spindle revolution.
The higher the spindle pitch, the more efficient the actuator becomes since there is less friction between the nut and the spindle.
But a high spindle pitch also entails a low self-locking ability. With the self-locking ability, the actuator does not back drive when stopped at its target position, not even if is it exposed to high load or vibrations; unless, of course, it is supposed to move.
Generally, if you have a spindle with a low efficiency, the actuator is self-locking.
If the actuator is not self-locking, a brake is used to keep the actuator in a fixed position.
What is the stroke length?
The stroke length of an actuator refers to the maximum distance the actuator will move or extend. This is the range of linear motion from its fully retracted position to its fully extended position. In essence, it is a measure of how far the actuator's rod or piston can travel in a single motion.
The stroke length of an actuator depends on the length of the spindle. LINAK® actuators are generally very versatile and stroke lengths up to 1.20 meters can be specified according to customer requests. But, when considering actuators with long stroke lengths, there are some limitations. When running long strokes in push, we reduce the maximum load specification. The reason is that the higher the load and the further away from the inner position the nut travels on the spindle, the bigger the strain is on the actuator.
Why add a safety nut in an actuator?
It is possible to add a safety nut in an actuator, for machinery where safety is a high priority. If, for example, the thread inside the nut on the spindle wears off due to wear and tear, the nut will immediately carry the full load and the actuator travels inwards. In this case, the actuator can no longer run outwards, and it must be replaced.
A high-quality spindle is the essence of achieving an optimal actuator performance. The iron bars used for LINAK® spindles are carefully selected before rolling the spindle threads.
Which spindle type and spindle nut to select depend on the load and performance requirements of the actuator. For example, a long spindle nut is better for lifting heavy loads. To obtain a long and reliable service life for actuators with high spindle pitches, more tracks are added to efficiently distribute the forces from the industrial application to the spindle and the nut.
The core diameter of the actuator spindle (not including the tracks) determines the strength of the spindle, thus the actuator.
