Actuator is a device which facilitates motion or movement in industrial machines or equipment. This movement be linear or rotational. Actuators which facilitate linear or straight-line motion are called linear actuators. The accurate positioning of actuators and their movement are crucial aspects for the product or work piece to function correctly. The mounting position and the amount of force applied plays an important role as well. There are a variety of actuators, and to select appropriate linear actuators suited for your application there are some key factors you may want to consider. This post discusses the calculation of linear actuator position and their selection process.
Steps to Calculate Moment Load for Accurate Linear Actuator Position
Electric linear actuators find a wide usage across industries. However, designing these can be quite complex. The size of these actuators impacts the size of the machine. Additionally, when the load shifts the position on the actuator, it creates moment load thus multiplying its width and that of the machine. Apart from the load changes, this moment load also occurs owing to gravity. These moment loads can wear out the actuators in the long run. Hence, calculating moment loads on linear actuators is crucial, although it is challenging. Here are the steps for calculating moment loads:
- Integrate linear mechanical components with the motor; this saves on time with regards to installation and adjusting the equipment. Ensure the moment loads are within actuator specifications, and especially so for electric linear actuators.
- Check the environmental conditions in which the actuators would operate. Ensure the size and transportable mass of the linear actuator is in sync with the table height, force applied, and frame size.
- Accordingly check if the positioning and time and distance is according to your application requirements.
- Check the operating speed and ensure the dynamic permissible limit set for the actuator is not exceeded.
- The center point of the table is the support point from where the moment is applied to the load which has a hung center of gravity. So it is calculated by this formula:
Moment applied= load mass * hung distance * gravitational acceleration
- Moment is applied to the actuator in three directions— pitching, yawing, and rolling.
- These directions can change depending upon the installation condition of the load and actuator.
- Moment can be applied to the actuator when the load is transported or when it is stationary. These are called dynamic and static permissible moments respectively.
- Moment is applied to the actuator on X and Y axis both. For X axis, the formula to calculate is:
Pitching direction moment/Dynamic permissible limit in pitching direction + Yawing direction moment/ Dynamic permissible limit in yawing direction + Rolling direction moment/ Dynamic permissible limit in rolling direction
- The formula for calculating the moment load when installing the actuator in vertical direction is:
Pitching direction moment= (load mass*acceleration*load center of gravity overhung in Z axis) + (load mass*acceleration*arm center of gravity overhung in Z axis) + (load mass* gravitational acceleration*load center of gravity overhung in Z axis) + (load mass*gravitational acceleration*arm center of gravity overhung in Z axis)
Useful Factors to Select Appropriate Linear Actuators
Here are some pointers which will help you select the right linear actuator for single or multiple axes positioning systems:
- Consider the overall length of the actuator and the distance between the mounting holes.
- Ensure there is a built-in limit switch, which stops the motor in case the actuator is expanded or retracted totally. It does so by breaking the circuit.
- The mounting position of the actuator is extremely crucial. Leave enough space for the actuator to move, and it should be only connected to the mounting brackets.
- Calculate maximum force applied on the actuator.
- Check the length of the lever arm and the bar. The actuator needs a certain amount of force to negate the torque created by gravity, and this depends on the lever arm and the angle the actuator has with the bar.
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