vibrates and bows as it turns . Over time this can negatively impact the performance of the actuator , leading to premature wear and shortening its lifespan .
Whilst there isn ’ t a universal cut off point at which a ball screw linear actuator is no longer an option – it ’ s very much dependent on a range of factors including the dimensions and material of the screw and the actuators ’ use and environment – if you want to achieve higher speeds , up to 3m / s , then a belt actuator should be considered . Belt actuators perform better at higher velocities and also in applications that require a long stroke . Which brings us to our next key factor .
Key Factor 2 : Stroke Length Stroke length refers to the distance the linear rail actuator is required to move a load in one direction .
Linear ball screw actuators are usually designed at around 1000mm stroke length , although smaller and larger lengths can be accommodated by , for example , using different diameter balls . However , we would never recommend a ball screw actuator for stroke lengths over 54000mm . For longer stroke lengths , belt driven actuators are a better option . At Matara , we are able to manufacture linear actuators from 100mm to 6700mm stroke lengths .
One of the most important considerations when looking at stroke length , and one that all too frequently gets overlooked , is the safety stroke . The safety stroke is an allowance that provides room for the actuator to coast to a stop if an emergency stop of the system is necessary . This prevents the bearing table ( and the load ) from hitting the ends of the actuator , which can cause damage . Even if emergency stops are rare in your particular process , it ’ s still good practice to factor in a
safety stroke as linear actuators aren ’ t designed to constantly be run into a hard stop as this can cause wear and tear to the inner workings of the actuator over time .
To calculate the safety stroke , for belt driven actuators specify a distance equal to two turns of the motor on each end of the actuator ( or four turns in total ). For ball screw actuators , base it on twice the pitch of the ball screw . Other factors may have to be taken into consideration , but this calculation is a good starting point .
Key Factor 3 : Load Stroke length impacts on speed and vice versa , but load has a direct effect on both .
Anyone involved in an engineering capacity will appreciate the importance of load capacity on a structure and linear motion systems are no different in this respect . Miscalculate the load and at best there will be a loss of precision , but at worst you may be looking at catastrophic failure with damage to the actuator assembly and the product , and a potential serious health and safety risk .
Where linear motion systems differ from many other load capacity calculations is the need to base it on the dynamic load capacity . Unlike the static load , which is the load on the actuator when it is in a fixed position , a dynamic load is that which the actuator handles when in operation and in motion . In other words , how much work can the machine actually do ; how much can be pushed or pulled .
You need to base the calculation on both the radial and axial load capacity , as well as the moment capacity of the support carriage . Position of the load in terms of its size ( including any overhang ) as well as the orientation in which the load is being moved should also be considered .
Ball screw driven actuators can generally move higher loads and are widely used on applications that require movement on a vertical axis , such as gantry robots . A belt actuator should mostly be avoided for vertical axis movement as it is at risk of the belt snapping due to tension .
However , belt driven actuators can be ‘ beefed up ’ to achieve higher dynamic load ratings by using linear rail and carriages as external guides . Linear rails have two parallel tracks that contain rollers to support a moving load , providing guidance and support for a load carried by an actuator between two points . Linear rails are used in a whole range of applications and can carry loads that vary from extremely light electronic components , through to large loads weighing thousands of kilograms in heavy industry .
Ultimately , the choice of linear actuator will be impacted by all three factors and which factor takes priority for the machine being designed and the process for which it is intended . There will also be other factors to consider , including the direction in which your actuator is mounted , accuracy and repeatability , maintenance requirements and the operational environment . But without getting the big three right - speed , stroke length , load capacity – none of the others will matter !
Matara designs and manufactures a range of pneumatic and linear automation products , including linear rail actuators . Products are available from stock or can be custom built to order .
https :// www . matara . com / products / actuator-systems / linear-actuators / sales @ matarauk . co . uk 01684 850000 .
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