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Linear Actuators: what they are and how to decide on them
A linear actuator is a self-supporting structural system capable of remodeling a circular motion generated by a motor into a linear motion along an axis. Helping to produce movements such as the pushing, pulling, raising, decreasing or inclination of a load.
The most typical use of actuators includes combining them with multi-axis Cartesian robot systems or using them as integral components of machines.
The principle sectors:
industrial automation
servos and pick-and-place systems in production processes
meeting
packaging and palletisation
Indeed, just think of applications comparable to airplane, laser or plasma chopping machines, the loading and unloading of machined items, feeding machining centres in a production line, or moving an industrial anthropomorphic robot along an additional exterior axis with the intention to develop its range of action.
All of these applications use one or more linear actuators. In accordance with the type of application and the efficiency that it must assure by way of precision, load capacity and speed, there are various types of actuators to select from, and it is typically the type of motion transmission that makes the difference.
There are three fundamental types of motion transmission:
belt
rack and pinion
screw
How can you ensure that you choose the best actuator? What variables does an industrial designer tackling a new application have to take into consideration?
As is often the case when talking about linear motion solutions, the important thing is to consider the issue from the proper viewpoint – namely the application and, above all, the results and performance you might be expecting. As such, it is worth starting by considering the dynamics, stroke size and precision required.
Let’s look at these in detail.
High Dynamics
In lots of areas of business design, reminiscent of packaging, for instance, the demands made of the designer very often should do with pace and reducing cycle times.
It is no surprise, then, that high dynamics are commonly the starting level when defining a solution.
Belt drives are often the perfect solution when it comes to high dynamics, considering that:
they allow for accelerations of up to 50 m/s2 and speeds of as much as 5 m/s on strokes of as long as 10-12m
an X-Y-Z portal with belt-pushed axes is typically capable of handling loads ranging from extremely small to approximately 200kg
in accordance with the type of lubrication, these systems can offer particularly long maintenance intervals, thus ensuring continuity of production.
Wherever high dynamics are required on strokes longer than 10-12m, actuators with rack and pinion drives tend to be an excellent solution, as they allow for accelerations of as much as 10 m/s2 and speeds of up to 3.5 m/s on potentially infinite strokes.
The selection of a special type of actuator would not assure the same results: a screw system, which is undoubtedly much more precise, would definitely be too slow and wouldn't be able to handle such long strokes.
Lengthy Strokes
Systems created by assembling actuators in the typical X-Y-Z configurations of Cartesian robotics typically, in applications reminiscent of pick-and-place and feeding machining centres alongside production lines, have very long strokes, which may even reach dozens of metres in length.
Plus, in lots of cases, these long strokes – which usually involve the Y axis – are tasked with dealing with considerably heavy loads, usually hundreds of kilos, as well as numerous vertical Z axes which operate independently.
In these types of applications, your best option for the Y axis is certainly an actuator with a rack and pinion drive, considering that:
thanks to the inflexibleity of the rack and pinion system, they are capable of operating along potentially unlimited strokes, all whilst sustaining their inflexibleity, precision and efficiency
actuators with induction-hardened steel racks with inclined teeth which slide alongside recirculating ball bearing rails or prismatic rails with bearings are capable of handling loads of over 1000kg
the option of installing multiple carriages, every with its own motor, allows for numerous unbiased vertical Z axes.
A belt system is ideal for strokes of up to 10-12m, whilst ball screw actuators are limited – within the case of lengthy strokes – by their critical speed.
Positioning Repeatability
If, alternatively, the designer is seeking most precision – like in applications such because the assembly of microcomponents or sure types of handling in the medical area, for instance – then there's only one clear alternative: linear axes with ball screw drives.
Screw-driven linear actuators provide the most effective efficiency from this point of view, with a degree of positioning repeatability as high as ±5 μ. This efficiency can't be matched by either belt-pushed or screw-driven actuators, which both reach a most degree of positioning repeatability of ±0.05 mm.
Website: https://www.firgelliauto.com/collections/linear-actuators
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