A linear actuator is a self-supporting structural system capable of reworking a circular motion generated by a motor into a linear motion along an axis. Serving to to produce movements such as the pushing, pulling, elevating, reducing or inclination of a load.
The most common use of actuators entails combining them with multi-axis Cartesian robot systems or using them as integral parts of machines.
The main sectors:
servos and pick-and-place systems in production processes
packaging and palletisation
Certainly, just think of applications comparable to plane, laser or plasma cutting machines, the loading and unloading of machined pieces, feeding machining centres in a production line, or moving an industrial anthropomorphic robot along an additional exterior axis in order to expand its range of action.
All of these applications use one or more linear actuators. In response to the type of application and the efficiency that it must guarantee in terms of precision, load capacity and velocity, there are numerous types of actuators to select from, and it is typically the type of motion transmission that makes the difference.
There are three most important types of motion transmission:
rack and pinion
How can you ensure that you choose the best actuator? What variables does an industrial designer tackling a new application need to take into consideration?
As is usually the case when talking about linear motion solutions, the essential thing is to consider the problem from the fitting viewpoint – namely the application and, above all, the outcomes and efficiency you are expecting. As such, it is worth starting by considering the dynamics, stroke length and precision required.
Let’s look at these in detail.
In lots of areas of industrial design, equivalent to packaging, for instance, the calls for made of the designer very often have to do with velocity 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 permit for accelerations of as much as 50 m/s2 and speeds of up to 5 m/s on strokes of so long as 10-12m
an X-Y-Z portal with belt-driven axes is typically capable of dealing with loads starting from extremely small to approximately 200kg
in keeping with the type of lubrication, these systems can offer particularly long upkeep intervals, thus making certain continuity of production.
Wherever high dynamics are required on strokes longer than 10-12m, actuators with rack and pinion drives tend to be a superb solution, as they allow for accelerations of as much as 10 m/s2 and speeds of up to 3.5 m/s on doubtlessly infinite strokes.
The choice of a special type of actuator wouldn’t guarantee the same results: a screw system, which is undoubtedly much more exact, would certainly be too slow and would not be able to handle such lengthy strokes.
Systems created by assembling actuators within the typical X-Y-Z configurations of Cartesian robotics often, in applications corresponding to pick-and-place and feeding machining centres along production lines, have very lengthy strokes, which may even reach dozens of metres in length.
Plus, in many cases, these lengthy strokes – which often contain 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, the best choice for the Y axis is unquestionably an actuator with a rack and pinion drive, considering that:
thanks to the rigidity of the rack and pinion system, they’re capable of operating alongside potentially unlimited strokes, all whilst maintaining their inflexibleity, precision and effectivity
actuators with induction-hardened steel racks with inclined teeth which slide alongside recirculating ball bearing rails or prismatic rails with bearings are capable of dealing with loads of over 1000kg
the option of putting in a number of carriages, each with its own motor, allows for numerous independent vertical Z axes.
A belt system is good for strokes of as much as 10-12m, whilst ball screw actuators are limited – in the case of lengthy strokes – by their critical speed.
If, alternatively, the designer is seeking most precision – like in applications such because the assembly of microcomponents or certain types of dealing with in the medical subject, for example – then there is only one clear choice: linear axes with ball screw drives.
Screw-driven linear actuators provide the most effective performance from this viewpoint, 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 attain a most degree of positioning repeatability of ±0.05 mm.