Linear Actuators: what they are and the way to choose them

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 because the pushing, pulling, raising, reducing or inclination of a load.

The most typical use of actuators entails combining them with multi-axis Cartesian robot systems or using them as integral components of machines.

The main sectors:

industrial automation

servos and pick-and-place systems in production processes

meeting

packaging and palletisation

Indeed, just think of applications equivalent to airplane, 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 alongside an additional exterior axis in order to broaden its range of action.

All of those applications use one or more linear actuators. In accordance with the type of application and the efficiency that it should assure when it comes to precision, load capacity and pace, 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 foremost types of motion transmission:

belt

rack and pinion

screw

How can you make sure that you select the suitable actuator? What variables does an industrial designer tackling a new application should take into consideration?

As is commonly the case when talking about linear motion solutions, the essential thing is to consider the problem from the appropriate viewpoint – namely the application and, above all, the outcomes and performance you might be expecting. As such, it is price starting by considering the dynamics, stroke length and precision required.

Let’s look at these in detail.

High Dynamics

In many areas of commercial design, corresponding to packaging, for instance, the calls for made of the designer fairly often need to do with speed and reducing cycle times.

It is no shock, then, that high dynamics are commonly the starting point when defining a solution.

Belt drives are often the ideal solution when it comes to high dynamics, considering that:

they permit 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 starting from extraordinarily small to approximately 200kg

in keeping with the type of lubrication, these systems can provide notably 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 are usually a superb solution, as they permit for accelerations of up to 10 m/s2 and speeds of up to 3.5 m/s on doubtlessly infinite strokes.

The choice of a distinct type of actuator would not guarantee the identical results: a screw system, which is undoubtedly a lot more precise, would definitely be too slow and would not be able to deal with such long strokes.

Lengthy Strokes

Systems created by assembling actuators within the typical X-Y-Z configurations of Cartesian robotics usually, in applications resembling 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 lots of cases, these lengthy strokes – which normally involve the Y axis – are tasked with handling considerably heavy loads, typically 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’re capable of operating along potentially unlimited strokes, all whilst maintaining their rigidity, precision and efficiency

actuators with induction-hardened metal racks with inclined enamel which slide along 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, permits for numerous unbiased 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.

Positioning Repeatability

If, then again, the designer is seeking most precision – like in applications such as the meeting of microcomponents or certain types of dealing with in the medical discipline, for example – then there may be only one clear alternative: linear axes with ball screw drives.

Screw-pushed linear actuators offer the perfect efficiency from this perspective, with a degree of positioning repeatability as high as ±5 μ. This efficiency cannot be matched by either belt-pushed or screw-driven actuators, which both reach a most degree of positioning repeatability of ±0.05 mm.