Linear Actuators: what they’re and how to decide on them

A linear actuator is a self-supporting structural system capable of transforming a circular motion generated by a motor right into a linear motion along an axis. Serving to to produce movements such because the pushing, pulling, elevating, lowering or inclination of a load.

The commonest use of actuators includes combining them with multi-axis Cartesian robot systems or utilizing them as integral elements of machines.

The primary sectors:

industrial automation

servos and pick-and-place systems in production processes

meeting

packaging and palletisation

Indeed, just think of applications such as plane, laser or plasma reducing 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 with a view to broaden its range of action.

All of those applications use one or more linear actuators. Based on the type of application and the performance that it should guarantee when it comes to precision, load capacity and pace, there are various types of actuators to choose from, and it is typically the type of motion transmission that makes the difference.

There are three predominant types of motion transmission:

belt

rack and pinion

screw

How can you make sure that you choose the best 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 vital thing is to consider the difficulty from the best viewpoint – namely the application and, above all, the results and efficiency you might be expecting. As such, it is value starting by considering the dynamics, stroke length and precision required.

Let’s look at these in detail.

High Dynamics

In lots of areas of commercial design, resembling packaging, for instance, the calls for made of the designer fairly often must do with pace and reducing cycle times.

It’s no surprise, then, that high dynamics are commonly the starting point when defining a solution.

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

they allow for accelerations of up to 50 m/s2 and speeds of up to 5 m/s on strokes of as long as 10-12m

an X-Y-Z portal with belt-driven axes is typically capable of dealing with loads ranging from extraordinarily small to approximately 200kg

in accordance with the type of lubrication, these systems can provide significantly long maintenance 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 typically a superb solution, as they permit for accelerations of as much as 10 m/s2 and speeds of up to 3.5 m/s on probably infinite strokes.

The selection of a different type of actuator wouldn’t assure the same outcomes: a screw system, which is undoubtedly much more precise, would certainly be too gradual and wouldn’t be able to handle such long strokes.

Lengthy Strokes

Systems created by assembling actuators within the typical X-Y-Z configurations of Cartesian robotics usually, in applications comparable to pick-and-place and feeding machining centres alongside production lines, have very long strokes, which can even attain dozens of metres in length.

Plus, in many cases, these lengthy strokes – which usually involve the Y axis – are tasked with handling considerably heavy loads, often 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 working along probably unlimited strokes, all whilst maintaining their rigidity, precision and efficiency

actuators with induction-hardened steel racks with inclined teeth which slide along recirculating ball bearing rails or prismatic rails with bearings are capable of handling loads of over a thousandkg

the option of installing multiple carriages, each with its own motor, allows for numerous impartial vertical Z axes.

A belt system is good 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 as the assembly of microcomponents or certain types of dealing with within the medical area, for example – then there is only one clear choice: linear axes with ball screw drives.

Screw-pushed linear actuators offer the very best efficiency from this standpoint, with a degree of positioning repeatability as high as ±5 μ. This performance cannot be matched by either belt-driven or screw-pushed actuators, which each attain a most degree of positioning repeatability of ±0.05 mm.