Linear Actuators: what they’re 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. Helping to produce movements such because the pushing, pulling, raising, decreasing or inclination of a load.

The commonest use of actuators involves combining them with multi-axis Cartesian robot systems or using them as integral parts of machines.

The principle sectors:

industrial automation

servos and pick-and-place systems in production processes

assembly

packaging and palletisation

Certainly, just think of applications reminiscent of plane, laser or plasma slicing 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 the intention to broaden its range of action.

All of those applications use one or more linear actuators. In line with the type of application and the efficiency 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 essential types of motion transmission:

belt

rack and pinion

screw

How can you make sure that you choose 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 necessary thing is to consider the difficulty from the correct viewpoint – namely the application and, above all, the outcomes and efficiency you are 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 industrial 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’s no shock, then, that high dynamics are commonly the starting point when defining a solution.

Belt drives are sometimes the best solution when it involves high dynamics, considering that:

they permit for accelerations of as much as 50 m/s2 and speeds of as much as 5 m/s on strokes of so long as 10-12m

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

based on 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 are usually an excellent solution, as they permit for accelerations of up to 10 m/s2 and speeds of up to 3.5 m/s on probably infinite strokes.

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

Long Strokes

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

Plus, in many cases, these long strokes – which often involve the Y axis – are tasked with handling considerably heavy loads, typically hundreds of kilos, as well as quite a few vertical Z axes which operate independently.

In these types of applications, the only option 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 are capable of working along probably 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 one thousandkg

the option of putting in a number of carriages, every with its own motor, permits for numerous independent 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, then again, the designer is seeking most precision – like in applications such as the assembly of microcomponents or sure types of handling within the medical subject, for instance – then there may be only one clear selection: linear axes with ball screw drives.

Screw-pushed linear actuators provide the most effective performance from this viewpoint, with a degree of positioning repeatability as high as ±5 μ. This efficiency cannot be matched by either belt-pushed or screw-pushed actuators, which each reach a maximum degree of positioning repeatability of ±0.05 mm.