Linear Actuators: what they’re and the way to choose them

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 right into a linear motion along an axis. Serving to to produce movements such as the pushing, pulling, raising, decreasing or inclination of a load.

The commonest 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

Certainly, just think of applications comparable to aircraft, 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 as a way to expand its range of action.

All of these applications use one or more linear actuators. In keeping with the type of application and the performance that it must guarantee in terms of precision, load capacity and speed, there are numerous types of actuators to choose from, and it is typically the type of motion transmission that makes the difference.

There are three major types of motion transmission:

belt

rack and pinion

screw

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

As is often the case when talking about linear motion solutions, the necessary thing is to consider the difficulty from the proper viewpoint – namely the application and, above all, the results and efficiency you might be expecting. As such, it is price starting by considering the dynamics, stroke size and precision required.

Let’s look at these in detail.

High Dynamics

In lots of areas of industrial design, such as packaging, for example, the calls for made of the designer very often should do with speed and reducing cycle times.

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

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

they allow 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-driven axes is typically capable of handling loads ranging from extraordinarily small to approximately 200kg

in line with the type of lubrication, these systems can supply notably 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 are usually an excellent solution, as they allow for accelerations of up to 10 m/s2 and speeds of up to 3.5 m/s on doubtlessly infinite strokes.

The selection of a special type of actuator wouldn’t assure the same results: a screw system, which is undoubtedly a lot more precise, would certainly be too sluggish and would not be able to deal with such lengthy strokes.

Lengthy Strokes

Systems created by assembling actuators in the typical X-Y-Z configurations of Cartesian robotics often, in applications reminiscent of pick-and-place and feeding machining centres along production lines, have very long strokes, which can 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, often 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 definitely an actuator with a rack and pinion drive, considering that:

thanks to the inflexibleity of the rack and pinion system, they’re capable of working alongside potentially unlimited strokes, all whilst sustaining their rigidity, 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 dealing with loads of over a thousandkg

the option of putting in a number of carriages, each with its own motor, allows for numerous impartial vertical Z axes.

A belt system is ideal for strokes of as much as 10-12m, whilst ball screw actuators are limited – within the case of long strokes – by their critical speed.

Positioning Repeatability

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

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