Linear Actuators: what they are and how to decide on them

Linear Actuators: what they are 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 alongside an axis. Helping to produce movements such as the pushing, pulling, raising, lowering or inclination of a load.

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

The primary sectors:

industrial automation

servos and pick-and-place systems in production processes

meeting

packaging and palletisation

Certainly, just think of applications such as airplane, laser or plasma cutting machines, the loading and unloading of machined items, feeding machining centres in a production line, or moving an industrial anthropomorphic robot alongside an additional external axis with a view to expand 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 must guarantee by way of precision, load capacity and speed, 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 most important types of motion transmission:

belt

rack and pinion

screw

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

As is commonly the case when talking about linear motion solutions, the vital thing is to consider the problem from the fitting viewpoint – namely the application and, above all, the results and performance you’re 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 many areas of business design, akin to packaging, for instance, the demands made of the designer very often should do with pace and reducing cycle times.

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

Belt drives are sometimes the ideal solution when it involves 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-pushed axes is typically capable of dealing with loads starting from extremely small to approximately 200kg

according to the type of lubrication, these systems can supply notably lengthy 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 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 would not guarantee the identical outcomes: a screw system, which is undoubtedly a lot more exact, will surely be too sluggish and would not be able to handle such lengthy strokes.

Long Strokes

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

Plus, in many cases, these lengthy strokes – which normally involve 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, the only 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 working alongside potentially unlimited strokes, all whilst sustaining 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 dealing with loads of over a thousandkg

the option of installing multiple carriages, each with its own motor, allows for quite a few independent vertical Z axes.

A belt system is right for strokes of up to 10-12m, whilst ball screw actuators are limited – in 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 handling within the medical area, for example – then there’s only one clear choice: linear axes with ball screw drives.

Screw-driven linear actuators supply the best performance from this viewpoint, with a degree of positioning repeatability as high as ±5 μ. This performance can’t be matched by either belt-pushed or screw-driven actuators, which each reach a most degree of positioning repeatability of ±0.05 mm.