Linear Actuators: what they’re and how 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 alongside an axis. Helping to produce movements such because the pushing, pulling, elevating, decreasing or inclination of a load.

The most typical use of actuators involves 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

Certainly, just think of applications equivalent to aircraft, laser or plasma chopping machines, the loading and unloading of machined pieces, feeding machining centres in a production line, or moving an industrial anthropomorphic robot alongside an additional external axis with the intention to develop its range of action.

All of these applications use one or more linear actuators. In response to the type of application and the performance that it must assure when it comes to precision, load capacity and velocity, 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 main 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 have to take into consideration?

As is usually the case when talking about linear motion solutions, the essential thing is to consider the problem from the precise viewpoint – namely the application and, above all, the outcomes and efficiency 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 industrial design, corresponding to packaging, for instance, the demands made of the designer very often have to do with velocity 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 best solution when it comes to high dynamics, considering that:

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

in accordance with the type of lubrication, these systems can supply significantly long upkeep intervals, thus guaranteeing continuity of production.

Wherever high dynamics are required on strokes longer than 10-12m, actuators with rack and pinion drives tend to be 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 choice of a special type of actuator would not assure the identical outcomes: a screw system, which is undoubtedly a lot more precise, would definitely be too gradual and would not be able to handle such lengthy strokes.

Lengthy Strokes

Systems created by assembling actuators in the typical X-Y-Z configurations of Cartesian robotics often, 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 contain the Y axis – are tasked with dealing with considerably heavy loads, often 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 definitely an actuator with a rack and pinion drive, considering that:

thanks to the inflexibleity of the rack and pinion system, they are capable of working along probably unlimited strokes, all whilst sustaining their rigidity, precision and effectivity

actuators with induction-hardened metal 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 a number of carriages, each with its own motor, permits for numerous independent 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 long strokes – by their critical speed.

Positioning Repeatability

If, on the other hand, the designer is seeking most precision – like in applications such as the assembly of microcomponents or sure types of handling in the medical discipline, for instance – then there is only one clear selection: linear axes with ball screw drives.

Screw-pushed linear actuators supply the most effective performance 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 each reach a most degree of positioning repeatability of ±0.05 mm.