Linear Actuators: what they are and the way to choose them

A linear actuator is a self-supporting structural system capable of remodeling 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, decreasing or inclination of a load.

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

The main sectors:

industrial automation

servos and pick-and-place systems in production processes

assembly

packaging and palletisation

Indeed, just think of applications comparable to 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 external axis with a view to expand 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 should guarantee when it comes to precision, load capacity and velocity, 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 appropriate actuator? What variables does an industrial designer tackling a new application must take into consideration?

As is commonly the case when talking about linear motion solutions, the important thing is to consider the issue from the right viewpoint – namely the application and, above all, the outcomes and performance you’re 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 many areas of business design, resembling packaging, for example, the demands made of the designer fairly often should do with velocity and reducing cycle times.

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

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

they permit for accelerations of up to 50 m/s2 and speeds of as much as 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 usually a wonderful 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 distinct type of actuator would not guarantee the identical outcomes: a screw system, which is undoubtedly a lot more precise, would certainly be too slow 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 typically, in applications comparable 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 lengthy strokes – which normally involve the Y axis – are tasked with handling considerably heavy loads, usually hundreds of kilos, as well as quite a few vertical Z axes which operate independently.

In these types of applications, your best option for the Y axis is unquestionably an actuator with a rack and pinion drive, considering that:

thanks to the inflexibleity of the rack and pinion system, they’re capable of operating along potentially unlimited strokes, all whilst sustaining their inflexibleity, precision and efficiency

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 one thousandkg

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

A belt system is ideal for strokes of up to 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 most precision – like in applications such because the assembly of microcomponents or sure types of handling in the medical field, for example – then there is only one clear alternative: linear axes with ball screw drives.

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