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 along an axis. Helping to produce movements such because 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 principle sectors:

industrial automation

servos and pick-and-place systems in production processes

meeting

packaging and palletisation

Indeed, just think of applications reminiscent of aircraft, 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 the intention to increase 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 must assure in terms of precision, load capacity and pace, there are numerous types of actuators to select 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 ensure that you choose the precise actuator? What variables does an industrial designer tackling a new application need to take into consideration?

As is often the case when talking about linear motion solutions, the important thing is to consider the difficulty from the precise viewpoint – namely the application and, above all, the results 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 lots of areas of industrial design, reminiscent of packaging, for example, the calls for made of the designer fairly often need to do with pace and reducing cycle times.

It is no shock, 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-driven axes is typically capable of handling loads ranging from extremely small to approximately 200kg

in keeping with the type of lubrication, these systems can offer significantly lengthy upkeep intervals, thus guaranteeing continuity of production.

Wherever high dynamics are required on strokes longer than 10-12m, actuators with rack and pinion drives are typically a superb 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 choice of a distinct type of actuator would not assure the identical results: a screw system, which is undoubtedly a lot more precise, would certainly be too sluggish and wouldn’t 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 similar to pick-and-place and feeding machining centres along production lines, have very lengthy strokes, which may even attain dozens of metres in length.

Plus, in lots of cases, these lengthy strokes – which often involve the Y axis – are tasked with dealing with 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 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 operating along probably unlimited strokes, all whilst maintaining their inflexibleity, precision and effectivity

actuators with induction-hardened steel racks with inclined enamel which slide alongside recirculating ball bearing rails or prismatic rails with bearings are capable of handling loads of over a thousandkg

the option of putting in multiple carriages, every with its own motor, permits for quite a few unbiased 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 long strokes – by their critical speed.

Positioning Repeatability

If, however, the designer is seeking maximum precision – like in applications such because the meeting of microcomponents or sure types of dealing with in the medical field, for example – then there is only one clear selection: linear axes with ball screw drives.

Screw-driven linear actuators supply the most effective efficiency from this point of view, with a degree of positioning repeatability as high as ±5 μ. This performance can’t be matched by either belt-driven or screw-driven actuators, which each attain a maximum degree of positioning repeatability of ±0.05 mm.