Linear Actuators: what they’re and how to decide on them

Linear Actuators: what they’re 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 into a linear motion along an axis. Helping to produce movements such because the pushing, pulling, elevating, reducing 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 primary sectors:

industrial automation

servos and pick-and-place systems in production processes

assembly

packaging and palletisation

Certainly, just think of applications reminiscent of 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 exterior axis in an effort to expand its range of action.

All of those applications use one or more linear actuators. In keeping with the type of application and the performance that it must assure in terms of 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 primary types of motion transmission:

belt

rack and pinion

screw

How can you make sure that you choose the precise 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 necessary thing is to consider the issue from the appropriate viewpoint – namely the application and, above all, the results and efficiency 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 lots of areas of industrial design, such as packaging, for example, the calls for made of the designer very often need to do with speed 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 ideal solution when it involves high dynamics, considering that:

they allow 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 handling loads starting from extremely small to approximately 200kg

in response to the type of lubrication, these systems can provide notably long upkeep 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 typically an excellent solution, as they allow for accelerations of up to 10 m/s2 and speeds of up to 3.5 m/s on potentially infinite strokes.

The choice of a special type of actuator would not guarantee the same outcomes: a screw system, which is undoubtedly a lot more precise, would definitely 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 usually, in applications similar to pick-and-place and feeding machining centres along production lines, have very lengthy strokes, which may even reach dozens of metres in length.

Plus, in lots of cases, these long strokes – which normally contain 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 definitely an actuator with a rack and pinion drive, considering that:

thanks to the rigidity of the rack and pinion system, they are capable of operating along probably unlimited strokes, all whilst maintaining their inflexibleity, precision and efficiency

actuators with induction-hardened metal racks with inclined tooth 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 a number of carriages, each with its own motor, permits for numerous unbiased vertical Z axes.

A belt system is good 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, then again, the designer is seeking most precision – like in applications such because the assembly of microcomponents or sure types of handling within the medical discipline, for example – then there is only one clear alternative: linear axes with ball screw drives.

Screw-driven linear actuators offer the very best efficiency from this point of view, 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 maximum degree of positioning repeatability of ±0.05 mm.