Linear Actuators: what they’re 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 into a linear motion alongside an axis. Serving to to produce movements such as the pushing, pulling, elevating, reducing or inclination of a load.

The most typical use of actuators entails combining them with multi-axis Cartesian robot systems or utilizing them as integral components 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 similar to airplane, laser or plasma reducing machines, the loading and unloading of machined pieces, feeding machining centres in a production line, or moving an industrial anthropomorphic robot along an additional exterior axis with a purpose to increase 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 assure when it comes to precision, load capacity and velocity, there are various types of actuators to select from, and it is typically the type of motion transmission that makes the difference.

There are three principal types of motion transmission:

belt

rack and pinion

screw

How can you ensure that you choose the right actuator? What variables does an industrial designer tackling a new application have to take into consideration?

As is often the case when talking about linear motion solutions, the important thing is to consider the issue from the proper viewpoint – namely the application and, above all, the outcomes and performance you might be 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 commercial design, reminiscent of packaging, for example, the demands made of the designer very often must do with velocity 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 comes to high dynamics, considering that:

they allow for accelerations of as much as 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-pushed axes is typically capable of dealing with loads starting from extremely small to approximately 200kg

in keeping with the type of lubrication, these systems can offer significantly 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 tend to be an excellent solution, as they permit for accelerations of as much as 10 m/s2 and speeds of up to 3.5 m/s on potentially infinite strokes.

The choice of a different type of actuator wouldn’t guarantee the identical outcomes: a screw system, which is undoubtedly a lot more precise, will surely be too slow and would not be able to handle such long strokes.

Lengthy Strokes

Systems created by assembling actuators within the typical X-Y-Z configurations of Cartesian robotics often, in applications such as pick-and-place and feeding machining centres along production lines, have very long strokes, which can even reach dozens of metres in length.

Plus, in lots of cases, these long strokes – which usually 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 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 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 1000kg

the option of putting in multiple carriages, every with its own motor, permits for numerous independent 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 maximum precision – like in applications such because the assembly of microcomponents or certain types of dealing with in the medical subject, for instance – then there is only one clear alternative: linear axes with ball screw drives.

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