Linear Actuators: what they are and how to decide on them

A linear actuator is a self-supporting structural system capable of reworking a circular motion generated by a motor right into a linear motion alongside an axis. Helping to produce movements such because the pushing, pulling, raising, lowering 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 parts of machines.

The main sectors:

industrial automation

servos and pick-and-place systems in production processes

assembly

packaging and palletisation

Certainly, just think of applications comparable to aircraft, 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 external axis with a view to increase its range of action.

All of those applications use one or more linear actuators. In response to the type of application and the efficiency that it should assure by way of precision, load capacity and speed, 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 foremost types of motion transmission:

belt

rack and pinion

screw

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

As is usually the case when talking about linear motion solutions, the necessary thing is to consider the problem from the suitable viewpoint – namely the application and, above all, the outcomes and performance you might be expecting. As such, it is worth starting by considering the dynamics, stroke length and precision required.

Let’s look at these in detail.

High Dynamics

In lots of areas of commercial design, resembling packaging, for example, the calls for made of the designer very often must 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 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-pushed axes is typically capable of handling loads starting from extraordinarily small to approximately 200kg

in response to the type of lubrication, these systems can provide notably 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 superb solution, as they permit for accelerations of up to 10 m/s2 and speeds of as much as 3.5 m/s on probably infinite strokes.

The selection of a unique type of actuator would not assure the same results: a screw system, which is undoubtedly much more exact, would definitely be too slow and would not be able to handle such long strokes.

Long Strokes

Systems created by assembling actuators in the typical X-Y-Z configurations of Cartesian robotics typically, in applications such as pick-and-place and feeding machining centres along production lines, have very lengthy strokes, which can even reach 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, often hundreds of kilos, as well as quite a few vertical Z axes which operate independently.

In these types of applications, the best choice 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 working along doubtlessly unlimited strokes, all whilst sustaining their inflexibleity, precision and efficiency

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

the option of installing a number of carriages, every with its own motor, permits for quite a few impartial vertical Z axes.

A belt system is right 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, alternatively, the designer is seeking maximum precision – like in applications such because the assembly of microcomponents or sure types of handling in the medical subject, for example – then there is only one clear selection: linear axes with ball screw drives.

Screw-pushed linear actuators provide one of the best efficiency from this standpoint, with a degree of positioning repeatability as high as ±5 μ. This performance cannot be matched by either belt-driven or screw-pushed actuators, which both reach a most degree of positioning repeatability of ±0.05 mm.