A linear actuator is a self-supporting structural system capable of remodeling a circular motion generated by a motor right into a linear motion alongside an axis. Helping to produce movements such because the pushing, pulling, elevating, reducing or inclination of a load.
The most common use of actuators entails combining them with multi-axis Cartesian robot systems or utilizing them as integral parts of machines.
The primary sectors:
industrial automation
servos and pick-and-place systems in production processes
meeting
packaging and palletisation
Indeed, just think of applications reminiscent of airplane, laser or plasma chopping machines, the loading and unloading of machined items, feeding machining centres in a production line, or moving an industrial anthropomorphic robot alongside an additional external axis with a purpose to broaden its range of action.
All of those applications use one or more linear actuators. According to the type of application and the performance that it should assure by way of precision, load capacity and velocity, 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 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 commonly the case when talking about linear motion solutions, the vital thing is to consider the problem from the appropriate viewpoint – namely the application and, above all, the results and efficiency 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, corresponding to packaging, for example, the calls for made of the designer fairly often need to do with velocity 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 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-driven axes is typically capable of handling loads starting from extremely small to approximately 200kg
in keeping with the type of lubrication, these systems can supply significantly lengthy maintenance intervals, thus guaranteeing continuity of production.
Wherever high dynamics are required on strokes longer than 10-12m, actuators with rack and pinion drives tend to be a wonderful solution, as they allow for accelerations of up to 10 m/s2 and speeds of as much as 3.5 m/s on potentially infinite strokes.
The selection of a special type of actuator would not assure the identical outcomes: a screw system, which is undoubtedly much more exact, would certainly be too gradual and would not be able to deal with such lengthy strokes.
Lengthy Strokes
Systems created by assembling actuators within the typical X-Y-Z configurations of Cartesian robotics typically, in applications comparable to pick-and-place and feeding machining centres along production lines, have very long strokes, which may even attain dozens of metres in length.
Plus, in many cases, these lengthy strokes – which often involve the Y axis – are tasked with handling considerably heavy loads, typically hundreds of kilos, as well as numerous vertical Z axes which operate independently.
In these types of applications, your best 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 doubtlessly unlimited strokes, all whilst sustaining their inflexibleity, precision and effectivity
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 putting in multiple carriages, each with its own motor, permits for quite a few independent 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, then again, the designer is seeking maximum precision – like in applications such because the assembly of microcomponents or certain types of handling within the medical field, for instance – then there’s only one clear choice: linear axes with ball screw drives.
Screw-pushed linear actuators supply 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-driven actuators, which each reach a maximum degree of positioning repeatability of ±0.05 mm.