FEATURE
SENSORS & SENSING SYSTEMS
Error-proofing production
Spotting problems as soon as they occur minimises the impact of production errors during manufacturing processes. But while it is often believed that inline checking is too
expensive and/or complex, this is no longer the case, as Tim Dodd of ifm electronic explains
B
eing able to monitor and check the processes and products on a production line at every stage would result in
enormous potential benefits: wear and tear on moving parts detected before they start to cause serious problems; out-of-tolerance products detected before time and money is spent taking them through the whole production process; missing or incorrectly oriented components spotted before the end product is packed, and so on. Surely providing such comprehensive monitoring and inspection would be both costly and complicated? Adding inline checking to an existing plant – or designing it into a new plant – need no longer be a dream.
sensinG soLUTions
The first step is to realise that inline checking doesn’t necessarily have to be synonymous with complex vision systems. In many applications, much simpler solutions will do all that’s needed. Consider, for example, ordinary inductive proximity sensors. Not long ago, these had just one function: to indicate whether or not some piece of metal was present in a particular place. But, modern proximity sensors that incorporate IO-Link technology can do much more. In addition to sensing the presence or absence
of a metallic target, they can be configured to operate at a particular and very well defined distance or range of distances, which opens up new applications. They can, for example, be used to spot wear and tear in guides and clamps and, in some applications, to check component orientation, always giving a clear go/no-go indication. These new abilities mean that proximity sensors have an important role to play in inline checking solutions, especially as they are inexpensive, robust and extremely reliable. Proximity sensors are not for every application,
however, especially when non-metallic targets are involved. Optical sensors will often provide the required functionality. The latest types, which also have IO-Link interfaces, use time-of-flight laser technology to provide long-range measurement of distances, as well as other useful functionality. They can, for example, check the height of a
product on a conveyor belt with an accuracy of 1mm or better, even though they are mounted a metre or more from the conveyor. As well as measuring distance, these intelligent optical
sensors can simultaneously check the colour and reflectivity of the target. If required, the outcome of all the measurements – height, colour and reflectivity – can be logically combined in the sensor to produce a single pass/fail output, which saves on I/O capacity for the control system PLC. Where even more detailed inspection is
needed than can be achieved with a normal optical sensor, a laser profiler will often provide a straightforward solution. Effectively line-scan devices, these use time-of-flight and triangulation technologies to produce an accurate and detailed 2D profile of a reference object. After they have been configured – a simple teaching task – they can then be used to scan target objects to determine how similar they are to the reference. The profiler provides a pass/fail output based on the percentage match between the reference object and the target. Profilers are well suited to applications where
ordinary optical sensors do not provide sufficient functionality but a vision system would be overkill. These are less costly than vision systems and easier to configure and, as they use their own internal laser light source to scan the target, they have no special lighting requirements. Finally, advanced versions are now available that can store up to ten reference object profiles, which can subsequently be selected via the IO-Link interface. This makes them eminently suited for use in applications where a production line is required to handle multiple product types.
Vision sensors
While relatively simple sensors can satisfy many of the inline checking requirements associated with typical production processes, there are some applications, such as complex object recognition, where only a vision system can provide the functionality needed. Even in these cases, users now have a choice between traditional (and costly) full-function vision systems and much simpler and less expensive vision sensors. Vision sensors are available in 2D and 3D
versions, with the principal difference being that 2D sensors look at only the width and length of an object, whereas 3D sensors also take into account the height. Apart from this difference, 2D and 3D sensors offer similar functionality, allowing them to be used to assess the size, shape, position and orientation of objects as well
16 DESIGN SOLUTIONS JULY/AUGUST 2021
as their colour and reflectivity. They can also count the number of objects in their field of view. As with full-function vision systems, vision
sensors required good lighting if the best results are to be obtained, but in every other respect they are much easier to set up and use. Typically, they are configured using a software wizard to store multiple models against which they can compare the images they capture, working with user- defined percentage tolerances on parameters like object size and position. In inspection tasks they can readily be configured to provide a go/no-go output which saves a lot of PLC coding compared with evaluating the more complex results delivered by conventional vision systems. Users of vision sensors report that the time
required for setting them up is measured in minutes compared with hours for full-function vision systems, the prices are very much lower, and the on-board logic provided by vision sensors significantly simplifies overall control system design and implementation. Today’s smart sensors can perform
invaluable quality checking roles and, by using combinations of proximity sensors, optical sensors, laser profilers and vision sensors, it is possible to develop versatile and highly effective quality checking systems.
ifm electronic
www.ifm.co.uk
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82
