Safety laser scanners are complex devices with a rich history.
With the vast number of choices in the market in regards to range, connectivity, size, and robustness, there are many variables to consider when designing a safety solution using scanners. Here are six common mistakes made when setting up safety laser scanners.
1. Thinking about safety last during installation and mounting
Many times when a machine is built and almost completely setup, the last thought is where to put the safety laser scanner. Inevitably, what ends up happening is that blind spots (shadows created by obstacles) become apparent. This requires mechanical patches and possibly even additional scanners to cover the complete area, when one scanner may have been sufficient if the cell was designed properly in the first place.
In safety, designing something in advance is by far the most cost effective and robust solution. If you know you are going to be using a safety laser scanner on your machine, design it in from the beginning. It could save you a world of pain.
On top of this, it’s important to consider blind zones, coverage, and the location of hazards surrounding the machine. This also goes for automated guided vehicles (AGVs) and automated guided carts (AGCs). For example, the most appropriate position to completely cover an AGV/AGC is to have two safety laser scanners adjacent to each other on the corners of the vehicle.
2. Incorrect multiple sampling values configured
An often misunderstood concept, multiple sampling indicates how often an object has to be scanned in succession before a safety laser scanner reacts. By default, this value is usually x2 scans, which is the minimum value. However, this value may range from manufacturer to manufacturer. A higher multiple sampling value reduces the possibility that insects, weld sparks, weather (for outdoor scanners), or other particles will cause the machine to shut down.
Increasing the multiple sampling can make it possible to increase a machine's availability, but it can also have negative effects on the application. Increasing the number of samples is basically adding an OFF-Delay to the system, meaning that your protective field may need to be bigger due to the increase in the total response time.
If a safety laser scanner has a robust detection algorithm, you shouldn’t have to increase this value too much. But when this value is changed, you could be creating a hazard due to lack of effectiveness of the protective device. If it is changed, you should make a note of the safety laser scanner’s new response time and adjust the minimum distance from the hazardous point accordingly to ensure it remains safe.
Furthermore, in vertical applications, if the multiple sampling is set too high, it may be possible for a person to pass through the protective field without being detected, which is a concern.
3. Incorrect selection of a safety laser scanner
The maximum protective field that a scanner can facilitate is an important feature, but this value alone should not be the deciding factor on whether the scanner is suitable for an application.
A safety laser scanner is a Type 3 Device, according to IEC 61496 and an Active Opto-Electric Protective Devices responsive to Diffuse Reflection (AOPDDR). This means that it is depended on to diffuse reflections off objects. Therefore, to achieve longer ranges, scanners must be more sensitive.
In reality, this means that sometimes scanning angle, but certainly detection robustness, can be sacrificed. This could lead to a requirement for an increasing number multiple samples and, maybe, lack of angular resolution. The increased response times and lack of angle could mean that larger protective fields are required and even additional scanners – even if you bought the longer range one. A protective field should be as large as required, but as small as possible. Shorter-range scanners may be more robust than its longer-range big brother, which helps to keep the response time down, reduce the footprint and cost, and eliminate annoying false trips.
4. Incorrect resolution selected
The harmonized standard EN ISO 13855 can be used for the positioning of safeguards with respect to the approach speeds of the human body. If the positioning/configuration is incorrect, people or parts of the body that need to be protected may not be recognized in time or at all.
The safety laser scanner should be mounted so that crawling beneath, climbing over, and standing behind the protective fields is not possible. If crawling under could create a hazardous situation, the safety laser scanner should not be mounted any higher than 300 mm. At this height, a resolution of up to 70 mm can be selected to ensure that it is possible to detect a human leg. However, it is sometimes not possible to mount the safety laser scanner at this height.
If mounted below 300 mm, a resolution of 50 mm should be used. It is a very common mistake to mount the scanner lower than 300 mm and leave the resolution on 70mm. Reducing the resolution may also reduce the maximum protective field possible on a safety laser scanner so it is important to check.
5.Environmental conditions were not considered
Sometimes safety laser scanners just aren't suitable in an application. However, scanners are electro-sensitive protective equipment and infra-red light can be a tricky to adjust.
Scanners have become very robust devices over the last decade with increasingly complex detection techniques (e.g., SafeHDDM). There are even safety laser scanners certified to work outdoors (e.g., outdoorScan3). However, there is a big difference between safety and availability, and expectations need to be realistic right from the beginning.
A scanner might not maintain 100% machine availability if there is heavy dust, thick steam, excessive wood chippings, or even dandelions constantly in front of the field of view. Even though the scanner will continue to be safe and react to such situations, trips due to ambient conditions may not be acceptable to a user.
For extreme environments, the following question should be asked: “What happens when the scanner is not available due to extreme conditions?” This is especially true in outdoor applications in heavy rain, snow, or fog. A full assessment of the ambient conditions and proof tests should be carried out. This particular issue can become a very difficult (and sometimes impossible) and expensive thing to fix.
6. Non-safe switching of field sets
A field set in a safety laser scanner can consist of multiple different field types. For example, a field set could consist of four safe protection fields (Field Set 1) or it could consist of one safe protective field, two non-safe warning fields and a safe detection field (Field set 2).
A scanner can store lots of different fields that can be selected using either hardwired inputs or safe networked inputs (e.g., CIP Safety, PROFISAFE, EFIPro). This is a feature the industry finds very useful for both safety and productivity in Industry 4.0 applications. However, the safety function (as per EN ISO 13849/EN 62061) for selecting the field set at any particular point in time should normally have the same safety robustness (PL/SIL) as the scanner itself.
A safety laser scanner can be used in safety functions up to PLd/SIL2. If we look at AGVs, for example, usually two rotary encoders are used to switch between fields achieving field switching up to PLe/SIL3. There are now also safety-rated rotary encoders that can be used alone to achieve field switching to PLd/SIL2. However, sometimes the safety of the mode selection is overlooked.
For example, if a standard PLC or a single channel limit switch is used for selecting a field set, this would reduce the PL/SIL of the whole system to possibly PLc or even PLa! An incorrect selection of field set could mean that an AGV is operating with small protective field in combination with a high speed and, hence, long stopping time, creating a hazardous situation.
Find the Right Safety Laser Scanner For You
If you are new to this technology, it is a good idea to contact a manufacturer for advice on the application of these devices. At SICK, we offer complimentary services to our customers for consulting, on-site engineering assistance, risk assessment, safety concept, and safety verification of electro-sensitive protective equipment (ESPEs).
Contact a SICK representative today to learn how you can start working safer!
This article was originally written by Dr. Martin Kidman, Machinery Product Specialist from SICK (UK) Ltd.