How to select and integrate multi-dimensional safety systems to protect workers from cobots
uses Safety Integrity Levels (SILs) to define safety requirements, while ISO 13849 defines the Required Performance Level (PLr). ISO 13849 and IEC 61508 are based on the concept of the probability of dangerous failure per hour (PFHd). The ISO 13849 functional safety analysis considers three factors: the severity of a possible injury, the frequency or exposure to a hazard, and the potential of limiting the hazard and avoiding harm (Figure 1): Severity of injury ■ S1: Slight (normally reversible injury) ■ S2: Serious (normally irreversible or death) Frequency and/or exposure to hazard ■ F1: Seldom-to-less-often and/or exposure time is short ■ F2: Frequent-to-continuous and/ or exposure time is long Possibility of avoiding hazard or limiting harm ■ P1: Possible under specific conditions ■ P2: Hardly possible How does LiDAR work? Certification to PLb according to ISO 13849 is required for the use of 2D LiDAR safety sensors in personal protection applications. The TiM 2D LiDAR sensor family includes models meeting that requirement. 2D LiDAR sensors
is suitable for fine positioning in applications like docking. HDDM+ processes edge reflections particularly well, making it best suited for localization and anti- collision applications in dynamic environments. In both cases, the patented HDDM/ HDDM+ multi-pulse technology enables TiM 2D LiDAR sensors to detect the entire scanning range without gaps, ensuring consistent measurement precision, and they can handle different surfaces and remission factors. Types TiM1xx, TiM3xx, and TiM7xx detect whether objects are in a pre-defined field. Sixteen field sets, each with three preconfigured fields, support quick adaptation during operation (Figure 3). Individual field geometries can be specified, or reference contour fields can be defined for static contour monitoring. Digital filters, masked areas, and response times can also be defined to maximize performance even in the presence of heavy rain, snow, or dust. Models that provide field evaluation data or field evaluation and measurement data are available. Field evaluation sensors only determine the presence of an object, while field evaluation and measurement data can be used to provide an accurate picture of a scanned surface. In addition to distance data, TiM 2D LiDAR sensors are available that also provide angular data and a
Figure 1: Derivation of PLr levels in ISO 13849 and corresponding SILs in IEC 62061. Both standards are based on the concept of dangerous failure per hour (PFHd). Image source: SICK
Figure 2: TiM 2D LiDAR sensors use a rotating mirror and laser pulses to create a picture of the surroundings that can be updated up to 15 times every second. Image source: SICK
This article starts with a brief refresher on the requirements of ISO 13849, IEC 62061, and IEC 61800-5-2 and a review of the basics of two-dimensional (2D) light detection and ranging (LiDAR) safety laser scanners. It then provides a deeper dive into how layered safety envelopes can be implemented to protect people from cobots, AMRs, AGVs, and similar equipment. Included is a review of the use and integration of 2D LiDAR sensors and a look at the benefits of combining those sensors with a modular programmable safety controller to provide an additional dimension of safety, plus the use of an event camera to enable fault analysis of unexpected interruptions of protective fields. Exemplary devices from SICK are included.
standard for ‘Functional Safety of Electrical/Electronic/ Programmable Electronic Safety- related Systems (E/E/PE, or E/E/ PES)’ and applies to all industries. In addition, there are industry and application-specific subsections and variants. IEC 62061, ‘Safety of machinery: Functional safety of electrical, electronic and programmable electronic control systems’, is the machinery-specific variant of IEC 61508. IEC 61800-5-2, ‘Adjustable speed electrical power drive systems – Part 5-2: Safety requirements – Functional,’ is also related to IEC 61508 and is a standard for the design and development of adjustable speed drive systems. ISO 13849 was developed independently and not derived from IEC 61508. Both are concerned with functional safety. IEC 61800-5-2
scan their surroundings using optical time-of-flight (ToF) technology. ToF is implemented by sending laser pulses using a rotating mirror and detecting the reflected light. The longer it takes for the reflected light to arrive back at the sensor, the further away the object. The time measurement combined with the strength of the returned signal enables the sensor to calculate the position of multiple objects with millimeter accuracy. The resulting picture of the surroundings is updated up to 15
times every second (Figure 2). It can support real-time navigation, orientation, control, and safety functions. TiM 2D LiDAR sensors detect objects in defined areas (fields) to be monitored. Depending on the model, they have a scanning range of up to 25 m and a working range of up to 270°. The return pulse data from the laser is processed using high-definition distance measurement (HDDM) or HDDM+ technology. HDDM achieves a very high measurement accuracy at short distances and
The time measurement combined with the strength of the returned signal enables the sensor to calculate the position of multiple objects with millimeter accuracy.
IEC 61508 is the foundational
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