Collaborative Robots, sometimes referred to as cobots, are designed to work alongside humans in a ‘collaborative workspace’, an area where the robot and the human can perform tasks simultaneously. This means that unlike more traditional machines, which are ‘caged’ by a guarding mechanism, collaborative robots often operate in the human-occupied workspace without safety fencing. However, not all collaborative robots are guard-free, depending on their function and related safety requirements. Besides the robot itself, the collaborative robot might include an ‘end effector’, that is the tool adapted on the robot arm with which the robot performs tasks, and the objects moved by it, and the risks associated with these parts also need to be considered.

The increased need for adequate protection of people from the safety risks associated with industrial robot systems led to the development of EN ISO 10218:2011, an international and European standard which covers the safety requirements for industrial robots. The standard is in two parts and replaced the 2006 version.

In order to ensure that humans are not exposed to unacceptable risks when working collaboratively the current standards describe four separate measures that can be used to provide risk reduction. These are safety-rated monitored stop, hand guiding, speed and separation monitoring, and power and force limiting by inherent design or control. It is required that at least one of these requirements needs to be fulfilled, in addition to having visual indication that the robot is in collaborative operation.

While EN ISO 10218 contains some guidance on the use of collaborative robots, with the rapid pace of technological development, it was widely acknowledged that this guidance needed to be enhanced. Consequently, a Technical Specification (ISO/TS 15066 Robots and robotic devices – Safety requirements for industrial robots – Collaborative operation) was published in 2016. ISO/TS 15066 covers:

• The design of the collaborative work space
• The design of the collaborative operation
• Methods of collaborative working
• Changing between: Collaborative/non-collaborative; And different methods of collaboration
• Operator controls for different applications

The methods of collaborative working ‘speed and separation monitoring’ and ‘power and force limiting’ are particularly elaborated on in ISO/TS 15066. This includes recommendations for ‘biomechanical limits’ of pain thresholds for specific parts of the human body.

The rationale for creating biomechanical limits was established in conjunction with testing conducted by the University of Mainz (Germany). Testing was conducted using 100 healthy adult test subjects on 29 specific body areas, and for each of the body areas, pressure and force limits for quasi-static and transient contact were established evaluating onset of pain thresholds. There are also working groups of the standards organisations reviewing various aspects of human-machine interactions, which will also inform the development of future standards. But for now, EN ISO 10218 Parts 1 and 2, and the ISO/TS 15066 specification defines the safety requirements for the sphere of collaborative robots, with the most relevant published guidance being contained in EN ISO 10218.

In all four of the measures described above, the safety related control system that provides this functionality needs to meet either:

• Safety Performance Level d (PLd), with Category 3 architecture (the identified level to which the safety related parts of a control system resist faults and their subsequent behaviour if a fault occurs) outlined within the standard EN ISO 13849, or
• Safety Integrity Level 2 (SIL 2) with hardware fault tolerance (HFT) 1, as set out in EN [IEC] 62061.

The cobot sees the dawn of robotic systems that can safely interact with human workers while effectively performing simple industrial tasks. While the advent of the cobot offers exciting possibilities for industry, some end-effectors may create hazards, especially as contact between the collaborative robot and the operator can lead to the possibility of collision. It is therefore vital that a complete risk assessment is undertaken before a cobot is deployed, as you would with any machinery in the workplace. This must cover the intended use of the cobot, as well as any reasonably foreseeable misuse, with the basis for this risk assessment being EN ISO 12100, in order to provide a presumption of conformity with the Machinery Directive.

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Collaborative Robots – sometimes referred to as ‘CoBots’ – are robots that are designed to work alongside humans in a collaborative work-space, an area where the robot and the human can perform tasks simultaneously.

There are many sectors where collaborative operation has some advantages including: medical (where robots are used during various procedures including surgery); healthcare (where robots perform tasks such as assistance with mobility); service (both domestic and professional applications); space (for example on the International Space Station); defence (robots assisting in bomb disposal and “wearable” robots for enhanced mobility); and of course in manufacturing as well as other applications.

The current standards for the use of robots in the manufacturing sector are ‘EN ISO 10218-1:2011 Robots and robotic devices – Safety requirements for industrial robots’ and ‘EN ISO 10218-2:2011 – Part 2: Robot systems and integration’. Both of these standards already contain some guidance on the use of collaborative robots but it is acknowledged that the guidance needs to be enhanced, especially with the rapidly growing technological measures that are being developed and introduced.

With this in mind a Technical Specification is under preparation (ISO/DTS 15066 Robots and robotic devices – Safety requirements for industrial robots — Collaborative operation). There are also working groups of the standards organisations looking at various aspects of ‘human-machine interactions’ which will also inform the development of future standards.

But for now at least the most relevant published guidance is contained in the EN ISO 10218 standards, an HSE Research Report (RR906) “Collision and injury criteria when working with collaborative robots” also has some useful guidance.

Safety measures

In order to ensure that humans are not exposed to unacceptable risks when working collaboratively the standards currently describe four separate measures that can be used to provide risk reduction. It is required that at least one of these requirements needs to be fulfilled in addition to having visual indication the robot is in collaborative operation.

Safety-rated monitored stop: This measure requires that when it is detected that a human has entered the collaborative workspace the robot should be stopped, and the stop condition should be maintained until the human leaves the workspace. The safety related control system that provides this functionality needs to meet PLd with Category 3 architecture (EN ISO 13849), or SIL 2 with hardware fault tolerance (HFT) 1 according to EN [IEC] 62061.

Hand guiding: In this mode the human can guide the robot at the end effector by hand. Additional requirements for safety include safe limited speed monitoring and the use of an ‘enabling device’ (a three position device that has to be held in the centre position) as well as a local emergency stop.

Speed and separation monitoring: In this mode the robot must maintain a specified separation distance from the human and operate at a determined speed. This measure requires careful risk assessment and needs to take account of safety distances with consideration of approach speeds of parts of the human body as described in EN ISO 13855.

Power and force limiting by inherent design or control: In this mode the power and force of the robot actuators need to be monitored by safety related control systems to ensure that they are within limits established by a risk assessment. In all four of the measures described the safety related control systems need to meet PLd with Category 3 architecture (EN ISO 13849), or SIL 2 with hardware fault tolerance (HFT) 1 according to EN [IEC] 62061.

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