Human-robot collaboration (HRC) describes a work scenario in which humans and automated machines share and work in the same workspace at the same time. Driven by Industry 4.0, this model of collaboration promises highly flexible workflows, maximum system throughput and productivity, as well as economic efficiency. However, ensuring that HRC is actually able to live up to this promise requires exactly the right safety technology for the application in question. By Fanny Platbrood, Product Manager for Industrial Safety Systems at SICK.

One of the major issues associated with Industry 4.0 is making work processes flexible. At the extreme end of the spectrum, this may involve manufacturing products in batch size 1 under industrial mass-production conditions – that is, manufacturing unique items on a conveyor belt. This type of smart factory – where products and production processes are one with state-of-the-art information and communication technology – is becoming home to machines that are increasingly intelligent, and increasingly autonomous as a result.

Not only that, but interaction between humans and machines is also set to increase in industrial manufacturing. This is because combining the abilities of humans with those of robots results in production solutions that are characterised by optimised work cycles, improved quality, and greater cost-efficiency, to name a few examples. At the same time, however, machines that are autonomous but primarily interact with humans require new safety concepts that provide effective support for making production processes more flexible.

Human-robot interaction: a question of space and time

Industry 4.0 is not the first time that industrial automation has focused on interaction between humans and machines. To date, the two-interaction scenarios of co-existence and co-operation have dominated, accounting for around 90% of cases. Space and time are crucial interaction parameters in these scenarios.

Coexistence denotes cases in which humans and machines stay in neighbouring areas at the same time while they interact. A typical example of this is an insertion station with a rotating table on a robot cell. Humans and machines work in neighbouring workspaces at the same time, with the area between the two being monitored by a deTec4 Prime safety light curtain, for example.

Co-operation, on the other hand, is when humans and machines work in a shared workspace but at different times. An example of this type of work situation is a transfer station for assembly robots. A worker inserts a workpiece and, at the same time, a S3000 safety laser scanner with multiple simultaneous protective fields that detect the worker ensures that the robot speed is reduced or that the robot is brought to a safety-monitored stop.

Industry 4.0 is seeing a third form of interaction shifting increasingly into the spotlight: collaboration between humans and robots. This involves both humans and robots sharing the same workspace at the same time. An example of this is a mobile platform with a robot that takes parts from a belt or a pallet and transports them to a workspace, where they are presented and given to the worker stationed there.

In collaborative scenarios such as this, the conventional safe detection solutions used for coexistence or co-operation are no longer sufficient – instead, the forces, speeds, and travel paths of robots now need be to monitored, restricted, and stopped where necessary, depending on the actual level of danger. The distance between humans and robots is therefore becoming a key safety-relevant parameter.

The risk assessment is always the first step – even for “cobots”

No two examples of human-robot collaboration are the same. This means that an individual risk assessment for the HRC application is required even if the robot concerned has been developed specifically to interact with humans. “Cobots” like this therefore have many features of an inherently safe construction, starting from their basic design.

At the same time, the collaboration space also has to meet fundamental requirements such as minimum distances to adjacent areas with crushing or pinching hazards. General standards such as IEC 61508, IEC 62061, and ISO 13849-1/-2 are one way in which the foundations for the functional safety of HRC applications are laid. It is also important to give particular consideration to ISO 10218-1/-2, which concerns the safety of industrial robots, and ISO TS 15066, which relates to robots for collaborative operation.

Developers and integrators of robot systems not only have to perform thorough checks on the structural safety measures taken by robot manufacturers, with regard to their functions and compliance with the aforementioned standards, but are also required to consider any hazards or risks that may remain. This means carrying out a risk assessment in accordance with EN ISO 12100 for the robot system, its motion sequences, and its planned collaboration area in order to determine which safety measures are appropriate – such as implementing suitable types of collaboration as defined in ISO/TS 15066.

Safety-related operating modes of collaborative robot systems

These technical specifications can be used to discern four types of collaborative operation. The “safety-related monitored stop” prevents robots from interacting with humans, while “hand guiding” ensures safe HRC by guiding the robot manually at an appropriately reduced speed. The third type of collaboration, “power and force limiting”, achieves the required safety by reducing the power, force, and speed of the robot – through safety controller limiting functions, for example – to a biomechanical load capacity at which no hazards or injuries are to be expected. This takes place regardless of whether there is unintentional or intentional physical contact between robots and humans.

The “speed and separation monitoring” type of collaboration is completely in keeping with the concept of highly flexible work scenarios – and therefore with the principles of Industry 4.0 and production processes in smart factories. It is based on the speed and travel paths of the robot being monitoring and adjusted according to the working speed of the operator in the protected collaboration area. Safety distances are permanently monitored and the robot is slowed down, stopped, or diverted when necessary. If the distance between the operator and the machine becomes greater than the minimum distance again, the robot system can continue moving at typical speeds and along typical travel paths automatically. This immediately restores robot productivity.

Functional safety for HRC: expertise, portfolio, and implementation from a single source

Of the different types of ISO/TS 15066 collaboration, speed and distance monitoring in HRC applications offers the greatest potential as we move into the future. When considered in relation to these, and in view of the interaction scenarios of coexistence and co-operation that have dominated up to this point, it is clear that safety-related sensor and control technology is facing new challenges to ensure that HRC is able to continue operating unimpeded.

It is also worth noting that the more the requirements imposed on the safety of shared workspaces increase, the more collaborative future work situations will become. As a manufacturer of sensor, control, and system solutions for functional safety and a supplier of comprehensive safety services that range from risk assessment and safety concepts through to system solution implementation, SICK has extensive expertise in designing safe robot applications.

What’s more, SICK offers a range of sensors and controllers that has developed along with the requirements of safe robot applications over the decades. Safety solutions based on various technologies are becoming more and more intelligent and are constantly making new HRC applications possible because they are able to fulfill requirements that are becoming increasingly demanding.

As things stand, HRC only accounts for a small share of all applications involving human-robot interaction. Innovative solutions for functional safety in robot applications, like those developed and implemented at SICK, can help to increase this share significantly in the foreseeable future.