Collaborative robot risk assessment: the 2021 guide

Unlike standard industrial robots, cobots directly interact with workers. This obviously implies compliance with safety regulations in the workplace.

But even if your cobot model is certified by recognized standards (ISO), you still have to assess the safety of their applications. Depending on the work process and the external devices involved, using cobotic products can mean added risks for your workers.

Here are the existing norms around cobot safety, and how to perform a full assessment of your cobotic applications to protect your employees and your company.

What are the safety standards for collaborative robots?

ISO 10218

In 2011, the ISO (international standard of standardization) established the ISO 10218-1 and ISO 10218-2 standards to regulate the manufacturing of industrial robot systems. To be certified, they require them to comply their robotic system with strict safety standards. They have to cover not only the risks of their system’s design but also of their accessories and their intended use in the workspace. And most cobot manufacturers (Universal Robot, Techman Robot, Fanuc, Kuka…) already comply with these standards.

ISO/TS 15066

ISO/TS 15066 is a technical specification added in 2016 to ISO 10218-1 and ISO 10218-2 to specify the case of collaborative robots. It explains 4 features that collaborative robots must have to certify as collaborative applications (described just below). Eventually, it may become a full-fledged standard, but for now, it acts only as a clarification.

So if the cobots you buy provide ISO 10218 certification, you have a certified safe robotic system for your work process. But you are still legally entitled to perform a safety assessment of your application for this product.

Which safety features existing cobots provide ?

According to ISO 10218, certified collaborative robots must provide at least one of 4 safe collaborative applications. Here is how they are defined and what forms they take on existing cobot models:

Safe stop

The emergency stop button on Universal Robots

This application stops when it detects the presence of users in its workspace. Whether through a smart vision feature, a laser scanner, or an emergency button, it is designed to stop the cobot’s work by preventing a collision.

In existing models, this can take many forms. Most of them provide an emergency button on the control interface to stop any ongoing process. Others use sensory sensors to stop the process in case of a collision.

Manual Guidance Operation

Techman’s hand guidance feature

One of the most common applications involves users’ manual manipulation to guide the cobot and teach it tasks. Since workers use their strength, the interaction is obviously safe for the worker.

Cobot models typically use force sensors to detect the pressure exerted by workers. Free motion mode also enables easy and safe interaction for users. With this mode, they can move freely the arm of cobots along different axes.

Speed and separation tracking

The collaborative space feature on Doosan cobots

Cobots can also have space-delimitation features. Users can determine different zones where cobots should adapt their speed depending on the situation. For example, an area close to the application can allow a maximum process speed, while other areas will require a measured speed. In this way, the cobot can optimize its productivity, while still acting in proximity to humans.

In current models, the user can for example define a default work zone that cobots cannot step without stopping. They can also define collaboration zones where the cobot adapts its process to the human presence.

Power and force limitation

ABB cobot’s force sensor

By design, cobots can also detect anomalies when using their force. Based on their feedback, they can calculate the difference between the force produced and the force actually required. This allows them to react automatically to a collision by braking or reversing the movement.

Existing models have force and torque sensors to stop unwanted interaction. Touch detection technologies go a step further by preventing collisions in advance. In general, the default robot design (low weight and speed) also significantly reduces impact.

Risk assessment for cobotic application: how to write it?

When you implement a cobot in a work process, you are legally responsible for assessing the risk of its use for your employees. Even if the robotic system you have chosen is certified, you must assess the entire robotic cell, including the robotic system, its environment, and other accessories used.

According to ISO 10218, you must perform a risk assessment document of these robotic systems following these standards. Although the ISO/TS 15066 specifications are not yet recognized as a full-fledged standard, it is also interesting to conform the document to them.

This document should therefore mention 5 categories of essential information:

1. The identification of the document

The first category of your document must certify the validity, date, and author of the document. You must indicate the name of your project, its version, and revisions, the date of publication, and the author(s) of this document. Your signature makes you responsible for the information you write in it.

2. The Project Description

This part describes in a general way why and how you intend to install the robotic cell and the related work process. You have to explain the motivation of your automation project, the application you want to realize and the actors involved.

3. Details of the machines

It is important to annotate the essential details of the machines you use in your application. For this reason, you should give the references of all the cobot models and accessories you use (manufacturer’s name, serial number, date of manufacture).

4. Risk assessment

Now that you have detailed the machines, you need to assess the risks involved in using them. In a table, you can use Pilz Hazard Rating to numerically estimate the risks for each of your applications. You need to combine 4 factors to get an overall risk figure (PHR):

  • Degree of possible harm
  • Possibility of a hazardous event occurring
  • Possibility of avoidance
  • Frequency of exposure

You can then compare this result with the table provided here.

5. The risk-reducing methods

For each risk you have found, you must then indicate the methods to reduce it in order of priority, from the most serious to the least serious. In each case, you should explain how you intend to apply these methods and their limitations.

With all this, you are then ready to deploy your new robotic system. You ensure it is safe for your employees and your company!

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