How Safety Levels Are Decided for Cobots

These steps are:

  1. A new work item is proposed. In our case, the collaborative robot standard.
  2. Expert consensus is built by the technical committee. A “committee draft” is produced of the standard.
  3. The technical committee works towards a consensus. From this, an ISO/TS is produced. This is the stage where ISO/TS 15066 is currently.
  4. After all changes are made, an enquiry is made to the Draft International Standard. The final text is then submitted for processing.
  5. A formal vote of the completed standard is made. This vote is used to determine if the technical specification is turned into a full ISO standard.
  6. The new standard is published.

The development of a standard usually takes around 3 years. However, ISO/TS 15066 has been published as a technical specification and looks to stay that way for the moment. At some point in the future, it will be published as a full ISO standard, but not yet.

As a result, the safety limits are likely to change.

The big issue: Injury vs pain

One of the big questions around collaborative robot force limits is: What does safe mean?

There are two ways you can define safety:

  1. The robot does not injure a person when it collides with them.
  2. The robot does not hurt a person when it collides with them.

These two definitions may look similar, but the difference between them can be huge. Consider the difference between dropping a heavy book on your foot so that it hurts and dropping a book which is so heavy that it actually breaks your toe.

In the early drafts of ISO/TS 15066, the safety limits for cobots were defined as the “onset of injury.” However, they were later changed to be the “onset of pain.” This leads to power and force limits which are lower, which means the robot has to move much slower to stay within the limits. This “onset of pain” is what Esben Østergaard was objecting to at the RUC. Pain is subjective and pain thresholds are conservative.

Although it is possible that the current limits are overly conservative, there is a good reason for keeping them low. The ALARA principle (which stands for As Low As Reasonably Achievable) says that you should reduce the risk as much as you can. If it’s possible to achieve lower pain limits with cobots then you should.

How to make sure your cobot is safe

Now that you know where the safety limits for cobots come from, you can probably see that it is quite a gray area. We don’t yet know what the final safety limits will be for collaborative robots when the technical specification is turned into a full standard.

The solution is to focus on the specific risk of your application. Risk assessment is vital. This is something that all of our experts at RUC 2018 could agree on. Safety levels are very application specific.

When you perform a good risk assessment, you can be sure that your application will not injure or harm people.

Check out our eBook How to Perform a Risk Assessment for Collaborative Robots to find out how to perform good risk assessments.

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