Robotiq is a company that mainly makes grippers for industrial robots, specialising in two-finger and three-finger robotic hands for the collaborative robots made by Universal Robots.
However, Robotiq also regularly publish much useful and timely information about the robotics industry, often technical information which only experts in the field – such as those who work at Robotiq – would be able to provide.
This week, Robotiq has published an explanation of the new ISO safety requirements pertaining to collaborative robots, and gave Robotics and Automation News permission to publish the article, which follows.
ISO/TS 15066 explained
ISO/TS 15066, the world’s first specifications of safety requirements for collaborative robot applications, is here at last.
It’s been a long journey for the ISO committee containing members from 24 participating countries, including representatives from leading collaborative robot manufacturers, who began work on ISO/TS 15066 back in 2010.
Designed to supplement the requirements and guidance on collaborative industrial robot operation provided in ISO 102181 and ISO 102182 (Safety Requirements for Industrial Robots), ISO/TS 15066 specifies safety requirements for collaborative industrial robot systems and the work environment.
Specifically, ISO/TS 15066 provides comprehensive guidance for those conducting risk assessment of collaborative robot applications.
What is a risk assessment?
The risk assessment process basically analyzes all the motions, interactions and operations the robot is going to perform during its normal operation. The complete operation is sectioned into separated tasks and risk analyses are done for each task.
These tasks and their associated risks are evaluated and rated. With certain criteria these risks are classified and those that are considered dangerous are evaluated and ways are sought to reduce their risk.
That is the brief description, however, this can be a complex process where any motion is considered a risk. In fact, the simple motion of closing a gripper is considered a risk. In order to know what type of risk is associated with the closing action of a gripper (for example) you need to consider a couple of aspects.
The severity of the risk, the possibility of avoiding the risk and the redundancy of the risk. Each of these criteria can be evaluated in the following manner:
Severity of Risk: The principal way to evaluate this criteria is by evaluating the force and/or pressure that is applied on the human body part by the robot. The tech spec provides a complete chart for human body parts and their associated pain value. There is also a difference between a quasi-static impact and a transient impact, with a quasi-static impact being an impact against a fixed object and a transient impact being an impact involving the free movement of the body part. In general, a factor of 2 is added to the maximum allowable force/pressure when you are free to move; which basically allows the robot contact to be 2 times stronger when you are free to move. The least severe or more acceptable risks are rated the lowest.
Possibility of Avoidance: This factor is normally inversely proportional to the speed of the robot. In an example where a robot is running at full speed VS a robot that is running at 50% speed, you clearly have more chance to avoid the slower robot than the faster one. Therefore, the faster a robot is moving the lower your chances of avoiding it are and thus the higher your risk. If the robot is moving slowly then you have more chance to avoid contact and have an increased possibility of avoidance, thus lowering your risk.
Redundancy of the Risk: This factor is evaluated according to the amount of time the risk is possible calculated over a fixed amount of time. For example, does this risk happen every 2 minutes or once per month. The less frequent the risk is, the lower the number you will get; but all risks need to be analyzed in relation to each other. I.e. do you have the possibility of small impacts frequently or a large injury infrequently?
Note that data for specific body parts and the forces that they can withstand without injury are listed in the ISO/TS 15066.
As explained earlier, the score you get represents the danger level of the risk for a particular section of the robotic cell. The highest scores should be reduced to acceptable levels. You need to keep in mind that every time you reduce one risk you need to make sure that it does not increase another risk somewhere else in the process.
At the end of the day, there is no rigid guideline on what is dangerous and what isn’t. It is the end users responsibility to make sure the robotic cell that they set up is safe enough for human robot collaboration, regardless of whether the robotic cell is using collaborative or industrial robots. For more information, download this guide on How to do a risk assessment.
When considering risk, a quote that I like to refer to is the following by Lasse Kieffer, Universal Robots, who says: “Risk assessment is not about avoiding hazards altogether, but about choosing one risk over another. For example, if you’re looking to cross the street and a bus is coming and there’s a 5 per cent chance that you would be run over, then it’s unlikely that you would take the risk. But if there is a child running after a ball crossing the street in front of the bus, you would not hesitate to run in front of the bus to save the child.’’
It’s the same with collaborative robotics: you may choose to accept the risk of a bruise, in order that you avoid the risk of more serious injury somewhere else in the production process.
While not normative in the way that ISO standards are, ISO/TS 15066 describes the state of the art in collaborative robot safety. Whether you are an integrator, a production manager, or an application engineer, the new technical specifications provide essential, data-driven information and guidance needed to evaluate and control risks, and support a risk assessment for collaborative robot systems and applications.
So, if you’re wondering, “When is a good time to get started with collaborative robot safety risk assessment?” The answer is, “Now.”
The hard data and formulas in ISO/TS 15066 enable new levels of detail in cobot risk assessments. It also provides the data-driven safety guidance needed to evaluate and control risks.
Article provided by Olivier Grenier-Lafond, sales and marketing co-ordinator, Robotiq.
