Cobot Safety: Risk Assessments are Critical

Every cobot cell deployment requires a risk assessment in accordance with ISO/TS 15066 that contains a checklist of items that must be considered before deploying a collaborative cell. Image courtesy of OnRobot.

When installing a collaborative cell, safety risks in any possible scenario must be evaluated, including power outages and all types of human interaction.

By: Kristian Hulgard, Contributor

Collaborative automation — a term that encompasses collaborative robot (‘cobot’) and lightweight industrial robot arms and peripherals such as grippers — is unique in the world of industrial automation because it can, in some circumstances, be deployed next to humans without safety fencing.

This is due to the nature of collaborative automation itself, which provides a wide range of built-in safety features. For example, pressure and force limiting means that if there is contact between the operator and the robot, limits are in place to ensure that the force does not exceed established thresholds.

Meanwhile, speed and separation monitoring allow cobots to slow down when a human enters the workspace and to come to a complete stop when a human reaches a specified distance from the robot. Cobot end-effectors such as grippers are also designed with no sharp edges and no pinch points.

To avoid scenarios where items fall through the air after a power outage, be sure to select grippers that will hold onto the object being gripped even when power is lost, as demonstrated by the MG10. Image courtesy of OnRobot.

ASSESSING RISK

But these standard features don’t mean that cobots are inherently safe. Every cobot cell deployment requires a risk assessment in accordance with ISO/TS 15066 (and ISO 10218‑1 and ISO 10218‑2). ISO/TS 15066 contains a checklist of items that must be considered before deploying a collaborative cell, including the thresholds for forces and pressure that cobots cannot exceed.

ISO/TS 15066 lays out the whole formula for performing a risk assessment, but in simple terms the process requires you to determine any possible scenario of failure while accounting for movement, such as operators walking into the space. Similarly, you need to assess any type of scenario where the cell potentially could inflict injury on a human and whether this presents an actual risk of injury.

If the answer to either of those questions is ‘Yes,’ you will need to deploy further safety equipment such as light curtains to make sure that that injury cannot occur.

DIFFERENT LEVELS OF HUMAN-ROBOT INTERACTION

A minority of collaborative applications involve direct interactions with humans, such as a human handing something to the robot and vice versa. More commonly, we see indirect human-robot interactions, such as an operator walking over to the cell and placing a tray of products for the robot to pick from.

When installing a collaborative cell, remember that the risk assessment is done based on how much the operator or the human resource will interact with the robot. And, of course, the higher the interaction, the more complex the risk assessment will need to be.

You need to make sure that every single scenario is covered so that there are no sharp edges, pinch points, or any excess force that can hit the human resource. So, the further away the human is from the robot, the lower the level of concern around the risk assessments. Remember that no matter the precise level of human-robot interaction in the application, the risk assessment has to be done.

Additional considerations include the speed of the robot, the payload it’s handling and the nature of the payload (for example, whether it has sharp edges). Light curtains and other safety-related sensors are available to help with collaborative applications. In fact, most out-of-the-box collaborative palletizing systems come with some form of proximity sensor in addition to the standard cobot safety features. This means that if an operator comes close to the robot, the robot will slow down so that the force will not be sufficient to cause injury.

Software can make your cobot risk assessment easier by allowing you to define obstacles and boundaries that the robot and end-effector will not go beyond, as demonstrated with D:PLOY software. Image courtesy of OnRobot.

POWER OUTAGES

Don’t forget to consider the scenario of a power outage that strikes when the robot is in operation. With the wrong equipment an outage could cause items to fall from your gripper. Avoid accidents and injury by selecting collaborative grippers that are able to keep the grip/suction on your parts even when power is lost.

SOFTWARE SUPPORT

While performing the risk assessment is a job for human safety specialists, software can help support and simplify the risk assessment process.  For example, our software, D:PLOY, simplifies and automates the deployment process, allows users to input boundary settings and obstacle avoidance based on a detailed 3D rendering of the cell.

You can see where the robot is in its environment, and you can then drag and drop obstacles into the workspace of the robot to match obstacles in the physical world. Once those boundaries have been determined in the software, the robot will not move outside them. If you want to ensure the robot does not move within a specific area, such as the space in which an operator normally stands, simply define an obstacle boundary in in the software.

SAFETY SETUP

While software can help make your risk assessment process easier, you will ultimately rely on things like the cobot’s safety system, external scanners or light curtains to finalize your safety setup. Conversely, if you just put a cage around the cobot cell and install an emergency safety stop that’s triggered whenever the cage is opened, then the risk assessment will be pretty easy.

However, a wide assortment of technology and tools are available to address risk assessment findings, and enhance the safety and efficiency of collaborative applications. For example, we produce award winning gripping technology and electric, vacuum and magnetic grippers; force/torque sensors, a 2.5D vision system, screwdriver, sander kits and tool changers. E-learning platforms also make it easier to deploy and operate cobots, regardless of previous robotics experience or skill levels. WMHS

Kristian Hulgard is General Manager – Americas at OnRobot. OnRobot produces a wide assortment of tools and software for collaborative applications. Supported by the free Learn OnRobot e-learning platform, OnRobot makes it easy to deploy collaborative automation on tasks such as packaging, quality control, materials handling, machine tending, assembly, and surface finishing regardless of skill level or previous robotics experience. Learn more at https://onrobot.com/en.