Omron - Cobot safety strategies: Collaborative applications that are safe and effective

Cobot safety strategies: Collaborative applications that are safe and effective

By Peter Lange, Business Development Manager Robotics, Omron Europe

Collaborative robots (‘cobots’) are a key aspect of Industry 4.0 and the ‘factory of the future’. They can be used in a wide range of industrial applications. Because they have various integral safety features, they can work with or near people and can also adapt easily to changing needs. This means that the productivity of many repetitive tasks can be significantly increased, enabling manufacturers to reap the benefits of a high return on their investment.

The safety features of cobots include lightweight  body, collision detection technology and minimised pinch points. However, further safety measures might still be needed for specific applications - including the  end effector, the product and other equipment  in the collaborative workspace (a safe space where robots and people can work together). For a cobot application to be successful, it must incorporate safety considerations based on comprehensive risk assessments.

So, what are the industry safety standards and solutions that will enable a company to gain the maximum value from cobots within a collaborative workspace?

Safe teaching and operation

Prior to teaching, the robot must be stopped before the operator enters its workspace, even if its force and speed limiting functionality has been activated. Alternatively, a safety device (e.g. an area scanner) must carry out a protective stop as soon as the operator is detected.

The operator can use a simple trigger, button or mode selection to activate teaching if safety force and speed monitoring are in operation. If not, a three-position safety enable is required. According to the safety standards, the teaching mode transition must be deliberate, mustn’t lead to any unexpected motion, and mustn’t create additional hazards. The operator must be aware of surrounding equipment and possible safety issues at all times. To enhance operator safety, it’s possible to enforce limits on motion: for example, space and soft axis limits.

Prior to operation, the operator must vacate the safeguarded space. This can be verified by safety sensors or additional operator verification. Intentional mode selection is needed to re-enable the robot for operation.

Safety in the collaborative workspace

Cobots operate near other equipment that could be dangerous. It’s therefore important to list and map out all additional equipment in the collaborative workspace (which must be clearly marked). Each device must be assessed for potential hazards and for safety sensors that could prevent human and equipment damage.

Non-collaborative safety-rated equipment that might need safety devices includes material handling; tooling; grippers and actuators; and machines. Safety devices can usually be integrated easily into a cobot application.

Several solutions can be used to safeguard the collaborative workspace. In open areas and applications with low hazards, these include safety area scanners and mats. In gated or limited areas with more hazardous applications or high-speed operations, safety light curtains and safety switches can be used. In areas with active hazards or operations that could cause a hazard, operators can enable a ‘deadman’ switch, which automatically turns off if the user stops exerting pressure on it.

For maximum safety in collaborative operations, manufacturers must validate the safety of their cobot applications across all operations. There are some guidelines they can follow when evaluating the safety of a robot while performing a given task with a human operator. Some dangers, such as drive and power hazards, might still exist even if the robot isn’t moving.

Operator safety

To protect operators, before starting a cobot or recovering from an emergency stop, there must an intentional act to enable the robot. For example, when an operator activates an e-stop, the robot shouldn’t be able to re-enable automatically but should first need verification from a second operator.

During the design and safety setup, hand guiding must only be allowed if the robot has stopped; there has been intentional mode selection; and speed and force monitoring are active. If hand guiding is activated without a stop command or safety input, this should initiate a safety stop and fault.

For the automatic operation of a cobot, the operator must make an intentional mode selection that requires all safety devices and conditions to be validated.

For validation, a safety assessment review should be made of the surrounding areas and equipment, and a safety remediation service performed if necessary. Safety service groups should make an onsite inspection of the safety of equipment; confirm certifications; verify safety parameter settings; and finally document the completion of the validation.

Specific safety considerations

1) Machine tending

Experts who have completed many inspections and safety assessments report that machine tending applications are one of the industry’s top safety concerns. For maximum safety, manufacturers should use a safety-rated gripper to protect operators against injury. They should also investigate whether the product presents any dangers (such as extreme heat or sharp edges).

2) Material handling

Material handling applications that benefit from cobots include picking, packing, palletising and sorting. For safety considerations, the wide use of these applications makes them a site-specific solution. Operators and other workers often move or transport other materials around the cobot, so additional planning is needed to avoid hazardous contact.

Safety-rated grippers are currently rare: manufacturers tend to use pneumatic grippers, with potential safety issues relating to impacts and the loss of power or suction. Application designers must also investigate whether the product presents any dangers that could cause problems if it was dropped.

3) Assembly 

Assembly applications that use cobots often involve special tooling and close collaboration with operators while also requiring high-speed operation zones. The extensive variety of custom end-of-arm tooling makes these applications especially complex. If multiple robots are involved, application designers must carefully co-ordinate the safety solutions for each one.

For all three of the above areas (machine tending, material handling and assembly applications), it’s very important to review the entire area for the risk of an operator being trapped or clamped by the robot and nearby equipment; and for any heavy or hazardous products.

Conclusion

Cobots are usually considered as safe for use with people. However, they still need risk assessments throughout to ensure the safety of human operators. It’s vital for manufacturers to consider all of the potential hazards associated with hand-guided teaching, as well as possible issues when the robot is involved in an emergency stop.

Designers of automated machine tooling, material handling and assembly applications should look at all of the interactions between the cobot and the human operator, along with the risks of clamping or entrapment, and the dangers from end-of-arm tooling due to high heat, sharp edges or other hazards.

In summary, manufacturers that want a successful cobot application that will boost efficiency and productivity must first carry out a thorough risk assessment, and then implement any necessary safety measures.

Visit website