Safety in collaborative applications
Pubblicato il 2020-02-10 13:09:11 UTC a Flexible Manufacturing
Collaborative robots can be used in a wide range of industrial applications. Thanks to various integral safety features, they can work safely with or near people. In addition, they can easily adapt to changing needs. This results in increased productivity, especially in repetitive tasks, enabling manufacturers to reap the benefits of a high return on their investment.
However, 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?
Cobots are more compact than conventional robots and incorporate force and speed monitoring capabilities. When fitted with safety devices that detect anyone entering the collaborative workspace, they can also work at higher speeds.
Two key safety standards that define the safety functions and performance of a cobot are ISO 10218-1, ISO 10218-2 and ISO TS 15066. The latter sets the force and speed monitoring of the cobot, based on application data, human contact area and workspace hazards. There are two types of human contact: transient (non-clamping contact) and quasi-static (involving situations that can cause a body part to be clamped).
Manufacturers who aren’t familiar with the requirements of ISO TS 15066 can hire a safety assessment provider to make the calculations, take the measurements and to recommend improvements to the safety of the collaborative application.
ISO 10218 and ISO TS 15066 also provide guidance on cobot teaching. Many cobots, such as Omron’s TM Series, use intuitive ‘hand guiding’ mechanisms for teaching new tasks. This avoids the need to program the specific movements of the robotic arm. The hand guiding mode monitors force and speed so that the teaching process complies with safety standards.
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.
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
- 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).
- 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.
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.
Other considerations for all three areas include:
- Should the safety controls of other machines be linked to prevent one from operating when another is in a safety stop condition?
- As cobots can be moved from machine to machine and from application to application, how is their safety validated?
- Are there warning zones for the operator that indicate hazards or operation interference?
In a nutshell, manufacturers must first carry out a thorough risk assessment, and then implement any necessary safety measures. This will that ensure a successful cobot application that will boost efficiency and productivity.
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