Rise of the machines: Done safely
Rise of the machines: Done safely
Industrial automation leader Omron explains how humans and robots can safely share collaborative workspaces.
Industrial robots are generally designed for one of three tasks: high-speed movements, high-payload movements, or high-precision placement. There are readily apparent health and safety risks to workers when operating these robots (for example, if a large robot is moving heavy payloads at high speeds in proximity to workers). Consequently, few would question the need to use hard guarding, safety interlocks, and safety sensing devices to isolate industrial robots from human contact during operation.
Cobots: a collaboration between human and machine
Collaborative robots (cobots), on the other hand, are not high-speed, high-payload, or exceptionally high-precision devices. Instead, they are designed to function alongside workers in a collaborative space, boosting production and reducing employee fatigue by automating repetitive tasks. They have been introduced as being safer than industrial robots thanks to their design profile and built-in safety features, but this conception is contrary to established safety standards.
As a hybrid technology that collaborates in the industrial automation space, cobots are a bridge between isolated industrial robots and human assembly line operations. That said, more effort is needed to demystify cobots; the early expectations and assumptions surrounding this technology have led to some disappointment in their performance. Early adopters have found perceived deficiencies such as built-in safety features that are neither comprehensive nor failproof, a slower overall motion relative to conventional robots (making cobots seem safer), and smaller payloads.
Conversely, there have been unexpected upsides for some users due to the features and performance of cobots. These include the ease with which they can be taught compared to standard robots, their highly intuitive software, and the fact that robot integrators are not required.
The need for comprehensive safety solutions
Because of the mismatch between perception and reality regarding cobot features and usability, a comprehensive safety solution cannot be ignored. This drives the need for a standards-based risk assessment to consider application-specific risks posed by each particular cobot, as well as the creation of an external safety package to supplement its built-in safety features.
The cobot work environment introduces new terminology. The area in which it operates, along with associated tooling or extra equipment, is known as the collaborative workspace. As defined by ISO 10218/ANSI RIA 15.06, this is the space within the safeguarded area where cobot and human operator can simultaneously perform tasks during production. Similarly, ISO/TS 15066 defines it as the area within the operating space where the robot system and a human operator can perform tasks concurrently during production. Risk mitigation becomes more important when operators and cobots share a space.
Cobots have features designed to help mitigate risk, but they don’t eradicate potential danger. They include force feedback, speed monitoring, low-inertia servomotors, elastic actuators, lightweight frames, collision detection technology limiting power and force to levels suitable for contact, and other features.
Cobots’ defining ability is force and speed monitoring; the ISO 10218 safety standard and the technical specification in RIA TS 15066 define cobot safety functions and performance. Under TS 15066, cobot force and speed monitoring is set based on application data, human contact area, and workspace hazards, while it provides further detail on force against the human body.
Switching modes key to safety and efficiency
Cobot design includes a feature absent in standard robots: the ability to switch between collaborative and non-collaborative modes. Cobots enter the collaborative mode when their speed drops below the 250mm/sec per axis cut-off speed. ISO 10218 has defined this cut-off as a relatively safe speed for humans in the robot’s proximity, and the cobot can safely “bump into” a human without causing grievous harm. Combining the force feedback with speed sensing, the cobot can respond by stopping if either it or the human exceed the set limits.
By integrating a safety detection device that detects the presence of a human nearby, such as a scanner or set of light curtains, the cobot can alternate between this lower speed and its maximum design speed, which is an option when the human has vacated the area. It is necessary to perform a stop time measurement to set the safe distance for the detection device(s).
This ability to switch back and forth enables the cobot to be as safe as possible when a human is nearby, and to be at its most efficient at carrying out tasks when humans are not present. The supplementary safety measures not only enhance its ability to operate safely with humans and comply with safety standards, but also help to optimise its usability and offer the best return on investment.
Holistic safety assessments
Part of what makes a cobot an ideal, safe workspace partner is the potential for easy integration of safety devices into its work environment. With hand-guided teach functions, built-in safety functions, available vision packages, safety device connections, and software monitoring capability, cobots are prepared to function with an integrated safety package.
Maximum operator safety is achieved through an understanding of the functionality of both the cobot and its comprehensive safety package. A safety risk assessment establishes a standards-based functional safety performance level.
Since cobots are designed to share a workspace with humans, the entire workspace and its peripherals must be considered. Beyond the cobot itself, other factors play into safety. To understand all the elements at play, a safety risk assessment based on industry safety standards is needed to establish the required safety level.
Safety solution designs should be validated. Safety risk assessments not only consider the cobot’s intrinsic design features, but look at the collaborative workspace environment holistically. This includes cobot gripper and end effector risks, payload dangers (mass, movement envelope, and movement profile), proximity to cobots, severity of potential risk, frequency of collaboration and non-collaboration, supplementary safety devices added to cobots, and desired safety protection levels.
The value of a cobot in terms of both performance and efficiency is fully realised by supplementing intrinsic safety with an external safety solution. A standards-based safety risk assessment identifies where supplementary safety devices are needed to ensure worker safety when working near a cobot, and how to optimise a cobot’s efficiency potential when in collaborative and non-collaborative modes.
If properly safeguarded, cobots can also play a role in the Industry 4.0 work environment. This technology has the required flexibility, ease of use, human-machine collaboration capability, and interoperability between vendors.
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