Three ways to ensure collaborative robot success

Collaborative robots, often referred to as cobots, are robotic devices specifically designed to physically interact with humans in a workspace. Conventional industrial robots require the use of safety guarding and other devices to protect humans while they work.

Cobots are gaining in popularity in traditional and non-traditional markets, and can come with a unique set of challenges. While using cobots can be a very similar undertaking to traditional robots, the initial stages of implementation will determine how successful the system is.

There are three phases to consider in the successful application of collaborative robots: Education, assessment and design.

Collaborative robot education

The first phase with any new type of technology is education. How does this device work? What are its capabilities and limitations? How does this impact our understanding of safety?

The unique position of cobots in the robotic field is due to their internal design that includes force-sensing technology. The robot is designed to stop when external forces beyond thresholds are detected in order to prevent injury. The speed and torque allowed during robot motion are restricted to eliminate unsafe contact with human operators. Many cobot models allow programmable control for these settings so that the level of restriction can be tuned to the needs of the system. However, this implies those implementing this technology must be educated on proper safety requirements for automated systems and cobot technology.

A great deal of safety strategy for conventional robots is centered on separation between the robotic automation and human. This includes safeguards like fences to restrict human access to robotic operating areas. In shared workspaces where humans and robots can operate, it is typical to employ monitoring devices like light screens and floor scanners. There also are numerous standards for required operating distances between automation and humans to address these different scenarios.

One of the most important steps for implementation of collaborative technology is designating an authority on safety. It requires a shift in how safety is approached when the intent is for humans and robots to work together. Guidelines continue to develop and it is critical to have a designated champion who is up to date on industry standards and best practices. These regulations include ANSI/RIA R15.06-2012 for general robotic system safety and RIA R15.806-2016 which more specifically addresses collaborative robot technology. Technical report RIA TR15.806-2018 provides additional guidance on testing that may be required when designing a collaborative workspace.

Collaborative robot assessment and planning

One of the most common misconceptions of collaborative robots is using this type of device makes the system safe for humans. In reality, the power and force limiting features only apply to the robot itself. They do not account for any other potential hazards including other components mounted to the primary robot body like end-of-arm-tooling (EOAT).

The second phase of implementing collaborative technology is to properly assess the system safety. A safety risk assessment is a task-based review of potential hazards in the system. Hazards are rated according to characteristics such as severity and frequency and then reviewed for the ability to mitigate the risk through design. This is an ongoing process that should be started in system pre-design and continued through build. Following this type of iterative procedure will ensure safety considerations are met during design and not as an afterthought.

A key component during this phase is to consider what tasks are going to be performed by automation. A general rule of thumb is let humans do what humans do best. This typically includes tasks that involve critical decision-making, high dexterity/perception, technical know-how, and non-routine operations. Robots are best suited to take over workload that is repetitive and routine. Programming can be taught to include decision-making processes, but it is an efficient tradeoff when the decision outputs are limited. With collaborative robots, this task assignment decision is expanded to consider how it will impact the risk assessment.

The assessment phase will rely upon knowledge of collaborative devices and standards. Task assignment will be impacted by the capabilities of the robot itself. Power and force limiting devices work with restrictions on payload and speed to control force. For example, cobot devices from one robotic manufacturer vary in maximum payload capacity from 4 to 35 kg. This is a relatively light range in comparison with industrial robots, which can have payload capacities of more than 2000 kgs. Similarly, arm speed is limited by a significant factor compared with conventional robot models. This can affect the ability of a device to achieve cycle time targets. Each task delegated to a cobot will need to be evaluated against these parameters for feasibility.

Collaborative robot design

The third critical phase for collaborative robot implementation is design. From the perspective of a collaborative space, we must include human contact analysis during the design concept. Even though a cobot is being used, it is not just about the robot. All tooling and devices need to be considered in conjunction with the risk assessment evaluation. Tasks must be reviewed for potential crush and impact contact hazards because humans can be in direct proximity to equipment.

There are specifications in the safety standards to clarify what kinds of forces are acceptable for hazards that involve different parts of the human body. For example, considerations for contact differ for a leg than a human eye. The flexibility of cobot programming and setup makes it necessary to understand these specifications and how they can be tested to ensure proper limitations are in place for operator safety. Tools like simulation can help identify hazards and design resolutions.

Most cobot devices have adopted rounded contours to increase surface areas and decrease forces in contact situations. Similar types of deliberate design choices need to be reflected in other tooling and devices that will be part of the workspace. This may involve the use of special covers to prevent unnecessary access to components that could pose a hazard for a nearby worker. When maintenance tasks are required, the cover can be removed for access.

Sometimes, there are tasks that pose a hazard that cannot be resolved due to the nature of the process. For example, a force that is required to fasten a part to an assembly may be beyond the specification limitation. Another option is to use auxiliary equipment to control human access to a controlled space during that particular operation. This could involve components like light screens that would monitor for human access to the area around the device. The design of the system should provide safety control during the hazard of the insert task, but otherwise allow for a cooperative process between the human and robot.

Cobots are providing unique opportunities for manufacturing and automation companies. However, a lack of understanding about how to approach collaborative technology too often makes the process more difficult. Treating cobots like standard robots will limit the value they can bring. Ignoring safety considerations required in a collaborative workspace will create unnecessary challenges during build. The key to realizing the value is designing the workspace with collaborative technology in mind from the beginning.

Kelly Chalmers is senior project manager at Applied Manufacturing Technologies, a CFE Media content partner. Edited by Chris Vavra, web content manager, Control Engineering, CFE Media and Technology, cvavra@cfemedia.com.

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Keywords: collaborative robots, cobots

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