Robot-Human Interaction Getting Safer

Advanced technologies are allowing people to safely work in close proximity to and react with robots in manufacturing settings.

Collaborative robotic applications are fundamentally changing the way people and machines interact on the plant floor. This collaboration allows manufacturers and industrial operators to combine the strength, repeatability, and tirelessness of machines with the flexibility, adaptability, and intelligence of humans. The result is an unmatched combination that improves production efficiency and flexibility, while also reducing the physical burden on humans. Such capabilities are more important than ever as companies seek new ways to retain their skilled but aging workers.

According to George Schuster of Milwaukee-based Rockwell Automation (rockwellautomation.com), a key enabler of collaborative robotic applications is the safety technology that allows plant personnel and robots to share the same workspace with less risk of human injury. Advancements in this technology are reducing the need for safety cages, freeing floor space, saving money, and increasing flexibility in the way robots are used on the plant floor.

As Schuster points out, safety technology is increasingly embedded in the robot and in the cell controller. Sophisticated sensors, safety controllers, and communication networks provide real-time safety data that allow robots to automatically respond to potential incidents, such as coming into contact with an operator. Referencing standards provided by the Robotic Industries Association, Ann Arbor, MI, (robotics.org) and various safety-standards bodies that offer guidance on how robots and humans can work together, he provided the following insight.

Implementing collaborative robotics

A robot is not collaborative by itself. A collaborative robot is only one part of a collaborative robotic application—and it doesn’t achieve safety compliance on its own. “The way the system is designed,” Schuster noted, “is critical for optimizing worker safety and enabling compliance.”

According to standards ANSI/RIA R15.06-2012 and ISO 10218, the term “collaborative robotics” describes an automatically operated robot system sharing the same workspace with a human. There are four types of collaborative operations:

Safety-rated monitored stop: This method is the most common and has been used in industrial operations for many years. Sensors in the safety-control system detect human presence and immediately stop the robot if a person gets too close. This is commonly used when people and robots are working in close proximity or with overlapping work envelopes. For example, a worker can load parts directly onto a robot end-effector while it is in a safe-stop condition. This can help improve productivity because the machine can keep running independent from the robot.

Hand-guiding operation: This less-common method allows operators to manually control or reposition the robot for its next task. The operator is in direct contact with the robot arm and can reposition it with hand controls. This generally doesn’t work well for tasks that require fast speeds.

Speed and separation monitoring: Allows operators and robots to work in the same space while maintaining sufficient distance from each other. If a human comes too close to a robot, sensors will trigger the robot to slow down or stop. New safety-sensor technology is making this capability more popular in industrial operations.

Power and force limiting: If a robot accidentally comes into contact with a human, it reduces its force or torque so the human isn’t hurt. This is an emerging method and arguably the least commonly implemented. The robot needs to actually come into contact with a human before it knows to stop. Implementing this method requires understanding the relationship between different levels of force and pain thresholds on various parts of the human body. Studies are being conducted to explore and implement the power- and force-limiting method. For example, standard ISO/TS 15066 outlines findings from one study on pain tolerance, which includes a list of maximum force and pressure levels for each part of the human body to help determine power and force limits. The standard provides some guidance on how to conduct a risk assessment for each part of the human body that could come into contact with a robot.

While most of these methods are intended to prevent humans from coming into physical contact with robots and machinery, Schuster reminds end users that it’s still crucial to follow the functional safety lifecycle when designing collaborative robotic applications. “The lifecycle, as defined by ISO 12100 and ANSI B11:0,” he said, “includes conducting a risk assessment as the first step, followed by defining functional specifications, using proper guarding, and completing verification and validation testing. Following the safety lifecycle is increasingly important as humans and machines work more closely together.”

Assessing risk

A proper risk assessment evaluates the way humans, machinery, and robots interact with each other during all modes of operation. “This type of assessment,” Schuster explained, “helps identify all of the ways a human could potentially come into contact with a robot, evaluate the associated level of risk, and mitigate that risk using appropriate measures.”

ISO/TS 15066 provides guidance for the design of collaborative workspaces and how to conduct a risk assessment for collaborative-robot applications. It supplements ISO 10218-1 and ISO 10218-2. In addition, RIA TR R15.306 provides a recommended methodology for conducting task-based risk assessments to meet the standard.

Collaborative robotics usefulness spans different sectors and applications, from taking over repetitive and heavy-lift tasks, to handling complex assemblies. However, getting there will involve adopting new standards, tools, and risk-analysis methods.

“Organizations that embrace these changes,” Schuster concluded, “will be better positioned to realize the many efficiency and productivity gains afforded by collaborative robots while optimizing worker safety and compliance.” 

George Schuster is the TÜV functional safety expert (FSExp), business development manager at Rockwell Automation, Milwaukee. Experts from the company will speak about collaborative robotics and related technology at the Safety Leadership Conference, Sept. 19 to 21, 2016, in Pittsburgh. Learn more about these sessions and the Smart Manufacturing track, sponsored by Rockwell Automation at safetyleadershipconference.com.