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Cobots: addressing current issues

29 September 2017

Control Engineering Europe looks at some of the current issues related to the use of collaborative robots in the manufacturing environment.

Collaborative robots have become one of the latest the industry buzzwords and to address the obvious safety issues related to the interaction of robots and humans the ISO/TS 15066 was published in February 2016 providing guidelines on safety in collaborative robot systems. It lists four types of collaborative operation:

a. Safety-rated monitored stop
b. Hand guiding
c. Speed and separation monitoring
d. Power and force limiting 

When it comes to the safety-rated monitored stop, the robot system needs to stop before the human operator can access or be exposed to any hazard in the collaborative workspace. Only when there is no human operator can the robot move as a non-collaborative robot. In other words, either the robot system or the human operator moves, not both at the same time. This method cannot utilise the advantages of collaborative operation and it requires safeguarding of a traditional industrial robot.  The benefit that it offers is the ease and speed to resume automatic operation.

With respect to hand guiding operation, the human operator uses a hand-operated device and the robot system moves based on motion commands of the operator. It is a kind of manually controlled operation in that the operator is in direct control of the robot system’s operation.  This is considered automatic, not manual operation.

In reality, only option c and d in the above list are used for beneficial collaborative applications in industry, according to Roberta Nelson Shea and Seungmin Baek or Universal Robot. “Currently, most collaborative robots are inherently designed to limit power and force. If the robot detects a certain level of power or force, the robot stops to protect the human operator. Due to the safety-functions for motion, speed, force, and power monitoring, the human and robot system can move at the same time in the same workspace,” said Shea and Baek. ”As long as the risk assessment is conducted properly, traditional guards and protective devices are not needed.”

The power and force limiting method assumes that the human can contact the moving robot system. “It is important to consider the impact to human body during the risk assessment process. To prevent pain or injury, the application also restricts payload and speed. As a result, the robot speed will likely be too low to be useful for high risk applications,” continues Shea and Baek. “In order to use the speed and separation monitoring method, external safety devices, such as a safety scanner, have been used to lower speed as a person approaches the collaborative workspace.” 

Assessing risk
So, improvements in safety technology are now allowing industrial robots to be used in collaborative operations, providing many of the same benefits that a cobot brings, along with increased speed and accuracy. Of course, this collaboration can only be implemented after the appropriate risk assessment — but that is no different than when choosing a cobot. “What many are unaware of is that almost any robot is capable of collaborative operation with the appropriate safety mechanisms in place,” said Nigel Smith, CEO at TM Robotics. “It is the application that defines the ability for human and machine to collaborate. Some manufacturers may specify a cobot assuming it will work without caging. However, they may find their risk assessment shows the need for a safety cage or force limiters to keep human workers safe. The additional charge of these safety features would render the total cost of the cobot similar to that of an industrial robot, but without the additional capabilities of speed and accuracy. Suddenly, this initially low-cost, low-risk investment in cobots isn't turning out as planned.

“The growth in the cobot market represents a view that cobots can be a good first step towards automated processes. If the application doesn't require safety guarding, then the initial investment is low. However, as applications evolve, multiple cobots may soon be required for scalability, and the cost of the additional equipment and additional human workforce will soon exceed the cost of an industrial robot, and you will still lack speed and the benefit of unattended production. It’s imperative that business owners assess the application and the needs of their business’ future carefully before making their decision and carefully consider one important question — is a cobot actually what you need? 

Complementing the workforce
Martin Walder, VP industry at Schneider Electric in the UK, believes that the breakthrough to ensuring continued modernisation of production facilities lies in human-robot collaboration, where compact and easy-to-use synergic automation will drive the market in the coming years. He said: “In many cases, robots can be employed to complement rather than replace workers. This concept, often known as ‘cobotics’ teams operators and machines in order to make complex parts of assembly processes faster, easier, and safer.
 
“In meat packaging lines, for example, part of the process involves handling products with a high degree of variability which is often more suited to humans, whereas the remaining packaging process can easily be performed by robotics. This cobotics collaboration, with both humans and robots working within the same area and packaging line, provides a more flexible and efficient outcome for all.
                
“Robotic functionality provides full adaptability to new processes, reduces footprint requirements and even enables the automation of manual tasks  – often the most dangerous, monotonous and/or dirty ones which help keep our workforces safe.
 
Walder says that ensuring the safety of humans in collaborative scenarios should always take priority and this can be supported through both technology advancements and upskilling staff. “Tapping into advances in computer vision, information technology, and engineering can enable manufacturers to deliver real-time information and guidance at the point of use,” he said. “These insights help to notify and inform operators of the quality risks involved and the appropriate action to be taken. In addition, a conscience investment in upskilling workforces on how to mitigate the risks on the factory floor when working alongside bots will go a long way to ensuring the safety of all those involved.
 
“As Industry 4.0 remains central to global manufacturing moving forward, where automation developers introduce more sophisticated sensors and more highly functional robotic equipment, the collaboration between humans and machines interacting on the factory floor will be imperative. 
 
“The health and longevity of the industrial sector will boil down to our ability to meet the high-performance demands of modern production lines. Only when we have greater collaboration with greater control, will we have the opportunity to profit from the true benefits of robotic alliances and have a holistic approach capable of optimising the production process for the modern Industry 4.0 environment.”


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