Written by Fotis Dimeas & Keerthi Sagar on 22 April 2021.
Collaborative robots or ‘сobots’ are a class of robots specifically developed to enable direct physical human-robot interaction. This is a paradigm shift from the traditional robots working in cages with total isolation from humans. The primary focus in сobots are their safety features which make them an ideal solution for direct deployment as a plug and play system in many automation scenarios. With minimal to no safety modifications in the factory floor, cobots can be commissioned to work both in the proximity and alongside humans.
What are Cobots and what can they be used for?
Modern cobots are equipped with a plethora of integrated sensors ranging from cameras, light-curtains, force-torque sensors, and tactile sensors. These sensors effectively detect and quickly respond to unwanted human contacts, robot collisions in a cluttered industrial environment, and human intent for robot manipulation and positioning, minimizing any risk. Humans can safely interact and work with these robots to efficiently complete tasks.
Interaction with these robots is very fluidic and intuitive for human operators. In manufacturing, they are replacing mundane repetitive or droning tasks done by humans in material handling, visual quality inspection, picking, packing and palletizing, etc.
Apart from the primary application scenario of manufacturing, collaborative robots have entered unique applications domains such as MedTech, Agriculture. These systems are developed for easy adaptation and use by untrained workers. Cobot manufacturers are constantly focused towards developing operating methodologies involving a very minimal learning curve, making them a great end-user commercial product.
What are the safety issues of introducing cobots?
Since robots and humans will be working alongside and share their workspace without fences, it is of vital importance to guarantee their safety.
The importance of this issue was highlighted at least 80 years ago from the novelist I. Asimov who drafted the first of the famous three laws of robotics: “A robot may not injure a human being or, through inaction, allow a human being to come to harm.”
With the rise of collaborative robots, a lot of research is being conducted towards this aim. In CoLLaboratE, we are trying to address this issue at multiple levels including both hardware and software.
How is CoLLaboratE contributing to reducing safety risks in cobots?
The objectives of the CoLLaboratE project are to provide robots with adaptive skills during close collaboration and to develop advanced safety strategies. Some examples of the shared workspace are when a robot and a human perform assembly over the same component and one can get to the way of the other. For that purpose, we developed a new robotic skin that not only detects contact of the robot with the environment but also discriminates the type of contact. Using deep learning, the robot can detect voluntary contacts of the human from involuntary and react appropriately in a safe manner.
In addition, a novel methodology that has been developed in the CoLLaboratE project uses 3D cameras to track the movements of the human and shapes the trajectory of the robot to avoid collisions. While the robot performs its operation autonomously, it can change its motion so that it keeps a safe distance from the human. Moreover, a second safety level has been developed that is always active and makes the robot compliant with external forces. So, if the camera fails to detect a sudden motion of the human and the contact isn’t avoided, the robot is compliant and the contact forces are small. These features increase the safety of the operator and allow a fenceless collaboration environment.
Do industries need to integrate cobots differently from conventional robots?
The type of robot used for performing a task are mainly dependent on the complexity of the task, size/payload of the object, and Return on Investment (ROI). Careful decisions should be made while choosing a cobotic solution over a traditional robot. Although cobots are designed to act as a very flexible system, industries need to decide the role of the cobot in the production line based on these four types defined by International Federation of Robotics (IFR): (a) Co-existence: robot and a human work alongside one another in the same workspace, but with no direct overlap in the minutiae of their labor, (b) Sequential collaboration: robot directly works alongside operator but not on the same product at any instant of time, (c) Responsive Collaboration: robots that respond directly to the actions undertaken by the human operator. They react appropriately to the process time after the human operator performs a more complicated task along the assembly line, (d) Co-operational cobots: they operate alongside humans at the same time while working together towards the same task. Task and operator planning greatly benefits from this type of prior identification.
- Not all existing robotic tasks can be replaced with Cobots, tasks which demand very high throughput, payload and speed are not ideal for cobots as they operate at a much-reduced speed.
- Appropriate use-cases should be chosen such as involving high-variant products, repetitive operations inside a human-in-the loop task, inherently safe assembly or operation use-case. The application is the most-critical factor to consider while choosing cobots.
- Cobots are best suited for highly synchronous human collaborative tasks which will offer a very high ROI and reduce operator idle time.
- Cobots provide distinct independence to the manufacturers in the perspective of shop floor planning, conventional robots demand extensive prior planning for installation and commission whereas cobots can be easily integrated into an existing line with minimal changes and cost. This minimizes both labor and maintenance costs. Also resulting in huge savings of factory floor space.
- Traditional robots are predominantly allocated for a particular task and an expert technician performs detailed programming with proprietary software to achieve the required accurate robot movements.This method is completely re-oriented in collaborative robots, where a very user-friendly approach of providing an intuitive 3D interface for easily positioning the robot and also an important feature of manually guiding also called Teaching by demonstration is available. These features eliminate the need for expert technicians to reprogram the robot for different tasks, hence reducing robot idle time and making the robot multi-functional. With this functionality, businesses can shave off operator’s robot technical training costs.
- Cobots with their proximity to human operators require with absolute certainty safe and reliable network infrastructure at all times to guarantee real-time safety-critical service.
- Cobots offer businesses to evolve rapidly with its artificial intelligence capability which was not possible with traditional design driven robots. Industries need to take advantage of this feature by enabling a cyber-physical architecture.
- Industries need to follow the ISO/TS 15066 technical specifications while integrating the cobotic solution to ensure a safe system.
- Detailed risk-assessment analysis and Key-Performance Indicator (KPIs) needs to be performed comparing the choice of traditional robot and cobot, and only with low-risk outcome should a cobot be chosen.
Are there any differences in cobots safety and safety regulations depending on the industry?
With the growing interest in human-robot interaction (HRI) and Industry 4.0, it was deemed necessary to formulate safety guidelines to provide clarity and regulations for safe human-robot collaboration (HRC). The International Organization for Standardization (ISO) has provided a detailed technical specification for safety associated with Cobots, ISO/TS 15066: Robots and Robotics devices – Collaborative robots. The technical report provides in its content, a comprehensive guidance on conducting risk analysis for a collaborative robotic application. The central objective of this specification is that if contact between cobot and humans is allowed, and if incidental contact occurs, then the contact shall not result in onset of pain or injury to the human.
ISO/TS 15066, an evolving technical specification to become a future standard, has built upon the existing robot safety standards: EN ISO 10218-1:2011 (hardware and functional safety characteristics that a collaborative robot has to fulfil) & EN ISO 10218-2:2011 (allowed behavior of the COBOT in Human Robot Collaboration applications, through the definition of the collaborative modes and the rules for the integration in the collaborative workspace), where four collaborative features for a cobot are described:
(a) Safety Monitored Stop: When robots, such as traditional robotic manipulators are working alone, but from time-to-time human operator enters the robot’s workspace to either work on the part handled by the robot or performs a secondary operation, the robot performs a complete halt and is in standby mode waiting for the human to leave the restricted workspace.
(b) Hand guiding: Teaching the robot to perform a particular task, where the human manually holds and positions the robot to demonstrate the manipulation required by the robot. Additional information on how much pressure and force the robot needs to exert is demonstrated by the human with aid of force sensors on the robot.
(c) Speed and separation monitoring: an extended version of Safety monitored step, where the robot slows down in response to humans entering a restricted robot workspace.
(d) Power and force limiting: robot appropriately reacts to external and unwanted forces during its operation by performing the most safe response concerning the human inside the collaborative work area. Contact of robot to human’s head, throat & neck should be prevented
The technical specification provides detailed numerical limits for the physical parameters such as force, velocity, power and methodologies which embody Cobots.
Depending on the industry, the suitable collaborative mode is used such as, heavy machine industry for direct part loading or unloading to end-effector, Work-in process inspections (safety rated monitored stop), in automotive assembly for robotic lift assist, highly variable applications/product industry (hand guiding mode), simultaneous assembly tasks and direct operator interface in electronics manufacturing (speed & separation monitoring), and small or highly variable applications, MedTech industries (Power and force limiting). The operating modes can be used singularly or in combination when designing a collaborative application.
The use and application of standards is voluntary in most countries and only become mandatory if they are referred to in contracts, laws or regulations. Safety standards are thus recommendations which, when followed, provide legal certainty and thus acts as a technical reference that end-users have to consider as a best practice.
The ISO/TS 15066 are prescribed only for industrial robots, although the safety principles documented can be applied to other areas of robotics. They should be followed in adherence to other safety regulations pertaining to the specific application scenario. Certain safety regulations are not exclusively declared yet for human-robot collaborative (HRC) components such as mobile robots (ex: AGV: autonomous guided vehicle, AMR: autonomous mobile robot), Grippers within the HRC framework. Existing standards such as ISO 13849, IEC EN 62061 and Machine directive (2006/42/EC, for Europe), ISO/TR 20218-1 2018 (Grippers/End-effectors) and other technical standards can be adapted as a reference depending on the industry, application, functional and safety similarities. Considering the mechanical risks involved due to unwanted contact to the human operator, a categorical list of general international deliverables regarding the safety of machinery requirements for HRI approach is:
- Laws & Regulations: Machinery Directive (2006/42/CE, Mandatory for European Union)
- “Type A” standards, basic safety standards valid for all types of machines: ISO 12100:2010 (Safety of machinery- General principles for design, Risk assessment and risk reduction)
- “Type B” standards, generic safety standards valid for one safety aspect or one or more type(s) of safeguard: ISO 13849-1:2015 (Safety of machinery-Safety related parts of control systems—Part 1: General principles for design), ISO 13850:2015 ( Safety of machinery, Emergency stop function, Principles for design), ISO 13851:2002 ( Safety of machinery, Two hand control devices, Functional aspects and design principles), ISO 13855:2010 ( Safety of machinery, Positioning of safeguards with respect to the approach speeds of parts of the human body), IEC EN 62061:2015 (Safety of machinery-Functional safety of safety related electrical, electronic and programmable electronic control systems), IEC 60204-1:2016 (Safety of machinery. Electrical equipment of machines. Part 1. General requirements).
- “Type C” standards, detailed machine safety standards, valid for a particular family of machines: ISO/TS 15066 (Robots and robotic devices-Collaborative robots), ISO 10218-1:2011 (Robots and robotic devices-Safety requirements for industrial robots-Part 1:Robots), ISO 10218-2:2011 (Robots and robotic devices-Safety requirements for industrial robots-Part 2: Robot systems and integration)
These standards and technical specifications try to encapsulate the major factors and scenarios to ensure safety in a human-robot collaboration application. The hierarchical consideration and following of these standards in addition to other industry specific regulations while selecting and designing Cobots and workcells will ensure a strict adherence to a safe industrial collaborative robot.
Finally, CE Marking (defined and regulated in the “Machine Directive 2006/42/EC” which is a mandatory European regulation) demonstrates conformity with the essential safety requirements laid down in EU legislation. Risk assessment is conducted on the application with the precisely specified constraints and components and re-evaluated with additional measures if possessing a high risk. The CE mark can only be affixed by the manufacturer if the risk assessment confirms a sufficiently low residual risk, hence declaring the product safe.