Requirements for safe human-robot-collaborations

It is impossible to imagine our production applications without robot systems. They ensure productivity, quality and perform heavy and dangerous tasks. Since industrial robotic systems are assessed with high risk, protection concepts are usually designed in such a way that robots and humans work separately from each other in terms of location and/or time.

 

Author: Ulrich Hochrein

Except for training and maintenance, which are subject to special requirements, humans do not directly correspond with the actuators of industrial robot systems. The safety standards EN ISO 10218-1 (requirements for industrial robots) and EN ISO 10218-2 (design specifications and requirements for the robot system) must be observed.

If the application is planned to be safe, new technologies meanwhile make it possible for the robot to collaborate directly with humans - the human-robot collaboration, or MRK for short. In this way, the advantages of robot systems can be optimally combined with human capabilities. In addition, MRK applications allow for novel production concepts. MRK applications thus play an important role in answering overriding questions, such as demographic change, the optimized integration of "performance-reduced employees" and the improvement of general work ergonomics.

BASIC PRINCIPLES OF HUMAN-ROBOT-COLLABORATION

HRC applications are based on protection principles or a combination of different basic principles. These are:

  • Safety-related, monitored stop - The robot stops when an employee enters the shared work area and continues to move if necessary when the employee has left the area.
  1. Manual guidance of the robot - The robot movement is actively guided by the employee.
  1. Speed and distance monitoring - contact between the operator and the robot in motion is prevented by the robot system.

Force and pressure limitation - Contact forces between man and robot system are possible, but are limited to a safe level.

KUKA Greifer frei.pngA common feature of all HRC applications is that security must be performed with precision and integrity throughout the entire application, taking into account all functional and production aspects. However, what can be retrofitted to conventional systems, for example by means of fixed structural separation or additional safety components, functions only to a limited extent or is not applicable at all for HRC, depending on the protection principle.

If the principle of force and pressure limitation is applied, HRC-compliant design is essential for plant development from the outset. This includes the following aspects:

  • Selection of an appropriate HRC system
  • Safe design of grippers and tools
  • Consideration of part properties (geometry and mass)
  • Work processes, limitation of working space and speed
  • Production technologies used

In principle, there is no intrinsically safe HRC robot. Also, the use of an HRC robot alone does not result in a safe HRC application. For example, if a sharp scalpel or pointed needle is used as a "robot tool", any HRC robot equipped with it will cause injury. Therefore, a decisive factor in assessing safety is not only the force, but also the pressure (power / effective area) that the HRC system can cause in the worst case.

Tool and part geometries therefore determine the specifications of possible travel speeds and performance specifications, for example the torque.

LIMITATIONS OF HUMAN ROBOT COLLABORATION

The limits for tolerable forces and pressures are defined for different body parts in ISO/TS 15066. A validation of the force and pressure specifications by measurement with a compliant measuring system is undoubtedly necessary. A risk assessment is used to define the safety concept with safe working area restrictions of the robot and the affected body parts. From this, the possible speeds can be derived.

However, there are still no useful tools available for this purpose, for example, in order to derive a safe traversing speed of the HRC robot by specifying geometries and pressure limits. This makes early cycle time specifications difficult, because only validation under nominal conditions can show whether the system exceeds individual limit values critically.

The legal framework for the HRC application is the Machinery Directive 2006/42/EC. The relevant standards are:

  • EN 10218 Part 1+2: Robot and robot system
  • EN 12100: Safety of machinery - Risk assessment and risk reduction
  • EN 13849 Part 1+2: Safety-related parts of control systems

ISO/TS 15066 "Robots and Robotics Devices - Collaborating Robots" is an unlisted standard that describes HRC applications with forces and pressures as the only international set of rules.

CONCLUSION

EDAG PS's experience with HRC applications shows that the limits of HRC applications are often underestimated. HRC robots are considerably reduced in performance. Speeds, accelerations, possible forces and torques are not equivalent to standard industrial robots. Due to safety requirements, these are further reduced by the applications. In HRC operation, the cycle time specifications are very often not fulfilled.

Different production processes are not easy to implement due to payload or other production factors such as recoil. Furthermore, the performance of the control system and the functional capabilities of the HRC system are important factors. This also explains the large price dispersion of HRC robot systems on the market. The correct MRK robot selection is thus the first decisive step for the functionality and safety of the application.

In addition to technical safety, the psychological impact on affected employees should not be underestimated and must therefore be taken into account in good time. In addition to involving affected employees, the applications should be designed in such a way that movements and actions are predictable for the affected employees. Visualizations or special signal movements before the actual MRK movement increase the acceptance of the employees involved.

EDAG PS has many years of experience in the field of robotics and machine safety for HRC systems. Our services include

  • Specification of systems,
  • Selection of the HRC robotic system,
  • Safety concept and risk assessment,
  • Planning of the overall system,
  • Realization of the application,
  • Safety validation,
  • Seminars and validation.

 

As the author of this blog post, I am happy to answer your questions. You can reach me by e-mail at: ulrich.hochrein@edag-ps.com

Source cover picture: © Ford/Friedrich Stark