When collaborating robots need an enabling switch
In classic robot applications, a protective barrier separates man and machine in automatic mode to ensure the safety of employees. However, sometimes a person must also move it from inside the protective area - for example, to steer the robot precisely to a position to be approached. The person is then no longer protected. In this case, EN 10218-1/-2 requires a three-step enabling switch as an additional safety function.
Cobots can work side by side with humans in automatic mode without a safety fence. The prerequisite for this is a successfully completed risk assessment. That means:
- The designer has to find out where a collision between man and robot is possible in the so-called collaboration space. This is the area in which robot and human being meet and physical contact can occur.
- Then the designer has to determine that the forces and pressures that occur do not pose a risk of injury to the worker, due to the always active safety functions of the system in automatic mode.
Do Cobots need a three-step enabling switch as required by EN ISO 10218?
Cobots differ from conventional industrial robots because of these safety functions contained in the system. The answer to this question is given in the Technical Specification (TS) ISO TS 15066 "Robots and robotic devices - Collaborating robots". The following is defined there in Section 5.4.5:
... if a risk assessment determines that the risk reduction normally achieved by the use of an enabling device would alternatively be achieved by inherently safe design measures or safety-assessed mitigation functions, the handheld robot controller may be equipped for a collaborative robotic system without an enabling device.
This means: If the robot and the application as such are sufficiently protected, no enabling switch is required. However, this definition leads to further questions:
- Is the risk assessment based on force and power limitation and not on other protective measures such as stopping the robot with a laser scanner?
- When validating the forces and pressures in all collision scenarios, was it established that there is no danger to an operator or user?
- Are the safety functions of the robot system always active and protect the worker in both automatic and manual mode?
If the answer to these three questions is YES, then their robot system can operate without an enabling switch, since the system's always active safety functions replace the enabling switch.