Mobile operating devices have been firmly established in the field of machine and robot operation for years. Mobile operating devices have become indispensable wherever potentially dangerous movements can and must be triggered at different points. The transmission of safety-critical signals is often realized via cable, although wireless solutions do exist. The latter offer advantages such as greater operating freedom due to the elimination of the cable, easy switching to other operating positions or even other machines or robots. So why is wireless safe machine operation not catching on more quickly despite its many advantages?

Wired versus wireless

In addition to the low level of awareness and acceptance, a more practical reason plays a role: the length of the cable also limits the distance between the operator and the machine. The risk and hazard analysis required for machine and system planning often results in a certain cable length being necessary. As the operator must be able to see the danger zone according to the standard, it makes sense to select the cable length so that the operator cannot simply move over the next machine or corner and enable movements from there by pressing the enabling switch. In practice, the usual distances and cable lengths are 5, 10 and 15 m. With wireless solutions, however, care must be taken to ensure a stable radio connection. This means that a wireless solution must be dimensioned in such a way that robust communication is also possible at a distance of 15 or even 20 meters. The background: If the connection between the machine or system and the control unit is lost, an emergency stop is triggered immediately. The signal quality or signal strength must be so good that there are no radio interruptions. This can lead to a conflict: The maximum availability of a radio solution is just as much a basic requirement as safety certification. However, if the signal strength at the edge of the planned operating area is not throttled due to the desire for high availability, the signal may extend too far for the protective measure selected in the risk and hazard analysis. Alternative protective measures would have to be considered. Structural measures or indoor GPS could be considered, for example. However, the effort and costs involved in planning and implementation speak against this; an organizational solution should be avoided if possible.

Operating area monitoring in the Safe Wireless System

If the operator of the system enters the hatched area, he receives a warning.

© KEBA Industrial Automation

Keba has addressed the problem just described and developed the safety-certified 'operating range monitoring' function for its Safe Wireless System. In those cases in which the risk and hazard analysis previously defined a limitation of the cable length as a suitable protective measure, a virtual cable length can be set by selecting the new function.

If, for example, a cable length of 5 m was defined for robot A, 5 m is set as the value for operating range monitoring when the operating system is commissioned at the connection box, i.e. the base station. A pairing or coupling process is carried out so that an operator can move the robot with the mobile operating device. This tells the operating device how to behave in 5 m operating mode. For the planner, it can therefore be regarded as a solution with a 5 m cable. The operator thus has all the advantages of the cable (limitation) without the disadvantage of the cable (tripping, interference). As the interface to the machine looks the same as that of a wired installation, the installation is also suitable for retrofitting existing systems. Another advantage of the Safe Wireless operating system is that it is easy to switch from one operating point to another, thus reducing the number of operating devices required. If the operator wants to switch from robot A to machine B, he can take the control unit with him. To do this, the Safe Wireless System, including the operating range monitoring, again defines a virtual cable length, this time 10 m, by pairing. The operator only receives a warning when a distance of 10 m is reached. This warning does not yet trigger an emergency stop; the pulsing of the emergency stop and vibration of the device guide the operator back to the intended operating area without disrupting the work flow. However, if the operator moves further away, the system switches to the safe state - it triggers the emergency stop.