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Safety grippers

Humans and robots working together

Schunk, known for its safety grippers, has presented safety concepts for each of its mechatronic pillars. The goal: a method for collaboration between humans and handling systems. CAN plays a role in the control of the grippers.

Man and robot will work hand in hand in the future – safety gripping systems create the basis (Photo: Schunk)

RALF STEINMANN, DIRECTOR OF THE BUSINESS UNIT for gripping systems at Schunk, is convinced that human-robot cooperation will extend throughout the entire production process in the medium and long term. "Instead of working next to each other in mechanically separated spaces as at present, man and robot will cooperate in a barrier-free environment in the future. Especially in assembly, there will be a drastic increase in the number of collaborating systems," Steinmann explains. While present-day systems generally have to be switched to a safe position in order to remove defective parts, to supply new parts, or for troubleshooting, in the future the respective system components will only have to be temporarily slowed down or stopped for the duration of the human intervention. As soon as the safety zone is free, the system will automatically return to regular operating mode.

The EGN and EZN safety gripping systems are certified according to DIN EN ISO 13849 (Photo: Schunk)

SLS, SOS, and STO functions

With the EGN and EZN safety gripping systems certified in accordance with DIN EN ISO 13849, Schunk established a benchmark in 2014. In combination with the ECM controller and the ECS safety module, the ready-to-use modules enable SLS (safe limited speed), SOS (safe operation stop), and STO (safe torque off) functions. They fulfill performance level d and SIL-3.

The EGN/EZN is controlled by an ECM controller, which features connection technology, either via Profibus (up to 12 Mbit/s) or a CAN network (up to 1 Mbit/s). This facilitates commissioning and parameterization via a PC, USB drive, or rotary code switch. In order to use the certified SLS, SOS, and STO functions, the gripper and the controller are supplemented by the ECS safety module, which in turn monitors the resolver. No modifications to the gripper are necessary for this purpose. Due to the modular design, the safety functions can be retrofitted. Depending on the size, gripping forces of up to 1000 N are possible.

When they are used together with pressure mats, door switches, light curtains, or 3D cameras for room monitoring, it is possible to define different safety zones without having to completely interrupt the production process by means of emergency shut-downs in case the contact between man and machine is too close. Instead, the grippers either switch to a safe limited speed or a safe operating stop, depending on the activated safety zone. As opposed to existing solutions on the market, the two safety gripping systems are supplied with power continuously in case of a safe operating stop, so that gripped parts are held reliably even without mechanical gripping force maintenance. As soon as the safety zone is released, the grippers switch back to the regular operating mode without delay and without having to restart the system. This will allow new scenarios of direct man-machine cooperation.

The gripping force, speed, and finger position of the modules can be adjusted and controlled during the handling process. A resolver, which is connected directly to the motor, continuously monitors the position of the servo motor and enables exact positioning of the gripper fingers.

The ECS Safety module transforms the EGN and EZN grippers into certified safety gripping systems, without modification (Photo: Schunk)

Safety strategy for all pillars

Schunk has developed safety concepts for each of its mechatronic pillars. While the "alternative" mechatronic modules achieve their safety functions by means of the PILZ safety controller and redundant monitoring, the "adaptable" mechatronic modules allow freedom in the choice of the drive and the safety functions. Users can decide which servo motor and which controller they want to use to define safety functions. It is possible to implement a standardized safety strategy for all components. This applies both to grippers and to rotary or linear modules.

The third pillar of "intelligent" mechatronic modules, which includes the two EGN and EZN safety grippers, uses the ECS safety module to monitor the integrated controller. The acceleration, gripping speed, gripping force, and position can be defined and varied. All control and power electronics are integrated in the ECM controller. Since the ECS safety module can also be added at a later time, this facilitates retrofitting of existing intelligent solutions with safety functions.

The next step in the safety concept is already laid out: in the near future, the ERD miniature rotary module will feature an SIL-2-certified absolute-value transducer, which can be evaluated in order to ensure position and standstill monitoring as well as a safe operating stop and a safe limited speed. The Hyperface interface allows combination of the module with the Bosch-Rexroth Indra Drive CS or Indra Drive Advanced drive control devices and integration in existing controllers.

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