Car wash

Safe battery change on electric buses

Whereas on "conventional" electric vehicles the battery usually remains on board, "battery swapping" follows a different approach: The emptied batteries are replaced with recharged batteries. The safety solution is an important part of safe and accident-free procedures.

A system that is safe for humans and machines is needed if robots are to replace batteries autonomously.

In order to replace or repair batteries, the electric vehicle has to be placed in a separate servicing area. Because the battery swapping area is relatively open, barriers are not used to control entry and exit of the electric vehicles and robots operate in the battery swap area, this is a danger zone in which the following main danger factors must be considered:

  • People must be prevented from entering the battery swap area while the robots are operating.
  • After the driver has driven into the zone and before the robots start their task, it must be ensured that the driver has already exited the zone.
  • As soon as an emergency occurs, it must be possible to place the robots in the safe stop state either from the central control room or locally.
  • The speed requirement of the electric machines of the robot system is monitored. As soon as the set speed range is exceeded or undershot, the robot is switched to the safety state.
In summary, a design with safety functions is required for the battery swap zone.

Safety relay type selection

The safety concept for the battery replacement system has three components:

  • Monitoring to ensure that no one enters the safety zone
  • Monitoring the safety of the robots
  • Monitoring the safety from the control room and locally

In the 45-mm version, safety relay 3SK2 incorporates 20 safety inputs and 6 independent safety outputs in order to implement such a solution.

Additional 5 safety output modules could be retrofitted. The functions of all safety inputs and outputs can be configured in any way with the Safety ES software. The safety status can be monitored directly on the front LCD screen.

The right relay for speed monitoring

Speed monitoring and static speed monitoring of the travel and lifting motors is required for the robot system.

In addition, feedback of the outputs to the safety relay must be ensured.

To meet these requirements, we recommend speed monitoring relay 3TK2810-1. This relay has function settings for monitoring the speed and static speed and supports many rotary encoder types. Parameters can be set and the status monitored on the LCD screen.

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