The general idea for a capacitive sensor is to allow the moving part of a machine to stop before it touches a person. In the following, we focus on collaborative robots as they are both economically most interesting and technically most demanding.
If such a robot approaches and detects an electrically conductive surface in its surroundings it stops. The sensor cannot distinguish between a human being that needs to be protected and an immobile part of its setting. The robot should only stop for the person but not for the immobile part. The robot also stops when its arms come closer together or when it needs to work close to its own stand. The most complicated case poses a cable that is outside the robot used to control the robot’s tool. Since the directivity of capacitive sensors is very low the cable is detected as an outside structure. It is difficult to construct capacitive sensors to protect people when there is a cable close-by.
The most recent state of the art was to reduce the range of the sensors; meaning the distance needed for the machine to stop. The maximum speed of the robot is defined by how quickly the machine comes to a complete halt after it detects an obstacle. Obviously, a reduction in speed is not desired. The main goal for the robot is to do its job as fast as possible.
It is not easily understood that the robot needs to slow down only because the distance between the sensors of its arms is reduced. The external cable to the robot’s tool renders a capacitive sensor of any reasonable range useless.
In Adjacent Sensors you will find a description of how our capacitive sensors cooperate with other arms of the same robot, and with other robots as well. Neither the range of any sensor nor the speed of any robot need to be reduced in any case. When electrodes are placed on objects around the robot or on the robot itself, they can be fed a signal so that they appear invisible to the sensors. This works also for the external cables of the robot.
It is possible to cover any obstacle with an electrode and make it thus invisible for the capacitive sensor. The collaborative robot will hence work with full speed and most safely.