How do automatic car washes prevent damage to vehicle

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How do these automatic car washes with hunks of rotating metal not completely obliterate cars as they go through, and how fool proof are the systems that prevent them from going haywire?

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Pressure sensors attached to the washing arms tell a PLC controller to stop pushing forward and start the next step (usually to wash the sides and roof of the vehicle.)

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Edit: The systems are like 99% accurate. The same systems used to wash your car are used in large scale industrial fabrication.

Any control system will generally include a property called feedback which allows for the system to dynamically adjust to new input conditions. Sensors will provide data of car location to the control system “brain” which can convert the sensor reading into a “command” for the arms to extend to a specific position which does not harm the vehicle. Systems like this usually include a lot of redundancy and sensor checks to ensure that the reading is reliable. If you were to get a sensor reading that a car is 12 inches away when it is actually 2 inches away, then the “command” might overextend the washing arms and hurt the car. Sometimes control systems will include “voting” logic which allows for multiple sensors to be compared to reach a consensus to be reached. If no consensus is reached, a fail-safe mode can activate where the arms are returned to a safe distance and an error transmitted to drive troubleshooting.