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Anti-pinch : from physical to soft sensor

Context and principle of anti-pinch

Nowadays, more and more opening devices are becoming motorized on vehicles: windows, roof, sliding side doors, trunk… So as to guarantee user safety, anti-pinch standards were made and have become mandatory. Two methods are developed by industrialists:

  • Direct detection: very reliable but quiet expensive
  • Indirect detection thanks to speed measurements: pretty popular, but complicated to calibrate and it sometimes reacts “too late”.

Anti-pinch is increasingly regulated on systems with electro-mechanic closure, either for windows or doors. For instance, European standards for electrical windows require an anti-pinch system between 100 and 125 N, meaning between 10 and 12 kg. It is one of the problems industrialists and vehicle manufacturers have to cope with.

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Anti-pinch with physical sensor

In order to meet these standards, carmakers sometimes use complex systems with physical sensors. On a larger scale, the cost is non-negligible. Currently, existing systems are:

  • sides made of rubber with capacitive or resistive sensors (a door of a subway train)
  • obstacle detectors (radar)

Anti-pinch with soft sensor

Soft sensors appear as an alternative solution to physical sensors. The aim is to obtain the same accuracy (or more) than a physical sensor so as to promptly determine the presence of an obstacle and accordingly react (step back for instance). For a motorized system (like a door), the solution may consist in measuring speed while closing and compare results to the “regular” speed (expected).

If a substantial difference is observed, we can boil down to the conclusion that an obstacle is on the closure path. Then, the system stops and goes backward. This speed difference is linked to a force exerted by an obstacle on the door. The maximum force authorized before going back is conditioned by the measured difference.

Soft sensor to determine pinching effort

Acsystème helped an R&D team of a vehicle manufacturer company to conceive a motorized side door with an innovative anti-pinch system based on a resistive force soft sensor. It consists in a real time evaluation of resistive efforts preventing the door from closing thanks to available measurements: Hall Effect sensor, voltage, and eventually, current measurements. Results are analyzed to make a decision about the presence or not of an obstacle.

Delivery of our services went through several steps:

  • First of all, the team created the opening device model and simulated it on computer with its control loop. During that time, we looked for different solutions to replace physical sensors with soft ones.
  • Then, with the R&D team, we built a complete testbed (see picture). This testbed allowed us to optimize the command in real situations before validation with scenarios in accordance with conditions of use.
  • During a test, effort measurement is calculated with the soft sensor while it is confirmed by a physical force sensor (see picture).
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Motorized side door test bench

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Resistive force sensor

This research resulted in the creation of a soft sensor producing faster results than other soft sensors which are only based on the observation of speed. During seven months of development,

Acsystème’s partnership with the carmaker contributed to the drafting of two patents.

Other references

Here are some other references in the field of soft sensors:

  • Automatic tire position detection
  • Tire pressure estimation for different applications (car, truck trailer…)
  • Pinch force estimate for roof occulting device
  • Accurate estimation of a submarine’s immersion

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