Anti-Pinch Safety For Auto-Up Windows

FordNoMore · 04-05-2008, 08:49 PM

I have yet to see any safety features for not pinching your fingers with automatic roll up windows. Has anyone devised anything? Or does it just not hurt too badly?

I think most (if not all) OEM systems have some anti-pinch safety feature, but I'm not sure how they work. I saw a Honda salesman demonstrate it once, and it looked like the window barely touched his arm before rolling back down.

Any ideas?

Bugbyte · 04-05-2008, 08:53 PM

I thought they worked by measuring the amperage. If it spikes, it reverses.

FordNoMore · 04-05-2008, 09:48 PM

I thought they might, but two things make me wonder:

1. How do they tell the difference between my fingers and the end of travel? An OEM system might have a position sensor that disables the safety at the last second, but that doesn't seem ideal.

2. What about when the car gets old and the window drags a bit? Lots of old cars I've seen seem to struggle getting the electric windows up as the tracks get worn and dirty, the mechanisms aren't greased so well anymore, etc. Seems like that would cause problems. (Or maybe it does cause problems? I suppose I haven't seen an old car with auto-up windows.)

quantum · 04-05-2008, 11:42 PM

I just looked over my owners manual (Caddy has this feature on all 4 windows with express up). Mentions nothing about how it works, but at the risk of losing an arm I tried it and it in fact does.

Nothing like putting your faith into some overworked engineer at GM! Whew!

Bugbyte · 04-07-2008, 12:10 AM

According to How Stuff Works, the system monitors the motor speed. If it slows, it will reverse. There is probably a limit switch for top and bottom.

JayD1056 · 06-10-2008, 01:08 PM

They work many different ways. First generation hads a counter in the motor. (8 actually) and it counts from the top to bottom. There is a very complicated algorithm for figuring out if a reversal is needed. But correct it mostly works off current sense. These days we are moving to a sensorless motor. Saves 2 dollars a motor over 4 motors a car by many many cars per year. As for temperature change. The module stores the profile of the window and notes changes everytime it goes up and down. If a change is out of range of the calibration then a reversal occurs.

Jay

FordNoMore · 06-10-2008, 11:33 PM

Interesting! That's more complex than I would have guessed. But I guess even a mid-grade processor is worlds cheaper than adding sensors and associated wiring and such.

So, without any direct "sensor" or encoder to tell it where the window position is, it monitors current as the window raises, and if it's more than it expects for that (estimated) position in the track it figures something is wrong? I've had some old cars where the windows are really reluctant to go up... I'd imagine the auto-up would stop working at that point?

Quantum: How hard did it squeeze your arm before reversing? When I saw a Honda salesman do it, it looked like it barely touched his arm... but maybe he was just acting like it didn't hurt.

2k1Toaster · 06-10-2008, 11:43 PM

Quote: Originally Posted by FordNoMore

Interesting! That's more complex than I would have guessed. But I guess even a mid-grade processor is worlds cheaper than adding sensors and associated wiring and such.

So, without any direct "sensor" or encoder to tell it where the window position is, it monitors current as the window raises, and if it's more than it expects for that (estimated) position in the track it figures something is wrong? I've had some old cars where the windows are really reluctant to go up... I'd imagine the auto-up would stop working at that point?

Quantum: How hard did it squeeze your arm before reversing? When I saw a Honda salesman do it, it looked like it barely touched his arm... but maybe he was just acting like it didn't hurt.

Auto-up does stop working as it gets really really old. And current sensors are what is used for some.

As for how hard, it depends. That honda salesman and the lexus saleman we spoke to both must have had arms of steel because I tried it myself and it works for the wrist and up very well but with fingers it is a crap shoot. Scared the crap out of me a couple times with me trying it. I didnt think it was going to stop so I pulled my fingers out. I think it needs constant current buildup. so it needs to squeeze and not you pressing down on it type thing. But I dont want to try again!

kibble · 06-11-2008, 12:05 AM

Awwww funny story! We had just gotten an new car in 2001, an I30. Well we had the salesman showing us all kinds of stuff that it did and what not and one of the things he showed us was the whole window reversal if something got in the way of the windows or sunroof closing.

Well my mom wanting to show her friend how it worked, a few days later, told him to put his arm through the sunroof. The system didn't work. I wasn't in the car at the time so I didn't know about this, until she came to me and asked why the windows weren't working the way they're supposed to. I told her to show me. We go out to the car and she says: "I told him to put his hand out of the sunroof and then I did this."

At this point she pushed on the button to close the sunroof and held it there. She didn't release the switch. I said: "WAIT! You held the button down?!?!?!?" She goes: "Yeah, isn't that how it works?" I laughed and said: "NO! You push it once and let it go, if something interferes with it closing, the system stops and returns!"

She got red faced with embarrassment and told me that all the guy did was sit there and say: "Owww...." Then his hand was all red.

crooper · 06-12-2008, 03:02 PM

the main issue that manufacturers face when designing auto-close systems isn't the adult arm or hand, it's kids necks and fingers, which are smaller and therefore easier to damage. the system's reaction time to stoppage is even a factor, given that a movement of 1/4" is enough to sever a finger or crush a windpipe.

CaveDog · 07-12-2008, 11:14 PM

Quote: Originally Posted by Bugbyte

I thought they worked by measuring the amperage. If it spikes, it reverses.

This is how I am monitoring my system with a phidget...
http://www.phidgets.com/products.php?product_id=1119
One of these suckers on the supply line for my windows. If the amperage spikes 10% over what it was for the first second, then it automatically cuts the power to the windows for 3 seconds. I have the issue where the system will continue to try and put the windows up even if they are fully up. Maybe one day I will hard-code the spike value in the system and have it stop that way. Its only monitoring when the computer is on, and as such I can still theoretically jam someones head in the window if the computer is off, and I operate the windows by the buttons.

Curiosity · 07-13-2008, 02:12 AM

I've replaced my motors a couple times now because I got a some cheap ones off ebay the first time and noticed there's a resettable breaker inside the motor (that wears out). It works good for manual, but automatic measures amps with a shunt or low ohm resistor as everyone says. That can react a lot faster, but yeah it's going vary over time.

stangtjk · 07-22-2008, 07:54 PM

Check this out it a development kit from microchip that is already set up as and anti pinch device

http://www.microchip.com/stellent/id...cName=en026014

RallyPikester · 07-23-2008, 09:14 AM

There is a good application note about this on the atmel site:
http://www.atmel.com/dyn/resources/p...ts/doc7559.pdf
http://www.atmel.com/dyn/resources/p...ts/doc7678.pdf

This is quite a common system in the auto industry.
The force limit varies between manufacturers, but I believe <100N is a fairly standard number.

mitchjs · 07-27-2008, 03:14 AM

Directed Electronics 530T (window Rollup module)

Detects NOISE from the motor..
very cleaver, and works great!

mitch