V90 technology object - HW limit switch polarity reversed

Hello everyone,

Can you please explain to me what is a reason of technology object alarm:

"HW limit switch polarity reversed, free travel not possible."

Sometimes in automatic cycle of the machine hardware limit switch is reached. In most cases alarm "Pos. HW limit switch reached." is displayed, which operator can reset and machine can work again. But from time to time alarm "HW limit switch polarity reversed, free travel not possible." and the only remedy is to switch off and on the power supply (for the operator).

How can I prevent this error being triggered? I checked the wiring, also everything looks fine with the sensor. It would be helpful to know exact condition when this alarm is triggered and how it differes from regular approach to limit switch.

Thank you in advance for your response.

I think Tech Team's response is far better than anything I can come up with.

However, it does depend on the HW limit switch used in the application.  If for some reason the motion has enough momentum that is runs past the overtravel so far the limit switch looks happy again.  In that case, the V90 TO saw the switch get unhappy, then happy, yet the position indicated it was beyond the unhappy switch location and as such, thinks it must be lost, or possibly even off a track or rail, so human intervention is required.

If there is no hard-stop, add one so the motion cannot get past the overtravel limit switch enough that the V90 TO can see it go unhappy after hitting the overtravel switch.

Or, reduce approach speed as it nears an overtravel.

Or, get a different overtravel switch that stays unhappy no matter how far past the unhappy spot it goes.

Or, any combination of all the above, including Tech Team's suggestions.

 Hello,

Thanks for you answer! I think there may be something wrong with the sensor then, because it is not possible for axis run past. There is a metal part mounted on moving part of the mechanical system, and when hardware limit switch is reached by it then it should remain activated untill a real hard-stop position. So the sensor should be always unhappy then. Maybe for some reason there a glitch in the input signal?

0_Einstein

I think Tech Team's response is far better than anything I can come up with.

However, it does depend on the HW limit switch used in the application.  If for some reason the motion has enough momentum that is runs past the overtravel so far the limit switch looks happy again.  In that case, the V90 TO saw the switch get unhappy, then happy, yet the position indicated it was beyond the unhappy switch location and as such, thinks it must be lost, or possibly even off a track or rail, so human intervention is required.

If there is no hard-stop, add one so the motion cannot get past the overtravel limit switch enough that the V90 TO can see it go unhappy after hitting the overtravel switch.

Or, reduce approach speed as it nears an overtravel.

Or, get a different overtravel switch that stays unhappy no matter how far past the unhappy spot it goes.

Or, any combination of all the above, including Tech Team's suggestions.