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Floating Z? Ohmic sensor?

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wallyblackburn
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Floating Z? Ohmic sensor?

Postby wallyblackburn » Fri Jul 14, 2017 2:46 pm

Can someone point me to a basic description of those terms? Or, more specifically, how they are used.

I'm thinking that a floating head lowers until it is touching and then "floats" on the cut surface, thus riding along any changes in height? How does it lower to touch and then float? Is that where ohmic sensor comes in? Does it just provide continuity when cutting head touches?

Thanks,
Wally

tcaudle
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Re: Floating Z? Ohmic sensor?

Postby tcaudle » Sun Jul 16, 2017 3:33 pm

Close. The floating head acts like a shock absorber and suspension similar to a car. It allows the end of the torch to contact the material and then for the Z ti continue down unto it trips a sensor (usually a mechanical switch). Its a process called IHS (Initial height sensing ) and it has one purpose: Find the top of the material and Z the Z position . its also called "touch - off" Its like feeling for the floor with your toes when you get out of bed. Is a reference point. The Floating head is the easiest and most reliable way to do the process. The floating head is not there to do anything during a cut. The THC is there to keep the torch tip above the material by a specified amount as it cuts.

The one down side the Floating head presents is that it pushes down with the weight of the torch so on thinner material it deforms the material DOWN and causes the touch off to not be accurate (metal moves down then pops back up as the torch lifts. Enter the Ohmic sensor. It uses a low voltage electrical current (just like a continuity tester ) to sense the metal as soon as it touches so there is no overrun or metal being deformed.

You need two forms of sensing. Why? because ohmic is not 100% reliable. It fails if there is surface rust, heavy oil, or paint. The sensor needs a backup. It needs to be able to stop the motion if you miss the ohmic or on more sophisticated systems be able to switch to the alternate touch off method and apply any mechanical offsets required and continue to cut.

IHS is a fundamental and highly important part of the cutting process. Without it you either have to manually touch off and zero the Z before each pierce or cut metal that does not warp and is very flat. Having a THC without a method of automatic touch off is a waste of money on cutting thinner material

IS a floating head the ONLY way. No, but other methods (like torque sensing of the Z motor) are usually more complex and have to be part of the overall Z electronics and motor control circuit.

wallyblackburn
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Joined: Tue May 23, 2017 8:36 am
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Re: Floating Z? Ohmic sensor?

Postby wallyblackburn » Mon Jul 17, 2017 8:23 am

Thanks! I was thinking floating head was *instead of* THC.

Great explanation. Love this forum.

Wally


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