Precise distance measuring

Hi all Arduino enthusiasts,

I want my Arduino to measuring a small distance (5cm -10cm).
Google gets me a lot of results (Arduino +ultrasonic measuring) but the problem is the accuracy, most are 1cm accurate, I need at least 1mm.
Is it possible to tweak the sensors so it will work more accurate?
I know there are other ways off measuring but it has to be ultrasonic.

It is going the be used as a Torch Height Controller on my CNC-Plasma table.
When cutting metal with a plasma cutter the cut height is very important, sounds easy but while cutting the metal sheet heats up and begins to warp, this warping must be compensated to get a smooth and good finish.

Option 1: Voltage measurement (cancelled)
The voltage between the tip off the plasma cutter and the work piece is proportional to the distance.
In theory you can make a voltage measuring scheme with a voltage divider and some filters. But in real life you’ll notice this won’t work.
There are to many variables for making a diy system. (speed, corners, humidity, type of metal, hf noise ...)

Option 2: Laser / IR measuring (cancelled)
To work well the measurement has to be as near as possible to the plasma arc, I can imagine that het arc will make a correct measurement difficult if not impossible.

[Option 3: Ultrasonic measuring (under construction)
There are similar Torch Height Systems on the market. The Ultrasonic Sensor has a faster reaction response time which use sound waves
It is immune to bright light from flame / plasma that lasers THC devices have trouble with
Reads through smoke, dust and mist

Option 4: Ohmic touch probe (last option)
With a touch probe and a sliding pot getting a measurement.

Thanx,
Sjuul

An ultrasonic signal at 40kHz has a wave length of 7.5mm, so about 1cm is the highest precision you will get with a standard ultrasonic distance sensor. With special time of flight measurement techniques (peak to peak) it should be possible to achieve a higher precision but these kind of sensors are much more expensive than the usual HC-SR04.

Example (operating at over 300kHz): http://www.sick.com/us/en-us/home/products/product_news/distance_sensors/Pages/um30_2.aspx

It never hurts to do a search. This question was discussed a few days ago.

Google gets me a lot of results (Arduino +ultrasonic measuring)

Did you try Googling "Torch Height Controller on CNC-Plasma table" ? I noticed there are some DIY solutions that don't need a microcontroller.

Thanx for the directions, and sorry for being lazy.
I red the similar post and I came to the conclusion that the standard arduino ultrasonic sensor we all use can’t help me with my thc.

There are many ways to make a thc some are more difficult than others. The simplest way is an adjustable skate where the torch is mounted on, the skate runs over the plate with some kind of suspension or spring-loaded.
Getting the distance with an touch probe and a sliding potmeter is also an option. Problems with these both is that you have to touch the plate as you go along, when the probe or skate hits spatter or already cutted grooves problems are waiting to happen.

Best way of measuring is a “no touch” measurement that won’t be affected by the plasma arc, smoke dust or mist.
The cutting material is always metal. Maybe I’ll get a better result by using a capacitive sensor.
I’ll look into that maybe someone has some tips, but with a plasma arc next to it I can imagine it won’t work

Also is has to be not to difficult, I only have some basic electronic knowledge.
The search go’s on

Is there anything you can do by hacking a laser based electronic tape measure? There are some with the accuracy you need, it's just a question of how you would read it. Of course, if money is no object, Leica apparently make one with a bluetooth interface and phenomenal accuracy (Disto D8) which would need no hacking at all.

IFM Sells optic distance sensors that come with 2 digital an 1 analog out (mA or V). I used them very often at the mill where I work.
The problem with laser is that on shiny metal or wet surfaces they aren’t so accurate anymore.
The metal plate that is going to be cut at the plasma table lies just above a water basin to minimize heat, dust and sparks. Therefore it can occur that water drops are lying on the surface this is no problem for the cutter but the laser has problems with it.

Another method is using Ohm’s law. (Just an idea)
I measure the resistance of the plate before cutting, and with a Hall-effect sensor I can measure the current during the cut.
With both known, I can figure out what the voltage is, And the voltage is proportional for the distance.
Question is: does the plate resistance change during cutting?

Sjuul

I'm interested in this ultrasonic guy with accuracy to 1mm-

I'm also about to embark on solving the problem for a cnc plasma cutter.
i saw this product on the market that got me thinking on this track

one issue is how do you deal with a hole in the material? there could be a massive slot or even no material at all where the sensor is directed.
heres my log on a potential approach using reflectors.
http://opensourceecology.org/wiki/Ultrasound_Torch_Height_Controller

It could be possible to get a circular pattern around the hole torch head.

I would like to be able to just point the beam toward the torch head at an angle, but theres a lots of problems when you hit holes that don't seam easy to resolve. knowing distances and angle of the beam isn't enough information if the beam itself is at an angle and you hit a hole or area with no material

I'm interested in this ultrasonic guy with accuracy to 1mm-
Maxbotix Ultrasonic Rangefinder - HRLV-EZ4 [HRLV-EZ4] : ID 985 : $33.95 : Adafruit Industries, Unique & fun DIY electronics and kits

Where on that page did you find that the accuracy is 1mm. Remember, a resolution of 1mm is not an accuracy of 1mm. You can make a resolution of 1µm but you'll never get such an accuracy.

I'm also about to embark on solving the problem for a cnc plasma cutter.
i saw this product on the market that got me thinking on this track
Torch Height Control

For $500 I would expect that they're able to use high enough frequencies to get sub-mm accurancy, so this an option for your problem.

What about a Digital caliper? You can interface it via arduino.

Sjuul:
Another method is using Ohm’s law. (Just an idea)
I measure the resistance of the plate before cutting, and with a Hall-effect sensor I can measure the current during the cut.
With both known, I can figure out what the voltage is, And the voltage is proportional for the distance.
Question is: does the plate resistance change during cutting?

A friend of mine purchased a custom-built CNC plasma cutter table - and that’s basically how it works, except without the measurement of the resistance.

You should be able to just track the current of the torch, and adjust the height from that. So yes, this is more or less how commercial CNC plasma cutters work, you’re just complicating it a bit in regards to the measurement of the resistance (which isn’t done on commercial tables, AFAIK).

how to mesure height using ultrasonic transmitter with arduino uno?
please tell me…

distance measuring programing is available