Mach 3 Tube Bender Build - Implementing a strain gage

[supahonkey]

I built an NC tube bender last year and had a thread going on CNCZone.

http://cnczone.com/forums/showthread.php?t=68163

I use Mach3 to control the directional control valve. I load the tube and start the bend. Unfortunately, the first 10+ degrees are used to absorb the slop in the system. I would love to use a strain gage or some sort of torque meter to measure the strain on the die so I know when the slop has been absorbed.

Assuming I can purchase a torque meter that will output different voltages and different torque levels, how can I configure Mach3 to read these voltages?

Lets assume 10 ft-lbs corresponds to 2.5V. 10 ft-lbs is the torque at which the system has no more slop. How could I get Mach3 to read this voltage?

I currently use a macropump that gets a reading from a rotary encoder. It constantly analyzes the desired bend angle to the actual bend angle and makes the "cylinder extend output pin" high until the desired and actual bend angles are equal. Once they are equal the "cylinder extend output pin" goes low and the directional control valve centers itself. I want Mach3 to zero the actual bend angle once the theoretical 10 ft-lbs has been reached.

I can handle the programming, but how do I interface a sensor that sends a voltage reading (assuming it sends a voltage) to Mach3?

[gmfoster]

Do you only need the one point where the slop is taken up?

If so you could feed the strain signal to a comparator and set a flag. I know Mach can read the status of a pin using VB scripting. Not sure how to write it but I am sure Art Brian or one of the regulars on Mach could help you out..

To read a actual voltage and make a decision in Mach would be more difficult I think..

Garry

[supahonkey]

Garry,

Thanks for your reply. I only need one point where the slop is taken up. I actually need two, but the value of "slop taken up" is equal. I need one to remove the slop at the start of the bend and one to remove the tension in order to repin the die. The cylinder will retract until very little or zero strain is detected and then sop, allowing the operator to repin the die to bend past 90 degrees.

I am not aware of comparators. Do they just compare an input to a known value and then output a signal?

It isn't absolutely necessary, but it would be nice to read a voltage, and as you said, have Mach make a decision based on a defined voltage (torque reading).

I would rather use a torque meter over a strain gage. A strain gage would be difficult to implement. I don't know if it exists, but I would prefer a torque meter shaped like a donut where the ID connects to the die pivot pin and the OD bolts to a fixed surface that doesn't rotate. The OD will measure the ID's rotation.