Stepper-Driven Power Drawbar

[bill south]

Hey John.
I'm using 30# of air on my small cylinder. The socket is a 6 point mounted to the 100:1 planetary gear box. I don't use a stepper motor just a simple dc motor (750) series powered by a independent 12 volt supply (started with a inexpensive 12 volt battery). When the PDB is called, the spindle rotates less than 1 360° rotation to the hall effect sensor which then fires into position, the pin locks the spindle and the dc motor rotates the required direction for function. The unlock function is just a timed event (arduino control) and the lock event is a function of the current draw through the motor controller. Once the predetermined current is met, the drawbar has reached the required torque then the system disengages. Thus the magic!! Oh yeah, I also had a problem with the drawbar sticking and corrected it by bumping the torqueing motor in the opposite direction (just a bump) at the end of the cycle to help release the socket/drawbar interface. Thanks for the pictures of your system. Looks impressive. Hope this helps.
Bill

[jcdammeyer]

Thanks.
That helps a lot. I had my air pressure at 90 PSI because of the butterfly impact wrench. Now I can turn it down and better regulate the flow so the cylinder doesn't slam the assembly down. The delay between switching off and on the pneumatic wrench also caused issues to the point where I used PWM on the air cylinder to restrict the tightening but give me full power for loosening.

Here's the air panel. Main regulator for the panel. Then a small regulator for the mist coolant system behind an air solenoid which, although not wired at the moment is controlled by the same module that runs the drawbar. The higher pressure goes through the oiler for the impact wrench. Not really needed for the air cylinder.


Hadn't thought of a blip in the opposite direction to release the socket. But of course impact wrench that would have been a crap shoot too.
My code is all written in C. I'm using a version of CANopen that I call CANopen Lite. Simple messages and buttons on the LinuxCNC screen for remote control of the draw bar instead of the two buttons attached to my module.
John

[jcdammeyer]

Hey Bill,
What type of air cylinder?
Bidirectional?
Or one direction and return springs send it back up?
Mine is bidirectional so one valve sends it down and then it stays there. The other sends it up and it stays there. In case air disappears there are helper springs to push it back up so the socket is disconnected.

And there's the problem with mine. The springs are so strong that it takes a lot of air to overcome them. And in the release mode it whams up really fast and hard. Probably why a stuck socket pulls out of the 3/8" drive rather than off the nut.
John

[jcdammeyer]

Hi Bill,
Oh Crap. I just realized I dropped (or added) a zero in all my calculations. So my 25:1 harmonic drive is not going to work with the motor I have which after testing is looking a little anemic.

You said 750 series motor? What is that? Can you post some pictures of your power draw bar assembly? Maybe some more information on the motor?

Thanks
John