Hey Steve,

    So, give me a web site where I can get those Springs I REALLY, REALLY like that idea over Belviells, I guess my concern would be, how would you keep the spring centered so it would not wobble the shaft?

Also:  Having built a Prototype ATC, I would NOT try and use "Air Cylinders" for any type of speed control. It is very hard to get the flow valves right, and the instant that your pressure, or humidity changes at the source, then those speeds are not longer valid........ Other than Bang-Bang motion, they are not good velocity or positioning devices.  It would probably make MUCH more sense to do a Rack/Pinion or acme screw/nut for linear motion.

Having said the above, another way, but more expensive, is to drive the entire contraption via PLC brain, you could use "High Speed counters" or Stepper/motion cards to drive or read, or drive/read your motors.  You can use inexpensive AC or DC motors, and put an Encoder on the motor or on the moving part, your choice, and read its distance via the High speed counter,  you can set all kinds of very good positioning that way. The next level up would be stepper (or servos), controlled via a motion card on the PLC (with Encoder feed back). Many of these cards you can select various "Motion Profiles" and set up motion/velocity tables, with set positions that can be called. (this applies to both linear and rotary motion).

IF your real, real hell bent for leather, then you could just use analog cards, with linear rheostat for feed back coupled with a PID loop per motion axis/device...
Many, Many ways to kill that cat, even do PID loops in a plugin if you like the pain....

Scott

Scott,

If he were to do what I suggested, using a PWM-driven solenoid valve, if he put some kind of encoder, or even just a potentiometer, on the arm, I bet he could actually control the speed of the air cylinder quite easily, with a very simple, very low bandwidth PID controller.

Regards,
Ray L.

You could push Light hydraulic fluid(ATF) instead of air .

Just a thought, (;-) TP

You could push Light hydraulic fluid(ATF) instead of air .

Just a thought, (;-) TP

But that would require a hydraulic cylinder, pump, reservoir, etc....

Regards,
Ray L.

Quote from: BR549 on January 04, 2013, 09:55:13 PM

You could push Light hydraulic fluid(ATF) instead of air .

Just a thought, (;-) TP

But that would require a hydraulic cylinder, pump, reservoir, etc....

Regards,
Ray L.

We use air cylinders with a parallel mounted oil filled cylinder and res. with flow controls to control the movement. (I mentioned this option early on but didn't describe it well). There are cushions built into the "OIL" cylinder which decells and softens the stopping at each end of the stroke. We use Festo mfg'd. units as well as making up our own and they work VERY well. I am in the process of changing one out for a servo and ballscrew on a precision saw slide as we want to vary the feedrate for different materials/conditions.
This method however does not addres the the issue of changing the actual speed with the SW. Will be interesting to see if you folks can come up with a feasible way to incorporate the two. That would be something I could possibly use in the future.
Russ

Similar to Ray's approach, there is a board ...
http://www.cnc4pc.com/Store/osc/product_info.php?cPath=25&products_id=179
that could possibly be affixed to a FCV instead of a Pot to control the speeds via SW.
Would be cool to try.
Russ

The software is the "Easy(er)" part, if you go with PWM air solinoids, your still having to drive that solinoid with a PWM source, and you would also need
some type of feedback, i.e. analog, pwm, encoder etc. I think this is probably just as expensive to do as using a PLC with motion card (and/or Analog card).

BUT, having said THAT......  Aurturo sells a Mod bus card and Peter Homann sells a Modbus card, both are very cheap, and both can do PWM (spindle control).
They also have multiple analogs on them, so you could also do some kind of feedback.....  cheaply.

Hydraulic/hybrid system was mentioned above, air over hydraulic. That adds a large cost, in the hydraulic components, even small units are usually close to or over 1k.

I personally, like the "KISS" principle, which may be just push a ACME screw with a nut, with a cheap stepper and drive (Chinese drives are real cheap), and/or use cheap AC or DC motors to push the screw and use mechnical Micro switches (or proxes if you have a little more cash), to handle your bang-bang limits. You could even put micros before the end micros, that could be used to cut the speed toward the end of travel prior to the stop micro.

Really, for an ATC "Kit" or even OEM targeted device, especially if for smaller machines (ran by primarily hobbyist), cost would be a major issue.
You would have to add in your Warranty and Liability cost as well.

Unless your shop is tooled up to run production on your ATC product, it might be better for you to just sell the IP outright with the understanding of you being clear of all claims and support.

been there, done that......... 

Another option, that might make you some ongoing cash, is to offer the kit in "Plan" form, or DVD etc. I would probably go with real paper Prints, since it is just to easy to copy/distribute DVD materials. You could offer phone Support "Packages" for some set amount for some hours, as an option. At the end of the day, it's your show and your choice on how you would like to proceed.

But, I really like the changer your doing, and still want a source for those MONDO springs!!

Scott

A simple Air/Hydraulic unit consists of a reservoir of oil with air pressure feeding in the top and oil flowing out the bottom.  I use an Air solenoid to charge the Reservoir when flow is needed. Control the feedrate from the oil side with an orifice or needle valve.  Great for simple single side cylinder charging and spring return OR you can use a double side double feed valve to do double side cylinder control.

This works WELL for low pressure applications such as this.

You can also do the Charge cyylinder trick with air pressure and a closed loop for the Oil side. Single or double acting as well.

There are many low cost ways

Just a thought, (;-) TP

Don't want to use air (;-) Use a power steering pump to drive your hydraulics. Low cost self contained reservoir drive it with a small electric motor at a lower RPM.

(;-) TP

Scott,

I don't think you quite understood what I was suggesting.  For control, the PWM is implemented purely in software, the only hardware being an external pass transistor to drive the solenoid.  Then there's just the solenoid valve itself.  An automotive idle air control valve would probably do the trick for next to nothing.  Feedback is provided by a simple potentiometer, read by a built-in A/D in the MCU.  Can't get any cheaper than that.  I'd bet the whole thing wouldn't cost $10.

Regards,
Ray L.