Variable pitch belt driven spindle

Chris,

I -could- detect the ends of the mechanical "throw" by making an encoding disk/limit switch arm to go in place of the original speed indicator (you can see it on the head of the one in this picture: igor.chudov.com/projects/Bridgeport-Seri...Interact-2-CNC-Mill/ )

I am currently using the gearchange component for the high/low (backgear) switch. I had considered using some logic and processing to take in the calculated RPM and drive a dynamic gearchange float, which may still be an option.

I would prefer to lock the VFD at 60Hz, and just make it a FWD/REV On command; then purely drive the speed based on the variable pitch belt. If I stay within the original speeds available through the belt system, I really don't see why I would need the mechanical pitch detection? At least, if the VFD is at 60Hz.

I was giving you ideas that could be used. it depends a lot on what you want and what is easy to add.

I don't know how fast mechanical adjustment can adjust, nor if you need to adjust fast. I also don't know what happens if you hit one end of the max adjustment and continue to try to adjust - if it's not a problem then you don't need limit switches.

Chris

Chris,

I really appreciate your help and ideas.
The more I chew on it, the more I think you're onto something with the mechanical detection. I don't currently see why I would need to ramp speed quickly, but I may need to in the future. You are correct in suspecting that the belt will take longer than the VFD to change speeds.

I'm using a similar method with my lathe, where I use some switches to detect the current gear position (set manually), in order to use the correct ratio for the gearchange component. I've got a funky issue where I can only run open-loop, but it stays close to command.

When I designed my breakout for a 7i73, I made a pretty convenient connection for some potentiometer inputs. I could use a pot on the speed indicator at the front to set the belt pitch in ClassicLadder pretty easily...

I'll give it a good look this evening.
Thanks!

Hi.
As you have only two digital actuators (valves) it will not be an advantage do use some kind of analog regulation. So a simple 2-point regulation with deadband will give you the solution. At the endpoints of your mechanics set two switches. (You can connect them as breakers even into the valves circuits). That way the "regulator" is easy to solve. Compare the ("commanded" speed - deadband value) with the "measured" speed. If it is to low switch on the "faster-valve". And vise vers if ("commanded" speed + deadband value) is to high switch on the "slower-valve".

You can play with the deadband values so you come near to the "oscillation" point.

This is so easy to solve in classic ladder that it will take you only few time

P.S. That's what a lazy engineer like me would do.
Mike

I would have assumed it already had limits switches. If it does i certainly would start with that.
Detection of the mechanical speed position is useful if you want to be able to adjust mechanical and VFD at the same time for wider range/more power or faster speed changes.

But if adding analog position is easier, then that certainly gives you more info to use.

I think the vari drives are great for manual machines. I have a series 1 and if I had to do it over gain, I probably would ditch the vari discs and replace them with a timing belt drive and just use a vfd for rpm change. I had a terrible time re-machining and balancing them after a bushing rebuild. I'm not sure on your application but over driving them probably isn't a good idea.
I added an encoder to my machine and it gives me the rpm readout but haven't added the vfd yet. How are you planning on getting an index signal? Are you planning on rigid tapping? I wonder if there is better setup to fit an encoder on your type of BP then on the standard heads. Also, keep in mind that the vari disks need to be spinning before changing the rpm dial which may need some delay component added.