Thread: VSD suggestion

Hi Stustoys,
The Foot Peddles are usually connected to a Limit Switch which has its NC Contact wired in series with the either Stop Switch or Emergency Stop Switch. It then depends if the Control Circuit is wired in a Maintained Switch arrangement or an Impulse Start arrangement. Do you have a contactor that latches when you press Start and The Stop Button's NC Contact drop out a latch circuit from the axillary on the Contactor that holds the power to the coil of the Contactor. if it is wired like this then you can put a Emergency Stop in that line, since the Contactor directly controls the Motor. In this arrangement it would be Catagarized as a Category B -1 Circuit. If you wanted monitioring then you would use a Failsafe Controller which the Emergency Stop would wire to an it then dropps out the Contactor, for a Category 4 configeration the Emergency Stop would have 2 x NC Contacts and there would be two Contactors wired in series with a Positivily Guided Contact wired in series of the Auxillary Contact on the Contactors that would feed into the Feed-back Circuit of the Failsafe Controller, this also may have a NO Rest Pushbutton in it so a reset to check the Circuit Functions can be obtained.
Sound complicated huh ? but its common practice, I attach a pdf of a typical Emergency Stop setup.

Regards,
Keith.

Originally Posted by Stustoys

In fact if you dont have a camloc spindle it might be an idea to lock out revs and go easy on the braking. Or you might find the chuck rolling towards you(has any one heard of anything like this?)

I had a lathe (for only a short time) that had a threaded spindle nose and both forward and reverse controls. Not once did the chuck unwind while in use or during a stop (even if I assisted the chuck to stop).

Having said that I never actually turned anything in reverse (i.e. the tool never contacted the work piece while in reverse), I would only ever use it to return the tool to the start position when threading.

Vernonv,
Good point, forget the rev lock out, a VSD is going to start slower than a "normal" motor.

"Assited the chuck to stop" meaning? using reverse or running your hand on it?
Stuart

Keith,
Its going to take me a while to figure out what you've said.

Stuart

Originally Posted by Stustoys

"Assited the chuck to stop" meaning? using reverse or running your hand on it?

Just using some gentle hand pressure on the chuck to speed up the slow down after turning off the motor ... I'd only ever do it while the lathe is running in reverse, as there is much less likelihood of things going wrong.

Keith,
My lathe as a latching relay that allows it to run. For that relay to close the FWD/OFF/REV lever has to be off and none of the NC switches in the E/stop circuit can be open. Once that relay has latched you move the lever and it closes the motor contactor. If an E/stop NC is opened you have to reset the relay.(standard stuff I assume you know exactly what I am trying to describe). My pedal opens the NC circuit so that's Cat B-1

So if I add 2 contactors in series upstream of the 240V input with a big red button. Isn't that Cat 4? What would the monitor be monitoring in that circuit? Am I missing something?

Stuart

p.s. you now have me thinking about the jog button. It might be possible to have the machine start sort of unexpectedly, if the machine was running and was stopped with a foot pedal, the jog but is then pushed and nothing would happen, then the fwd/off/rev lever is moved to off and the relay would latch and the machine would start. I guess the answer is don't hold the jog button while its not running.

Here's my first setup for my SAJ VSD on the Hercus. I say "first" because no doubt I will fiddle with it extensively. Eventually I will make up a remote control for it but this will do for now.


I placed the VSD in a plastic box with the controls outside the box and have located the box on the wall next to the lathe. AC comes into the box on the RHS and there is an eswitch on the lathe that can kill the supply. There is also an independent earth on the machine near the eswitch.


Here you can see how close the control box is to the lathe and I can easily reach the controls from the operating position although I do not like reaching across my body to stop the lathe which is why I will eventuially will set up a remote right on the lathe


Here is a close up of the box. Can you guess it's origins, bonus points if you can guess the original exact contents of the box? For many years I used this box to carry chainsaw chains and it was the only one I had that was deep enough for this job so I had to do a fair but of cleaning up on it as it was covered inside and out with sawdust and bar oil. Because I have a box full of them (extracted from PC power supplies I decided to go the "kettle cord" plug and socket route as I hate dangling cords when moving stuff.

My guess is this is what you are interested in seeing.

Yes I could have simplified things by wiring everything to the VSD connectors but I find that is very messy and eventiually I end up breaking a contact and I needed at least one break out for the e-switch anyway. The 12V PC fan (again from a PC power supply) is active whether the eswitch is active or not so the unit does get some cooling if the eswitch is activated.

No doubt some of you will be amused by my somewhat "klunky" electrical work but I like to lay out stuff in a clear and obvious way so I can check everything along the way.

How does it work - fine so far but let me play with it for a while and I'll report back later.

Hi Stustoys,
Sorry I did not come back to you sooner.
I attach a diagram that shows an Emergency Stop Wired to a Category B type Circuit.
I have also attached a diagram showing an Emergency Stop Wired to a Category 4 Type Circuit.
In the Category 4 Circuit you will see two Safety Contactors that are wired in Series, why special Contactors, they have a Positively Linked NC Contact, this means that the NC contact can never be in the same state as the Main Contacts(L1, L2 & L3). The Failsafe Monitoring Unit (NSO13DB24SA used as an example in this diagram) can see that both CAS7 Contactors have opened. The Emergency Stop is wired to the Input of the Failsafe Monitoring Unit via S11 - S12 & S21 & S22 and the Feedback is wired into the S33 - S34. The Failsafe Monitoring Unit breaks the feed going to the Start/Stop Pushbuttons. Normal Operaton is via the Start and Stop and its Wired as an Impulse Start Circuit which latches the Contactor via the NO of the Contactors and I show the Overload with a NC Contact in the Latching Circuit.
Control Category 4 says that a Single Fault in the Safety Related Parts of the Control System must not lead to the Loss of Safety Function, that is why there is 2 NC Contacts on the Emergency Stop, 2 Contactors and a Failsafe Monitoring Unit which its self is internally Dual-Redundant to monitor the parts that make up the Safety Side of the Circuit.

I have not included a Forward/Reverse or Jog Buttons in the Circuit so to try and not confuse things too much.
The Circuit is showing as a simple ElectroMechanical setup, if a VSD was to be in the Circuit it would be wired differently as you would appreciate.
I am not suggesting that via the Diagrams that you wire your Lathe to the Diagram as it is represental of what a Control Category 4 is.

Regards,
Keith.

Nice job Bob and thinking outside the square.
That will bring the old Hercus to life, let us know how it goes.
I will be able to report about mine sometime in the near future.

Dave

I see you have your Emergency stop located on the right side of the lathe,is it possable to move it to the left.
The reason I say left is that is generally the direction you will be looking when the lathe is opperating,in my opinion having it there would make it quicker to shut off if the need arose.
Also do you plan on running coolant on the lathe,if so looking at your pictures it appears that the power point at the rear could at some stage be in the line of fire,from coolant or swarf or both,maybe some sort of cover might be good.

Cheers Dave. The only things I wanted to fit were a couple of leds to tell me the the ewitch had been triggered - see below.

Originally Posted by pipeclay

I see you have your Emergency stop located on the right side of the lathe,is it possable to move it to the left.
The reason I say left is that is generally the direction you will be looking when the lathe is opperating,in my opinion having it there would make it quicker to shut off if the need arose.

If this lathe was new to me I would agree but I have used this lathe before many times and the stop/start and eswitch buttons were where the eswitch is now and in an emergency my brain will send me direct to that spot. Already I have hit the eswitch a couple of times when I thought I was turning it off. I have also hit the eswitch with my leg which was initially a bit confusing (an appropriate led will help here) but I have no issues with that.

Also do you plan on running coolant on the lathe,if so looking at your pictures it appears that the power point at the rear could at some stage be in the line of fire,from coolant or swarf or both,maybe some sort of cover might be good.

Yep - the lathe came with a decent full width splash back which I have not yet fitted. The bonus of the powerpoint being behind the machine like that is it can power my coolant pump - am working on it now.

Keith,
I think I'm getting it. The logic control can't be reset if one of the contactors fails to open when the E/stop is operated? (would this also apply if power was removed from the logic control? i.e. do you have to reset the logic control on power up?)

I don't understand the double pole stop and start buttons. The failure of any one of those won't stop the lathe from running, although the failure of the two that can power the latching circuit wouldn't allow it to keep running. Am I still missing something?

Thank you

Stuart

Hi Stustoys,
Yes the Failsafe Controller needs to be reset, this can be Manual via a NO Pushbutton or Automatic where there would be no NO Pushbutton.
As for the Start and Stop Pushbuttons it can be a Single set of contacts in each, but as the Failsafe Controller has several Release Paths(internal relays) I used two of them, also spreads the Inrush that the Coils has over to paths.
The Start and Stop Pushbuttons are not monitored as they are not part of the Safety- Related parts of the control circuit.
In essance its a normal Start/Stop Circuit where the Emergency Stop and the Contactors are monitored as they are used to provide the Safety.

Regards,
Keith.

Keith,
I do believe I've finally got it.

Thanks for your time

Stuart