[DeanW]

The servo drives I am using have inputs for P-OT and N-OT = Positive/Negative Over-Travel.
There are settings for what happens when a switch opens.

Should I use these or should I use KFlop inputs. Or should I use both?

Thanks

[Al_The_Man]

These are generally used for drives or controllers in a stand alone application, one common industry method is to just monitor the O/T switches in the E-stop string and then use a disable input on the drive to disable the motors.
If you were to use those +- inputs on the drive, the CNC controller would not be aware of your drive disable condition.
Al.

[DeanW]

I have seen limits in the E-Stop / safety circuit. But, I do not think I want to provide a hardware limit override to get out of E-Stop and jog off of the limit.
I am researching the E-Stop using a safety relay circuit. I think questions on that may need another thread.
I assume you are saying not to wire the OT inputs on the drives and just signal KFlop inputs?
The switches are already wired (Shizuoka AN-S mill) and they do not use shielded cable.
If I only use KFlop inputs for the limit switches, can I feed the switches with 5v or is that going to be too noisy?
Do I need a resistor on the inputs?

I have spent many, many hours researching this conversion but I have not really found any wiring diagrams with KFlop that answer my questions.

Thanks

[Al_The_Man]

Personally the main concern I would have is if the drive +-OT are wired to limits then the controller is not aware that the drive has stopped, unless there is other logic on the drive that can make the controller aware.
If you really do want the +- overtravel direction sense, then I would think that input the OT switches to Kflop and use logic in the controller to provide the jog off direction?
This way the controller is aware that the program should be halted and the necessary routine be initiated.
Al.

[DeanW]

This is a chicken and egg problem also. If KFlop/KMotion is getting encoder signals, it should fault on following error even if the limit switches are not connected to it.
I do not know what problems that will cause, but I would think if a limit is hit, any program will have to be re-written / restarted with the correct coords etc.
It does not appear that the drives active the ALM output on overtravel. So, I do not see a way to notify KFlop/KMotion except the following error.
Of course, if the switches are just connected to KFlop, then the software stops the motors. And, since the software is controlling the motors, I do not see a safety issue with that.

I may be a little dense... it guess you are saying that I could leave the drives OT inputs empty and run the limit switch wires just to KFlop.
If so, what is the circuit connection? I know which KFlop pins to use (suggested pins). I do not know the rest.
Should switches ground the KFlop pin w/pull up resistor? Switch power KFlop pin with pull down? Resistor values? Voltage? Source?
I have missed any diagrams for KFlop connections? Does anyone have some hints on how to find some?

It seems like I should have found this info. Sorry. I have looked.

Thanks.

[TomKerekes]

Hi Dean,

I believe hardware wired limits will always be safer than software limits. With software there can be a bug or simply something not configured or configured wrong to leave you unprotected.

You are correct that if the Job is written to drive into the limit it will need to be changed to solve such a problem. But there are a number of other events where not losing position might be useful.

To wire Limits to KFLOP any input can be used as they are configurable in software. The ones marked are only examples.

KFLOP itself has only 3.3V LVTTL inputs. Some are high impedance and some have pull down resistors. See here. Some are +5V tolerant but it still is not recommended to pull them above 3.8V. Most Systems like to use optically Isolated 24V for limits. It will be up to you to come up with an appropriate interface. If you have our Kanalog option it has 8 5-24V opto inputs.

Regards
TK

[DeanW]

I swear I posted a reply, but now it is gone?
Oh well....

I will wire the switches to the drives.

You talk about KFlop inputs... is that just in case I only want to connect the switches to KFlop?

I'm sorry... I just need clarification :
I plan on connecting the switches to the OT inputs on the servo drives.
Should I also signal KFlop when a limit switch opens?
If so, for what purpose / Action?

Thanks

[TomKerekes]

Hi Dean,

I can't think of a compelling reason.

Regards

[Al_The_Man]

In the past when I have had the option of both such as drives which have the +-OT's, which BTW do not shut down the drive, just inhibit that particular axis direction.
I have also had the option in the motion cards I was using, these also have +-OT for each axis, so it made sense to use the Motion card or controller rather than the drive and this way the card automatically inhibited that particular axis dir, but I also had the feature of the controller being aware of it and allowing program steps to stop the program or tool retract etc or programming any other option.
Al.

[DeanW]

Thanks Al.
This is my first CNC machine - I have spent countless hours reading and planning but I have not gotten very far.

I see the KFlop Config for Limits that have Action settings that are a lot like the drives settings for what happens if a limit is hit. But, I do not know anything about how to configure or program anything to "stop the program or tool retract etc or programming any other option". I figure that the "Limit Action" in the config stops the program? I am not sure what I else can be done.

I purchased a KAnalog so I will have its inputs available. I guess it would be just as easy to connect the switches to it as is is to connect them to the drives.
However, for the same functionality I would be using 2 inputs per drive. I've read that Mach3 can use one input and "know" which direction it was moving to allow reverse direction off of the switches. I am not sure about KMotion. I have not decided if I will use Mach3 yet.
I worry that somehow a bug / lost setting / programming mistake etc. could cause an open limit to be ignored. I am a programmer so I have experience writing lots of bugs. I know that a setting on the drives could be incorrect but it just seems less likely to me for some reason.

I guess it is possible that a limit can be hit on the edge of the working area of the program causing the drive to stop motion in that direction without tripping a following error in the software because the program could immediately change direction and continue. That would not be good. It seems highly unlikely. I am not sure what damage it could cause to the machine.

It just seems to me that if a limit is hit something went very wrong and I just want to make absolutely sure that motion stops ASAP before the machine is damaged... and I would like the solution to be easy to wire and for it to be easy to jog off of a limit. And, I think I want to save as many controller inputs I can for other uses. Gee... I want a lot!

I would feel better if I knew of a simple way to use the drive inputs and also just one input on the controller.
I cannot find any info on the drives about an output signaling an OT state. I only have one set of contacts (NC) on each switch - already wired for use by the old Bandit I controller.
The drives switch inputs are optos powered by 24v (all optos connected) . One switch terminal wire goes to an OT input and the other is connects to the 0v on the 24v supply.
Do you know of a simple way that I can keep this wiring and also send one signal to KFlop/KAnalog?

I have a lot of research to do before I can draw up a complete wiring plan. At this rate, I will be lucky if I can have this machine running before winter is here.

I really appreciate the help.

Thanks

[DeanW]

OK, I was mistaken about my limit switches. I checked and luckily I have 4 Double Pole NC switches per axis. The Positive/Forward limit activates two at the same time. Another is activated by Negative/Reverse. The last one is Home.
There are 5 wires run to the switches. So, I can wire the servo drives OTs and send one single signal for all axis to KAnalog. I will use one KAnalog input per axis for the Homes so I can concurrently home all axis. That will leave me some 24v ins for future use. If I run out, I can put the Homes in series to free up inputs.

I figure I can check the limit input in the watchdog loop and if it goes low issue a halt command and activate an on screen LIMIT indicator.
I guess that is what Al meant by stopping the program, tool retract, etc.
Or, is there already something built in to the motion software for this?

Thanks.