[mackeym]

To prevent damage if a run-away should happen I want to use 2 latching switches per axis on my 3-in-1 machine (shopmaster patriot). Is it better to use these switches to disconnect the "enable drive" pins...or cut the supply power? These are the two options that I came up with, but also what is the normal method that this is handled?

[mactec54]

To prevent damage if a run-away should happen I want to use 2 latching switches per axis on my 3-in-1 machine (shopmaster patriot). Is it better to use these switches to disconnect the "enable drive" pins...or cut the supply power? These are the two options that I came up with, but also what is the normal method that this is handled?

Enable Drive Pins, may be the best choice for your setup, a complete disconnect can be done, this will depend if the servo Drive likes this or not, some Servo Drive you have to keep the Brain alive, & disconnect the Servo Power

[engnerdan]

To answer your exact question as you asked it, "Is it better to use these switches to disconnect the "enable drive" pins...or cut the supply power?" as far as system safety cutting the power would be the BEST. By removing all sources of energy supply you eliminate all chances of energy output from the motors. Technically your enable line could short in an "on" state and leave the drive enabled, or something could go wonky in the drive and it not dis-able cut the enable signal. I know the chances are rare, but you should give it some thought like this.

Up until about a year and a half ago I worked for one of the sensor and safety products manufactures in the USA. As part of my employment I went through training on selecting devices and how to use them. The level of redundancy and monitoring required in an proper OSHA installation is impressive. I am not telling you you have to spend $500+ on OSHA rated parts, I have yet to see a hobby level mill build on this forum that complies with OSHA regulations.


So before going any further, I don't want to be tied to any liability of telling someone a shortcut to making their machine safe, if you want to make your machine meet all possible government regulations I can point you in the direction of some books. Anything but complying with those regulations has to be assumed to be "un-safe" and used at your own risk. Being this is a hobbyist level machine, you are going to do what ever you are going to do. I would recommend putting a little extra effort in on the emergency stop portion of any machine. Read on if you wish




So if I was stranded on an island (not in the reach of OSHA) with only a skipper, professor.........
What I would do as a bare minimum on my own machine would be
- If the only safety feature will be using a switch (like a locking E-Stop red mushroom switch), I would use 2 separate terminal blocks one for each side of the signal power (one connected to the + of the signal and one to the - of the signal).
- If I was using some relays to cut power somewhere I would use 2 of the same relay wired in series. (again 2 sets of contacts per relay, one to break each line of the supply source).


Now moving on a little more advanced, If your drives have separate control power and main power terminals like the picture below, (the TECO and Yaskawa drives I have used both have this setup). Then proper wiring would use a pair of "force guided contact" relays (in series) to break the power to the "Main Power" terminals, if you wanted to do it in a manner that complies with industry approved practices. You would also want the control to drop the "enable" input and most likely activate a "EDM" (external device monitor) pin. You would want the enable pin to not come back on until you have the motion signals (Step/Dir, analog in or other) stopped.

For instance if you hit the E-Stop and it cuts the enable pin, but your controller, breakout board, ect kept sending motion signals to the drive, as soon as you reset that E-Stop the drive may try moving from the commanded motion signals. So ensuring the source of the motion signals has stopped in important. This can also be where the EDM signal comes in, some drives will require a reset pin to be activated to clear the drive after detecting an EDM condition. Depending on your drives and your controls you will use one or a combination of these features.


Attachment 293206

Sorry for all the CYA text above, you just never know where a money hungry lawyer is hiding these days.

-Dan

[Al_The_Man]

As previous post it depends if you want to conform to electrical standards or just do the minimum, disable etc.
There are N.A. standards for permitted E-stop actions spelt out in the NEC/CEC and NFPA79 for industrial machinery.
As also mentioned there is a tendency now to favour a special force guided contacts relay called a Safety Relay rather than the older method of a simple control relay to drop all the motive power sources.
They have been in place in Europe for some time now.
Al.

[rowbare]

I always thought that it was preferable to cut the enable signal over removing power to a drive. The reason being is that when you cut the enable, the drive tells the motor to stop RFN and, barring other catastrophic failure, it will while if you cut power to the drive/motor the load inertia can backdrive the motor and ballscrew. I may well be wrong though....

bob

[mackeym]

Well, I decided what I want to do (unless all these relays/switches are more than I want to buy). I want to cut the enable pins and the power to the drives and maybe the spindle (just like pressing an E-stop button)....everything stops. In case something causes wonky/sporadic motion i'm going to use double pole latching relay with 2 coils so that once a limit switch is hit subsequent limit switch hits won't do anything....and i'll have a battery pack or something to "reset" those latching relays when i want to start up again. Never thought of backscrew happening (maybe i'll test this) though (this is why it's good to stop the spindle too)...don't want to run into a spinning chuck or endmill.

[mackeym]

Sorry for reviving my old thread. Now I have decided on an alternative solution. I want to feed lines from the glass scale cables back to mach 3. This way mach3 will know the actual position at any given time. Then i'll make a brain to set the criteria when to activate the safety shutdown (which will be both to disable the enable pins and cut the power to the drives and also spindle power). If the travel goes beyond given limits or if the position error exceeds a certain value then the signal to active the safety stop will be activated. I appreciate the advice so far and eager to hear any new comments/concerns.

[mactec54]

Sorry for reviving my old thread. Now I have decided on an alternative solution. I want to feed lines from the glass scale cables back to mach 3. This way mach3 will know the actual position at any given time. Then i'll make a brain to set the criteria when to activate the safety shutdown (which will be both to disable the enable pins and cut the power to the drives and also spindle power). If the travel goes beyond given limits or if the position error exceeds a certain value then the signal to active the safety stop will be activated. I appreciate the advice so far and eager to hear any new comments/concerns.

If you setup Mach3 correctly, you have a Charge pump to use, which will take care of most of your safety needs, why try to reinvent what is already in place

when set, soft limits, work with Mach3 very well, you will never be able to hit a limit switch if set correct