Ready Steady Eddy

[EddyCurrent]

Some reading.

LPC Siemens Micromaster440
HMK Direct High Performance Drives and Positioning Systems
Motor drives & safety interlock circuits: AC Drives: FAQ (part 3)
Variable Speed Drives - E-stop

My conclusion is that when someone hits the emergency stop button the drive control signals must instantly tell the drive to stop and after a short delay the power is removed from the drive input via a suitable contactor. A braking resistor would be used to slow down the load as quickly as possible but as far as I'm aware it would only be operational if the drive was powered up.
As it happens the ABB drive I'm using has the STO function built in. I'll add a new drawing ASAP.

[JAZZCNC]

Ok lets have a reality check.!!

The spindle is a low powered affair, even at 2.2Kw and if the shit hit's the fan then reality is the situation will be one of just few things gone wrong.
E-stop is hit due to Limit or some other none spindle related condition then doesn't really matter how long spindle takes to slow down and coasting to a stop isn't long or problem.
E-stop is hit due to tool sticking etc then bloody thing will have stopped anyway or will grind to a halt dam quick.!!
E-stop is hit because you have been stupid enough to stick a hand or some other bodily part in the spindle then Yes you'll want the Spindle to stop quick has possibly but again your flesh or clothing will do a good job of acting has a braking and the spindle isn't powerful and doesn't have massive torque so will stall.!! . . So what I'm saying is the VFD's built in DC braking will be enough no resistor required.

Now regards the Kill power or Kill signal to VFD then I used to be Kill Signal guy but I'm now I Kill all power. Reason being what happens if the signal breaks or Even the VFD goes faulty.? Kill power and all doubt is removed. In practice the reality is the spindle will be jammed, either in material or flesh or in a situation where doesn't affect safety and the DC braking allowed without need for a resistor is more than enough.

For DIY use then it's more than good enough to just kill power and Let the spindle coast.

[EddyCurrent]

Dean, you are correct in that every situation has to be risk assessed on it's own.
I also think the braking resistor is not required because of the fairly low inertia of the load.
I agree that for DIY either strategy is fine but maybe not everyone reading this is in a DIY situation, in which case they should be referring to the relevant regulations.
The main aim of this is to get a good emergency stop system using the gear we've got.

It would be useful if we could define some scenarios and strategies for stopping a cnc machine, your input is valuable here.

I've listed some ways to stop the machine and the strategy to adopt, I'm not saying it's comprehensive so please add or amend as you think.

*emergency stop button pressed - strategy 1 or 2
*limit switch activated (not home limits) - strategy 2
*spindle over temperature switch activated - strategy 3
*Stepper driver alarm relay activated (e.g. AM882) - strategy 3
*'Stop' button pressed - strategy 4
*Charge Pump error - strategy 1 or 2

Strategy 1
----------
* remove power to all devices immediately

Strategy 2
----------
* remove power to stepper drives immediately
* remove power to ancillary devices immediately e.g. air, water, dust extraction
* issue stop command to VFD then after delay remove power to VFD

Strategy 3
----------
* issue audio visual alarm before taking action (with time delay)
* controlled stopping of all machine actuators and ancillary devices
* leave power supply on to VFD

Strategy 4
----------
* controlled stopping of all machine actuators and ancillary devices
* leave power supply on to VFD

[JAZZCNC]

I agree that for DIY either strategy is fine but maybe not everyone reading this is in a DIY situation, in which case they should be referring to the relevant regulations.
The main aim of this is to get a good emergency stop system using the gear we've got.

It would be useful if we could define some scenarios and strategies for stopping a cnc machine, your input is valuable here.

Yes Agree in industrial situation then machine needs to be safe and Regs followed to keep the HSE police happy but mostly folks here are DIY and there's world of difference between Reg compliant and being used safely in a shed.!! . . . Practical common sense is all that's needed IMO.

Regards Strategy's then here's my take.!! (which has changed over the years.! I used to kill everything regardless)

E-stop means Foooooooking Hell EVERYTHING STOP NOW.!! . . . So Strategy 1 only.!

Limit/s trip means machine is outside it's working parameters so do something about it.!! . . So disable the drives using the drives enable signal, Not killing power to drives so maintaining holding torque. At same time inform the Control software so it's halts program execution.
Send Stop signal to Spindle/VFD again leave power on has it's not an emergency, it's a machine position error so we just need it to come to a controlled stop.
Along side this you could if wanted turn off other things like vacuum etc either by informing control software or by locally controlling on/off thru Relays but all this should just be on the Limit circuit NOT The E-stop.
Same regards the Fault signals from drives, It's a machine Error not an emergency so same applies just stop the machine in a controlled manner.

If any of the above happens then it should be wired in such away that some form of Latch is dropped and not allowed to re-latch until fault is cleared and then only with Push of a Momentary button not Reset switch.

The E-stop should have ultimate control and Kill power to everything in the event of an emergency so all Latches are dropped and won't reset or start again without some input. Ie Pushing Reset momentary button.

Charge pump and over Temp etc are again machine errors not emergency conditions so just bring machine to stop in controlled manner.

Personally I wouldn't have Temperature control anything over than alert the user thru audible or Visual means. Problem comes from the manner in how the machine is stopped.? To safely stop the machine and not wreck the work piece or lose position requires a Feed hold not a Stop command.! If you stop the machine while it's moving, either thru E-stop, limit trip/machine error or just pushing Stop button on control screen then you MUST presume you have lost position thru inertia pushing, THE ONLY SAFE WAY to bring the machine to stop and not lose position is to use Feed hold and allow the control software to do a controlled stop.
Problem with this is it's doesn't do it instantly so there's always some delay until look ahead buffer is cleared or it's finished the current move. If you have an overtemp problem you won't want to wreck the job so a controlled stop is required so feed hold must be used.
It is possible to use an input and have Mach watch it then use an OEM trigger to activate the Feedhold if the state changes but personally I wouldn't and just have a Spindle siren scream at me.!!

This also answers your "Stop Button" option.! . .Pressing stop will only stop the machine and other attached devices in a semi controlled manner but it won't be controlled and can't reliably be resumed from without first homing the machine to get back into position.

Also noted you said Home limit's.? Home switches are not limits of any kind neither are they part of any system, e-stop or limit etc. They solely define the Machine coordinate Zero position and are purely input's to the Control system and nothing else..!! . . . .(Eddy I know you probably know this but others may not)

[Jonathan]

Looks like we're all largely saying the same things now.

This also answers your "Stop Button" option.! . .Pressing stop will only stop the machine and other attached devices in a semi controlled manner but it won't be controlled and can't reliably be resumed from without first homing the machine to get back into position.

For the non-emergency stop button, you could just wire it to an input set to activate the feed hold, so the machine does in a controlled manner. It's still likely to leave a mark on the work, but prevent something worse.

[JAZZCNC]

Looks like we're all largely saying the same things now.

Didn't see your post until after I'd posted that.

For the non-emergency stop button, you could just wire it to an input set to activate the feed hold, so the machine does in a controlled manner. It's still likely to leave a mark on the work, but prevent something worse.

Erm.!! . . . Well that would just be a Feed hold so why not Call it Feed Hold.??

[cncJim]

.....
The main aim of this is to get a good emergency stop system using the gear we've got.

It would be useful if we could define some scenarios and strategies for stopping a cnc machine, your input is valuable here.

I've listed some ways to stop the machine and the strategy to adopt, I'm not saying it's comprehensive so please add or amend as you think.
.....

This is a great idea Eddy, great for noobs like me. Might be nice to add example circuits for each strategy (might be getting carried away now...)?
I have made some changes based on some of the feedback and tried to make clear which things should be done in hardware and software, hope that's ok. Maybe it could make a good sticky?

List of scenarios and possible strategies for dealing with them.

Scenarios

• Emergency stop button pressed - Strategy 1, 2 or 2.5
• Limit switch activated (not home limits) - Strategy 2 or 2.5
• Spindle over temperature switch activated - Strategy 3 or 3.5
• Stepper driver alarm relay activated (e.g. AM882) - Strategy 3 or 3.5
• 'Stop' button pressed - Strategy 4
• Charge Pump error - Strategy 1, 2 or 2.5

Strategy 1

• remove power to all devices immediately (Hardware)
• Inform control software of Estop condition (Software)

Strategy 2

• remove power to stepper drives immediately (Hardware)
• remove power to ancillary devices immediately e.g. air, water, dust extraction (Hardware)
• issue stop command to VFD then after delay remove power to VFD (Hardware)
• Inform control software of Estop condition (Software)

Strategy 2.5

• Issue stop to stepper drives then after delay remove power to stepper drives (Hardware)
• issue stop command to VFD then after delay remove power to VFD (Hardware)
• remove power to ancillary devices immediately e.g. air, water, dust extraction (Hardware)
• Inform control software of Estop condition (Software)

Strategy 3

• issue audio visual alarm before taking action (with time delay) (Hardware/Software)
  After delay:-
• Stopping of all machine actuators and ancillary devices (Software - "Stop" Command)
• leave power supply on to VFD

Strategy 3.5

• issue audio visual alarm before taking action (with time delay) (Hardware/Software)
  After delay:-
• inform control software to activate Feedhold (Software)
• Move to safe Z (Software)
• Issue stop command to spindle (Software)
• leave power supply on to everything

Strategy 4

• Stopping of all machine actuators and ancillary devices (Software - "Stop" Command)
• leave power supply on to VFD

[m_c]

E-stop systems are always a good cause for debate.
Ultimately they should stop movement likely to cause personal injury, and how that can be acheived depends on the machine.

We've got some quite expensive lorries at work with external equipment where some will kill everything including the lorry engine when an E-stop is pressed, whereas others will only kill the external equipment. There are pros and cons to both.
The key requirement is they should be fail safe, and periodically checked.

One question for everybody is, when did you last check all your limits and E-stop buttons worked?

[JAZZCNC]

One question for everybody is, when did you last check all your limits and E-stop buttons worked?

Don't have limits but I must hit the Oh shite button at least ounce per day. . .Lol

[EddyCurrent]

Thanks to all who contributed it's been very rewarding I think and thanks to Dean and Jim for pointing out the FeedHold function of Mach3. With all of this each individual will have to make their own judgement, this is just mine.
After going through the available information I decided to list the 'stopping methods' for each of the major components, i.e. VFD, stepper motors, Mach3, ancillary equipment.
I decided that cutting power directly to the VFD was not for me so will implemented method 1 below.
Also I decided that control of the ancillary equipment was currently outside the scope of my control cabinet but if later on it does fall within the scope changes will have to made.

VFD stopping methods
---------------------------------
1. immediately issue 'emergency stop' command and after delay remove power to input ('e/stop' command can be set to stop drive faster than 'stop')
2. immediately issue 'stop' command and leave power to input
3. use STO function if available to prevent restart (this is not a stopping function)

Stepper Drivers stopping methods
-----------------------------------------------
4. immediately remove power to stepper drivers
5. immediately activate 'enable' signal (breakout board also uses charge pump signal to disable outputs to stepper drivers (not using 'enable' signal)

Ancillary equipment stopping methods
-----------------------------------------------------
6. immediately issue stop command (varies according to equipment)

Mach3 stopping methods
-----------------------------------
8. immediately issue Feed Hold command to Mach3
9. immediately issue Stop command to Mach3

Other stopping methods
---------------------------------
7. immediately issue audio visual signal

Next I looked at the stopping scenarios, developed strategies and assigned 'stopping methods' to them, I felt it was important to minimise the number of strategies so carried out some mental boolean algebra and Karnough mapping.

Only strategy 1 will be considered Safety related, it also aligns with the suggested drawing in Mach3 documentation.
Emergency stop is obvious, for me limit switch activation may lead to a dangerous situation, charge pump activation means Mach3 has lost control so anything could happen.

*emergency stop button pressed - strategy 1
*limit switch activated (NOT home limits) - strategy 1
*Charge Pump error - strategy 1
*'Stop' button pressed - strategy 2
*spindle over temperature switch activated - strategy 5 (assumes someone is in attendance otherwise use strategy 4)
*Stepper driver alarm relay activated (e.g. AM882) - strategy 3

Strategy 1 ( 1,4,9 )
Strategy 2 ( 2,5,9 )
Strategy 3 ( 2,4,9 )
Strategy 4 ( 2,5,8 )
Strategy 5 ( 7 )

Next up will be some updated drawings to implement this.