Yaskawa Sigma 5 Drive Reset for Light Curtain Integration

[irishismyname]

In order to comply withe ISO 13849 performance level C, I'm having to use the Hard Wire Base Block (HWBB) function on the Sigma 5 drives to disable powered motion when a light curtain beam is broken. I've made some concessions in the PLC logic to pause or prevent motion such as turning on Feed Hold and preventing jog and MPG functionality and this has all worked well so far. However, the final step is to force the /S-ON input on the drive low and then high again after the light curtain is cleared. Is this possible to do from the PLC or CNC system? I'm afraid the only other option I have is to break that conductor out of each cable and run it through a safety relay and I desperately want to avoid that.

[cncsnw]

If you are opening the HBB circuit (CN8), then I don't see any reason to worry about the S_ON signal. The servo is not going to move.

If your issue is that you have not been able to get the control to remove the axis enable, so that the drive can be brought back on line, then that is because you need to finish integrating the light curtain into the PLC.

If interrupting the light curtain is going to assert HBB, then interrupting the light curtain should also trigger a fault condition in the PLC program. The Fault condition will automatically remove the enable (release S_ON); and will force the operator to press and release emergency stop to restore operation.

See the first part of http://www.cncsnw.com/PLCApplicationsMPU11.htm for guidance on how to trigger and report a Fault.

Once you have established the light curtain interruption as a fault condition, then you will no longer have to mess with Feed Hold, jog inhibits, MPG inhibits, etc..

With a little more effort, you could make it a self-resetting fault which clears SV_STOP after the light curtain is cleared, provided no other fault condition remains. However, you should defer that until you have the basic fault logic working (with emergency stop required for reset).

[irishismyname]

Breaking the curtain in this configuration is considered a Category 1 stop, which is essentially a very high integrity motion inhibit while the operator is in the machine. I need to prevent the fault and prevent the Category 0 stop (e-stop) when the curtain is broken. The drive won't come out of HWBB until the /S-ON signal goes low and then high again. I tried resetting and setting SV_MASTER_ENABLE (I think that was it) but that of course caused a CAT 0 e-stop anyway and didn't get me far.

Edit: I'll try a self-resetting fault tomorrow, that's an interesting idea.

Edit 2: Scratch that, the fault will still cause a CAT0 stop that has to be manually reset. If I could just get control of the drive enable signal I would be done. Otherwise I'll have to redesign the e-stop logic.

[cncsnw]

If your goal is to allow the operator to interrupt the light curtain and cause hardware inhibit of the drives, while a program cycle is running, without cancelling that program cycle, then you are going to be frustrated.

It is a consistent premise of Centroid's control that, once you ask Centroid to take control of the drives and run a cycle, Centroid is going to want to keep control of the drives throughout the cycle. There is some very limited ability, within the context of pre-programmed CNC codes, to power off a servo (see M93). There is no provision at all for the PLC program to power off a servo at any time while a cycle is running, and expect that cycle to be able to continue running. Not even in Feed Hold.

My understanding of a "category 1 stop" is that the motors are actively decelerated to a stop, then power is removed; and that a "category 0 stop" is that power is removed immediately, such that the motors may coast to a stop.

My reading of the Yaskawa manual is that, whether you turn off S_ON; remove line power; turn off HWBB; or any combination of the three, the motor will dynamic brake to a stop (assuming the default value of 0 in Pn001.0). This sounds like a category 1 stop to me.

Therefore, triggering a Fault condition in the Centroid PLC (which will set SV_STOP; reset SV_MASTER_ENABLE; remove S_ON from the drives; cancel the program cycle; and open the emergency stop contactor) sounds more like a category 1 stop.

What features of that sequence (triggering a Fault condition in the Centroid PLC) are not acceptable in your design?

[irishismyname]

When the Centroid controller opens its e-stop output it becomes a Category 0 stop, which is the e-stop most people think of.

Category 0: e-stop button is pushed OR Centroid e-stop output goes low.
-Drives should be disabled either via contactor or HWBB
-Control/actuator power for powered devices should be turned off

Category 1: light curtain beam is broken
-Controller should pause or stop attempting to move
-Drives should be disabled by HWBB (perf. level c+)
-Control/actuator power for certain hazardous devices should be turned off

Im understanding you when you say the controller wasn't designed with this scenario in mind. Aborting the cycle is ok, I can do that instead of feed hold, but when I allow the e-stop contacts to open I have to manually reset with another button on the back of the machine. This would be a very odd implementation of a light curtain for this type of application.

Edit: I should mention that the categories as I've described them is how I intend to use them, not their actual definitions per ISO 13849 and 13850. From the servo's perspective, they are both CAT1 as they are powered until stopping. However, the rest of the machine is currently fitting the CAT0 & CAT1 designations.

[irishismyname]

M93 followed by M93 P1 got me what I needed for now, thanks for the tip. I tied that to an aux key to re-enable the drives, which is a bit goofy but will suffice for the time being. If this functionality was available from the PLC I'd be in great shape. I don't have high hopes, but does Centroid accept feature requests?