New to AB-CompactLogix programming concept

Hello All,


It has been several years since I have been in the PLC world, and most of my prior experience is with Automation Direct PLCs, Yaskawa programmable motion drives, and Adept robotic controllers. I have been given a new project to retrofit a relay controlled machine with PLC control. The client has specified that the PLC and touchscreen HMI be Allen Bradley. This machine is a small saw that consists of a spindle drive, a hydraulic cut feed cylinder, and Kollmorgen electric cylinder for part indexing (the electric cylinder/stepper drive was a retrofit several years back). The hydraulic cylinder has a Heidenhein linear encoder attached, but it will be integrated in the future. For now, the cylinder is controlled with adjustable cut depth and retract limit switches. Initially, the client would like to duplicate the current functionality of the relay controlled saw, and upgrade capabilities in the future through programming. There are several identical machines to be retrofitted, so the first stage on the first saw is basically a proof of concept.



Here are the major components of my control system:

• 1769-L32E PLC with input and output modules, a high-speed/encoder module for spindle speed feedback and linear encoder use
• AMCI 3602 module for control of a Kollmorgen electric cylinder (labeled as IDC, but it is a Kollmorgen N2)
• PowerFlex 40 AC drive (with Ethernet comms card)
• PanelView Plus 6 1250 touchscreen with Ethernet
• Stratix 8000 Ethernet switch (the machines will likely be connected to the corporate network at some point in the future)

I have created a block diagram for the basic functionality of the machine, but I wanted to make sure that I am thinking about this the correct way - I would love some feedback! My concept is to have a separate "safety" part of the ladder that monitors critical machine functionality like pneumatic air pressure (the spindle runs on an air bearing, so a drop in pressure means an immediate stop is warranted), EStop button status, coolant flow, cover latch proxy, etc. The main program of the ladder would actually run the cutting, indexing, jogging, etc. - normal machine functions and programmed routines. Am I thinking about this correctly? I can try to post the block diagrams if needed.


Additionally, I have never used a motor control module integrated into a PLC like the AMCI module. The former retrofit used an IDC SmartStep power supply/programmable stepper controller on the Kollmorgen cylinder. It looks like I can use the AMCI to directly control the cylinder, but what do I use for powering it? I have always just connected my controller to integrated drives in the past... I suppose I can use the SmartStep drive to provide power only, but that seems like a kludge.

Thanks in advance - I look forward to learning a lot on this project!

Chip

cstech said:

My concept is to have a separate "safety" part of the ladder that monitors critical machine functionality like pneumatic air pressure (the spindle runs on an air bearing, so a drop in pressure means an immediate stop is warranted), EStop button status, coolant flow, cover latch proxy, etc. The main program of the ladder would actually run the cutting, indexing, jogging, etc. - normal machine functions and programmed routines. Am I thinking about this correctly?

Click to expand...

Yes, the more info the PLC has the better, but it can't be the ONLY device handling this. The PLC is not a safety device. There should ALWAYS be hardwired safety circuits, independent of the PLC, especially on anything involving the safety of the person operating the machine.

I'm not familiar with the AMCI, but you usually need a separate drive for a stepper or servo. You just need a 'dumb' drive that takes step and direction commands from the motion controller. The motion controller cannot power the motor directly. By the way, Automation Direct sells some pretty inexpensive stepper drives...



-Eric

Sounds like a good solution. Like Eric said above, the safety system needs to be hardwired. You may need to use a redunant Cat 3 Safety Relay/module/control & wiring for Estop and guarding switches/systems(depends on the risk assesment).

I am not a fan of the stratix switch. They take 5 minutes to boot up, are overly complex, and quite expensive. AB makes a less expensive industrial switch (forgot the model number).

I had a stepper motor application last year and looked at the AMCI card. It would have worked for the application but found a way to drive the stepper directly from a 16PT issolated digital output card and thus avoided that expense. If you need to retain the Kolmorgen control, you will need to go with AMCI module due to AB I/Os being non-sycronous. Fluctuations in timing will drive the motion control nuts and the AMCI module is the only way I know of to avoid this. If the motor is a stepper, and cost is an important factor, you could drive it directly with PLC IO. Let me know if this is an option, if so, I can pass along more details on how to do this.

cstech,

in regards to the air pressure monitoring circuit, have a time delay response, not an immediate stop. air pressure can and will suddenly drop below your comfort zone due to lots of valves turning on, or the other production machinery.

i always have a 1 - 2 second time delay before shutting off the machine due to loss of air. this delay catches the sudded losses without shutting down the machine. if the timer expires, there is a problem.

regards,
james

Thanks for the input everyone! I found the legacy IDC drive that formerly powered the Kolmorgen electric cylinder cannot take simple step/direction input. I have spoken with tech support at AMCI, and plan to use their ethernet combination indexer/drive instead (model SD17060E). I like this option because it can take an encoder input as well.

On the safety circuit, I like the advice on the safety relay. I will integrate one for the E-stop and the proximity switch on the door latch as both of these relate to operator safety. I will use the PLC to monitor the safety relay so related messages can be displayed on the HMI. In my experience, machine safety (as opposed to operator safety) is just handled by the PLC. For example, James mentioned a pressure monitoring circuit that has a small timer delay (great idea, BTW) - I plan to put machine and process monitors like that in a separate area of the logic to continuously look for problems (low air, low coolant flow, etc). Does RSLogix 5000 accommodate a separate machine monitor ladder? Or do I simply put everything in one ladder, and run in parallel?

Thanks again!
Chip

RonHowellDotCom said:

I had a stepper motor application last year and looked at the AMCI card. It would have worked for the application but found a way to drive the stepper directly from a 16PT issolated digital output card and thus avoided that expense. If you need to retain the Kolmorgen control, you will need to go with AMCI module due to AB I/Os being non-sycronous. Fluctuations in timing will drive the motion control nuts and the AMCI module is the only way I know of to avoid this. If the motor is a stepper, and cost is an important factor, you could drive it directly with PLC IO. Let me know if this is an option, if so, I can pass along more details on how to do this.

Click to expand...

Could you elaborate on how you did this? I've experimented in the past with driving stepper motors from standard PLC I/O and the results have always been disappointing... the outputs just aren't fast enough to produce smooth motion.