Programmable Relay to Watch Dog the Limit/Home sequence

[smreish]

Hey Forum,
I have this crazy idea...and so far it works on paper.
Use a programmable Relay (Small form PLC) to run the sequence of events for a standard home routine and also watchdog as a over travel limit system.

I was reading in the Shopbot and CNCforums recently on a group of folks that were using a "ladder logic" approach with their limit system to work up permutations of and, or, and/or andxor and the such while only sending a single or contact closure to the PMDX. Which, without getting into the true table that was represented....I thought, hey..maybe I can do that.

The thought is to use a PLC or Programmable relay like


TECO Genie II Programmable Relay, 12 AC Inputs, 8 Relay Outputs, Keypad / Display, Expandable (Max. 34) I/O Or the similar PLC from Automation direct to handle the logic and disable sequence to the geckos. Since the Geckos will allow an external disable, you could theoretically use the plc to stop the drives when they have reached limit and then use an external switch/input to reset the drives while holding position. As position is held....Mach3 is then made aware that the current position is true Machine 0,0.

The most appealing part of this idea is the Relay or PLC both will source/sink 3 wire PNP or NPN proximity switches that will keep the MM design intact.

....Let's all chip in ideas here and keep the feedback coming. This could be a really affordable solution. I expect to hear from Doug, Alan, Greg, Mike, Gerald and JR soon

Sean

[Doug_Ford]

Sounds like a great idea to me. I'd love to add that capability to my machine.

[Richards]

I've only taken a few minutes to visit the FactoryMation web site. The Teco comes in several variations, AC input, DC input, Relay output, Transistor output, etc. If I were considering one of the Teco modules, I would first make a list of the various inputs that I needed to use, then I would make a list of the various outputs that I would be sending to the MechMate controller. Finally, I would make a list of things that I expected the module to do, i.e., get the signal from proximity switch #1, send that signal to the MM controller and then wait for an acknowledge signal from the MM controller, etc.

Price-wise and feature-wise, the Teco looks pretty good. But, as they say, the devil is in the details - especially when it comes to computerized controllers.

[smreish]

Mike,
Thanks for the quick review. You and I are on the same page. At a first glance, I think I have found a few devices like the TECO that seem to work. I will be working on a true flow/signal chart in the upcoming week or so to work out the details....I just thought starting a thread would help jog everyone's memory with regard to limits.

Details that are important to consider:
- controller operation voltage/current
- controller signal isolation (or lack of)
- cycle time
- output (relay, transistor source, etc.)
- input ac/dc or dry contact

Or.....maybe just add a second PMDX and run it all from inside Mach3

Keep the idea's coming....
Sean

[BernardR]

Hope you guys don't mind if I jump in with a few thoughts.

First, I believe the main control program should have absolute control over the ESD condition, of which positional control relative to home and limit switches is integral.

I am at a disadvantage of not being aware of some of the controllers you are discussing.
This is because after stumbling around in 2001/2 with various controllers I came across Master5, which was the forerunner of the MachX controllers. After futzing around with it the free version I sprang the then $75 for the license and have been updated for free ever since. The overwhelming reason for getting the license was because I was able to see up close and personal every detail of the development cycle. Without doubt that group had the most dedicated forum I have ever come across.

The phenomenal success of MachX, IMO, is due to three things, one, without question and speaking as a programmer, Art Fennerty is or is close to a genius. Second, he listens to everybodys input and suggestions, and then implements the optimum solution. Third, regular forum members ranged across the whole spectrum, professional engineers, safety specialists, programmers, lifetime big CNC machine operators and lots of dedicated small engineering shops and home shop operators. The net result of all this is every aspect of the design has been picked over and refined by all users.

This is especially true in the safety circuits, including the Home / Limit switches.

I hope I haven't put too much of a damper on your proposal and at the end of the day in the hobby field you are the ultimate decider, I would just hate to see anyone put any significant time and money into something that I already know has been picked over by experts.

My own recommendation, if you don't already have Mach3, use the money and buy a license. Not only do you get a router controller, but also lathe, foam and plasma.

Disclaimer: No association with ArtSoft or Art Fennerty, apart from the greatest respect and unfailing assistance (mostly from my own misinterpretions.

[Richards]

Bernard,
I agree with you about Mach 3. It is one of the best programs that I've ever used for process control.

The Enco device actually acts as a single (usually) input to Mach 3. It monitors various input lines and then activates the e-stop signal or any other input signal, depending on the devices that the Enco is monitoring. In effect, if offloads the tedium from Mach 3, but uses standard Mach 3 inputs to control the machine.

In effect, the Enco can be programmed to act as a tool changer, a proximity switch monitor, a multiplexer to turn on/off various devices external to the Mach 3 program, etc.

I've never used latter-logic devices in my designs because back in the mid-1980s, when I last looked at them, ladder-logic devices were both expensive and underpowered. On first glance, the Enco device seems to be moderately priced and powerful enough to be of value; however, it is a programmable device, and its usefulness depends on the ability of the program writer.

[BernardR]

Mike,

Do you have an URL to the Enco device? I haven't used one before.

What I'm also doing is trying to catch up with whats been happening in the Mach world, especially with things like Geko's GRex and other high speed serial devices (tcp/ip, usb etc). It is now absolutely clear that the parallel port Mach3 is on the wind down and only essential maintenance and remaining long term development items are being completed.

I've also recently being looking through some of Art's video tutorials and viewing the brains and modbus modules shows that Machx for all practical purposes can deal with virtually any number of inputs, using a tcp/ip modbus 1024 16 bit input and 1024 16 bit outputs are available either as digital or analog signals.

Again watching the Brainsintro 1 it is apparent that the Brain element processing time is incredibly fast, Art claims that even with 100 brain sub programs running he has never seen the Brains DRO raise above 0.

The way I am looking at the moment is that in the reasonably near future I will upgrade to one of the serial interface boards, abandoning my two PIOs, some of the various forums like the Grex, but others feel it is a bit limited. I have no doubt that there will soon be a greater number of hardware solutions available and for the moment I can bring myself back up to speed and get ready for when I feel the time is right. Right now my inclination is to get the simplest possible box which can handle a wide variety of opto isolated i/o, mechanical and solid state relays and a reasonably fast analog system. Reasonably the Home/Limit switches could come through this box, so for the moment I would prefer to look at an integrated solution.

[Richards]

Bernard,
I'm sorry. I was thinking Teco and typed in Enco. You'll find information about the Teco programmable logic controller at www.factorymation.com.

Gecko is no longer promoting the G100 device. Mariss announced a few weeks ago that he just ordered another 500 units, which will probably be the last batch that he builds. I have both the G100 and the G101/G102 that pre-dated the G100. It is an excellent device, but Art and Steve have not been able to make it useful when the parts file contains a lot of small moves. The feed-back loop time is just too long for that type of tool path.

Personally, the difficulty of extending G-code is the main reason that I'm still using a Shopbot controller on my machine. The SB controller has easy-to-use I/O, which makes it easy to interface other devices to the controller. G-code is excellent, but I haven't taken the time to learn how to program in other non-standard functions - yet.

[BernardR]

Mike,

You sound about as bad as me, my wife and I have a 1 bedroom 2500 sq ft home!! and no I'm not really a MCP my wife in her own way is as bad as I, mine just takes up a bit more space. The reason I haven't done anything about the MM is because at present I don't have the space, our extra wide garage houses a full size knee mill, a sliding table 12" table saw with a 50" extension / router table, a SB 10" lathe, TIG welder and an array of grinding tools including a home made Quorn T&C grinder. When you add a workbench and a bunch of handtools there isn't room left to swing a cat. (Thats just the mechanical stuff).
I drew up the plans to build a L shaped garage 48' long with one half extending an additional 20' to have separate wood, metal and grinding areas. So far still pretty plans. but we both feel that its getting time to implement. OTOH we may just pour a slab and put up a steel building.

[smreish]

Bernard and others.
Thanks for the round-a-bout discussions on the ancillary controller. I am still researching all the voltages and such, but on paper, the ladder logic appears to work with the current needs of the MM.
Does anyone know what the true switching Latency/hysteresis cycle time is for the PMDX? I would like to make certain that the TECO or Koyo (automation direct) PLC/Relay is fast enough to scan and report it's I/O structure.

Sean

[Richards]

Sean,
I don't have any specifications for the PMDX-122 except those published in the manual. However, because everything is standard TTL type logic (with some opto-couplers), latency would be in the low nano-second range for the TTL and sub-millisecond for the opto-couplers. Normally the main latency-hog would be the interval between interrupts on the PC side. I assume that Art uses interrupts to time the interval between port scans.

I think that if you determined the maximum distance that you could allow an axis to move between the time that a proximity sensor was first triggerd and the point that the axis movement was near a hard stop, you would know the maximum latency for your machine. I can't imagine that you would need anything less than 250 milliseconds for your maximum latency period. Although I don't know the step rate for the PLC, it should be able to scan an input in less than millisecond. So, even with 10 or 12 inputs, you should have a safety factor of at least 15X to 20X. (Because actual homing would be done at low speeds, your final accuracy would be acceptable.)

[Gerald D]

Sean, the only thing that appeals to me with the PLC is that one would be able to get a lot of proximity switches to give a single output.

I feel that the extra logic offered by the PLC does not add to the capability of Mach3's logic. Mach3 already handles homing and limits off a single input (all switches in series). (Gantry squaring is also built into Mach3, but then one more switch is needed). When Mach3 is in "homing" mode, it treats a switch signal as a reference point.....when it is in "cutting" mode, that same switch is treated as a limit switch.

However, I don't speak from experience, since neither of our MM's have any switches on them. The only time we feel the need for a switch is when we want to restart a file after a power failure, and homing would give the reference to get the cut path to continue at the same place.

[J.R. Hatcher]

Gerald do you have soft limits setup in mach for your machines?

[Gerald D]

Very rarely. I don't think that Sean has them set now, but he hasn't had a new operator person in the shop for a while. Suspect he will set them if he hears a few loud bangs coming from the workshop. The hard stops can take the punch......and they teach one to be more careful next time.