The Craftmans Shop > New from Old
The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
RotarySMP:
Thanks Andrew, since you have done a lot of this work, have there been cases where you went the other way and retrofitted?
Mark
awemawson:
VERY many years ago I did a Denford ORAC lathe and a Denford TRIAC mill. I bought both with totally destroyed controllers and fitted PC's running TurboCNC, as Mach hadn't got off the ground in those days. They worked very well and had the advantage that I knew the control programs inside out as I wrote them. Too small though so they financed the purchase of a Bridgeport Interact.
Prior to that I had semi-done a Bridgeport / Moog (*) Hydropoint-1000 NC machine - it had hydraulic servo positioning, and pneumatic instruction reading by blowing air though punched paper tape 24 bytes at a time. I made a 'behind the tape reader' interface for it reading and writing driven serially off a PC parallel port using compressed air and tiny valves !! (and it worked!)
(* The MOOG in question was the brother of the Moog Synthesiser one which is where he got his pneumatic read concept. He went on to make hydraulic control valves for NASA for the 'man on the moon' program. In fact there is one of his hydraulic proportional control valves in the control loop of my Eurospark H425 die sinker EDM machine)
awemawson:
Just to show you that I've not been entirely idle I'm attaching the main PLC program block 'PB202' with the Inputs, Outputs, Flags, Timers etc that I have so far managed to identify labelled.
Sadly the way the STEP5 'Documentation' function works, it lists the named items under the particular segment, rather than substituting the names in the actual segment of the ladder, but hey-ho it's better than nothing.
I think I've identified everything that is in the bits of documentation that I have, so from now on it's going to be a case of trying to work out the function of items then naming them myself.
An example is in Segment 61 where there is an S / R latch that is SET by the dynamic M code M20 (that is giving me the issues) Now I KNOW that Flag bit 31.4 is set for an M20 from documentation that I have, so it's been given an appropriate name. But the actual R/S latch, being implemented by Beaver when they built the machine, is NOT in any of the Siemens documents, but it still needs naming to understand the rest of the ladders, so I've christened it M20ACTV (or M20 active the label is limited to 8 characters) - so references to F 149.4 (bit 4 in flag byte 149) will later in the ladder have a name that MIGHT prompt more understanding !!
. . . lots more to do though
awemawson:
No activity yesterday other than printing out my latest cross reference list, as a reunion with friends in Littlehampton was the order of the day - early departure and late return.
However four hours of thinking time on the journey got me to a diagnostic method that I applied this morning. Now that I have the entire PLC program on paper, and can inspect inputs, outputs and flags using the inbuilt facility in real time I can trace what is happening.
So the problem is, that issuing an M20 ('Enable Spindle Drive') command that is the preparation for M19 'Spindle Orientation' the M20 is entered but then locks the control by not asserting the 'Read In Enable' line, so the control is freezing and not reading the next command. However the bits are set in the flag words that the spindle is indeed enabled by the M20.
Now having the PLC ladder in front of me like a circuit diagram, I can go through the logic that asserts 'Read In Enable', which is segment 77 that is a simple dependency on both F 136.6 and F 138.5 being False (or 0). This showed me that F 138.5 was the problem being at a '1'
The previous 'Segment 76' produces the flag bit F 138.5 from a twelve input structure requiring all it's inputs to be '0' (apart from one where the logic is inverted for 'Turret Card Fault') and the failing input was traced to the third input element being F 149.4 (M20 Active) in series with I 5.1 (Spindle Clamp Pressure Switch)
Well guess what - although the spindle clamps OK with an M31 and unclamps OK with an M32 the input on I 5.1 is the inverse of what I would have expected, with a '1' for unclamped and a '0' for clamped.
How could this possibly happen :scratch: Well think back to the end of July, when I got all enthusiastic replacing the solenoid and pressure switch sockets as the old ones had perished - I couldn't possibly have wired it wrongly could I - oh yes I could :palm:
So a quick wire move from the NC to the NO terminal, and guess what - the M20 command now completes as it should and the following M19 command is read in :ddb:
However I'm not out of the woods yet, as the M19 keeps the 'Run' light on and doesn't orientate the spindle but just sits there glowing :bang:
OK never mind, this IS actually major progress as now I can hopefully trace out what is happening just as you might with the equivalent physical relay circuit and a multi-meter.
Not every item in the PLC ladder is yet named, and probably never will be, but this method will let me concentrate on the area with the issue rather than having a scatter gun approach
russ57:
You must be chuffed Andrew...
I reckon that is indeed significant progress.
-beating step 5 into grudging cooperation if not actual submission
- a window into the logic, if not a door.
-substantial progress in your spindle issue
-fixed one of hopefully only two defects (even if it was one you introduced )
Russ
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