Problem- Interact 4-TNC 155 will not home X

[Daninwyoming]

Working on a Bridgeport Interact 4 with a Heidenhain 155 control that will not home on the X axis. It will travel in the X+ direction as expected, but when the reference dog switch is reached it jumps rapidly in the X+ direction and trips out with usually a "gross positioning error D" message. Pushing the reference switch at mid travel will produce the same effect but will only travel less than half an inch before the trip out and error message. The X axis hard limit switch funtions properly. The switches seem to be working and there appears to be no wiring problem because the control is recognizing the switch signals. All four of the green LEDs on the axis drive board will light before the trip out. This machine came with no documentation and we are using a list of "generic" parameters. We changed the X axis drive motor and encoder with one from the "cannibal" machine, but did not improve upon the problem. The Y and Z axis work fine.
On the other Interacts, pushing the reference switch will reverse the direction of travel and upon releasing the switch will stop when receiving the next reference pulse.
Has anyone had this similar problem and found a cure? Thanks, Dan

[machintek]

First make sure the tach circuit is not open.

George

[Woody111]

Try swapping X and Y motors see if it the problem follows the motor. Also use an ohm meter and check your X-axis cables back to the cabinet. Could be a bad motor, bad encoder, bad cable, bad interface board. Sounds like the switch is working but make sure it is not sticking clean it first with contact cleaner and work it up and down with axis power off.

[D-Money]

What are your X and Y max-travel distances (i.e. table size) set to (such as 30" on x and 12" on y)? Sometimes a bad entry there will cause all sorts of strange issues, including gross positioning errors and a "jumpy" x-axis (happened to me on an EZ-Trak).

To me, it sounds like the X travel (table size) has been set to 0. Automatic-homing will hit the limit switch, but when it tries to retract the default distance, it errors out because of the 0 size.

Also make sure your limit switch wiring is physically good. When we replaced ours, the old stuff had cracks in the casing, bare spots, and one section connected by only 2 individual wires in the strand.

[Daninwyoming]

We do not have the original documentation for this machine. I found on a "borrowed" schematic that the tacho for the X axis should go to inputs 4 and 6 on DC1 ( wires 40 and 41)and input 5 (wire 42) on DC1 appears to be a grounded sheilded cable. Is that correct? What would the resistance be if the tach and wiring is OK? If open would we assume we have a wiring problem?
We have already switched motors and encoders and the reference and limit switches are sending their signals. (We have a machine we canabalize for parts.)
I do not believe the travel distances would have any meaning before the machine is referenced (?).

[D-Money]

Originally Posted by Daninwyoming I do not believe the travel distances would have any meaning before the machine is referenced (?).

If you want help, then don't discount our input before you even try it. Do me a favor and check the travel-settings/table-size. A bad entry was enough to KO an EZ-Trak, the same might hold true for you too. Besides, checking a simple entry in the software config is a hell of a lot easier than swapping motors & encoders back and forth.

[gus]

If the tach is ok:

check the parameters for x axis counting direction and direction while passing over reference.



jumping when it hits the ref can mean it is expecting to be moving in the other direction.

remember while homing , all the control does is send out 'x' volts to the servo amps, it does not look at or care what the encoder says until it hits the trip dog and sees the encoder pulse

[Daninwyoming]

Would you happen to know which parameter would change the direction of movememt? That seems to be what is happening. The other two Interacts 4's we have both have TNC 2500's and the parameter set looks totally different from what the TNC 155 is expecting. The parameter set from our Interact 1 Mk 2 looks somewhat similar, but it was for a TNC 151: not TNC 155. We have some parameter sets from other internet sources that are for the TNC 155, but those list have more parameters than this control will take. This control stops taking parameters at (I believe) MP 235.

I agree with you Gus, I do not think the numbers mean any thing until the machine is referenced.

It was 24 below here last night and didn't get above zero today, so didn't go out to the far shop to check to tacho yet. George suggested that is where to start. Supposed to get a warm day on Wednesday, 20 above!

I found in the maintenance manual that the resistance thru the potentiometer R23 (Tacho) should be 1.4K, but that doesn't tell me what the resistance would be thru the wiring and the tach. Any ideas? I suppose I could check the value on the other two working Interact 4's for a comparison. I guess if the circuit is open, as George said, then look at the wiring and then the tach. Thanks , Dan

[gus]

there is no set resistance for the tacho pot, that is just a starting point when setting up a new machine/amp

[machintek]

I believe the velocity loop (tach) should read about 100 ohms. Measured from inside the electrical cabinet. I am suspecting the cable just due to the age of the machine. This is a gut type of reaction while reading the initial posting. BUT parameters could be an issue as well.

George

[Daninwyoming]

Checked the resistance thru the tach on a motor we have on the shelf (from the cannibal machine) and measured 50 to 60 ohms. Heat wave today, warmed up to 27 degrees. Went to the far shop and measured the resistance thru the tacho circuit (velocity as described by George) to be 49 ohms. Spun the motor by hand and resistance behaved just like the shelf motor. We concluded the tach and wiring to be OK.

From the several listings of parameters we have for the TNC155 we changed the parameters to a set that had only 236 parameters listed. Thinking the control will only accept 236, that list was most likely to fit the machine. Holding our hand close to the E-stop, powered up and began referencing. The Z referenced, hit the reference switch and jerked -Z about 3 inches and the " gross positioning error" (also known as the blue screen of death) showed its evil head. Luckily the table was set low enough that we didn't crash. We finally got the machine to reference by examining the difference between the several sets of parameters and using the SWAG method got everything working. Set the X, Y, and Z limits and were home free. Not quite! The Z moved the 150 mm, but the display only registered 75 mm. Again using the SWAG method, changed one of the parameters from a 2 to a 1. and fixed it. We really need a description of the function of each parameter. Thanks to all who helped and if anyone has a description of the parameter functions, we would love to have a copy. Special thanks to George, as usual your advice was right on. Thanks, Dan

[awemawson]

Go to the Heidenhain web site - OMA documentation and down load the installation manual which lists all the parameters