POLAR 115 EM MON -- No pulses from the LMS --

Dear colleagues,

I have a problem with our Polar 115 EM Mon, Ser. 6331385
After power on the machine I have the message ,no pulses from the length measurement system'. It's not possible for me to make a reference drive for the backgauge. The machine is also in mode help operation.

Further when I actuate the backgauge I hear the noise from the brake motor, but the brake will not open.

I think we have to change the very expensive LMS length measurement system.
Maybe ther is someone in the forum who can confirm assumption.

Kind regards,
Georg

 

Try check the guiding cable (screen cable) first and please take a look at here http://welvin.byethost7.com/lms/

 

We have already changed the trailing cable of the LMS against a new one

 

Hi,
Is the backgauge actually moving?
If not first check the backgauge motor overload.(I think it's good because you said there is a hum from the motor)
Anyway, go through following steps,
Check the fuses first. All the fuses are located under the cover of the left leg of the machine.
then check the motor brake coil using a multimeter. If all above fails, we have to check voltages. It's a bit complicated procedure. So please check above and let me know. Then we'll go further.

Hope this helps.

 

Hi NimeshSilva,
thank you for your reply.
The backgauge is not moving.
As I wrote in my description it is not possible for me to make the reference drive because message no pulses from the length measurement system appears.
The motor overload is O.K.
The fuses are O.K.
When I actuate the motor with the handwheel, the brake coil shows an unstable measurement sometimes till 13VDC.
But I think maybe the time period for a stable measurement is too short because the brake coil is for approx. 2 seconds actuated then the machine has the fault status after 'beep beep' - no pulses from the length measurement system.

The voltages of the PS Power supply are O.K.
For the brake coil Y17 I see there should be 24VDC from the wiring diagram.
The light emitted diode V33 from the PI Interface card will be emitted after actuation of the motor brake.

 

Hi,
I suspect the brake is not releasing. Let's find out.

Have you tried the secondary operation?
If not, try to put the machine in secondary operation mode. This can be activated by pressing the = sign (or in some machines the letter "A" ) instead of activating the reference run. Then the basic machine functions will be available. You can clamp, cut and move backgauge without the measurement. If still the backgauge cannot move, then let's check the break. (In this mode, if you press handwheel button, the high speed is activated and if the brake is stuck, the overload might trip. If that happens, wait a few minutes and turn it on)

Then we'll check the mechanical adjustment of the brake itself. Remove the back cover of the motor and you can see the air gap between brake plate and the pressure plate. Grab a feeler gauge and check. 0.2mm is the ideal adjustment. If they are too much apart, loosen the 3 nuts and try to get them as close as possible to 0.2mm. Tighten the 3 nuts equally. (This needs a bit practice. So be careful if you do it wrong, the next error will be "position not achieved")

If that is OK, then we'll measure voltages.
In this machines, the brake (a.k.a brake lifting solenoid) is activated in a special way. Listen carefully.

Can you see the aluminum capacitor down on the MC unit? (Right next to the 3 ERNI relays) This capacitor is responsible for the activation (lifting) of brake solenoid. As soon as you apply power to the machine, this capacitor will charge to 42VDC via the green resistor next to it. Then as soon as the backgauge movement is initiated, this 42V charge in the capacitor immediately dumped to the brake coil. So that it lifts very rapidly. (Now the brake is released) Then it is holded by the 24V until the movement is finished.

The 42V is really quick so that you can't measure it by a multimeter. But I'll tell you a small trick. You need an analog (moving coil) multimeter. Put it into the 50V range and connect the 2 probes to the brake coil. Since you're in the secondary operation mode, you can manually release the brake by pressing the handwheel itself. (Ask somebody to do it) and watch carefully the meter needle. If the 42V is present, the meter needle should move faster than usual. (Hope you understand what I try to say)

If the 42V fails, then we have to check it from the transformer all the way to the capacitor. So try above first and let me know results.

Cheers

 

Hi Nimesh Silva,

Thank you for your detailed information.
I'm in the secondary operation mode.
Further we have dismanteld mechnically the brake from the motor. Now we can move the backgauge both with the handwheel and the keyboard without brake. The backgauge will also move in the normal operation mode.
The mechanical adjustment of the brake is O.K. We have your proposed air gap of 0,2mm.

For the voltage measurement of the brake coil.
We measured the 42VDC with an analog multimeter while the backgauge has been activated through the handwheel.
The 42VDC will not drop off and stays as long as the backgauge is moving. The brake will not be released.

Is it possible that after this results the brake coil itself is defective.
But we have a resistance of 13 Ohm on the brake coil.
That should be O.K. with the values of 30W and 20V.

Kind regards

 

Hi Nimesh Silva,

I'm sorry I gave you a wrong information about the measurement.
We measure constantly a value of 7VDC at the brake coil.

Behind the transfo before the rectifier we have 45VAC after the rectifier we measure 60VDC?

Kind regards

 

Hi,
Based on your information all above points seems fine. If the v33 is lighting up, the brake release signal from microprocessor is also OK.

Ideal resistance of the brake coil is 19ohms and your reading is (13ohms) fine.
The voltages you've mentioned is also fine. Since these voltages are unregulated, 42V can get as high as 60V.

But constant 7V at the brake coil is totally unacceptable. So based on these information, now I suspect the control transistor of the PI card. So you might need to replace the PI card.

If you're able, check the transistors V37 V38 V39 and surrounding components on the PI card. They might be defective.

 

Hi Nimesh Silva,

again thank you for your support.
Regarding the voltage from the transfo I wanted to ask you again to get sure.
From the transformer site I come with unregulated 45VAC to the rectifier.
After the rectifier I have a regulated 60VDC? voltage which seems to me a little bit suspicious.

Kind regards

 

Hi,
What is your input voltage (phase to neutral)?

Ideally, If you have exactly 220V at the primary, then you should get 40VAC at secondary. Then after rectification and filtering (according to math) you'll get around 55VDC. since you have 45 now 60VDC is normal. If you feel it's too much, you can try move the primary tapping to 240V terminal. Please note that these voltages are only "rectified" not "regulated" so these can be vary from the ideal values.

But it's not the case I think. I think the PI has some issue. (In fact, I'm unable to diagnose exactly where the fault is without actually looking at the machine. These all are only assumptions based on your information.) If you are able, you may move the PI card to another machine just to make sure. (But do it at your own risk).

 

Hi Nimesh Silva,

thank you for the explanation.
I'll keep you informed about our result when we change the PI card.

Kind regards

 

Have you tried the reference run with the brake removed? If the counting appears on the monitor, we can confirm the linear scale (LMS) is good.

 

Hi
What happened.? Have you solved it?

 

Hi Nimesh Silva,

we where lucky with exchanging the Transistors V37,V38,V39 from PI Board.
Now the backgauge motor brake is working normally and everything is fine.
I appreciate your very professional support. Thank you.
Kind regards

 

Hi,
Great. Pleasure to help you out.

Cheers..

 

Hello Sir, do anyone have an electrical diagram of Polar 115 5D P? Please