DG4S setup problems

[kurt]

Hi I am trying to setup newly purchased DG4s drivers with fairly old servo motors. Here is a link to the motors I am trying to setup (500watt version)
https://drive.google.com/open?id=1QqwJQ ... c1LePiowU_
I have connected as in the manual (A+ A- B+ B- POWER ETC). I did not connect my Bob board yet and have a programming stick. Sometimes when I apply power I get a flashing green light (on the driver) and I can connect thru the software to the drive. When I try to do any setup or diagnostics the motor runs but overshoots the set # of steps by a mile. Sometimes when I apply power I get a red blinking light but if I tweak the motor by hand I can get it to change to green. It seems like the driver is getting the steps from the encoder because if I turn the motor both lights (red and green) light up solid then it changes to either red blinking or green blinking. There are three servo motors and all of them give the same response so it makes me think there is a different problem. I have tried switching the armature connections which makes no difference either..any ideas?

[cncdrive]

What do you mean by "overshoot"?
You running the motor via the Servoconfig3 test?
If so then that ofcourse overshoots, it is a 1(t) step response analyser and what it does is that it tells the drive to change the command position with the set amount of steps.
This means a unit step change in the position which is called the 1(t) function and what the drive does is it compensates the position to the new value and the step response is drawn and can be analysed to get some ideas about the system and tuning goodness.

If the red LED is blinking and the green LED is off means that the drive lost the encoder connection.
The drive detects if the encoder signals are OK or not.
How it does that is it checks the A and the _A signals and the same way the B and the _B signals.
The signals are inverted pairs, so A is always the inverse of _A and B is always the inverse of _B.
If it is not like that then the drive knows the encoder signals are not OK.
And when any of the encoder signals gets disconnected, e.g. A is disconnected while _A is still connected then the A input is internally pulled to _A so again the drive will see that the encoder signals are not OK.
So, you getting blinking red LED and green LED off means that your encoder or it's wiring or it's powering has a problem.

And it is not possible that changing the armatures gives you no difference.
I say it is an incorrect observation, because if you changing out the armature connections then one way will cause the servo to compensate to the wrong direction (away from the position setpoint) which will cause the servo to runaway and stop when the setup servo error limit is reached.
It is just not possible that the servo runs the loop OK with both ways armature connections, I mean it is physically not possible.

If you get both the LEDs solid by turning the encoder gives me the suspicion that your input voltage is too low or your encoders uses so much power that the voltage drops,
because the PSU can't handle it or the current limit in the drive's digital part kicks in. It can supply about 500mAmps for the encoder.
The current limit kicks in at about 750mAmps (the drive internally uses about 200-250mAmps). When current limiting is ongoing then ofcourse the 5Volts power which the internal switching regulator creates from the 12V input, that 5Volts starts to run lower than 5Volts and if it runs under about 4Volts then the drive goes to undervoltage lockout and enters to the bootloader which makes both LEDs to go solid on.
So, I would verify that the digital PSU input voltage is 12Volts and it is not fluctating too low and that the 5Volts to the encoder is solid and is not dropping.

[kurt]

Okay sorry for the long delay I was waiting to use an Oscope to verify the signals coming out of the encoder. I first did what you suggested and monitored the 5vdc and 12vdc with a multimeter (in this case two one on each A & B) to make sure the voltage was not dropping out which it isn't it stays a solid 4.95vdc as well as the 12vdc. You are correct changing the armature does in fact change the direction I just didn't explain that well. I used an oscope to verify the signals coming out of A+A-B+B- were opposite (see attachment) note also b- a- share the same ground. I also used the oscope to adjust the waveforms so they were exactly the same width (suggested in the servo encoder manual)...Any further ideas? Also when I run the PID setup in the servo driver software (servoconfig3) and set it for 10 steps the drive runs for a few seconds then stops with the graph showing a sharp step up and then the green line runs off the screen to the right not coming back down to 0...
THanks!!!


Kurt

WAVE1.pdf

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[cncdrive]

The encoder signal looks good.

If you run a step response analysation with the servoconfig and if then the motor turns some and then stops with limit override fault then you have the motor arms to encoder direction connected up in reverse.
What happens is the drive rotates the motor from the setpoint when it should rotate to the setpoint and so the motor runs away until the position error becomes larger than the max.error parameter.

And one more thing is to analyse only upto a value what your max.error parameter is.
If you set the max.error for example to 1000 value and you try to analyse a 2000 steps then the drive will immediately fault with a limit override, because then you change the position with more than the allowed max. position error and so the fault condition will meet as soon as you hit the analyse button.

[kurt]

Well something doesn't seem right somewhere...I have tried a few more things. First I flashed the DG4S just to make sure that was up to date. Switching the armatures did not produce different results except for running the drive in the opposite direction. Just for the heck of it I connected up a logic analyser and here are the things I noticed... When the encoder is sitting in the position with +a & b+ are both logic 1 (5vdc) the DG4s is happy and flashes green. In any other position (i.e 10, 01, or 00) the DGS4 is not happy (flashes red) even if I reset power. If I manually rotate the motor (even the tiniest bit) both red and green light up at the same time solid if I stop on +a&+b logic 1 (5vdc) then it flashes green otherwise red flashes. The setup software for the DGS4 only will connect to the DGS4 when the green led is flashing. If I run the PID diagnostic while the green led is flashing the motor runs for a few seconds top speed. If the motor stops on a place when the red led is blinking then the software looses connection with the drive and cannot re-establish connection again unless the encoder is +a&+b logic 1. If it stops and green led is flashing there is no results (or errors) with the exception of a step up on the graph that runs off the screen.
Thanks!!!

Kurt

[cncdrive]

Kurt,

The red LED flashes and the green LED is off means that the encoder signals are not OK.
That the drive says the encoder signals are not OK in different positions and it says it is OK in other positions makes me think that you have the encoder signals connections mixed up.
It is very important that you have the A+ and A- to one channel and the B+ and B- to the other channel.
If for example A- is mixed up with B- then A+ will be paired with B- and B+ will be paired with B- which will cause exactly what you described, that in some positions the drive will say the encoder signal is not correct and it will flash the red LED, because A+ can be on the same voltage as B- and so there will be positions where the drive will show you an encoder fault when it disconnects and stops running the motor.

I suggest you to check the DG4S manual and check the encoder connector pinout and then measure the signals pairs, both pairs.
If they are paired properly then A+ is always the opposite as A- and B+ is always the opposite as B-.
If they show the same voltage levels at any positions then your have the channels mixed up.

[kurt]

Ahhh I see the problem...I thought I had something I don't! My encoder must be a single a and b channel...the -a & -b are just signal grounds and just stay zero of course...wow why didn't I catch this before...so I am guessing I will need the differential line driver to make it work?

THanks

Kurt

[cncdrive]

Kurt,

Yes, you need a differential encoder or a single ended encoder connected to a differential line driver which then connects to the drive.
The drive needs differential encoder lines to operate.
Connecting ground to the - signals will not work, then exactly that will happen what you described, the drive will show an encoder fault as soon as the A or B have 0 Volts level, because then the signal and it's negated pair are on the same voltage level, both are on 0 Volts (GND level) which is not allowed in differential signals, so the drive will detect this and will give a fault.