Lagunmatic 3516-SX Retrofit

PCW wrote:

I would (with power off) disconnect the analog signals at the 7I77 end

The reason you should not run velocity mode servos with the tachometer
disconnected is that they will usually run away, perhaps at high speed.
This is because the velocity feedback from the tachometer forms
a PI loop, and without feedback the integral term can increase to full torque
in a short time with just a minor balance error.

An analog velocity mode servo that is enabled, and has its analog input open
(but has tachometer feedback) will typically hold position but drift slowly
(this is normal and OK)

If you apply a small voltage (1.5V would be 15?% of full speed) the motor should
and immediately stop (go back to very slow drift) when the voltage is removed

If you got no response when you ran LinuxCNC (and you have some non-zero P term)
I would suspect a wiring issue. We have seen people attempt to change feedback direction
by swapping the 7I77s AOUT/GND pins at the drive. This will work if the drive has differential inputs
(IN+ and IN-) but will short out the 7I77s analog outputs if the drive has single ended inputs
(IN and common or GND)

Sounds good - thank you for the explanation.

The servo amps have 2 modes: single-ended or differential. Just looking at the photo from last night I can see that the servos are wired and jumpered for differential mode.

I will pull the leads on the 7i77 side tonight and apply a voltage across them.

I'm using the Glentek GA370: www.glentek.com/download/ga370-rev-f-manual/?wpdmdl=359

PCW wrote:

I would (with power off) disconnect the analog signals at the 7I77 end

The reason you should not run velocity mode servos with the tachometer
disconnected is that they will usually run away, perhaps at high speed.
This is because the velocity feedback from the tachometer forms
a PI loop, and without feedback the integral term can increase to full torque
in a short time with just a minor balance error.

An analog velocity mode servo that is enabled, and has its analog input open
(but has tachometer feedback) will typically hold position but drift slowly
(this is normal and OK)

If you apply a small voltage (1.5V would be 15?% of full speed) the motor should
and immediately stop (go back to very slow drift) when the voltage is removed

If you got no response when you ran LinuxCNC (and you have some non-zero P term)
I would suspect a wiring issue. We have seen people attempt to change feedback direction
by swapping the 7I77s AOUT/GND pins at the drive. This will work if the drive has differential inputs
(IN+ and IN-) but will short out the 7I77s analog outputs if the drive has single ended inputs
(IN and common or GND)

This was really helpful advice, and I've made some progress. [Long story short = all axes are drifting very slowly now]

I unplugged the servo signals from the 7i77 and applied 1.5v but saw no movement.

I plugged everything back in and tried jogging again, no movement of course but this time I probed the signal connections and measured 10v!

So at this point I knew I was getting signal so something else was causing trouble. I studied the charts again and realized the servo amp lock-out could be the cause. I had assumed I had bypassed this before.

The lockout pins on the servo amp card connect through a NC relay. To test my theory I disconnected one input into the relay, turned the power on and boom - instant table response.

When I fired up LinuxCNC I got the usual limit errors on all 3 axes. I activated each switch manually (doing this is starting to terrify me], hit Machine On, and the Y-axis jumped suddenly and triggered a following error. At this point I could see all axes drifting in the DRO and verified with an indicator.

I shut everything down and am going to look at this lockout relay further...

Going to start from square 1 here because I think bypassing the relays is just muddying the waters.

Step one is figuring out why the 'Machine On' relay is not triggering. It is a 24v relay shown below:



Wires [2] and [1] are the incoming 120v hot and neutral from the main transformer. Supplying 24v to wire [20] is supposed to switch the relay and connect wires [2] and [3] and the other connected leads. When I bypassed this relay before, I only jumpered wires [2] and [3] and that supplied power to my servo amps and other areas.

Wire [20] is connected to the 7i77 at Output 9 (TB7 Pin 18). My hal file looks like this:



How I thought this would work: Output 9 would measure 0v when measured against the field supply ground Wire [G] when LinuxCNC is started. When I hit Machine On in the control, Output 9 would activate and send 24v to the relay and it would switch on.

What is happening: Output 9 measures 24v from field Ground as soon my LinuxCNC configuration is started and the relay does not turn switch.

I have confirmed my relay is good by using a standalone power supply to supply 24v to wire [20] which caused the relay to switch on and power was sent to the rest of the machine (servo amps activated). Yes, I did disconnect wire 20 from the 7i77 before doing this! I've also confirmed continuity between TB7 pin 18 and the wire [20] screw terminal at the relay.

So I'm confused by two things: why isn't the relay switching, and why is 24v being sent as soon as my configuration loads?

andypugh wrote:

What controls "Machine-is-enabled" ?

Is that signal permanently "true" ?

You are not mentioning the 0V lines at any point, are you sure those are continuous and common where they should be?

Hey Andy,

I thought that was a built-in parameter I selected from a drop-down in PNConf but now I'm second-guessing that...? So I had assumed it was controlled by the Machine On button in Axis.

If I typed my own parameter name in then I can see how it might be permanently on. At one point I did Invert that pin in my .hal file and it still went to 24v upon opening Axis

Which 0v lines are you asking about?

Got it - I will look into the signal names. I did notice most of my outputs were active but some were 0v.

My 0v all seem to be correctly connected to each other and functioning properly. When I connected my external power supply to that relay, I only connected the live side and the switch flipped.

The only thing that makes sense to me is if I am doing something wrong by measuring voltage against the 7i77 field ground

If you measure 24V at the 7I77 output with the relay connected the relay should be on
(if the relay common is connected to field ground)

Are you saying that the relay is permanently stuck on?

(measuring the 7I77 outputs with no load will not yield any useful information)

PCW wrote:

If you measure 24V at the 7I77 output with the relay connected the relay should be on
(if the relay common is connected to field ground)

Are you saying that the relay is permanently stuck on?

(measuring the 7I77 outputs with no load will not yield any useful information)

You may have just solved this, because the relay common is not connected to the field ground.

So I should connect wire [G] in my diagram to the relay common, wire [1]? That is the common for all the auxiliary power on the machine.

The relay seems to be working correctly - I'm certain the problem is how I've supplied power to it and the above would explain that.

*EDIT- I'm going to have to verify this... the field power is fed by a 24v power supply that is being powered by the same 120v as wire [2] and wire [1]

*EDIT 2- just checked for continuity and the 7i77 field ground is not tied into the common ground

I did some testing today and didn't find a solution. I tested continuity between the 7i77 field power ground and the machine common ground and found that it was isolated. I put together some images to show what I tried - any time I tried to tie the 7i77 field power ground into the machine common ground I lost field power (no LED on the 7i77)

Here is how I have it setup currently. I have a 24v power supply feeding power to the 7i77 Field I/O. The 120v neutral line coming into the power supply is tied the common ground. The 120v lines are daisy-chained to the 5v power supply feed the 7i77. This means the 7i77 5v power is tied into common ground but the field I/O is not. I am getting field power and 24 volts out of Output 9 but the relay is not switching.



I attempted to tie the field I/O into common ground three ways. The first time I disconnected the field I/O ground wire from the 24v power supply and connected it to the output of the 5v power supply. When I turned main power on, I did not have power to the field I/O (no LED indicator). I measured 24v at the field power IN when measured against the screw terminal of the power supply, but 0v when measured against common ground.



Next I tried daisy-chaining the ground from the 120v supply side of the 5v power supply. Same result, no power to field I/O.



Lastly I reconnected the field power ground to the 24v power supply and added a jumper from wire [1] at the relay (common ground) to the 24v output. My thinking was that I should definitely get 24v between the field power IN and GROUND and still tie everything in. However this caused the power supply to act wonky, with an intermittent green LED which indicates 24v. supply is active



Hopefully these notes make sense. I didn't take a photo of each setup so I just added notations to the original image. Clearly I'm lost here... but once I get this sorted out I think I'll be ready to tune the servos.