Lagunmatic 3516-SX Retrofit

PCW wrote: You really should never unplug servo interface connections live nor should you operate
the drives without tachometer feedback..

I wish I could say I learn from past mistakes... have certainly caused problems in the past by messing with live connections.

How do you think I should apply a test voltage?

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)

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?

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?