434 servo alarm: Z axis detect error

[padobranac]

I have this problem on my machine.
It is Fanuc OM and machine DAH-LIH.

Everything is fine, machine is working and sudenly at one moment, z axis goes down and tool hits into table.
And display "434 servo alarm: Z axis detect error"

And after that i restart machine and everything is ok, and from time to time, it happens again.

What could that be?

Sorry if this is wrong forum

[bob1371]

Originally Posted by padobranac I have this problem on my machine. It is Fanuc OM and machine DAH-LIH. Everything is fine, machine is working and sudenly at one moment, z axis goes down and tool hits into table. And display "434 servo alarm: Z axis detect error" And after that i restart machine and everything is ok, and from time to time, it happens again. What could that be? Sorry if this is wrong forum

Look for loose cables or worn spots in the cables that may be causing a short. Then look at other items (motor, amp).

[Al_The_Man]

If you look a the diagnostic work for that axis it should tell you precisely the alarm type
diag, 720~727 for up to 8 axis.
as per the attached PDF.
Also if the axis runs away, you should be able to set a deviation error in one of the parameters to avoid a crash, it should shut the servo's off.
Al.

[diggityds]

If This Is A Vertical Machine Look To See If There Is Any Type Of Hydraulic Conterbalance It Might Need To Be Refilled. If There Is No Counterbalance Then Do What Was Suggested Above With The Cables Or The Brake On The Motor.

[Alan B]

How are you switching the machine off at the end of work. On Vertical machines in particular but on all machines really you should press the E.Stop button first then power down. This allows the brake to come on and hold everthing in place. If you just power down the vertical axis will drop slightly each time, normally this will give soft overtravel alarms when you reference up on switching but it is feasable that the axis is incrementing itself down so you are out of position when you start.
Alan B

[Bluesman]

On most Fanucs any disconect error is normally caused by a break in the encoder cable. In rare case for some reason I have seen exsesive backlash throw of this error but I amnot sure why. The easy way to test this cable is to swap the ecoder cables from the X and Y axis and if the error now follows to the X axis you know it is the cable.

Bluesman

[padobranac]

Originally Posted by Alan B How are you switching the machine off at the end of work. On Vertical machines in particular but on all machines really you should press the E.Stop button first then power down. This allows the brake to come on and hold everthing in place. If you just power down the vertical axis will drop slightly each time, normally this will give soft overtravel alarms when you reference up on switching but it is feasable that the axis is incrementing itself down so you are out of position when you start. Alan B

Well, i think that isn't problem, because that error appears in the middle of the work, not mmediately after starting machine

[padobranac]

Originally Posted by diggityds If This Is A Vertical Machine Look To See If There Is Any Type Of Hydraulic Conterbalance It Might Need To Be Refilled. If There Is No Counterbalance Then Do What Was Suggested Above With The Cables Or The Brake On The Motor.

Hydraulic Conterbalance???
I don't understand what that could be?

[diggityds]

Some vertical machines come with a gas or a chain type counterbalance that help support the head, this puts less load on the motor and doesn't wear on the ballscrew as much. If the pressure of the gas counterbalance is low the head will drop when the the power to the motor is off. This might not be the problem since it's happening while it's running. You can aslo check if your machine has scales or not, if the reader head is loose or if there is any debri on the scale could cause the cnc to run looking for location. Don't count out the fact that the cable might be damaged or pinched, it can short out at any spot during operation. You can swap cables between drive cards and see if the problem follow's itself.

[Alan B]

I'm sorry but that is not correct. The [soft disconnect alarm] in the the Fanuc book will tell you it is a broken cable. However any machine using glass scales will give this alarm. If you look at the alarm logically it is saying "I (Fanuc control) have commanded the axis to xx mm and the encoder(on the motor) says the axis hasn't therefore the encoder wire is broken" If you use a glass scale it is not attached to the motor but the axis itself and the motor encoder is not read. Fanuc doesn't allow for this even though the parameters are set so if the external encoder sends the "I haven't moved signal" because, for example the axis is tight/siezing, Fanuc throws up disconnect alarms. As a service engineer of many years(too many) the first question on disconnect alarms has to be "Do you have glass scales? What is in parameter xxxx dependent on control"

Originally Posted by Bluesman On most Fanucs any disconect error is normally caused by a break in the encoder cable. In rare case for some reason I have seen exsesive backlash throw of this error but I amnot sure why. The easy way to test this cable is to swap the ecoder cables from the X and Y axis and if the error now follows to the X axis you know it is the cable. Bluesman

[ajl6549]

Originally Posted by Alan B If you use a glass scale it is not attached to the motor but the axis itself and the motor encoder is not read.

So when glass scales are used the encoder is completly disabled? Even in rapid etc. I thought the scales were for "fine" positioning and both scales and encoders were used???

[padobranac]

How will i know if my machine uses glass scales?