fanuc servo problem

[james patricio]

hi guys,

Can anyone help me solve my problem with this old, old analog fanuc servo amplifier. Originally, it was using "customized" digital to analog converter to feed the amplifier with 0 to 10vdc. When the converter was damaged, I try to replace it with A1S62DA Mitsubishi D/A converter controlled by A1SH CPU. My problem is when I ramp up and down the speed (rotating the speed control knob), it generates an overcurrent alarm. The speed control knob is a 16-position selector switch serves as my digital input to the PLC and consequently converted to analog by D/A module to be fed to the servo amp. Is it caused by abrupt acceleration and deceleration or something else?

Thank you very much in advance.

jap

 

[John Gaunt]

It seems like your acceleration rate is too fast.
You probably need to find some way of limiting the acceleration rate. Does the D/A converter have a ramp rate you can set? Or can you set some conversion rate to a longer time between conversions to slow it down. Or can you do something in the CPU you mention.

 

[ToolGuyFred]

I'd limit acceleration by updating your analogue output from a timed interrupt. 100msec should do. Just compare the setpoint from your speed control with the actual output and if the difference is greater than the acceptable ramp increment, just add the increment to the output.

 

[james patricio]

thanks John and toolguyfred.

I check with the D/A converter's manual and I can't find any instruction on how to set the ramp rate. Maybe I would try to modify my program to provide some sort of gradual acceleration. My previous program was a direct proportion with my 16-position selector switch, i.e. position 0, 0 on data register and 0vdc output and motor stops. At position 15, maximum digital value on my data register, output of 10vdc, maximum speed of the motor.

Thanks again guys.

jap