[toninlg]

Hello,

I’m working on an application where 5 ICD B8001 drives with B41 servomotors are used. This application used step and dir to control the movements of 5 linear actuators. I would like to change this in order to use a +/- 10V analog command with an external position loop (PLC modules + PC). I have made some trials but I’ve got problems.

I attempted to cancel the offset on one drive (configured with analog input) by algorithm but it only works if the other 4 drives are disabled. If the other drives are enabled and configured with step and dir inputs, the offset can’t be canceled and the actuator keeps moving weakly and not linearly (visible with the encoder signal) while the others are stationary. If the other drives are enabled and configured with analog inputs (0V at inputs), all of the actuators are moving strongly. Is it an EMC problem or is there another possible reason?

I have used different configurations but the last one is:


• Encoder and power signals are shielded at both sides (between motors and drives).

• PLC modules are supplied with 24V DC supply with transformer on the main, but same power supply as drives.

• Analog PLC modules are +/-10V single-ended outputs connected with twisted-pair cables. The shield is connected to the isolated analog ground of the module and to the analog ground of drive. Analog out (module) to Command + input and analog ground to Command – input.

• Encoder feedback uses also twisted-pair cables. The shield is connected only to the 0V of the modules supply and the 0V modules supply is also connected to the common input of the drive. Module inputs are differential inputs.

• It seems that the drives (single phase) are supplied from three phases in order to balance phases.



Do you have any idea what could be the origin of these problems or how to solve it?

Thanks a lot.

[toninlg]

Has nobody an idea about this problem?

[Al_The_Man]

It is not all that clear how you are closing the loop.
I gather you have servo drives that are ±10v analogue control?
The controller/feedback loop must be constantly updated in order to keep the servo's in position or to create controlled motion.
The controller must be capable of producing a PID loop.
Does the system conform to this as far as you know?
Al.

[toninlg]

I know that if I want to control position using an analog speed command I have to close the position loop with my controller.
While the loop isn't closed, if the analog command is 0V, the servo must stay at rest because the drive close the speed loop. But it moves, so I think there is a speed offset (like analog offset of operationnal amplifier). With the last try I've made, I've seen that if I wire like that:
analog output of controller to command + of drive
analog ground of controller to command - of drive
shield to analog ground at controller and at analog ground at drive
encoder feedback to controller
The motor stay at rest with 0V at drive input, but only if one drive is on. If the other are on, the motor moves.