JB2020 (Customer) asked a question.
I need to know what mode to use on SureServo2 to allow me to use a servo to operate a screw jack that applies pressure between rollers. I have a rubber coated roller that is raised and lowered by 2 screw jacks (basically super heavy duty linear actuators). In between the screw jack and the roller axle are load cells that I'm monitoring. These cells provide a lbs-force number that will be the feedback to the PLC (P1000). When the roller is all the way down the only force on the screw jack will be the weight of the roller (approx 600 lbs) This roller, upon command, needs to raise up and contact a die roll and maintain x amount of pressure/force as the rollers run. (no greater than 6000 lbs force).
I have done extensive calculations with the screw jack ratios and gearboxes and have figured out that the system can be run with 400W motors.
On the some machine, there is a knife that will be operated in PR Mode I believe because I only need to run it up to x position and hold it there. There is some pressure on it but no where near what the other roller has on it. Correct me, if I'm wrong here..........
Back to the roller, is this a torque control mode or what mode is needed? I know the motor will need to run at a higher speed to get the rollers to contact each other, but as the pressure climbs and gets closer to the threshold/setpoint it needs to slow down and stop and hold. And if the pressure drops then it would automatically maintain it.
Forgive my ignorance, I'm kinda new to servo control. Any help is appreciated......
Torque mode does seem to be ideal to run at a specific load setpoint. I worry a bit about each side of the roller being on its own screw and motor and keeping them in sync. Theoretically they should never have an issue if it is mounted correctly and both servos are started up and have the same parameters, so it would travel in parallel properly. However the theory of how something should work and real life are often two different things. It still seems to be a good way to do it, but another way you could test would be to run one servo in torque mode and be the one that is sent commands for the torque setpoint, while the other servo is in a PT mode. The torque servo would output its position from the drive to the 2nd servo which would just be a follower. That way the 2nd one always moves a step when the 1st servo moves a step and maintains a following position exactly (theoretically).
I like the response, however, I was hoping to operate these independently. This is on a rotary molding machine that molds pet treat dough into treat shapes and it is critical to maintain pressure across the roller. Sometimes the operators adjust the pressure on one side to help the release of the treats coming out of the die roll.
To do the follower option may not work because of the independent adjustments being made. Each side of the roller has a load cell that is measuring force. Is most of this program done in the PLC software or in the servo drive itself?
How to even start with torque mode is where I'm stuck, because there are videos on all the other modes but not torque mode.
If the roller doesnt need to be absolutely parallel then both in torque mode and operated with their own torque setting is fine. Nearly everything will be done on the servo itself, and the PLC only need to write the torque setpoint to the drive's proper memory location
You will likely want to run the servo in dual mode, so you can have it operate in torque mode in the direction you need, and then use the PLC to initiate a mode switch to PR (via a DI signal) so you can move the roller back out away to a specific position. When going back into torque mode and moving the roller in, the velocity parameters you configure in the drive will be how fast the roller moves inward.
edit: alternatively, I believe torque mode setpoint can be an analog signal level as well. So if you dont want to write a value to a register over modbus you could have the PLC send an analog signal to the drive.
I was wondering if I was going to need to switch modes. They say a drive power cycle is needed everytime a mode switch takes place. I guess I could program the PLC to do this with a contactor on the drive power circuit.
I could also stay in PR mode while moving the roller up until it contacts the die roll and then switch modes.
In torque mode, as you said, the torque setpoint needs to be written to the drive. Does that mean I will have to convert a lbs-force value from my load cell to a torque value?
I dont believe that is the case. It has been a long time since I have used a dual mode configuration, but I am fairly sure you just turn a DI on/off to change between PR mode and V mode. I dont recall having to use any elaborate setup to reset anything back when I did this, but it has been years so I could be wrong.
Do I need the Productivity Motion Controller for something like this?