Running Kinetix servos at redline.

Hello All:
First I hope that Kinetix servo questions are still on topic.
If not can someone point me in the right direction?

So I have just finished up a simple indexing job. The load on the drive varies about 10:1 depending on the material running through the machine. My customer would like to have the servo always working as hard as it can. That is on tough jobs run a little slower and on easy jobs run a little faster. Ideally it would tune it self, but if not a work-o-meter on the HMI would work and the operator can make adjustments.

So the ideal parameter for the work-o-meter would be the I^2T value that the drive keeps as an approximation of motor temp. How do I expose that number?

(No lectures on running the drives / motors at 100%. The cost of worn gear box / motor / drive is insignificant compared to production gains. Also I am not running them over rating, just at rating).

You give to little information, what kind of Kinetix servo on what kind of job....

Jack

It is a Kinetix 6500 drive. I did state that it was a simple indexing job.
That is move relative 36 inches. rinse and repeat.
We want to run what amounts to constant power. Run faster with lighter materials. Slow down with heavier. So that the RMS power into the motor is always at rating. If I run the motor too hard it will run for a while then give an I^2T fault, as it should. I am just looking to expose that number.

A Kinetix 300 servo has a Torque function which could do this function. As you say it is a simple indixing job, it could be done with a simple servo solluction like the Kinetix 300 system.
In you're application you can program something dynamic with a PID which has the motor current as PV and motorspeed as CV...

NevisGroup said:

Hello All:
First I hope that Kinetix servo questions are still on topic.
If not can someone point me in the right direction?

So I have just finished up a simple indexing job. The load on the drive varies about 10:1 depending on the material running through the machine. My customer would like to have the servo always working as hard as it can. That is on tough jobs run a little slower and on easy jobs run a little faster. Ideally it would tune it self, but if not a work-o-meter on the HMI would work and the operator can make adjustments.

So the ideal parameter for the work-o-meter would be the I^2T value that the drive keeps as an approximation of motor temp. How do I expose that number?

(No lectures on running the drives / motors at 100%. The cost of worn gear box / motor / drive is insignificant compared to production gains. Also I am not running them over rating, just at rating).

Click to expand...

The purpose of motor I²t is to calculate or measure the motor temperature and disable the inverter if the
motor is in danger of overheating.
The motor temperature will be dependent on many factors, including the size of the motor, the ambient
temperature, the previous history of the loading of the motor, and of course, the load current. (The square of
the current actually determines the heating of the motor and the temperature rises with time - hence I²t).

As stated in the OP I know what I^2T tells me. The question is how to get to it.

It's an interesting question.

There are usually three discrete overtemperature limits switches in a Kinetix 6000 system; one on the incoming converter section, one on the output power inverter section, and another between pins 6 and 11 of a typical MPL motor's feedback connector. These will produce fault codes E36, E72, and E04 respectively.

There is no actual temperature sensor inside the drive.

If you have a Stegmann encoder you can read the actual temperature of the encoder (Knowledgebase #62638), which might be relatable to the winding temperature of the motor.

I don't know if the Kinetix really does attempt to track and integrate the heat capacity of the motor. Could you use the .MotorCapacity value over time and calculate it yourself ?

How about another possibility?

I have a clamp system that has to push and hold. Sometimes the position that it is moving to is impossible (product is in the way) so the % torque sits at say 130%
this is ok normally as the machine holds that position for a short time but sometimes the machine stalls (lack of product) at the hold position when this occurs I change the Maximum permitted overload torque to 98% and all is good I2T is not increasing.

In your case how about attempting to move at the fastest speed possible and limiting the torque to 100% - you will have to monitor the position feedback error and use it to control your feedrate.
For the Index move to complete without overshoot do not allow the position error get too large.

Think about a virtual axis to control the feedrate and position cam it to the index axis. The speed of the virtual axis is a modified by the index axis position error.

I know I know why use a control logix to do something a true motion controller already has programmed but it is what we have been given.


Depending on your tuning you may just get away with setting torque limit to 100% (there must not be any wind up in the control ie integral or it will overshoot)

Just to close the loop:
I ended up putting a pilot light near one of the operating stations.
It illuminates whenever the drive is above 120% torque or more than 1 inch of following error. (I don't fault until 6 inches... yes inches)
The operator keeps an eye on it and will adjust the cycle based on his 'feel' as to how much this light is on.

A bit cheesy, but quite effective.

I would not recommend this, but hey...happy customer!