Motion Reference unit, MRU, for control of motion

[KRAZE4LV]

I have to receive the signal for MRU unit, we will use kongsberg MRU unit for getting the heave, roll and ptch of the ocean. This signal will be transferred to the Hydraulic cylinder. The cylinder will move accordingly in a heave motion.

I have been using the labview for monitoring till now but now it is to control the motion. I wish to know what module is needed or toolset needed for programming and hardware.

[Matt-J]

Hi KRAZE4LV,

What kind of hydraulic cylinder do you need to drive? Do you need to set up a feedback loop for the cylinder? I assume you need to control the pump for this cylinder based on your MRU readings, and this would probably be a DAQ application. If a control loop is necessary, and you have the sensors for it, our PID toolkit would be great. Please clarify the behavior you want with your system and I will try to make a recommendation.

Best regards,

[KRAZE4LV]

Thank you Matt for the info!

[KRAZE4LV]

Hello,

I have to buy a MRU for measuring the heave, roll and pitch of the ocean. I identified the MRU maker. ButI am not sure about its compatibility with NI DAQ M-Series 6251.

Please  let me know:

1. If the attached data sheet MRU is compabitle for the measurement with NI DAQ 6251.

2. I think we need to connect with RS232 using VISA. but the details of measurement I dont know.

3. I need to program it, signal from ocean-> received by MRU-> feeded to the PXI-> to the servo valve-single acting cylinder moves accordingly-> Encoder measures the position, displacement-> signal sent to PXI-> to the servo valve. Its a PID control but I never used the PID I need some example or some suggestion. I am attaching the concept design.The aim is to achieve heaving.

Please let me if the MRU is appropriate or not.

[Matt-J]

Hi KRAZE4LV,

Here are my thoughts:

1. The MRU you are referring to appears to communicate with either the RS-232 or RS-422 serial protocol. This would not be something that could "plug and play" with your M-series DAQ.

2. You could indeed use VISA, if you connect the MRU up with an RS-232/422 compliant port. If your system is PXI based, something like this could do it (if you do not already have a controller with a serial input).

3. You could probably program this behavior without the PID toolkit, but it may make it easier. I assume you will use one of our PXI motion control modules if you do not already have one. What I would encourage you to do is download the 30-day free trial of the PID toolkit. You can download it here. The toolkit will install numerous examples that show its use. These can be accessed by opening LabVIEW's example finder from Help >> Find Examples. Once open, expand the folder for Toolkits and Modules >> PID and Fuzzy Logic Control >> PID and explore the numerous use cases presented.

Please let me know if I can be of any further assistance or can clarify anything.

Best regards,

[KRAZE4LV]

Hello Matt,

Yes! I need to send the heave signal from the MRU and feed it to the Hydraulic power Unit, HPU, as fluid velocity, on the basis of fluid velocity the servo loop will 20% open, 50% Open or fully open, Oil will flow to Hydraulic Cylinder which will move the hydraulic cylinder.

Heave valve->fluid velocity in HPU-> servo-valve condition-> Hydraulic Cylinder move

How can I develop this loop? and VI?

[KRAZE4LV]

Correction of the last post

Heave signal ->data is collected and fed->Servo valve-> this will control the pressure between the hydraulic Cylinder A side abd B-side->then the hydraulic cylinder will be move...

The signal will be sent to servo valve or proponal valve not to HPU .

Please see the attached servo valve picture.

[Matt-J]

At what state is your current code? And, how frequently do you need to monitor the MRU and send appropriate signals to the valve? If the system can update relatively slowly, I would just have the serial communication running in line with DAQ code. Then, if the reading from the MRU fits a certain criteria, an appropriate voltage is sent out to your valve. You could control the behavior by using a case structure (or series of case structures). This example might be useful. It only performs a certain action (logging data point) when a signal meets a certain criteria.

[KRAZE4LV]

I am still confused about how to use the PID logic for the servoamplifier and servo valve. Please see the attached datasheet of the servo valve and servo amplifier.

How to identify the PID gain, set-point, process variables, output range? I hav eto create a feedback loop..

heave signal->NI program(or my VI)->servo amplifier->servo-valve->hydraulic cylinder(which will move on th basis of change in flow rate), On the hydraulic cylinder is the encoder->position signal ->back to the NI program(my program)

In the program i need to calculate the flow rate or the percentage of open and close of the servo valve....which will effect the motion of hydraulic cylinder as the pressure is generated.

[Matt-J]

It's sounding like you could create your system without the PID toolkit (depending on how quickly things need to respond). Since you have distinct conditions for what voltage will be output to the servo-amp, you could create this with a sort of state machine. IE, read the MRU signal via serial, depending on this reading, a certain voltage is written out to the servo-amp. You will need to incorporate pulse counting to bring in the position from your encoder. What does your code currently do?