hydraulic system - how to control a servo valve?

[szuhsien]

Thanks for ur attention.

I just set up a oil hydraulic system and mechanism that is such a MTS(material test system).

And my question is how to let my cylinder go forward at a constant velocity.

Because when the cylinder contact my specimen(I have many different specimens), it will produce a reacting force and let the cylinder can't go forward at a constant velocity I set. 

So I know it needs adjusting input voltage to servo valve .

I have looked much information from Ni discussion forums, but I totally have no idea about this.

I only know that I need to use PID control.  My feedback signal is from LVDT.

What kind of ni card I need? I have pci-6033e, although its analogy outpout only can + - 10v.

At least, 6033e can let me test servo valve between -5v to 5v.

Can I use DAQ-card to achieve my goal? Because I'm not sure if 6033e supported pid toolkit.

By the way, this question is just the beginning.

I need to finish displacement control, force control, and fatigue loading control at 10Hz.

----------  

servo valve: + - 10v input , 0v is at centered position. 10v is P port 100% to A Port.  threshold<0.1%

platform: XP, Labview 8.2 (includes Real-time module, PID toolkit)

[hrh1818]

On Jan 21, 1:10 pm, szuhsien <x...@no.email> wrote:
> Thanks for ur attention.
> I just set up a oil hydraulic system and mechanism that is such a MTS(material test system).
> And my question is how to let my cylinder go forward at a constant velocity.
> Because when the cylinder contact my specimen(I have&nbsp;many different specimens), it will produce a reacting force and let the cylinder can't go forward at a constant velocity&nbsp;I set.&nbsp;
> So I know it needs&nbsp;adjusting input voltage to servo valve .
> I have looked much information from Ni discussion forums, but&nbsp;I totally have no idea about this.
> I only know&nbsp;that I need to use PID control.&nbsp;&nbsp;My feedback signal is from LVDT.
> What kind of ni card&nbsp;I need? I have pci-6033e, although its analogy outpout only can + - 10v.
> At least, 6033e can let me test servo valve between -5v to 5v.
> Can I&nbsp;use&nbsp;DAQ-card to achieve my goal? Because I'm not sure if 6033e supported pid toolkit.
> &nbsp;
> By the way, this question is just the beginning.
> I need to finish displacement control, force control, and fatigue loading control at 10Hz.
> &nbsp;
> ----------&nbsp;&nbsp;
> servo valve: + - 10v input , 0v is at centered position. 10v is P port 100% to A Port.&nbsp; threshold&lt;0.1%
> platform: XP, Labview 8.2 (includes Real-time module, PID toolkit)

First thing when you say MTS do you Mean the Company located in
Minneapolis, MN that makes hydraulic test systems that do the type of
testing you describe or are using the word as an acronym? Yes, you
will need a closed loop control system to do all you want to do. The
system should have both a load cell for measuring the axial force
applied to a specimen and a LVDT for measuring the displacement of the
piston and provisions for either load or position control. My
recommendation is you use Labview strictly for data acquisition and
you you use an all analog control system in your application. With
position control you could use a ramp input to move the piston at a
constant velocity. You can build an analog PI controller fairly
easily. You should not use the D part of PID in a closed loop system
that uses a hydraulic piston for an actuator.

Howard

[szuhsien]

sorry so truoble,

Yes, I was using the word as an acronym. I meant i designed a simply material test system.

And definitely I also have loadcell feedback, i just didn't mention it.

Beacuse in thist case i don't think it's necessary. (let cylinder go forward at a constant velocity)

And Each specimen has different force response, so i can't directly use a ramp input.

I think the close-loop system have to know how to auto-tune input voltage to servo valve.

and my servo valve has response limit. It is 50 hz and 90 degree phase lag.

so i think i should know how to build a VI which can auto-tune input voltage under different specimen and let actuator go forword at a constant velocty.

[Kodeeswaran]

What servo amplifier you are using & is it double acting or directional control valve, what was your controlling ramp rate and time to reach set load.

[szuhsien]

Here are some information about my servo valve.

--

Command signal 0 to ±10 V,
Valves with voltage command input
The spool stroke of the valve is proportional to (Ud– Ue).

100% valve opening P ->A and B ->T is achieved at (UD – UE) = +10 V.

At 0 V command the spool is in centered position. The input
stage is a differential amplifier.

--

It is a direct drive servo-proportional control valve.

Therefore I should know how to control a dynamic input voltage to control fluid rate (equal to control the actuator) and

deal with different specimens at a constant velocity I set.

[Kodeeswaran]

then I feel that you can go for PCI - M series card dependig upon your cost factor, but sure of  your complexity of code and performance, 

[szuhsien]

Thank for ur reply.

I was confused by NI product. There're too much NI products that are very similar.

1. Can u tell me what different between pci-e series and pci -m series?

I checked out pci-m series.

Some fo pci-m serise mentioned measurement type is quadrature encoder.

But my measurement type is voltage.(from LVDT and LoadCell) Or I just don't need to consider that.

Beacuse all of Pci-M series and Pci-E series support analogy input.

2. why did u choose PCI-M series? or it's just cheaper than pci-e series?

  pci-6221 is so cheap.

3. Does the performance only depend on my computer or it also involve what kind of NI card you used when my program run a loop?

[hrh1818]

On Jan 22, 12:10 am, szuhsien <x...@no.email> wrote:
> Here are some information about my servo valve.
> --
> Command signal 0 to ±10 V,Valves with voltage command inputThe spool stroke of the valve is proportional to (Ud? Ue).
> 100% valve opening P&nbsp;-&gt;A and B&nbsp;-&gt;T is achieved at (UD ? UE) = +10 V.
> At 0 V command the spool is in centered position. The inputstage is a differential amplifier.
> --
> It is a direct drive servo-proportional control valve.
> Therefore I should know how to control a dynamic input voltage to control fluid rate (equal to control the actuator) and
> deal with different specimens at a constant velocity I set.

The beauty of a closed loop position control system is it can
automatically adjust the force applied to a specimen and move the
piston at a constant rate when a ramp signal is used as a command
signal. There is no need to fuss with a dynamic input signal o
control the fluid flow rate when you use different specimens.

Howard

[hrh1818]

On Jan 21, 9:10 pm, szuhsien <x...@no.email> wrote:
> Yes, I was using the word as an acronym. I meant i designed&nbsp;a simply material test system.
> And definitely I also have loadcell feedback, i just didn't mention it.
> Beacuse in thist case i don't think it's necessary. (let cylinder go forward at a constant&nbsp;velocity)
> And&nbsp;Each specimen has different force response.

You mention in your first post you will be doing force control in the
future. If you need to control the force applied to a specimen you
need a load cell. Even for the simple case of letting the cylinder go
forward you need a load cell to measure the force applied to your
specimen.

Howard

[hrh1818]

On Jan 22, 9:40 am, szuhsien <x...@no.email> wrote:
> Thank for ur reply.
> I&nbsp;was confused by NI product. There're too much NI products that are very similar.
> 1. Can u tell me what different between pci-e series and pci -m series?
> &nbsp;

PCIe series are designed for applications when you need to acquire a
lot of data at a high rate. For example capturing a TV signal. The NI-
M series is more than adequate for your application.

> I&nbsp;checked out pci-m series.
> Some fo pci-m serise&nbsp;mentioned measurement type is quadrature encoder.
> But my measurement type is voltage.(from&nbsp;LVDT and&nbsp;LoadCell)&nbsp;Or&nbsp;I just don't need to consider that.
> Beacuse all of Pci-M series and Pci-E series support analogy input.
> &nbsp;
> 2. why did u choose PCI-M series? or it's just cheaper than pci-e series?
> &nbsp; pci-6221 is so cheap.
> &nbsp;
> 3.&nbsp;Does&nbsp;the performance&nbsp;only depend on my computer or it also&nbsp;involve what kind of&nbsp;NI card&nbsp;you used&nbsp;when my program run a loop?

It depends upon the application as to whether the computer or the data
acquisition card is the limiting factor. But in your application if
you are using a computer built with in the last two
years and a NI-M series data acquisition card you will have more than
adequate computer and data acquisition power for your task.

Howard