ME/ECE 4710 Motion and Control
Lab #5 Closed Loop Position Control of a Hydraulic Actuation System
Introduction
This laboratory focuses on the use of a National Instruments (NI) closed loop control system
consisting of a DAQ card (NI 6052E or NI 6251) and LabVIEW software to control the position of a
hydraulic actuator. The LabVIEW code used for this exercise was specifically written to interface with the
data acquisition hardware and the electro-hydraulic trainers in the laboratory. It allows the user to select a
desired position of the actuator (in inches), a proportional control gain, a position tolerance (in inches),
and a sampling rate. The code sends voltage commands to the D1FX proportional control valve to
control the position of a hydraulic cylinder. It reads the valve command voltage and the LVDT voltages
from the valve spool and the hydraulic cylinder.
It is assumed in this exercise that the valve spool has been centered and dead-band minimized.
Components
1. Motor; pump; relief valve
2. Pressure gage
3. D1FX proportional control valve
4. Vertical hydraulic cylinder
(2 inch bore, 1 inch diameter rod)
5. LVDT for hydraulic cylinder
6. Loose components: hoses, coaxial cables
Pressure
Vent Valve
0.00 Psi
Pressure Relief Valve
Motor
Fixed Displacem e nt Pum p
Max. Flow Rate 3 GPM
Procedure
a) Set up a simple hydraulic circuit for the 2 inch bore vertical hydraulic cylinder as shown.
 Connect a second pressure port on the supply/return manifold to the “P” port of the manifold
on the electro-hydraulic trainer.
 Connect a return port on the supply/return manifold to the “T” port of the manifold on the
electro-hydraulic trainer.
 Connect the “A” port of the D1FX valve to the cap end of the hydraulic cylinder.
 Connect the “B” port of the D1FX valve to the rod end of the hydraulic cylinder.
 Follow the Initial Startup Procedure and set the pressure relief valve to 250 PSI.
 Follow the Shutdown Procedure to stop the trainer.
b) Check the valve command connections: Identify the wires on the BD 101 board that provide
voltage input from the potentiometer circuit. Replace those wires with wires from the BNC
connector labeled Valve Command. The black (or green) wire is the common ground.
c) Set the switches on the electronic control panel as follows:
 Power switch: OFF (down)
 Enable switch: OFF (down)
 Open Loop/Closed Loop switch: Open Loop
 0-10V CMD/  10V CMD switch:  10V CMD
d) Check the coaxial cable connections:
 Connect the voltage command (analog output channel 0 and analog input channel 2) from
the computer to the BNC connector labeled “valve command” on the underside of the
electronic control box on the electro-hydraulic trainer.
 Connect the analog input channel 1 to the spool feedback BNC connector on the front of the
electronic control box.
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
e)
f)
g)
h)
i)
j)
k)
l)
m)
n)
o)
p)
q)
r)
s)
Connect the analog input channel 0 to the BNC connector for the cylinder LVDT on the
underside of the electronic control box.
Start LabVIEW and Open the closed loop control program.
Start the hydraulic power, making sure the pressure relief valve is still set to 250 PSI.
Change the switches on the electronic control panel as follows:
 Power switch: ON (up)
 Enable switch: ON (up)
Select filename and destination: Using the file folder on the front panel of the LabVIEW
software, browse to the folder “ME471Data” on the Desktop. Select a file from that folder and
change the filename to GroupXXPYYRunZZ. Replace XX with your group number, YY with the
position command, and ZZ with the run number. Separately record the conditions under which the
data was collected (working pressure, position command, sampling rate)..
Set the desired position in the Position Command input box to 6 inches (This is also 6 volts on the
cylinder LVDT, because the LVDT reads 1 volt/inch).
Check the sample rate: Make sure the sample rate (samples per second) in the Sampling
Information box to 100 samples per second.
Set the position tolerance to 0.01 (inches) in the Control Parameters box.
Set the proportional control gain in the Control Parameters box to one of your selected gains.
Press the Run Arrow to start the program. After a few seconds, you should see data streaming in
the Waveform Chart.
Press the Command button to execute the position command. After the cylinder reaches its final
value, press the Command button to stop the closed loop control. This returns the system into
open loop mode.
Set the Reposition voltage to 5 volts to reposition the cylinder to its bottom-most position.
Press the Write File/Stop button on the bottom right of the front panel. This writes the collected
data to the specified file and stops the program execution.
Repeat steps (m)-(p) to execute closed loop control and collect data for at least five more gains.
Follow the Shutdown Procedure to stop the trainer.
Change the switches on the electronic control panel as follows:
 Power switch: OFF (down)
 Enable switch: OFF (down)
Questions
1. What kinds of closed loop response (over-damped, under-damped, etc.) did you observe as you
increased the proportional control gain? Were these types of responses predicted by your root
locus analysis?
2. How does the response of the system compare with your simulated results? Does the simulated
response differ from the actual response in predictable ways?
3. What aspects of the closed loop hydraulic actuation system make it non-linear?
4. The feedback subroutine (vi) calculates the voltage command to the D1FX valve using the formula
voltage  ( gain  error )  0.22 . What is the role of term “ 0.22 ?”
5. Why can the (open loop) data acquisition program you used in Lab #4 sample more quickly than
the closed loop LabVIEW program used in this lab?
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