Computer-Controlled Hydraulic Cylinder Actuation Research

Valparaiso University

Eaton Corporation

Spring 2014

RESEARCH STUDENT: Garret Stec

RESEARCH ADVISOR: Professor Shahin S. Nudehi

Abstract

Create a compact hydraulic setup that can actuate a high-pressure hydraulic cylinder

forwards and backwards from a user control in LabView.

Introduction

The purpose of this project was to develop a hydraulic system that could actuate a

cylinder both forwards and backwards using an electronic valve. This system would be used to

test a goal proposed by Eaton Corporation, to design a control feedback loop to position a 60

meter cylinder within 0.5 millimeter accuracy with leakage occurring in the cylinder. Due to the

complexity of a cylinder of that size, the hypothesis would be tested on two smaller cylinders

provided by Eaton. The system developed this semester can actuate a cylinder safely from a

computer, monitor pressure and flow rate, and can be applied to future iterations to verify or

deny Eaton’s hypothesis.

Overview

During the spring semester of 2014, a hydraulic setup was created to further develop a

control feedback loop that would allow for accurate positioning of a hydraulic cylinder. This

setup features a 4/3 Directional Tandem Valve that is solenoid actuated. This valve’s maximum

operating pressure is 5000 Psi and has maximum tank pressure of 3000 Psi. An Omega PX303-

3KG5V Pressure Transducer monitors the pressure and is energized by a 24V power supply. The

flow of the outbound fluid is measured by an Omega Turbine Flow Meter that is also powered

by a 24V power supply. With these components, the pump drives fluid to the 4/3 valve where

it is directed to either side of the hydraulic cylinder. The pressure created in back or in front of

the cylinder dictates the direction of motion. As the fluid leaves the port acting as the outlet

from the cylinder, it is directed through the outlet port of the manifold where it then passes

through the turbine flow meter. The fluid enters the tank where it then goes through the

process again. The overall setup is shown in Figure 1 and the flow diagram is shown in

Appendix A. The system offers the capability to control a hydraulic cylinder’s direction from a

user interface in LabView on a computer.

System Details

The directional valve is a 4/3 spring centered valve, allowing fluid to flow through its

manifold and back into the reservoir while it is in the neutral position. It also allows for the

mass flow meter to be positioned on the low pressure side of the manifold at all times. This is

because of the configuration of the valve, which allows the exiting fluid to leave the same port

on the manifold no matter what direction the cylinder is being driven. The direction of its

activation can be controlled from the LabView user interface, which sends a 20mA signal that is

excited to 5V. This signal is sent to a transistor circuit, where it then goes to the necessary

terminal on the valve.

The pressure transducer, labeled PT on the flow diagram in Appendix A and seen in

Figure 1, is located on the pressurized side of the manifold. This sends an analog signal

between 0V and 5V to the National Instruments Compact DAQ. The calibrated signal value is

displayed on the LabView user interface as absolute pressure (Figure 2). By interfacing the

pressure transducer with LabView, safety mechanisms can be installed so that if the pressure

rapidly increases, cutoffs will initiate to center the valve and lower the pressure.

Similarly, the turbine flow meter outputs a 24V pulse for every revolution of the turbine

inside its housing. Using a conversion factor, the signal is translated to a frequency. It was

important to locate the flow meter on the outlet side of the manifold so that it is always at

atmospheric pressure, alleviating the need for a high pressure turbine flow meter.

To ensure safety, a variety of measures were implemented to prevent injury or damage

to the system. These measures included a bypass valve, pressure gage, and a pressure

transducer. A bypass valve was installed to prevent over pressurization in the event of a

pressure spike. The pressure could spike if the cylinder reaches its minimum or maximum

extension. A pressure gage is also installed and gives a real-time manual reading, which is

beneficial if the pressure transducer were to malfunction. The pressure transducer is also

beneficial because its signal is sent through the Compact DAQ to LabView. Once in LabView, a

pressure tolerance can be integrated that will neutralize the solenoid position and lower

pressure. Later, limit switches will be integrated that will change the direction of the cylinder’s

actuation once a minimum or maximum has been reached to prevent over pressurization.

Three major components control the function of the setup: the power supply, Compact

DAQ, and the transistor circuit. Due to the voltage and current requirements of the directional

valve, an outside power source was needed to provide 24V and 1.38A. Because the Compact

DAQ cannot provide these requirements, a transistor circuit was created to modulate the

supplied voltage and current. The transistors receive the signal from LabView and direct the

voltage to the intended solenoid in the valve. LED’s were incorporated into the circuit to

further indicate which solenoid was activated. The schematic of the transistor circuit can be

referenced in Appendix B. The signals from the three peripherals are all acquired through the

Compact DAQ (Figure 3) and are displayed on the LabView user interface. The wiring diagrams

for the Solenoid DAQ Module, Mass Flow Meter DAQ Module, and Pressure Transducer DAQ

Module can be seen in Appendix C.

The user interface created in LabView features a variety of signal displays and controls.

A virtual 2-position toggle switch controls the direction of the valve, while a “Neutral” button

centers the valve to cycle fluid through the manifold to the tank. This can be seen in Figure 2.

The waveform graph shows the pulse signal generated by the turbine flow meter. The absolute

pressure is also shown below the graph, displayed as an updating value

Holding the hydraulic setup is a compact steel stand. This stand is bolted to the rear of

the hydraulic cylinder and is held together with 5/8” bolts and welds. The stand also holds the

valve and manifold assembly, as well as the mass flow meter over the cylinder itself, making it

compact. An automotive grade, oil resistant paint was used to seal the steel plate to prevent

corrosion or degradation due to oil. This setup can be seen in Figure 4.

Conclusion

Through this project a compact, laboratory ready hydraulic testing setup was developed.

With the foundation for a hydraulic controls system laid, further research will be able to be

performed in the areas of both hydraulics and controls. This project will further be used to

develop a control feedback loop to perform research to test Eaton’s goal of controlling a 60

meter hydraulic cylinder.

Figure 1: Labeled power unit and hydraulic cylinder assembly

Pressure Gauge

Bypass Valve

Power Unit

Hydraulic Cylinder

Hydraulic Cylinder Control Unit

Pressure Transducer

Figure 2: LabView User Interface

Figure 3: National Instruments Compact DAQ

4/3 Directional Valve rated for 5000 psi

Control Circuit that modulates solenoid

actuation though 2 LabView inputs,

powered by 24V DC Power Supply

Hydraulic Manifold with Supply,

Return, and A & B ports

Omega Turbine Mass Flow Meter

Figure 4: Labeled hydraulic control system

Appendix A – Flow Diagram

Tank

PT

4/3 Tandem Directional Valve

on Manifold

Pump

Legend

Low Pressure

High Pressure

A B

P T

Bypass

Valve

Turbine Mass Flow Meter

Hydraulic Cylinder

Appendix B – Transistor Circuit

Transistor A Transistor B Solenoid A Input Solenoid B Input

LabView A Input LabView B Input

Appendix C – Wiring for DAQ to Solenoids

AO

AO 0

AO 1

AO 2

AO 3

COM 0

COM 1

COM 2

COM 3

COM

SUPP

Solenoid A

Solenoid B

24V

GND

4.7K ohm Resistor

4.7K ohm Resistor

Appendix C – Wiring for Mass Flow Meter to DAQ

DI

DI 0

DI 2

DI 4

DI 6

DI 1

DI 3

DI 5

DI 7

COM

24V

GND

Mass Flow Meter

1K ohm Resistor

DI 8

Appendix C – Wiring for Pressure Transducer to DAQ

AI

AI 0

AI 2

AI 4

AI 6

AI 1

AI 3

AI 5

AI 7

COM

24V

GND

Pressure Transducer

AI 8