Hydraulic controller nets best-paper win

Mondeep Duarah and Vijay Jayabalan of Captronic Systems, Bangalore, India, won Best Paper in the control category at NIWeek 2007 with their article entitled “Digital Electro-Hydraulic Servo Controller.”

08/23/2007


Austin, TX —Mondeep Duarah and Vijay Jayabalan of Captronic Systems, Bangalore, India, won Best Paper in the control category at NIWeek 2007 with their article entitled “ Digital Electro-Hydraulic Servo Controller .” The paper describes a PC-based digital controller they developed using LabView and PXI/Compact PCI hardware from National Instruments (NI).

“Although electrical motors are used in many motion control systems, electro-hydraulic systems often address applications requiring either very high force or wide bandwidth more efficiently,” they point out in the paper. “In general, electro-hydraulic systems better serve applications with control bandwidths greater than about 20 Hz, or control power greater than about 15 kW.”

Such servo-hydraulic systems are mechanically “stiffer,” producing higher machine frame resonant frequencies for a given power level, higher loop gain, and improved dynamic performance. The driving fluid effectively acts as a cooling medium, carrying heat away from the actuator and flow control components, making such systems run cooler.

“Unfortunately,” the authors continue, “hydraulic systems also exhibit several inherent non-linear effects which can complicate the control problem.”

The fact that the vast majority of electronic closed-loop controllers are based on simple analog circuit designs makes it difficult to deal with these non-linear effects. Control designers have traditionally chosen these designs because they offer robust, low cost implementations of the well known PID control strategy. This approach works well in systems with simple topology and limited bandwidth.

The growing use of complex control strategies and complicated mechatronic architectures, however, coupled with the need to support enhanced features such as data logging and digital communications, has led to increased interest in digital processors for control of hydraulic servo-systems.

The authors list some of the benefits of going to a PC-based digital controller:

  • Improved immunity to component tolerances, thermal drift, and aging;

  • Improved noise immunity;

  • Ability to modify and store control parameters;

  • Ability to easily implement digital communications;

  • System fault monitoring and diagnostic capabilities;

  • Data logging capability;

  • Automated calibration;

  • Diagnostic monitoring identify mechanical vibrations and predict failure modes;

  • High-order digital filters to suppress resonant modes; and

  • Lower overall system cost.

The test system that the authors built uses an electro-pneumatic actuator load a test specimen according to a test-waveform created by a PXI-based signal generator capable of producing sine, triangle, square, or combination waveforms.

To control loads on the test specimen strain-gauge load cells monitor the actual load. The resulting electrical signals go through a National Instruments SCXI-1520 signal conditioner and compared to the original test waveform. The error signal is then amplified and used to control a servo valve, which controls oil flow rates from a high pressure pump to the actuator, driving the piston to modify the force on the test specimen.

Control is achieved by using a software implementation of a PID controller NI PID Control Toolkit. The PID controller uses the position form of the PID algorithm. PID controller is capable of loading the system defined by the wave form. The PID Control toolkit provided resources for shunt calibration, offset nulling, and programmable excitation.

Unfortunately, the nonlinear behavior of the system forces conservative loop gains and the gain scheduling feature of the PID Control Toolkit helped implement them. The controller was tuned at multiple operating points to take care of the systems nonlinearity.

The authors say that the digital servo controller developed is highly flexible, rugged, and cost effective. Tests show that it can achieve an average accuracy of 2 A

Other Control Engineering NIWeek 2007 coverage includes software advancements.

C.G. Masi , senior editor, Control Engineering





No comments
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
Each year, a panel of Control Engineering editors and industry expert judges select the System Integrator of the Year Award winners.
Control Engineering Leaders Under 40 identifies and gives recognition to young engineers who...
Learn more about methods used to ensure that the integration between the safety system and the process control...
Adding industrial toughness and reliability to Ethernet eGuide
Technological advances like multiple-in-multiple-out (MIMO) transmitting and receiving
Virtualization advice: 4 ways splitting servers can help manufacturing; Efficient motion controls; Fill the brain drain; Learn from the HART Plant of the Year
Two sides to process safety: Combining human and technical factors in your program; Preparing HMI graphics for migrations; Mechatronics and safety; Engineers' Choice Awards
Detecting security breaches: Forensic invenstigations depend on knowing your networks inside and out; Wireless workers; Opening robotic control; Product exclusive: Robust encoders
The Ask Control Engineering blog covers all aspects of automation, including motors, drives, sensors, motion control, machine control, and embedded systems.
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
News and comments from Control Engineering process industries editor, Peter Welander.
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
This is a blog from the trenches – written by engineers who are implementing and upgrading control systems every day across every industry.
Anthony Baker is a fictitious aggregation of experts from Callisto Integration, providing manufacturing consulting and systems integration.
Integrator Guide

Integrator Guide

Search the online Automation Integrator Guide
 

Create New Listing

Visit the System Integrators page to view past winners of Control Engineering's System Integrator of the Year Award and learn how to enter the competition. You will also find more information on system integrators and Control System Integrators Association.

Case Study Database

Case Study Database

Get more exposure for your case study by uploading it to the Control Engineering case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.

These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.

Click here to visit the Case Study Database and upload your case study.