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ABSTRACT

The objective is to give the students practical experience in tuning a digital speed controller for a rotary hydraulic system starting with the Ziegler-Nichols method. Digital controller basics and the tuning method are discussed. In using this method the critical tuning area of system operation must first be determined. This impacts the selection of fixed controller tuning parameters which are used for command changes, load changes and startup. For this system, as long as transient startup is acceptable, it was concluded that the settings should be selected for the more restrictive minimum speed operating condition. The resulting operation at higher operating speeds is then somewhat less responsive than the selected tuning point.

BACKGROUND

An assembled automatic control loop1,2,5 must have the controller gains properly selected to provide a completed suitable response. The Zeigler-Nichols (Z-N) method helps the students to more easily tune or select the proportional, integral, and derivative gains as needed in a practical laboratory environment by selecting an initial starting point for further trial and error work. Engineering education occurs as the students are able to progress from their own poorly selected gains and the resulting poor responses to more desirable gains and responses in a timely “hands on” manner. Although no actual student surveys are available at this time, the conclusion of one student group lab report6 does state “The results that were achieved for this experiment appear to be very good. The plots of the system response versus the load appear to match up very well with what was expected. The values of the ultimate gain and ultimate period seem appropriate, as do the estimated initial controller settings determined using the Ziegler-Nichols tuning method.” Thus, loop response improvements similar to those shown here have been made in a timely manner and do give a positive indication of student learning. The Z-N method is also presently used by the other professors teaching these courses. Having benefited by this engineering education the students will be able to use it as a fundamental tool in other appropriate industrial applications in the wide world of automatic control.

The physical system arrangement will now be described. The plant consists of an axial piston motor which drives an identical axial piston pump through a shaft mounted torque speed transducer. The pump is loaded using a remotely controlled relief valve in the output loop. A rotational speed feedback signal is available from a speed transducer system using a pickup and 60 toothed wheel. The shaft torque and additional pressures and flows are displayed on the stand panel face. Additional instrumentation is available to provide and select needed electrical signals. The system is shown schematically and pictorially in figures 1 - 4. Note: The schematic omits the clutch and frictionally driven flywheel.

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Ficken, J. (2010, June), Implementing The Digital Speed Controller Tuning Of A Laboratory Rotary Hydraulic System Paper presented at 2010 Annual Conference & Exposition, Louisville, Kentucky. 10.18260/1-2--15730