Research Papers

An Approach for Actuation Specification and Synthesis of Dynamic Systems

[+] Author and Article Information
Thomas J. Connolly1

Department of Mechanical Engineering, University of Texas at San Antonio, One UTSA Circle, EB 3.04.24, San Antonio, TX 78249thomas.connolly@utsa.edu

Raul G. Longoria

Department of Mechanical Engineering, University of Texas at Austin, Cockrell School of Engineering, 1 University Station C2200, Austin, TX 78712r.longoria@mail.utexas.edu


Corresponding author.

J. Dyn. Sys., Meas., Control 131(3), 031012 (Mar 23, 2009) (15 pages) doi:10.1115/1.3089558 History: Received February 13, 2007; Revised December 19, 2008; Published March 23, 2009

Refinement or improvement of a dynamic system to meet a frequency response specification can benefit from the option to use passive or active compensation, or a combination of both. The process becomes more effective when supplemented with methods derived from classical network theory to synthesize candidate designs for actuators and their control systems. The synthesis procedure presented here provides an explicit way to formulate system topologies that employ passive and active elements to achieve a desired targeted performance specification, i.e., frequency response. Active elements are used to represent elements that are not physically realizable, such as negative impedances and elements that have ill-defined connectivity. A working premise is that these elements indicate the need for actuation technology. Coupled with a topological description of the system, the synthesis procedure provides a systematic approach that offers design solutions not previously conceived of through insight or experience. These “first draft” designs can be improved upon by later utilizing complementary approaches, such as optimization methods, as dictated by detailed system requirements and operating regimes. The flexibility of this synthesis approach allows the consideration of design restrictions unrelated to frequency response, but critical nonetheless in assessing the viability of candidate designs. Further, the procedure does not require assumption of a particular control/compensation architecture at the outset; this renders novel architectures that depart from traditional architectures such as proportional integral, propotional-integral-derivative, etc. The procedure is couched within a simulation basis, so that extension to state-space simulation and thus growth of the system and inclusion of more complex and nonlinear representations become possible. The concept of a virtual state space is introduced, which is integral to the development of controller architectures and associated parameters. It is found that customized passive/active compensation systems can be derived using a bond graph approach, making this approach more easily applicable to multi-energetic systems. Examples are used to demonstrate the approach, including a case study of an electromechanical vehicle suspension, from which an experimental model is derived to illustrate the synthesis procedure. Comparison of results between these examples illustrate the practical utility of the synthesis procedure. In particular, simulations reveal that increasing the number of realized passive elements for a particular system does not necessarily minimize actuator energy consumption. Detailed analysis of synthesis results show that certain design candidates feature active devices that work against either passive elements or other active devices within the system.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

(a) Use of a NIC to represent negative impedance. (b) Ideal NIC in electrical systems. (c) Bond graph of ideal electrical NIC.

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Figure 2

(a) Bond graph representation of negative impedance. (b) Realization using controlled effort source.

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Figure 3

(a) Realization of negative capacitive impedance. (b) Effort-controlled actuator realization. (c) Flow-controlled actuator realization.

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Figure 4

Schematic and model of oscillator

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Figure 5

Desired transfer function, dTF(s)

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Figure 6

Decomposition of Z(s)

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Figure 7

Hybrid design No. 1 with all possible passive elements realized

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Figure 8

Hybrid design No. 2

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Figure 9

Fully active design

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Figure 10

Inclusion of motor winding resistance, Rw, for hybrid design No. 2

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Figure 11

Impedance decomposition flowchart

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Figure 12

Overall procedure flowchart

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Figure 13

Photograph and schematic of EM suspension test configuration

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Figure 14

Bond graph of EM suspension test configuration

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Figure 15

Measured amplitude frequency response data and plot resulting from curve-fitting algorithm

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Figure 16

Bond graph showing impedance decomposition

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Figure 17

Schematic representation of decomposed impedances (nonrealizable elements labeled in gray)

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Figure 19

Actuator behaviors for design No. 1

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Figure 21

Actuator behaviors for design No. 2

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Figure 23

Actuator behaviors for design No. 3

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Figure 24

Energy consumption totals for design Nos. 1–3

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Figure 25

Close up of pertinent power bonds and schematic

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Figure 26

Powers (W) associated with (a) bond leading into 0-junction, (b) bond connected to damper b51, and (c) bond connected to actuator A3

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Figure 27

Velocities of actuator A3 and damper b51

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Figure 29

Actuator behavior for design No. 4

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Figure 30

Power consumptions (W) of removed passive elements in arriving at design No. 4

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Figure 31

Fully active design with motor winding resistance effects

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Figure 32

Voltages and current for electromechanical actuator

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Figure 33

Power and energy consumption for electromechanical actuator

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Figure 34

Controller for fully active design

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Figure 35

Comparison of simulated and experimental data for the velocity of the sprung mass




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