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Research Papers

Design of Adaptive and Controllable Compliant Systems With Embedded Actuators and Sensors

[+] Author and Article Information
Brian Trease

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109trease@asme.org

Sridhar Kota

Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109kota@umich.edu

J. Mech. Des 131(11), 111001 (Oct 06, 2009) (12 pages) doi:10.1115/1.3149848 History: Received October 16, 2007; Revised April 18, 2009; Published October 06, 2009

We present a framework for the design of a compliant system, i.e., the concurrent design of a compliant mechanism with embedded actuators and sensors. Our methods simultaneously synthesize optimal structural topology and component placement for maximum energy efficiency and adaptive performance, while satisfying various weight and performance constraints. The goal of this research is to lay an algorithmic framework for distributed actuation and sensing within a compliant active structure. Key features of the methodology include (1) the simultaneous optimization of the location, orientation, and size of actuators (and sensors) concurrent with the compliant transmission topology, and (2) the implementation of controllability and observability concepts (both arising from consideration of control) in compliant systems design. The methods used include genetic algorithms, graph searches for connectivity, and multiple load cases implemented with linear finite element analysis. Actuators, modeled as both force generators and structural compliant elements, are included as topology variables in the optimization. The results from the controllability problem are used to motivate and describe the analogous extension to observability for sensing. Results are provided for several studies, including (1) concurrent actuator placement and topology design for a compliant amplifier, (2) a shape-morphing aircraft wing demonstration with three controlled output nodes, and (3) a load-distribution sensing wing structure with internal sensors. Central to this method is the concept of structure/component orthogonality, which refers to the unique system response for each component (actuator or sensor) it contains.

Copyright © 2009 by American Society of Mechanical Engineers
Topics: Actuators , Design , Stress , Sensors
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Figures

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Figure 10

Symmetric motion amplifier: dout=29.1 mm and din=∼0.5 mm/actuator. Dashed lines represent deformed structure. System efficiency=51%. Left: MATLAB optimization results. Right: ANSYS nonlinear finite element analysis.

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Figure 11

Aircraft wing cross section subject to unknown and arbitrary air load f(x). Points P1 and P2 are to be controlled by internal actuators and monitored by internal sensors.

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Figure 12

Design space for the “design for control” synthesis problem. Two output ports are indicated, as well as two actuators. The location and orientation of the actuators are to be determined via synthesis. Actuation will result in deflections at P1 and P2. In this case, we are only concerned with the vertical (y) component of displacement.

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Figure 15

Surface displacement under external load dmaxext (mm). Here, the 0.5 N load designs are best, providing the least deflection under load.

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Figure 16

Achievable displacement of wing surface under actuation load dminact (mm). Here, the 0.05 N load designs are best, providing the most deflection under actuation.

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Figure 17

Physical prototype of three-actuator shape-morphing wing. Material is ABS plastic fabricated via fused deposition modeling. Actuators are simplified as springs to allow for finger actuation. The structure is fixed to ground on the left edge.

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Figure 18

Response of “embedded and distributed sensors” to different applied loads. The loadings are designed to be orthogonal, with the intent that the actuators respond differently and uniquely to each loading case.

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Figure 19

Three example solutions that exhibit the property of observability. Starting parameters are the same for each design. Length units are in mm. The material is ABS plastic. External load magnitude: 0.2–2 N. Sensor elements are shown in green (lighter color).

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Figure 20

Optimal sensor set response to orthogonal load vectors. The magnitude of the external load is 0.2 N. The normal strain components on the beam surfaces are reported. Units are in microstrain.

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Figure 1

Various steps in the synthesis scheme: (a) design specifications, (b) initial array of beam elements as a ground structure, (c) optimized topology of beams, actuators, and sensors, (d) size optimization, (e) deformed position verified with solid model FEA, and (f) physical interpretation, fabricated for experimental verification

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Figure 2

(a) Design domain for an asymmetric actuator amplifier. An output spring is used as a basis for calculation of energy efficiency. (b) Discretization: 6×6 grid, 250 elements.

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Figure 3

Actuator model parameters. Only the stiffness curve (kact) is provided. Interaction with the system determines the actual output force (Fo) and displacement (dd).

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Figure 4

System efficiency (%) as a function of the total element length and number of actuators. Standard deviation of GA performance is indicated. The x-axis indicates the total element length (ltot) in terms of the length ratio ηL. (ltot=ηLldiag).

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Figure 5

Desired displacement (mm) as a function of the total element length and number of actuators. Standard deviation of GA performance is indicated. The x-axis is the length ratio ηL.

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Figure 6

Undesired lateral displacement (mm) as a function of the total element length and number of actuators. Standard deviation of GA performance is indicated. The x-axis is the length ratio ηL.

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Figure 7

Asymmetric problem results, indicating effect of increasing number of actuators. Actuators are indicated by red, hashed lines. Power input equal for all cases. Both efficiency and constraint satisfaction tend to increase with the number of actuators used. Multiple actuators cooperate to constrain lateral motion: kout:0.05 N/mm, population size: 200, mutation: 4–12%, and crossover: 95%.

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Figure 8

Summary of actuator studies. Increasing system efficiency (%) as a function of the number of actuators and output spring stiffness. Length ratio=2. Units for k are N/mm.

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Figure 9

Summary of actuator studies. Desired y-displacement (mm) as a function of the number of actuators and output spring stiffness. Length ratio=2. Units for k are N/mm.

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Figure 13

An example of two possible orthogonal actuation modes. It is seen how the deformations due to each actuator are not only different, but also not redundant.

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Figure 14

Results of optimization for controllability. Each figure shows the response of a different actuator (dashed red line) firing. Dotted black lines indicate deformed structure. Linear results shown on left; nonlinear shown on right. Parameters: population=200, generations=1500, external load=−0.1 N at each output node, actuator modulus=500 MPa, skin element thickness=0.5 mm, orthogonality=99.99%, maximum deflection under load=0.29 mm.

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