Research Papers

Twelve Degree of Freedom Baby Humanoid Head Using Shape Memory Alloy Actuators

[+] Author and Article Information
Yonas Tadesse1

Department of Mechanical Engineering, Center for Energy Harvesting Materials and Systems (CEHMS), and Center for Intelligent Material Systems and Structure (CIMSS), Virginia Tech, Blacksburg, VA 24061yonas@vt.edu

Dennis Hong

Department of Mechanical Engineering, Robotics and Mechanism Laboratory (RoMeLa), Virginia Tech, Blacksburg, VA 24061dhong@vt.edu

Shashank Priya

Department of Mechanical Engineering, Center for Energy Harvesting Materials and Systems (CEHMS), and Center for Intelligent Material Systems and Structure (CIMSS), Virginia Tech, Blacksburg, VA 24061spriya@vt.edu


Corresponding author.

J. Mechanisms Robotics 3(1), 011008 (Jan 10, 2011) (18 pages) doi:10.1115/1.4003005 History: Received January 19, 2010; Revised October 01, 2010; Published January 10, 2011; Online January 10, 2011

A biped mountable robotic baby head was developed using a combination of Biometal fiber and Flexinol shape memory alloy actuators (SMAs). SMAs were embedded in the skull and connected to the elastomeric skin at control points. An engineered architecture of the skull was fabricated, which incorporates all the SMA wires with 35 routine pulleys, two firewire complementary metal-oxide semiconductor cameras that serve as eyes, and a battery powered microcontroller base driving circuit with a total dimension of 140×90×110mm3. The driving circuit was designed such that it can be easily integrated with a biped and allows programming in real-time. This 12DOF head was mounted on the body of a 21DOF miniature bipedal robot, resulting in a humanoid robot with a total of 33DOFs. Characterization results on the face and associated design issues are described, which provides a pathway for developing a humanlike facial anatomy using wire-based muscles. Numerical simulation based on SIMULINK was conducted to assess the performance of the prototypic robotic face, mainly focusing on the jaw movement. The nonlinear dynamics model along with governing equations for SMA actuators containing transcendental and switching functions was solved numerically and a generalized SIMULINK model was developed. Issues related to the integration of the robotic head with a biped are discussed using the kinematic model.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Blocking stress-strain relationship of actuator technologies for humanoid face. (a) Wide range stress, (b) inset of lower stress, and (c) logarithmic plot. CP=conducting polymer, SMA=shape memory alloy, DE=dielectric elastomer, and PM=pneumatic muscle.

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Figure 2

CAD design of robotic head. (a) Isometric view of CAD (front), (b) rear isometric view, and (c) SMA actuators and a pulley system. (Note: skin layer is not shown in this figure.)

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Figure 3

Pictures of prototype robotic head development. (a) Prototype solid support structure, (b) modified natural looking skull structure, and (c) elastomeric skin with the skull.

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Figure 4

Vision system. (a) Pictures of the vision system of the head. (b) CAD drawing.

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Figure 5

Skin stiffness characterization. (a) Picture of the experimental setup, (b) schematic diagram of the experimental setup, and (c) force versus displacement diagram for the synthesized skin along the deformation lines shown in the inset.

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Figure 6

Action unit and direction of movement on the skull. Schematic diagram in (a) frontal view, (b) side view, and (c) frontal view of the actual prototype, in pictorial view.

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Figure 7

SMA actuator-skin deformation relationships. (a) Generalized actuation characteristics, (b)–(g) Comparative force-displacement characteristics of AUs utilizing Flexinol wire (127 μm wire), and (h)–(m) Biometal fiber (100 μm wire) in parallel configuration.

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Figure 8

(a) Skin-skull-actuator assembly, (b) back side of the head with a slot created in the skin to gain access inside the head, which can be sealed using zipper, and (c) inside of the head after completing the assembly

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Figure 9

(a) Schematic diagram of the driving circuit for the SMA head. (b) Sequence of facial activation for 1 cycle.

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Figure 10

Facial expression around the mouth, (a) lips normal position, (b) mouth open by lower jaw movement, (c) upper lip protruded outward, and (d) lower lip pulled inwards

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Figure 11

Face movement characterization, (a) displacement response for two period activation, (b) before smiling action unit (AU4L) is activated, and (c) after AU4L is activated

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Figure 12

(a) Gray scale image of the face, (b) object identification with dark value 100 amplitude, (c) normal position of the mouth with centroid tracking, and (d) mouth opening when jaw was activated (AU10)

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Figure 13

Measurement and characterization of the jaw movement: (a) pictures of circular disk mounted on the lip, (b) cropped image after processing, and (c) jaw response for a square wave with 2 s activation and 6 V amplitude

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Figure 14

Nodding of the head mounted on biped DARwIn. ((a) and (b)) Nodding gesture motion.

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Figure 15

Schematic diagram of pulley system and SMA actuator. (Note that Au represents action unit.)

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Figure 16

Jaw mechanism: (a) isometric view of jaw-SMA routing pulley, (b) frontal view indicating local coordinates of pulleys, (c) isometric view of jaw, and (d) top view

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Figure 17

Free body diagram of SMA actuated jaw

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Figure 18

SIMULINK model of SMA actuated jaw with constant modulus

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Figure 19

Numerical results constant modulus modeling of SMA actuatored jaw. (a) Strain versus temperature,(b) angular movement, (c) fraction of martensite versus temperature, (d) stress-strain, (e) torque due to SMA, (f) torque due to spring, (g) temperature states, and (h) torque due to gravity. (Tec=−11×10−6 Pa/°C; CA=10.3×106 MPa/°C; CA=10.3×106 MPa/°C; Cp=320 J/kg °C; h=110; Ks=270 N/m; Mj=0.0128 kg; Ie=1∗9.88×106 kg m2; initial stress=0; and V=4.8 V amplitude square wave 2 s pulse period.)

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Figure 20

Numerical and experiment angles of jaw movement for a 50 MPa step stress input to the dynamic block

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Figure 21

Numerical and experimental results of time domain force, displacement for square wave input voltage under prestress condition (SMA wire diameter=127 μm)




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