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Research Papers

Robogami: A Fully Integrated Low-Profile Robotic Origami

[+] Author and Article Information
Amir Firouzeh

Reconfigurable Robotics Laboratory,
Swiss Institute of Technology Lausanne,
EPFL,
Lausanne, CH 1015, Switzerland
e-mail: amir.firouzeh@epfl.ch

Jamie Paik

Reconfigurable Robotics Laboratory,
Swiss Institute of Technology Lausanne,
EPFL,
Lausanne, CH 1015, Switzerland
e-mail: jamie.paik@epfl.ch

Manuscript received August 5, 2014; final manuscript received December 31, 2014; published online February 27, 2015. Assoc. Editor: Aaron M. Dollar.

J. Mechanisms Robotics 7(2), 021009 (May 01, 2015) (8 pages) Paper No: JMR-14-1198; doi: 10.1115/1.4029491 History: Received August 05, 2014; Revised December 31, 2014; Online February 27, 2015

Intelligent robotic systems that can react to unprogrammed tasks and unforeseen environmental changes require augmented “softness.” Robogami, a low-profile origami robot, addresses intrinsic (material-wise) and extrinsic (mechanism-wise) softness with its multi-degree-of-freedom (DOF) body driven by soft actuators. The unique hardware of the Robogami and its submillimeter thick construction enable diverse transformations as those achievable by the paper origami. The presented Robogami shows the first fully integrated version that has all the essential components including its controller within a thin sheet. Construction of this robot is possible via precise, repeatable, and low cost planar fabrication methods often reserved for microscale fabrications. In this research, we aim at expanding the capabilities of Robogamis by embedding bidirectional actuation, sensing, and control circuit. To assess the performance of the proposed sensors and actuators, we report on the performance of these components in a single module and in the four-legged crawler robot.

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References

Figures

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Fig. 1

The crawler Robogami: a schematic of the assembled robot (a). The exploded view of the functional layers (b). Actuators are in layer (i), (ii), and (v) are glass fiber layers that make the body. Layer (iii) contains the heaters and layer (iv) contains the sensors. Layer (vi) is the controller circuit. The final prototype (c).

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Fig. 2

A curvature sensors and a close up of the sensing area to show parallel score marks. These score patterns increase the sensitivity in a desired direction causing increased sensitivity in bending without affecting the sensitivity in twisting (a). The schematic of the sensor (b). The exploded view presenting the base polyimide layer (i), carbon ink layer (ii), hotmelt adhesive layer (iii), and the cover polyimide layer (iv) (c).

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Fig. 3

A module with antagonistic bending actuators. One of the actuators has its annealed shape in folded state while the other has unfolded annealed shape. By activating each of the two, we can transform between the folded and unfolded states (a). Unfolded module and the schematic of its side view (b). Folded state and its side view schematic (c). In the side views, the design parameters of the actuator are depicted.

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Fig. 4

Torque in the folding and unfolding actuators. Blocked torque of the unfolding actuator is presented by lines at zero value at −90 deg, it corresponds to the memory shape of the actuator. The schematics in the figures present the corresponding shape of actuators in each bending angle. Based on the temperature of the actuators (the phase of the material), each bending angle corresponds to two values: one for active (heated) and one for passive (cold) actuator. For folding actuator, the memory shape (zero torque point) is at 270 deg and its trend is similar as before. There are two equilibrium points that correspond to the intersection of the blocked torque of an activated (heated) actuator with the other actuator in inactive (cold) state. After reaching the equilibrium point and cutting off the current, the equilibrium point starts to shift along the elastic relaxation line of the passively deformed actuator till reaching the new equilibrium where both actuators are cold.

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Fig. 5

Schematic of the test setup for measuring blocked torque of SMA actuators in their whole range of motion. The actuator is fixed to the rotating base on one side and is in contact with the load cell on the other side. The tile in contact with the load cell is longer (its length is 5 times the length of the active part of the actuator) in effort to get more uniform moment throughout the actuator (a). Free body diagram depicting the force measured by the load cell and its moment arm. We report F·L as the blocked torque of the actuator in different bending angles (b).

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Fig. 6

Result of the blocked torque tests which corresponds to the theoretical result presented in Fig. 4. Torque generated by the actuators in motion toward 180 deg (the folded state) with the folding actuator activated and passive unfolding actuator (a). Torque generated by the actuators in motion toward 0 deg (the unfolded state) with the unfolding actuator activated and passive folding actuator (b). The elastic relaxation in both plots corresponds to unloading of the passive actuator, which happens when the current to the active actuator is cut off and it starts to cool down and its blocked torque decreases.

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Fig. 7

Thermal analysis for an SMA torsional actuator. The temperature gradient in the actuator and the tiles, corresponding to the instance that all SMA material has transformed to austenite phase (a). SMA phase transition versus time (b).

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Fig. 8

Mean value and standard deviation for normalized readings of the sensor versus the bending angle in 50 cycles. The result shows very good repeatability and small hysteresis loop compared to conductive silicone-based sensors previously suggested in Ref. [13].

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Fig. 9

A Robogami module with embedded sensors and actuators reaching three goal angles: 60 deg (a), 90 deg (b), and 120 deg (c)

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Fig. 10

A Schematic of the goal configuration for the robot in each phase and the equivalent mechanisms for different phases of locomotion. (a)–(d) represent the phase numbers 1–4 introduced in Table 1, respectively. The 2D schematic in (a) and (c) is the view of the robot along the locomotion direction (y axis), which presents the motion of active legs in these two phases (legs 1–3). The 2D schematic in (b) and (d) shows the view of the robot from the side (along x axis in negative direction) to present the motion of active legs in these two phases (legs 2–4).

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Fig. 11

The sequence of the motion of the crawler. (e) and (i) Phase 1; (b), (f), and (j) phase 2; (c), (g), and (k) phase 3; and (d), (h), and (l) phase 4. These snapshots are from an experiment on the robot without the on-board electronics. In this version, the sensor readings are transferred to computer for analysis and the command is transferred back to the robot.

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