Page 415 - IJB-9-3

International Journal of Bioprinting Cellular metamaterial flexure joints

joints and then due to the changes in the stiffness of the 5. Conclusions and future works
joints, the trajectory of the wooden cube will change, and
the object will move toward the finger with lower stiffness This paper presents a heterogeneous architecture of
joints. This example shows that more complex motions can the cellular mechanical metamaterial for flexure-based
be encoded in the robotic grippers with MFJs. revolute joints using 2D-designed auxetic unit cells.
The proposed architecture enables soft flexure joint
4.4.2. Grasping linear objects with large range of rotation without requiring a large
notch in the structure and also provides tunable multi-
The second application focuses on demonstration of the level bending stiffness behavior. These characteristics
large bending angle of the MFJs through grasping linear
objects with small diameters. In robotic community, of the MFJs enable the design of soft robotic fingers
objects such as ropes, rods, strings, and cables are referred with complex pre-programmed motions and highly
to as linear objects . At present, most of the robotic functional soft robotic hands for grasping wide range of
[24]
hands/grippers are using pinch-type grip for grasping and objects without the need for bulky actuators or complex
manipulation of the linear objects as they are not able to control systems.
grasp linear objects with small diameter using power grasp. The future work will focus on inverse design of the
As a result, a high force pinch grip is required to manipulate MFJs to obtain the geometrical parameters of the joints
the linear objects for performing a task, such as making a for a desired motion of the fingers. The main challenge
knot. Human hand uses power grasp for grasping linear in the inverse design is developing a general model of the
objects (Figure 5A) and due to distributed forces on the MFJ. Since developing a theoretical model that is reliable
objects, low force grasps are sufficient for stable grasping is difficult because of the large deformation and large
without slipping. This problem is more prominent in soft number of self-contacts in the MFJ, data-driven models
robotic hands since due to the compliance of the structure, can be developed using FE simulations or real-world
they cannot exert a high level of pinch forces. experiments.

To demonstrate the advantage of the MFJs in grasping Acknowledgments
linear objects with small diameter, which requires large
bending angle of the finger joint, an anthropomorphic None.
5-fingered soft robotic hand is fabricated where each
[5]
finger consists of three MFJs with different tuning Funding
parameters. The proximal interphalangeal (PIP) joint of This project is funded by the Valma Angliss Trust and the
the fingers of the robotic hand has a MFJ with maximum University of Melbourne.
bending angle of 110° similar to human finger. The
metacarpophalangeal (MCP) and distal interphalangeal Conflict of Interest
(DIP) joints of these fingers have higher stiffness in The authors have declared that no competing interests
comparison to the PIP joint. The resultant trajectory of exist.
this architecture of the finger is similar to human hand for
grasping linear objects with small diameter, as shown in Author Contributions
Figure 5B and 5C.
Conceptualization: Alireza Mohammadi, Elnaz Hajizadeh
The performance of the robotic hand in grasping three Formal analysis: Alireza Mohammadi
different linear objects is shown in Figure 5 and Videoclip S2, Methodology: Alireza Mohammadi, Elnaz Hajizadeh
including a fishing line with diameter of 0.6 mm (Figure 5D), Supervision: Peter Choong, Denny Oetomo, Ying Tan
blind rope with diameter of 2 mm (Figure 5E), and also a Validation: Alireza Mohammadi
wire with diameter of 0.3 mm (Figure 5F). Since the stiffness Visualization: Alireza Mohammadi
of the joint is nonlinear, the stiffness level is much higher at Writing – original draft: Alireza Mohammadi
the end of the range of the bending angle, which results in Writing – review & editing: Alireza Mohammadi, Ying Tan,
firm power grasping, and it will not be easily opened because Denny Oetomo
of the external force of grasping the objects. For instance, for
pulling the rope with high force, the robotic hand should Ethics approval and consent to participate
be able to not only grasp the rope but also hold it with high
force. This is demonstrated in Figure 5G where the soft Not applicable.
robotic hand can hold a rope with a 1-kg weight attached Consent for publication
to that, showing the advantages of MFJs with large bending
angle and variable stiffness. Not applicable.

Volume 9 Issue 3 (2023) 407 https://doi.org/10.18063/ijb.696