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Materials Science in Additive Manufacturing 3D-printed LMPA-integrated soft robots

methods. Second, LMPAs melt and solidify at relatively actuated by a cable, the LMPA is in its melted state, thus
low temperatures compared to traditional metal powders exerting minimal resistance to the cable-driven motion.
used in processes like selective laser melting. The lower This results in a reduced force requirement for actuating
processing temperatures further reduce thermal stresses. the LMPA-integrated gripper compared to the fully dense
TPU gripper. In addition, the presence of cavities and the
3.2. State-changing effect and recovery rates softened state of TPU at elevated temperatures contribute
The state-changing effect of the LMPA-integrated TPU to easier deformation.
gripper was a pivotal aspect of this study. When heated The tensile test outcomes of robotic arms with
above 70°C, the LMPA transitioned from a solid to a liquid pure TPU and LMPA-integrated TPU are presented in
state, allowing the gripper to alter its shape and grasp Figure 4B. The LMPA-integrated robotic arm exhibited
objects effectively. This state change enabled the gripper enhanced mechanical strength, withstanding a tensile
to conform to various shapes and sizes, enhancing its force of approximately 350 N, compared to the pure TPU
versatility and functionality. robotic arm’s endurance of around 270 N. This significant
Upon cooling to room temperature, the LMPA solidified, improvement in mechanical strength can be attributed to
enabling the gripper to maintain its hold on objects the reinforcing effect of the solidified LMPA within the
without external power. This passive holding capability gripper structure.
is particularly advantageous for applications requiring It is important to emphasize that the showcased soft
prolonged gripping, as it reduces energy consumption. gripper serves as an illustrative instance. The benefits of
The recovery rate, or the time required for the LMPA to energy utilization and mechanical strength enhancement
solidify and secure the grip, was found to be dependent can also be extended to other soft grippers employing
on ambient conditions and the specific heat capacity of diverse energy sources (e.g., pneumatic). The integration
the LMPA. Experimental observations indicated that the of LMPA offers a versatile approach to improving the
LMPA could solidify within 30 s to 1 min under typical performance of soft robotic systems, making them more
laboratory conditions. This relatively quick transition efficient and capable of handling a wider range of tasks
supports practical applications, ensuring that the gripper with minimal energy consumption.
can rapidly secure objects without significant delays.
4. Conclusion
3.3. Mechanical strength and energy efficiency
This paper introduces the utilization of material extrusion
The mechanical performance and energy efficiency of for the fabrication of soft grippers incorporating LMPA.
the soft grippers were evaluated through a series of tests. The primary concept revolves around harnessing the
Figure 1 illustrates the final 3D-printed soft grippers. favorable property of LMPA’s low melting temperature,
As depicted in Figure 1B and C, a clear distinction is enabling the soft gripper to transition between a pliable
observed between the pure TPU soft gripper and the state and a solid one. Upon heating the LMPA within the
LMPA-integrated soft gripper. The pure TPU gripper soft gripper beyond its melting point, the gripper operates
requires continuous external force to maintain its grip on conventionally providing the necessary flexibility and
components. In contrast, the LMPA-integrated gripper adaptability to grasp various objects. In contrast, as the
can maintain its grasp without external force due to the LMPA temperature decreases to ambient levels, the soft
solidification of the LMPA, particularly during the motion gripper transforms into a solid state, becoming capable of
of components. securing objects without the need for external power or
This behavior stems from the unique properties of force.
LMPA. When the gripper is heated beyond 70°C, the LMPA This innovation effectively curtails energy consumption
transitions into a liquid state, without compromising the during the motion process, particularly during long-
gripper’s functionality. Upon cooling to temperatures distance transportation, by eliminating the need for
below 70°C, the LMPA solidifies, enabling the gripper continuous external power to maintain grip. The integration
to hold onto the components securely. This transition of LMPA not only contributes to energy efficiency but also
obviates the need for continuous external energy or force, enhances the mechanical performance of the soft robots.
thus conserving energy during prolonged gripping or The tensile tests demonstrated that the LMPA-integrated
transportation tasks.
TPU grippers exhibit superior mechanical strength
The pure TPU gripper is fully dense, as shown in compared to their pure TPU counterparts, withstanding
Figure 2. In contrast, the LMPA-integrated soft gripper greater tensile forces and providing more robust and
contains cavities filled with LMPA. When the gripper is reliable operation.

Volume 3 Issue 3 (2024) 6 doi: 10.36922/msam.4144