A Soft Transporter Robot Fueled by Light

Abstract

Mobile organisms with ability for locomotion and transportation, such as humans and other animals, utilize orchestrated actuation to perform actions. Mimicking these functionalities in synthetic, light-responsive untethered soft-bodied devices remains a challenge. Inspired by multitasking and mobile biological systems, an untethered soft transporter robot with controlled multidirectional locomotion with the ability of picking up, transporting, and delivering cargo driven entirely by blue light is created. The soft robot design is an ensemble of light-responsive liquid crystalline polymers that can harness motion either collectively or individually to obtain a high degree of motion control for the execution of advanced tasks in a dry environment. Through orchestrated motion of the device's "legs", single displacement strides, which exceed 4 mm and can be taken in any direction, allow for locomotion around objects. Untethered cargo transportation is demonstrated by a pickup and release mechanism using the device's "arms". This strategy demonstrates the constructive harnessing of orchestrated motion in assemblies of established actuators, performing complex functions, mimicking constructive behavior seen in nature.

Keywords: light‐driven soft robots; liquid crystal soft robots; photoactuators; untethered soft robotics.

Figure 1

The soft robot is composed of four identical light‐responsive liquid crystalline polymer films that operate as legs, connected to and supporting a polymeric hub (polypropylene) which hosts an assembly of liquid crystalline films acting as soft robotic arms that operate as the device's cargo holder and handler. The hub is symmetric with four triangular “cuts” for decreased weight while maintaining the supportive structure. A) The soft robotic device is of centimeter size (spanning 2 cm across) and weighs 20 mg. B) A schematic depiction of the device, demonstrating the two different light‐responsive azobenzene chromophores (depicted in yellow and red) used to separately address the legs (yellow) and arms (red) of the cargo handler.

Figure 2

Characterization of a photoresponsive liquid crystal network composed of photothermal azobenzene chromophores. A) Illustration of the actuation of a splay aligned network, secured on one side by tweezers. The LCN consists of liquid crystals (gray) and photoisomers (yellow) responding to illumination. Starting from a curled geometry, the film unbends toward its planar surface when illuminated. B) Plot displaying the high temporal resolution of the unbending and recurling processes of a LCN strip (2 cm in length and 0.4 cm in width), containing photoswitch A1 corresponding to application (“light on”) and removal (“light off”) of illumination, respectively. C) Graph depicting the actuation performances of the LCN arms and legs as a function of illumination intensity.

Figure 3

Light‐driven locomotion of the soft robot in multiple directions over a paper surface. A) The simple robot (without integration of LCN arms) is demonstrated to move from its initial position (i) around a palm tree (ii) toward its finish line (iii). B) The walking mechanism for one stride consists of three main steps and two light sources.

Figure 4

Investigation of the importance of leg dimension and shape for locomotion. A) Schematic depiction of the robot, showing leg length and width dimensions. B) Schematic drawing of the leg design with a wider leg base which enhances walking locomotion. C) The effect of leg length and width on both the directionality and efficiency of locomotion. We plot the average distance covered by one illumination cycle (described in Figure 3B) for robots with varying leg dimensions and the standard deviation of these values for ≈10 steps. We observe that short 8 mm legs result in walking in a direction away from the illumination and longer, 10 and 12 mm legs, in locomotion toward the light source. Little variation is observed between legs of 10 and 12 mm, yet an increase in leg base largely increases the distance covered by one stride.

Figure 5

Cargo pickup, transportation, and release. A) Snapshots of the untethered cargo pickup activity. B) Schematic depiction of the pickup mechanism. The cargo hangs from a glass surface coated with an adhering coating to keep the cargo in place until the robot's arms actuate and release it. C) Snapshots of the untethered transportation and cargo release. D) Schematic depiction of the release mechanism when the robot approaches the delivery boxes. For cargo release, both the LC gripper (located in the center of the hub) and one of the “arms,” are actuated to cause gripper opening and thrust the cargo in either one of the boxes. Additionally, actuation of one LC leg causes the robot to slightly lift, enhancing the directed cargo thrust into the delivery box.