Chunshan Liu

Soft and smart modular structures actuated by shape memory alloy (SMA) wires as tentacles of soft robots

This paper introduces the design and fabrication of a multi-layered smart modular structure (SMS) that has been inspired by the muscular organs and modularity in soft animals. The SMS is capable of planar reciprocal motion of bending in heating process and recovering in cooling process when SMA wires carry out phase transformation. An adaptive regulation heating strategy is applied to avoid overheating and achieve bending range control of the SMS based on the resistance feedback of the SMA wires which as actuator of the SMS. The SMS can modular assemble soft robots with multiple morphologies such as lateral robots, bilateral robots and actinomorphic robots. A five-armed actinomorphic soft robot is conducted to crawling in terrestrial ground (max speed: 140 mm s−1, 0.7 body s−1), swimming in underwater environment (max speed: 67 mm s−1, 2.5 height s−1) and griping fragile objects (max object weight: 0.91 kg, 15 times the weight of itself). Those demonstrate that the performance of the SMS is good enough to be modular units to establish soft robots which possess a high speed of response, good adaptability and a safe interaction with their environments.

A starfish robot based on soft and smart modular structure (SMS) actuated by SMA wires

This paper describes the design, fabrication and locomotion of a starfish robot whose locomotion principle is derived from a starfish. The starfish robot has a number of tentacles or arms extending from its central body in the form of a disk, like the topology of a real starfish. The arm, which is a soft and composite structure (which we call the smart modular structure (SMS)) generating a planar reciprocal motion with a high speed of response upon the actuation provided by the shape memory alloy (SMA) wires, is fabricated from soft and smart materials. Based on the variation in the resistance of the SMA wires during their heating, an adaptive regulation (AR) heating strategy is proposed to (i) avoid overheating of the SMA wires, (ii) provide bending range control and (iii) achieve a high speed of response favorable to successfully propelling the starfish robot. Using a finite-segment method, a thermal dynamic model of the SMS is established to describe its thermal behavior under the AR and a constant heating strategy. A starfish robot with five SMS tentacles was tested with different control parameters to optimize its locomotion speed. As demonstrated in the accompanying video file, the robot successfully propelled in semi-submerged and underwater environments show its locomotion ability in the multi-media, like a real starfish. The propulsion speed of the starfish robot is at least an order of magnitude higher than that of those reported in the literature-thanks to the SMS controlled with the AR strategy.

Mechanical system and stable gait transformation of a leg-wheel hybrid transformable robot

This paper proposes a novel and mechanically decoupled leg and wheel hybrid transformable robot called HyTRo-I that combines the fast speed of wheeled vehicles on a flat ground and the high degree of flexibility of legged robots over irregular terrains. According to different terrain conditions, HyTRo-I can choose from three motion modes: wheeled rolling, quadrupedal walking mode and leg-wheel hybrid mode. By shifting among these moving patterns, the mobility of HyTRo-I over various surface conditions can be fully realized. While the control technology of actuating the wheeled vehicles is mature and simple, the control of quadruped walking is an area of active research. Therefore, we develop a statically stable gait controller for our robot. In addition, we study the locomotion mechanism of transformation that concerns the feasibility of three moving methods of HyTRo-I. By the mutual transformation gaits illustrated in details, HyTRo-I can be smoothly and reciprocally transformed between wheeled rolling mode and quadrupedal walking mode. Finally, we experimentally test the mode transformations of HyTRo-I.

Design and development of a leg-wheel hybrid robot “HyTRo-I”

This paper proposes a novel and mechanically decoupled leg and wheel hybrid transformable robot called HyTRo-I that combines two mobility concepts. For example, while wheeled vehicles shares higher speed than legged and tracked machines on a flat ground, they have relatively lower degree of flexibility than the other two on irregular terrain. The HyTRo-I robot evolves three motion modes: wheeled rolling, quadrupedal walking and leg-wheel hybrid mode. Despite the over-whelming complexity of obstacles, only several typical obstacles are selected for the study, which are stairs, large protrusions and ditches. Firstly, the transition locomotion mechanism between wheeled rolling mode and quadrupedal walking mode should be studied in detail. In the course of reciprocal transition locomotion, the static and reversible transformation gait not only guarantees the shifting stability and a small number of transition steps, but also the relatively balanced torque of joints. Secondly, after HyTRo-I converting to effective locomotion mode, the adaptive gait control strategies are proposed to traverse three types of obstacles. Finally, a serial of experiments were performed to verify the validity of the proposed transformation gait and adaptive step-up gaits.

Generation and Analyses of the Reinforced Wave Gait for a Mammal-Like Quadruped Robot

The statically stable gait control of a mammal-like quadruped robot that provides an adequate or stable manner of traversing over irregular terrain was addressed. The reinforced wave gait which integrates new parameters of the lateral offset and displacements of the center of gravity (COG) based on the profiles of standard wave gait was investigated. The continuous and discontinuous motion trajectory of a robot’s COG in the periodic reinforced wave gait could be realized. The longitudinal and lateral stability margins of a reinforced wave gait were formulated for the gait generation and control of a quadruped robot. Moreover, the effects of the lateral offset on the stability, velocity and the energy efficiency were studied in details. The reinforced wave gait with lateral sway motion adequately improved the stability, and two particular gait patterns that involve the lateral sway motion for a maximal velocity and maximum achievable stability were described. With consideration of a quadruped robot with asymmetric carrying loads on its body, a scheme that relates to the gait parameters of the displacement of a robot’s COG to avoid losing stability was proposed. The simulation and experimental results about the effects of lateral offset added in the reinforced wave gait on the minimum power consumption during a quadruped robot walking on a flat terrain indicated that the reinforced wave gait with a larger lateral offset would generate a better wave gait with a higher velocity and energy efficiency.

Locomotion analysis and optimization of actinomorphic robots with soft arms actuated by shape memory alloy wires

This article presents the locomotion analysis and optimization of actinomorphic soft robots, which are composed of soft arms actuated by shape memory alloy wires. The soft arm that is a composite modular structure is actuated by a self-sensing feedback control strategy. A theoretical model was established to describe the deformation of the soft arm, combining the Euler–Bernoulli beam model of the soft arm with the constitutive model and the heat transfer model of the shape memory alloy wire. The kinematics of the actinomorphic soft robot was analyzed using the modified Denavit–Hartenberg method, and the motion equation of the actinomorphic soft robot was presented based on the quasi-static hypothesis. Results show that the actinomorphic soft robot moves with a zig-zag pattern. The locomotion of four actinomorphic soft robots with three to six arms was analyzed, and the gait parameters of each locomotion type were optimized. The optimization results indicate that the three-arm actinomorphic robot with certain gait parameters has the best performance and achieves a maximum stride length of 75 mm. A series of experiments were conducted to investigate the movement performance of the three-arm actinomorphic robot in various environments.

A novel biomimetic jellyfish robot based on a soft and smart modular structure (SMS)

This paper introduces the design, fabrication and experiment of a biomimetic jellyfish robot based on a soft and smart modular structure (SMS) to mimic the behavior of the alternating shrinkage and expansion of the real jellyfish. The SMS consisted of two layers including an actuating layer and a recovery layer. And to mimic the actinomorphic structure of the jellyfish, the jellyfish robot had six SMSs or tentacles symmetrically extending from its central disc and a bell covering the SMSs and one central disc. We measured the force acting on the end of the SMS and results showed the force was around 1N and varied with the input current. The force increased as the heating input current increased, and the amplitude of the force gradually reduced and stabilized. Besides, the vertical floating displacements of the jellyfish robot at different frequencies were measured. As results showed that, the floating velocity of the robot was variable. The robot was able to achieve the maximum velocity of 111 mm/s at the frequency of 1.0 Hz, about 1.6 body length per second. Compared with current state of the art of robotic jellyfish actuated by smart actuators, the jellyfish robot achieved the most proficiency at 1.6 s−1. In the case where SMSs were actuated at 1.0 Hz, robot shows better performance in comparison with other frequencies based on the Strouhal Number. Finally, the jellyfish robot was able to accomplish three-dimensional locomotion with the input of sequential pattern.

Research of a dual stage bending dexterous robotic hand with EMG control

This Paper presented a new dual stage bending dexterous robotic hand whose soft composite finger (SCF) was consisted of a soft composite structure and a solid hinge both driven by shape memory alloy (SMA) wires. There are three layers of the soft composite structure: an equivalent natural plane with elastic PVC plate, an actuation layer with SMA wires and the basal structure using soft material polydimethylsiloxane (PDMS). The designation of the SCF was inspired by human fingers whose dimension information and movement principle determined the parameters of the bionic finger. The bending principle of the SCF can be describe as below: the hinge provides relative rotation between phalanx and metacarpal bone; the soft composite structure bends on this basis and provides a soft touch. The dual stage bending structure enhances deformation and force output. Several SCFs of different length form the dexterous robotic hand. Various gestures are achieved by the dexterous robotic hand through controlling the kinestate of the actuators. Electromyography (EMG) was used to control the bionic hand.

Design and analysis of a two-DOF coupling motion robotic joint

In this paper, a robotic joint with a two-DOF coupling motion is proposed for higher payload ability, power density and speed. With these advantages the joint is ideal for use in robots, especially multi-DOF manipulators. The entire robot manipulator composed of these joints is not involved in this paper. It will be reported in detail in a future publication. Here we just focus on the robotic joint. This robotic joint which is configured as a series-parallel hybrid structure can be called as angular swivel joint. And the joint can move on a spherical surface whose apex angle is 100° by the coupling motions of two independent motor-reducer drive systems. Details of the mechanism design, kinematics analysis and differential kinematics will be depicted. In addition, all motions of the joint can be divided into two modes: mode 1 is that the two motor-reducer systems work in the same speed and with the opposite direction (SSOD); and mode 2 is that the two motor-reducer drive systems work in the same speed and with the same direction (SSSD). Moreover, a unique control strategy based on these two basic motion modes are presented. Finally, simulations and experiments are implemented to verify the feasibility and performance of the joint.

Locomotion of an actinomorphic soft robot with soft composite structures

In this article, we present an actinomorphic soft robot with soft composite structures actuated by Shape Memory Alloy (SMA) wires. The composite structures act as arm function in the robot and incorporate soft materials, elastic plate and SMA wires. We analyze the relationship of frequency response of structures with the heating voltage and distance between PVC board and SMA wires. Based on resistance feedback of SMA wires, an adulation heating (AH) strategy was applied in composite structures. The strategy can adjust amplitude response of reciprocal motion of structures. Two kinds of rhythmic gaits were proposed for realizing the locomotion of the robot in different circumstances, e.g. circular undulation gait and horizontal undulation gait. The robot applied a hierarchical control system including a integral control layer to plan robot locomotion and several sub-control layers to control arm state. The maximum locomotion speed of the soft robot on flat ground was able to reach 140 mm/s in the air.