Lianjun Wu

Nylon-muscle-actuated robotic finger

This paper describes the design and experimental analysis of novel artificial muscles, made of twisted and coiled nylon fibers, for powering a biomimetic robotic hand. The design is based on circulating hot and cold water to actuate the artificial muscles and obtain fast finger movements. The actuation system consists of a spring and a coiled muscle within a compliant silicone tube. The silicone tube provides a watertight, expansible compartment within which the coiled muscle contracts when heated and expands when cooled. The fabrication and characterization of the actuating system are discussed in detail. The performance of the coiled muscle fiber in embedded conditions and the related characteristics of the actuated robotic finger are described.

HBS-1: A Modular Child-Size 3D Printed Humanoid

An affordable, highly articulated, child-size humanoid robot could potentially be used for various purposes, widening the design space of humanoids for further study. Several findings indicated that normal children and children with autism interact well with humanoids. This paper presents a child-sized humanoid robot (HBS-1) intended primarily for children’s education and rehabilitation. The design approach is based on the design for manufacturing (DFM) and the design for assembly (DFA) philosophies to realize the robot fully using additive manufacturing. Most parts of the robot are fabricated with acrylonitrile butadiene styrene (ABS) using rapid prototyping technology. Servomotors and shape memory alloy actuators are used as actuating mechanisms. The mechanical design, analysis and characterization of the robot are presented in both theoretical and experimental frameworks.

A deformable robot with tensegrity structure using nylon artificial muscle

This paper describes the design and experimental investigation of a self-reconfigurable icosahedral robot for locomotion. The robot consists of novel and modular tensegrity structures, which can potentially maneuver in unstructured environments while carrying a payload. Twisted and Coiled Polymer (TCP) muscles were utilized to actuate the tensegrity structure as needed. The tensegrity system has rigid struts and flexible TCP muscles that allow keeping a payload in the central region. The TCP muscles provide large actuation stroke, high mechanical power per fiber mass and can undergo millions of highly reversible cycles. The muscles are electrothermally driven, and, upon stimulus, the heated muscles reconfigure the shape of the tensegrity structure. Here, we present preliminary experimental results that determine the rolling motion of the structure.

Compact and low-cost humanoid hand powered by nylon artificial muscles

This paper focuses on design, fabrication and characterization of a biomimetic, compact, low-cost and lightweight 3D printed humanoid hand (TCP Hand) that is actuated by twisted and coiled polymeric (TCP) artificial muscles. The TCP muscles were recently introduced and provided unprecedented strain, mechanical work, and lifecycle (Haines et al 2014 Science 343 868-72). The five-fingered humanoid hand is under-actuated and has 16 degrees of freedom (DOF) in total (15 for fingers and 1 at the palm). In the under-actuated hand designs, a single actuator provides coupled motions at the phalanges of each finger. Two different designs are presented along with the essential elements consisting of actuators, springs, tendons and guide systems. Experiments were conducted to investigate the performance of the TCP muscles in response to the power input (power magnitude, type of wave form such as pulsed or square wave, and pulse duration) and the resulting actuation stroke and force generation. A kinematic model of the flexor tendons was developed to simulate the flexion motion and compare with experimental results. For fast finger movements, short high-power pulses were employed. Finally, we demonstrated the grasping of various objects using the humanoid TCP hand showing an array of functions similar to a natural hand.

System Identification of Force of a Silver Coated Twisted and Coiled Polymer Muscle

The demand of using artificial muscle similar to the human muscle is significantly increased during past decades. Recently, silver coated Twisted and Coiled Polymer (TCP) muscle was reported and used in many research projects. A first order differential equations (1st ODE) was used to predict the force of this muscle. assuming that the TCP muscle acts similar to a mechanical spring that has variable stiffness depending on the electrical power supplied. Thus, extensive study should be performed on different types of TCP muscles to reach to a conclusion. In this paper, a black box system identification method is used to examine the behavior of TCP muscles under different input conditions. Different order differential equations are compared with experimental results. In this way, prediction error method (PEM) is used to estimate the force of silver coated TCP muscle with several linear time invariant (LTI) discrete time state space system. In addition, we suggest a fast method (rule of thumb) to model a TCP muscle. Moreover, two key parameters have been introduced to compare the quality of the TCP muscle from force perspective.

Humanoid robot hand with SMA actuators and servo motors

This paper describes the design of a child humanoid robot hand with SMA actuators and servo motors. Human hands can grasp and manipulate complicated objects relying on its flexible structure and real-time control. However, it is difficult to replicate an exact human hand using rigid structures because of intricate biomechanical structure. In human hand, one metacarpal and three phalanges make up each finger, except for the thumb which only has two phalanges. Each finger except the thumb is composed of 3 joints: the metacarpophalangeal (MCP), the proximal interphalangeal (PIP) and distal interphalangeal joints (DIP). The DIP and PIP joints are always moving simultaneously, while the MCP joint can move independently. The child-sized robot hand is developed which replicates a seven year-old child’s hand in its fundamental structure. The robot hand has five fingers and all the fingers consist of 3 links. Servo motors and shape memory alloy actuators were used as a drive mechanism for the fingers and mathematical model of the SMA actuators are described to study the finger dynamics. A prototype humanoid robot hand was fabricated using 3D printing techniques and experimental results are presented.Copyright

Biorobotic systems design and development using TCP muscles

Actuators are the most important elements that affect the performance of biorobotic systems design and development. One of the objectives of this project is to design stronger, lighter, 3D printable, functionally graded bone-like structures and bio-inspired musculoskeletal system for the articulation of robots. Another objective is to identify the fundamental science of manufacturing and modeling of the muscle systems. A modular building block is presented consisting of bone-like structures, cartilages and artificial muscles (that are inexpensive and powerful), which can be cascaded to create complex robots. In this paper, we present terrestrial robots as a demonstration of the building blocks for biorobotic systems. We particularly illustrate a humanoid robot developed using soft actuators based on twisted and coiled polymer (TCP) muscles. The integration of TCPs in biorobotic systems has some challenges to overcome such as initial pre-stress, adding multiple actuators in parallel or in antagonistic pair and speed of actuation and other accessories. We will quantify the performance of these robots experimentally. We presented two TCP muscles types, one without heating element and the other one that incorporates a heating element that allows electrical actuation.

Musculoskeletal system for bio-inspired robotic systems based on ball and socket joints

Musculoskeletal system is the fundamental structure that allows complex mobility of biological systems. A lot of efforts have been made in the past to mimic this structure using synthetic materials for use in robotic systems. Development challenges for this technology include design and manufacturing, system integration, control methods and energy usage. One of the key elements of musculoskeletal system is artificial muscles or actuators used in this system. Actuators presented in the literature do not match the performance of natural muscles in most of the metrics such as force generation, strain output, frequency, power density, ease of control and repeatability. This paper briefly describes the recently introduced Twisted and Coiled Polymer (TCP) muscles integrated into a ball and socket joint made of ABS plus® material. The proposed structure consists of a class of ball-and-socket joint that incorporates TCP muscles and silicone to generate multidimensional actuation. Most traditional joint-and-actuator assemblies include passive rotary joints actuated by servomotors via gears transmission. Our proposed ABS based 3D printed joint is actuated by artificial muscles without any complex mechanical transmission system. In comparison with other such assemblies, the proposed joint system is a promising solution to the diverse applications in robotics, especially where soft actuators and cost effective solutions are needed.Copyright

Artificial heart for humanoid robot

A soft robotic device inspired by the pumping action of a biological heart is presented in this study. Developing artificial heart to a humanoid robot enables us to make a better biomedical device for ultimate use in humans. As technology continues to become more advanced, the methods in which we implement high performance and biomimetic artificial organs is getting nearer each day. In this paper, we present the design and development of a soft artificial heart that can be used in a humanoid robot and simulate the functions of a human heart using shape memory alloy technology. The robotic heart is designed to pump a blood-like fluid to parts of the robot such as the face to simulate someone blushing or when someone is angry by the use of elastomeric substrates and certain features for the transport of fluids.