Biological musculoskeletal system (MSK), composed of numerous bones, cartilages, skeletal muscles, tendons, ligaments etc., provides form, support, movement and stability for human or animal body. As the result of million years of selection and evolution, the biological MSK evolves to be a nearly perfect mechanical mechanism to support and transport the human or animal body, and would provide enormously rich resources to inspire engineers to innovate new technology and methodology to develop robots and mechanisms as effective and economical as the biological systems. This paper provides a general review of the current status of musculoskeletal biomechanics studies using both experimental and computational methods. This includes the use of the latest three-dimensional motion analysis systems, various medical imaging modalities, and also the advanced rigid-body and continuum mechanics musculoskeletal modelling techniques. Afterwards, several representative biomimetic studies based on ideas and concepts inspired from the structures and biomechanical functions of the biological MSK are dis-cussed. Finally, the major challenges and also the future research directions in musculoskeletal biomechanics and its biomimetic studies are proposed.

This paper reports the design methodology and control strategy in the development of a novel hexapod robot HITCR-II that is suitable for walking on unstructured terrain. First, the entire sensor system is designed to equip the robot with the perception of external environment and its internal states. The structure parameters are optimized for improving the dexterity of the robot. Second, a foot-force distribution model and a compensation model are built to achieve posture control. The two models are capable of effectively improving the stability of hexapod walking on unstructured terrain. Finally, the Posture Control strategy based on Force Distribution and Compensation (PCFDC) is applied to the HITCR-II hexapod robot. The experimental results show that the robot can effectively restrain the vibration of trunk and keep stable while walking and crossing over the un-structured terrains.

Legged robots have better performance on discontinuous terrain than that of wheeled robots. However, the dynamic trotting and balance control of a quadruped robot is still a challenging problem, especially when the robot has multi-joint legs. This paper presents a three-dimensional model of a quadruped robot which has 6 Degrees of Freedom (DOF) on torso and 5 DOF on each leg. On the basis of the Spring-Loaded Inverted Pendulum (SLIP) model, body control algorithm is discussed in the first place to figure out how legs work in 3D trotting. Then, motivated by the principle of joint function separation and introducing certain biological characteristics, two joint coordination approaches are developed to produce the trot and provide balance. The robot reaches the highest speed of 2.0 m•s−1, and keeps balance under 250 Kg•m•s−1 lateral disturbance in the simulations. The effectiveness of these approaches is also verified on a prototype robot which runs to 0.83 m•s−1 on the treadmill. The simulations and experiments show that legged robots have good biological properties, such as the ground reaction force, and spring-like leg behavior.

We make a thorough kinematic comparison of forward and backward swimming and maneuvering on a self-propelled robot platform that uses sub-carangiform swimming as the primary propulsor. An improved Central Pattern Generator (CPG) model allowing free adjustment of phase relationship and directional bias is employed to achieve flexible swimming and smooth transition. Considering the characteristics of forward swimming in carangiform fish and backward swimming in anguilliform fish, various backward swimming patterns for the sub-carangiform robotic fish are suitably created by reversing the direction of propagating propulsive waves. Through a combined use of the CPG control and closed-loop swimming direction control strategy, flexible and precise turning maneuvers in both forward and backward swimming are implemented and compared. By contrast with forward swimming, backward swimming requires a higher frequency or an increased lateral displacement to reach the same relative swimming speed. Noticeably, the phase difference shows a greater impact on forward swimming than on backward swimming. Our observations also indicate that the robotic fish achieves a larger turning rate in forward maneuvering than in backward maneuvering, yet these two maneuvers display comparable turning precision.

An experiment-based approach is proposed to improve the performance of biomimetic undulatory locomotion through on-line optimization. The approach is implemented through two steps: (1) the generation of coordinated swimming gaits by artificial Central Pattern Generators (CPGs); (2) an on-line searching of optimal parameter sets for the CPG model using Genetic Algorithm (GA). The effectiveness of the approach is demonstrated in the optimization of swimming speed and energy effi-ciency for a biomimetic fin propulsor. To evaluate how well the input energy is converted into the kinetic energy of the pro-pulsor, an energy-efficiency index is presented and utilized as a feedback to regulate the on-line searching with a closed-loop swimming control. Experiments were conducted on propulsor prototypes with different fin segments and the optimal swimming patterns were found separately. Comparisons of results show that the optimal curvature of undulatory propulsor, which might have different shapes depending on the actual prototype design and control scheme. It is also found that the propulsor with six fin segments, is preferable because of higher speed and lower energy efficiency.

In this study, we present a complete structural analysis of Allomyrina dichotoma beetle’s hind wings by investigating their static and dynamic characteristics. The wing was subjected to the static loading to determine its overall flexural stiffness. Dy-namic characteristics such as natural frequency, mode shape, and damping ratio of vibration modes in the operating frequency range were determined using a Bruel & Kjaer fast Fourier transform analyzer along with a laser sensor. The static and dynamic characteristics of natural Allomyrina dichotoma beetle’s hind wings were compared to those of a fabricated artificial wing. The results indicate that natural frequencies of the natural wing were significantly correlated to the wing surface area density that was defined as the wing mass divided by the hind wing surface area. Moreover, the bending behaviors of the natural wing and artificial wing were similar to that of a cantilever beam. Furthermore, the flexural stiffness of the artificial wing was a little higher than that of the natural one whereas the natural frequency of the natural wing was close to that of the artificial wing. These results provide important information for the biomimetic design of insect-scale artificial wings, with which highly ma-neuverable and efficient micro air vehicles can be designed.

Despite the recent influx of increasingly dexterous prostheses, there remains a lack of sufficiently intuitive control methods to fully utilize this dexterity. As a solution to this problem, a control framework is proposed which allows the control of an arbitrary number of Degrees of Freedom (DOF) through a single electromyogram (EMG) control input. Initially, the joint motions of nine test subjects were recorded while grasping and catching a cylinder. Inherent differences emerged depending upon whether the cylinder was grasped or caught. These data were used to form a distinct synergy for each task, described as the families of parametric functions of time that share a mutual time vector. These two Temporally Synchronized Synergies (TSS) were derived to reflect the task dependent control strategies adopted by the initial participants. These synergies were then mapped to a dexterous artificial hand that was subsequently controlled by two subjects with transradial amputations. The EMG signals from these subjects were used to replace the time vector shared by the synergies, enabling the subjects to perform both tasks with a dexterous artificial hand using only a single EMG input. After a ten minute training period, the subjects learned to use the dexterous artificial hand to grasp and catch the cylinder with 100.0% and 65.0% average success rates, respectively.

A lower extremity exoskeleton, SJTU-EX, is proposed, which mainly aims to help soldiers and workers to support a payload in motions. To solve the issues of the exoskeleton-environment and exoskeleton-human interactions, four types of foot contact are proposed based on their different kinematic characteristics. By the combination of single leg states, sixteen exo-skeleton states are presented using a series of meaningful notations from the topological point of view. The generalized function set (GF set) theory is employed to achieve the kinematic characteristics of the end effectors in different states. Moreover six mathematical formulations of the dynamics of the exoskeleton and its interactions with the human wearer are developed for different exoskeleton states. The applicability and potential of the proposed classification method are demonstrated by analyzing common lower limb motions, which are described concisely by a sequence of notations. Finally, a new concept of characteristic state is put forward to uniquely indicate the type of motion.

While total knee replacement is successful, hemiarthroplasty is necessary for some young, obese and active patients who are especially not suitable for unicompartmental or total knee prostheses. Hemiarthroplasty also provides an opportunity for children with bone tumors. The design of hemiarthroplasty should be patient-specific to reduce contact stress and friction as well as instability, compared to conventional hemi-knee prosthesis. A novel bipolar hemi-knee prosthesis with two flexion stages was developed according to a healthy male’s knee morphological profile. The motion mode of the bipolar hemi-knee prosthesis was observed through roentgenoscopy in vitro experiment. The biomechanical properties in one gait cycle were evaluated though finite element simulation. The bipolar hemi-knee prosthesis was found to produce knee flexion at two stages through X-ray images. The first stage is the motion from upright posture to a specified 60? flexion, followed by the second stage of motion subsequently to deep flexion. The finite element simulation results also show that the designed hemi-knee prosthesis has the ability to reduce stresses on the joint contact surfaces. Therefore, it is possible for the bipolar hemi-knee prosthesis to provide better biotribological performances because it can reduce stresses and potentially wear on the opposing contacting surface during a gait cycle, providing a promising treatment strategy in future joint repair and replacement.

The silk moth (Bombyx mori) exhibits efficient Chemical Plume Tracing (CPT), which is ideal for biomimetics. However, there is insufficient quantitative understanding of its CPT behavior. We propose a hierarchical classification method to segment its natural CPT locomotion and to build its inverse model for detecting stimulus input. This provides the basis for quantitative analysis. The Gaussian mixture model with expectation–maximization algorithm is used first for unsupervised classification to decompose CPT locomotion data into Gaussian density components that represent a set of quantified elemental motions. A heuristic behavioral rule is used to categorize these components to eliminate components that are descriptive of the same motion. Then, the echo state network is used for supervised classification to evaluate segmented elemental motions and to compare CPT locomotion among different moths. In this case, categorized elemental motions are used as the training data to estimate stimulus time. We successfully built the inverse CPT behavioral model of the silk moth to detect stimulus input with good accuracy. The quantitative analysis indicates that silk moths exhibit behavioral singularity and time dependency in their CPT locomotion, which is dominated by its singularity.

The mechanical properties of the skull and the anti-shock characteristics of woodpecker’s head were investigated by ex-periment and numerical simulation. We measured the micro-Young’s modulus of the skull by nano-indentation method and calculated the macro-equivalent Young’s modulus of the skull at different positions using homogenization theory. Based on the Computerized Tomography (CT) images of woodpecker head, we then built complete and symmetric finite element models of woodpecker’s skull and its internal structure and performed modal analysis and stress spectrum analysis. The numerical results show that the application of pre-tension force to the hyoid bone can increase the natural frequency of woodpecker’s head. The first natural frequency under the pre-tension force of 25 N reaches 57 Hz, which is increased by 21.3% from the non-pre-tension state and is more than twice the working frequency of woodpecker (20 Hz – 25 Hz). On the application of impact force to the tip of beak for 0.6 ms, high magnitudes of stress component occur at around 100 Hz and 8,000 Hz, far away from both the working frequencies and the natural frequencies of woodpecker head. The large gaps among the natural, working and stress response frequencies enable the woodpecker to effectively protect its brain from the resonance injury.

Thermal fatigue and wear both seriously affect the service life of some working parts. Environmental temperature will modify the surface conditions and influences the result of wear. In this research, to come close to working conditions, specimens were tested by a combination of thermal cycles and wear. Different cycles of thermal fatigue was carried out first on the gray iron specimens and subsequently wear test was performed to evaluate the effect of these thermal fatigue cycles. In this case, bionic laser processing was used to enhance the wear performance. The results indicated that bionic laser processing reduces the negative effects from thermal fatigue, such as grain fragmentation and oxidation. Because the initiation and growth of cracks as well as oxidation are suppressed in bionic processed areas. Bionic specimens exhibit high wear resistance compared with the common one. The process described can be considered as an effective method to improve the performance of gray iron in combined thermal fatigue and wear service conditions.

This paper aims to characterize the hydrophobic property of shark-skin-inspired riblets with potential engineering appli-cations. Based on the hydrophobic theory, a new hydrophobic model which is consistent with the special structure of shark-skin-inspired micro-riblets was proposed. Then, the contact angles of different droplets were measured by optical contact angle measuring device on the shark-skin-inspired micro-riblets and the smooth surface, respectively. The results show that the surface of micro-riblets possesses obvious hydrophobicity, and the actual contact angles of different droplets residing on the riblets decrease with the increase in the droplet volume. According to the new hydrophobic model and the measurement of contact angle, it was found that the arrangement and structure of the shark-skin-inspired micro-riblets significantly affect the surface hydrophobic property. Using the new hydrophobic model, the prediction error of contact angle can be less than 3% compared with the measured one. The research on hydrophobic property of biomimetic micro-riblets is proved to be necessary and important to well explain drag reduction and microbe-resistant property of micro-riblets.

In this study, CoCrMo alloy was oxidized in plasma environment at the temperatures of 600 ?C to 800 ?C for 1 h to 5 h with 100% O2 gas and its tribological behavior was investigated. After the plasma oxidizing process, the compound and diffusion layers were formed on the surface. XRD results show that Cr2O3, α-Co and ε-Co phases diffracted from the modified layers after plasma oxidizing. The untreated and treated CoCrMo samples were subjected to wear tests both in dry and simulated body fluid conditions, and normal loads of 2 N and 10 N were used. For the sliding wear test, alumina balls were used as counter materials. It was observed that the wear resistance of CoCrMo alloy was increased after the plasma oxidizing process. The lowest wear rate was obtained from the samples that were oxidized at 800 ?C for 5 h. It was detected that both wear environment and load have significant effects on the wear behavior of this alloy, and the wear resistance of oxidized CoCrMo alloy is higher when oxide-based counterface is used. The wear rates of both untreated and plasma oxidized samples increase under high loads.

This paper presents a biologically inspired local image descriptor that combines color and shape features. Compared with previous descriptors, red-cyan cells associated with L, M, and S cones (L for long, M for medium, and S for short) are used to indicate one of the opponent color channels. Stepping forward from state-of-the-art color feature extraction, we exploit a new approach to compute the color orientation and magnitudes of three opponent color channels, namely, red-green, blue-yellow, and red-cyan, in two-dimensional space. Color orientation is calculated in histograms with magnitude weighting. We linearly concatenate the four-color-opponent-channel histogram and scale-invariant-feature-transform histogram in the final step. We apply our biologically inspired descriptor to describe the local image feature. Quantitative comparisons with state-of-the-art descriptors demonstrate the significant advantages of maintaining invariance to photometric and geometric changes in image matching, particularly in cases, such as illumination variation and image blurring, where more color contrast information is observed.