A.k Dutta Anatomy Pdf Lower Limb

[Virgil Gardiner]

Anexoskeleton is a rigid external covering for the body in certain animals, such as the hard chitinous cuticle of arthropods, derived from biology. An exoskeleton protects and supports the body and provides points of attachment for muscles [1], in contrast to the endoskeleton, which is completely located in the animal body. Human beings are endoskeleton animals and do not have the functions of exoskeletons. Due to the increasing demand for self-protection, support, strength and rehabilitation, people have been developing exoskeletons, generally referring to wearable devices that can support, protect and enhance specific human abilities. The connotation has been rich in the development process of things, the armor of ancient soldiers and the Extra Vehicular Activity (EVA) suits of modern astronauts can be regarded as an exoskeleton, as can prosthetics, which are used to recover structural damage to the human skeletal system.

A lower limb robot exoskeleton system is reviewed. Specifically, first, its assisting human lower limbs, excluding upper limbs; second, it has at least one active joint, excluding unpowered passive exoskeletons; and third, its being dependent on the human limbs, excluding the assisting Supernumerary Robotic Limb.

This review is organized as follows: Sect. 1 presents the definition of LEEX. Section 2 presents the development of LEEX from the perspective of the Industrial Revolution. Section 3 presents typical prototypes and products in classification of LEEX from four special angles. Afterwards, Sects. 4 and 5 present the key technologies and existing problems involved in the practical application of LEEX. Finally, Sect. 6 submits future research hotspots.

Human LEEX exploration has nearly 200 years of history since the concept originated. According to the Industrial Revolution development order, relevant research can be divided into five stages, the embryonic stage (after the Industrial Revolution), exploration stage (after the Second Industrial Revolution), reserve stage (after the Third Industrial Revolution), development stage (enter the Fourth Industrial Revolution) and present stage (research hotspots), as shown in Fig. 1.

With the germination of the Fourth Industrial Revolution (the Era of Industry 4.0 Intelligence in the early twenty-first century), UC Berkeley accepted an investment of $50 million from the Defense Advanced Research Projects Agency (DARPA) in 2000 and developed the "Berkeley lower extreme exoskeleton", BLEEX (2004) [27,28,29,30,31,32]. It focused on improving the wearer's load, shifting the design focus to the support structure between the waist and legs, allowing the US army to easily carry a load of 90 kg. When the BLEEX is underpowered, the wearer can remove it from the leg and fold it into a normalized backpack for easy storage and transportation. HULC (2009) was applied in military layout in the United States, marking the rapid development and application of LEEX technology [33]. The Guardian XO exoskeleton, which takes only one minute to put on and take off, released by Sarcos Robotics in 2020 can allow the wearer to carry 90 kg of weight for a long time [34], and the muscle activity curve is highly similar to that of normal walking [35], indicating good following performance. Meanwhile, advanced countries around the world are developing exoskeletons for a variety of applications. Examples include HAL-5 from Japan (2005) [36], REX from New Zealand (2008) [37], ReWalk from Israel (2010) [38], ExoAtlet from Russia (2016) [39], and Atalante from France (2018) [40]. In addition, China's AiWalk from Ai-robotics Technology [41] (2016), HIT-LEX from Harbin Institute of Technology (HIT) (2016) [42], UGO from Hangzhou RoboCT Technology (2018) [43], and ExoMotus from Fourier Intelligence (2019) [44] are also developing rapidly. Overall, the accumulation of information technology has contributed to the development of robot intelligence. New breakthroughs in LEEX control strategies continue to emerge, such as Sensitivity Amplification Control (SAC) used in BLEEX, force control method based on myoelectric signals used in HAL-5, and position control method based on interactive force detection used in HIT-LEX. Compared to the twentieth century, LEEX is vastly more reliable, more versatile and less costly.

Human lower limbs are composed of many joints, and not all joints need assistance. Sometimes only one or several joints need to be assisted, such as to enhance human walking endurance or assist patients with hemiplegia or knee joint damage. Sometimes complete assistance is needed, such as patients with complete paralysis of the lower limbs. Therefore, LEEX can be divided into a single-joint type and a multi-joint type for different parts.

Yan et al. [50] mentioned that a single-joint type can be divided into three groups, namely, hip, knee and ankle, which are used for specific individual parts. The functions of these joints are completely different [51]. During steady state walking, the knee joint is almost undamped in the swing stage but almost locked in the standing support stage [52]. The hip and ankle joints are related to the dynamic process of the swinging leg in the swinging stage, the propulsion of the supporting leg in the stepping off stage, and the braking of the body during landing, but research in recent years also shows that they are interdependent [53,54,55,56,57]. Some examples of single-joint exoskeletons are shown in Fig. 2. The Honda Walking Assist is a hip robotic exoskeleton [58] designed by Honda for gait training after a stroke. It consists of two motors located at the hip and transmits torque to the user's thigh through two strap frames. Angle and current sensors are used for gait stage detection, through which an application parameterizes the inspection results and provides the corresponding torque [59]. The MAK (Marsi Active Knee) is a knee robot exoskeleton developed by Marsi Bionics [60]. It is not only suitable for hemiplegia patients with the knee joint as the main pathogenesis site but also for rehabilitation after total knee replacement. Active auxiliary control and zero-force control are carried out through a human motion force sensor, pressure detection sensing insole and knee angle sensor, and monitoring data are uploaded to an application for analysis [61]. The Autonomous Leg is an ankle-assisted exoskeleton designed by the Herr team [62] of the MIT media lab that is used to enhance human walking ability. The system fixes a glass fiberglass rod with the front of the shoe and pulls a rope through an actuator on the lower leg to provide plantar flexion assistance to the ankle, reducing the metabolic cost of walking on horizontal ground [63].

According to the structural form, lower extremity robotic exoskeletons can be classified into Rigid Lower Extremity Robotic Exoskeletons (RLEEX) and Compliant Lower Extremity Robotic Exoskeletons (CLEEX).

An RLEEX structure is composed of many rigid connecting rods, and the drive has a large servo stiffness, such as hydraulics or a motor. It provides the disabled with the ability to walk again. In RLEEX research, the United States has been the most active. In the twentieth century, relevant technologies have been studied in depth, and mature products have been developed in various fields. For example, the BLEEX of the UC Berkeley, the HULC of Lockheed Martin [33], the Guardian XO of Sarcos Robotics [35], and the United States have become leaders in the development of exoskeletons. Successively, Asian and European countries have carried out many studies on rigid lower limb assisted exoskeletons, such as the HAL [70] of the University of Tsukuba in Japan and the MINDWALKER [71] of the Delft University of Technology in the Netherlands.

Lockheed Martin launched the Human Universal Load Carrier (HULC) [72, 73] based on the BLEEX results and aimed at the BLEEX exoskeleton's shortcomings, such as a complex structure and short endurance, and conducted a series of wearable tests with the US Army. See Fig. 4a. The design of the HULC takes fully into account the unsymmetrical driving torque of people in the process of heavy walking, optimizes the driving mode and control method, and achieves an endurance of 20 km distance with a heavy load. Moreover, supports can be added on the back to expand the function of carrying equipment. Although the HULC was tested by the US Army, it was never fielded. In addition, the project was a failure as it hindered certain movements and actually increased strain on muscles, going directly against what a powered exoskeleton is supposed to do [74].

To realize the center of gravity transfer, the Delft University of Technology in the Netherlands added an active drive to the hip joint swing/adduction degree of freedom and developed the MINDWALKER exoskeleton robot [83], as shown in Fig. 4c. In addition, an elastic drive structure was connected in series at the end of each actuator (Series Elastic Actuator, SEA) to improve the control performance of the exoskeleton. However, the issues related to the control of stiffness in springs present a limitation. The MINDWALKER weighs 28 kg and can adapt to wearers between 153 and 188 cm in height and less than 100 kg in weight. The target maximum walking speed is 0.8 m/s. MINDWALKER is characterized by use of EEG signal sensors to measure brain activity and pioneered EEG-based position control. However, the decoding of EEG is still in its infancy. The classification accuracy of human intentions by EEG is not high. And there is a great delay, which cannot be applied in scenarios requiring high real-time performance.

Research on RLEEX in China started relatively late and can be traced back to the paraplegic walking machine of Tsinghua University [22,23,24]. There were sporadic achievements in the early twenty-first century, mainly concentrated in universities and research institutes.

In 2007, the University of Science and Technology of China (USTC) and the Hefei Institute of Intelligent Machines (IIM) of the Chinese Academy of Sciences (CAS) began to research technologies related to exoskeleton robots. The resulting Walking Power Assist Leg (WPAL) [84,85,86] is shown in Fig. 5a. According to the requirements of walking function, a total of four active degrees of freedom were set up in the hip joint and the knee joint, while only one rotational degree of freedom was set up in the ankle joint to obtain sole pressure change information in the process of gravity transfer more effectively. In terms of interaction mode, the WPAL takes the interaction force between the wearer and the exoskeleton as the basis to judge the wearer's intention and uses two-dimensional force sensors to measure it directly. An encoder at the joint measures the joint state of the exoskeleton and forms a closed-loop feedback control with the controller. In the weight-bearing walking control strategy, the WPAL estimates the load weight through a plantar pressure sensor to adjust the controller parameters to improve the assistance efficiency of the WPAL.

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