Abstract—Active upper-limb exoskeleton robots have been developing from 1960s. In recent years, the mechanical designs and control algorithms of active upper-limb exoskeleton robots were developed significantly. This paper reviews the state-of-the-art of active upper-limb exoskeleton robots that are applied in the areas of rehabilitation and assistive robotics. In addition, the main requirements of the active upper-limb exoskeleton robot are identified and the mechanical designs of existing active upper-limb exoskeleton robot are classified. The design difficulties of an active upper-limb exoskeleton robot are discussed. I. INTRODUCTION HE exoskeleton robots have been considered in the industry, military and medical applications. In recent years, they have been applied in the areas of rehabilitation and power assist for daily activities. The use of exoskeleton robots is increasing in the areas of rehabilitation and power assist in the society in which the number of physically weak (aged, injured and/or handicapped) individuals are increasing. Active exoskeleton robots were studied for the purposes of industry or medical applications in the 1960s and 1970s [1]-[5]. In addition, some exoskeleton robots were proposed to extend the strength of the human force [6], [7] in early 1990s. In recent years, many active upper-limb exoskeleton robot systems [13]-[58] have been proposed for rehabilitation and power assist. The identification and clarification of the requirements, design challenges and the state-of the-art of an active upper-limb exoskeleton robot is very important to provide solutions for the design difficulties. Therefore, this paper reviews literatures of active upper-limb exoskeleton robots to identify and clarify the requirements, design difficulties and the state-of the-art of active upper-limb exoskeleton robots that are applied in the areas of rehabilitation and assistive robotics. Several researchers [59]-[61] have carried out reviews of exoskeleton robots. However, almost all of their reviews are general review of all types of exoskeleton robots and they have not specially concentrated on the mechanical designs of active upper-limb exoskeleton robot. They rarely reviewed about the Manuscript received January 23, 2009. R. A. R. C. Gopura is a doctoral student of the Dept. of Advanced Systems Control Engineering, Saga University, 1 Honjomachi, Saga 840-8502, Japan (e-mail: gopura@ieee.org). K. Kiguchi is with the Dept. of Advanced Systems Control Engineering, Saga University, 1 Honjomachi, Saga 840-8502, Japan (phone: +81-952-28-8702; fax: +81-952-28-8587; e-mail: kiguchi@ieee.org). mechanical designs of active upper-limb exoskeleton robots. Therefore, the state-of-the-art, requirements and design difficulties specific to the active upper-limb exoskeleton robots are addressed in this review. In this paper, the upper-limb anatomy toward the development of a proper active upper-limb exoskeleton robot is explained in Section II. The requirements of an active upper-limb exoskeleton robot are discussed in Section III. In Section IV, the design difficulties of developing a proper upper-limb exoskeleton robot are briefly discussed. The performance evaluation methods of mechanical designs of active upper-limb exoskeleton robots are highlighted in Section V. Recently developed important mechanical designs of active upper-limb exoskeleton robots are evaluated after classifying them in Section VI. Final section presents conclusion and areas that should be addressed for future research in the mechanical designs of active upper-limb exoskeleton robots. II. UPPER-LIMB ANATOMY TOWARDS DEVELOPMENT OF AN UPPER-LIMB EXOSKELETON ROBOT As shown in Fig. 1(a), the human upper-limb mainly consists of shoulder complex, elbow complex and wrist joint. In addition, fingers have several joints. Shoulder complex shown in Fig. 1(b) consists of three bones: the clavicle, scapula and humerus, and four articulations: the glenohumeral, acromioclavicular, sternoclavicular and scapulothoracic, with the thorax as a stable base [8], [9]. The glenohumeral joint is commonly referred as shoulder joint. The sternoclavicular joint is the only joint that connects the shoulder complex to the axial skeleton. The acromioclavicular joint is formed by the lateral end of the clavicle and the acromion of the scapula. The sternoclavicular joint is a compound joint which has two compartments separated by articular disks. It is formed by the parts of clavicle, sternum, and cartilage of the first rib. In true sense, the scapulothoracic joint can not be considered as a joint as it is a bone-muscle-bone articulation which is not synovial. It is formed by the female surface of the scapula and the male surface of the thorax. However, it is considered as a joint when describing motion of the scapular over the thorax [8]. Basically, shoulder complex can be modeled as a ball-and-socket joint. It is formed by the proximal part of the humerus (humeral head) and the female part of the scapula (glenoid cavity). However, position of the center of rotation of shoulder joint is changing with the upper-arm motions. The main motions of the shoulder complex which are provided by the glenohumeral joint of shoulder complex are shoulder Mechanical Designs of Active Upper-Limb Exoskeleton Robots State-of-the-Art and Design Difficulties R. A. R. C. Gopura, Student Member, IEEE, Kazuo Kiguchi, Member, IEEE T 2009 IEEE 11th International Conference on Rehabilitation Robotics Kyoto International Conference Center, Japan, June 23-26, 2009 9781-4244-3789-4/09/$25.00 ©2009 IEEE 178