İnsansı robotlar için modüler yapay omurga tasarımı

Abstract

Yirminci yüzyılın son çeyreğinde insana benzeyen ve insan gibi hareket edebilen robotlar geliştirilmeye başlanmıştır. Gelecekte insansı robotların sanayi ve servis sektörlerinde, okul öncesi ve özel durumları bulunan çocukların eğitiminde ve birçok başka alanda toplum hayatına gireceği çeşitli araştırmacılar tarafından savunulmaktadır. İnsansı robotlar en basit hali le yürüme için iki bacak ve iş yapma için iki kol kullanan mekanik yapılardır. Yürüme ve iş yapma işlevleri geleneksel olarak açık seri kinematik zincirler kullanılarak gerçekleştirilmiştir. Seri açık kinematik zincirlerin ileri ve ters kinematik çözümlemelerinin kolay elde edilebilmesi kontrol uygulamalarında sıklıkla kullanılmasına yol açmıştır. İnsansı robotlarda kullanılan mekanik tasarımlar bu sebep ile seri açık kinematik zincirlerin bir araya getirilmesi ile ortaya çıkmıştır. Ancak, çok serbestlik dereceli insansı robotlarda yukarıda bahsedilen geleneksel mekanik çözümler, robot hareketlerinin süreksiz ve insansı olmayan bir biçimde eylemlenmesine sebep olmaktadır. Bu çalışmada, sürekli ve insansı hareketler elde edebilmek için uzuvların hatta gövdenin birbirine göre bağıl hareket edebilen modüler yapılardan oluşması gerektiği öngörülmektedir. İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, Makina Mühendisliği Ana Bilim Dalı, Sistem Dinamiği ve Kontrol Programında Yüksek Lisans tezi olarak hazırlanan bu çalışmada insansı bir robotta kullanılmak üzere modüler yapay bir omurga geliştirilmiştir. Amaç sürekli ve insansı bir hareketi mümkün olan en az sayıda motorla elde etmektir. Tez kapsamında dört adet gövde tasarımı yapılmıştır. İlk üç tasarımın iyileştirilmesi ile elde edilen nihai tasarımın istenilen hareket işlevlerini yerine getirdiği gözlemlenmiştir. Geliştirilen Omurga birbirine modüler bir şekilde eklenen paralel mekanizmalardan oluşturulmuştur. Bu amaç için özgün bir paralel mekanizma modülü geliştirilmiştir. Geliştirilen konsept tasarım, yapılan benzetimlerde insan gövde hareketlerini gerçeğe çok yakın bir biçimde taklit edebilmiştir. Yeni geliştirilen sistem sürekli hareket sağlamasının yanı sıra motor tahriki kesildiğinde konumunu koruyacak mekanik kararlılığı da sağlamaktadır. Yapılan sonlu elemanlar ve dinamik analizler sonucu nihai boyutlandırma ve malzeme seçimi gerçekleştirilmiştir ve tasarım çalışması son bulmuştur. Bu tez kapsamında yapay omurganın tasarım süreci ile ilgili çalışılmıştır. İlerleyen yıllarda devam eden proje doğrultusunda prototip üretilecek ve kontrol uygulamaları gerçekleştirilecektir.

In recent decades, various types of humanoid robots with the goal of acting like human beings have been developed by many research groups. The earlier humanoids which resemble the human form were constructed as biped walkers with limps as legs and arms and a torso to carry the loads and components required for robot operations. The conventional solutions for limp and body structures consist of dedicated motors for each degree of freedom axis, which establishes a serial open-loop kinematic chain. While a simple approach like this enabled the control of the robot as an achievable task, the lack of fluidity in the motions caused by a low degree of freedoms and serial kinematic chains made the movements of the robots discontinuous and not human-like. Until recent years the importance of the mechanical aspect of mimicking human skeletal and muscular structures has been neglected. However, robots like Robota, Kotaro, Kojiro, and Kenzo introduced new approaches to the mechanical design of limps and bodies. Furthermore, the works of these researchers showed the validity of the applications of human-like artificial skeletal and muscular structures in robotics. Conventional designs like Honda's ASIMO fail to create human-like motions while the mentioned Kojiro and Kenzoh achieve this criteria but fails to avoid nonlinear behavior and maintain mechanical stability. In this thesis, the design of a torso will be discussed, as the motion of the torso is a crucial element to achieve human-like movements in robots and also the trunk is the main part where all other limps are connected. As mentioned above, conventional mechanical applications in humanoid robots cause non-human-like and discontinuous motion. In this work, to create human-like motions, a modular structure where every module can move relative to the preceding or the following module has been suggested. A novel parallel mechanism as a module has been designed for this purpose. Parallel mechanisms are attached to each other as modules to constitute the spine. In addition to the continuous movement, the mechanism is able to maintain its position when the motors cease to work, which makes the system mechanically stable. In simulations, the new concept design was achieved to mimic human spine movements successfully. The modular spine-like mechanism is designed as a part of an ongoing humanoid project in Istanbul Technical University, Faculty of Mechanical Engineering, System Dynamics and Control Laboratory. The design requirements of the torso may be summarized as below: 1) The design must allow fluid, human-like motions 2) Nonlinear behavior characteristics must be avoided in order to achieve the model and controllability of the system in future works 3) The structure must be able to hold its position in any given state without help from motors 4) The structure should provide space and carry equipment for other parts First the kinematic specifications of the human trunk must be investigated. The trunk part of the human body is from neck to hip. The neck can roll and pitch, the waist can yaw and the hip can yaw, pitch and roll. The main parts of the trunk are the thorax, waist, and pelvis. Thorax plate can yaw, pitch, and roll relative to pelvis plate. Thorax plate is connected to pelvis plate through the spine. The spine consists of 33 vertebrae in 5 main zones; cervical, thoracic, lumbar, sacral, and coccyx, coccyx is attached to Sacrum. Due to the lack of motion of the sacral group, only cervical, thoracic and lumbar parts of the spine will be considered in our work. The spine is divided into four main groups. These groups are reduced to four planes in our design. These planes are as follows; Plane D is the end of the lumbar group and the start of the sacral group. Plane C is the end of the thoracic group and the start of the lumbar group. Plane B is the end of the cervical group and the start of the thoracic group. Plane A is the starting point of the cervical group. Movement capabilities of the human spine will be recreated through these four planes. When the longitudinal axis of the spine is accepted as Z-axis, In order to achieve continuous motion of the body, each plane must be able to; Pitch, yaw, and move in X, Y, and Z directions. However, with the consideration of human spine restrains, the transitional displacement in the X and Y axis must be constrained. These planes will be the end actuators of each parallel mechanism. The artificial spine will be constructed with the serial connection of these parallel mechanisms. Parallel mechanisms are closed kinematic chains with a high degree of freedom. They have many advantages over serial kinematic chains as being stiffer, accurate construction with a low moment of inertia. The desired degrees of freedom were mentioned. To achieve these degrees of freedom a novel 5 DOF RRURR/RRUCR asymmetric parallel mechanism is suggested. Where, R stands for one-directional rotation (Rotation), C for one-directional rotation and linear displacement at the same axis of rotation (Cylindrical), U for two degrees of a freedom universal joint (Cardan coupling). Also, two screw joints are used. One, two, or three of these modules can be used together to obtain any desired degree of freedom. It should be noted that this is still ongoing research and the design will be refined after a set of analyses. The CAD model of the suggested spine module has been created in SOLIDWORKS. Parts are mated together as explained in the kinematic design process. With using SOLIDWORKS motion add in yaw, pitch, and transitional X, Y, Z motions have been simulated. The bottom plane is fixed in the simulations. The position of the top plane has been changed with various inputs. The spine structure is also modeled in SOLIDWORKS. With using motion add-in, the motion of the spine structure has been observed. Strength-related finite element and dynamical analysis has been done as a part of the work. Final dimensioning and material selections have been done according to these simulations. In the future, the design will be improved and a prototype will be manufactured. Kinematic and inverse kinematics of the mechanism will be solved and known control methods will be applied. The spine structure will be combined with an arm design which is also an undergoing project under the humanoid robot project.