Design and Control of an Aerial Manipulator for Contact–based Inspection
Varun Nayak1, Christos Papachristos2, and Kostas Alexis3
Abstract—Manipulator dynamics, external forces and moments raise issues in stability and efficient control during aerial manipulation. Additionally, multirotor Micro Aerial Vehicles impose stringent limits on payload, actuation and system states. In view of these challenges, this work addressed the design and control of a 3-DoF serial aerial manipulator for contact inspection. A lightweight design with sufficient dexterous workspace for NDT (Non-Destructive Testing) inspection is presented. This operation requires the regulation of normal force on the inspected point. Contact dynamics have been discussed along with a simulation of the closed-loop dynamics during contact. The simulated controller preserves inherent system nonlinearities and uses a passivity approach to ensure the convergence of error to zero. A transition scheme from free-flight to contact was developed along with the hardware and software frameworks for implementation. This paper concludes with important drawbacks and prospects.
- INTRODUCTION
Unmanned Aerial Vehicles (UAV) are being widely used today for applications such as mapping, inspection, exploration and photography [1], [2], [3], [4], [5]. An important observation regarding most applications of aerial robots is that they do not involve any kind of contact with the environment. This phenomenon can be attributed to several challenges. Traditional robotic manipulators whose base links are fixed to the ground (earth) are able to efficiently dissipate external and inertial forces encountered during manipulation. The reaction forces necessary for balancing external as well as inertial forces acting on the manipulator are available immediately owing to the fixed contact relationship of the base link with the infinitely dissipative ground. However, this is not the case for aerial manipulators as multirotor vehicle dynamics are relatively sensitive and “slow” because of inherent aerodynamic forces as well as inertia. Therefore, the task of maintaining the desired vehicle attitude against these external contact forces becomes a challenge. Along with performing control during contact, the transition between the free-flight regime and the contact regime can present some complications. Physical properties of the UAV platform such as payload, limits on thrust and inertia lead to intricate design challenges.
Fig. 1. The fully assembled aerial manipulator system developed in this work. The image shows the 3-DoF RRR serial manipulator mounted on top of a DJI Matrice 100 quadrotor.
Researchers have employed a variety of approaches in design and control methodologies in aerial manipulation applications [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. Previous research touches on topics such as kinematics for workspace and dexterity, full-body control, lightweight design, accurate end-effector position control, interaction control, etc. The work in [9] developed a novel parallel manipulator with a large workspace and current based torque control to employ impedance control schemes. The work in [6] designed a lightweight 5-DoF aerial manipulator for pick and place applications. It has a smart self-folding mechanism to minimize space occupation and static CoG imbalance. A special differential mechanism to cancel attitude disturbances was also designed. The research presented in [11] used delta-kinematics for designing a fast and precise aerial manipulator for contact-based inspection. The sophisticated delta structure possesses compliance allowing for slight tracking errors. The researchers in [17] demonstrated the design and operation of a unique superstructure manipulator that has the ability to perch on a vertical surface through impact. It is lightweight and possesses unilateral compliance for perch and release operations.
The authors in [8] developed a 7-DoF aerial manipulator for heavy payloads. Hence, it used a backstepping-based controller for the multi-rotor, which considers full coupled dynamics and the rapidly shifting CoG. An admittance-based manipulator controller is outlined in the paper. The contribution in [10] presented a multi-objective full-body controller for the system described in. The fast dynamics of the parallel manipulator ensured efficient kinematic tracking. Furthermore, the work in [16] addressed the problem of interaction in order to track desired contact force using hybrid control for the manipulator, using an impedance-based controller for position and a PI controller for regulating normal force. The authors in [7] presented the design and control of a parallel aerial manipulator for industrial inspection. The approach considered the environment as a compliant contact and used the Hunt-Crossley interaction model. This work modeled the NDT (Non-Destructive Testing) inspection task as a force regulation problem [7] and designed a lightweight 3-DoF RRR manipulator with sufficient dexterity. A planar model of the dynamics during contact was developed, along with a passivity-based PD controller while preserving the nonlinearity of the model. Keeping in mind actuation limits and stability requirements, a simulation of the closed-loop dynamics is presented with a smooth free-light to contact transition scheme. This paper also describes the hardware and software framework for implementation.
- MANIPULATOR DESIGN
Although most aerial manipulators have been mounted below the plane of the rotor and t were designed for pick and place tasks. This makes sense spatially as well as for stability. However, since our objective was to achieve continuous contact in the horizontal plane, the manipulator was mounted as a super-structure. Placing the manipulator on top makes the external force a stabilizing moment and also reduces the require
剩余内容已隐藏，支付完成后下载完整资料
英语译文共 9 页，剩余内容已隐藏，支付完成后下载完整资料
资料编号：[609911]，资料为PDF文档或Word文档，PDF文档可免费转换为Word
以上是毕业论文外文翻译，课题毕业论文、任务书、文献综述、开题报告、程序设计、图纸设计等资料可联系客服协助查找。
