# Design and Motion Planning of a Biped Climbing Robot with Redundant Manipulator
## 1 Introduction  
Steel guardrails and brackets are important structures that support railway bridges and provide protection for passing trains. Continuous maintenance and inspection are required to ensure the longevity of steel structures. Hazardous conditions due to the bridge height and wind pressure from moving trains can cause difficulties in maintaining or inspecting railway bridges. To guarantee safety, workers must use heavy personal protective equipment and stop working when a train passes by. Therefore, traditional manual operation encounters many problems, such as poor security and low efficiency. Deploying special robots to replace humans can solve the problems mentioned above. The basic function of the robot is to climb bridges in a reliable and flexible way. In addition, the robot should be able to manipulate different tools to reach the surface of steel structures without collisions. There have been several types of robots capable of climbing a wide variety of infrastructures in the past decades [1]. According to the characteristics of different infrastructures, robots have different climbing mechanisms and adhesion methods. Wheeled, tracked, legged, and combined types are the most commonly used climbing mechanisms of climbing robots [2]. Generally, robots with wheels or tracks are used on continuous surfaces with few obstacles since they have a higher speed than legged climbing robots. If the surface of an infrastructure has a complex structure or irregular obstacles, the legged climbing mechanism is more applicable than other mechanisms. Adhesion methods such as magnetic attraction [3, 4], vacuum attraction [5, 6, 7, 8], electric adhesion [9, 10], gripping adhesion [11, 12, 13], and adhesive elastomer [14] have been applied in the field of climbing robots. Robots with magneticfeet can be applied to steel structure surfaces, robots with vacuum suction can be used on smooth plane surfaces, and robots with claws or grippers are most commonly used on rough surfaces. The skid-steer mobile robot, which is a magnetic-tracked robot, can climb a vertical planar steel surface and perform welding operations [15]. [PERSON] et al. [16] designed a tracked climbing robot with an electromagnetic array for ship inspection in shipbuilding. Equipped with probe clamping devices, the robot can perform tasks in human unfriendly environments. Inspired by rock climbers and cats, [PERSON] et al. [12] designed a quadruped climbing robot that can climb a rough wall surface using cross-arranged claws. [PERSON] et al. [13] proposed a three-legged astronaut robot to assist human astronauts in space stations. Thanks to grippers with a self-locking property, the robot can move outside the space station via the special aluminum handrails freely and steady. [PERSON] et al. [17] designed an inchworm-inspired climbing robot with two magnetic pads for the inspection of a steel bridge and proposed a real-time motion planning method to enter the limited space inside the steel bridge. [PERSON] et al. [18] designed a modular five-degrees-of-freedom (5-Dof) biped climbing robot with a suction module and analyzed the safety of suctions. Biped climbing robot (BiCR) was also a 5-Dof biped climbing robot with two grips. Due to the optimal collision-free grip sequence generated by a grip planning method, BiCR can climb in a complex truss environment [19]. However, the climbing robots mentioned above neglect the ability to manipulate, so their potential applications are limited to surveillance and inspection. To perform complex maintenance tasks such as rust removal and spray painting, a manipulator must be mounted on the climbing robot, which will result in problems such as body balance and motion planning. There is work that remains to add manipulating functions on the climbing robot. Motivated by the above observation, a climbing robot with a redundant manipulator, termed as CMBOT (climbing manipulator robot), was designed to perform the inspection and maintenance tasks of railway bridges in this paper.