Introduction

Background

Climbing robot is one of the hottest research topics that gains much attention from researchers. Within this field, most of the climbing robots reported in the literature are designed for climbing manmade structures, such as vertical walls and glass windows [1-9], or structural frames [10-14]. Few climbing robots have been designed to work on natural structures such as trees. Trees and manmade structures are very different in nature. Tree surfaces are seldom flat and smooth, and some trees have soft bark that peels off easily. In addition, the inclined angle on trees is usually not vertical. Hence, most of the climbing methods for manmade structures are not applicable to tree climbing.