Design of Nonlinear Spring and Mechanism for Internally-balanced Magnetic Unit

Internally-balanced Magnetic Unit (IB Magnet) has been developed as a fundamental technique of wall climbing robots. This unit comprises of a permanent magnet which generates a strong sticking force, and a spring unit which cancels the internal force so that the unit can provide easy sticking and releasing actions. In this paper, the authors aim to enlarge usefulness of IB Magnet by several approaches. At first, two novel methods to design nonlinear springs which canceled the internal force of IB Magnet were proposed, and two types of IB Magnets which comprised the nonlinear spring designed by each method of them were developed. Effects of the design methods were confirmed by comparing control forces of the units and magnetic forces. Next, two evaluation methods for nonlinear springs were also proposed. By using the evaluation methods, we can choose the appropriate type of nonlinear spring in various conditions. In addition, a middle yoke that increases the adhering force of the magnet and protects the magnet from dusts, and a mechanism that adjusts the balance force of the nonlinear spring in order to adapt to painted walls were discussed. At last, it was concluded that these studies enlarged usefulness of IB Magnet for various situations.