Disk Rover: A Wall-Climbing Robot Using Permanent Magnet Disks (1992)

A new wall climbing vehicle using permanent magnet disks for wheels is proposed which is capable of steady and smooth omni- directional locomotion on the surface of a flat or curved iron wall. The optimum shape of the permanent magnet disk is found through finite element analysis and confirmed in mechanical experiments. A self-sustained radio-controlled wail climbing robot about 600 mm in diameter, 240 mm in height, 25 kg in weight and employing a pair of permanent magnet disks is constructed. Its operating characteristics and the results of motion experiments are described. 1. INTRODUCXON Robots with the ability to adhere to the surface of an iron structure could be useful in many types of facilities, such as oil reservoirs, spherical gas tanks and the steam drums of nuclear power plants for performing several tasks, e.g. inspections, shot-blasting or painting. Operations in such environments are dangerous and a great amount of man- power and time is required for the 'non-productive' work of erecting scaffolding. Automating such tasks with wall- climbing robots could permit a large savings in monetary and human costs. Several experimental models of wall-climbing robots have been made, but few have proven to be practical in terms of their ability to adhere to the surface and their maneuverability. This report describes a new wall-climbing robot named Disk Rover which uses disk-shaped permanent magnets as wheels in a new mechanism. The decisions made during the course of design optimization are discussed and the results of operation of a working model are described. 2. )PERMANENT MAGNET DISK WHEEL The permanent magnet can be regarded as the most promising adhesion device for moving around on a wall made of iron. The permanent magnet can easily generate more than 10 times the adhesion of the vacuum sucker in terms of adhesive force per unit area; electromagnets also generate high forces, but require considerable amounts of power. Nonetheless, the physical design of the permanent magnets is of critical importance in the development of a successful wall climbing robot. One of the authors has proposed a device using a permanent magnet named the 'Internally Balanced magnet' or the 'IB magnet', which can regulate the adhesive force of the magnet with, in principle, zero control force (l). The U3 magnet consists of a permanent magnet which is supported by a nonlinear spring from a non-magnetic frame; its adhesive force is designed always to be balanced by the force of the spring at any altitude of the magnet from the surface of the wall. This arrangement treats the permanent magnet as an energy conservation system, rather than an energy dissipation system. The IB magnet could also be utilized as the adhesive force unit in the feet of a wall climbing robot which moves by 'walking'. In this paper the authors would like to propose a new permanent magnet unit which moves with a rolling motion. It has been known for years that a wheel-shaped permanent magnet as shown in Fig. l(a) could effectively fulfill both the functions of adhesion and translation and in fact, several wall-climbing robots using magnetic wheels have been constructed (2,3). These driving systems are remarkably simple and lightweight. However, the roller configuration means that the region of the wheel contributing to adhesion is limited to that along the linear area of contact with the wall. Therefore, the ratio of adhesive force to mass is not very high. We propose a disk-shaped magnetic wheel of which the inner side is a permanent magnet and which contacts the wall at a shallow bevel around the rim, as illustrated in Fig. l@). rnlb configuration permits moat of the body of the magnet to be in the immediate vicinity of the wall surface, enabling it to producc a highcr net adhesive force, in other words, a higher ratio of adhesive force to mass, than the magnetic roller. This paper discusses the design of the permanent magnet unit and of a wall climbing robot based on this device.