Design of Track-Based Climbing Robots Using Dry Adhesives
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Proceedings of the ASME 2017 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference IDETC2017 August 6-9, 2017, Cleveland, Ohio, USA DETC2017-67999 DESIGN OF TRACK-BASED CLIMBING ROBOTS USING DRY ADHESIVES Matthew W. Powelson Stephen L. Canfield Tennessee Technological University Tennessee Technological University Dept. of Mechanical Engineering Dept. of Mechanical Engineering Cookeville, Tennessee, 38505 Cookeville, Tennessee, 38505 United States of America United States of America [email protected] [email protected] ABSTRACT ability to climb on surfaces of varying curvature using dry This paper focuses on the design of track-type climbing adhesives and a linkage based leg design [9]. Tracked based robots using dry adhesives to generate tractive forces between designs, while less common, have also proven to be effective the robot and climbing surface to maintain equilibrium while in utilizing dry adhesives. Tankbot demonstrated the ability to motion. When considering the design of these climbing robots, climb rough and smooth surfaces while traversing obstacles but there are two primary elements of focus: the adhesive required the use of a tail to maintain adhesion [10]. MaTBot mechanisms at the track-surface interface and the distribution utilized a belt system combining dry adhesives with magnets to of these forces over the full contact surface (the tracks). This climb glass substrates at high angles as well as fully vertical paper will present an approach to integrate a generic adhesion ferrous substrates [2]. model and a track suspension system into a complete model that can be used to design general climbing robot systems While legged robots are more common, tracked vehicles utilizing a broad range of dry adhesive technologies. exhibit several advantages. They are intuitive kinematically and allow the application of off the shelf path planning algorithms. Further, tracked vehicles utilize a continuous contact patch in 1. INTRODUCTION motion relative to the robot. This means that the forces on an There are a variety of means incorporated to generate the adhesive material will be continuous, eliminating the possibility adhering forces needed for climbing, which include magnetic, of impact loading that could result from discrete legs in the suction, micro-gripping, electro-statics and adhesives. Magnetic event of an adhesive failure. Likewise, a tracked vehicle has adhesion provides a widely available adhering mechanism but many stable and marginally stable climbing positions [1] that is not suitable for climbing on nonferrous materials [1, 2]. allow the possibility for a robot to recover from an adhesion Microspines have been demonstrated in robotics both for failure without falling whereas a robot with discrete contact climbing robots [3] and perching of aerial robots [4, 5]. While patches exhibit significantly fewer stable climbing these have been shown to be a reliable source of very high configurations. Due to the larger contact area, tracked vehicles adhesive forces [6], they have been demonstrated to be are able to carry larger payloads [10] making them more readily ineffective for smooth surfaces [3]. This paper will instead scalable. focus on dry adhesive adhering approaches. While tracked vehicles for climbing have been previously In recent years, many robots utilizing dry adhesives for studied [1, 2, 10], the literature shows no models that integrate climbing have been developed with legged robots being the properties unique to dry adhesives with models for track design most common. Waalbot is one such robot that utilizes a set of 3 that distribute the climbing load. This paper will present an footed wheels coated in a dry adhesive material to climb on approach to integrate models for dry adhesives and track both smooth and nonsmooth surfaces [7]. Geckobot uses a suspension systems into a complete model that can be used to climbing gate similar to a gecko to climb with a set of adhesive design general climbing robot systems. footpads with active peeling mechanisms [8]. The RiSE platform demonstrates the ability to climb using both microspines and dry adhesives [3]. AnyClimb demonstrates the 1 Copyright © 2017 by ASME 2. DESIGN PROCEDURE FOR TRACKED CLIMBING ROBOTS Another consideration is effect of peeling on the adhesion 2.1 Overview of Design Procedure strength. Whether considering patterned or unpatterned An overview of the robot design procedure is now adhesives, the observed adhesion force is the result of the sum presented. First, the design considerations specific to dry of many small areas of contact. As such, the force required to adhesives are discussed. Second, a model is adapted to describe remove the adhesive is much larger when the load is distributed the distribution of climbing forces at the interface of the robot across an entire contact patch compared to when the load is and the climbing surface by taking into account these unique concentrated at the edge of the contact patch, as is the case considerations. The paper then demonstrates the use of these during peeling [11]. For this reason, it is important that track- models to design a specific climbing vehicle platform with a based climbing robots utilize a force distribution system representative dry adhesive. Design charts are created and their thereby avoiding the concentration of loading seen in track- use is demonstrated. Finally, a physical prototype of the based climbing robots using a tail [10]. climbing robot as designed using the proposed strategy is constructed and tested to evaluate basic operational 2.3 Suspension Model performance. A design approach is now developed to incorporate the adhesion considerations discussed above into a model that 2.2 Adhesive Considerations defines stable climbing for the tracked robot system. This Dry adhesives are typically considered to achieve their approach assumes that the tracked robot contains a suspension adhesive properties primarily through intermolecular forces system that distributes the climbing forces along the length of such as van der Waals forces and hydrogen bonding [11]. They the track. Here, the track length considers the region of an achieve a high degree of contact by conforming to surface endless track that is in contact with the climbing surface. asperities either through micropatterning or through the Further, the climbing forces considered are those in a direction elasticity of the adhesive. Regardless of the technique used to normal to the climbing surface and orthogonal to gravity. The achieve contact, dry adhesives exhibit unique characteristics approach is based on developing a generalized model for that must be considered when utilizing them in climbing determining forces needed for stable climbing and selecting applications. Most significantly is their loading specific nature. appropriate adhesive members using this model. While some adhesives have been developed such that increased shear loads, 휏, allow for higher normal loads to be applied [12] When considered in a kinetostatic sense, equilibrium [13], the most common dependence is that of the maximum equations are used to define the forces occurring at the normal adhesion pressure, 푤 , to the normal preloading boundary between the track and surface for climbing robots. 퐴 Stability occurs when the forces required do not exceed the pressure, 푤푃 – i.e. the relation of the magnitude of the negative pressure that can be sustained before adhesion failure occurs to allowable adhesive load provided by the adhesive material. the magnitude of the positive pressure with which the dry Therefore, a model to predict the forces as a function of adhesive is applied to the surface. Further, this relation is often location along the track surface is proposed for evaluation and nonlinear as the adhesion is typically driven by material design of track-type climbing robots. This model is based on a deformation at the microscopic level where adhesive geometry generalization of the tracked-type robot climbing model and surface asperities produce a nonlinear relationship between presented in [1] and will be called the PK model. A brief force applied and new contact area achieved. Additionally, as summary of the PK model is first presented. the conformity to the climbing surface generally depends on the asperity size, maximum adhesion is dependent upon surface roughness, R [11, 14]. Finally due to their viscoelastic nature, dry adhesives allow for the possibility of time dependent Adhesive Elements responses such as a dependency on preloading time, 푡푃 [11]. As such, the maximum adhesion pressure that a dry adhesive can sustain can be expressed as an equation of the general form, 푤퐴 = 푓(푤푃, 휏, 푡푃, 푅). (1) It can then be assumed that if the robot is travelling over a small range of velocities, the time variability can be neglected. Further, on a uniform surface RMS roughness can be Suspension Springs approximated as being constant. Since the shear loading would Load Transfer Guides be constant in kinetostatic equilibrium, the maximum adhesion is therefore considered to be a known function of the preloading condition only. FIGURE 1 – MODEL OF A TRACK BASED CLIMBING ROBOT UTILIZING PK SUSPENSION AND DISCRETE TRACK ELEMENTS [1] 2 Copyright © 2017 by ASME The PK model assumes that the robot contains a track running through a suspension that is able to distribute forces normal to and away from the climbing surface along the length of track in contact with the climbing surface (see Fig. 1). The PK model is applied to a single track and assumes that the robot mass and loads are uniformly distributed among all tracks on the robot. The climbing surface is assumed to be uniform along lines orthogonal to the direction of travel permitting a planar model of the suspension. This model further assumes that the local surface curvature is small relative to the length of the suspension such that individual suspension links undergo small changes in orientation relative to the local frame. Finally, the mass of the entire robot system (adhering members, track, suspension system, chassis, payload) will be included in the external loads Px, and Py and are not locally distributed.