Skid steer mobile robots (SSMR) are platforms with simplistic mechanical drives readily adapted for a variety of applications. Skid Steer robots require slipping when navigating general paths. This slipping behavior is a function of surface conditions (friction) as well as robot motion and forces (system dynamics). Slipping affects motion along the path as well as drive torques and power consumption and is therefore an important consideration in robot design. Slipping can be characterized through the instant centers of rotation of the contact patches of the left and right tracks, and it has been shown that these are functions of the system dynamics. Therefore, prediction of system dynamics is needed to better evaluate robot slipping behavior during run time. In this paper, these instant center locations are called the slip parameters. In particular, the paper looked at two alternative models for the slip parameters, one a kinematic estimate assuming constant slip behavior for a class of tasks and the other a dynamic estimate which predicts slip parameters to lie on continuous, closed curves that vary in size relative to payload conditions. Each of these models for slip parameters have been presented in the previous literature, but this paper experimentally tests the slipping for track-based SSMR’s and compares these results to the kinematic and dynamic estimates. This paper will evaluate the validity of each model through real-time tracking and will improve understanding of slip behavior during typical manufacturing tasks. The paper will then present guidelines for the design of SSMR systems based on knowledge of ICR behavior.
This paper demonstrates an approach for predicting and optimizing energy consumption in skid-steer mobile robots (SSMRs) conducting manufacturing tasks. This work is unique in that it considers the energy associated with real-time predictions of slipping in the SSMR and further considers a specific application in which the SSMR is operating in an inverted (climbing) configuration on metal surfaces with homogeneous properties. The approach is based on a dynamic model that provides estimates of SSMR slipping motion during simulation. The model is used to estimate the underlying components of energy and will serve as the tool for objective function evaluation. The approach will follow previous path optimization strategies, parameterizing the path to provide design parameters and using appropriate optimization tools. A method to select the desired trajectory prior to conducting a manufacturing task is demonstrated. This paper primarily focuses on a scenario in which a climbing SSMR maneuvers on a steel surface by means of magnetic-based tracks with strong adhering forces. For this case, the friction due to slipping represents the primary source of energy consumption. This implies that the path selection is the most important parameter for the optimization.
As mobile robotic systems advance, they become viable technologies for automating manufacturing processes in fields that traditionally have not seen much automation. Such fields include shipbuilding or windmill, tank, and pipeline construction. In many cases, these mobile robots must operate in climbing configurations and on non-planar surfaces due to the unstructured nature of these manufacturing tasks. Unit operations are commonly considered in a planar context, but in practice are performed on generally non-planar surfaces. One such example is welding a seam along a non-flat ship hull; these surfaces consist of common geometric shapes such as cylinders or spheres. This paper will present a kinematic analysis of one mobile robot topology performing specified tasks on cylindrical surfaces. The analysis will define a method to determine the robot path on a work-piece surface as well as the configuration joint parameters along when the motion is prescribed in local tool space coordinates. This method assumes that the robot operates following the no-slip, pure roll conditions. The effort is motivated by a practical application of welding on steel hulls or other surfaces and the results will be compared with these empirical experiences. A discussion of how these results can be used to guide future design of mobile robot platforms for manufacturing is provided.
Skid steer tracked-based robots are popular due to their mechanical simplicity, zero-turning radius and greater traction. This architecture also has several advantages when employed by mobile platforms designed to climb and navigate ferrous surfaces, such as increased magnet density and low profile (center of gravity). However, the suspension design plays a critical and unique role in track-based climbing systems relative to their traditional counterparts. In particular, the suspension must both accommodate irregularities in the climbing surface as well as transfer forces to the robot chassis required to maintain equilibrium. Furthermore, when properly designed, the suspension will distribute the climbing forces in a prescribed manner over the tractive elements. This paper will present a model for analysis and design of a linkage-type suspension for track-based climbing robot systems. The paper will further propose a set of requirements termed “conditions of climbing” that must be met to ensure stable (no falling) climbing for a given robot design over a range of climbing surface geometries. A recursive strategy is proposed to implement these conditions and yield a factor of safety in the current climbing state. This model will be compared through empirical testing with several prototype climbing robot systems. A method will also be demonstrated to use this model in the design of a preferred suspension system.
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