Chapter 10 A Technique for Minimizing Robot-Induced Modal Excitations for On-Orbit Servicing, Assembly, and Manufacturing Structures Cory J. Rupp Abstrac t Robot-driven on-orbit servicing, assembly, and manufacturing (OSAM) promises to enable and enhance a wide range of space technologies in the coming decades. Supporting technologies, however, are still nascent and must still be developed to manage the unique characteristics of this upcoming construction paradigm. Robotic operation on OSAM structures will introduce modal excitations that, if not controlled, may damage or fatigue the structure. This chapter develops a method for planning robot motions such that modal excitations are minimized, thereby reducing induced loads and risk to the structure. An example is presented using a relevant exemplary OSAM structure. Keyword s Structural dynamics · Vibration · OSAM · Robotics · Path planning 10.1 Introduction On-orbit servicing, assembly, and manufacturing (OSAM) is an upcoming in-space operation and construction paradigm enabled by autonomous and semi-autonomous robotic systems. It offers significant advantages for both government and commercial entities over current single-launch solutions in terms of lower risk and cost as well as enabling missions with repairability, life extension, and larger structures. Examples of structures that would benefit from this technology include very large diameter space telescopes and antennas and persistent space platforms [1, 2]. Although the concept of OSAM is decades old, relevant technologies in robotic autonomy have only recently matured to the point where extensive use of OSAM is possible. Nevertheless, several technological needs must still be developed in order to fully realize the promise of OSAM. Among these needs are techniques for performing in-space modal testing to capture the varying nature of the mode shapes and frequencies as an under-construction OSAM structure changes in size and shape [3], new adaptive control architectures for robotic and spacecraft stationkeeping systems that will take into account such modal changes [4], and, as to be described in this chapter, a way of minimizing modal excitations of the structure (which may cause damage or fatigue) during robotic operations. While this chapter focuses on OSAM structures, the technique described herein is equally applicable to terrestrial, lunar, or other gravity-bound situations in which a robot is operating while attached to a flexible structure. Many different types of robotic systems are envisioned for OSAM, including free-flyers, long-reach robotic arms, and traversing robots. Regardless of design, a robotic system attached to an OSAM structure will necessarily introduce structural dynamic excitations as the robot performs its tasks. As described in Ref. [3], there exists an intricate relationship between a robot’s design, how it is actuated, its attachment location on the OSAM structure, and the OSAM structure’s modal response. With this in mind, it is natural to conclude that the manne r in which the robot moves (i.e., the motions it makes during operations) will affect the manner in which the modal response is manifest. In most cases, and in particular for robotic arms, some form of path planning is necessary to define such motions. It is in this activity that we have the opportunity to tailor the robot motion with the intent of minimizing modal excitations. The generic robot path-planning or trajectory-planning problem can be described as defining the motions of the actuated robot degrees of freedom that will move the robot from one pose (or combination of joint angles) to another. Standard practice for solving this problem for robotic arms is to formulate an optimization problem that minimizes the duration of the motion under the constraints of the joint actuation limits. In some situations, it is beneficial to minimize a different quantity, C. J. Rupp ( ) ATA Engineering, Inc., Lakewood, CO, USA e-mail: cory.rupp@ata-e.com © The Society for Experimental Mechanics, Inc. 2024 B. J. Dilworth et al. (eds.), Topics in Modal Analysis & Parameter Identification, Volume 9, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-031-34942-3_10 89
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