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Institute for Robotics and Intelligent Machines (IRIM)

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Author: Alberts, Thomas Edward × End date: 1989 × Start date: 1980 × Has files: Yes ×

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Now showing 1 - 4 of 4
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    On the transfer function modeling of flexible structures with distributed damping
    (Georgia Institute of Technology, 1986-12) Alberts, Thomas Edward ; Dickerson, Stephen L. ; Book, Wayne J.
    The authors have suggested the use of distributed passive damping via constrained viscoelastic layer surface treatments, as a means of augmenting active controllers for flexible structures. This enhances system stability and provides justification for the use of low order dynamic models and controllers. In previous work a co located transfer. function based upon experimental measurements was employed in root locus analysis of a system with passive damping. Here we present a method of deriving co located and non-colocated transfer functions for flexible systems with distributed damping. The (sandwich) flexible structure is modeled as though it was constructed of an equivalent homogeneous material exhibiting linear viscoelastic behavior. Transfer functions are obtained through solution of a modified form of the Bernoulli-Euler equation which is derived using the standard constitutive relationship between stress and strain for viscoelastic materials in place of Hook's law. General observations are made with regard to open loop pole and zero locations for colocated and non-colocated transfer functions. The effect of joint damping is also considered.
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    Design strategies for high-speed lightweight robots
    (Georgia Institute of Technology, 1986-09) Book, Wayne J. ; Hastings, Gordon Greene ; Alberts, Thomas Edward
    Industrial robots today can lift objects no. heavier than about five percent of their own weight. Imagine a robotic weight lifter competing against the current Olympic human record of 750 lb. By today's standards, that robot would have to weigh about 15,000 lb, as opposed to its human competitor, who would weigh 165 lb (and who is "rated" at 450 percent of body weight). While this analogy is inexact, the point stands that improvements in the performance of robotic manipulators require engineers to consider the weight of the structural and drive components. The advantages of lighter weight include faster motion times for large motions, smaller actuators, lower energy consumption, reduced mounting requirements, and less weight to be transported. But there are also penalties such as lower (structural) strength and lower stiffness. The stiffness constraint arising from the dynamic and static behavior of the arm is the more critical for most uses of robotic arms. Therefore, we have concentrated on controlling the motion of robotic devices that have lightweight structures.
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    Combined approaches to lightweight arm utilization
    (Georgia Institute of Technology, 1985-11) Book, Wayne J. ; Dickerson, Stephen L. ; Hastings, Gordon Greene ; Cetinkunt, Sabri ; Alberts, Thomas Edward
    In order to use lightweight arms the combination of a number of new approaches in arm design and control may be necessary. This paper describes four complimentary research efforts and how their results will work together. The bracing strategy is proposed first as one scenario of arm usage. It braces the arm against a passive structure to increase rigidity during fine motions of the end effector. Large motions of the arm require path and trajectory planning. Research on minimum time motions that avoid unnecessarily exciting vibrations is described next. The damping of those vibrations that are excited can be accomplished through a combination of active modal feedback control and passive damping. The enhancement of the damping characteristics of arm structures is described. This is important for stable feedback control with actuators and controllers with limited bandwidth. Analytical and experimental results for constrained layer damping are described. in the context of the control problem. An active modal control has been implimented on a simple one link beam. As higher bandwidth is sought from this physical system deviations from the predicted results were observed. A refinement of the model to include anti-aliasing filter, sample-data, and amplifier effects explains the behavior as explained.
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    Experiments in Optimal Control of a Flexible Arm with Passive Damping
    (Georgia Institute of Technology, 1985-06) Alberts, Thomas Edward ; Hastings, Gordon Greene ; Book, Wayne J. ; Dickerson, Stephen L.
    This paper presents a hybrid active and passive control scheme for control ling the motion of a lightweight flexible arm. A straightforward development of LaGrange's equations using a series expansion of assumed flexible modes provides a time domain model for controller design. The active controller design was approached as a steady state linear quadratic continuous regulator. A constrained viscoelastic layer treatment was employed to achieve passive damping. The passive damping treatment serves to enhance the system's stability while providing sound justification for the use of a highly truncated dynamic model and reduced order controller. Initial experimental results comparing controller performance with and without passive damping demonstrate the merit of the proposed combined active/passive approach.