Timothy D. Tuttle

A zero-placement technique for designing shaped inputs to suppress multiple-mode vibration

The performance of many flexible systems can be improved by employing command shaping techniques to reduce machine vibration. The input shaping technique, in particular, has proven to be highly effective for a wide class of systems. Due to the mathematical complexity of higher-order problems, multiple-mode input shapers can be tricky to derive and difficult to understand. This paper proposes a new approach for deriving input shapers using zero-placement in the discrete domain. The flexibility and simplicity inherent in this formulation provide many options for maximizing shaper performance.

A nonlinear model of a harmonic drive gear transmission

Harmonic drives can exhibit very nonlinear dynamic behavior. In order to capture this behavior, not only must dynamic models include accurate representations of transmission friction, compliance, and kinematic error, but also important features of harmonic-drive gear-tooth geometry and interaction must be understood. In this investigation, experimental observations were used to guide the development of a model to describe harmonic-drive operation. Unlike less detailed representations, this model was able to replicate many of the features observed in actual harmonic-drive dynamic response. Unfortunately, since model parameters can only be derived from careful analysis of experimental dynamic response, it seems unlikely that any comparably sufficient representation can be constructed with parameter values obtained from catalogs or simple experimental observations.

Experimental Verification of Vibration Reduction in Flexible Spacecraft Using Input Shaping

The performance of many spacecraft can be improved by using closed-loop control and command-shaping techniques. However, because little information exists about the operation of controlled structures in zero gravity, it is dife cult for designers to anticipate and place cone dence in the on-orbit performance of their ground-based control designs. To address this issue, the middeck active control experiment was conducted aboard the Space Shuttle Endeavor in March of 1995. The results of the command shaping experiments implemented during the mission are presented, and guidelines forusing command shaping to suppress unwanted vibration in e exible space structures are proposed. HE combination of stringent performance specie cations and lightly damped structural modes makes the effective operation of many space systems vulnerable to vibration. To attack this problem, closed-loop control and open-loop command-shaping techniques are often enlisted. However, with only ground-based testing available prior to on-orbit implementation, uncertainty about zerogravity(0-g) behavior can hamper the success of these 0- g control designs. The Massachusetts Institute of Technology (MIT) middeck activecontrolexperiment (MACE)isaSpaceShuttlee ightexperiment designed to expose critical issues associated with the design of controllers and shaped commands for 0 g. As part of this experiment, data were collected from a e exible structure on-orbit, and results illustrated that both the control and command-shaping strategies employed on the test article could effectively reduce problematic vibration. Additionally, as a result of careful ground-based modeling efforts, predictions of 0- g behavior were accurate enough to achieve high-performance control and command shaping without on-orbit redesign. After introducing the MIT MACE project and the MACEcommand-shaping efforts, this paper presents the results from a specie c subset of the mission experiments: the MACE input shaping tests. Based on these results, key points are summarized and conclusions are drawn.

Vibration reduction in 0-g using input shaping on the MIT Middeck Active Control Experiment

The performance of many spacecraft can be improved by using closed-loop control and command-shaping techniques to reduce problematic vibration. However, due to uncertainties about the operation of controlled structures in zero-gravity, little information exists to give designers confidence in eventual on-orbit performance. The Middeck Active Control Experiment (MACE), scheduled for launch aboard the Space Shuttle Endeavor in March 1995, is designed to investigate these issues by collecting on-orbit data from a controlled flexible structure. In addition to providing a description of the MACE project, this paper presents 0-g predictions for some of the MACE command shaping experiments and describes how the anticipated mission results will be used to understand how to improve the performance of other space systems.

Modeling a harmonic drive gear transmission

In order to capture the dynamic behavior of harmonic drives, dynamic models must include accurate representations of transmission friction, compliance, and kinematic error. Experimental observations are used to guide the development of a model to describe harmonic-drive operation. This model is able to replicate many of the features observed in actual harmonic-drive dynamic response. Valuable insights are gained about the factors which govern harmonic-drive dynamic response. Using these insights to guide the gradual development of a harmonic-drive model, the tradeoffs between model accuracy and complexity are exposed. In particular, despite careful measurement and characterization of transmission friction, compliance, and kinematic error, model performance cannot be improved without acknowledging gear-tooth rubbing losses as well. When a model incorporating gear-tooth behavior is implemented, predicted results reproduce many of the complexities of the experimental dynamic response.<<ETX>>

Creating Time-Optimal Commands with Practical Constraints

In applications that demand rapid response, time-optimal control techniques are often enlisted. Recently, a new technique has been presented for deriving time-optimal command proe les by solving a set of algebraic constraint equations. This time-optimal solution framework is shown to be easily extendable to derive commands satisfying a variety of practical constraints, particularly constraints on command length and sensitivity to modeling errors.

Vibration Reduction in Flexible Space Structures Using Input Shaping on MACE: Mission Results

Abstract The performance of many spacecraft can be improved by using closed-loop control and command-shaping techniques. However, since little information exists about the operation of controlled structures in zerogravity, it is difficult for designers to anticipate and place confidence in the on-orbit performance of their ground based control designs. To address this issue, the Middeck Active Control Experiment (MACE) was conducted aboard the Space Shuttle Endeavor in March of 1995. This paper presents the results of the command shaping experiments implemented during the mission and proposes guidelines for using command shaping to suppress unwanted vibration in flexible space structures.

Creating time-optimal commands for systems with denominator dynamics

Many high-performance applications demand that machines execute rapid and precise point-to-point motions. In order to achieve these motions, time-optimal command profiles can typically be employed. This work presents a strategy for deriving time-optimal commands that takes into account all possible types of system denominator dynamics. Unlike other approaches, the method presented here can account for real modes as well as rigid-body and flexible modes. Since this is a more general strategy for deriving time-optimal commands, results illustrate that this technique always meets or exceeds the performance of existing methods.

Deriving and verifying time-optimal commands for linear systems

In high-performance systems that require rapid and precise motion, time-optimal control techniques are regularly employed. Recently proposed techniques have demonstrated that these time-optimal commands can be derived for systems with complicated linear dynamics. When coupled with a strategy for verifying optimality, this derivation scheme can be guaranteed to yield only time-optimal results. The paper outlines a general method for deriving commands and then describes a detailed procedure for verifying their optimality. Experimental results reveal that this approach is both practical and effective.