James D. Huggins

Application of Singular Perturbation Theory to Hydraulic Pump Controlled Systems

In this paper, we use singular perturbation theory to simplify control designs for hydraulic systems and to make designs more feasible for engineering practice. The paper presents the derivations, simulations and experimental tests of control laws for a hydraulic displacement-controlled actuator. Analyses of applied conditions and stability proofs are provided. The developed control design procedure is simplified and is robust to variations in the bulk modulus. The proposed design is simulated with cases of different control input models. Experiments are conducted on a novel hydraulic circuit. The results show that position tracking error exponentially decays and control efforts are dominated by low-frequency signals.

Dynamics of Flexible Manipulator Arms: Alternative Derivation, Verification, and Characteristics for Control

This work seeks to provide an effective way for developing the dynamics of a multi-link flexible manipulator consisting of rotary joints connecting two links. Kinematics of both the rotary joint motion and the link deformation are described by 4×4 transformation matrices as proposed in previous works (Book, 1984). The link deflection is assumed small so that the link transformation can be composed of summations of assumed link shapes. To determine the appropriate choice of component mode shapes, two essential techniques employed here are experimental and finite element methods. The resulting equations of motion allow the complete nonlinear model to be recursively derived from the Jacobian matrix and the mass properties via symbolic manipulation. Two prototype models of flexible manipulators are used to verify the dynamics with frequency and time responses. This paper contributes several new results: (1) the velocity terms (Coriolis and centrifugal forces) are related to variations in the mass matrix, (2) the skew symmetry of certain useful terms are shown, (3) the system is theoretically demonstrated to be stable with joint P.D. controllers in addition to an experimental approach, (4) practical and effective incorporation of actuator dynamics (hydraulic cylinder) and structural complexity (non-uniform cross section) is achieved through selection of mode shapes, (5) geometric constraints are incorporated through simplified coordinate transformations and (6) the results are verified on two physical cases.

A Hydraulic Circuit for Single Rod Cylinders

| Introduction | The Flow Control Circuit With Dynamical Compensations | Stationary Stability Analysis | Dynamic Stability Analysis | Compensation Algorithms for the Flow Control Valves | Simulations and Experiments | Conclusion | Acknowledgements | References Abstract < > FIGURES IN THIS ARTICLE Related Content Customize your page view by dragging and repositioning the boxes below. Related Journal Articles

A novel approach to fabric control for automated sewing

This paper describes a novel fabric manipulation method for fabric control during the sewing process. It addresses issues with past attempts concerning fabric position and tension control. The method described involves replacing the current sewing feed mechanism with a servo controlled manipulator to both feed and control the fabric. The manipulator is coupled with a machine vision system that tracks the threads of the fabric to provide real-time position control that is robust with respect to fabric deformations. A prototype of the manipulator is used to demonstrate the feasibility of the concept, reaching accelerations up to 27 gs and following a closed loop trajectory with open loop control while operating in coordination with an industrial sewing machine. The system described also offers a general solution to high accuracy and high acceleration position control systems.

Experimental Verification of a Large Flexible Manipulator

A large experimental lightweight manipulator would be useful for material handling for welding or for ultrasonic inspection of a large structure such as an airframe. The flexible parallel link mechanism is designed for high rigidity without increasing weight. This constrained system is analyzed by singular value decomposition of the constraint Jacobian matrix. This paper presents a verfication of the modeling using the assumed mode method. Eigenvalues and eigenvectors of the linearized model are compared to the measured system natural frequencies and their associated mode shapes. The modeling results for large motions are compared to the time response data from the experiments. The hydraulic actuator are also verified.

Impedance Shaping for Improved Feel in Hydraulic Systems

Applying haptic control to mobile hydraulic equipment presents a practical yet challenging application. One criticism of newer electro-hydraulic system is a lack of “feel.” To a haptics researcher this sounds like a call for haptic feedback in the human-machine interface. However, for an operator the “feel” of the system likely has more to do with how the actual system responds to forces or higher work port pressures. At some point, the high pressures slow down the system or naturally redirect flow to lower pressure circuits in a hydro-mechanical system. How this is done plays a large part in the “feel” of the system. In this paper, a paradigm is presented that tries to merge these two concepts of “feel.” Instead of trying to make the system transparent, the goal is to make the system react to forces acting on the system then use haptic feedback to help alert the operator to these forces. This is done by shaping this impedance so that the system provides a response or “feel” that is closer to a typical excavator. A haptic interface is used to enhance the haptic feel. Performance is evaluated using data from human-in-the-loop testing.Copyright

Compensation for biodynamic feedthrough in backhoe operation by cab vibration control

This research investigates and seeks to mitigate the undesirable effects of biodynamic feedthrough in backhoe operation. Biodynamic feedthrough occurs when motion of the controlled machine excites motion of the human operator, which is fed back into the control input device. This unwanted input can cause significant performance degradation, which can include limit cycles or even instability. Backhoe user interface designers indicate that this is a problem in many conventional machines, and it has also proved to degrade performance in this testbed. A particular backhoe control system, including the biodynamic feedthrough, is modeled and simulated. Cab vibration control is selected as a means to mitigate the biodynamic feedthrough effect. Two controller based methods are developed based on these models and presented, both of which use the working implement itself to reduce the cab motion. In this case, the backhoe arm has dual functionality, to perform excavation operations and to cancel cab vibration. Results show that significant reductions in cab motion can be obtained with minimal tracking performance degradation, without additional actuators.

Control of a Multi-Link Flexible Manipulator with a Decentralized Approach

Abstract This work seeks to provide an effective way for the development of the dynamics of a multi-link flexible manipulator. Due to the presence of nonlinearities, uncertainty, and link flexibility, a decentralized control is implemented here to provide robust stability without increasing the burden of on-line computation. Simulations and experiments show agreement with the analytic work.

Small Motion Experiments on a Large Flexible Arm with Strain Feedback

Initial experiments on state space feedback control of a large flexible manipulator with a parallel linkage drive are described. A linear controller using joint angle and strain measurements was designed to minimize a quadratic performance index with a prescribed stability margin. It is based on a simplified model that accounts for the constraints of the parallel linkage kinematically rather than through constraint forces. The results show substantial improvement over a simple P.D.joint control.

Modeling of Biodynamic Feedthrough in Backhoe Operation

An advanced backhoe user interface has been developed which uses coordinated control with haptic feedback. Results indicate that the coordinated control provides more intuitive operation that is easy to learn, and the haptic feedback also relays meaningful information back to the user in the form of force signals from digging forces and system limitations. However, results show that the current system has significant problems with biodynamic feedthrough, where the motion of the controlled device excites motion of the operator, resulting in undesirable forces applied to the input device and control performance degradation. This unwanted input is difficult to decouple from the intentional operator input in experiments. This research presents an investigation on the effects of biodynamic feedthrough on this particular backhoe control system, using system identification to empirically define models to represent each component. These models are used for a preliminary simulation study on potential methods for biodynamic feedthrough compensation.Copyright