Latest Papers

ASME Journal of Mechanisms and Robotics

  • Stable Inverse Dynamics for Feedforward Control of Nonminimum-Phase Underactuated Systems
    on January 25, 2023 at 12:00 am

    AbstractAn enhanced inverse dynamics approach is here presented for feedforward control of underactuated multibody systems, such as mechanisms or robots where the number of independent actuators is smaller than the number of degrees of freedom. The method exploits the concept of partitioning the independent coordinates into actuated and unactuated ones (through a QR-decomposition) and of linearly combined output, to obtain the internal dynamics of the nonminimum-phase system and then to stabilize it through proper output redefinition. Then, the exact algebraic model of the actuated sub-system is inverted, leading to the desired control forces with just minor approximations and no need for pre-actuation. The effectiveness of the proposed approach is assessed by three numerical test cases, by comparing it with some meaningful benchmarks taken from the literature. Finally, experimental verification through an underactuated robotic arm with two degrees of freedom is performed.

Spring Configurations and Attachment Angles Determination for Statically Balanced Planar Articulated Manipulators


Admissible spring configurations for statically balanced planar articulated manipulators have been investigated in previous studies. However, in these spring configurations, springs are only identified by the connection between links. The attachment angles and distance for springs to be properly installed remain unaddressed. In this study, a method to determine attachment angles and distance for springs is developed to ensure all the springs are acting for the benefit of static balancing. Here, the gravitational and elastic potential energies are represented in stiffness matrix form, it is shown that term by term compatibility exists between the first row of gravitational stiffness matrix and the first row of the elastic stiffness matrix. In accordance with these compatibility conditions, the admissible spring attachment angles are found to ensure all the ground-connected springs are acting for the benefit of gravity balancing. And the remained components below the first row of the elastic stiffness matrix are offset by the non-ground-connected springs. In accordance with the compatibility between the remained components and the elastic stiffness matrix of non-ground-connected springs, the spring attachment angles to ensure all the non-ground-connected springs acting for the benefit of elastic balancing are found. The determination of the admissible spring configurations is revisited in addition to the connection between links, and the attachment angles of springs are also specified. The admissible spring configurations of statically balanced planar articulated three- and four-link manipulators are derived. A four-link planar manipulator is used as an example for illustration.

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