A new, seven parameter class of micromanipulators is found with decoupled dynamics. The flexibility of the new class is demonstrated by designing a Stewart platform with fully equalized and decoupled dynamics (i.e., all resonant frequencies are equal). Although this has been attempted before by other researchers, it has not been previously accomplished. The ability to design the dynamics so they are amenable to control leads to significant increases in closed loop performance and robustness. The dynamically decoupled and equalized manipulator is compared to an asymmetric manipulator in closed loop. Even though both manipulators control the same payload over the same bandwidth with exactly the same struts, the H∞controller for the equalized manipulator is five times less sensitive to worst case disturbances than the H∞controller for the asymmetric manipulator. Moreover, the decoupling facilitates the design of Nyquist stable compensators which give the decoupled manipulator one hundred times higher performance at low frequencies. This greatly increased performance and robustness requires implementation of only the six compensators along the diagonal of the six degree-of-freedom system, versus implementation of all 36 compensators for the asymmetrical manipulator.

This paper analytically finds a new, significantly more general class of locally decoupled 2p - UPS, parallel manipulators encompassing and expanding several earlier classes. Its closed form solution leads directly to simple analytic formulas for the system eigenvalues in terms of geometric design parameters. To illustrate the power of the theory, the new methods are used to re-design an actual manipulator currently in use on the International Space Station. Unlike the existing manipulator, the new design is dynamically decoupled and isotropic.

New methods are found for arranging force actuators around a rigid body so that the system has locally decoupled and optimal manipulation characteristics. The closed-form solution leads directly to simple analytic formulas for the singular values of the manipulator Jacobian in terms of geometric design parameters. This makes it possible to easily design the local kinematics so that they meet desired specifications. Explicit formulas for designing the wrench/twist capabilities, achieving isotropy, maximizing the volume of achievable motions, and maximizing the minimum singular values are derived. Applications include design of generalized Gough-Stewart platforms (GSPs) and other parallel machines. To illustrate the power of the theory, the new methods are used to redesign an actual manipulator currently in use on the International Space Station (ISS). Unlike the existing manipulator, the new design is kinematically decoupled, isotropic, and fault tolerant - all highly desirable properties, especially in aerospace applications.

In this paper, a novel composite 6-DOF parallel robot is introduced. Two independent components are included in this new mechanism. One is a planar 3-RPR mechanism, the other is a spatial 3-UPS-l-PU mechanism. The planar mechanism provides translations along the x and y axes and rotation around the z axis. As a complement, the 3-UPS-l-PU mechanism provides translation along the z axis and rotations around the x and y axis. These two mechanisms are combined using a serial connection. Different combinations of these two mechanism are proposed in this paper.

While a number of researchers have published results in the area of parallel robot singularity determination and the a posteriori elimination of these singularities, far less work has been published in the area of singularity free workspace design. Several researchers have committed substantial funds to design hardware prototypes that have proven worthless because of unavoidable singularities. This trend, if carried over to industrial applications, could prove especially detrimental to the future of applied parallel robotics. A comprehensive and straightforward design strategy that guarantees a singularity free workspace is presented in this paper. The design problem is mathematically modeled, and relaxations are suggested for finding solutions. The translational 3-UPU parallel robot is studied to verify the efficacy of the design approach.

A method to design a singularity-free 3-arm planar parallel mechanism is presented. Parallel mechanism singularities are categorized by their relationship to the design problem. A sequential design procedure is explained, whereby two arms are designed first to satisfy workspace requirements, then the third arm is designed to provide a singularity free workspace. The method is used to develop a singularity-free workspace design for the 3-RPR mechanism.

Parallel mechanisms frequently possess an unstable type of singularity that has no counterpart in serial mechanisms. When the mechanism is at or near this type of singularity, it loses the ability to counteract external forces in certain directions. The determination of unstable singular configurations in parallel robots is challenging, and in the past, has been tackled by exhaustive numerical searches of the mechanism workspace using an accurate analytical model of the mechanism kinematics. This paper considers the singularity-determination problem from a geometric perspective for n-legged spatial parallel mechanisms. By using the constraints on the passive joint velocities, a necessary condition for an unstable singularity is derived.

This paper develops new, analytical methods to find a large class of Orthogonal Gough-Stewart Platforms (OGSPs) having desired manipulabilities at a single point. In contrast, prior methods have been computationally intensive, relying on numerical search techniques. The new techniques are directly applicable to clean sheet design of micro-manipulators, vibration isolators, and Cartesian stiffness matrices. In addition, straightforward methods for retro-fitting existing OGSPs are illustrated. The approach relies on symmetrically repeating a strut at least three times.

Parallel mechanisms frequently possess an unstable type of singularity that has no counterpart in serial mechanisms. When the mechanism is at or near this type of singularity, it loses the ability to counteract external forces in certain directions. The determination of unstable singular configurations in parallel robots is challenging, and in the past has been tackled by exhaustive numerical searches of the mechanism workspace using an accurate analytical model of the mechanism kinematics. This paper considers the singularity determination problem from a geometric perspective for n-legged spatial parallel mechanisms. By using the constraints on the passive joint velocities, a necessary condition for unstable singularity is derived that identifies the reason for such singularities.

Parallel mechanisms frequently possess an unstable type of singularity that has no counterpart in serial mechanisms. When the mechanism is at or near this type of singularity, it loses the ability to counteract external forces in certain directions. The determination of unstable singular configurations in parallel robots is challenging, and in the past has been tackled by exhaustive numerical searches of the mechanism workspace using an accurate analytical model of the mechanism kinematics. This paper considers the singularity determination problem from a geometric perspective for n-legged spatial parallel mechanisms. By using the constraints on the passive joint velocities, a necessary condition for unstable singularity is derived that identifies the reason for such singularities.

Parallel mechanisms frequently contain an unstable type of singularity that has no counterpart in serial mechanisms. When the mechanism is at or near this type of singularity, it loses the ability to counteract external forces in certain directions. The determination of unstable singular configurations in parallel robots is challenging in general, and is usually tackled via an exhaustive search of the workspace using an accurate analytical model of the mechanism kinematics. This paper considers the singularity determination problem from a geometric perspective for planar and spatial three-legged parallel mechanisms. By using the constraints on the passive joint velocities, we derive a necessary condition for the unstable singularities. Using this condition, certain singularities can be found for certain type of platforms. As an example, new singular poses are discovered using this approach for a six-degree-of-freedom machining center.

Parallel mechanisms frequently contain an unstable type of singularity that has no counterpart in serial mechanisms. When the mechanism is at or near this type of singularity, it loses the ability to counteract external forces in certain directions. The paper considers an interesting alternative to redundant actuation through the application of additional kinematic constraint via passive joint braking in the close neighborhood of unstable poses. The brake has the advantage of not requiring additional actuator/sensor pairs or mechanism architecture redesign, and of being implemented only when necessary to stabilize the system. The kinematic analysis of braked mechanisms is supported with results using a six degree-of-freedom parallel machining mechanism.

Parallel mechanisms frequently contain an unstable type of singularity that has no counterpart in serial mechanisms. When the mechanism is at or near this type of singularity, it loses the ability to counteract external forces in certain directions. By altering the mechanism through, for example, additional kinematic linkages, the singularity can be modified or even removed. Another approach is to actuate certain unactuated degrees of freedom. The manipulability is guaranteed to improve over the original mechanism, but the mechanism is now over-actuated. By studying a recently proposed parallel machining center, we examine the effectiveness of singularity modification through redundant actuation. As a metric, we use the condition number of the recently developed manipulability ellipsoid for general parallel mechanisms.