V. van der Wijk

Design and experimental evaluation of a dynamically balanced redundant planar 4-RRR parallel manipulator

Shaking forces and shaking moments in high-speed parallel manipulators are a significant cause of base vibrations. These vibrations can be eliminated by designing the manipulator to be shaking-force balanced and shaking-moment balanced. In this article an approach for the design and evaluation of high-speed dynamically balanced parallel manipulators is presented and applied to a comparative experimental investigation of a balanced and unbalanced DUAL-V planar 4-RRR parallel manipulator. For precise simulation of the manipulator motion, the inverse dynamic model of the manipulator is derived and validated. Experiments show that the balanced manipulator has up to 97% lower shaking forces and up to a 96% lower shaking moment. For small inaccuracies of the counter-masses or for a small unbalanced payload on the platform, base vibrations may be considerable for high-speed manipulation, however their values remain significantly low as compared to the unbalanced manipulator. For the balanced manipulator the actuator torques are about 1.6 times higher and the bearing forces are about 71% lower as compared to the unbalanced manipulator.

Inherently balanced 4R four-bar based linkages

Synthesis of mechanisms with their center of mass (CoM) at an invariant point on one of the elements is useful for the design of statically balanced and shaking-force balanced mechanisms and manipulators. For this purpose, a kinematic architecture based on a general 4R four-bar linkage is found by applying the method of principal vectors as a linkage together with a similar four-bar linkage. The balance conditions are obtained for an arbitrary mass distribution of each of the elements and a balanced grasper mechanism and a balanced two-degree-of-freedom manipulator are derived as practical examples.

Mass Equivalent Dyads

In this paper it is shown how a general 2-DoF dyad can be designed mass equivalent to a general (1-DoF) link element. This is useful in the synthesis of balanced mechanisms, for instance to increase or reduce the number of DoFs of a balanced mechanism maintaining its balance. Also it can be used as a simple approach for synthesis of complex balanced mechanisms. For finding the parameters for mass equivalence, a mass equivalent model with real and virtual equivalent masses is used. First the characteristics of this model are explained, then the properties of a mass equivalent dyad are shown. Subsequently with two methods the parameters of a mass equivalent dyad are derived and application examples are illustrated and discussed.

Closed-Chain Principal Vector Linkages

For high-speed robotics dynamic balance is an important property for low base vibrations and short cycle times. To consider dynamic balance in the beginning of the design process of a manipulator, mechanism solutions can be synthesized from principal vector linkages, which are fundamental kinematic architectures with inherent force balance. In this paper it is shown how a closed-chain principal vector linkage can be analyzed as an open-chain principal vector linkage by modeling one element in a closed chain with two real and two virtual equivalent masses. The results are validated with a dynamic simulation.

On the addition of degrees of freedom to force-balanced linkages

The design of shaking-force balanced linkages can be approached by deriving these linkages from balanced linkage architectures. When desired, a possible step is to add degrees-of-freedom (dof), for instance by substituting a link with a n-dof equivalent linkage for which the balanced design of the other links is not affected. This paper shows how the coupler link of a shaking-force balanced 4R four-bar linkage, applied as a 5R five-bar linkage, can be substituted with an equivalent 2-dof pantograph.

The work of Otto Fischer and the historical development of his method of principal vectors for mechanism and machine science

This article gives an overview of the distinctive work of Otto Fischer (1861-1916) on the motion of the human musculoskeletal system. In order to be able to derive the individual muscle forces for human in motion, he invented the method of principal vectors to describe the motion of the centers-of-mass and the inertias of body segments. This method has proven to be successful, not only for the studies on biomechanics but in particular also for mechanism and machine science. A historical development of the application of the method is presented for today’s potential.

A Cable-Driven Parallel Mechanism for the Interaction with Hemispherical Surfaces

In this paper, a device based upon a specific cable-driven parallel mechanism to interact with hemispherical surfaces is proposed and investigated. This device could be of use in, for example, the automated cleaning of glass domes. Because the cables move on the hemispherical surface, they are curved. A method is developed to calculate the inverse kinematics and the workspace of this mechanism. This method and device are applied to and evaluated for an example of a large glass dome, showing its potential for this purpose.

Investigation of a cable-driven parallel mechanism for interaction with a variety of surface, applied to the cleaning of free-form buildings

In this paper, the capability of a specific cable-driven parallel mechanism to interact with a variety of surfaces is investigated. This capability could be of use in for example the cleaning of large building surfaces. A method is presented to investigate the workspace for which the cables do not interfere and a surface interaction force can be generated. This method takes into account the influence of cable mass. As an example, this method is used for the design of a mechanism with a workspace conform to the dimensions of a typical building facade. The mechanism is concluded to be feasible as long as there is room to locate the pulleys at an adequate distance from the surface.

The method of principal vectors for the systhesis of shaking moment balanced linkages

The design of shaking-moment-balanced linkages still is challenging. Considering moment balance in the very beginning of the design process of mechanisms is important for finding applicable solutions. For this purpose, the method of principal vectors is investigated, showing a compact notation of the angular momentum with respect to the center of mass. The moment-balance conditions are derived for three links in series from which balance solutions are synthesized and illustrated. The application for moment balancing of a 4R four-bar linkage is shown.