Synthesis method for linkages with conter of mass at invariant link point-Pantograph based mechnisms

This paper deals with the synthesis of the motion of the center of mass (CoM) of linkages as being a stationary or invariant point at one of its links. This is of importance for the design of inherently shaking force balanced mechanisms, static balancing, and other branches of mechanical synthesis. For this purpose Fischer's mechanism is investigated as being a composition of pantographs. It can be shown that linkages that are composed of pantographs and of which all links have an arbitrary CoM can be inherently balanced for which Fischer's method is a useful tool. To calculate the principal dimensions for which linkages have their CoM at an invariant link point, an approach based on linear momentum is proposed. With this approach it is possible to investigate each degree-of-freedom individually. Equivalent Linear Momentum Systems are proposed to facilitate the calculations in order to use different convenient reference frames. The method is applied to planar linkages with revolute joints, however it also applies to linkages with other types of joints. As a practical example a shaking force and shaking moment balanced 2-DoF grasper mechanism is derived. -------------------------------------------------------------------------------

Generic method for deriving the general shaking force balance conditions of parallel manipulators with application to a redundant planar 4-RRR parallel manipulator

This paper proposes a generic method for deriving\ud the general shaking force balance conditions of parallel\ud manipulators. Instead of considering the balancing of a parallel\ud manipulator link-by-link or leg-by-leg, the architecture is\ud considered altogether.\ud The first step is to write the linear momentum of each element.\ud The second step is to substitute the derivatives of the\ud loop equations, by which the general force balance conditions\ud are obtained. Subsequently specific kinematic conditions are\ud investigated in order to find advantageous, simple balance solutions.\ud As an example, the method is applied to a planar 4-RRR parallel\ud manipulator, for which the force balance conditions and\ud solutions are discussed and illustrated for each step respectively.\ud By including the loop equations, linear relations of the\ud motion among mechanism elements lead to an increase of balance\ud possibilities.For specific kinematic conditions, additional\ud linear relations among the motion of mechanism elements may\ud be obtained, resulting in another increase of balance possibilities.\ud For the latter, symmetric motion is an important feature\ud for which a 4-RRR manipulator is advantageou

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

International audienceShaking 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 for the evaluation of high speed dynamically balanced parallel manipulators is presented and applied for a comparative experimental investigation of the balanced and the 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

Search for gamma‐ray emission from AGN with COMPTEL

The COMPTEL data (∼0.7–30 MeV) were searched for emission from AGN. Four sources have been detected so far: the quasars 3C 273, 3C 279, PKS 0528+134, and the radio galaxy Centaurus A. 3C 273 and 3C 279 were detected in CGRO observation period 3 with quite different spectral shapes. There is also evidence for 3C 273 at a weak flux level in observation period 11. The quasar PKS 0528+134 was detected above 3 MeV as part of a search for AGN already observed by EGRET. Cen A was seen up to 3 MeV by combining data from different observation periods

COMPTEL observations of the inner galaxy

This paper presents a first global study of COMPTEL observations of the inner Galaxy in the energy range 0.75–10 MeV. Preliminary findings demonstrate COMPTEL’s capabilities for mapping the observed gamma radiation and disentangling the contributions from point sources and diffuse emission

Gamma‐ray burst studies by COMPTEL during its first year of operation

During the first year of Compton GRO operations, more than 20 cosmic gamma‐ray burst‐detected by the BATSE instrument ‐ occurred inside the 1 sr field of view of the imaging gamma‐ray telescope COMPTEL. Using COMPTEL’s primary mode of operation (the telescope mode) direct images (with ∼1° GRB location accuracy) and event spectra (0.7 MeV – 30 MeV) with spectral resolution better than 10% FWHM have been obtained. In its secondary mode of burst operations, COMPTEL has recorded time resolved spectra (0.1 MeV – 10 MeV) from its large NaI detectors. This paper summarises the results on cosmic GRB sources obtained by COMPTEL during its first year of operation

Spectral properties of gamma‐ray bursts observed by COMPTEL

During the first year of operation, the COMPTEL instrument on board the Compton Gamma Ray Observatory detected 22 γ‐ray bursts within its field of view. Spectra and time histories for the strongest 7 of these bursts have been obtained from both the main instrument (0.75–30 MeV) and the burst modules (0.1–10 MeV). The deconvolved photon spectra for the majority of bursts are fit by a single power law model with spectral index between −1.6 and −2.8. One strong burst, GRB 910814, exhibited significant curvature and could not be fit by a single power law model. A broken power law model with a break in slope at ∼2 MeV is a good fit to the time averaged spectrum of this burst. There is evidence, at the 2.8σ level, for a change in the break energy of GRB 910814, from above 2 MeV to below 1 MeV during the first 9 s of the burst