Variable stiffness actuators (VSA) are finding wide applications in robotics to enhance safety during interactions with stiff environments. Researchers have proposed various design architectures like antagonistic actuation, which requires both the motors to be powered simultaneously for varying the stiffness or equilibrium position. In this paper, the design of a novel joint module, named as variable stiffness joint module (VSJM), is proposed, which consists of a lead-screw arrangement for varying the stiffness range and a cam based mechanism to change the stiffness within the set range quickly. The cam profile has been synthesized to maximize the stiffness variation as well as to maintain the cam and cam follower in static equilibrium when the output link is in the equilibrium position. This was achieved by properly positioning and orienting the friction cones at the contact points. By mechanically compensating the moment due to unbalanced forces at the contact points, the continuous usage of stiffness motor has been eliminated, leading to reduced power consumption. Details of the proposed mechanism are presented along with the mathematical model for cam profile synthesis and static analysis. A simplified prototype of the proposed design has been fabricated to perform the experiments. A hammering-a-nail experiment has been conducted to show the capability of the mechanism, and the results are presented.
This paper presents a comprehensive study of the forward and inverse kinematics of a six-degrees-of-freedom (DoF) spatial manipulator with a novel architecture. Developed by Systemantics India Pvt. Ltd., Bangalore, and designated as the H6A (i.e., Hybrid 6-Axis), this manipulator consists of two arm-like branches, which are attached to a rigid waist at the proximal end and are coupled together via a wrist assembly at the other. Kinematics of the manipulator is challenging due to the presence of two multi-DoF passive joints: a spherical joint in the right arm and a universal in the left. The forward kinematic problem has eight solutions, which are derived analytically in the closed form. The inverse kinematic problem leads to
$160$
solutions and involves the derivation of a
$40$
-degree polynomial equation, whose coefficients are obtained as closed-form symbolic expressions of the pose parameters of the end-effector, thus ensuring the generality of the results over all possible inputs. Furthermore, the analyses performed lead naturally to the conditions for various singularities involved, including certain non-trivial architecture singularities. The results are illustrated via numerical examples which are validated extensively.
A study was designed on the way to evaluate and identify the pre and post emergence herbicide combinations in transplanted rice variety ‘ASD 16’ during February-May 2020 at the Experimental Farm, Department of Agronomy, Annamalai University, Tamil Nadu, India. The experiment was laid out in randomized block design with three replications and fourteen treatments. The treatment details includes sequential application of pre and post emergence herbicide viz., pre-emergence herbicides (butachlor, pretilachor and pyrazosulfuron ethyl) and post emergence herbicides (bispyribac sodium, metsulfuron methyl + chlorimuron ethyl, fenoxaprop-p-ethyl and triafamone + ethoxysulfuron), hand weeding twice (20 and 40 DAT) and unweeded control plot. All the weed management practices were found to be significantly influenced the weed biometrics, growth attributes, grain and straw yields of transplanted rice. The result of the study clearly showed that hand weeding twice at 20 and 40 days after transplanting (DAT) significantly registered lesser weed dry matter production, weed index, maximum weed control index (WCI), higher growth attributes viz., plant height, number of tillers hill-1, DMP, grain and straw yields.
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