On the Structural Constraint and Motion of 3-PRS Parallel Kinematic Machines

This paper presents a consistent analytic kinematic formulation of the 3-PRS parallel manipulator (PM) with a parasitic motion by embedding the velocity level structural constraint equation into the motion expression. Inverse rate kinematics (IRK) is solved with a simple constraint compatible velocity profile, which is obtained by projecting the instantaneous restriction space onto the motion space. Moreover, the systematic method to reveal the parasitic motion is introduced. Thus, the parasitic terms are automatically identified from the main motions. Unlike the usual approach, this study does not consider any explicit parasitic motion expression. Consequently, the derivation of constraint compatible input velocity, which comprises the parasitic term, is simplified. To incorporate the parasitic motion into the task velocity, constraint Jacobian of the manipulator is analytically obtained first. The manipulator Jacobian is extended to incorporate the passive joint’s information apart from the active joints and structural constraint. Hence, the dimension of the Jacobian matrix used to solve IRK is 9 × 6. The validity of the IRK is proved by the Bordered Gramian based forward rate kinematics (FRK). Then, an accurate numerical integration, RK4, is applied to the joint velocity of IRK to obtain the manipulator’s joint values. Consequently, the moving plate’s pose is obtained via forward position kinematics computed using integrated active and passive joint values for validation. The projection matrix used to get compatible constraint motion adjusts our input velocity and makes it compatible with the structural constraint policy, and the parasitic motion is embedded easily. Thus, an explicit formulation of the parasitic motion equation is not required, as the usual practice. Finally, the study presented numerical simulations to show the validity of the outlined resolutions. This paper’s result and analysis can be uniformly applied to other parallel manipulators with less than 6 DoFs.

Normal form approach in the motion planning of space robots: a case study

We examine applicability of normal forms of non-holonomic robotic systems to the problem of motion planning. A case study is analyzed of a planar, free-floating space robot consisting of a mobile base equipped with an on-board manipulator. It is assumed that during the robot’s motion its conserved angular momentum is zero. The motion planning problem is first solved at velocity level, and then torques at the joints are found as a solution of an inverse dynamics problem. A novelty of this paper lies in using the chained normal form of the robot’s dynamics and corresponding feedback transformations for motion planning at the velocity level. Two basic cases are studied, depending on the position of mounting point of the on-board manipulator. Comprehensive computational results are presented, and compared with the results provided by the Endogenous Configuration Space Approach. Advantages and limitations of applying normal forms for robot motion planning are discussed.

GEOECOLOGICAL RISKS OF TECHNOGENIC NOISES AT LOW FREQUENCIES

The article considers the estimation and prevention problem of ecologically dangerous influence of technogenic noises generated by moving transport, such as heavy tracked and wheeled transport, railway transport. The influence on the man and the environment of a low-frequency controlled CV-40 seismic vibrator [1] used for seismological research separately is considered. The influence of vibrations located in the area of low and infra-low frequencies is estimated. The field records of technogenic noises are analyzed. Numerical analysis and estimation of levels of geoecological risks associated with seismic vibration in the ground and acoustic oscillations in the atmosphere are presented. Spectral and spectral-time analysis of technogenic noises records are performed. The main ecologically dangerous frequency areas, which are the most characteristic for these sources, are separated. The dynamics of changes of the vibration velocity level over distances for heavy wheeled and tracked types of transport has been determined.

Optimization of 3-DoF Manipulators’ Parasitic Motion with the Instantaneous Restriction Space-Based Analytic Coupling Relation

This paper presents a velocity-level approach to optimizing the parasitic motion of 3-degrees of freedom (DoFs) parallel manipulators. To achieve this objective, we first systematically derive an analytical velocity-level parasitic motion equation as a primary step for the optimization. The paper utilizes an analytic structural constraint equation that describes the manipulator’s restriction space to formulate the parasitic motion equation via the task variable coupling relation. Then, the relevant geometric variables are identified from the analytic coupling equation. The Quasi-Newton method is used for the direction-specific minimization, i.e., optimizing either the x-axis or y-axis parasitic motion. The pattern-search algorithm is applied to optimize all parasitic terms from the workspace. The proposed approach equivalently describes the 3-PhRS, 3-PvRS, 3RPS manipulators. Moreover, other manipulators within a similar category can be equivalently expressed by the proposed method. Finally, the paper presents the resulting optimum configurations and numerical simulations to demonstrate the approach.

Effect of gamma irradiation and oxidized bitumen on the performance of the modified crumb rubber for various applications

The objective of this study is to enhance the properties of crumb rubber (CR) derived from the tread and sidewalls of passenger and truck waste tires by adding bitumen (B) and oxidized bitumen (OB). On this context, CR was activated and modified by adding different chemical ingredients to convert it into modified crumb rubber (MCR). OB was irradiated at 25 kGy to get irradiated oxidized bitumen (IOB) with the aim of study the effect of irradiation on the samples in the presence and absence of sulfur element. The crosslinking density, mechanical parameters and thermal stability of the developed blend were examined. Furthermore, chemical resistance behavior, vibration tests which reflecting the velocity level and sound proofing performance were discussed. Remarked improvement in the mechanical, thermal and various applications of MCR were achieved by the incorporation of OB especially at 10 phr and gamma irradiation.

A Two-Stage Extension of the Generalized-α Method for Constrained Systems in Mechanics

We present a new two-stage second order extension of the generalized-α method of Chung and Hulbert for systems in mechanics having nonconstant mass matrix and holonomic constraints. Both the position and velocity level constraints are preserved. The extension lends itself to efficient implementation.

Evaluation of the Electromyographic Amplitude-to-Work Ratio in the Infraspinatus Muscle During External Shoulder Rotation Exercises: A Comparison of Concentric Isotonic and Isokinetic Exercises

Background: Isotonic exercise is commonly adopted for shoulder rehabilitation, but the efficacy of isokinetic exercise for rehabilitation has not been evaluated. Purpose: To evaluate the efficacy of isotonic and isokinetic external shoulder rotation exercises. Study Design: Controlled laboratory study. Methods: Using surface electromyography (EMG) and the Biodex system, we investigated the EMG amplitude of the infraspinatus (IS), total work (tWK), and EMG(IS)/tWK ratio and examined the relative IS and posterior deltoid (PD) contributions to all exercises. A total of 24 healthy participants without musculoskeletal injuries were included. Participants performed isotonic external shoulder rotation at 10%, 20%, 30%, 40%, and 50% of the maximum voluntary isometric contraction (MVIC) as well as isokinetic external shoulder rotation at angular velocities of 60, 120, 180, 240, and 300 deg/s. Levels of intensity were classified from 1 to 5: level 1 corresponded to 10% of the MVIC and a 300-deg/s angular velocity; level 2 corresponded to 20% MVIC and 240 deg/s; level 3 corresponded to 30% MVIC and 180 deg/s; level 4 corresponded to 40% MVIC and 120 deg/s; and level 5 corresponded to 50% MVIC and 60 deg/s. Normalized IS and tWK amplitudes were calculated for each exercise. Results: During isotonic exercise, the EMG(IS)/tWK ratio significantly decreased from level 5 to 3, 2, and 1; from level 4 to 2 and 1; and from level 3 to 1. During isokinetic exercise, the EMG(IS)/tWK ratio at level 3 was greater than that at all other levels except level 1. Statistical differences were found between isotonic and isokinetic modes at levels 1, 2, and 3. The IS/PD activation ratios were not significantly different between exercise modes at any level. Conclusion: Isokinetic resistance may provide more effective stimulation of the IS muscle compared with isotonic resistance. Clinical Relevance: Isokinetic exercise needs to be considered as a method of rehabilitation that effectively increases infraspinatus muscle activity.

Trajectory Planning of the Humanoid Manipulator

The paper presents a method of planning a collision-free trajectory for a humanoid manipulator mounted on a rail system. The task of the robot is to move its end-effectors from the current position to the given final location in the workspace. The method is based on a redundancy resolution at the velocity level. In addition to this primary task, secondary objectives are also taken into account. The motion of the robot is planned in order to maximize a manipulability measure in purpose of avoiding manipulator singularities. State inequality constraints resulting from collision avoidance conditions are also considered. A computer example involving a humanoid manipulator operating in a three dimensional task space is also presented.