Papers by Keyword: Singularity

Abstract: This paper deals with singular configurations of a 5-axis machine tool in high speed milling which may lead to the appearance of large incoherent movements of rotary axes near singularity points. These movements generate slowdowns of the actual feedrate during the execution of the tool path, which affect quality and productivity. Thus, this paper proposes a method to detect these behaviors during machining simulation and correct the tool path. Unlike the literature methods, this correction consists in modifying the tool axis orientation by going through the singularity point while respecting maximum velocity, acceleration and jerk of the rotary axis. For that purpose, the initial articular positions of the rotary axis near the singularity point are fitted with B-spline curves, modified and finally discretized for linear interpolation. Experimental investigations on a test part are carried out to show the efficiency of the method.

Abstract: A numerical method is proposed for calculating the fractional order derivative and successfully resolving the integrand singularity problem based on Zhang-Shimizu algorithm. And then a method is developed to calculate the twice nonlinear fractional derivative, numerical examples demonstrate the numerical method with high precision and good stability.

Abstract: According to the kinematics equation of the test tilter for the optical landing aid system, the velocity Jacobi matrix of the tilter is established. The determinant and the condition number of Jacobi matrix based on the numeric analysis in the preset workspace, as the evaluating indicator of the singularity and the dexterity. Simulation result indicates that there is no singularity in the tilter workspace because the determinant of the matrix is not equal to zero, and the tilter has higher rotary dexterity due to the smaller condition number of the rotational velocity Jacobi matrix. At the same time, the tilter has isotropy and the best dexterity in the vertical motion direction due to the condition number of the linear velocity Jacobi matrix is equal to 1.

Abstract: The singularity, namely, the output movement of the mechanism is uncertain due to kinematic bifurcation at the singular position, is the intrinsic characteristic of mechanism, resulting in movement out of control. To find a practical solution for this vexed question to make mechanism able to avoid its singular position is the greatest challenge in the field of mechanism. Based on the study of the planar four-bar linkage with singularity, the ideology of introducing self-adaptive mechanism theory into the solution of avoid singularity problem is firstly put forward in this paper. Using self-adaptive mechanism to complement the out of control parameters of singular position can make the mechanism have the ability to avoid singularity. Then the mechanism passes through the singular position smoothly with determined movement and load capability. Finally, the purpose of avoiding singularity is achieved.

Abstract: In this paper, a three-axis attitude control of a small satellite employing control moment gyroscope (CMG) is presented. A four single gimbal control moment gyroscopes (4-SGCMG) cluster has been employed as the actuator and a proportional-derivative (PD) based attitude control approach has been utilized. The singularity robust (SR) steering law has been employed to investigate its capability in avoiding the singularity state of the CMG system with respect to the mission operation by setting the initial gimbal angle further from the singularity state. The presented control law was simulated in the MATLAB^® SIMULINK^® software. Results obtained from the simulation show the effectiveness of the control algorithm.

Abstract: The paper deals with a workspace problem of the 3 RRR planar parallel mechanism, used as parallel robot structure. Depending on the dimensional parameters and constructive characteristics, the authors search to depict the shape and particularities of the mechanism workspace of a 3 RRR planar parallel mechanism. This characterization of the mechanism workspace depending on the dimensional parameters can be usefull in mechanism designing accorded to some functional particularities and also can help in avoiding singular configurations.

Abstract: The paper presents some authors results regarding working quality inside workspace of a 3 DoF, 3 RRR planar parallel mechanism, used as parallel robot structure. Namely we deal with singularities avoidance inside workspace as is wide known in scientific literature this represents a major disadvantages of these mechanisms. To this purpose, the configuration determinant notion has been used as principal mechanism work parameter.

Abstract: This paper continues some ideas accepted in scientific literature or enunciates by us in previous papers. As title indicates, we treated the case of 0/3/3 structural group with revolute joints, and application of this group in mechanisms. Three different proposals were done and discussed for the forces transmission indices. Finally an application was shown for a mechanism used in a leather ready-made industry.

Abstract: The paper deals with singularity problem of the closed-loop planar mechanisms. This problem is approached in addition with the force transmission quality in mechanism and mechanism self-locking. Another characteristic of this approach consist in the fact that it is based on the structural group notion. Taking into account its frequent usage in practice in the paper were treated only RRR, RRT and RTR structural groups.

Abstract: A heavy-load positioner with series-parallel mechanism was put forward according to the heavy-load positioner’s task demand. Two rotational DOFs were realized by the spherical 3-DOF mechanism with a restricted embranchment instead of traditional gear-driven mechanism, the other by the serial part. The mechanism has the advantages of large workspace, good flexibility and high stiffness-to-weight ratio. The kinematics, statics and singularity of the positioner mechanism were analyzed. The mathematic model of the positioner mechanism was established. Combining the workspace demand of the positioner, dimension optimization of the mechanism was researched. Finally, the kinematics,statics and the singularity analysis of the positioner mechanism was verified through virtual prototype designed with one group of satisfied dimensions.