Kinematic synthesis method and eccentricity effects of a Stephenson mechanism

When implementing the technological process on crank presses, it is necessary to provide a predetermined working cycle of the slider motion: fast lifting, dwell, and slow lowering. The cycle cannot be realized without controlling the motor. In addition, using controllable motors increases the manufacturing cost. Due to the geometric and kinematic capabilities of the mechanism, changing the kinematics of the working link is the best choice. Thanks to the use of the Stephenson II mechanism, the slider skew is eliminated due to the parallel connecting rods and the increased area of slider contact. This study presents a numerical method for kinematic synthesis of the Stephenson mechanism that has kinematic advantages. The method is based on mean square deviation which is the minimizing of an objective function. Thanks to the proposed synthesis method, approximate dwell movement can be performed when the slider is on the bottom dead center. In this study, values of the crank length and parallel connecting rods' lengths, angular coordinates of the crank and connecting rods, and the eccentricity of the guide slider relative to the crank rotation axis were obtained. It is observed that eccentricity affects the lower forward and higher backward speed of the slider. The kinematic results of the slider movement are comparatively presented in this article.

A method for dynamic modeling and simulation of the translational joint with clearance and LuGre friction

The main purpose of this paper is to present a method for dynamic modeling and simulation of the translational joint with friction and clearance. The sizes of the clearances and the impacts between the slider and the guide in the translational joint can be neglected when the clearance sizes are very small. The geometric constraints of the translational joint are treated as bilateral constraints. The contact forces acting on the slider are reduced to the forces on the slider corners. The LuGre friction model is used to describe friction between slider and guide, because it can capture the variation of the friction force with slip velocity and the slider motion with stick–slip phenomenon. The problem of computing the normal forces on the slider is formulated and solved as a horizontal linear complementarity problem (HLCP), which is embedded in the event-driven method. Finally, a numerical example is considered and numerical results are presented to show the feasibility and the effectiveness of the method.

Uneven Preload for Improving Motion Straightness in Closed Hydrostatic Guideways

Hydrostatic guideways have varied applications in precision or ultra-precision machine tools due to their high motion accuracy and low friction coefficient. Slider motion straightness is an important accuracy index for evaluating precision of hydrostatic guideways. It can be defined as the linear deviation of the slider center within the entire or any assigned stroke. This paper mainly focuses on the relationship between the keeper rail (upper guiderail) preload and slider motion straightness in the closed hydrostatic guideways, where the slider is enveloped by the guiderails. A finite element method was used to calculate keeper rail deformation under different screw preloads, slider motion straightness was measured by laser interferometer. Mapping relationship between screw preload and slider motion straightness was obtained. Experimental results shown that the end of the keeper rail had larger deformation for same preload conditions on all screws. This had an obvious effect on slider motion straightness. When oil supply pressure was 0.85 Mpa, slider motion straightness was 2.08 μm and 1.85 μm (within the entire stroke 330 mm) with torque on all screws as 15Nm and 20Nm, respectively. After uneven preload was employed, slider motion straightness was 0.87 μm and 0.84 μm for the above mentioned two cases. Accuracy increased by more than 50 percent. Screw preload approach proposed in this study can be used to guide the assembly processes of closed hydrostatic guideways with other forms for improving the motion straightness.

The Kinematics Analytical Method and Simulation with ADAMS Based on Bias Slider-Crank Mechanism

This paper selects bias slider-crank mechanism with a constant angular velocity as the research object. First the motion law of mechanism is derived by adopting complex vector method, and then the motion law curve of slider is solved and drawn with MATLAB which can accurately reflect the actual slider motion law; meanwhile output ADAMS simulation result data and compare ADAMS simulation results with the derived results with MATLAB. The results show slider motion law of ADAMS simulation coincides with the theoretical derivation result, which is simulation intuitive and easy to measure.

Performance Analysis of Triangular Elbow Servo Press

The objective of this paper is to study performance of triangular elbow transmission mechanism for servo press. Then kinematics models are deduced and given. Kinematics curves along slider motion direction are drawn. Moreover, under the same driving condition, the effects of different link ratios on slider output motion are examined and compared with common six bar transmission mechanism in the article. Through motion curves comparison, it can be seen that this triangular elbow mechanism has significant force increasing effect and good quick-return characteristics. In addition, we carried on triangular elbow servo press virtual design and simulation. The case study provides more visual and reliable decision basis for designer. The results would be useful reference for optimization design of transmission mechanism.