Browsing by Author "Cheing, WH"

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A constrained multibody system dynamics avoiding kinematic singularities
(2002-03-01)
Huang, CF
;
Yan, CD
;
Jeng, SL
;
Cheing, WH
;
機械工程學系
In the analysis of constrained multibody systems, the constraint reaction forces are normally expressed in terms of the constraint equations and a vector of Lagrange multipliers. Because it fails to incorporate conservation of momentum, the Lagrange multiplier method is deficient when the constraint Jacobian matrix is singular. This paper presents an improved dynamic formulation for the constrained multibody system. In our formulation, the kinematic constraints are still formulated in terms of the joint constraint reaction forces and moments; however, the formulations are based on a second-order Taylor expansion so as to incorporate the rigid body velocities. Conservation of momentum is included explicitly in this method; hence the problems caused by kinematic singularities can be avoided. In addition, the dynamic formulation is general and applicable to most dynamic analyses. Finally the 3-leg Stewart platform is used for the example of analysis.
Analysis of two-dimensional fixture clamping with friction
(1999-06-01)
Tzen, JJ
;
Jeng, SL
;
Cheing, WH
;
機械工程學系
;
Department of Mechanical Engineering
Fixtures that constrain the unwanted motion of a workpiece are important tools in automated manufacturing today. In this paper, we analyze the stability of clamping with passive friction force. The concept of the instant center of rotation is applied to transform the stability analysis into a search for a static equilibrium state. Many properties related to the stability analysis are studied. According to these properties, we design an efficient algorithm for searching the static equilibrium state. The maximum allowable cutting force or the minimum normal stress, which are key concerns in automated design of fixtures, can be calculated precisely by using the search operation. The algorithm can also be extended to the case of multiply distributed friction forces with differently configured clamping areas. Several examples are provided to illustrate cutting force design for different fixture conditions.