As a simple example of this solution procedure, consider the single link in pure rotation
shown in Figure 11-la. In any of these kinetostatic dynamic force analysis problems,
the kinematics of the problem must first be fully defined. That is, the angular accelerations
of all rotating members and the linear accelerations of the CGs of all moving members
must be found for all positions of interest. The mass of each member and the mass
moment of inertia 10 with respect to each member's CG must also be known. In addition
there may be external forces or torques applied to any member of the system. These
are all shown in the figure.
While this analysis can be approached in many ways, it is useful for the sake of consistency
to adopt a particular arrangement of coordinate systems and stick with it. We
present such an approach here which, if carefully followed, will tend to minimize the
chances of error. The reader may wish to develop his or her own approach once the principles
are understood. The underlying mathematics is invariant, and one can choose coordinate
systems for convenience. The vectors which are acting on the dynamic system
in any loading situation are the same at a particular time regardless of how we may decide
to resolve them into components for the sake of computation. The solution result
will be the same.
We will first set up a nonrotating, local coordinate system on each moving member,
located at its CG. (In this simple example we have only one moving member.) All externally
applied forces, whether due to other connected members or to other systems
must then have their points of application located in this local coordinate system. Figure
11-1b shows a free-body diagram of the moving link 2. The pin joint at 02 on link
2 has a force F 12 due to the mating link I, the x and y components of which are F12x and
F12y' These subscripts are read "force of link I on 2" in the x or y direction. This subscript
notation scheme will be used consistently to indicate which of the "action-reaction"
pair of forces at each joint is being solved for.
As a simple example of this solution procedure, consider the single link in pure rotationshown in Figure 11-la. In any of these kinetostatic dynamic force analysis problems,the kinematics of the problem must first be fully defined. That is, the angular accelerationsof all rotating members and the linear accelerations of the CGs of all moving membersmust be found for all positions of interest. The mass of each member and the massmoment of inertia 10 with respect to each member's CG must also be known. In additionthere may be external forces or torques applied to any member of the system. Theseare all shown in the figure.While this analysis can be approached in many ways, it is useful for the sake of consistencyto adopt a particular arrangement of coordinate systems and stick with it. Wepresent such an approach here which, if carefully followed, will tend to minimize thechances of error. The reader may wish to develop his or her own approach once the principlesare understood. The underlying mathematics is invariant, and one can choose coordinatesystems for convenience. The vectors which are acting on the dynamic systemin any loading situation are the same at a particular time regardless of how we may decideto resolve them into components for the sake of computation. The solution resultwill be the same.We will first set up a nonrotating, local coordinate system on each moving member,located at its CG. (In this simple example we have only one moving member.) All externallyapplied forces, whether due to other connected members or to other systemsmust then have their points of application located in this local coordinate system. Figure11-1b shows a free-body diagram of the moving link 2. The pin joint at 02 on link2 has a force F 12 due to the mating link I, the x and y components of which are F12x andF12y' These subscripts are read "force of link I on 2" in the x or y direction. This subscriptnotation scheme will be used consistently to indicate which of the "action-reaction"pair of forces at each joint is being solved for.
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