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Ensuring the correct work of mechanical connection matings |
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To ensure the expected mutual movement of components connected by a mechanical connection mating, it is recommended that these components have minimum degrees of freedom necessary for making movements within the mechanical connection matings. You can reduce the number of degrees of freedom for a component using its positioning matings with other objects, as well as using fixation.
Usually, if the positioning matings in the product model are imposed so that the components have the same degrees of freedom as the parts and nodes in the actual structure, then the operation of the mechanical connection matings does not require additional restrictions.
See the examples.
1. Rotation – Rotation
Consider a mating between two gear wheels where the wheels should rotate around fixed axles (for example, wheels 1 and 2 in the figure).
Before overlaying a mechanical connection mating, you need to ensure:
•immobility of the axes in the coordinate system of the model,
•coaxiality of the wheels and their respective axles.
Usually the wheels do not have the ability to move along the axes of rotation — this can be achieved by associating the flat end faces of the wheels with any fixed flat object by a Coincidence or At Distance mating.
Thus, each wheel will have one degree of freedom of rotation around the axis.
After applying the mating Rotation – rotation rotation of either wheel will result in the rotation of the other wheel.
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Please note that immobility of the rotation axes of the wheels is necessary for this particular example. In other cases, the axes may be able to move, for example, the axes of the satellite wheels in planetary gears. |
2. Rotation – Movement
Example 1. Consider a mating between a wheel and a rail where the wheel, while rotating, should move the rail (for example, as in the figure).
Before overlaying a mechanical connection mating, you need to ensure:
•immobility of the wheel axis in the coordinate system of the model,
•coaxiality of the wheel and the axis,
•consistency of the rail orientation with respect to the wheel axis (this can be done in different ways, for example, by connecting a straight rail edge to one fixed plane using an At Distance mating and to another one using a Coincidence mating),
As in the previous example, you can overlay a mating that prevents the wheel from moving along the axis.
Thus, the wheel will have one degree of freedom of rotation around its axis, and the rail will have one degree of freedom of translational motion.
After applying the mating Rotation – Translation, the rotation of the wheel will cause the rack to move and vice versa, moving the rack will cause the wheel to rotate.
Example 2. Consider a mating between a screw and a nut where the screw, while rotating, should move the nut.
Before overlaying a mechanical connection mating, you need to ensure:
•inability for the screw to drift along the axis of rotation,
•coaxiality of the screw and the nut.
Thus, the screw will have one degree of freedom of rotation around the axis, and the nut will have two degrees of freedom: rotation around the axis and moving along it.
After applying the mating Rotation – Linear Movement , the rotation of the screw will cause the movement of the nut and vice versa, the movement of the nut will cause the screw to rotate.
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The screw in this mate may be fixed. Then the nut will rotate when moving. If both the screw and the nut have two degrees of freedom (rotation and movement), then the correct operation of the mate will become impossible. |
3. Cam – Pusher
Consider a mating where the cam, while rotating, should move the pusher along a straight path (for example, as in the figure).
Before overlaying a mechanical connection mating, you need to ensure:
•immobility of the cam rotation axis in the coordinate system of the model,
•constancy of the orientation of the pusher with respect to the trajectory of its movement (this can be done in different ways, for example, if the pusher has a circular cross section, by setting its coaxiality with the fixed axis).
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Work surfaces of the cam and the pusher are automatically brought into contact after the Cam-Pusher mate by moving the pusher along its trajectory. You need to make sure that the shape and interposition of the cam and the pusher, as well as overlaying the mate on them, do not hinder this. There is no need to overlay the Tangency mate on the cam and the pusher. |
It is recommended to overlay matings on the cam preventing it from moving along the axis of rotation — in order to keep the cam in contact with the pusher.
Thus, the cam will have one degree of freedom of rotation around the axis, and the pusher will have one degree of freedom of translational motion; the fact that the pusher has a degree of freedom of rotation around the trajectory does not matter.
After overlaying the Cam-Pusher mating rotation of the cam will cause the pusher to move. Transmission of movement in the opposite direction — from the pusher to the cam — in the Cam-Pusher mating is not provided.
