why the angular position of bar2 is negative?

In the four bar linkage, I do not understand why the angular position of bar 2 is negative. I attached the matlab figures showing the positions of the 4 joints as well as the simscape model of the four bar linkage. I also need to understand why the position of the motor joint is linear. I expected it to be periodic (after achieving a cycle of 2pi, it will restart from zero).

Thanks in advance

Answer 1

[Vinay]

Hi Ouchen,

The angular position of the second bar linkage is negative due to the opposite connection of the base frame and the follower frame.

The position is not periodic due to the fixed linear position of the first “revolute joint”,causing the linear motion of the successor joints in the linkage.

Kindly refer to the below Simulink example of “4-bar linkage” for more details:

https://www.mathworks.com/help/sm/ug/prescribe-joint-motion-in-four-bar-model.html