【Mechanical Equipment Technology Exchange Edition】Mechanical Equipment 【Daily Question】20210417
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True or False: In a crank-rocker mechanism, when the crank is the driving element, a dead center position occurs. (X) For the daily question activity in the moving equipment section, please reply within three days. Correct answers earn rewards ranging from 5 to 15 points; those who provide detailed answers receive additional rewards. Those who get it wrong receive no points. All forum members are welcome to participate actively and help promote the development of the forum! ! !
Error: In a crank-rocker mechanism, when the crank acts as the driving element, there are no dead points. From Ft = Fcosα, it can be seen that when the pressure angle α = 90°, the force or torque acting on the follower is zero; at this point, the linkage cannot drive the follower to move. The mechanism finds itself at this position, which is a dead point, also known as a limit point. The dead center is the position on a straight line. In planar link mechanisms, if the rocker or slider serves as the driving element, the mechanism cannot be activated no matter how large the driving force is, when the other two moving components are in a position on the same straight line. An internal combustion engine is a specific example of a crank-slider mechanism. The piston in an internal combustion engine’s cylinder acts as the slider in such a mechanism, while the crankshaft functions as the crank; therefore, an internal combustion engine also has two dead center positions during its operation. When starting the mechanism, it is necessary to avoid the dead center position; during movement, inertia can be utilized to get past the dead center. In practical engineering applications, the dead points of mechanisms are often utilized to meet specific operational requirements. To enable the mechanisms to pass through the dead points and operate normally, appropriate measures must be taken. For example, it is possible to use a combination of two or more groups of mechanisms, so that the dead points of each group are staggered relative to one another; or a flywheel can be installed to increase inertia, allowing the mechanism to overcome the dead points thanks to this inertia, and so on.
Wrong; in a crank-rocker mechanism, a \"dead center\" position only occurs when the rocker is the moving element
This post was last edited by Yang Qing on 2021-4-18 at 19:26. Correct; maybe the understanding is reversed,,,;P
Wrong; in a crank-rocker mechanism, a \"dead center\" position only occurs when the rocker is the moving element