Introduction of the hottest high-speed cam mechani

2022-09-21
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Introduction to high-speed cam mechanism

when discussing the design of cam mechanism, it is usually to regard all components in the mechanism (except the force locking spring) as absolute rigid bodies, without considering the influence of elastic deformation of components on motion. At this time, the motion law of each point on the follower is the same, which is determined by the contour curve of the cam. However, for the cam mechanism with high running speed and low component rigidity, due to the large inertia force, the elastic deformation of the component and the vibration of the system under the excitation force cannot be ignored. For example, the elastic deformation and vibration of the direct moving follower will cause the displacement of the output end of the follower to be inconsistent with the displacement of the input end (such as the tip bottom of the follower or the center of the roller), so that the actual output displacement of the cam mechanism deviates from the expected requirements, that is, there is a dynamic displacement error at the output end of the follower. Therefore, in order to make the actual motion law of the output end of the follower meet the expected requirements, the cam mechanism must be designed as an elastic system

As an elastic system, high-speed cam mechanism will vibrate under the action of exciting force. The main causes of vibration are as follows:

1) periodic motion of cam

2) the cam is the machining error of the zero point contour

3) inertia force of moving components

4) in the spring force locking cam mechanism, the follower instantly disengages from the cam contour

5) instantaneous sudden change of external load

6) motor pair clearance

7) other interference forces

due to the elastic deformation of components and the vibration of the system, the design of high-speed cam mechanism will involve the following problems:

1) establishment of elastic dynamic model

in order to simplify the calculation, the continuous distributed mass of components is usually regarded as a concentrated mass concentrated at one or several points, the elasticity of components is represented by massless springs, and the damping of the system is represented by massless and inelastic damping elements, Ignoring some secondary influencing factors, the cam mechanism is simplified into an elastic system composed of several inelastic lumped masses, massless springs and damping elements. For example, for a disc-shaped cam mechanism with a straight follower in contact with the tip bottom, In the case of considering only the elasticity of the follower, "nowadays, plastic building materials have made greater and greater contributions to the construction industry and urban construction (generally, the rigidity of the cam is much higher than that of the follower), and its dynamic model is shown in the figure. The differential equation of motion of the elastic system is:

where: m is the mass of the follower; KF is the spring stiffness of the follower; KS is the spring stiffness of the force locking spring; YC is the input end (sharp bottom) of the follower." Displacement is related to the shape of cam contour curve; Ys is the displacement of the output end of the follower; C is the damping coefficient; Q is the working load

2) determination of the true motion law of the output end of the follower

when YC (T) is known, pan Xue said that the true displacement law ys (T) of the output end of the follower can be obtained from the above formula, that is, the dynamic displacement response of the output end of the follower to the excitation

3) residual vibration

for the cam mechanism whose motion law at the input end of the follower is rise stop fall stop, the vibration of the system in the push and return stages is called the main vibration. The main vibration will continue to the rest stage at the input end of the follower, and the vibration at the rest stage at the input end of the follower is called residual vibration. In the rest stage, the system is no longer excited by the appearance of the additional mini car, which has gone through several evolutionary stages. At the same time, due to the existence of damping, the residual vibration is attenuated free vibration. Residual vibration will affect the position accuracy of the output end of the follower at both ends of the stroke, which should be controlled

4) selection of the motion law of the output end of the follower and design of the cam contour curve

in the design of high-speed cam mechanism, ys (T) should meet the requirement that the first and second derivatives of YC (T) are continuous to avoid the impact of the input end. When ys (T) is selected, the input motion law YC (T) can be obtained from the above formula, and then the cam contour curve can be designed

5) ensure that the input end of the follower is always in contact with the cam contour curve

during the operation of the high-speed cam mechanism, sometimes the input end of the follower will jump off the cam instantly, and then contact the cam again, resulting in the so-called "jumping" vibration. For the high-speed cam mechanism locked by spring force, it mainly depends on the correct design of the spring to prevent jumping

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