The composition and classification of Cam mechanisms
The cam mechanism generally consists of two moving parts, namely the cam and the follower, both of which are fixed to the frame. The cam device is highly versatile and can generate almost any arbitrary movement.
A cam can be defined as a component with a curved surface or groove. By swinging or rotating it, another component, the follower, can provide a predefined movement. The follower path is mainly limited to a slit to achieve alternative movement.
Although they sometimes rely on their own weight during the return stroke, some mechanisms use springs as a return force to achieve precise movements. Others use guide rails to move along specific paths.
According to the shape of the cam, it can be divided into three types: disc cam, movable cam and cylindrical cam.
Followers can be divided according to their purposes into three types: pointed followers, roller followers and flat-bottomed followers.
(a) Pointed follower; (b) Roller follower: (c) Flat bottom follower
Due to the point contact between the sharp tip follower and the cam, which leads to high tension and rapid wear, it is not suitable for low-speed cam mechanisms with large impact. The roller follower can overcome these shortcomings.
To improve the transmission efficiency, we can also introduce a flat-bottom follower perpendicular to the direction of force on the bottom surface.
The transmission components we considered previously have the form of rectilinear motion, but they can also have the form of oscillating motion. The former is called a direct action follower and the latter is called an oscillating follower.
We can also make it so that the cam's center of rotation is not in the linear path of the follower's movement. Right now, we call this displacement. Similarly, if the center of rotation is on the linear path of the follower's motion, we can call it concentric.
In addition, we can also consider methods to maintain high-voltage locking relationships and divide the mechanism into geometric locking and forced locking.
By combining the cam shape, follower end, and follower movement patterns, we can determine the name of the designed mechanism, such as: the disc cam with a sharp-edge direct-acting follower (relative position of follower cam + end follower + follower movement pattern + cam shape).
The Movement Process of Cam Mechanisms
First, we have a camera with a follower placed on it. When the cam rotates at an angular velocity ω by φs degrees, the follower does not move. At this time, we call φs the angle of stay, and the circle corresponding to it is called the base circle. Similarly, the radius of this circle is called the base circle radius r0.
Then, as we continue to rotate the cam at an angular velocity ω by φ degrees, the follower moves up h. At this time, we call φ the stroke angle and h is called the stroke.
Later, when the follower reaches point h, we let it stay for a period of time. Meanwhile, the cam rotates φs', which corresponds to the lift angle.
Finally, we need to bring the follower back to its original position, so we rotate the cam by φ'. At this point, the follower returns to the starting point. We call φ' the return angle.
How to design a Cam mechanism ?
There are two main methods for designing cam mechanisms, one is the graphical method and the other is the analytical method.
The first is relatively simple, only requiring the desired impulse motion diagram to be provided and then obtaining the corresponding contour curve based on the angle-process relationship provided by the diagram.
The accuracy is not very high. The latter is calculated and its calculation is relatively complex, which is suitable for designing cam mechanisms with high precision requirements.
