The cam mechanism is a complex auxiliary mechanism consisting of three main components: a cam, a follower, and a frame.
The cam is a component with a curved profile or groove and serves as the active member for continuous rotary motion at a constant speed or reciprocating linear motion.
Introduction
The follower is a component that comes into contact with the cam profile and transmits power to produce a specific motion, typically reciprocating linear motion or oscillation.
One of the key features of the cam mechanism is that it can produce more complex motions for the follower.
The motion of the follower is determined by the cam profile curve, so the cam’s contour curve can be designed to meet the desired motion for the follower.
Cam mechanisms are commonly used in a variety of automatic machinery, instruments, and steering controls due to their ability to fulfill a wide range of complicated motion requirements and their simple and compact structure.
Common materials
45, 40Cr, 9sicr, 40crMo
Working Principle
The cam mechanism propels the reciprocating movement or oscillation through the rotary motion or reciprocating motion of the cam.
The cam can have various shapes including a disc cam, a cylindrical cam, a moving cam, etc. The groove curve of the cylindrical cam is a space curve and is referred to as a space cam.
The follower is in either point or line contact with the cam and can be a roller follower, a flat bottom follower, or a tip follower. The tip follower can maintain contact with any complex cam profile for any movement, but it is susceptible to wear and is suitable for low-speed mechanisms with low transmission force. To keep the follower in contact with the cam, a spring or gravity can be used.
The cam mechanism is compact and ideal for applications that require intermittent movement of the follower. It is reliable in motion and is commonly used in automatic machine tools, internal combustion engines, printing presses, and textile machines.
However, the cam mechanism is prone to wear and noise, and the design of high-speed cams can be complicated and requires high manufacturing standards.
Classification of cam mechanisms
By shape:
1) Disc cam
2) Moving cam
3) Cylindrical cam
By follower type:
1) Apex follower;
2) Roller follower;
3) Flat bottom follower
By locking:
- Force locking: spring force, gravity, etc.;
- Geometric locking: equal-diameter cam, equal-width cam;
Characteristics
Advantages:
- Simple, compact and easy to design structure, making it widely used in machine tools, textile machinery, light industrial machinery, printing machinery, and electromechanical integration.
- The cam profile can be designed to produce any desired motion for the follower.
Disadvantages:
- High wear due to point or line secondary contact between the cam and the follower.
- Difficult and costly to process the cam profile.
- Limited stroke.
Characteristics of motion
In a disc-actuated counter-moving disc cam mechanism with a roller, the cam rotates one revolution to complete the four actions of ascending, stopping, descending, and stopping. The displacement curve, which represents the relationship between the follower’s displacement or stroke height and the cam angle or time, determines the shape of the cam profile curve.
The stroke height of the follower has both a push and return stroke. In some cases, the displacement curve is set by the process, but usually, only the stroke and corresponding cam angle are determined based on the work requirements, and the curve shape is selected by the designer.
There are various conventional cam motion laws, including constant velocity, equal acceleration, cosine acceleration, and sinusoidal acceleration. The constant velocity motion law has a strong rigid impact and is only suitable for low speeds.
In order to make the acceleration of the cam mechanism and its speed change rate not too high, and considering factors such as momentum, vibration, cam size, spring size, and process requirements, various motion laws can be designed.
There are a variety of useful motion curves, such as deformation sinusoidal acceleration, deformation trapezoidal acceleration, and deformation velocity law. These motion laws can also be combined using an electronic computer.
Additionally, a motion law represented by a polynomial can be used to obtain a continuous acceleration curve. To achieve the most satisfactory acceleration curve, the acceleration curve can be given in numerical form, and then the displacement curve can be obtained using the finite difference method, and finally the convex contour can be designed.
To ensure that the movements of various parts controlled by multiple cams are coordinated, it is important to prepare a correct motion cycle diagram and reduce the surface roughness before the cam design process.
The working conditions for the cam include air drying, clean lubricating oil, or lubricating oil with various additives. The viscosity of the lubricating oil and the oil supply method should be chosen based on the shape of the follower and the rotational speed of the cam.
The materials used for the cam and follower should be properly matched for high-speed sliding, such as hard steel and cast iron. Hard steel and phosphor bronze can reduce vibration and noise, and compensate for inaccuracies in the profile.
Pairing cast iron with cast iron is acceptable, but the combination of hard nickel steel and hard nickel steel or mild steel and mild steel is not effective. Comprehensive calculations, including geometric parameters, lubrication, materials and surface roughness, can be made using elastic fluid dynamic lubrication theory to reduce wear.
