The work of most man-made mechanisms is based on the energy of rotation. Sometimes, observing from the side the functioning of a machine (in this case, it is not a car, but a mechanism), it may seem that there is no rotation, but often the first impression is misleading. The fact is that many machines use various technical solutions that allow you to convert the original nature of the movement in its other form. One of the most striking examples is the cam mechanism. With its help, it becomes possible to “get” translational or oscillatory from rotational motion . Where exactly can we meet the cam mechanism?
Unobvious facts
Surely, in every family, among the necessary tools, there is an electric drill of shock: on its body there is a special switch that allows you to choose the operating mode - only rotation of the drill or translational-reverse displacement along with rotation. In the first case, no questions arise: the electric motor transmits part of its revolutions to the drill through the shaft and gearbox. But what happens when the punch mode is turned on? There is nothing complicated - just the cam mechanism comes into effect, which converts part of the torque to horizontal displacement. A similar solution is used in many tools and household appliances. Also, without such mechanisms, the existence of internal combustion engines in their classical form would be impossible.
Simplicity of construction and low cost are the main advantages of such mechanical converters. There is also a drawback - if the actuator is subjected to excessive pressure (resistance to movement), then damage to the elements is possible. For example, in order to break a percussion drill , it is enough to press the drill to the surface when drilling a hole, actually blocking its translational movement.
From examples to practice
The cam mechanism is one of the varieties of the kinematic pair, consisting of only two links (the presence of a stand is implied) - a pusher and a cam. The surface of the latter, on which the sliding occurs, is made profiled, which allows you to transmit a momentum of movement to the pusher mated to it. Cams can be of the most diverse form: flat, spherical, cylindrical, complex spatial configuration, etc. Thus, it is possible to divide only into two generalizing groups - spatial and flat.
Consider how the simplest cam mechanisms of a flat type are arranged. The output link can move both translationally (slider) and rotate (rocker). The side of the link in contact with the cam can be made in the form of a plane, hemisphere, tip, or equipped with a roller to reduce wear.
In the case of a slider, a cam with an egg-shaped cross section rotates around its axis. Since the shape is different from the circle, at the tops the pusher with the roller is lifted, making translational movement along the guides. The decline of the top - and the roller goes down, returning the link back. The design with the beam is devoid of a guiding device, so the roller is completely “rolled” along the cam, which causes the link to move in accordance with the axis of rotation.
Reliable operation of cam mechanisms is possible only with reliable contact of the pusher and the cam itself. To solve this issue, several approaches are used: the output link is spring-loaded; in the body of the rotating part, a groove is made in which the pusher roller is fixed. The recess itself can allow the roller to roll, rather than fixing it at one point.
The synthesis of the cam mechanism is necessary for the accurate selection of the required process parameters. First, the structural part of the scheme is created, which takes into account the number of kinematic pairs, links, their degrees of freedom, types of connections. The next step is the metric. Depending on the required parameters, the sizes of all the main elements are selected. This takes into account the most rational form of the cam, the force at the vertices, the consumption of material to create the structure.