Cam Mechanism

cam mechanism

[′kam ‚mek·ə‚niz·əm]
(mechanical engineering)
A mechanical linkage whose purpose is to produce, by means of a contoured cam surface, a prescribed motion of the output link.

Cam Mechanism

 

a mechanism that usually consists of two moving parts (a cam and tappet) and a fixed part (the support). Cam mechanisms produce almost any type of motion of the driven element (the tappet) with continuous motion of the drive element (the cam). To reproduce a complex path of motion of the working units, such as in knitting machines, two cams transmit motion to the tappet.

Cam mechanisms are compact and may be easily introduced into the general scheme of a machine. Some of their drawbacks are heavy wear in the double-action kinematic pair and a tendency toward disconnection at high speeds. To reduce wear, the elements of a cam mechanism are made of high-quality steel and then are tempered and carefully worked. Loss of contact between the cam and the tappet is prevented by forcible connection of the pair, using springs that constantly press the tappet to the cam, or geometrical fastening, in which the cam or tappet is given a shape that makes impossible separation of the tappet from the cam (for example, the cam is constructed with a groove into which the tappet roller fits).

Cam mechanisms are used in various areas of machine building, such as internal-combustion engines, metal-cutting machines, and machines of the food industry, in which the cam mechanism performs a programmed operation, as well as in automated machines, in which cam mechanisms perform control functions, connecting and disconnecting working parts at the proper moment.

REFERENCES

Mashinostroenie: Entsiklopedicheskii spravochnik, vol. 9. Moscow, 1949. Pages 102–10.
Levitskii, N. I. Kulachkovye mekhanizmy. Moscow, 1964.
Popov, N. N. Raschet i proektirovanie kulachkovykh mekhanizmov. Moscow, 1965.

I. G. GERTSKIS

Cam mechanism

A mechanical linkage whose purpose is to produce, by means of a contoured cam surface, a prescribed motion of the output link of the linkage, called the follower. Cam and follower are a higher pair. See Linkage (mechanism)

Classification of camsenlarge picture
Classification of cams

A familiar application of a cam mechanism is in the opening and closing of valves in an automotive engine. The cam rotates with the cam shaft, usually at constant angular velocity, while the follower moves up and down as controlled by the cam surface. A cam is sometimes made in the form of a translating cam. Other cam mechanisms, employed in elementary mechanical analog computers, are simple memory devices, in which the position of the cam (input) determines the position of the follower (output or readout).

Although many requisite motions in machinery are accomplished by use of pin-jointed mechanisms, such as four-bar linkages, a cam mechanism frequently is the only practical solution to the problem of converting the available input, usually rotating or reciprocating, to a desired output, which may be an exceedingly complex motion. No other mechanism is as versatile and as straightforward in design. However, a cam may be difficult and costly to manufacture, and it is often noisy and susceptible to wear, fatigue, and vibration.

Cams are used in many machines. They are numerous in automatic packaging, shoemaking, typesetting machines, and the like, but are often found as well in machine tools, reciprocating engines, and compressors. They are occasionally used in rotating machinery.

Cams are classified as translating, disk, plate, cylindrical, or drum (see illustration). The link having the contoured surface that prescribes the motion of the follower is called the cam. Cams are usually made of steel, often hardened to resist wear and, for high-speed application, precisely ground.

The output link, which is maintained in contact with the cam surface, is the follower. Followers are classified by their shape as roller, flat face, and spherical face. Followers are also described by the nature of their constraints, for example, radial, in which motion is reciprocating along a radius from the cam's axis of rotation; offset, in which motion is reciprocating along a line that does not intersect the axis of rotation (illus. b); and oscillating, or pivoted (illus. a). Three-dimensional cam-and-follower systems are coming into more frequent use, where the follower may travel over a lumpy surface.

References in periodicals archive ?
"The Court construes 'cam mechanism' and the 'member' term to mean 'a structure including two or more cams.' In adopting this construction, the Court has modified DePuy's proposal to account for the fact that cams, by definition, 'make[] sliding or rolling contact with the tibial post as the knee bends.' It is unnecessary to repeat that phrase in defining 'cam mechanism' and the 'member' term, as it is implicitly incorporated by the word 'cam.' The construction adopted by the Court is supported by the intrinsic evidence.
The heart of BorgWarners new EMOD transfer case is a motor-driven rotational cam mechanism which provides both robust clutch control and range shift function.
The cam mechanism has several parameters that must be chosen (i.e., member length and initial position), and for each set of those parameters, a different cam profile able to generate a translational trajectory for the seat can be obtained according to the previous equations.
For example, some works have studied cam applications; an inverter cam mechanism for input torque balancing a high-speed, industrial cam-follower mechanism is designed and optimized (Demeulenaere & De Schutter, 2004).
The case B has a large twist angle, as the control system represented with a kinematically actuated cam mechanism is placed outside the working cavity.
To ensure smooth running and fast response, the flow of air is controlled by a simple cam mechanism in many CAE systems [7-9].
These include a roller gear cam mechanism for the C-axis, a different design for the slideway covers, a new tool-change mechanism, and an increased tool capacity.
The cam mechanism alters the vertical position of drawers up to 1/8 in.
The 1940 version is an improvement over the 1914 adjustable wrench for auto assembly, but still a far cry from the self-adjusting RoboGrip pliers of today, which include a cam mechanism that adjusts the jaws as the handle is squeezed.
The parts are connected with ingenious two-part knock-down fasteners consisting of a connecting bolt that screws into the side panels and a cam mechanism mounted in each fixed shelf and cleat.
(1988) for a CAM mechanism that would couple [H.sup.+] disposal with [K.sup.+] uptake.