Mechanized systems of food and fiber production used in agriculture. The mechanized systems comprising agricultural machinery are utilized in numerous aspects of agriculture, including the initial tillage of the soil (Fig. 1), planting, cultural practices during the growing season, protection from pests, harvesting, conditioning, livestock feeding, and delivery for processing. The use of hydraulic power, which offers the advantages of being easily controlled and automated, made possible highly specialized mechanisms to perform intricate operations. Modern technology has been used to increase the precision needed in modern agriculture, with examples including lasers for laying out fields for surface irrigation systems; microprocessors for sensing and controlling intricate operations, such as controlling feed mixtures for dairy cows and grading fruits and vegetables; and electronic devices in the automation of many harvesters. See also: Agricultural engineering; Agricultural science (animal); Agricultural science (plant); Agricultural soil and crop practices; Agriculture; Dairy machinery; Hydraulics; Laser; Microprocessor

The lowest-cost means for transmitting power between shafts that are not necessarily parallel. Belts run smoothly and quietly, and they cushion motor and bearings against load fluctuations. Belts typically are not as strong or durable as gears or chains. However, improvements in belt construction and materials are making it possible to use belts where formerly only chains or gears would do.

Combination of a rope or other flexible material and independently rotating frictionless pulleys; the pulleys are grooved or flat wheels used to change the direction of motion or application of force of the flexible member (rope or chain) that runs on the pulleys. As in a lever, the summation of torques about the axis of rotation of the pulley equals zero for static equilibrium. Tension T in the rope is the same on both sides of the pulley. See also: Lever

A cylindrical fastener with an integral head on one end and an external screw thread on the other end designed to be inserted through holes in assembled parts and to mate with an internally threaded block, called a nut, which is turned to tighten or loosen the bolt. Tensioning the fastener by turning the nut differentiates a bolt from a screw, which is tightened by turning its head. See also: Bolted joint; Nut (engineering)

An assembly of two or more parts fastened together by inserting bolts through matching clearance holes in the parts and engaging nuts that are then tightened to clamp the assembly. The term bolted joint also colloquially denotes a screwed joint, for which screws are inserted through clearance holes in one part and tightened into internal threads in another part by turning the screw head. See also: Bolt

An instrument with two legs used for measuring linear dimensions. Calipers may be fixed, adjustable, or movable. Fixed calipers are used in routine inspection of standard products; adjustable calipers are used similarly but can be reset to slightly different dimensions if necessary. Movable calipers can be set to match the distance being measured. The legs may pivot about a rivet or screw in a firm-joint pair of calipers; they may pivot about a pin, being held against the pin by a spring and set in position by a knurled nut on a threaded rod; or the legs may slide either directly (caliper rule) or along a screw (micrometer caliper) relative to each other. See also: Micrometer

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 also: Linkage (mechanism)

A link in several kinds of mechanisms. Usually one end of a connecting rod is intended to follow a circular path, while the other end follows a path along a straight line or a curve of large radius. The term is sometimes applied, however, to any straight link that transmits motion or power from one linkage to another within a mechanism. Figure 1 shows conventional arrangements of connecting rods in typical mechanisms. In some applications (for example, the connecting rod between the crank and an overhead oscillating member or walking beam in a well-drilling rig, or between the steering column and cross-links in an automobile) the connecting rod is called a pitman. See also: Automotive steering

Specifications of materials, physical measurement processes, performance of product, and characteristics of services rendered. Design standards (see figure) may be established by individual manufacturers, trade associations, and national or international standards organizations. Design standards may also be de facto standards; that is, the standards may be informally but universally accepted by those using them. The general purpose of design standards is to realize operational and manufacturing economies, to increase the interchangeability of products, and to promote uniformity of definitions of product characteristics. See also: Manufacturing engineering; Product design

The ratio, expressed as a percentage, of the output to the input of power (energy or work per unit time). As is common in engineering, this concept is defined precisely and made measurable. Thus, a gear transmission is 97% efficient when the useful energy output is 97% of the input, the other 3% being lost as heat due to friction. A boiler is 75% efficient when its product (steam) contains 75% of the heat theoretically contained in the fuel consumed. All automobile engines have low efficiency (below 30%) because of the total energy content of fuel converted to heat; only a portion provides motive power, while a substantial amount is lost in radiator and car exhaust. See also: Automotive engine; Boiler; Power