Editing Simple machine (section)

==Modern machine theory==
Machines are studied as mechanical systems consisting of [[actuator]]s and [[mechanism (engineering)|mechanism]]s that transmit forces and movement, monitored by sensors and controllers. The components of actuators and mechanisms consist of links and joints that form kinematic chains.

===Kinematic chains===
[[File:Kinematics of Machinery - Figure 21.jpg|thumb|right|200px|alt=Illustration of a Four-bar linkage from Kinematics of Machinery, 1876|Illustration of a four-bar linkage from [[s:The Kinematics of Machinery|Kinematics of Machinery, 1876]]]]Simple machines are elementary examples of [[kinematic chain]]s that are used to model [[mechanical systems]] ranging from the steam engine to robot manipulators. The bearings that form the fulcrum of a lever and that allow the wheel and axle and pulleys to rotate are examples of a [[kinematic pair]] called a hinged joint. Similarly, the flat surface of an inclined plane and wedge are examples of the kinematic pair called a sliding joint. The screw is usually identified as its own kinematic pair called a helical joint.

Two levers, or cranks, are combined into a planar [[four-bar linkage]] by attaching a link that connects the output of one crank to the input of another. Additional links can be attached to form a [[six-bar linkage]] or in series to form a robot.<ref name="Uicker2003"/>

===Classification of machines===
The identification of simple machines arises from a desire for a systematic method to invent new machines. Therefore, an important concern is how simple machines are combined to make more complex machines. One approach is to attach simple machines in series to obtain compound machines.

However, a more successful strategy was identified by [[Franz Reuleaux]], who collected and studied over 800 elementary machines. He realized that a lever, pulley, and wheel and axle are in essence the same device: a body rotating about a hinge. Similarly, an inclined plane, wedge, and screw are a block sliding on a flat surface.<ref>Hartenberg, R.S. & J. Denavit (1964) [http://kmoddl.library.cornell.edu/bib.php?m=23 Kinematic synthesis of linkages], New York: McGraw-Hill, online link from [[Cornell University]].</ref>

This realization shows that it is the joints, or the connections that provide movement, that are the primary elements of a machine. Starting with four types of joints, the [[revolute joint]], [[prismatic joint|sliding joint]], [[Cam (mechanism)|cam joint]] and [[gear train|gear joint]], and related connections such as cables and belts, it is possible to understand a machine as an assembly of solid parts that connect these joints.<ref name="Uicker2003"/>

===Kinematic synthesis===
The design of mechanisms to perform required movement and force transmission is known as [[kinematic synthesis]]. This is a collection of geometric techniques for the mechanical design of [[linkage (mechanical)|linkage]]s, [[Cam (mechanism)|cam and follower mechanisms]] and [[Gear train|gears and gear trains]].