Each of the component parts constituting a mechanism.
Solid body as a mechanism element, having one or more kinematic pairs with other bodies.
Link for which at least one of the position components is considered as an independent variable.
Link performing the required motion or force as intended for the design of the mechanism.
Link of a mechanism deemed to be fixed.
Link that carries only revolute joints.
Link able to rotate completely about a fixed axis.
Link that oscillates within a limited angle of rotation about a fixed axis.
COUPLER [FLOATING LINK]
Link that is not connected directly to the frame.
Link that forms a prismatic pair with one link and a revolute pair with another link.
Compact element of a prismatic pair which slides along a guiding element (e.g. in a slot).
Element of a prismatic pair that is fixed to the frame and constrains the motion of a sliding block.
Component between a piston and a connecting rod which, by forming a prismatic joint with the frame, provides a reaction to the component of force in the connecting rod normal to the line of stroke of the piston.
Coupler between a piston or a crosshead and a crank shaft.
Component with a curved profile or surface whereby it imparts a displacement either by point or line contact with a cam follower.
Disk that rotates about an axis perpendicular to its plane and drives a follower through contact with its profile.
Rotating cam that makes contact with a follower by means of a groove in or a rib on a plane surface that is perpendicular to the axis of the cam.
CYLINDRICAL [BARREL] CAM
Rotating cylinder with a curved groove in its surface or a curved rib on its surface whereby contact is made with a follower.
Rotating hollow sphere with a groove in or a rib on its inner surface to make contact with a follower.
Constant-breadth radial cam designed to mesh with a yoke follower.
Component that receives motion directly from a cam.
Cam follower with two surfaces integral with each other and each in contact with the same cam.
Shaft on which a cam or cams are fitted.
Wheel with teeth on its surface designed to mesh with another gear or rack.
Gear with teeth formed on a cylindrical surface.
Cylindrical gear with external teeth.
Cylindrical gear with internal teeth.
GEAR SECTOR [SEGMENT]
Segment of a spur gear or annulus.
Gear with teeth wrapped helically on a cylindrical surface.
HERRING-BONE [DOUBLE-HELICAL] GEAR
Gear comprising two integral helical gears, the helices of the gears being of opposite hand.
BEVEL [CONICAL] GEAR
Gear with teeth formed on a conical surface.
Spiral-bevel gear pair with offset between the gear axes.
Gear with one or more teeth wrapped helically on a cylinder (or a globoid), the pitch of the helix being less than the diameter of the gear.
Gear that mates with a worm gear.
PLANETARY [PLANET] GEAR
Gear that rotates on an axle whose own axis is constrained to rotate about another axis.
1. The smaller of a pair of meshing cylindrical gears. 2. Cylindrical gear meshed with a rack.
Segment of a cylindrical gear of infinite radius.
Gear intermediate between a driving and a driven gear, which affects the sense of rotation of the latter but does not affect the velocity ratio.
Wheel that transmits a driving force to the surface of a second component by friction at the point or line of contact.
Flexible element such as a strap or rope used in tension to transmit force and motion.
Wheel used to change the direction of motion of a belt by wrapping the belt round part of its periphery.
Mechanism element consisting of a number of short rigid links hinged together for use in the manner of a belt.
Wheel with teeth (sprockets) round its rim designed to engage the links of a chain.
Shaft used to transmit torque.
Drive shaft connecting two universal couplings.
1. A fixed axis about which revolute motion can take place 2. Inner element of a revolute joint
The inner element of a revolute or cylindrical joint
Machine component that allows relative motion (rotation, translation) and transmission of force between adjacent components.
PAWL [CLICK, DETENT]
Component which is intermediate between two elements and which prevents motion between them in one direction.
Movable component which holds another component in place by entering a notch or a cavity, e.g. the locking device of a ratchet.
Element which has a frictional or serrated surface to engage with a pawl.
Component of a machine that makes intermittent contact with another component to provide a limit to their relative motion.
Identifiable set of components forming part of a machine.
Physical representation of a kinematic pair.
Connection between two links restricting their relative motion.
Assembly of surfaces, lines or points of a solid body through which it may contact with another solid body.
DEGREE OF FREEDOM [CONNECTIVITY] OF A KINEMATIC PAIR
Number of independent coordinates needed to describe the relative positions of the links involved with the kinematic pair.
CLOSURE OF A KINEMATIC PAIR
Process of constraining two rigid bodies to form a kinematic pair by force (force closure), geometric shape (form closure), or flexible materials (material closure).
FORCE-CLOSED [OPEN] PAIR
Kinematic pair the elements of which are held in contact by means of external forces.
Kinematic pair the elements of which are constrained to contact each other by means of particular geometric shapes.
Kinematic pair that is formed by surface contact between its elements.
Kinematic pair that is formed by point, or line, contact between the elements.
REVOLUTE PAIR [HINGE]
Pair that allows only rotary motion between two links.
Pair that allows only rectilinear translation between two links.
HELICAL [SCREW] PAIR
Pair that allows only screw motion between two links.
Pair for which the degree of freedom is two and that allows a rotation about a particular axis together with an independent translation in the direction of this axis.
Pair for which the degree of freedom is three and that allows independent relative rotations about three mutually orthogonal axes
PLANAR CONTACT [SANDWICH] PAIR
Pair for which the degree of freedom is three and that allows relative motion in parallel planes.
Kinematic pair consisting of a cam and follower in direct contact.
UNIVERSAL [CARDAN, HOOKE'S] JOINT; [UNIVERSAL COUPLING]
Kinematic joint connecting two shafts with intersecting axes.
Joint using a pin as the connecting component between two rigid bodies.
Higher kinematic pair formed by successively contacting elements ("teeth") of two links.
Device for joining two moving members, e.g. two shafts at their ends.
Coupling for torque transmission along a shaft that allows for easy engagement and disengagement during operation.
Rotor used for storing kinetic energy.
Sub-assembly which causes relative motion between the parts to which it is attached in response to a signal.
System of mutually connected devices for setting in motion one or several parts of a machine or a mechanism.
Difference between dimensions of mating parts that allows unconstrained motion.
INPUT KINEMATIC PAIR [INPUT JOINT]
Kinematic pair [joint] for which the position of one link relative to the other link is considered as an independent variable.
STRUCTURE (OF A MECHANISM)
Number and kinds of elements in a mechanism (members and joints) and the sequence of their contact.
Equality of structures in respect of the numbers of members and joints, and the sequence of their inter-connections.
Mechanism whose kinematic properties are equivalent in some respects from those of another mechanism with a different structure.
Mechanism that is geometrically different from another but which, nevertheless, has the same transfer function.
System of interconnected links permitting relative motion of any one link with respect to the remaining links.
CLOSED KINEMATIC CHAIN
Kinematic chain each link of which is connected with at least two other links.
OPEN KINEMATIC CHAIN
Kinematic chain in which there is at least one link connected to only one other link.
Kinematic chain whose kinematic properties are equivalent in some respects to those of a kinematic pair.
Subset of links that forms a closed circuit.
Kinematic chain that contains no loops.
DEGREE OF FREEDOM [MOBILITY] OF A MECHANISM OR KINEMATIC CHAIN
Number of independent variables that must be considered for input motion.
Smallest kinematic chain which when added to, or subtracted from, a mechanism results in a mechanism that has the same mobility as the original mechanism.
Any condition that reduces the degree of freedom of a system.
Transformation of one mechanism into another by choosing a different member to be the frame.
LIMIT POSITION OF A MECHANISM
Configuration of a mechanism in which one of its links is in a limit position.
LIMIT POSITION OF A LINK
Position of a link for which a coordinate which describes its position relative to an adjacent link is a maximum or a minimum.
Mechanism in which all points of its links describe paths located in parallel planes.
Mechanism in which all points of its links describe paths located on concentric spheres.
Mechanism in which some points of some of its links describe non-planar paths, or paths located in non-parallel planes.
Mechanism that guides a link through a prescribed sequence of positions.
Mechanism that generates a required functional relationship between the displacements of its input links and output links.
Mechanism in which a point on a member generates a given path.
Mechanism whose output motion is uni-directional with periodic dwells.
Mechanism whose output motion is uni-directional overall, but has periodic reversals.
Mechanism in which the output link performs reciprocating or rocking motion with periodic dwells.
Mechanism for which the degree of freedom is two and which may accept two inputs to produce one output or may resolve a single input into two outputs.
Mechanism that is incapable of transmitting motion and power from the output to the input.
Mechanism whose primary dimensions (e.g. link lengths) can be altered.
Kinematic chain whose joints are equivalent to lower pairs only.
Linkage with four binary links.
Mechanism with four binary links.
Four-bar mechanism with a crank and a rocker.
DOUBLE-CRANK [DRAG-LINK] MECHANISM
Four-bar mechanism with two cranks.
Four-bar mechanism having cranks of equal length and a coupler with length equal to that of the frame.
Four-bar mechanism with two rockers.
Four-bar mechanism with a crank and a slider in which the frame forms one element of the prismatic pair.
Four-bar mechanism with two sliders in which the frame forms one element of each of the prismatic pairs.
Four-bar mechanism in which a crank is connected by a slider with another link which, in turn, forms a prismatic pair with the frame.
Mechanism that includes at least one cam.
Mechanism that includes at least one screw pair.
Mechanism whose links form prismatic pairs only.
Assembly containing more than one pair of gears.
Bevel gear pair with equal gears whose axes intersect at right angles.
EPICYCLIC [PLANETARY] GEAR (TRAIN)
Gear train in which a planetary gear meshes with two gears that are both centred on the axis about which the centre of the planet rotates.
Combination of a linkage and a gear mechanism.
GENEVA MECHANISM [GENEVA DRIVE]
Mechanism involving a crank whose pin intermittently engages a slot in a driven member, e.g. in the form of a Maltese cross.