1

Structure of Machines and Mechanisms

English

1.1


Components

1.1.1 MECHANISM ELEMENT
Each of the component parts constituting a mechanism.
1.1.2 LINK
Solid body as a mechanism element, having one or more kinematic pairs with other bodies.
1.1.3 INPUT LINK
Link for which at least one of the position components is considered as an independent variable.
1.1.4 OUTPUT LINK
Link performing the required motion or force as intended for the design of the mechanism.
1.1.5 FRAME
Link of a mechanism deemed to be fixed.
1.1.6 BAR
Link that carries only revolute joints.
1.1.7 CRANK
Link able to rotate completely about a fixed axis.
1.1.8 ROCKER
Link that oscillates within a limited angle of rotation about a fixed axis.
1.1.9 COUPLER [FLOATING LINK]
Link that is not connected directly to the frame.
1.1.10 SLIDER
Link that forms a prismatic pair with one link and a revolute pair with another link.
1.1.11 SLIDING BLOCK
Compact element of a prismatic pair which slides along a guiding element (e.g. in a slot).
1.1.12 GUIDE
Element of a prismatic pair that is fixed to the frame and constrains the motion of a sliding block.
1.1.13 CROSSHEAD
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.
1.1.14 CONNECTING ROD
Coupler between a piston or a crosshead and a crank shaft.
1.1.15 CAM
Component with a curved profile or surface whereby it imparts a displacement either by point or line contact with a cam follower.
1.1.16 DISK CAM
Disk that rotates about an axis perpendicular to its plane and drives a follower through contact with its profile.
1.1.17 FACE CAM
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.
1.1.18 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.
1.1.19 SPHERICAL CAM
Rotating hollow sphere with a groove in or a rib on its inner surface to make contact with a follower.
1.1.20 YOKE CAM
Constant-breadth radial cam designed to mesh with a yoke follower.
1.1.21 CAM FOLLOWER
Component that receives motion directly from a cam.
1.1.22 YOKE FOLLOWER
Cam follower with two surfaces integral with each other and each in contact with the same cam.
1.1.23 CAMSHAFT
Shaft on which a cam or cams are fitted.
1.1.24 GEAR
Wheel with teeth on its surface designed to mesh with another gear or rack.
1.1.25 CYLINDRICAL GEAR
Gear with teeth formed on a cylindrical surface.
1.1.26 SPUR GEAR
Cylindrical gear with external teeth.
1.1.27 ANNULUS
Cylindrical gear with internal teeth.
1.1.28 GEAR SECTOR [SEGMENT]
Segment of a spur gear or annulus.
1.1.29 HELICAL GEAR
Gear with teeth wrapped helically on a cylindrical surface.
1.1.30 HERRING-BONE [DOUBLE-HELICAL] GEAR
Gear comprising two integral helical gears, the helices of the gears being of opposite hand.
1.1.31 BEVEL [CONICAL] GEAR
Gear with teeth formed on a conical surface.
1.1.32 HYPOID GEAR
Spiral-bevel gear pair with offset between the gear axes.
1.1.33 WORM
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.
1.1.34 WORM WHEEL
Gear that mates with a worm gear.
1.1.35 PLANETARY [PLANET] GEAR
Gear that rotates on an axle whose own axis is constrained to rotate about another axis.
1.1.36 PINION
1. The smaller of a pair of meshing cylindrical gears. 2. Cylindrical gear meshed with a rack.
1.1.37 RACK
Segment of a cylindrical gear of infinite radius.
1.1.38 IDLER
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.
1.1.39 FRICTION WHEEL
Wheel that transmits a driving force to the surface of a second component by friction at the point or line of contact.
1.1.40 BELT
Flexible element such as a strap or rope used in tension to transmit force and motion.
1.1.41 PULLEY
Wheel used to change the direction of motion of a belt by wrapping the belt round part of its periphery.
1.1.42 CHAIN
Mechanism element consisting of a number of short rigid links hinged together for use in the manner of a belt.
1.1.43 SPROCKET WHEEL
Wheel with teeth (sprockets) round its rim designed to engage the links of a chain.
1.1.44 DRIVE SHAFT
Shaft used to transmit torque.
1.1.45 CARDAN SHAFT
Drive shaft connecting two universal couplings.
1.1.46 PIVOT
1. A fixed axis about which revolute motion can take place 2. Inner element of a revolute joint
1.1.47 JOURNAL
The inner element of a revolute or cylindrical joint
1.1.48 BEARING
Machine component that allows relative motion (rotation, translation) and transmission of force between adjacent components.
1.1.49 PAWL [CLICK, DETENT]
Component which is intermediate between two elements and which prevents motion between them in one direction.
1.1.50 LATCH
Movable component which holds another component in place by entering a notch or a cavity, e.g. the locking device of a ratchet.
1.1.51 RATCHET
Element which has a frictional or serrated surface to engage with a pawl.
1.1.52 STOP
Component of a machine that makes intermittent contact with another component to provide a limit to their relative motion.

1.2


Sub-assemblies

1.2.1 SUB-ASSEMBLY
Identifiable set of components forming part of a machine.
1.2.2 JOINT
Physical representation of a kinematic pair.
1.2.3 KINEMATIC PAIR
Connection between two links restricting their relative motion.
1.2.4 PAIRING ELEMENT
Assembly of surfaces, lines or points of a solid body through which it may contact with another solid body.
1.2.5 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.
1.2.6 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).
1.2.7 FORCE-CLOSED [OPEN] PAIR
Kinematic pair the elements of which are held in contact by means of external forces.
1.2.8 FORM-CLOSED PAIR
Kinematic pair the elements of which are constrained to contact each other by means of particular geometric shapes.
1.2.9 LOWER PAIR
Kinematic pair that is formed by surface contact between its elements.
1.2.10 HIGHER PAIR
Kinematic pair that is formed by point, or line, contact between the elements.
1.2.11 REVOLUTE PAIR [HINGE]
Pair that allows only rotary motion between two links.
1.2.12 PRISMATIC PAIR
Pair that allows only rectilinear translation between two links.
1.2.13 HELICAL [SCREW] PAIR
Pair that allows only screw motion between two links.
1.2.14 CYLINDRICAL PAIR
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.
1.2.15 SPHERICAL PAIR
Pair for which the degree of freedom is three and that allows independent relative rotations about three mutually orthogonal axes
1.2.16 PLANAR CONTACT [SANDWICH] PAIR
Pair for which the degree of freedom is three and that allows relative motion in parallel planes.
1.2.17 CAM PAIR
Kinematic pair consisting of a cam and follower in direct contact.
1.2.18 UNIVERSAL [CARDAN, HOOKE'S] JOINT; [UNIVERSAL COUPLING]
Kinematic joint connecting two shafts with intersecting axes.
1.2.19 PIN JOINT
Joint using a pin as the connecting component between two rigid bodies.
1.2.20 GEAR PAIR
Higher kinematic pair formed by successively contacting elements ("teeth") of two links.
1.2.21 COUPLING
Device for joining two moving members, e.g. two shafts at their ends.
1.2.22 CLUTCH
Coupling for torque transmission along a shaft that allows for easy engagement and disengagement during operation.
1.2.23 FLYWHEEL
Rotor used for storing kinetic energy.
1.2.24 ACTUATOR
Sub-assembly which causes relative motion between the parts to which it is attached in response to a signal.
1.2.25 DRIVE
System of mutually connected devices for setting in motion one or several parts of a machine or a mechanism.
1.2.26 BACKLASH [CLEARANCE]
Difference between dimensions of mating parts that allows unconstrained motion.
1.2.27 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.

1.3


Mechanisms

1.3.1 STRUCTURE (OF A MECHANISM)
Number and kinds of elements in a mechanism (members and joints) and the sequence of their contact.
1.3.2 ISOMORPHISM
Equality of structures in respect of the numbers of members and joints, and the sequence of their inter-connections.
1.3.3 EQUIVALENT MECHANISM
Mechanism whose kinematic properties are equivalent in some respects from those of another mechanism with a different structure.
1.3.4 COGNATE MECHANISM
Mechanism that is geometrically different from another but which, nevertheless, has the same transfer function.
1.3.5 KINEMATIC CHAIN
System of interconnected links permitting relative motion of any one link with respect to the remaining links.
1.3.6 CLOSED KINEMATIC CHAIN
Kinematic chain each link of which is connected with at least two other links.
1.3.7 OPEN KINEMATIC CHAIN
Kinematic chain in which there is at least one link connected to only one other link.
1.3.8 KINEMATIC JOINT
Kinematic chain whose kinematic properties are equivalent in some respects to those of a kinematic pair.
1.3.9 LOOP
Subset of links that forms a closed circuit.
1.3.10 TREE [MOBILE]
Kinematic chain that contains no loops.
1.3.11 DEGREE OF FREEDOM [MOBILITY] OF A MECHANISM OR KINEMATIC CHAIN
Number of independent variables that must be considered for input motion.
1.3.12 ASSUR GROUP
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.
1.3.13 CONSTRAINT
Any condition that reduces the degree of freedom of a system.
1.3.14 KINEMATIC INVERSION
Transformation of one mechanism into another by choosing a different member to be the frame.
1.3.15 LIMIT POSITION OF A MECHANISM
Configuration of a mechanism in which one of its links is in a limit position.
1.3.16 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.
1.3.17 PLANAR MECHANISM
Mechanism in which all points of its links describe paths located in parallel planes.
1.3.18 SPHERICAL MECHANISM
Mechanism in which all points of its links describe paths located on concentric spheres.
1.3.19 SPATIAL MECHANISM
Mechanism in which some points of some of its links describe non-planar paths, or paths located in non-parallel planes.
1.3.20 GUIDANCE MECHANISM
Mechanism that guides a link through a prescribed sequence of positions.
1.3.21 FUNCTION-GENERATING MECHANISM
Mechanism that generates a required functional relationship between the displacements of its input links and output links.
1.3.22 PATH-GENERATING MECHANISM
Mechanism in which a point on a member generates a given path.
1.3.23 STEP MECHANISM
Mechanism whose output motion is uni-directional with periodic dwells.
1.3.24 PILGRIM-STEP MECHANISM
Mechanism whose output motion is uni-directional overall, but has periodic reversals.
1.3.25 DWELL MECHANISM
Mechanism in which the output link performs reciprocating or rocking motion with periodic dwells.
1.3.26 DIFFERENTIAL MECHANISM
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.
1.3.27 SELF-LOCKING MECHANISM
Mechanism that is incapable of transmitting motion and power from the output to the input.
1.3.28 ADJUSTABLE MECHANISM
Mechanism whose primary dimensions (e.g. link lengths) can be altered.
1.3.29 LINKAGE [LINKWORK]
Kinematic chain whose joints are equivalent to lower pairs only.
1.3.30 FOUR-BAR LINKAGE
Linkage with four binary links.
1.3.31 FOUR-BAR MECHANISM
Mechanism with four binary links.
1.3.32 CRANK-AND-ROCKER MECHANISM
Four-bar mechanism with a crank and a rocker.
1.3.33 DOUBLE-CRANK [DRAG-LINK] MECHANISM
Four-bar mechanism with two cranks.
1.3.34 PARALLEL-CRANK MECHANISM
Four-bar mechanism having cranks of equal length and a coupler with length equal to that of the frame.
1.3.35 DOUBLE-ROCKER MECHANISM
Four-bar mechanism with two rockers.
1.3.36 SLIDER-CRANK MECHANISM
Four-bar mechanism with a crank and a slider in which the frame forms one element of the prismatic pair.
1.3.37 DOUBLE-SLIDER MECHANISM
Four-bar mechanism with two sliders in which the frame forms one element of each of the prismatic pairs.
1.3.38 SCOTCH-YOKE MECHANISM
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.
1.3.39 CAM MECHANISM
Mechanism that includes at least one cam.
1.3.40 SCREW MECHANISM
Mechanism that includes at least one screw pair.
1.3.41 WEDGE MECHANISM
Mechanism whose links form prismatic pairs only.
1.3.42 GEAR TRAIN
Assembly containing more than one pair of gears.
1.3.43 MITRE GEAR
Bevel gear pair with equal gears whose axes intersect at right angles.
1.3.44 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.
1.3.45 GEARED LINKAGE
Combination of a linkage and a gear mechanism.
1.3.46 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.