Post on 05-Feb-2018
transcript
Mechanical Function
Mechanisms and Mechanical Functions
O Technical systems are made up of different
mechanisms and components.
O A mechanism is an arrangement of parts assembled to
work as a whole
O Function: transmits or transforms outside force that puts
it in motion
O Each component (solid, liquid or gas) in a mechanism
plays an important role in the overall functioning of the
system.
O The role played by a component in a technical system is
called a mechanical function.
Basic Mechanical Functions
OThere are 4 types of basic mechanical functions:
OLinks
OGuiding control
OAdhesion
OLubrication
Links
A link connects, fastens, or puts together two or more components of a
technical object.
Ex: nail, screw, nut, bolt, glue
Characteristics of Links
O links are characterized in four
ways:
O 1. Direct vs. Indirect
O 2. Rigid vs. Flexible
O 3. Removable vs. Non-removable
O 4. Complete vs. Partial
Direct vs. Indirect Link
O The link between 2 components in a technical
system can be either direct or indirect.
O A direct link means that 2 parts connect to one
another WITHOUT a 3rd linking component.
O An indirect link means that there is a linking
component (welding, glue, nail, screw, bolt, etc.)
holding the 2 components together.
O Examples: Classify as direct or indirect
O a) Link between tire and wheel
O b) link between blade & shoe
Direct
Indirect
Rigid vs. Elastic (Flexible)O The rigid link cannot be bent or deformed
O The elastic/flexible link can be stretched, bent or
deformed
O a) Link between tire and wheel
O b) link between blade & shoe
Flexible
Rigid
Removable vs. Non- removableO What’s the difference from the point of view of
destruction?
O The non-removable link cannot be removed
without wrecking what’s linked.
O a) Link between tire and wheel
O b) link between shoe and sole
removable
Non-removable
Complete vs. Partial
O In a partial link at least one part is capable of
motion with respect to the other
O A complete link has no movement between
linked parts (both parts moving together)
O a) Link between tire and wheel
O b) link between blade & shoe
complete
partial
Examples
O What are the characteristics of the links below?
O 1. The link between link between nut and bolt:
O Direct, rigid, removable, partial
Examples
O What are the characteristics of the links below?
O 2. The link between the two gears :
O indirect, flexible, removable, complete
Examples
O 3. The link between two blocks of lego
O Direct, rigid, removable, complete
Degrees of Freedom of Movement
O The DEGREES OF FREEDOM are the set of
independent movements that are possible
for a given part in a technical object.
O There are 6 possibilities of independent
motion: 3 translational motions (side to side)
and 3 rotational motions (circular)
Degrees of Freedom of Movement
O Translational motion
O Translation from left to right or from right to left (Tx)
O Translation from top to bottom or from bottomto top (Ty)
O Translation from front to back or from back to front (Tz)
O Rotational motion
O Rotation about the x axis (Rx)
O Rotation about the y axis (RY)
O Rotation about the z axis (RZ)
Degrees of FreedomO How many degrees of
freedom does this soap
dispenser have?
O Two degrees of freedom
TyRy
Guiding Controls
O A guiding control or component is a component
whose function is to force (guide) the motion of
the moving parts forces the parts to follow a
specific path
O Also prevents unwanted motion
O 3 main types of guiding:
O Translational
O Rotational
O Helical
O Translational Guiding: guides the object in a
straight back and forth, side to side or up
and down motion
O Translation guiding is usually characterized
by groves or walls that guides the motion
O Example: drawer slides, window grooves
O Rotational guiding: moves object in a
circular motion
O Rotational guiding is characterized by
cylindrical objects that guide the motion
O Examples: an axle attached to the fork guides the wheel
hub of a bicycle in a rotational motion
O Helical Guiding: guides an object in a back
and forth motion as it rotates about the
same axis
O Helical guides are usually characterized by
the threads that guide motion
O Example: Threads inside the C-clamp
Adhesion
O 2 surfaces stay in
contact without
slipping
O Holds 2 parts
together
O EX: Car tires on a
steep hill.
Adhesion
Factors the Affect AdhesionO The STRENGTH OF ADHESION between 2 surfaces depends
on 5 factors
O 1) The nature of materials in contact.
O Rubber & asphalt vs. Steel & asphalt.
O 2) The presence of a lubricant.
O Oil on the road will make tires slip.
O 3) Temperature.
O The warmer the weather, the better the adhesion.
O 4) The state of the surfaces in contact.
O The rougher the surface, the better the adhesion.
O 5) The perpendicular FORCE exerted by one surface on another.
O More force, better adhesion.
Friction
O FORCE that resists
slipping
O Increases with
adhesion
When is it Useful to have Adhesion and Friction
O Useful
O Need grip for movement (climbing boots, car
tires)
O Parts move efficiently (friction wheels)
O Not Useful
O Pulling something heavy (sleigh on snow vs
ice)
O Parts need to slide (pistons)
Lubrication
O LUBRICATION is the mechanical function
that reduces friction between two parts.
O Lubricants can be oil, grease, water etc
O Polishing also reduces friction