PLATE NO.2
Use an A4 paper for this activity.
Research about the different kinds of mechanism then write at least 3 pages of discussion
about the different kinds of mechanism.
Note:
Write ONLY in Engineering lettering.
Height of lettering should be 4mm.
Space between paragraph line is 1mm.
Have a word count of atleast 800 words.
In kinematics, a mechanism is a means of transmitting, controlling, or constraining relative
movement. Movements which are electrically, magnetically, pneumatically operated are
excluded from the concept of mechanism. The central theme for mechanisms is rigid bodies
connected together by joints.
1. Linkage mechanisms
Linkage mechanisms consist of interconnected rigid bodies, often referred to as links, joined
together by movable joints. These mechanisms convert input motion or force into the desired
output motion or force, enabling machines and devices to perform complex tasks with
remarkable efficiency and precision.
1.1 Four bar linkages
a mechanical linkage which consists of four rigid bars connected by joints or pivots. It forms
a closed loop and exhibits a range of motion and mechanical advantages. Four-bar linkages
are widely used in various applications, such as in machinery, robotics, and automotive
systems, to achieve controlled and predictable movements, including rotation, translation,
and oscillation.
Linkages have different functions. The functions are classified depending on the
primary goal of the mechanism:



Function generation: the relative motion between the links connected to
the frame,
Path generation: the path of a tracer point, or
Motion generation: the motion of the coupler link
Examples:
Crane - An application of path generation is a crane in which an
approximate horizontal trace is needed.
Hood - An example of motion generation is a hood which opens and closes.
Parallelogram Mechanism - In a parallelogram four-bar linkage, the
orientation of the coupler does not change during the motion.
1.2 Slider-crank mechanisms
The slider crank mechanism is a typical mechanical linkage that changes
rotational motion into linear motion or the other way around. It is widely used in
various applications, including internal combustion engines, pumps and
compressors, presses, robotics, toy cars, and human-powered vehicles.
The slider-crank mechanism consists of three main components: a crank, a
connecting rod, and a slider. The crank is a rotating shaft driven by a motor or
other power source. The connecting rod is a linear link that connects the crank to
the slider. The slider is a sliding element that moves back and forth along a straight
line. As the crank rotates, it drives the connecting rod and slider through a series of
pivot points, causing the slider to move back and forth. The speed and distance of
the
slider’s
movement
can be
controlled
by
adjusting
the
connecting
rod’s
length, the
crank’s
speed,
or the
pivot
points’
position.
Examples:
Crank and Piston - You can also use the slider as the input link and the
crank as the output link. In this case, the mechanism transfers translational motion
into rotary motion. The pistons and crank in an internal combustion engine are an
example of this type of mechanism.
Block Feeder - The block feeding mechanism comprises a mechanical arm
used for picking up blocks and a first power part used for driving the mechanical
arm to carry out feeding, and the first power part is fixedly connected with the
mechanical arm.
2. Cam mechanisms
Linkages, while useful, cannot achieve all possible motions. For example, if the
output link must remain stationary for a certain period of time while the input link
keeps turning, linkages cannot be used. Cam mechanisms can realize any required
output motion. The composition of a cam mechanisms is simple: a cam, a follower
and a frame.
3.
Gears
Gears are mechanisms that mesh together via teeth and are used to transmit rotary
motion from one shaft to another. Gears are defined by two important items: radius
and number of teeth. They are typically mounted, or connected to other parts, via a
shaft or base.
EXAMPLES
Rack and pinion - A rack and pinion is a type of linear actuator that
comprises a circular gear (the pinion) engaging a linear gear (the rack). Together,
they convert rotational motion into linear motion. Rotating the pinion causes the
rack to be driven in a line. Conversely, moving the rack linearly will cause the
pinion to rotate.
Ordinary gear trains - Gear trains consist of two or more gears that transmit
motion from one axis to another. Ordinary gear trains have axes, relative to the
frame, for all gears comprising the train.
Planetary gear train - Generally, planetary gears are used as speed reducers. They
are used to slow down motors and increase the torque. Torque is the working
power of the machine.
4. Ratchet mechanism
Ratchets are mechanisms that serve to limit either rotary or linear motion to only
one direction. A ratchet is composed of three main parts: a round gear, a pawl, and
a base. A ratchet mechanism is based on a wheel that has teeth cut out of it and a
pawl that follows as the wheel turns. Studying the diagram you will see that as the
ratchet wheel turns and the pawl falls into the 'dip' between the teeth. A wheel with
suitably shaped teeth, receiving an intermittent circular motion from an oscillating
member, is a ratchet wheel.
5. Geneva Wheel
The Geneva wheel, or Maltese cross, is a cam like mechanism that provides
intermittent rotary motion & is widely used in both low and high-speed machinery.
Although originally developed as a stop to prevent over winding of watches, it is
now extensively used in automatic machinery, e.g. where a spindle, turret, or
worktable must be indexed. It is also used in motion picture projectors to provide
the intermittent advance of the film.