This site will help you to know the basics of Mechanical Engineering concepts and terms. We have tried our level best to make the definitions and explanations as simple as possible
This to know about the basic mechnaical concept behind the mechanical
- Kinematic link It is a resistive body which go to make a part of a machine having relativemotion between them.
- Kinematic pair.When two links are in contact with each other it is known as a pair.If the pairmakes constrain motion it is known as kinematic pair.
- Kinematic chain.When a number of links connected in space make relative motion of any point ona link with respect to any other point on the other link follow a definite law it is known askinematic chain.
- Klein’s equation for joints.
h-Higher pair joint
l-Number of links
j-Lower pair joint
- Degree of freedom.Of mechanism.It is defined as the minimum number of input parameters which must beindependently controlled inorder to bring the mechanism into a useful engineeringpurpose.
- Kutzbach’s relation.
n-Degree of freedom.
l-Number of links.
h-Higher pair joint
j-Lower pair joint
- Grashoff’s law.Sum of shortest link length and sum of longest link length is not greater than thesum of remaining link length.
- Inversion of mechanism.The method of obtaining different mechanism by fixing different links in akinematic chain is known as inversion of mechanism.
- Mechanical advantage of mechanism.It is defined as the ratio of output torque to the input torque also defined as theratio of load to effort.
- Transmission angle. The acute angle between follower and coupler is known as transmission angle.
- Toggle position. If the driver and coupler lie in the same straight line at this point mechanicaladvantage is maximum.Under this condition the mechanism is known as toggle position.
- few types of rocking mechanism Pendulam motion is called rocking mechanism.1.Quick return motion mechanism.2.Crank and rocker mechanism.3.Cam and follower mechanism.
- pantograph It is device which is used to reproduce a displacement exactly in a enlargedscale.
- application of crank and slotted lever quick return motion mechanism
1.Shamping machines.2.Siotting mechanism.3.Rotary internal combustion engine.
- structure It is an assemblage of a number of resistant bodies having no relative motion betweenthemand meant for carrying loads having straining action.
- simple mechanism A mechanism with four link is known as simple mechanism.
- equivalent mechanism The mechanism, that obtained has the same number of the degree of freedom,as theoriginal mechanism called equivalent mechanism.
- single slider crank chain mechanism A single slider crank chain is a modification of the basic four bar chain. It consist ofone sliding pair and three turning pair.
- double slider crank chain mechanism A kinematic chain which consist of two turning pair and two sliding pair isknown as double slider crank mechanism.
Classification of kinematic link
Classification based on relative motion between links.
1)Sliding pair.In a sliding pair minimum number of degree of freedom is only one.
2)Turning pair.In a turning pair also degree of freedom is one.when two links are connected suchthat one link revolves around another link it forms a turning pair.
3)Cylindrical pair.In a cylindrical pair degree of freedom is two.If one link turns and slides alonganother link it forms a cylindrical pair.
4)Rolling pair.In a rolling pair degree of freedom is two.The object moves both linearly andangularly.
5)Spherical pair.In a spherical pair degree of freedom is three.It can both move left and right,up anddown,and rotate along the same point.
Based on nature of contact.
1)Lower pair.If contact between two links is surface contact also having degree of freedom one,then the pair is known as lower pair.Example: Sliding pair.
2)Higher pair.If contact between two links is either point contact or line contact then the pair isknown as higher pair.Example: Point contact-Rolling pair.Line contact-Cylindrical pair.
3)Mechanical pair.
(a)Open pair.In this pair everything is open to the admosphere.
(b)Closed pair.In this pair everything is closed from the admosphere.
(B)Indexing mechanism.This type of mechanism is used in automatic lathe’ s etc.
- Snap action mechanism.It is used in calling bells, bicycle bells etc.
- Motion adjustment mechanism.The mechanism used to adjust or modify any one of the links in a mechanism isknown as motion adjustment mechanism. Differential screw used in bench vice, pipewrench, Lathe chuck and screw jack are some of the examples of motion adjustmentmechanism.
- Scott Russel mechanism.This is one of the mechanism to produce straight line motion mechanism.The mechanismin which the straight line is copied from a existing straight line constrain is known asScott Russel mechanism.
- Quick return motion are of two types.
They are,
1)Crank and slotted lever quick return motion mechanism.
2)Whitworth quick return motion mechanism
Crank and slotted lever quick return motion mechanism.
In this mechanism,the link AC forming the turning pair is fixed.The driving crank CBrevolves with uniform angular speed about the fixed center C.A sliding block attached tothe crank pin at B slides along the slotted bar AP and thus causes AP to oscillate aboutthe pivorted point A.A short link PR transmits the motion from AP to ram which carriesthe tool and reciprocates along the line of stroke R1R2.In the extreme positions,AP1 andAP2 are tangential to the circle and the cutting tool is at the end of the stroke.The forwardor cutting stroke occurs when the crank rotates from the position CB1 to CB2 in theclockwise direction.The return stroke occurs when the crank rotates from the positionCB2 to CB1 in the clockwise direction.Since the crank has uniform angularspeed,therefore
Time of cutting stroke
Time of return stroke =Since the tool travels a distance of R1R2 during cutting and return ,
thereforelength of stroke =R1R2=P1P2=2AP
Whitworth quick return motion mechanism.
In this mechanism,the link CD forming the turning pair is fixed.The driving crank CArotates at a uniform angular speed.The slider attached to the crank pin at A slides alongthe slotted bar PA which oscillates at a pivoted point D.The connecting rod PR carries theram at R to which a cutting tool is fixed.The motion of the tool is constrained along theline RD produced along a line passing through D and perpendicular to CD.When thedriving crank CA moves from the position CA1 to CA2 through an angle in theclockwise direction,the tool moves from left to right through a distance 2PD.Now whenthe driving crank moves from the position CA1 to CA2 through an angle in theclockwise direction,the tool moves back from right to left hand end.Since CA rotates atuniform angular velocity therefore time taken for return stroke is less than time taken forcutting stroke.then ratio between time taken for cutting and return stroke is,
Time of cutting stroke
Time of return stroke
- components of acceleration
i Radial component of accelerationii Tangential component of acceleration
- instantaneous center axis
Instantaneous axis is a line drawn through an instantaneous centerand perpendicular to the plane of motion.
- .What are the names of instantaneous center
i. Virtual center.ii. Centro.iii. Rotopole.
- objective of Kinematic analysis
The objective of Kinematic analysis is to determine the Kinematicquantities such as displacement,velocity and acceleration of the element in amechanism.
- two rules to locate Instantaneous center
a) When two links are connected by a pin joint the instantaneouscenter lies on the center of the pin.b) When two links have a sliding contact,the instantaneous centerlies at infinity in a direction perpendicular to the path of motionof slide.
