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
h-Higher pair joint l-Number of links j-Lower pair joint
n-Degree of freedom. l-Number of links. h-Higher pair joint j-Lower pair joint
1.Shamping machines.2.Siotting mechanism.3.Rotary internal combustion engine.
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.
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
i Radial component of accelerationii Tangential component of acceleration
Instantaneous axis is a line drawn through an instantaneous centerand perpendicular to the plane of motion.
i. Virtual center.ii. Centro.iii. Rotopole.
The objective of Kinematic analysis is to determine the Kinematicquantities such as displacement,velocity and acceleration of the element in amechanism.
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. |