Mechanical Actuation SystemsMechanical systems Device which can be considered to be motion converters in that they transform motion from one form to some other required form. Eg: Transform linear motion into rotational motion and vice versa.Mechanical elements can include the use of linkages, cams, gears, rack-and-inion, chains, belt drives, etc.Eg:rack-and-inion can be used to convert rotational motion to linear motion.Many of the actions which reviously were obtained by the use of mechanism are, however, often nowadays being obtained, as a result of a Mechatronics aroach by the use of microrocessor systems.Mechanisms still, however, have a role in Mechatronics systems. !or e"amle, the Mechatronics system in use in an automatic camera for ad#usting the aerture for correct e"osures involves a mechanism for ad#usting the si$e of diahragm.%thers function: !orce amlification & given by levers. 'hange of seed & given by gears. Transfer of rotation about one a"is to rotation about another & timing belt.The term kinematics is used for the study of motion without regard to forces. (hen we consider #ust the motions without any consideration of the forces or energy involved then we are carrying out a kinematic analysis of the mechanism.Tyes of Motion Rotation which has components rotating about one or more of the axes.Rotation which has components rotating about one or more of the axes.Freedom and Constraints)n imortance asect in the design of mechanical elements is the orientation and arrangement of the elements and arts. ) body that is free in sace can move in three, indeendent, mutually erendicular directions and rotatein three ways about those directions.*t is said to have si" degree of freedom. The number of degree of freedom is the number of comonents of motion that are required in order to generate the motion.!igure +a, shows a #oint with #ust this one translational degree of freedom.!igure +b, shows a #oint which has one translational degree of freedom one rotational degree of freedom.Kinematic Chains Each art of a mechanism which has motion relative to some other art is termed a link. ) rigid body which has two or more oints of attachment to other links is termednodes. Each link is caable of moving relative to its neighboring links. ) #oint is a connection between the connected links at their nodes and which allows some motionbetween the connected links. -evers, cranks, connecting rods and istons, sliders, ulleys, belts and shafts are all e"amles of links. ) sequence of #oints and links is known as kinematic chain. !or a kinematic chain to transmit motion, one link must be fi"ed. Movement of one link will thenroduce redictable relative movements of the others. (b) with three nodes *t is ossible to obtain from one kinematic chain a number of different mechanisms by having a different link as the fi"ed one. The designs of many mechanisms are based on two basic forms of kinematic chains, the four-bar chain and the slider-crank chain.The Four-bar Chain'onsist of . links connected to give . #oints about which turning can occur.Fixed frameE"amle of a mechanism can be used to advance the film in a cine camera.-ink / rotates, so the end of link 0 lock into a srocket of the film, ulls it forward before releasing and moving u and back to lock into the ne"t srocket. The !our-bar 'hain 1ome linkages may have toggle ositions. These are ositions where the linkage will not react to any inut from one of its links. !igure below illustrates such a toggle, being the linkage used to control the movement of the tailgate of a truck so that when link 0 reaches the hori$ontal osition no further load on link 0 will cause any further movement. There is another toggle osition for the linkage and that is when links 2 and . are both vertical and the tailgate is vertical.The 1lider-crank Mechanism 'onsists of a crank, a connecting rod and a slider. Double-crank mechanismCine flm adance mechanismCams 'am is a body which rotates or oscillates and in doing so imarts a recirocating motion to a second body called follower, with which it is in contact. The length of times sent for the rotation is deending on the shae of the cam. The cam shae required to roduce a articular motion of the follower will deend on the shae of the cam and the tye of follower used. !art that dries the follower upwards" its profle determining how #uickl$ the cam follower will lifted.!art that dries the follower upwards" its profle determining how #uickl$ the cam follower will lifted. !igure below shows the tyes of follower dislacement diagrams that can be roduced with two other different shaed cams and either oint or knife followers.!igure below shows a number of e"amles of different tyes of cam followers.Displacement diagram for an eccentric cam(rise and fall s$mmetricall$)(rise and fall s$mmetricall$)!igure below shows a number of e"amles of different tyes of cam followers.Gears 3ear trains are mechanisms which are very widely used to transfer and transform rotational motion. They are used when a change in seed or torque of a rotating device is needed. !or e"amle, thecar gearbo" enables the driver to match the seed and torque requirements of the terrain with the engine ower available. %owerfrictionthanslidingcontactbutcan be more expensie%owerfrictionthanslidingcontactbutcan be more expensieMushroom A = number of teeth on B=dBBnumber of teeth on AdAA = number of teeth on B=dBBnumber of teeth on AdA&ngular elocit$Diameter Two meshed gears3ear 4atio:.Gear trains& a series of intermeshed gear wheels.1imle gear train & used for a system where each shaft carries only one gear wheel(a) !arallel gear axes" (b) axes inclined to one another" (c) axial teeth" (d) helical teeth" (e) double helical teethG= A=ABC= AC DB CDBDG= A=ABC= AC DB CDBDx x x4atio of the angular velocities, 'omound gears trains & two wheels are mounted on a common shaft.4atio of the angular velocities,!or the inut and outut shafts to be in line, we must also have for the radii of the gears.Rotational to translational motion G= A=AB

CBCG= A=AB

CBCr& ' r( ) rD ' rCr& ' r( ) rD ' rCTtwo intermeshed gears with one having a base circle of infinite radius. 1uch gear can be used totransform either linear motion to rotational motion or rotational motion to linear motion.Eg: The rack-and-inion.-inear velocity,Belt and Chain Drives 5air of rolling cylinders with the motion of one cylinder being transferred to the other by a belt. 6elt drives use the friction that develos between the ulleys attached to the shaft and the belt around the arc of contact in order to transmit a torque. The transmitted torque is due to the differences in tension that occur in the belt duringoeration.This difference results in a tight side and a slack side for the belt. *f the tension on the tight side is T/, and a slack side is T0, then with ulley ) as a driver,Revolution*or#ue on & ) (*+ , *-) r&*or#ue on & ) (*+ , *-) r&5ulley 6 as a driver,1ince the ower transmitted is the roduce of the torque and the angular velocity, and since the angular velocity is v7r) for ulley ) and v7r6 for ulley 6, then for either ulley we have )s a method of transmitting ower between two shafts, belt drives have the advantage that the length of the belt can easily be ad#usted to suit a wide range of shaft to shaft distance and the system is automatically rotected against overload because sliing occurs if the loading e"ceedsthe ma"imum tension that can be sustained by frictional forces. *f the distance between shafts is large, a belt drive is more suitable than gears, but over small distances gears are to be referred. Different si$e ulleys can be used to give a gearing effect. 8owever, the gear ratio is limited to about 2 because of the need to maintain an adequate arc of contact between the belt and ulleys. !igure below shows two tyes of reversing drives. (ith both forms of drive, both side of the belt comes into contact with the wheels and so 9-belts or timing belts cannot be used.

Types o belts !lat.- 8as rectangular cross section.- 8as an efficiency about :;< and roduces little noise.*or#ue on & ) (*+ , *-) r&*or#ue on & ) (*+ , *-) r&!ower ) (*+ , *-) !ower ) (*+ , *-) Open belt 4ound. - 8as a circular cross section and is used with grooved ulleys. 9 Tye- 9 & belts are used with grooved ulleys and are less efficient that flat belts but a number of them can be used on a single wheel and so give multile drive. Timing- 4equire toothed wheels, having teeth which fit into the grooves on the wheel.- =nlike the other belts, timing belt does not stretch or sli and consequently transmits ower at a constant angular velocity ratio.- The teeth make it ossible for the belt to be run at slow or fast seeds.Bearin!s(henever there is relative motion of one surface in contact with another, either by rotating or sliding, the resulting frictional forces generate heat which wastes energy and results in wear.The function of bearing is to guide with minimum friction and ma"imum accuracy the movementof one art relative to another. 3ive suitable suort to rotating shaft. The term thrust bearing is used for bearings that are designed to withstand forces along the a"is of a shaft when the relative motion is rimarily rotation."lain #ournal bearin!s =sed to suort rotating shafts which are loaded in a radial direction +#ournal & shaft,. 'onsist of an insert of some suitable material which is fitted between the shaft and the suort. 4otation of the shaft results in its surface sliding over that of the bearing surface. The bearing may be a dry rubbing bearing or lubrication.Ball and roller bearin! (ith this tye of bearing, the main load is transferred from the rotating shaft to its suort by rolling contact rather than sliding contact. ) rolling element bearing consists of . main elements : an inner race, an outer race, the rolling element either balls or rollers, and a cage to kee the rolling elements aart. The inner and outer races contain hardened tracks in which the rolling elements roll.a) Deep-grooeb) Filling-slotc) &ngular contacta) Deep-grooeb) Filling-slotc) &ngular contactd) double-row e) .elf-aligninge) *hrust" grooed raced) double-row e) .elf-aligninge) *hrust" grooed racea) .traight rollerb) *aper rollerc) /eedle rollera) .traight rollerb) *aper rollerc) /eedle roller