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As an industrial manufacturing mechanic, students will be maintaining and repairing a wide variety of machines, mechanical systems including factory machinery, food processing machinery, textile machinery, transportation equipment, and metal fabrication machinery. Students will diagnose mechanical pneumatic, hydraulic, and electrical problems. Students will be working with mathematics, blueprint reading, welding, electronics, and computers.

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As an industrial mechanic, students will be maintaining and repairing a wide variety of machines, mechanical systems including factory machinery, food processing machinery, textile machinery, transportation equipment, and metal fabrication machinery. Students will diagnose mechanical pneumatic, hydraulic, and electrical problems. Students will be working with mathematics, blueprint reading, welding, electronics, and computers.

Yi Zhangwith Susan FingerStephannie BehrensTable of Contents 6 Cams6.1 Introduction6.1.1 A Simple Experiment: What is a Cam?Figure 6-1 Simple Cam experimentTake a pencil and a book to do an experiment as shown above. Make thebook an inclined plane and use the pencil as a slider (use your handas a guide). When you move the book smoothly upward, what happens tothe pencil? It will be pushed up along the guide. By this method, youhave transformed one motion into another motion by a very simpledevice. This is the basic idea of a cam. By rotating the cams in thefigure below, the bars will have either translational or oscillatorymotion. 6.1.2 Cam Mechanisms The transformation of one of the simple motions, such as rotation,into any other motions is often conveniently accomplished by means ofa cam mechanism A cam mechanism usually consists of two movingelements, the cam and the follower, mounted on a fixed frame. Camdevices are versatile, and almost any arbitrarily-specified motion canbe obtained. In some instances, they offer the simplest and mostcompact way to transform motions. A cam may be defined as a machine element having a curvedoutline or a curved groove, which, by its oscillation or rotationmotion, gives a predetermined specified motion to another elementcalled the follower . The cam has a very important functioninthe operation of many classes of machines, especially those of theautomatic type, such as printing presses, shoe machinery, textilemachinery, gear-cutting machines, and screw machines. In any class ofmachinery in which automatic control and accurate timing areparamount, the cam is an indispensable part of mechanism. The possibleapplications of cams are unlimited, and their shapes occur in greatvariety. Some of the most common forms will be considered in thischapter.6.2 Classification of Cam Mechanisms We can classify cam mechanisms by the modes of input/output motion,the configuration and arrangement of the follower, and the shape ofthe cam. We can also classify cams by the different types of motionevents of the follower and by means of a great variety of the motioncharacteristics of the cam profile. (Chen 82) Figure 6-2 Classification of cam mechanisms4.2.1 Modes of Input/Output MotionRotating cam-translating follower. (Figure 6-2a,b,c,d,e)Rotating follower (Figure 6-2f): The follower arm swings or oscillates in a circular arc with respectto the follower pivot.Translating cam-translating follower (Figure 6-3).Stationary cam-rotating follower: The follower system revolves with respect to the center line of thevertical shaft.Figure 6-3 Translating cam - translating follower6.2.1 Follower ConfigurationKnife-edge follower (Figure 6-2a)Roller follower (Figure 6-2b,e,f)Flat-faced follower (Figure 6-2c)Oblique flat-faced followerSpherical-faced follower (Figure 6-2d)6.2.2 Follower ArrangementIn-line follower:The center line of the follower passes through the center line of thecamshaft.Offset follower:The center line of the follower does not pass through the center lineof the cam shaft. The amount of offset is the distance betweenthese two center lines. The offset causes a reduction of the sidethrust present in the roller follower.6.2.3 Cam ShapePlate cam or disk cam:The follower moves in a plane perpendicular to the axis of rotation ofthe camshaft. A translating or a swing arm follower must beconstrained to maintain contact with the cam profile.Grooved cam or closed cam (Figure 6-4):This is a plate cam with the follower riding in a groove in the faceof the cam.Figure 6-4 Grooved camCylindrical cam or barrel cam (Figure6-5a):The roller follower operates in a groove cut on the periphery of acylinder. The follower may translate or oscillate. If the cylindricalsurface is replaced by a conical one, a conical cam results.End cam (Figure 6-5b): This cam has a rotating portion of a cylinder. The follower translatesor oscillates, whereas the cam usually rotates. The end cam is rarelyused because of the cost and the difficulty in cutting its contour.Figure 6-5 Cylindrical cam and end cam6.2.4 Constraints on the FollowerGravity constraint:The weight of the follower system is sufficient to maintain contact.Spring constraint:The spring must be properly designed to maintain contact.Positive mechanical constraint:A groove maintains positive action. (Figure 6-4 and Figure 6-5a)For the cam in Figure 6-6, the follower has two rollers, separated by a fixeddistance, which act as the constraint; the mating cam in such an arrangement is often called a constant-diameter cam. Figure 6-6 Constant diameter cam A mechanical constraint cam also be introduced by employing a dual orconjugate cam in arrangement similar to what shown in Figure 6-7.Each cam has its own roller, but the rollers are mounted on the samereciprocating or oscillating follower.Figure 6-7 Dual cam 6.2.5 Examples in SimDesign Rotating Cam, Translating FollowerFigure 6-8 SimDesign translating cam Load the SimDesign file simdesign/cam.translating.sim. If youturn the cam, the follower will move. The weight of the followerkeeps them in contact. This is called a gravity constraint cam.Rotating Cam/Rotating FollowerFigure 6-9 SimDesign oscillating cam The SimDesign file is simdesign/cam.oscillating.sim. Noticethat a roller is used at the end of the follower. In addition, aspring is used to maintain the contact of the cam and the roller. If you try to calculate the degrees offreedom (DOF) of the mechanism, you must imagine that the rolleris welded onto the follower because turning the roller does notinfluence the motion of the follower.6.3 Cam Nomenclature Figure 6-10 illustrates some cam nomenclature:Figure 6-10 Cam nomenclatureTrace point: A theoretical point on the follower, corresponding to the point of afictitious knife-edge follower. It is used to generate thepitch curve. In the case of a roller follower, the tracepoint is at the center of the roller.Pitch curve: The path generated by the trace point atthe follower is rotated about a stationary cam.Working curve: The working surface ofa cam in contact with the follower. For the knife-edge followerof the plate cam, the pitch curve and the working curvescoincide. In a close or grooved cam there is an innerprofile and an outer working curve.Pitch circle: A circle from the cam center through the pitchpoint. The pitch circle radius is used to calculate a cam of minimum sizefor a given pressure angle.Prime circle (reference circle): The smallest circlefrom the cam center through the pitch curve.Base circle: The smallest circle from the cam center throughthe cam profile curve.Stroke or throw:The greatest distance or angle throughwhichthe follower moves or rotates.Follower displacement: The position of the follower from aspecific zero or rest position (usually its the position when the follower contacts with the base circle of the cam) in relationto time or the rotary angle of the cam.Pressure angle: The angle at any point between the normal tothe pitch curve and the instantaneous direction of the follower motion. Thisangle is important in cam design because it represents the steepness of thecam profile.6.4 Motion events When the cam turns through one motion cycle, the follower executes aseries of events consisting of rises, dwells and returns. Riseis the motion of the follower away from the cam center, dwellis the motion during which the follower is at rest; and returnis the motion of the follower toward the cam center. There are many follower motions that can be used for the rises and thereturns. In this chapter, we describe a number of basic curves. Figure 6-11 Motion eventsNotation : The rotary angle ofthe cam, measured from the beginning of the motion event;: The range of therotary angle corresponding to the motion event;h : The stoke of the motion event of the follower;S : Displacement of the follower;V : Velocity of the follower;A : Acceleration of the follower.6.4.1 Constant Velocity Motion If the motion of the follower were a straight line, Figure 6-11a,b,c, it would have equal displacementsin equal units of time, i.e., uniform velocity from thebeginning to the end of the stroke, as shown in b. The acceleration,except at the end of the stroke would be zero, as shown in c. Thediagrams show abrupt changes of velocity, which result in large forcesat the beginning and the end of the stroke. These forces areundesirable, especially when the cam rotates at high velocity. Theconstant velocity motion is therefore only of theoreticalinterest. (6-1)6.4.2 Constant Acceleration Motion Constant acceleration motion is shown in Figure 6-11d, e, f. As indicated in e, the velocityincreases at a uniform rate during the first half of the motion anddecreases at a uniform rate during the second half of the motion. Theacceleration is constant and positive throughout the first half of themotion, as shown in f, and is constant and negative throughout thesecond half. This type of motion gives the follower the smallestvalue of maximum acceleration along the path of motion. In high-speedmachinery this is particularly important because of the forces thatare required to produce the accelerations. When,(6-2) 041b061a72