Cam- Mechanical element used to drive another element, called the follower, through a specified motion by direct contact. Link with a surface of contact so designed as to produce the desired motion. Irregularly shaped machine member which serves as a driving link COMPONENTS OF CAM MECHANISM 1. Cam – the driver 2. Follower – the driven element 3. Frame – the support for the cam and follower CLASSIFICATIONS OF CAM 1. Disk cam, Plate cam, of Radial cam a. It is a disk with a contoured edge that rotates about an axis perpendicular to the disk, transmitting motion to the cam follower that remains in contact with the edge of the disk. 2. Cylindrical cam or Barrel cam a. It is a type of cam with wedges or groove formed on the surface of a cylinder; the motion transmitted to the follower is either translating (reciprocating) or oscillating. It may have a follower guided so as to move in a straight line along an element of the cylinder b. The roller follower cannot have pure rolling contact because of the difference in the surface speed at the top and bottom of the groove. It is sometimes made in the form of the frustum of a cone (Figure 1.4) with the apex on the axis of revolution of the cam. 3. Conical cam a. It is a type of cam with wedge or groove formed on the surface of a cone and transmitting either translating (reciprocating) or oscillating motion. As illustrated below is a conical cam transmitting a reciprocating motion to the follower; movement of the follower 4. Positive-motion cam mechanism a. Positive-motion cam mechanism is cam in which the follower is compelled to move in a definite path by constraining surfaces and without the application of external force. It is a mechanism in which provision is made for controlling the motion of the follower in both directions by the re of two contact surfaces As shown in the figure 1.6 below, the mechanism used a grooved disk and roller follower 5. Translating or Wedge cam a. A translation or wedge cam mechanism is the one in which the profile of the is cut on one side of a block or sheet of metal or other material, and the cam has a reciprocating motion along a surface, as illustrated in figure 1.8 below. The same motion, reciprocating, is imparted to the follower during the rise and return movements 6. End or Face cam a. As shown in figure 1.9 below, the cam profile is constructed at the end of a cylindrical element and imparting a reciprocating motion to the follower TYPES OF FOLLOWER (DISK CAM) 1. Knife-edge follower a. This type of follower has no practical application. It is used merely as an aid in the analysis of cam and follower motion. It is suitable only for very light service because the edge cannot be effectively lubricated, pressure is concentrated on this portion, and wear is likely to be excessive b. As shown in figure 1.10 below, the follower point is in contact with the cam surface or profile; and with the follower axis passing through the center of rotation of the cam, the follower is said to be radial point follower. 2. Radial Roller follower a. This type of follower is using roller on the point of contact with cam surface for smooth operation. The follower is guided (frame) so as to move with rectilinear motion (translating or reciprocating). If the follower axis is passing through the cam center of rotation, the follower is said to be radial roller follower (Figure 1.12). Figure 1.13 illustrates an Off-set roller follower. 3. Oscillating Roller follower a. Oscillating Roller follower is also known as Pivoted roller follower, illustrated in Figure 1.14 below. The follower is pivoted about a fixed point while receiving an oscillating motion from the cam. 4. Flat aced follower a. A reciprocating flat-faced follower can be either In-line or Off-set, as shown in figure 1.15 and Figure 1.16, respectively. However, these two types are kinematically equivalent. This means that given a particular cam, the output motion of an in-line or off-set reciprocating flat-faced follower will be the same. 5. Oscillating flat-faced follower a. Oscillating flat-faced follower is also known as a pivoted flat-faced follower. As shown in figure 1.17 below, the follower is pivoted about a fixed axis while receiving an oscillating motion from the cam. 6. Oscillating spherical-faced follower a. As shown in Figure 1.18, iliustrates an oscillating spherical-faced follower pivoted about a fixed point as receiving an oscillating motion from the cam CAM NOMENCLATURE (TERMS) Trace point – a point on the follower that corresponds to the contact point of a fictitious knife-edge follower that would give the same output as the actual follower. Pitch curve – Path of the trace point relative to the cam. Base circle – The smallest circle tangent to the cam surface. Prime circle – The smallest circle tangent to the cam pitch surface. Pressure angle – an angle between the direction of motion of the direction of motion of the trace point and the line of action, also called the common normal. Stroke – The distance between the extreme positions of the follower. Displacement diagram – The relations between the successive positions of the driver and follower in a cam motion, whose abscissas are linear distances arbitrarily chose to represent angular motion of the cam and whose ordinates are corresponding displacements of the follower from initial position. TYPES OF FOLLOWER MOTION 1. 2. 3. 4. 5. Straight line, Uniform motion, or Constant Velocity motion Parabolic motion, Gravitational motion, or Uniformly Accelerated motion Simple Harmonic motion (SHM) Cycloidal motion Polynomial motion ANALYSIS OF FOLLOWER MOTIONS h or L – stroke β – cam angle θ – angle turned by the cam of distance s – any distance displaced by the follower V – velocity of the follower a – acceleration of the follower J – jerk (3rd derivative of s) Uniform Motion The simplest type of motion. It gives a constant Velocity for the rise and the return movement of the follower. Acceleration and Jerk are infinite at the beginning and end of motion causing extreme shock at these points. SIMPLE HARMONIC MOTION To analyze Simple Harmonic Motion, consider the generating circle shown below. Let radius CE rotating at constant angular velocity, together with point E moving on the rim of the generating circle. As point E moves, consider its projection, point P, also moves on the horizontal diameter of the circle. For one revolution of point E, point P completes on reciprocating motion on the horizontal diameter. The type motion of point is called simple harmonic motion. Analysis of Cycloidal Motion Cycloidal Curve is the path traced out by a point on a circle as the circle is rolled a straight line. As shown in the figure below, consider a disk roll for one revolution that displaces a horizontal distance equal to its circumference.
