Motions

MACHINE ELEMENTS 2 Cams ? Cam is a impinging having an irregular surface or groove that imparts doubtfulness to a colleague ? Cams are very important and frequently occurring elements in legion(predicate) typesetters cases of machines oddly AUTOMATIC MACHINES ? Cams are the heart of much(prenominal) automatic pistol devices as automatic devices as automatic machine tools, record changers, mechanical calculators, cash registers, and many other devices. Types of Cams interrogations Used for Cam Followers ? The head of the henchman is of primary gratify in the analysis of existing cams or in the design of bleak cams. It is easier to analyze the motion of cam accomplices if their motion is plotted as a graph often referred to as DISPLACEMENT DIAGRAM A. Displacement draw B. Motions that are most commonly used 1. Uniform Velocity (straight parenthood) motion UVM 2. Simple concordant Motion SHM 3. Uniformly Accelerated motion (Parabolic Motion) UAM or PM 4. change Unif orm-Velocity Motion MUVM a. Arc method MUVM-Arc b. Uniform quickening Method MUVM-UAM 5. rounded Motion CM A. Uniform Velocity Motion (Straight Line Motion)If the follower is to move with uniform velocity, its sack reaction must be the same for relate units of while. Its curve in the displacement draw, therefore, is a truthful LINE. subject 1 Lay kayoed the displacement diagram for a cam follower that is to form the following motions hatch 30O (at rest) Rise 2 indiumes in 90O (uniform velocity) exist 30O cutpurse 2 inches in 60O (uniform velocity) Dwell 150O B. Simple Harmonic Motion (SHM) As a point moves around the lap of a disseminate with a constant velocity, its projection on the diameter of the bent moves with simple harmonic motion.How to plot in the displacement diagram? Example 2 Lay out the displacement diagram for a cam follower that is to have the following motions Rise 2 inches in 120O (SHM) Dwell 30O Fall 1 inch in 90O (SHM) Dwell 30O Fall 1 inch in 60O (SHM) Dwell 30O C. Uniformly Accelerated Motion (Parabolic Motion) ? A motion of uniform or constant acceleration, often called parabolic motion because a graph of its equation ( s = at2 / 2 ) is a parabola. ? It is motion in which the displacement taking place in each successive musical interval of time proportional to the square of the time.How to plot in the displacement diagram? Example 3 Layout the displacement diagram for a cam follower that is to have the following motions Rise 2 inches in 120O (uniform acceleration and deceleration motion) Dwell 30O Fall 1 inch in 90O (uniform acceleration and deceleration motion) Dwell 30O Fall 1 inch in 90O (uniform acceleration and deceleration motion) D. Modified Uniform Velocity Motion a) Arc Method This method consists nevertheless in introducing arcs at the beginning and at the end of the displacement period.The surface of the arcs is arbitrary, but they are usually drawn with a radius equal to one half the displacement. The arcs are drawn first to an indefinite duration thence a straight line is drawn tangent to some(prenominal) arcs. b) Uniform Acceleration Method This method consists in introducing short periods of uniform acceleration or deceleration at both ends of the displacement period. D. Cycloidal Motion ? If a circle rolls along a straight line without slipping, a point on its circumference traces a curve that is called a cycloid. How to plot in the displacement diagram?In the figure infra shows how such motion is laid out in a displacement diagram. Line AB is drawn and is extended to some point such as C. A circle is drawn at C whose circumference is equal to the displacement s or whose diameter is equal to s over constant pi. The circumference of this circle is divided into a form of parts equivalent to the enactment of divisions along the horizontal scale. The points around the circle are projected to the vertical center line of the circle and then parallel to the line AB to the corre sponding vertical lines in the displacement diagram. - pic pic pic pic pic pic In this construction, it should be noted that the diameter of the semicircle is equal to the follower rise and that the number of divisions around the semicircle agrees with the number of divisions along the time axis (angle of cam rotation). pic pic The figure at the left shows the displacement, s of a go object compares with arbitrary time units pic a) First method (Figure the right)In laying out this type of motion in a displacement diagram, a habituated displacement is divided into two halves the first half is uniformly accelerated, and the abet half is uniformly retarded motion. It is therefore, necessary that the horizontal distance gnarly in the total displacement be divided into an even number of divisions. pic b) Second Method (Figure the left) Figure as shown, shows an alternative method of constructing this type of motion. In this case, the half displacement is divided into equal sized d ivisions corresponding to the number of horizontal divisions. pic pic pic pic