ME 222 Kinematics of Machines and Mechanisms L

ME 222: Kinematics of Machines and Mechanisms [L 33] Cam Design 5 2/27/2021 Suril V. Shah IIT Jodhpur 1

Cam Profile Generation Analytical Graphical Suril V. Shah 2

Cam Profile Suril V. Shah 3

Cam Profile Suril V. Shah 4

Cam Profile Suril V. Shah 5

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Some terminology The base circle is define as the smallest circle that can be drawn tangent to the physical cam The prime circle is defined as the smallest circle that can be drawn tangent to the locus of the centerline of the follower The locus of the centerline of the follower is called the pitch curve. Suril V. Shah 7

Important Factors Pressure angle is the angle between the direction of motion (velocity) of the follower and the direction of the axis of transmission Radius of curvature is the radius of a circle which touches a curve at a given point and has the same tangent and curvature at that point. Suril V. Shah 8

ISSUES: Pressure Angle Suril V. Shah 9

ISSUES: Radius of curvature (-ve or concave) Suril V. Shah 10

Sizing of CAM Pressure Angle Radius of Curvature Function of base/prime circle radius and s, v and/or a 2/27/2021 Suril V. Shah IIT Jodhpur 11

Pressure Angle: Eccentric Cam & Roller Follower Eccentricity is defined as the perpendicular distance between the follower's axis of motion and the center of the cam. • zero for an an aligned follower, Suril V. Shah 12

Pressure Angle Suril V. Shah 13

Pressure Angle The distance b to the instant center I 2, 4 is equal to the velocity of the follower v in units of length/radian Suril V. Shah 14

Pressure Angle Suril V. Shah 15

Pressure Angle Manipulate Rp and ε to get an acceptable maximum pressure angle (φ). As Rp is increased, (φ) will be reduced. Large values of Rp increase size and cost. Suril V. Shah 16

Pressure Angle For +ω, + ε will decrease the pressure angle on the rise but will increase it on the fall and vice versa. Affordable force-closed cam with spring return If adjustments to Rp or ε do not yield acceptable pressure angles, return to an earlier stage in the design Less lift or more time to rise or fall will reduce the causes of the large pressure angle. Design is, after all, an iterative process. Suril V. Shah 17

SVAJ DIAGRAMS Suril V. Shah 18

Pressure Angle Suril V. Shah 19

Thank you Next Class: Sizing of CAM 2/27/2021 IIT Jodhpur 20