tailieunhanh - Mechanical Devices Sourcebook 3rd ed mcgraw hil 2001 Episode 1 Part 7

Tham khảo tài liệu 'mechanical devices sourcebook 3rd ed mcgraw hil 2001 episode 1 part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CHAPTER 7 CAM TOGGLE cHaIN and BELT mechanisms CAM BASICS A cam is a mechanical component that is capable of transmitting motion to a follower by direct contact. The driver is called a cam and the driven member is called the follower. The follower can remain stationary translate oscillate or rotate. The motion is given by y 0 where y cam function follower displacement in. . external force lb and 0 wt - cam angle rotation for displacement y rad . Figure 1 illustrates the general form of a plane cam mechanism. It consists of two shaped members A and B with smooth round or elongated contact surfaces connected to a third body C. Either body A or body B can be the driver while the other is the follower. These shaped bodies can be replaced by an equivalent mechanism. They are pin-jointed at the instantaneous centers of curvature 1 and 2 of the contacting surfaces. With any change in relative positions the points 1 and 2 are shifted and the links of the equivalent mechanism have different lengths. Figure 2 shows the two most commonly used cams. Cams can be designed by Shaping the cam body to some known curve such as involutes spirals parabolas or circular arcs. Designing the cam mathematically to establish the follower motion and then forming the cam by plotting the tabulated data. Establishing the cam contour in parametric form. Laying out the cam profile by eye or with the use of appropriately shaped models. The fourth method is acceptable only if the cam motion is intended for low speeds that will permit the use of a smooth bumpless curve. In situations where higher loads mass speed or elas- Fig. 1 Basic cam mechanism and its kinematic equivalent points 1 and 2 are centers of curvature of the contact point. ticity of the members are encountered a detailed study must be made of both the dynamic aspects of the cam curve and the accuracy of cam fabrication. The roller follower is most frequently used to distribute and reduce wear between the cam and the .