Tham khảo tài liệu 'robotics designing the mechanisms for automated machinery part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Camshafts 123 FIGURE Mechanism for contour grinding. Views of contours produced when settings of parts 1 and 3 are changed. Camshafts It is not always possible to satisfy the desired position function by means of the mechanisms discussed in the previous section. The requirements dictated by the timing diagram see Chapter 2 vary but they can often be met by using cam mechanisms. The idea underlying such mechanisms is clear from Figure in which a disc cam is presented schematically. A linearly moving follower has a roller to improve friction and contact stresses at the cam profile-follower contact joint. It is easy to see that by rotating the cam from positions 0 to 11 the follower will be forced to move vertically in accordance with the radii of the profile. Graphical interpretation of the position function has the form shown in Figure . During cam rotation through the angle 0 positions 0-1-2-3-4-5 the follower climbs to the highest point during the angle 02 6-7-8-9-10-11 it goes down and during the angle 03 the follower dwells because this angle corresponds to that part of the profile where the radius is constant . Changing the profile radii and angles yields various position functions which in turn produce different speeds and acceleration laws for the follower movements. Figure illustrates the cosine acceleration law of follower movement. The analytical description of this law is given by the following formulas h 2 s n 0 4 l-cos r I 2l 01J TEAM LRN n dộ 2 . Ộ in yr 7Ĩ p sin 01 4 n 0 4 dộ2 2 ĨT2__Ộ cos r . 021 01 0 124 Kinematics and Control of Automatic Machines FIGURE a Disc cam mechanism b The follower motion law. To provide the desired sequence and timing of actions it is convenient to mount all cams needed for the machine being designed on one shaft thus creating a camshaft for example as shown in Figure . One rotation of this shaft corresponds to one cycle of the machine and thus one revolution lasts one period
