1. Learning with Purpose February 6, 2013 Learning with Purpose February 6, 2013 22.322 Mechanical Design II Spring 2013

2. Learning with Purpose February 6, 2013 Cam Project

3. Learning with Purpose February 6, 2013 Cam Project

4. Learning with Purpose February 6, 2013 Cam Project

5. Learning with Purpose February 6, 2013 Sizing the cam Base Circle (flat-faced followers) Pitch Circle (roller followers) Pressure Angle & Radius of Curvature Keep minimum radius of curvature of cam pitch curve at least 2-3 times as large as radius of roller follower Dumbbell Curl Example Designing a Cam to maximize workout efficiency Lecture 7 Review from Last Lecture

6. Learning with Purpose February 6, 2013 We would like to design a cam for an exercise machine using a negative cam design: Lecture 7 Negative Cam Design

7. Learning with Purpose February 6, 2013 So if the strength increases for a given angle, R must decrease since PRs is constant. Design the cam by inversion: Lecture 7 Negative Cam Design

8. Learning with Purpose February 6, 2013 So if the strength increases for a given angle, R must decrease since PRs is constant. Design the cam by inversion: Lecture 7 Negative Cam Design

9. Learning with Purpose February 6, 2013 Lecture 7 Negative Cam Design

10. Learning with Purpose February 6, 2013 Cams are usually made from medium to high carbon steels and sometimes plastics. To make a cam, a milling machine or grinder is needed. Usually continuous numerical control (CNC) machines are required to generate the precision needed. Common increments are 1/10, ¼, ½, and 1 degree. Since the machine only has the x and y coordinates of the specified displacement, the machine has to interpolate the missing data. Lecture 7 Cam Manufacturing and Practical Considerations

11. Learning with Purpose February 6, 2013 Manufacturing errors can occur due to: Cutting process feed rate Tool sharpness Milling speed Chatter Milling tool deflection Etc. Consider a cam that has a roller follower. The following cam was milled on a high quality CNC milling machine using 1 degree linear interpolation: Lecture 7 Cam Manufacturing and Practical Considerations The actual displacement is true to the theoretical, but the acceleration has a significant amount of vibratory noise.

12. Learning with Purpose February 6, 2013 Compare with the same shaped cam that has the same geometry except it was turned and ground (less noise & wear; smoother run): Lecture 7 Cam Manufacturing and Practical Considerations A ground cam is superior to a milled cam but is more costly to make (in small quantities, grinding almost doubles the cost of a cam). Automotive valve cams are ground. Made in large quantity, run at very high speed and are expected to last for a very long time with minimal maintenance.

13. Learning with Purpose February 6, 2013 Cam lubrication is also very important to reduce wear & heat (friction) Could lead to early failure Automotive cams are literally drowned in a flow of filtered and sometimes cooled engine oil. Unless there’s a good reason not to use lubrication, a cam-follower should be provided with generous supply of clean lubricant Camera mechanisms often run dry or else lubricant would find its way to the film Lecture 7 Cam Lubrication

14. Learning with Purpose February 6, 2013 Roller follower is a better choice from a cam design standpoint simply because it accepts negative radius of curvature on the cam. Allows more variety in the cam program Reduced friction Not too expensive Flat follower can save space Can be custom-designed More expensive Largest users are automobile engine makers  although many have switched to roller followers for improved friction/better fuel economy Lecture 7 Roller vs. Flat-Faced Follower

15. Learning with Purpose February 6, 2013 Lecture 7

16. Learning with Purpose February 6, 2013 Sketch the equivalent fourbar linkage for the position of the cam and follower shown: Lecture 7 Quiz