Page 325 - Cam Design Handbook
P. 325

THB10  9/19/03  7:28 PM  Page 313

                                     CAM MANUFACTURING                     313

            intensities and frequencies. These dynamic forces, which are of indeterminable magni-
            tude, affect the cam profile, accuracy, surface quality, and life. Moreover, the magnitude
            of these factors and the performance of the cam-follower systems are greatly influenced
            by the fabrication of the cam profile. The interrelated factors of accuracy, cost, and time
            are pertinent to the study. Poor manufacturing techniques can seriously impede the func-
            tional ability of the mechanism. Under most methods of fabrication, the actual and the
            theoretical cams rarely agree. Accuracies as close as ±0.0001in may be necessary in high-
            speed machinery. The following are some brief thoughts:
            • Make parts as rigid as possible to keep flexibility to a minimum. Use laminated ther-
              moset resins, carbides, and new materials if possible and practicable.
            • Make the component moving parts of the machine as light as possible. Use new materials
              such as titanium, magnesium, and aluminum, if feasible. We should aspire for a high
              natural frequency of the follower linkage. If resonance occurs in a given speed range, it
              will be with a higher harmonic number and consequently smaller amplitude harmonics.
            • Surface finish and accuracy of fabrication are of prime importance. Be sure that cams
              are cut accurately in accordance with the theoretical contours so that benefit from the
              mathematics is not lost. Keep surface errors to a minimum.
            • Backlash in parts should be held to a minimum. Preloaded bearings and followers are
              a possible solution.
            • Use low-friction bearings, and lubricate all mating surfaces.
            • Balance the cams with intelligent proportioning of the mass.
            • For high-speed production machinery DRD cam curve choices are the modified sine and
              the modified trapezoid. These yield low accelerations and no discontinuities. Both have
              excellent follower vibration performance.


            REFERENCES

            Barkan, P., The Calculation of High-Speed Motion of a Flexible Cam Actuated System, Ph.D. disse.,
              Pennsylvania State University, 1953.
            Grewal,  P.S.,  and  Newcombe, W.R.,  “Dynamic  Performance  of  High-Speed  Semi-Rigid  Follower
              Cam Systems—Effects of Cam Profile Errors,” Mech. Mach. Theory, 23 (2): 121, 1988.
            Harris, T.A., “Rolling Bearing Analysis,” John Wiley and Sons, New York, 1991.
            Johnson, R.C., “Method of Finite Differences in Cam Design,” Machine Design, 27: 195, 1955.
            Kim, H.E., and Newcombe, W.R., “Stochastic Error Analysis in Cam Mechanisms,” Mech. Mach.
              Theory, 13, 1978.
            Kim, H.E., and Newcombe, W.R., “The Effect of Cam Profile Errors and System Flexibility on Cam
              Mechanism Output,” Trans. ASME, Mechanism and Machine Theory, 17 (1): 57, 1982.
            Newcombe, H.R., and Kim, H.E., “Some Results of the Effect of Waviness in Cam Profiles on the
                               th
              Output Motion,” Trans. 8 OSU Applied Mechanisms Conference. St. Louis, Mo., 1983.
            Norton, R.L., “Effect of Manufacturing Method on Dynamic Performance of Cams,” Mechanism and
              Machine Theory, Parts 1 and 2, 23 (3): 291–208, 1988.
            Olderfield, J., “On Application of Finite-Difference Method for Kinematics of Mechanisms,” Zas-
              tosowania Matematyki IV (in Polish.), p. 176, 1958.
            Wiederrich,  J.L.,  Design  of  Cam  Profiles  for  Systems  with  High  Inertial  Loadings,  Ph.D.  thesis,
              Stanford University, Palo Alto, Calif. 1973.
   320   321   322   323   324   325   326   327   328   329   330