CAM CONTROLLED PLANETARY GEAR

DEVICES

How Gears Work

Gears are used in tons of mechanical devices. They do several important jobs, but most important, they provide a gear reduction in motorized equipment. This is key because, often, a small motor spinning very fast can provide enough power for a device, but not enough torque. For instance, an electric screwdriver has a very large gear reduction because it needs lots of torque to turn screws, but the motor only produces a small amount of torque at a high speed. With a gear reduction, the output speed can be reduced while the torque is increased.

Another thing gears do is adjust the direction of rotation. For instance, in the differential between the rear wheels of your car, the power is transmitted by a shaft that runs down the center of the car, and the differential has to turn that power 90 degrees to apply it to the wheels.

Planetary Gearsets

Any planetary gearset has three main components:

The sun gear The planet gears and the planet gears'

carrier The ring gear Each of these three components can be the

input, the output or can be held stationary. Choosing which piece plays which role determines the gear ratio for the gearset.

In general, a mechanism is driven by a motor at uniform speed. However, more and more researches indicate that there are many advantages if a mechanism can be driven at non-uniform speed, and this kind of mechanism is called a variable Input mechanism. The purpose of this work is to propose a novel approach for driving a variable speed mechanism by using a cam-controlled planetary gear train. First, the geometrical design is performed. Then, the kinematic equations and the cam profile equations are derived based on the geometry of the mechanism.

Finally, the validity of the design is confirmed by kinematic and dynamic simulations using ADAMS software. In addition, the feasibility of the proposed method is verified by conducting prototype testing. The experimental results show that the CCPGT is a suitable alternative for driving variable speed mechanisms. In addition, due to its mechanical nature, the CCPGT has the advantages of higher reliability, faster response, and larger power output compared to a servomotor solution.

Cam-controlled planetary gear trains (CCPGT) are planetary gear trains with cam pairs. it is composed of a cam groove (the frame), a sun gear (the output), a planetary gear, and an arm (the input). In general, the planetary arm rotates at constant speed, and drives the planetary gear to revolve around the sun gear and to spin around itself simultaneously. At the same time, the planetary gear produces an oscillatory motion through the contact of the attached roller and the cam groove. Therefore, the sun gear can produce a non-uniform motion by engaging with the planetary gear.

The main advantage is that it can produce a wide range of non-uniform output motion. In addition, it has the advantages of higher reliability, lower cost, faster response, and higher power transmission due to its mechanical nature. It is now at work in film drives. However, the design and analysis of the CCPGT is not easy due to its complex structure.

Moreover, the center distance between the sun gear and the planetary gear is

where Ts and Tp are,

respectively, the number of teeth for the sun gear and the planetary gear, and m is the modulus of both gears.

Also, the position vector of the roller center is

In addition, the length sum of two sides in a triangle must be greater than the length of the other. That is if

then an uncertain state exists such that the rocker will possess two different paths. The uncertain state of amechanism is called the change point, and the configuration is called the uncertainty configuration.

TheCCPGT is then called a change point mechanism, and it should be avoided in mechanism design in general.

The cam in a CCPGT is an inverse cam. The inverse cam is one in which the element corresponding to the follower of a cam mechanism is utilized as the driver. Therefore the cam is fixed, and the follower with a roller will swing if the planetary gear turns around the sun gear.

the solid model of the design is established by CATIA software,

Then the model is introduced into ADAMS software for kinematic and dynamic simulations,

their comparisons with the theoretical (analytical) angular velocity are shown in Fig. 8. Fig. 8(a) shows

that both the angular velocities of theoretical and kinematic simulation are identical; therefore the solid model has been exactly established. Also, the output angular velocity is continuous and smooth, therefore the angular acceleration is continuous. Furthermore, since the amplitude of the angular velocity is relatively large, a

CCPGT can produce a wide range of variable speeds. It is evident that the CCPGT is theoretically suitable for the input source of a variable speed mechanism.

References

[1] N.P. Chironis, Mechanisms & mechanical devices sourcebook, McGraw-Hill, New York, 1991.

[2] H.A. Rothbart, Cams: design, dynamics and accuracy, Wiley, New York, 1956.

[3] D. Tesar, G.K. Matthew, The dynamic synthesis, analysis and design of modeled cam systems, Lexington Books, Lexington, MA,

[4] W.H. Hsieh, Improving the state of motion of followers by controlling cam speed, Master thesis, Graduate School of Mechanical

Engineering, National Cheng-Kung University, Taiwan, ROC, 1991 (in Chinese).

[5] H.S. Yan, M.H. Hsu, M.K. Fong, W.H. Hsieh, A kinematic approach for eliminating the discontinuity of motion characteristics of

cam-follower systems, Journal of Applied Mechanisms and Robotics 1 (2) (1994)

[6] H.S. Yan, M.C. Tsai, M.H. Hsu, A variable-speed method for improving motion characteristics of cam-follower systems, ASME

Transactions, Journal of Mechanical Design 118 (1) (1996) 250–258. [7] H.S. Yan, M.C. Tsai, M.H. Hsu, An experimental study of the effects of

cam speed on cam-follower systems, Mechanism andMachine Theory 31 (4) (1996) 397–412.

Thank you