Page 159 - Mechatronics with Experiments

MECHANISMS FOR MOTION TRANSMISSION 145

Crank position
& speed
r*cos(u(1)) + l* (1- ((r/l)* sin(u(1)))^2)^0.5
Crank angle: Fcn: x(theta)
2pi rad Slider position
& speed
sin(u(1))+(r/(2*l)) *(sin(2*u(1))/(1-((r/l)*sin(u(1)))^2)^0.5)
20*2*pi
Fcn1
Crank
speed [red/s] –1 x
r
Product
Gain

FIGURE 3.8: Simulation result of slider crank mechanisms: r = 0.3m, l = 1.0 m, speed of crank
shaft is constant at ̇ = 1200 rpm. The resulting slider position and speed functions are shown
in the figure.
®
®
The MATLAB or Simulink environment can be conveniently used to generate the results
(Figure 3.8).

3.4.2 Cams
Cams convert the rotary motion of a shaft into translational motion of a follower (Figure 3.9).
The relationship between the translational motion and rotary motion is not a fixed gear ratio,
but a nonlinear function. The nonlinear cam function is determined by the machined cam
profile. A cam mechanism has three major components:

1. the input shaft,
2. the cam,
3. the follower.

If the input shaft axis of the cam is parallel to the follower axis of motion, such cams are
called axial cams. In this case, cam function is machined into the cylindrical surface along
the axis of input shaft rotation. If they are perpendicular to each other, such cams are called
radial cams and the cam function may be machined either along the outside diameter or face
diameter. All cam profiles can be divided into periods called rise, dwell, and fall in various
combinations. For instance, a cam profile can be designed such that for one revolution of
the input shaft, the follower makes a cyclic motion that is various combinations of rise, fall,