Model 07: dwell mechanisms
Kinematic scheme:
Dimensions:

Measured at model [m] 

a 
0.050 
m 
0.210 
b 
0.166 
n 
0.173 
c 
0.180 
p 
0.135 
d 
0.280 
q+t 
41.0 
e 
0.108 
r 
0.235 
f 
0.075 
s 
0.105 
g 
0.132 
u 
0.274 
h 
0.131 
v 
0.086 
j 
0.092 
x 
0.136 
k 
0.165 
y 
0.076 
Explanation:
Coupler points C and D are used to connect a dyad (twolink) to the
frame, yielding rocker angles β and γ as output. At the coupler curve position where the radius
of curvature has a maximum value, the matching circle with that radius has been
determined. The connection bars in C and D respectively have the length of the
matching circle radius, while the other connection point is in the centerpoint
of the circle. The rockers have then instantaneous dwell. The model
demonstrates which of the two dwell mechanisms (red or blue) has the “best”
dwell. The points C and D have been determined by a graphic construction, using
the circlepoint curve and the point of Ball on the coupler plane. Theoretically
the red one (D matches the point of Ball) is better, and this is confirmed by
moving the model. Numeric calculation of β(α) and γ(α) with
the model dimensions confirms also the conclusion, see below.
Literature:
Remarks: For convenience
of comparing the two dwell mechanisms the extra links p and q (blue) have been
added in the model. Note that the rockers m and q are not exactly parallel, but
the demonstrated effect is still clear.