Civil Engineering Reference
In-Depth Information
FIGURE 3.6
Block diagram of model of the system with the grinding process.
FIGURE 3.7
MRR vs. Normal grinding force (3 Set-ups for 1020 steel).
the lower section of the figure. Here the relationship between the measured output of the position
loop, (
x
e
) and the actual ground surface position,
x
f
, for a plunge grinding is seen. Note the interaction
between the servo controlled position measurement,
x
e
, and the workpiece may be thought of as a spring,
K
S
, and damper,
B
S
. Higher order system effects of the grinding wheel are generally neglected in this
approach. It can be readily seen from examining
Fig. 3.6
,
that the grinding process affects the overall
system response and any attempt to control the grinding normal force.
The process model of the complete grinding system is given in the box with the dotted line in
Fig.
3.6
.
It is apparent that the part surface in contact with the grinding wheel is continuously being ground
away, thus its position is always changing. Therefore, the position of the part surface (
x
f
) is subtracted
from the controlled position (
x
e
) in order to determine the relative compression of the system. When
this relative compression is multiplied by the effective impedance of the servo stage/force sensor/grinder
(
K
s
s B
s
), the normal force (
F
N
) between the part and the wheel is found.
The normal force, less the threshold normal force, is entered into grinding force model equation
(multiplied by
K
P
V
) to determine the expected material removal rate (
Q
). This material removal rate is
assumed to be uniform over the contact area, and so dividing the material removal rate by the contact
area yields the velocity at which the ground surface is advancing
()
x
˙
f
. Integrating this value produces the
