Cam Shaping Method; Cam Characteristics - ABB AV3 Instruction Manual

CAM SHAPING METHOD

10 0
9 0
8 0
7 0
6 0
% O F
5 0
S IG N A L
4 0
3 0
2 0
1 0
0
0 10
Figure C-6. Cam Characteristics
6. If the required characteristic cannot be obtained using the
above procedure, or if more exact characteristics are required, alter
the shape of a standard A, B, or C cam or cut a new cam from a blank
cam as outlined under CAM SHAPING
To assist in the alteration process, a graph is imprinted on each cam.
This graph consists of radial lines and concentric arcs. The first and
last radial lines mark the angles at which zero and 100 percent of cam
rotation occur for control purposes; the radial lines in between are
equal intervals of rotation. These lines are indexes of percentage of
piston (or valve) travel.
The concentric arcs on the cam correspond to actual control signal
pressure values shown in Table
used. Together, the radial lines and concentric arcs form a polar dia-
gram on which a new cam shape (and characteristic) can be plotted.
NOTE: Before cutting any cam, make sure that shaping will involve
removal of cam material and not build up of cam material. For exam-
ple if the characteristic plotted lies between the A and B cams
(Figs. C-1 and C-2), cut the A away.
1. Use the cam selected in Step 4 under
have available a graph of control signal versus actuator travel for the
characteristic desired. (Such a graph may be derived from the cam
characteristic curve developed in Step 3 of
ply replace the percent values on the vertical axis with the corre-
sponding actual signal from Table C-1 for the positioner being used.
CAM CHARACTERIZATION
20 30 40 50 60 70
% O F P IS TO N O R VALV E T R AV E L
METHOD.
C-1 for the particular positioner being
CAM
CAM
CAM SHAPING METHOD
8 0 9 0 10 0
T 00 7 96 A
SELECTION. Also
SELECTION). Sim-
C - 5