User`s manual
6-2 Motion Mate™ DSM314 for Series 90™-30 PLCs User's Manual
–
January 2001 GFK-1742A
6
switch. An OFF to ON transition of the
Find Home
%Q command yields the following home
cycle. Unless otherwise specified, acceleration is at the current
Jog Acceleration
and configured
Jog Acceleration Mode
.
Find Home Routine for Home Switch
If initiated from a position on the positive side of the home switch, in which case the home switch
must be OPEN (Logic 0), the Find Home routine starts with step 1 below. (All of the first several
steps of the following routine are necessary to allow for a variety of possible home switch designs
and starting positions.) If the Find Home routine is initiated from a position on the negative side
of the home switch, in which case the home switch must be CLOSED (Logic 1), the routine starts
with step 3 below.
1. The axis is moved in the negative direction at the configured
Find Home Velocity
until the
Home Switch input closes.
2. The axis decelerates and stops.
3. The axis is accelerated in the positive direction and moved at the configured
Find Home
Velocity
until the Home Switch input opens.
4. The axis decelerates and stops.
5. The axis is accelerated in the negative direction and moved at the configured
Final Home
Velocity
until the Home Switch input closes.
6. The axis continues negative motion at the configured
Final Home Velocity
until a marker
pulse is sensed. The marker establishes the home reference position.
7. The axis decelerates and stops (at a position past the marker pulse).
8. The axis is moved, at the current
Jog Velocity
, the number of user units specified by the
Home Offset
value from the home reference position. If
Home Offset
= 0, the axis moves
back to the position of the marker pulse.
9. The axis decelerates and stops.
10. The DSM314 sets the
Commanded Position
and
Actual
Position
%AI status words to the
configured
Home Position
value. Finally, the DSM314 sets the
Position Valid
%I bit to
indicate the home cycle is complete.
Home Switch Example
Many different home switch designs are possible. The switch may be normally open or normally
closed, and may be mounted in one of several possible locations. The example given in this
section illustrates a fairly common arrangement used for linear axes. In the following picture, the
home switch is a normally open proximity switch, mounted near the end of the machine slide’s
travel range (in the negative direction). The imaginary line that divides the home switch’s
positive and negative sides is the home switch’s operating point, located approximately on the
switch’s centerline. If the machine slide travels in the negative direction far enough so that the
right-hand edge of the home switch cam causes the home switch to close, we consider the machine
slide as having crossed over to the “negative side” of the home switch. The home switch cam is
long enough so that while the machine slide is on the negative side of the home switch, it will
keep the normally open home switch closed.
Note the relationships of the home position, the negative overtravel position, and the positive stop
position. A small amount of distance is provided in the negative direction between the home
position and the negative overtravel position. This is to allow some “working room” for