User`s manual

4-14 Motion Mate™ DSM314 for Series 90™-30 PLCs User's Manual – January 2001 GFK-1742A
4
This ratio is too small, so something must be changed. Any of the following system
components could be changed to solve the problem:
•
Change the spur gear diameter to 15.92 inch or larger
•
Change the encoder lines per revolution to 1800 or less
•
Change the gear reduction to 18:1 or less
•
Change the desired programming unit to 0.001 inch
By far, the easiest component to change is the desired programming unit to 0.001 inch.
4. Now, recalculate to determine the revised User Units per revolution using 0.001 inch
programming unit.
14.336 inches diameter * pi = 45.0378 inches circumference
45.0378 inches / 0.001 inch programming unit = 45,037.8 User Units per revolution of
spur gear
Thus, the User Units to Counts ratio is 45,038 / 160,000 = 0.2815 or about 1:3.6 which is
within the valid ratio range.
So a 45,038 / 160,000 ratio would be used except that 160,000 is larger than the maximum
65,535 range value. Dividing both numbers by 10 solves this to make the ratio 4,504 /
16,000. Note that in the above example, we simply reduced the fraction and ignored the
slight rounding error
One method of avoiding “rounding” is to express the numeric ratio as a fraction. From the
previous example, any number set that produced a 0.2815 ratio could be used. An
example is 2815 / 10000.
Another approach is to rationalize the fraction (reduce it to its lowest terms). This is done
by evenly dividing both the numerator and denominator by successively smaller prime
numbers, beginning with the largest prime that will evenly divide into both the numerator
and the denominator, until no more division without remainders is possible.
Always maintain an exact integer fraction, a decimal ratio expressed as a fraction, or a rationalized
fraction when configuring the User Units to Counts ratio for the best accuracy. The user must
determine if the rounding error, if present, is of significance. A rotary mode application that always
operates in one direction will accumulate rounding errors over time and “drift”. A linear
application will only accumulate error for the length of travel then “rewind” as the axis reverses.
5.02 Overtravel Limit Switch
.
Selects whether the DSM300 Series module uses the hardware
over travel limit switch inputs.
DISABLED
, the faceplate overtravel inputs (IN09 and IN10) may be used as general-purpose
motion program flow control and program branching inputs (assigned to CTL01-CTL24).
ENABLED
, indicates that the DSM300 will check the axis over travel inputs continuously, every
10 milliseconds whenever the %I
Drive Enabled
input is true. If either limit switch opens (the
input goes to logic zero, Off) all motion is immediately commanded to stop. No deceleration
control is active; the servo velocity command is set to zero. The solid state axis enable relay will