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User Manual
Chapter 4
GFK-1742F
Jan 2020
Configuration
112
above example, we simply reduced the fraction and ignored the slight
rounding error
One method of avoiding “rounding” is to express the numer
ic 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 not open until after the %Q Enable
Drive command is set to zero. An error code indicating which limit is tripped is
reported to the %AI Axis Error Code. At this point, only one DSM314 action is
allowed: the appropriate %Q Jog and %Q Clear Error bits may be used simultaneously
to back away from the Limit Switch. The %Q Clear Error bit must be maintained ON
to Jog off the limit switch. The user may also manually move the disabled axis off the
limit switch. After the alarm is cleared, normal operation may resume.
CAUTION
Force D/A commands ignore the limit switches and should be used with caution.