Mitsubishi Electric MELSEC iQ-R Series User Manual page 345

Precautions
• Values less than one which could not be output during machine movement are managed in the motion system, and the
cumulated values will be output when the value reaches one pulse or more.
• When machine homing is completed, the function clears to "0" the cumulative values of less than one pulse which could not
be output.
• When the driver unit conversion numerator/denominator is changed, the homing request flag turns TRUE.
• Double-precision floating-point type variables are used for calculation of the cumulative current value and the target
position that is sent to the driver. Therefore, values that can not be expressed within the effective digits of the double
precision floating point format (the range of the mantissa part 53 bits) include errors due to rounding processing.
• The target position is calculated by a formula, "cumulative machine position from home position  driver unit conversion
numerator / driver unit conversion denominator". Set so that the integral part of the calculation result does not exceed the
effective digits range.
Since the target position send a value which is obtained by truncating the fractional part of the operation result, errors due
to rounding processing is truncated when it is less than or equal to the decimal point. However, when the integer part
becomes larger than the effective digit, the command value actually output will also contain rounding error.
• When the cumulative current value per pulse after the driver unit conversion ("1  driver unit conversion denominator /
driver unit conversion numerator") is a small value less than effective digits to the present cumulative current value, the
correct command cannot be sent in units of 1 [pulse].
• When the error size is a problem, change the following setting.

Reduce the multiplying factor of "driver unit conversion numerator / driver unit conversion denominator".
For example, when setting 20 [mm] to the machine movement amount per motor rotation, set "20000" in
AxisName.Pr.Drive_UnitConvRatioDen, and set [

m] in AxisName.Pr.Unit_Position. (20.0 [mm]  20000.0 [m])
11 CONTROL SUB FUNCTIONS
11.1 Compensation Function
11
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