12 Functional Descriptions 12.93
12.16.3 Installation
The acceleration values are derived from | a | = v2/r from the radius and travel velocity. The
acceleration value can easily be varied using the override switch.
Before entering these acceleration values a3, a2 and a1 in machine data 1244*, 1248* and
1252*, it may be necessary to convert to the input format of the machine data ([mm/s2]
[100 units MS/s2] and/or [10000 units MS/s2]).
A monitoring function in the control ensures that incorrect parameterization of the
characteristics for the friction feedforward control are avoided.
The following conditions must be met when entering accelerations a3, a2 and a1 for the
characteristic. a1<a2<a3
If this condition is not met, parameter error 328 is output. The user should therefore follow the
input sequence a3, a2 and then a1 when entering the acceleration values . Parameter error
328 is also output if internal formats are exceeded as a result of calculation errors when
determining the accelerations from inputs a3, a2 and a1. If this happens, the user must check
whether the break points in the curve have been correctly calculated and/or have been entered
in the correct input format (caution: MD 1252* uses a format factor 100 larger than MDs 1244*
and 1248*!)
Example for setting the characteristic:
a) To derive the actual acceleration
The acceleration when passing through zero speed in a circular path is calculated as
follows:
a = v2/r
A radius of 10 mm and a circular velocity of 1 m/min = 16.7 mm/s produces an
acceleration a = 16.72/10 [mm/s2] = 27.78 mm/s2.
b) Entering the characteristic break points
The following accelerations were determined as the characteristic break point:
a1 = 1.11 mm/s2, a2 = 27.78 mm/s2, a3 = 695 mm/s2
The position control resolution 0.5
.
10 - 4 mm was selected, resulting in:
1000 units[MS] = 1 mm
The characteristic break points are therefore:
a1 = 11100 units/s2, a2 = 277800 units/s2, a3 = 6950000 units/s2
The following values must therefore be entered in the machine data in the given order:
MD 1252* = 695, MD 1248* = 2778, MD 1244* = 111
If unsatisfactory results are obtained for very low speed values,a) increase the position control resolutionb) raise the smoothing time constant (MD 1256*), values 100 ms arerecommended
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SINUMERIK 840C (IA)