Siemens SINUMERIK 840C - Manual (Page 899)

12 Functional Descriptions 12.93
12.16.3 Installation
The acceleration values are derived from | a | = v 2 /r from the radius and travel velocity. The
acceleration value can easily be varied using the override switch.
Before entering these acceleration values a
3
, a
2
and a
1
in machine data 1244*, 1248* and
1252*, it may be necessary to convert to the input format of the machine data ([mm/s 2 ]
[100 units MS/s 2 ] and/or [10000 units MS/s 2 ]).
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 a
3
, a
2
and a
1
for the
characteristic.
a
1
<a
2
<a
3
If this condition is not met, parameter error 328 is output. The user should therefore follow the
input sequence a
3
, a
2
and then a
1
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 a
3
, a
2
and a
1
. 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 = v 2 /r
A radius of 10 mm and a circular velocity of 1 m/min = 16.7 mm/s produces an
acceleration a = 16.7
2 /10 [mm/s 2 ] = 27.78 mm/s 2 .
b) Entering the characteristic break points
The following accelerations were determined as the characteristic break point:
a
1
= 1.11 mm/s 2 , a
2
= 27.78 mm/s 2 , a
3
= 695 mm/s 2
The position control resolution 0.5 . 10 - 4 mm was selected, resulting in:
1000 units[MS] = 1 mm
The characteristic break points are therefore:
a
1
= 11100 units/s 2 , a
2
= 277800 units/s 2 , a
3
= 6950000 units/s 2
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 resolution
b) raise the smoothing time constant (MD 1256*), values 100 ms are
recommended
12–124 © Siemens AG 1992 All Rights Reserved 6FC5197- AA50
SINUMERIK 840C (IA)