Siemens SINUMERIK 840D Description Of Functions page 238

A Hydraulics
A.1 Servo solenoid valves
Flow
characteristic,
knee-shaped
Linearization of
knee-shaped
characteristic
A-238
SINUMERIK 840D/SIMODRIVE 611 digital Descr. of Functions HLA Module (FBHLA) – 04.00 Edition
In addition to valves with a linear characteristic, values with a knee-shaped
characteristic are used in many cases to increase the finer resolution in the
positioning range to better control the effects of static/sliding friction. These are
achieved by means of corresponding windows (control edges) in the steel valve
sleeve. A constant machining velocity of the drive directly at the knee-point of
the valve is not recommended.
Definition for the position of the knee-point, e.g. 40% knee.
Up to 40 % of the spool value or setpoint signal, only 10 % of the maximum
opening cross-section (flow) is released.
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Fig. A-8 Definition of flow characteristic
Î Î Î Î Î Î Î
Î Î Î Î Î Î Î
Î Î Î Î Î Î Î
Î Î Î Î Î Î Î
Spool stroke
Fig. A-9 Valve with knee-shaped characteristic
The knee-shaped characteristic of the valve is linearized in the HLA module to
match it to the closed-loop control of the overall drive (cylinder). No steady-state
operating point should be defined in the knee-point area.
The corresponding valve data are stored in the HLA module and automatically
parameterized when the order number is entered.
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Fig. A-10 Linearization of knee-shaped characteristic
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Rapid traverse
10%
40%
Machining velocity
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Q
40 % U
E
+Q
Valve characteristic
Linearized characteristic
10%
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40%
Compensation
–Q
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