Siemens Sinumerik 840D Series Function Manual page 33

10.03
Servo solenoid or
HR servo solenoid
valves
Valve size
Linear/knee-shape
d flowrate
characteristic
 Siemens AG, 2003. All rights reserved
SINUMERIK 840D/SIMODRIVE 611 digital, HLA Module (FBHLA) - 10.03 Edition
The choice of valve for a particular application is made with reference to the
following criteria.
HR (High Response) valves are characterized by their improved dynamic qual-
ity, i.e. by a higher limit frequency compared to servo solenoid valves. They
react with greater sensitivity to setpoint changes especially in the small-signal
range. The use of HR servo solenoid valves is recommended in the following
cases:
1. When extremely high contour precision is required in high-speed continu-
ous-path control machining operations.
2. When very high response sensitivity is required to achieve the best possible
positioning accuracy.
Note that HR servo solenoid valves do not generally have a fail-safe position.
The connector is also 12-pin, rather than 7-pin as with servo solenoid valves.
The valve size is determined by the maximum flowrate Q
rate is calculated according to the law of flow:
v: Maximum drive speed for extension and retraction
A: associated cylinder surface area
The calculated maximum flow rate must not exceed the limit for use of the
valve. This limit is generally specified in the catalog by the valve manufacturer
(e.g. Rexroth: /BR1/, "Servo solenoid valves" catalog).
Within the limits for use, the flow rate that can be achieved with the valve is cal-
culated by
@
Q=Q
nom
In practice, the cylinder speeds that can actually be achieved depend on the
operating pressure, the load pressure and flow-specific characteristics of the
drive. The dimensioning is left to the hydraulic configuration engineer, who has
access to a number of design calculation and simulation programs.
Values with either a linear or knee-shaped characteristic can be selected.
The latter are suitable for obtaining a higher resolution in the low signal range
(machining) and sufficient flow in the high signal range (rapid traverse).
The definition of the knee-point position as 40% or 60% means that only 10% of
the nominal opening cross-section (nominal flowrate) is released at 40% or 60%
of the nominal control signal (i.e. at U=4 V or 6 V).
The knee-shaped characteristic of the valve must be linearized in the HLA mod-
ule to adapt it to the closed-loop control of the entire drive (cylinder).
2.3 Configuring the hydraulic drive
X
=v @ A
Q
X
np
np
nom
2 Configuration
. This maximum flow-
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