User Manual

Bosch Rexroth AG
RE 95 350/03.06
VAC Valve Control System
3/12
Method of function
The VAC electronic valve control system allows the pressure
in pressure reduction valves to be controlled via signals from
a joystick in accordance with a parameterizable characteristic
curve. In this way, the volume fl ow in hydraulic cylinders or
hydraulic motors is controlled via directional valves.
The valves form part of a control block with which the move-
ment speed of machine parts can be controlled. Each valve
controls the speed of one movement axis, i.e. for two move-
ment directions (A and B).
The electronic valve control system is designed for controlling
directional valves in the open circuit.
Operating behavior
The following explains how a valve is controlled in a control
block.
The position of the connected joystick is detected via the ana-
log input or CAN connection.
The valve control behavior is controlled by various variables:
• The target value is defi ned with the joystick.
• The output value for the specifi ed target value is specifi ed in
the parameterizable control characteristic.
• The time ramps on all inputs and outputs determine how
quickly the output value is changed.
It is possible to automatically switch to counter operation de-
pending on the joystick signals.
Control behavior
• The joystick is in the neutral position if it is positioned within
a user-defi nable range around the zero position. This is
called the deadband. It can be set in the parameters.
When the joystick is in the neutral position, the outputs for
controlling the valve are deactivated.
• If the joystick is moved to a position outside the deadband,
the value at the respective output (for movement direction
A or B) increases according to the position of the joystick
and the set curve. The valve is controlled. In addition, the
acceleration behavior can be selected via a parameterizable
time ramp.
In counter operation, the time ramp of a movement axis is
changed temporary. Other ramp times are used.
Special function
Depending on the variant, different switched outputs can be
controlled via switched inputs. For this purpose, unused inputs
are used for endswitches.
Safety functions
Various options are available for monitoring the operating
behavior:
• Start condition
The start condition is used to prevent the valves from being
opened unintentionally.
After the controller is switched on (ignition switch switched
on), all activated target value generators must be in the
neutral position. In addition, the safety switch must be closed
in order for the valves to be controlled.
To acknowledge faults, all activated target value generators
must be moved to the neutral position.
• Monitoring of inputs and outputs
The lines for the target value inputs and proportional soleno-
id outputs are monitored for wire breaks and short circuits.
In the event of an error or if the emergency stop switch is ac-
tuated, the valve control system is switched off immediately.
In the event of an error, an error lamp is also controlled.