Specifications
Table Of Contents
- Electrohydraulic Valves...A Technical Look
- Electrohydraulic Valve Applications
- Electrohydraulic Valve Selection Guide
- How to select a Servo or Proportional Valve
- How toSelect, continued
- Electrohydraulic Technologies
- Types of Servo Systems
- General Terminology: Electric
- General Terminology: Hydraulic
- Hydraulic Characteristics
- Performance Characteristics
- Electrical Characteristics
- Electrical Characteristics
- Nozzle Flapper Servovalve Operation
- Servojet Servo-Proportional Valve Operation
- Direct Drive Servo-Proportional Valve Operation
- Practical Considerations when laying out EH Control Systems
- Practical Considerations, continued
- Routine Maintenance
- Routine Maintenance, continued
- Moog Worldwide
FORCE
COMMAND
GENERATOR
SERVOVALVE
CYLINDER
SERVOAMPLIFIER
+
–
load
null
valve
driver
error
signal
summing
and gain
sensitivity
PRC
1
C
2
force feedback
TYPICAL FORCE SERVO
AMO
LOAD CELL
VELOCITY
COMMAND
GENERATOR
HYDRAULIC
MOTOR
TACHOMETER
load
valve
driver
integrated
error
signal
integrating,
summing
and gain
PRC1C2
velocity feedback
SERVOAMPLIFIER
command
sensitivity
G
TYPICAL VELOCITY SERVO
SERVOVALVE
POSITION
COMMAND
GENERATOR
SERVOVALVE
CYLINDER
SERVOAMPLIFIER
POSITION TRANSDUCER
+
–
+
–
load
null
valve
driver
error
signal
summing
and gain
sensitivity
P
S
RC
1
C
2
I
position feedback
TYPICAL POSITION SERVO
POSITION SERVO SYSTEM
A load positioning servo system is comprised of a Servo, ServoJet
®
or Direct Drive Valve, actuator, position feedback transducer,
position command generator, and a Servoamplifier. A typical linear
position servo system using a double-ended piston is shown to
the right (a rotary position servo system can be created by
substituting the appropriate rotary components).
The valve’s two output control ports are connected across
the load cylinder. In the Servoamplifier, the command input is
compared to the present position output of the position
transducer. If a difference between the two exists, it is amplified
and fed to the valve as an error signal.The signal shifts the valve
spool position, adjusting flow to the actuator until the position
output agrees with the command input.
VELOCITY SERVO SYSTEM
A velocity servo system is comprised of a Servo, ServoJet
®
or
Direct Drive Valve, hydraulic motor, tachometer, velocity com-
mand generator, and a Servoamplifier whose summing and gain
amplifier are configured to also act as an integrating amplifier.A
typical rotary servo system is shown to the right (a linear velocity
servo system can be created by substituting the appropriate linear
components).
The valve’s two output control ports are connected across
the hydraulic motor. In the Servoamplifier, the command input is
compared to the present velocity output of the tachometer. If a
difference between the two exists, it is integrated over time and
subsequently fed to the valve as an error signal.This signal shifts
the valve spool position, adjusting flow to the motor until the
velocity output agrees with the command input.
FORCE SERVO SYSTEM
A force servo system can be created with a Servo, ServoJet
®
or
Direct Drive Valve, actuator, load cell or pressure transducer,
and a Servoamplifier (an Adjustable Metering Orifice may be
used to improve system performance). A typical force servo
system is shown to the right.
The valve’s two output control ports are connected across
the cylinder. In the Servoamplifier, the command input is com-
pared to the present force output of the load cell. If a difference
between the two exists, it is amplified and fed to the valve as an
error signal.The signal shifts the valve spool position, adjusting
pressure to the actuator until the force output agrees with the
command input.
TYPES OF SERVO SYSTEMS
7