Page 525 - Mechatronics with Experiments

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JWST499-c07
JWST499-Cetinkunt
ELECTROHYDRAULIC MOTION CONTROL SYSTEMS 511
In summary, the load conditions determine the three specifications:
Given {w ,(w , T )} (for linear actuator {V ,(V , F )}).
nl r r nl r r
As design choices, pick P hydraulic pump rated pressure output and pick ΔP load
s L
pressure differential.
Then calculate the rest of the sizing parameters: D , D , Q , Q , ΔP , Q , which are
m p nl r L v
the size requirements for pump, valve and motor/cylinder.
Notice that the pump and motor displacement and pressure ratings are available in
standard sizes, such as

3
D , D = 1.0, 2.5, 5.0, 7.5in ∕rev (7.279)
m
p
P = 3000–5000 psi (7.280)
s
Similarly, the valves are available at standard rated flow capacity (measured at ΔP =
v
1000 psi and at maximum current i = i max for servo valves) such as
Q = 1.0, 2.5, 5.0, 10 gpm. (7.281)
v
Based on the calculated sizes and safety margins, one of the closest sizes for each component
should be selected with appropriate safety margin.

Example Consider a single axis EH motion control system as shown in Figure 7.85,
which may be used for a hydraulic press. The system will be controlled in one of two
possible modes:

Mode 1: closed loop speed control where the commanded speed is obtained from
a programmed command generator or from the displacement of the joystick. The
cylinder speed is measured and a closed loop control algorithm is implemented in the
electronic control unit (ECU) which controls the valve.
Mode 2: closed loop force control where the force command is obtained from a pro-
grammed command generator or from the displacement of the joystick. The cylinder
force is measured using a pair of pressure sensors on both ends of the cylinder.

In order for the operator to tell the ECU which mode to operate (speed or force)
and from where to obtain the command signals, there should be two two-position discrete
switches. Switch 1 OFF position means speed control mode, and ON position means
force control mode. Switch 2 OFF position means the source of the command signal is
programmed into the ECU, ON position means the joystick provides the command signal
(Figure 7.84).
Select the proper components (components with appropriate technology such as
variable displacement or fixed displacement pumps, ON/OFF or proportional or servo
valves), and the proper size (calculate component size requirements) for pump, valve, and
cylinder in order to meet the following specifications:

1. Maximum speed of the cylinder under no load conditions is V = 2.0m∕s.
nl
2. Provide an effective output force of F = 10 000 Nt at the cylinder rod while moving
r
at the speed of V = 1.5m∕s.
r
3. The desired regulation accuracy of the speed control loop is 0.01% of maximum
speed.
4. The desired regulation accuracy of the force control loop is 0.1% of maximum force.