Page 529 - Mechatronics with Experiments

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JWST499-c07
JWST499-Cetinkunt
ELECTROHYDRAULIC MOTION CONTROL SYSTEMS 515
P.S.
Pump/Tank
Controller
Valve
PID
Sensor AMP solenoids Cylinder Load
analog circuit (V to I)
A & B
Sensor

FIGURE 7.86: Components and block diagram of a single axis electrohydraulic motion control
system. The controller is an analog op-amp which implements a closed loop PID control
between the operator command, sensor signal, and valve-drive command.

in both return line and pump input line from the reservoir, as well as a cooler and
pressure relief valve.
2. Cylinder: Parker industrial cylinder (“Series 2H”) with 2.0 in bore, 40 in stroke, with
threaded rod end for load connection, with base lugs mounting options at both ends,
3. Valve: MOOG servo valve model D791, rated flow upto 65 gpm at 1000 psi pressure
drop across the valve when the valve is fully open, equivalent first-order filter time
constant is about 3.0ms.
4. Valve Drive (Power Supply and Amplifier): MOOG power supply and amplifier circuit
matched to the servo valve: MOOG model “snap track” servo valve drives.
5. Sensors: Position sensor: linear incremental encoder. DYNAPAR series LR linear
scale, range 1.0m, 5.0 μ (0.0002 in) linear resolution, maximum speed 20 m∕s, fre-
̄
quency response 1 MHz, quadrature output channels A, B, C, ̄ A, ̄ B, C.
Pressure sensor: differential pressure sensor, Schaevitz series P2100, up to
5000 psi line pressure, and up to 3500 psi differential pressure, bandwidth in the
15 KHz range. Pressure sensors can be placed on the valve manifold.
6. Controller: PC based data aquisition card (National Instruments: NI-6111) with I/O
interface capabilities for encoder interface, two channels of 16-bit DAC output, two
channels of 12-bit ADC converter, 8 channels of TTL I/O lines. The control logic can
be implemented on the PC and the data aquisition card is used for the I/O interface.
7. Operator Input–Output Devices: Joystick and Mode Selection Switches (Switch 1
and 2). One degree of freedom joystick with a potentiometer position sensor and
analog voltage output in the 0 to 10 VDC range – Penny and Giles model JC 150 or
ITT Industries model AJ3.

Example As an extension of the previous example, let us assume that we have selected
two sensors for the hydraulic cylinder (Figure 7.87):

1. a position sensor (i.e., an absolute encoder or an incremental encoder plus two
discrete proximity sensor to indicate mechanical travel limits and establish an absolute
reference position: ENC1, PRX1, PRX2), and
2. a pair of pressure sensors which measure the pressure at both ends of the cylinder
(P1, P2).

It is desired that the actuator is to operate in programmed mode and ignore the
joystick input. The objective is that the actuator is to approach the load at a predefined
speed until a certain amount of pressure differential is sensed between P1 and P2 signals.