Page 512 - Mechatronics with Experiments

JWST499-Cetinkunt
JWST499-c07
498 MECHATRONICS Printer: Yet to Come October 9, 2014 8:41 254mm×178mm
A B A B A B

T P T T P T T P T
(a) (b) (c)

Under-
(a)
(a) lapped
Under-lapped P s
(c)
Zero-lapped
Flow (Q) (a) (b) Over-lapped Pressure (b) Zero- (c)
Over-
lapped
lapped
Current Current
(d) (e)
FIGURE 7.72: Spool and sleeve orifice geometry at null position: under-lapped, critically
lapped, over-lapped. The resulting flow versus current and pressure versus current gains are
also shown.

designed and machined. It is a mechanical geometric property of the valve. Let us assume
that the spool actuation mechanism (i.e., solenoid or solenoid motion amplified by a pilot
stage) generates a spool displacement proportional to the control (current) signal to the
solenoid and that the pressure drop across the valve is constant. Then, the current signal to
flow-rate relationship would have the same shape as the spool position versus the orifice
area opening function. In closed loop precision position and force regulation applications,

A v A v A v
100% 100% 100%

X v X v X v
–100% 100% –100% 100% -100% 100%

-100% –100% -100%
(a) (b) (c)

A v A v A v
100% 100% 100%

X v X v X v
–100% 100% –100% 100% –100% 100%

–100% –100% –100%
(d) (e) (f)
FIGURE 7.73: Valve geometries: spool position versus orifice area opening. (a) Linear
(proportional valve), (b) valve with deadband and single gain, (c) valve with dual gain, (d) valve
with deadband and dual gain, (e) nonlinear gain, (f) non-symmetric (asymmetric) gain.