Chapter 17:Advanced Electdrical Controls For Fluid Power Systems

Example 17.1 pgno:610

In [1]:
# Aim:To determine the system accuracy of electrohydraulic servo system
# Given:
# servo valve gain:
G_SV=0.15; #(in^3/s)/mA
# cylinder gain:
G_cyl=0.20; #in/in^3
# feedback transducer gain:
H=4; #V/in
# weight of load:
W=1000; #lb
# mass of load:
M=2.59; #lb.(s^2)/in
# volume of oil under compression:
V=50; #in^3
# system deadband:
SD=4; #mA
# bulk modulus of oil:
beta1=175000; #lb/in^2
# cylinder piston area:
A=5; #in^2# Solutions:
# natural frequency of the oil,
om_H=A*(((2*beta1)/(V*M))**0.5); #rad/s
# value of open-loop gain,
open_loop=om_H/3; #/s
# amplifier gain,
G_A=open_loop/(G_SV*G_cyl*H); #mA/V
# repeatable error,
RE=SD/(G_A*H); #in

# Results:
print"\n  Results:  "
print"\n The repeatable error of system is  in.",round(RE,5)

  Results:  

 The repeatable error of system is  in. 0.00138

Example 17.2 pgno:610

In [2]:
# Aim:To determine the system accuracy of in SI units
# Given:
# servo valve gain:
G_SV=2.46; #(cm**3/s)/mA
# cylinder gain:
G_cyl=0.031; #cm/cm**3
# feedback transducer gain:
H=4; #V/cm
# mass of load:
M=450; #kg
# volume of oil:
V=819; #cm**3
# system deadband:
SD=4; #mA
# bulk modulus of oil:
beta1=1200; #MPa
# cylinder piston area:
A=32.3; #cm**2
from math import ceil
# Solutions:
# natural frequency of the oil,
om_H=(A*10**-4)*(((2*beta1*10**6)/(V*10**-6*M))**0.5); #rad/s
# value of open-loop gain,
open_loop=om_H/3; #/s
# amplifier gain,
G_A=open_loop/(G_SV*G_cyl*H); #mA/V
# repeatable error,
RE=SD/(G_A*H); #cm
# rounding off the above answer,
RE=round(RE)+(round(ceil((RE-round(RE))*100000))/100000); #cm

# Results:
print"\n  Results:  "
print"\n The repeatable error of system is  cm.",RE

  Results:  

 The repeatable error of system is  cm. 0.00352

Chapter 17.3 pgno:612

In [3]:
# Aim:Refer Example 14-3 for Problem Description
# Given:
# servo valve current saturation:
I=300.; #mA
# amplifier gain:
G_A=724.; #mA/V
# feedback transducer gain:
H=4.; #V/in
# feedback transducer gain in metric units
H1=1.57; #V/cm# Solutions:
# tracking error,
TE=I/(G_A*H); #in
# tracking error,
TE1=I/(G_A*H1); #cm

# Results:
print"\n  Results:  "
print"\n The tracking error of system is  in.",round(TE,3)
print"\n The tracking error of system in SI Unit is  cm.",round(TE1,3)

  Results:  

 The tracking error of system is  in. 0.104

 The tracking error of system in SI Unit is  cm. 0.264
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