Comparison Of Electric And Hydraulic Drive Systems - Siemens SINAMICS S120 System Manual

System overview

2.3 Comparison of electric and hydraulic drive systems

2.3 Comparison of electric and hydraulic drive systems
Table 2- 1 Comparison of electric and hydraulic drive systems
Criterion
Power density /
space requirement
Moment of inertia of
moving parts
Operational safety,
service life
Service
Energy storage
Maximum forces
Load stiffness
Maximum velocity
Maximum traversing
distance
Collision protection
30
Direct electric drive
Low weight
•
Lower space require-
•
ment of the electrical
section on the machine
table.
Low weight of the electrical
section on the machine
table
In principle, the service life
only depends on the linear
guides
Simple replacement
Peak requirement must be
installed as no storage is
possible
Peak thrust per unit area
approx. 40 to 80 kN/m
2
Very good;
Servo gain (Kv) can be set
10-100 times higher than on
the other two drives.
Up to 500 m/min
Unlimited
Mechanically difficult
Electric drive with leadscrew
Servomotor and leadscrew
•
large and heavy.
Problematic where mount-
•
ing space is restricted
Servomotor and leadscrew
have high moments of inertia
Shock sensitive
•
Service life is limited by
•
leadscrew
Sudden failure is possible
•
Complex replacement and
repair of leadscrew by special-
ists
Peak requirement must be
installed as no storage is pos-
sible
High forces are limited
Elasticity when large forc-
•
es are involved
Elasticity of leadscrew is
•
largely compensated using
closed-loop control
v = h × ω /2π
max s max
h = pitch
s
ω = maximum motor speed
max
≤6 m
Mechanically possible
System Manual, 04/2015, 6SL3097-4BA00-0BP1
Hydraulic drive
Cylinder and servo solenoid
•
valve are light and compact.
The electric motor is shifted to
•
the hydraulic unit
Piston and piston rod have very
low weights
Protected against overload
•
through pressure limiting
Sturdy, insensitive to shock
•
Cylinder seals and valve con-
•
trol edges have long service
lives.
Wear warning
•
Simple fault diagnostics
•
Simple replacement and repair
•
of valves and cylinders
Compensation of energy re-
•
quirement peaks using a hy-
draulic accumulator
Rapid traverse in a differential
•
connection
Reduction of installed power
•
Practically unlimited
(cylinder diameter, p = 700 bar)
max
Oil compressibility is compen-
•
sated using closed-loop con-
trol (I component)
Good zero overlap quality of
•
valve ensures very high load
stiffness
30 ... 300 m/min
(depending on the cylinder sealing
set)
≤3 m
Mechanically possible
Hydraulic Drive