Tolomatic User Guide:
ICR Rod Style Integrated Control Actuator
1-7
1.1.6 RMS Thrust and Velocity Considerations
Servo motor actuator systems have two speed/thrust curves: one for continuous
duty operation and another for intermittent duty. A servo system can be selected
according to the total thrust and maximum velocity indicated by the continuous
duty curve. However, by calculating the root mean square (RMS) thrust based on
the application duty cycle, you may be able to take advantage of the higher peak
thrust available in the intermittent duty range. The RMS thrust must fall within the
continuous duty region of the motor/drive and the application maximum thrust must
fall under the peak thrust of the actuator.
Use the following formulae when calculating the RMS thrust and velocity. When
selecting an integrated servo actuator system, it is necessary to add a margin
of safety to the thrust and velocity required to move the load. The recommended
margin for servo motors is 15%.
T
RMS
=
√
sum (
T
i
2
x
t
i
)
sum (
t
i
)
Where:
T
RMS
= RMS Thrust
V
RMS
= RMS Velocity
T
i
= Thrust during interval i
V
i
= Velocity during interval i
t
i
= Time interval i
V
RMS
=
√
sum (
V
i
2
x
t
i
)
sum (
t
i
)
1.1.7 ICR Screw Life
The L10 expected life of a ball screw linear actuator is expressed as the linear
travel distance that 90% of properly maintained ball screws manufactured are
expected to meet or exceed. This is not a guarantee and the graph in Figure
1-3 should be used for estimation purposes only. All curves represent properly
lubricated and maintained actuators.
The underlying formula that defines this value is: Where:
L
10
=
(
C
)
3
F
C = Dynamic load rating (lbf)
F = Cubic mean applied load (lbf)
L
10
= millions of inches
1
1,000
10,000
100,000
100
10
1,000,000
25,400
2,540
254
25.4
2.54
.254
0 445 890 1,334 1,779
0 100 200 300 400
THRUST (lbf)
THRUST (N)
LIFE (millions of inches)
LIFE (millions of meters)
MAXIMUM THR
UST
MAXIMUM THR
UST
BN02
BN05
Figure 1-3: ICR Ball Screw Life
I C R B A S I C A N D I C R P L U S P R O D U C T O V E R V I E W
: 1
1
1,000
10,000
100,000
100
10
1,000,000
25,400
2,540
254
25.4
2.54
.254
0 890 1,334 2,669 3,559
0 200 400 600 800
THRUST (lbf)
THRUST (N)
LIFE (millions of inches)
LIFE (millions of meters)
MAXIMUM THR
UST
MAXIMUM THR
UST
BN02
BN05
LMI & RP 1:1 Ratio
RP 2:1 Ratio
