Chapter 1 Overview of the RSF supermini series
- -
12
T – T
1
K
2
T – T
2
K
3
1-7 Torsional stiffness
When a torque is applied to the output flange of the actuator with the motor locked, the resulting
torsional wind up is near proportional to the torque.
The upper right figure shows the torsional stiffness
characteristics of the output flange applying torque starting
from zero to plus side [+T
0
]
and minus side [–T
0
]
.
This
trajectory is called torque-torsion characteristics which
typically follows a loop 0
A
B
A’
B’
A as illustrated.
The torsional stiffness of the RSF supermini actuator is
expressed by the slope of the curve that is a spring rate
(wind-up) (unit:N
m/rad).
The torsional stiffness may be evaluated by dividing
torque-torsion characteristics curve into three major regions.
The spring rate of each region is expressed K
1,
K
2,
and K
3
respectively.
K
1
: spring rate for torque region 0-T
1
K
2
: spring rate for torque region T
1
-T
2
K
3
: spring rate for torque region over T
2
The wind-up for each region is expressed as follows:
wind-up for torque region 0-T
1:
!
=
wind-up for torque region T
1
-T
2:
!
=
"
1
+
wind-up for torque region over T
2:
!
=
"
2
+
The following table shows average values of T
1
through T
3
, K
1
through K
3
, and
#
1
through
#
2
for different
gear ratios.
Model
RSF-3C
RSF-5B
Gear ratio
Symbol
30
50
100
30
50
100
T
1
Nm
0.016
0.016
0.016
0.075
0.075
0.075
Kgf m
0.0016
0.0016
0.0016
0.0077
0.0077
0.0077
K
1
Nm/rad
27
30
34
90
110
150
Kgf m/arc min
0.0008
0.0009
0.0010
0.003
0.003
0.004
#
1
x10
-4
rad
5.9
5.3
4.7
8.7
6.9
5
arc min
2.0
1.8
1.6
3
2.4
1.7
T
2
Nm
0.05
0.05
0.05
0.22
0.22
0.22
Kgf m
0.005
0.005
0.005
0.022
0.022
0.022
K
2
Nm/rad
40
47
54
110
140
180
Kgf m/arc min
0.0012
0.0014
0.0016
0.003
0.004
0.005
#
2
x10
-4
rad
12.5
10.6
9.3
22
18
13
arc min
4.2
3.6
3.1
7.5
6
4.4
K
3
Nm/rad
51
57
67
120
170
200
Kgf m/arc min
0.0015
0.0017
0.0020
0.004
0.005
0.006
1
K
T