Chapter 1 Overview of the RSF-B mini series
- 8 -
1-8 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-B mini 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:
◆
wind-up for torque region over T
2:
The following table shows average values of T
1
through T
3
, K
1
through K
3
, and
θ
1
through
θ
2
for
different gear ratios.
Model
RSF-8B
RSF-11B
RSF-14B
Gear ratio
1
：
30
1
：
50
1
：
100
1
：
30
1
：
50
1
：
100
1
：
30
1
：
50
1
：
100
T
1
Nm
0.29
0.80
2.0
kgfm
0.03
0.082
0.2
K
1
x10
4
Nm/rad
0.034
0.44
0.091
0.084
0.22
0.27
0.19
0.34
0.47
kgf
･
m/arc min
0.010
0.013
0.027
0.025
0.066
0.080
0.056
0.1
0.14
θ
1
x10
-4
rad
8.5
6.6
3.2
9.5
3.6
3.0
10.5
5.8
4.1
arc min
3.0
2.3
1.1
3.3
1.2
1.0
3.6
2.0
1.4
T
2
Nm
0.75
2.0
6.9
kgf
･
m
0.077
0.20
0.7
K
2
x10
4
Nm/rad
0.044
0.067
0.10
0.037
0.30
0.34
0.24
0.47
0.61
kgfm/arc min
0.013
0.020
0.031
0.13
0.090
0.10
0.07
0.14
0.18
θ
2
x10
-4
rad
19
13
8
19
8
6
31
16
12
arc min
6.6
4.7
2.6
6.5
2.6
2.2
10.7
5.6
4.2
K
3
x10
4
Nm/rad
0.054
0.084
0.12
0.16
0.32
0.44
0.34
0.57
0.71
kgfm/arc min
0.016
0.025
0.036
0.047
0.096
0.13
0.10
0.17
0.21
1
K
T
=
ϕ
2
1
1
K
T
T
−
+
θ
=
ϕ
3
2
2
K
T
T
−
+
θ
=
ϕ
