Chapter 1 Overview of the RSF supermini series
RSF-Super_V1_02
- 7 -
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:
◆
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-3
B
RSF-5A
Gear ratio
Symbol
30 50 100 30 50 100
Nm 0.016
0.016
0.016 0.075 0.075 0.075
T
1
Kgf m
0.0016
0.0016
0.0016 0.0077 0.0077 0.0077
Nm/rad
27 30 34 90 110 150
K
1
Kgf m/arc min
0.0008
0.0009 0.0010 0.003 0.003 0.004
x10
-4
rad
5.9
5.3
4.7 8.7 6.9 5
θ
1
arc min
2.0
1.8
1.6 3 2.4 1.7
Nm 0.05
0.05
0.05 0.22 0.22 0.22
T
2
Kgf m
0.005
0.005
0.005 0.022 0.022 0.022
Nm/rad 40
47
54
110
140
180
K
2
Kgf m/arc min
0.0012
0.0014 0.0016 0.003 0.004 0.005
x10
-4
rad
12.5
10.6
9.3
22
18
13
θ
2
arc min
4.2
3.6
3.1 7.5 6 4.4
Nm/rad 51
57
67
120
170
200
K
3
Kgf m/arc min
0.0015
0.0017 0.0020 0.004 0.005 0.006
1
K
T
=
ϕ
2
1
1
K
T
T
−
+
θ
=
ϕ
3
2
2
K
T
T
−
+
θ
=
ϕ
