US 2024/0189995 A1Published application

Cable force control method applicable to time-varying configuration

AssigneeSoutheast University

InventorsHuijun LI, Ye LU, Aiguo SONG, Ye LI, Baoguo XU

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Abstract

A cable force control method includes: establishing a friction model, and calibrating parameters; and calculating the parameters in real time, and controlling a force: identifying the parameters according to the friction model to obtain parameters of an auxiliary cable Bowden system and a power Bowden system: a friction coefficient μa of the auxiliary cable Bowden system, and a friction coefficient μp of the power cable Bowden system; calculating the auxiliary cable Bowden system θa in real time according to the model and a force value of a sensor, and using same as a cable bending angle of the power cable Bowden system θ; and obtaining an inverse control formula Fin=Fout·e−uλθ according to the friction model, and bringing the power cable Bowden system θp into the inverse control formula to serve as a feedforward controller, so as to achieve an effect of real-time force control.

A cable force control method applicable to a time-varying configuration, comprising:

step 1, establishing a friction model, and calibrating parameters, wherein
a quasi-static equilibrium equation of a (s+ds) segment in a cable is indicated as:
{
d
⁢
F
⁡
(
s
,
t
)
=
λ
⁢
f
⁡
(
s
,
t
)
f
⁡
(
s
,
t
)
=
μ
⁢
N
⁡
(
s
,
t
)
N
⁡
(
s
,
t
)
=
F
⁡
(
s
,
t
)
⁢
κ
⁡
(
s
,
t
)
⁢
ds
F
′
(
s
,
t
)
=
[
F
⁡
(
s
+
ds
,
t
)
-
F
⁡
(
s
,
t
)
]
/
ds
,
(
1
)
wherein F(s,t), F(s+ds,t), N(s,t), f(s,t) and κ(s,t) indicate a cable tension at a position s, a cable tension at a position s+ds, a positive pressure, a friction force and curvature respectively under the condition of time t;
λ=sign[F′(s)] is currently defined, such that
F
′
(
s
,
t
)
F
⁡
(
s
,
t
)
=
μ
⁢
λ
⁢
κ
⁢
(
s
,
t
)
(
2
)
is obtained according to the formula (1),
wherein λ indicates a direction of cable friction;
then the formula (2) is integrated on an interval (s+ds), such that the following expression
F
⁢
(
s
+
ds
,
t
)
=
F
⁢
(
s
,
t
)
·
e
μ
⁢
λ
⁢
∫
s
s
+
d
⁢
s
κ
⁡
(
s
,
t
)
⁢
ds
(
3
)
is obtained;
the above expressions are extended to a total length L, such that
F(L,t)=F(0,t)·eμλθ (4) is obtained,
wherein μ and θ indicate a friction coefficient and a total bending angle of the cable respectively;
Fout=F(L,t), Fin=F(0,t) is currently set, such that
θ
=
ln
⁢
(
F
o
⁢
u
⁢
t
F
i
⁢
n
)
μ
⁢
λ
(
5
)
is obtained by means of the formula (4);
and
in order to reduce an error between a model and experimental data, the parameter is optimized according to the following optimization rule:
min
⁢
∑
i
=
1
N
⁢
(
F
out
-
F
ˆ
o
⁢
u
⁢
t
)
2
N
,
(
6
)
wherein Fout, {circumflex over (F)}out and N indicate a force value actually measured, a force value predicted by the model and the times of sampling respectively;
and
step 2, calculating the parameters in real time, and controlling a force, which comprise:
S1, identifying the parameters according to the friction model to obtain parameters of an auxiliary cable Bowden system and a power Bowden system:
a friction coefficient μa of the auxiliary cable Bowden system, and a friction coefficient μp of the power cable Bowden system;
S2, calculating the auxiliary cable Bowden system θa in real time according to the model and a force value of a sensor, and using same as a cable bending angle of a power cable Bowden system θp;
and
S3, obtaining an inverse control formula Fin=Fout·e−uλθ according to the friction model, and bringing the power cable Bowden system θp into the inverse control formula to serve as a feedforward controller, so as to achieve an effect of real-time force control.

234 more elements

Facts

Application

18/398,031Filed 27 Dec 2023

Priority

CN 202211590778.312 Dec 2022

Published

13 Jun 2024

Term ends

Not estimatedThe source records don’t support an estimate.

Classification4 codes

B25J 9/1633
Characterised by the control loop: compliant, force, torque control, e.g. combined with position control
B25J 9/104
Characterised by positioning means for manipulator elements: with cables, chains or ribbons
B25J 9/1653
Characterised by the control loop: parameters identification, estimation, stiffness, accuracy, error analysis
B25J
Manipulators

Abstract

Claims4