Bionic soft robotic gripper with feedback control for adaptive grasping and capturing applications

doi:10.1007/s11465-023-0779-6

Front. Mech. Eng.

2024, Vol. 19

Issue (1) : 8 https://doi.org/10.1007/s11465-023-0779-6

Bionic soft robotic gripper with feedback control for adaptive grasping and capturing applications

Tingke WU^1,^2,³, Zhuyong LIU^1,^2,³(

), Ziqi MA^1,^2,³, Boyang WANG^1,², Daolin MA^1,², Hexi YU^1,²

¹. Department of Engineering Mechanics, School of Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
². State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
³. MOE Key Laboratory of Hydrodynamics, Shanghai Jiao Tong University, Shanghai 200240, China

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Abstract

Robots are playing an increasingly important role in engineering applications. Soft robots have promising applications in several fields due to their inherent advantages of compliance, low density, and soft interactions. A soft gripper based on bio-inspiration is proposed in this study. We analyze the cushioning and energy absorption mechanism of human fingertips in detail and provide insights for designing a soft gripper with a variable stiffness structure. We investigate the grasping modes through a large deformation modeling approach, which is verified through experiments. The characteristics of the three grasping modes are quantified through testing and can provide guidance for robotics manipulation. First, the adaptability of the soft gripper is verified by grasping multi-scale and extremely soft objects. Second, a cushioning model of the soft gripper is proposed, and the effectiveness of cushioning is verified by grasping extremely sharp objects and living organisms. Notably, we validate the advantages of the variable stiffness of the soft gripper, and the results show that the soft robot can robustly complete assemblies with a gap of only 0.1 mm. Owing to the unstructured nature of the engineering environment, the soft gripper can be applied in complex environments based on the abovementioned experimental analysis. Finally, we design the soft robotics system with feedback capture based on the inspiration of human catching behavior. The feasibility of engineering applications is initially verified through fast capture experiments on moving objects. The design concept of this robot can provide new insights for bionic machinery.

Keywords soft bionic gripper variable stiffness structure large deformation modeling feedback control soft robotic system

Corresponding Author(s): Zhuyong LIU

Just Accepted Date: 05 January 2024 Issue Date: 07 April 2024

Cite this article:

Tingke WU,Zhuyong LIU,Ziqi MA, et al. Bionic soft robotic gripper with feedback control for adaptive grasping and capturing applications[J]. Front. Mech. Eng., 2024, 19(1): 8.

URL:

https://academic.hep.com.cn/fme/EN/10.1007/s11465-023-0779-6
https://academic.hep.com.cn/fme/EN/Y2024/V19/I1/8

Fig.1 Internal structure and inspired design of the fingertip: (a) outline of the human fingertip, (b) internal structure of the human fingertip, (c) fingertip of a soft gripper, and (d) bionic structure of the fingertip.

Tab.1 Parameters of the soft robotic gripper

Fig.2 Grasping methods for different size objects: (a) pinching objects and (b) envelope objects.

Fig.3 Gripping pattern of soft gripper: (a) maximum envelope diameter of soft gripper, (b) straight envelope, (c) pinching of fingertips, and (d) curved envelope.

Fig.4 Solution results for different modeling methods: (a) finite element analysis (FEA) result for curved envelope (CE), (b) FEA result for straight envelope (SE), (c) FEA result for pinching contact (PC), (d) corotational formulation (CRF) result for CE, (e) CRF result for SE, and (f) CRF result for PC.

Fig.5 Frame of corotational beam element.

Fig.6 Computation flowchart for solving the differential-algebraic equations of the soft gripper.

Fig.7 (a) Experimental setups for measuring the input–output of soft actuator, (b) input force curve and output displacement curve in the free drive condition, (c) curved envelope corresponding to the semicircular type, (d) straight envelope corresponding to the flat type, and (e) pinching mode corresponding to the tip type.

Fig.8 Slope of the output force.

Tab.2 Parameters of the grasped objects

Fig.9 Adaptive grasping of multiple objects: (a) silicone bottle, (b) water-filled balloon, (c) ripe persimmon, (d) egg, (e) watery tofu, and (f) grapefruit.

Fig.10 Multilayer cushioning model of the bionic fingertip: (a) schematic diagram of the cushioning model and (b) corresponding grip status.

Fig.11 Nondestructive grasping of cactus: (a) sharp hard spines, (b) envelope grasp, (c) lift the cactus upwards, (d) contact deformation of the first layer, (e) contact deformation of the second layer, and (f) no damage to the cactus and to the soft gripper.

Fig.12 Grabbing of pufferfish: (a) experimental pufferfish; (b) the pufferfish can inflate freely, and the soft gripper would not cause damage.

Tab.3 Different stages of experimental results

Fig.13 Assembly process of the robot: (a) initial state, (b) gripping and trajectory control, (c) preparing for assembly, (d) complete assembly, and (e) trajectory motion.

Fig.14 Feedback capture of the robot: (a) three main modules are summarized from the feedback capture of moving objects by human, and (b) a feedback capture system is designed based on human behavior inspiration.

Fig.15 Strategy of feedback capture.

Fig.16 Initial state and geometric parameters.

Fig.17 Soft gripper quickly captures a moving object: (a) initial state, (b) object drop, (c) acceleration phase, (d) object recognition, (e) feedback capture, (f) grasping the object, (g) vertical perturbation, and (h) horizontal perturbation.

Abbreviations
CE	Curved envelope
CRF	Corotational formulation
DAE	Differential-algebraic equation
DIP	Distal interphalangeal
FEA	Finite element analysis
IACUC	Institutional Animal Care and Use Committee of Shanghai Jiao Tong University
PC	Pinching contact
SE	Straight envelope
Variables
c_max	Maximum damping coefficient
d	Penetration depth corresponding to the damping coefficient at its maximum value
d_c	Contact displacement between the object and the soft gripper
d₁	Distance between the second layer and the first layer
d₂	Distance between the third layer and the second layer
f	Gripping force f required to grasp an object
F_c	Contact force of the multilayer cushioning model
f₁	Local elastic force
f_g	Global elastic force
f_I	Inertial force vector
$f n c$	Normal contact force
$f τ c$	Tangential contact force
h	Initial height of the hanging object
H	Maximum envelope diameter
i_max	Maximum number of Newton iterations
k	Corresponding normal stiffness
k₁	Equivalent stiffnesses of the first layers
k₂	Equivalent stiffnesses of the second layers
k₃	Equivalent stiffnesses of the third layers
K_g	Global tangential stiffness matrix
l	Lengths of the element after deformation
l₀	Lengths of the element before deformation
L_g	Length of the soft gripper
L_h	Length of the pendulum
m	Mass of the grasped object
M	Generalized mass matrix of the system
M₁	Local mass matrix
n	Number of constraint equations
N	Number of the actuators
n	Normal vector at the contact point
p	Index number
q	Global generalized coordinates of the beam
$q ¯$	Deformation vector of the element
Q	Generalized external load including the contact force
Q_e	External force vector
R_max	Envelope radius
R	Rotation matrix
t_end	Total time of the computational process
T	Kinetic energy of the element
u₁	Horizontal displacements of node 1
$u ¯$	Deformation displacement of the element
v	Velocity of the object falling to the lowest point
v₀	Initial velocity of the suspended pendulum
v₁	Vertical displacements of node 1
W	Width of the drive port
x	Horizontal output displacement
$β$	Rotation angle between the global frame and the local frame
δ	Penetration depth
$δ ˙$	Penetration rate
Φ	Constraint equation of the system
Φ_q	Jacobian matrix
$λ$	Lagrange multiplier
$ρ ∞$	Spectral radius
$τ$	Tangential vector at the contact point
$η$	Distance of the object measured by ultrasonic sensor
θ	Initial mounting angle
θ₁	Rotation angle of node 1
θ_h	Angle between the thin wire and the vertical direction
$θ ¯ 1$	Deformation angle of the node 1
$θ ¯ 2$	Deformation angle of the node 2
Δt	Time step of integration

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