design and development of the soft robotic gripper used
TRANSCRIPT
Journal of Mechanical Engineering Research and
Developments ISSN: 1024-1752
CODEN: JERDFO
Vol. 44, No. 3, pp. 334-345
Published Year 2021
334
Design and development of the soft robotic gripper used for the
food packaging system
Hoang Minh Dang†, Chi Thanh Vo†, Nhan Tran Trong†, Viet Duc Nguyen‡, Van Binh
Phung‡†*
† Industrial University of Ho Chi Minh City, Ho Chi Minh City, Vietnam ‡ Thuyloi University, 175 Tay Son, Dong Da, Hanoi, Vietnam
‡† Le Quy Don Technical University, Hanoi, Vietnam
*Corresponding author’s email: [email protected]
ABSTRACT
This paper presents the design and development of the soft robotic gripper with four actuators, which are made of
hyperelastic material and operated by pneumatic systems. Simulation of the gripper deformation and dynamics
issue was performed by using the finite element method in the ABAQUS software. The actuator was made by
casting method and the mold was 3D printed. The auxiliary mechanical device, which is integrated to the gripper,
is a two degree of freedom mechanism. It can move up and down and turn left and right conveniently. The
developed gripper can handle the object of different shapes with a geometrical limit up to 8 cm and gripping mass
up to 300 gram. Experimental results showed that the gripper can operate with the productivity of 3 objects per
minute that meets the actual requirements of the product packaging line in practice.
KEYWORDS
Soft robotic gripper, pneumatic actuator, hyperelastic material, design and development, food packaging system
INTRODUCTION
Soft robotics has been the potential area that attracts the attention of many researchers [1-3]. Movements of soft
robots are modeled in accordance with the organisms. One of the typical research objects in soft robotics is a soft
gripper that can handle items of any shape, indeterminate size, especially suitable when working with fragile
objects, e.g. glass, or easily-deformed objects, e.g. food. These are the outstanding advantages of the soft actuator
in comparison with the traditional robotic actuator. It can be implemented for many industries including food,
biology, medicine, ocean exploration, etc. [4].
The soft robotic gripper appeared first in the 1970s with the aim of emulating the functions of animal tendons [1],
then this research direction continued to expand and develop in the 1980s and in the 1990s new designs, new
control methods, as well as new materials, have been introduced [2, 3]. By the 2000s, thank to the emergence of
electrodynamic polymers, various kinds of soft robotic gripper were developed rapidly and a number of products
were already commercialized. Carozza et al. studied artificial hands using soft materials for the disabled [4]. A
typical study in this period was the gripper using a flexible mechanism, integrated with load cells, controlled via
cable developed by Dollar et al. [5]. In the meantime, Nakai et al. at the University of Tokyo studied a soft robot
prototype that can be configured, the robot structure is made of low hardness aluminium, creating the ability to
configuration transform thanks to the deformation of the structure [6].
So far, the soft robot gripper has been evolved in the direction of using hyperelastic material e.g. silicon [7-8].
The most common one is a soft gripper made of hyperelastic material, with a structure of hollow cavities
connecting to the pneumatic system [9-12]. Although the calculation and simulation of this type of gripper have
had a certain success, there are still some limitations when applied in practice, especially in terms of the relatively
small mass of the items that need to be gripped. In addition, this type of gripper is mostly a prototype under
experimental research form, the application in real production systems is still limited.
Design and development of the soft robotic gripper used for the food packaging system
335
3D Fingers Design:
- Shape, Size
- Wall Thickness
- Number of Compartments
- Number of fingers
Force simulation
Perform Regression Fn=f(h,P)
Designing Gripper Equipment
- Configuration of Lifting -
rotating - lowering mechanism
Manufacturing
Control System Design
Pick-up Experiment
ENDSize requirements
Feasible in
Manufacturing
and Control?
Satisfying
productivity?
Satisfy Force
Condition?
YES
NO
YES
NO
Pick-up Simulation
YES
NO
Figure 1. Procedure of design and development of the soft robotic gripper for the food packaging industry
The purpose of this paper is to introduce the design process for developing a soft gripper (consists of several
actuators or fingers), as illustrated in Figure 1, which is directly applied to the food packaging system. The
technical requirements are the maximum weight of the gripping object 300 gram, the gripping capacity of 3 objects
per minute. The shape of the object might flexibly be rectangular, spherical, and conical with a maximum profile
size of 8 cm. The gripping process requires that food or objects, in general, will not be damaged or crushed. These
requirements are built up from the actual need at food packaging factory with eggs, fruit, soft cakes, etc. and they
need to be placed into trays or boxes for packing and delivered to a large number of people such as places like
universities, schools, factories, etc.
Based on the requirement on the size of the gripping object, the 3D model of the gripper with four actuators is
built. Then, simulation is conducted to evaluate the gripping force of a finger on the object at different pressure
levels. Using the simulation data, the correlation between the gripping force upon the pneumatic pressure and the
distance from the finger to the object is developed. Next, the dynamic simulation of the gripping process is
performed. The simulation allows for evaluating the ability to grasp and hold objects of the gripper in order to
determine the design option that meets the requirements. Once a suitable design option is defined, the subsequent
steps including structural design, fabrication and validation of the prototype are carried out.
DESIGN OF THE SOFT ROBOTIC GRIPPER
Simulation of the actuator deformation
Design and development of the soft robotic gripper used for the food packaging system
336
(a)(b)
(c) (d) (e)
(f) (g) (h)
(c)
Figure 2. 3D model of the gripper of four actuators: (a) and (b)-actuator, (c)-gripper
Each finger of the actuator is designed with the empty spaces connected together so that air can be pumped in, as
can be observed in Figure 2 (a) and (b). The size and number of compartments will affect the applied force as well
as the impact ability of the finger on the gripping object. How this influence can be studied based on the simulation
and experimental validation after the finger is fabricated. The 3D design model of the actuator is illustrated in
Figure 2(c). Figure 3 shows an illustrative result of air pressures effect on the strain state of a finger. The finger
simulation was performed by using hyperelastic material with many different hardness levels (from 20A, 25A,
30A, 35A, 40A, 45A) in order to define the suitable hardness material.
Fix
Applied pressure
(a) (b)
Figure 3. Effect of air pressure on the strain state of an actuator: (a) boundary condition; (b) strain state
Determination of force interaction between gripper and object
The most important parameter defining the working ability of the gripper is the force exerted on the object. The
exerting force is characterized by 2 normal components (Fn and Ft), in which the Fn can be defined by using the
simulation and the Ft is determined in accordance with Fn and the coefficient of friction μ between the finger and
the object. Coefficient μ is obtained from the experimental methods. The simulation procedure is described in
Figure 4.
Design and development of the soft robotic gripper used for the food packaging system
337
(a) (b) (c)
(d)
(e)
Figure 4. Simulation procedure of exerting force on the object from the finger
The correlation between Fn upon the pressure P and the distance from the gripper to the finger h is studied by
using the ABAQUS software. The Yeoh material model is used for the calculation. The finger model is meshed
with a tetrahedral C3D10H element, while the object model uses the C3D8R. The interaction of adjacent thin
walls is also taken into account to ensure the simulation results are similar to reality. The simulation process starts
from a 3D model of the finger (Figure 4a), then sets the boundary and load conditions (Figure 4b), then meshes
the model (Figure 4c) and finally run the computing program (Figure 4d). The calculation result of the Fn in
accordance with the different values of pressure P and distance h are shown in Table 1. Besides, the outcome is
also represented visually in Figure 5. From the experimental data, it is possible to build an approximate function
of Fn by using the least squares regression algorithm as follows:
( ) ( ) ( )
( )
( )
2 2
00 10 01 20 11 02
3 2 2 3
30 21 12 03
4 3 2 2 3 4
40 31 22 13 04
,nF h P p p h p P p h p hP p P
p h p h P p hP p P
p h p h P p h P p hP p P
= + + + + + +
+ + + + +
+ + + + +
(1)
Where, p00=0.03888; p10=0.0007751; p01=–0.002712; p20=–0.0003192; p11=0.0001123; p02=0.0004033;
p30=1.436e-005; p21=–1.039e-005; p12=–1.552e-006; p03=–6.734e-006; p40=–1.775e-007; p31=1.353e-007;
p22=8.847e-009; p13=1.051e-008; p04= 4.234e-008.
Table 1. The obtained result of Fn in accordance with the distance h and pressure P
h (mm)
P (kPa)
Design and development of the soft robotic gripper used for the food packaging system
338
Figure 5. Range of values to correlate Fn, h and P
The obtained function Fn(h,P) makes a firm basis for estimating the object mass corresponding to the different
pressure P and distance h. Also, the function Fn allows for defining the required pressure P for gripping the object.
Dynamic simulation of grasp process
To evaluate the working ability of the gripper with the objects of different shapes, the dynamic simulation of the
grasping process is carried out taking into consideration the objects with three typical shapes such as rectangular,
sphere and cone, as presented in Table 2. These are also common shapes for grasping objects in the packaging
system [13]. The simulation of the gripping process is performed by using the Abaqus/Implicit module. The four
main steps to be taken are 3D modelling, boundary and load application, mesh, and analysis. The coefficient of
friction μ = 0.3 is considered. The result shows that the air pressure P=55 kPa, and the fingers, which are made of
hyperelastic material with hardness 35A, are capable of gripping the object of 300 gram as the maximum mass.
Table 2. Simulation steps
Step Rectangular object Spherical object Conical object
1. 3D
modelling
2. Load
application,
boundary
condition
Design and development of the soft robotic gripper used for the food packaging system
339
3. Mesh
4. Result
analysis
Fabrication of the actuator
There are two principal methods of fabricating soft grippers such as 3D printing by using hyperelastic material
and casting. 3D printing is available for fabricating the gripper of complex shape, but it is quite costly. In this
study, the gripper is made by the casting method, the process of which is shown in Figure 6. Top, bottom and lid
molds are made by using the 3D printer, as shown in Figure 6 (a), (b), and (c) respectively. The process of pouring
the material, hardening and finishing process of the gripper fabrication are shown in Figure (d), (e), and (f)
respectively. Eventually, the actuators are assembled to make the entire gripper, as illustrated in Figure 7. (a)
(b)
(a) (b) (c)
(d) (e) (f)
Figure 6. Fabrication process of an actuator
Figure 7. Assembly of the gripper
Design and development of the soft robotic gripper used for the food packaging system
340
VALIDATION OF THE SOFT ROBOTIC GRIPPER
Fabrication of the auxiliary mechanism and control system
In order to validate the soft robotic gripper to be used for the food packaging system, an auxiliary mechanical
device that integrated with the gripper was prepared. It is a two degree of freedom mechanism, as illustrated in
Figure 8. The operating principle of the device is as follows: When it needs to pick the object or perform the
gripping process, the air is pumped into the pneumatic tank and then pumped into the gripper with four grippers.
Air pressure is measured by using a sensor. Once the intake air pressure reaches the pre-set magnitude, the
solenoid valve will automatically disconnect and the compressed air pressure inside the gripper is kept constant
during the gripping process. When it needs to drop the object, the solenoid valve opens and the air will be released
from the gripper out. To ensure sufficient air supply in the overall operation cycle, the tank is equipped with a
self-supply unit. When the air in the tank decreases, the device controls to re-inflate the tank, reaching a fixed
magnitude of 5 kgf/cm2.
A cluster
of soft
grippers
Pressure
Gauges
Translational
Mechanism
Rotating
mechanism
Stepper
motor
Figure 8. Two degree of freedom mechanism
The control system is also established to manage the device. Diagrama of the motor and air-pump control system
is shown in Figure 9 and Figure 10 respectively.
+5V
+5V
+5V
+5V
+5V+12V
+12V
+12V
DRIVER TB6600
TRANSLATIONAL
MOTION CONTROL
MOTOR
ROTATIONAL MOTION
CONTROL MOTOR
ARDUINO R3
PRESSURE REDUCING MODULE
12V-5V DC
MODULE
BLUETOOTH
ARDUINO NANO
POWER
SWITCH
EMERGENCY
SWITCH
STARTDOWN LEFT RIGHTUP STOP
+12V
GAS
CONTROL
CIRCUIT
POWER SUPPLY
12V DC
Figure 9. Diagrama of the motor control system
Design and development of the soft robotic gripper used for the food packaging system
341
SINGLE-DIRECTIONAL
ELECTRIC VALVE
PRESSURE
REGULATOR BUTTON
PRESSURE SENSORSARDUINO R3
EXHAUST GAS
AIR PUMP
+12V
+5V
A CLUSTER OF SOFT
GRIPPERS
MOTOR
CONTROL
CIRCUIT
Figure 10. Diagrama of the air-pump control system
Validation and analysis
To evaluate the working capability of the gripper and auxiliary mechanical device, a series of experimental pick-
up are performed. Different types of objects including food and fruits with mass varying from 28 gram to 300
gram. The experimental tests on the gripping process of different objects are presented in Table 3. The
experimental result shows that with the required air pressure of 55 ÷ 70 kPa, the developed soft robotic gripper
can handle objects with a mass of up to 300 gram. The object that needs to be picked can be in different types of
configuration. Also, the gripping process does not affect the food quality, for instance, it does not spoil the fruit.
In particular, the productivity of the grasping process is up to 3 objects per minute, which is suitable for application
in the food packaging system [13].
Table 3. Experimental tests on the gripping process of different objects
Object Mass Experimental Test
Croissant
Design and development of the soft robotic gripper used for the food packaging system
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Passion fruit
Apple
Yogurt
Onion
Design and development of the soft robotic gripper used for the food packaging system
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Baby Pumpkin
Tomato
Potato
Radicchio
Design and development of the soft robotic gripper used for the food packaging system
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Guava
CONCLUSION
The design and development of the soft robotic gripper with four actuators was carried out in this study. The
actuator was made of hyperelastic material and operated by using pneumatic systems. The developed gripper can
handle the object of different shapes with a geometrical limit up to 8 cm and gripping mass up to 300 gram. The
gripper was integrated with the auxiliary mechanical device to be used for the food packaging system.
Experimental results showed that the gripper can operate with the productivity of 3 objects per minute that meet
the actual requirements of the product packaging line in practice. The successful development of the gripper from
this study promises a bright future of upcoming more useful devices.
ACKNOWLEDGEMENT
The contribution to this paper and financial support from Industrial University of Ho Chi Minh City, Vietnam
under the research project № 20/1.1CK05 toghether with the contract № 20/HD-DHCN are highly acknowledged.
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