# A Modular Pneumatic Soft Gripper Design for Aerial Grasping and Landing*

Hiu Ching Cheung1, Ching-Wei Chang2, Bailun Jiang1, Chih-Yung Wen1 and Henry
K. Chu3 *This work was supported by the Research Centre of Unmanned Autonomous
Systems (RCUAS) [P0046487], The Hong Kong Polytechnic University1Hiu Ching
Cheung, Bailung Jiang, and Chih-Yung Wen are with Department of Aeronautical
and Aviation Engineering, The Hong Kong Polytechnic University, Hung Hom,
Kowloon, Hong Kong<EMAIL_ADDRESS>balun-
<EMAIL_ADDRESS><EMAIL_ADDRESS>Chang is with Hong
Kong Center for Construction Robotics, , Hong Kong<EMAIL_ADDRESS>K. Chu is
with Department of Mechanical Engineering, The Hong Kong Polytechnic
University, Hung Hom, Kowloon, Hong Kong<EMAIL_ADDRESS>
###### Abstract

Aerial robots have garnered significant attention due to their potential
applications in various industries, such as inspection, search and rescue, and
drone delivery. However, the ability of these robots to effectively grasp and
land on objects or surfaces is often crucial for the successful completion of
missions. This paper presents a novel modular soft gripper design tailored
explicitly for aerial grasping and landing operations. The proposed modular
pneumatic soft gripper incorporates a feed-forward proportional controller to
regulate pressure, enabling compliant gripping capabilities. The modular
connectors of the soft fingers offer two configurations of the 4-finger soft
gripper, H-base and X-base, allowing adaptability to different target objects.
Furthermore, when deflated, the gripper can function as a soft landing gear,
reducing the weight and complexity of aerial manipulation control and
enhancing flight efficiency. We demonstrate the efficacy of indoor aerial
grasping and achieve a maximum payload of 217 g for the proposed soft aerial
vehicle (SAV), with the weight of the soft drone being 808 g.

##  I INTRODUCTION

###  I-A Motivation

Aerial grasping [1] is a rapidly growing research field, particularly in the
context of unmanned aerial vehicles (UAVs) used for drone delivery such as
food delivery [2], search and rescue [3], environmental cleaning [4], and
medical goods delivery [5]. Ensuring the safety and efficiency of goods during
drone delivery is critical. Hence, we aim to address these concerns by
proposing a novel solution: a SAV equipped with a modular soft pneumatic
gripper, which has received limited attention in previous studies.

Figure 1: Illustration of the proposed modular pneumatic soft gripper with a
conventional drone.

Soft grippers offer a promising alternative to rigid grippers due to their
simplified control systems, reduced complexity, and excellent force absorption
capabilities. To leverage the principles of soft robotics, these lightweight
and controllable mechanisms provide stability during grasping by dampening
impact forces. Their flexibility allows for a broader range of object
dimensions, increasing grasping tolerance. Positioned beneath the center of
gravity of the SAV, the soft gripper can inflate and deflate to securely grasp
objects, improving grasping efficiency and reducing mission time. Moreover,
replacing the rigid landing gear with the proposed soft gripper as the landing
mechanism enhances the capability of aerial manipulation for the SAV. It
eliminates the need for additional actuators and simplifies the control system
by eliminating the complicated operations of the landing gear adjustment
during takeoff, landing, and grasping. Furthermore, the modular design of the
gripper enables configuration changes to accommodate various object sizes and
shapes, for instance, considering the diverse shapes of food packages
prevalent in food delivery scenarios.

###  I-B Related Work

Inspired by biological systems like birds [6], soft grippers have demonstrated
the ability to mitigate contact forces and compensate for grasping
inaccuracies, exemplifying the concept of morphological computation, which
combines passive mechanical components with explicit control [7]. To leverage
these advantages, some researchers have developed a bio-inspired tendon-
actuated soft gripper, as the bending capability of the gripper can be easily
controlled by manipulating the attached tendon [8, 9, 10]. In the context of
perching, Ramon et al. [11] have designed a soft landing gear system that
allows an aerial drone to autonomously perch on pipes in industrial
environments, providing robust attachment using nylon strands and offering a
modular design for gripper replacement. This soft gripper has demonstrated
successful closure around pipes in outdoor experiments, enabling the quadrotor
to perform well even in uncertain and windy conditions despite imperfect
centering or fastening. Furthermore, Fishman et al. [12, 13] have developed a
tendon-actuated soft gripper for a soft drone inspired by the dexterity of
human fingers. Their approach eliminates the need for gripper state
measurement, operating the soft gripper in an open-loop manner to grasp
objects of unknown shape on unknown surfaces, relying on the centroid of the
objects.

The fabrication process for the tendon-actuated soft gripper involves the
insertion of tubes inside the soft fingers to accommodate the passage of
tendons [14, 15]. In contrast, a pneumatic soft gripper requires only a
sufficient air chamber in each soft finger for bending [16]. Furthermore, the
location of the tendon-actuated gripper is constrained by the position of the
driven motor. Nevertheless, soft pneumatic grippers offer greater
configurational flexibility due to the flexibility of the air tube. The air
tube can quickly connect the pneumatic soft gripper with the pumps and valves.
Related work also explores the potential of pneumatic soft systems in aerial
grasping. Shtarbanov [17] developed FlowIO, a wearable and modular pneumatic
platform for soft robotics, which showcased the viability of pneumatic systems
in miniaturized applications that are cost-effective for UAVs engaged in
aerial grasping. Ping et al. [18] integrated a soft pneumatic gripper beneath
a conventional drone, similar to our design. However, their focus does not
explicitly revolve around autonomous aerial grasping tasks or alleviating the
need for additional rigid landing gear. The soft gripper in their work is
controlled by a single command: pneumatic pressure. They claim that the
installation of the entire Grasping Unit has minimal impact on the dynamics of
the quadrotor. Since their proposed soft gripper does not stick out by adding
extra degrees of freedom (DOF) to facilitate grasping, the rigid landing gear
of their UAV limits the grasping altitude. A 2 DOF robot arm with a pneumatic
soft gripper is installed under a traditional UAV with the rigid landing gear
in [19]. Compared to our proposed SAV, extra mechanisms and control algorithms
in the work of Sarkar et al. [19] are needed to ensure the manipulator can
reach its home and pick positions. Also, their fixed, rigid landing gear
increases the net weight of the UAV, which is over 3 kg in total.

###  I-C Contributions

To our knowledge, our proposed SAV is the first soft drone capable of
conducting aerial grasping using a soft pneumatic gripper while operating
without the need for a traditional rigid landing gear. The soft gripper,
incorporating a feed-forward P controller for precise pressure regulation,
also serves the dual purpose of functioning as a soft landing gear for the
SAV. This innovative design eliminates additional rigid landing gear,
resulting in a more streamlined and efficient aerial grasping system. Our
contributions are summarized as follows.

  * •

Integrating modular connectors reduces the configuration and fabrication time
for the soft gripper fingers. With just four fingers, the gripper can be
arranged into two configurations, providing a versatile range of options for
grasping target objects based on their shapes. This modularity enhances the
adaptability of the gripper to grasp various objects during aerial operations.

  * •

The dual capability of the soft gripper to serve as both a grasping mechanism
and a landing gear. The deflation of the soft gripper enables it to function
as a soft landing gear, obviating the need for an additional rigid landing
gear to reduce the weight of the SAV. This weight reduction enhances flight
efficiency and simplifies the complexity associated with aerial operation
control.

  * •

The proposed lightweight, soft gripper with a traditional quadrotor, which
weighs merely 808 g, successfully grasps a cylindrical plastic container
weighing 217 g while in mid-air. This payload-to-weight ratio surpasses that
observed in previous investigations [13, 18, 19].

##  II MODULAR SOFT GRIPPER DESIGN

###  II-A Mechanical Design

Figure 2: Dimensions of the X-base soft gripper when it is (a) initially
opened, (b) fully opened, and (c) fully closed. And the dimensions of the
H-base soft gripper when it is (d) initially opened, (e) fully opened, and (f)
fully closed.

The proposed soft fingers exhibit dimensions of 100 mm in length and 15 mm in
width. These fingers can be affixed to multiple bases at a 25∘ inclination
angle, giving the gripper increased grasping tolerance and diverse options for
target objects. Grasping tolerance refers to the available dimension for
grasping when the gripper is deflated, precisely the distance between the
fingertips when the gripper is fully opened in Fig. 2(b) and Fig. 2(e),
respectively. The diagonal distance of the fully opened X-base soft gripper is
180 mm, while the tip-to-tip distance of the fully opened H-base soft gripper
is 145 mm. The dimensions of the 2 bases are shown in Fig. 2(a) and Fig. 2(d).
When the complete closing of the soft gripper is undergoing, all tips of the
soft fingers of the X-base soft gripper touch each other, while the tips of
the two pairs of the 2-tip soft fingers of the H-base counterpart touch each
other too (see Fig. 2(c) and Fig. 2(f)).

The X-base and H-base configurations necessitate using four soft fingers to
grasp target objects, as discussed in prior works [18, 20]. Each finger of the
soft gripper is equipped with a single air chamber. These air chambers are
interconnected and equipped with one micro-pump and two solenoid valves. The
weight of the four-finger soft gripper (excluding the electronics) is 106 g.
The modular connectors of the soft fingers have been designed to simplify the
attachment of the soft fingers to various bases. Sliding the connector and
securing it with a screw allows each soft finger to connect to different bases
to grasp different objects quickly. This approach reduces the required number
of soft fingers to a maximum of four, significantly reducing assembly time.

###  II-B Fabrication

Figure 3: The exploded view (a) and assembly (b) of the mold of the soft
finger’s main body. The exploded view (c) and assembly (d) of the mold of the
soft finger’s cover. (e) The side view of a soft gripper.

The soft fingers are molded using silicone rubber with a proposed shore
hardness of 30 A. For manufacturing convenience, all the molds, soft finger
connectors, and bases are 3D-printed using Polylactic Acid (PLA). Fig. 3
illustrates the mold design for a soft finger, which consists of two parts.
One part forms the main body of the soft finger, including its air chamber,
while the other part produces the cover of the soft finger. This approach
allows for efficient production and assembly of the soft fingers.

Referring to [21], the main steps of the soft finger fabrication include
assembling the molds, applying mold release spray, pouring liquid silicone
rubber, cutting holes in the covers, inserting and securing silicone tubes,
and joining the main body and covers using silicone gel. The silicone tubes
are not sealed by silicone gel, and they are only connected with the tubing
connector by friction to enable the quick interchange between H-base and
X-base.

Only the mold for making the air chamber is disposable because it will be
twisted and bent during removal from the soft finger. The remaining parts of
the mold can be reused for future fabrication processes.

###  II-C Electronics

The main electronic components of the soft gripper include the
microcontroller, air pump, solenoid valves, and pressure sensor. Control of
the gripper is managed by an ESP32-S3 microcontroller, which receives a Pulse-
width Modulation (PWM) signal from the flight controller for regulating the
air pump and valve operations. The soft gripper is equipped with a single air
pump that facilitates both inflation and deflation, while two valves serve as
switches to control the airflow for inflation or deflation simultaneously. The
air pump has a pressure range of [-60, 120] kPa, and a pressure sensor with a
range of [-100, 300] kPa is incorporated to detect the internal airflow
pressure within the gripper and provide feedback to the microcontroller. To
meet all the requirements of the proposed soft gripper, except for the air
pump and the valves, all the electronic components are integrated onto a
customized Printed Circuit Board (PCB), as shown in Fig. 4.

In order to enhance the efficiency of the SAV by reducing its overall weight,
the soft gripper does not require an additional power source when installed
beneath a traditional quadrotor. This minimizes energy requirements, enabling
the soft gripper to operate efficiently with the existing quadrotor power
system. Hence, the payload capacity of the SAV can be maximized.

Figure 4: The exploded CAD view of the soft gripper.

##  III MODULAR SOFT GRIPPER CONTROL

###  III-A Airflow Control System

Figure 5: Airflow system of the soft gripper when (a) the valve operation for
inflation turns on; (b) the valve operation for deflation turns on.

As the soft drone approaches the target object, a deflation command is
transmitted from the ground control station to the flight controller and
subsequently to the ESP32-S3 microcontroller. This command activates the
deflation airflow through the valves and initiates vacuuming with the air
pump. The deflation process allows the soft gripper to open, release, and
land, while the inflation process activates the grasping of the gripper by
complete closing. During grasping, deflation continues until an inflation
command is received, triggering the gripper to close. Inflation follows a
similar procedure to deflation. The microcontroller receives three ranges of
PWM inputs to control the behavior of the soft gripper: staying at rest,
inflation, and deflation. The airflow patterns during inflation and deflation
are depicted in Fig. 5. Both valves are turned off to prevent airflow when the
gripper is initially opened. Only the relevant valve is activated during
inflation or deflation, while the other valve remains off to ensure proper
airflow direction. In Fig. 5, the blue solid block and the red solid block of
the air pump represent the inflation and deflation function of the pump that
is mainly used in the relevant airflow, respectively. Also, the blue and the
red airflows indicate the inflation and the deflation airflows of the gripper,
respectively.

###  III-B Pressure Regulation

Figure 6: Block diagram of feed-forward proportional control for the soft
gripper.

The pressure regulation of the soft gripper employs a feed-forward
proportional control strategy, as presented in Fig. 6. This approach combines
feed-forward and proportional control techniques to enhance performance by
anticipating the impact of input pressure changes on the output pressure. Due
to the limited performance of the lightweight air pump and the unseal soft
gripper system, which enables easy swapping between two configurations, a
slight air leakage can be predicted as a disturbance of the pressure
regulation. By integrating these control strategies, the gripper achieves
faster response times and improved stability in regulating the air pump.
Notably, the feed-forward proportional control only sets the PWM signal for
the air pump. At the same time, the PWM command of the flight controller
directly determines the digital signals for activating the valves. This valve
control strategy prevents excessive vibration caused by rapid changes in
airflow direction.

The feed-forward proportional controller in Fig. 6 can be computed by solving
the following equations:

$e(t)=r(t)-y(t)$ (1) $u(t)=K_{p}\times e(t)+p_{min}$ (2)
$K_{p}=\dfrac{p_{max}-p_{min}}{r(t)}$ (3) $f_{in}=0.8$ (4)
$f_{de}=\dfrac{1}{r(t)}$ (5) $g(t)=\begin{cases}u(t)+f_{in}\times
y(t)&\text{if inflation}\\\ u(t)+f_{de}\times y(t)&\text{if
deflation}\end{cases}$ (6)

where the minimum PWM duty cycle of the air pump, $p_{min}$, is an adjustable
parameter to optimize the performance according to the desired pressure. If
$p_{min}$ is too low, the response time of the system will be longer. The
maximum PWM duty cycle of the air pump, $p_{max}$, is fixed at the 8-bit
capacity of the microcontroller of the gripper. Referring to the experimental
results, we also observe the optimal feed-forward component for inflation,
$f_{in}$, and deflation $f_{de}$ to speed up the inflation and deflation time
of the soft gripper. Further details and explanations of the abovementioned
variables can be found in Table I.

TABLE I: Parameters in air pump regulation Variables | Definitions
---|---
$e(t)$ | Pressure error in $kPa$
$r(t)$ | Set (desired) pressure
$y(t)$ | Current pressure
$u(t)$ | Output by Proportional controller
$Kp$ | Proportional gain
$p_{max}$ | Max. PWM duty cycle of air pump $(100\%)$
$p_{min}$ | Min. PWM duty cycle of air pump $\begin{cases}$86\%$&\text{if inflation}\\\ $63\%$&\text{if deflation}\end{cases}$
$f_{in}$ | Feed-forward component for inflation
$f_{de}$ | Feed-forward component for deflation
$g(t)$ | Output by Feed-forward proportional controller
Figure 7: Comparison between feed-forward proportional controller and
proportional controller of the soft gripper.

The soft gripper focuses on achieving maximum openness and a secure grasp by
pressure regulation. After considering factors such as the air chamber
capacity, inflation time, performance of the lightweight air pump, and the
results of the feed-forward proportional controller, an inflation pressure of
85 kPa was determined as optimal for achieving the desired level of openness.
Also, a deflation pressure of -25 kPa was chosen to ensure rapid and effective
closure. We also observe the optimal $f_{in}$ and $f_{de}$ to speed up the
inflation and deflation time of the soft gripper. The step response graph in
Fig. 7 illustrates the pressure regulation performance with a set pressure
signal (set pressure in 0 kPa, -25 kPa, and +85 kPa) by the feed-forward
proportional controller and the proportional controller. Although the
deflation performance for both controllers is similar, the inflation time of
the feed-forward proportional controller is much faster than the one of the
proportional controller only. These results show that the feed-forward
component anticipates set pressure changes, facilitating stable current
pressure and reduced steady-state error. Also, in the feed-forward
proportional control, the desired inflation pressure can be reached faster,
compared with the proportional control only, but the desired deflation
performance of both control methods differs insignificantly.

##  IV EXPERIMENTAL RESULTS AND DISCUSSION

###  IV-A Experiment Implementation

####  IV-A1 Aerial Grasping Test

During the indoor autonomous grasping tests performed with the proposed soft
gripper installed under a conventional drone (with an F330 airframe), it is
observed that the mass of the object being grasped significantly influences
the grasping process. Objects that are too light (less than approximately 70
g) are susceptible to being blown away by the airflow generated by the SAV
before aerial grasping. Therefore, using objects with a mass greater than 70 g
is recommended. In the aerial grasping task, the target object was a water
bottle (including loads) weighing 75 g, while the proposed SAV weighed 808 g.
The water bottle was intentionally emptied to eliminate any non-static mass
caused by liquid flow during grasping. To prevent the water bottle from being
blown away by the airflow of the SAV, additional loads were added to increase
its weight.

The flight tests were conducted under a VICON motion capture system, which
provided real-time ground truth data to the ground station computer to ask the
flight controller to track the target item. The proposed SAV uses a nonlinear
model predictive controller (NMPC) [22, 23] for minimizing tracking error and
conducting aerial grasping. This paper does not include the details of the
NMPC of SAV, as we would like to concentrate on the contributions of the
modular pneumatic soft gripper in aerial grasping.

####  IV-A2 Static Grasping Test

To further evaluate the grasping performance of the SAV, a static grasping
test aimed to assess both the maximum load capacity of the soft gripper and
its ability to grasp objects with various base shapes. The test involved
evaluating the performance of the gripper under different load conditions and
its ability to grasp objects with diverse base configurations securely.

In this experiment, the SAV was put on an aluminum rack, and the Servo tester
provided the inflation or deflation PWM input signal to the microcontroller of
the gripper, making it independent of the drone system without receiving
inputs from the flight controller or ground control station. Target objects
were manually placed under the center of the gripper by human hands. To test
the grasping tolerance of the gripper, the positions of the centroid of the
objects did not require a precise alignment of the centroid of the gripper
before grasping. 10 graspings were conducted for each specimen. The 10 objects
in the grasping test are shown in Fig. 8. Successful grasping trials required
the gripper to hold the target object for at least 30 seconds. To ensure a
reliable grip, human hands intentionally moved and gently shook the SAV during
the test.

Figure 8: Tested Object Set: (a) Pen Holder with Loads, (b) Computer Mouse,
(c) Double-sided Tape, (d) Pen, (e) Spray Paint, (f) Syringe, (g) Membership
Card, (h) Pocket Tissue Paper, (i) Spherical Container with Loads, (j) Plastic
Box.

####  IV-A3 Soft Landing Test

The soft gripper establishes its landing ability by keeping a full opening as
a soft landing gear to stabilize the pose of the SAV and dampen the impact
forces during landing. The proposed soft gripper replacing the rigid landing
gear can increase the efficiency of the aerial manipulation of the SAV without
burdening its payload capability. To assess the landing ability of the SAV,
the SAV first conducted a simple landing test, which requested the SAV to land
on the ground. Then, the tilt landing test of the SAV was also handled by
landing it on a slope with 10∘ inclined angles.

####  IV-A4 Payload Test of the SAV

The maximum payload of the SAV with two configurations of its soft gripper was
discovered by grasping different objects while hovering. To focus on the
payload capability, the aerial grasping ability of the SAV was ignored in this
test by grasping the target items before taking off.

###  IV-B Results and Discussion

####  IV-B1 Soft Grasping Performance

Figure 9: Aerial grasping process with the H-base soft gripper: (a)
Approaching the target, (b) Starting grasping, (c) Picking up the object.

Figure 9 illustrates a successful aerial grasping demonstration performed by
the proposed H-base soft gripper. Despite minor tracking errors causing the
SAV to miss the desired grasping position of the empty water bottle, the
inherent softness of the soft gripper allows it to compensate for such errors
and provide ample grasping tolerance. As a result, the bottle could be
securely grasped without sustaining any damage.

Figure 10: Grasping success rate results of 2 configurations.
*The X-base gripper can hang and wrap the tape, while the H-base gripper always wraps the tape.

From Fig. 10, the soft gripper with both two configurations can grasp the pen
holder and the pocket tissue paper with a 100% success rate. The 4-tip soft
gripper with an H-base is designed for grasping cylindrical objects and offers
increased gripping force through the wrapping motion of its two pairs of 2-tip
fingers. The H-base gripper can grasp cylindrical objects up to 200 g with a
100% success rate, but it has an 80% success rate for grasping a can of spray
paint due to the non-static center of gravity. It cannot handle items more
miniature than the distance between its finger pairs, so it is less effective
with spherical objects. To address these limitations, a proposed X-base allows
all four fingers to align with the centroid of objects to grasp spherical
items. It can also grasp the pen holder with loads up to 330 g because one of
the soft fingers can hang the pen holder with the support of the other three
soft fingers. Nonetheless, the X-base does not provide the same wrapping force
for cylindrical objects as the H-base. Thus, X-base and H-base serve distinct
purposes. Some examples of this static grasping test are illustrated in Fig.
11.

Figure 11: Examples of grasping tests: Grasping (a) a pen holder with 270 g
loads and (b) a spherical container with 160 g loads by an X-base gripper;
Grasping (c) a computer mouse and (d) a can of spray paint with an H-base
gripper.

####  IV-B2 Soft Landing Performance

Figure 12: Simple landing test with (a) the H-base soft gripper and (b) the
X-base soft gripper, and tilt landing test with the (c) X-base and (d) H-base
soft gripper.

In Fig. 12(a) and Fig. 12(b), with the modular soft gripper, this novel SAV
can take off and land on the ground without the need for traditional rigid
landing gear. Since the landing pressure is equivalent to the deflation
pressure used during grasping, the soft gripper can remain fully opened,
serving as a landing gear to stabilize the pose of the SAV during takeoff and
effectively dampen impact forces upon landing. Besides, Fig. 12(c) and Fig.
12(d) present the successful tilt landing of the SAV (with its two
configurations of the soft gripper) on a 10∘ inclined platform. According to
our experimental results, the H-base soft gripper performs better for the tilt
landing as it can always be flattened, while the X-base soft gripper sometimes
may only have three fingers to be flattened. These tilt landing results show
that the H-base soft gripper can dampen more impact forces of the soft fingers
since the fingers have more contact areas with the tilt platform. Thus, the
modular soft gripper can successfully replace conventional rigid landing gear,
even for tilt landing.

####  IV-B3 Payload Ability Performance

Figure 13: Payload test of the SAV with the X-base (a) and (b) H-base soft
gripper.

In Fig. 13, the SAV demonstrates its successful grasping of a 217 g double-
sided tape using the X-base soft gripper and a 217 g plastic cylindrical
container using the H-base soft gripper. Both payload tests were conducted for
a duration of over 30 seconds. The focus of this test was to evaluate the
payload capacity of the SAV, with the aerial grasping capability intentionally
excluded.

##  V CONCLUSIONS

We have presented the design and control of a modular pneumatic soft gripper
equipped under a traditional quadrotor as a novel SAV for autonomous aerial
grasping tasks and landing. The primary objective of this soft gripper design
is to ensure its lightweight nature, thereby minimizing the impact on the
flight capabilities of the SAV. Therefore, we propose an 808 g SAV with a soft
gripper weighing 106 g, which includes the silicone rubber body and silicone
tube. The pressure control of the modular gripper employs a feed-forward
proportional controller to enhance the pressure regulation of the soft
gripper. The experimental results from the grasping tests demonstrate that the
total contact areas of the gripper on the target object influence the grasping
force. To accommodate objects with different shapes, we have investigated two
base configurations of the modular soft gripper. The H-base 4-tip gripper is
suitable for grasping cylindrical or rectangular objects, while the X-base
4-tip gripper is more appropriate for spherical or round objects. This paper
demonstrates a successful indoor autonomous aerial grasping task. Its payload
ability by grasping a 217 g payload in mid-air indicates a satisfactory
payload-to-weight ratio. Also, the soft gripper can effectively replace the
rigid landing gear. It implements competent landings on the ground and the 10∘
inclined platform. These findings contribute to developing autonomous aerial
grasping capabilities in soft robotic systems.

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