Strain Sensor-Embedded Soft Pneumatic Actuators for Extension andBending Feedback
Michelle C. Yuen1,2,3 , Rebecca Kramer-Bottiglio2 , and Jamie Paik1
Abstract— For soft robots to leave the lab and enter unstructured environments, proprioception is required to understandhow interactions in the field affect the soft structure. In thiswork, we present sensor-embedded soft pneumatic actuators(sSPA) that can observe both extension and bending. The
sensors are strain sensitive capacitors, which are bonded tothe interior of fiber-reinforced extension actuators on opposing
faces. This construction allows extension and bending to bemeasured by calculating the mean and difference in sensor
responses, respectively. The sSPAs are bonded together toform a flat fascicle to increase the force output and prevent
buckling under load, and are robust to component failure
by incorporating redundancy. In this paper, we discuss the
fabrication of the sensors and their subsequent integration into
the actuators. We also report the work capacity and sensor
response of the sSPA fascicles under extension, bending, andthe combination of both modes of deformation. The sensorembedded soft pneumatic actuators presented here will advancethe field of soft robotics by enabling closed-loop control of soft
robots.

I. I NTRODUCTION
There is a continuing need in the field of soft robotics
for sensing methods for soft actuators. These devices are
typically fabricated from soft materials, in particular silicone
elastomers which are flexible (Young’s modulus <10MPain the linear regime) and stretchable (elongation at yield of500%) [1]. While having many beneficial properties, silicone
elastomers are difficult to model because they exhibit nonlinear and time-dependent stress-strain behaviors, undergo
continuum deformations, and have effectively infinite degrees
of freedom [1], [2]. These characteristics make model-basedor open-loop control challenging to implement and thus,state feedback information is often necessary to perform
positional control of soft actuators. The field of soft sensing
addresses this need by developing sensors for measuring andwithstanding large deformations, with minimal impact on
the behavior of the system. Integration of the sensor andactuator into the same volume can yield a better measurementof the actuator state as compared to designs wherein thesensor can experience motion relative to the actuator, andthus inaccurately report the actuator state.
Researchers have worked towards directly integrating sensors into pneumatic actuators for proprioception. A common approach is to embed highly stretchable strain gauges
composed of liquid metal microchannels into the body of a
1 Reconfigurable Robotics Laboratory, Institute of Mechanical Engineering, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
2 School of Engineering and Applied Science, Yale University, New Haven,
CT, USA. 3 School of Mechanical Engineering, Purdue University, West
Lafayette, IN, USA email: jamie.paik@epfl.ch

Fig. 1. Sensor-embedded soft pneumatic actuators (sSPA). (Top) Two
capacitive strain sensors, with the interfaces protruding, are embedded along
the interior cavity of a soft pneumatic actuator (SPA). (Bottom) A soft
pneumatic actuator fascicle consisting of four parallel sSPAs to amplify
force and reduce buckling.

silicone-based pneumatic actuator to achieve varying levelsof feedback and control. Liquid metal microchannel sensors
have been embedded in linearly contracting pneumatic artificial muscles as radial and axial sensors [3]–[6]. Bending
actuators, including those used for soft pneumatic grippers,
have been fabricated with liquid metal microchannels tocreate resistive sensors for determining bend angle, degreeof grasp, or contact with an object [7]–[11]. By adding a
redundancy of strain sensors around a pneumatic actuator(more sensors than degrees of freedom) and using machinelearning techniques, researchers have shown that bending
motions in 3D space can be reconstructed [11]. Other emerging approaches for sensing motion of pneumatic actuators are
induction sensing with coiled wires to detect contraction of
bellows actuators [12], [13], resistive sensing using silversilicone conductive composites to measure bending angle[14], magnetic sensing between joints using a magnetic
silicone composite [15], optical waveguides for sensing
strain along a pneumatic actuator [16], [17], and siliconebased capacitive sensors embedded within a fabric sleeveto measure the bend angle of a bellows-actuated roboticarm [18]. A model for using dielectric elastomer sensors forcontraction sensing within a McKibben muscle described thedeformation expected within the muscle and related it to the
response of the sensor [19]. Finally, researchers have also

utilized commercial, off-the-shelf components for curvature
feedback on bending actuators. Some examples include theuse of air pressure sensors connected to a deformable air
void along the contacting surface of a pneumatic gripper[20], commercial optical fiber waveguides attached along theneutral axis of a bending actuator to measure curvature via
light intensity [21], and resistive flex sensors attached on
the inextensible layer of a bending actuator [22], [23]. Allof these applications of commercially available devices areintegrated in the non-extending region of the actuator, whichis indicative of the lack of highly deformable sensors withincommercially available devices.
The majority of the works cited here utilize an embedded
sensor to measure a singular value of strain or curvature.
While this approach is sufficient for pneumatic actuators
operating in free space or within an expected protocol (suchas grasping an object) in unstructured environments, theinformation provided by the sensors may not reflect thetrue configuration of the actuator. For example, consider
a single actuator that encounters an unexpected obstacle
during its programmed motion. A soft actuator can deformaround the obstacle, and the deformation transduced by thesensor is a coupling between the undesired deformation andthe commanded actuation. Therefore, there is a need tomeasure the deformation of pneumatic actuators such that
their deformation can be measured even when operating
outside of expected conditions.
In this work, we directly integrate highly deformable,
capacitive strain sensors into soft pneumatic actuators (SPA)
to create a sensor-embedded soft pneumatic actuator (sSPA)(Figure 1). By embedding a pair of displacement sensors into
the SPA, we are able to determine distinctly both extension
and bending by calculating the mean and difference ofthe two sensor measurements, respectively. This approach
is similar to that reported by [24], wherein the sum anddifference of the values reported from two curvature/strain
sensors mounted back-to-back were used to report linear
strain and curvature. Using the sSPAs presented here, theextension and bending angle can be determined from two
sensor values and the pneumatic pressure applied to theactuators. By measuring both extension and bending, a better
representation of the actuator deformation can be achieved,
an important step towards feedback control of soft pneumatic
systems in unstructured environments.
II. FABRICATION
A. Sensors
The sensors used in the sSPAs are closely based on
previous work by White, et al. [25] which presented capacitive strain sensors fabricated in large multi-layer films fromsilicone-based conductive composite and silicone elastomer
materials. In this work, we expanded upon the three-layer
devices (conductive electrode - dielectric layer - conductive
electrode) presented in [25] to a five-layer device (Figure 2(a,b)). This modification served two purposes: 1) it
increased the size of the strain-sensitive capacitance by aFig. 2. Image and schematic of the sensor and fabrication process. (a) Photoof the cross-section of the sensor. (b) Schematic of the cross-section (sideview) of a completed sensor. The layer types are indicated below in (c); thecopper-colored regions indicate copper strips for interfacing the active andground electrodes to the signal conditioning electronics, and copper wire toelectrically connect the two ground electrodes together. (c) Top, front, andside views of the sensor film at various stages in the fabrication process.

factor of four, and 2) it shielded the charged layer fromexternal electromagnetic noise.
Fabrication of the sensors requires five distinct processes:
1) creation of the conductive composite material for theelectrode layers, 2) rod-coating the ground electrodes, dielectric layers, and active electrode layers, 3) folding thefilm onto itself to create a 5-layer capacitor, 4) cuttingout sensors, and 5) interfacing with signal conditioning
electronics. The conductive electrode layers were made froma composite of silicone elastomer and expanded graphite. The
graphite was first expanded by placing 3g of expandable
graphite (Sigma Aldrich) into a ceramic crucible and thenwere then embedded in the actuators.
B. Actuators with Embedded Sensors

Fig. 3.
Cross-sectional views of the sensor-embedded soft pneumatic
actuator (SPA). The cross-section shows the two sensors bonded to the top
and bottom interior of the SPA (shown in pink). The tabs on the side areused to secure the inextensible fishing line reinforcements. The sacrificial
wax core is indicated by the dotted line; the center circle indicates thealignment rod used to center the wax core within the mold for the silicone.

roasting in a 450◦ C oven (Nabertherm B130) for 10 minutes.
The expanded graphite was then mixed with 150mL of
cyclohexane in a glass bottle and then sonicated for a totalenergy deposition of ≈ 130kJ (Vibracell Sonics VCX130,
100% amplitude, 1 hour). The mixture was filtered througha 220µm stainless steel sieve (Fisher Scientific) into a glass
beaker and then dried until the concentration of expandedgraphite in the cyclohexane mixture reached ≈6wt%. The
graphite-cyclohexane slurry was mixed into uncured silicone
elastomer (DragonSkin 10 Slow, Smooth-On Inc.) to obtain a
final composite ratio of 10wt% of graphite for 90wt% silicon,
after the cyclohexane evaporated.
Following preparation of the conductive composite material, the ground electrode, dielectric layer, and active electrode were rod-coated with a 1/2” Acme threaded rod ontoa polyethylene terephthalate (PET) substrate (Figure 2(c)(13)). Each film was rod-coated onto the previous film once
it had fully cured. The active electrode was rod-coated onto
half of the larger film, omitting a thin strip to allow theground electrodes to be connected by a copper wire throughthe sensor (Figure 2(b) and (c)(3)). Following this step,
the glue layer composed of native silicone elastomer wasapplied to the non-interfacing regions of the active electrode(Figure 2(c)(4)). While the glue layer was still uncured, thefilm was folded over and bonded onto itself to form a 5-layer
structure (glue layer is omitted) (Figure 2(c)(5)).
Following completion of the sensor film, individual sensors were cut out of the film using a laser cutter (Laserscript,
HPC Laserco.uk). The sensors were patterned such thatthe active region of the sensor (i.e., the full five layer
portions) matched the active length of the actuators, thus
leaving sufficient length for electrical interfacing to thesensor outside the actuator. The sensors were cleaned using
soap and water. Copper wire was sewn through the endof the sensor to electrically join the two ground layers.
Copper-clad polyimide film (Pyralux) and a PET backing
was bonded to the active and one of the ground electrodes
using a silicone adhesive (SilPoxy, Smooth-on). The sensors

The design and manufacture of the actuators are closely
based on previous work by Robertson, et al. [26]. The only
modification to the fabrication described in [26] was tothat of the sacrificial wax core. In this work, flats wereadded along the length of the wax core to accommodate thetwo sensors (Figure 3). After casting the wax core onto analignment rod, the sensors were secured on the flats using athin layer of silicone elastomer (EcoFlex 00-30, Smooth-On).
Following this step, the wax core with sensors was inserted
into the mold for the outer bladder of ElastoSil (M4601,
Wacker Chemicals). After filling and degassing the mold,the actuators were allowed to cure for 12 hours. Because all
the silicones used were platinum-cure silicone, the ElastoSilmaterial fully-bonded to the sensors, ensuring that the sensor
bodies did not move within the internal chamber of theactuator.
The sSPAs were then wrapped with inextensible fishingline (Trilene Monofilament 0.3571mm, Berkley) at a 57◦
bias to cause extension when pressurized [26]. The moldcontained tabs along the side of the actuator to space thefishing line and to hold it in place during extension andcontraction. After wrapping the fiber reinforcement, the wax
core was melted out of the core and a pneumatic line wasinserted into one end. Silicone adhesive was used to seal thepneumatic line and to plug and the other end of the actuator.
Four sSPAs were then bonded in parallel with EcoFlex 0030 to form a sSPA fascicle. In this way, the actuators havea multiplied force output and reduced tendency to buckle.
Finally, signal conditioning boards were soldered onto eachof the sensors to transduce the capacitance of each sensor
into an analog voltage [25].
We chose to embed the sensors within the SPA in order tofurther isolate the sensors from electro-magnetic interference
due to contact with charged bodies, such as human touch.
We had conducted preliminary tests with the sensors bonded
to the exterior of the actuators, but this resulted in large
fluctuations in the sensor signal (>100% of the full scalesensor response at maximum extension) upon touching thesensor. Furthermore, the more delicate conductive electrodelayers are not subjected to abrasion by the fishing line during
actuation and contraction cycles.
III. C HARACTERIZATION
We performed a series of tests on the sSPA fascicle tocharacterize the actuation and sensing capabilities, namely
the relationship between force, displacement, air pressure,and sensor response.
A. Blocked Force Tests
The blocked force tests simultaneously characterized theactuators’ ability to do mechanical work at various air supply
pressures and the sensors’ responses to displacements and airpressures. The sSPAs were inflated at 50, 100, and 150kPa
and the displacement was stepped in 5mm increments usingFig. 4. Blocked-force characterization under linear extension of the sSPA fascicle. Each error bar represents the mean and 95% confidence bounds of thevalue measured at steady state. (a) Force-displacement curves at pressures of 50, 100, and 150kPa. (b) Sensor responses corresponding to the same data
points plotted in (a). The sensor values were normalized by subtracting the value measured when the actuator was unpressurized.

a linear stage, while the force was measured with a load celland the sensor measurements were recorded via an Arduino
Uno at a rate of approximately 10Hz. The sampling rate
here was limited by the 8.4ms charge-discharge cycle formeasuring the sensors’ capacitances. Each test was run at a
specified pressure and fixed displacement. Upon beginning
the test, the baseline, unpressurized state was recorded for10s. The valve was then opened and the pressurized state
was held for 20s to allow the system to stabilize. Finally,
the air was vented through the valve and the unpressurizedstate was recorded for a further 20s.
The plots shown in Figure 4 show the force-displacement
behavior and sensor response to displacement of the sSPAs atvarious pressures. Each error bar on the plot shows the mean
and the 95% confidence bounds over 20 samples after thesystem had stabilized. The sensor responses were normalizedby subtracting the initial value recorded while the actuator
was unpressurized and unextended. As reported in [26], as
the displacement increases, the delivered force reduces. At
each pressure, we found that the force-displacement relationship is linear, indicating a constant work output at each
inflation pressure. The sensor response plot shows that as the
air pressure increases, the sensors’ output signal increases,
indicating an increase in capacitance due to compression. We
also observed that the sensor response is sensitive to both theinternal air pressure as well as the displacement, as demonstrated in the distinct offset of the curves corresponding toeach pressure value in Figure 4(b). The sensors are composedof DragonSkin 10, a softer elastomer than the ElastoSil usedin the bladder material, which will deform (i.e., compress inthickness) before the ElastoSil deforms (i.e., stretch). At aconstant pressure, the sensor response-displacement response
is approximately linear, as reported in [25]. Therefore, theembedded displacement sensors should ideally be used inconjunction with an air pressure sensor to decouple theeffects of internal pressure and displacement. We hypothesize

here that deviations away from the ideal linear fit, particularly
at higher pressures, arise from instabilities in the interface
between the sensor and the copper strips connecting to thesignal conditioning electronics. Over the courses of thesecharacterization tests, the actuators had a tendency to bendout of plane, particularly in tests with higher blocked forces.
In some cases, these deformations resulted in the sensor
partially losing contact with the copper strips, and in othercases, regaining contact with the copper strips. Improving thestability of the interface between the sensor and the signal
conditioning electronics will be further studied in futurework.
B. Free Extension
We also characterized the free extension length (Figure 5).
These values correspond to the displacement at which zeroforce is exerted. Because the blocked force tests were performed in 5mm increments, the true free displacement was
not captured in Figure 4(a). As the pressure is increased
linearly, the free displacement increases linearly as well,as measured by a time-of-flight sensor (SparkFun VL1680)(Figure 5(a)). This extension is tracked by the embedded
sensors, to a certain extent (Figure 5(b)). Similar to theresults in the blocked force tests, the sensors depart fromtheir expected behavior at higher pressures, as shown by thelarger error bars corresponding to the highest displacement
at 200kPa inflation pressure. It should be noted however, that
although the sensor signal at high pressures/displacements isless reliable, the sensors return to an operative state following
this deformation.
C. Bending Tests
By embedding two strain sensors on opposite walls of
the actuator chamber, we were able to measure bending by
calculating the difference in sensor outputs of two sensors inthe same actuator. In this test, the interface end of the fascicle
was fixed while the other end was left free. A wooden dowel

Fig. 5. Free displacement characterization under linear extension of the sSPA fascicle. Each error bar represents the mean and 95% confidence boundsof the value measured at steady state. (a) Plot showing the free displacement lengths of the actuator as a function of pressure. The blue error bars are
the measured data and the black line is the linear regression fit. (b) Responses of three sensors corresponding to the same data points plotted in (a). The
sensor values were normalized by subtracting the value measured when the actuator was unpressurized. Note that the colors used to plot the data here do
not correspond to those used in Figure 6.

and unextended. The sensor responses at a bend angle of0◦ correspond to the sensor responses at the final extension
values shown in Figure 4, representative of the free extension
length. As the bend angle increases, the two sensor responses
diverge more and more, but the mean value of the two sensors
stays consistent throughout the test. Therefore, by calculating
the mean and difference in the sensor responses on eitherside of the sSPA and measuring the applied air pressure, theextension and bend angle may be distinctly determined.
IV. C ONCLUSION AND F UTURE W ORK

Fig. 6. Plot of the normalized responses of a sensor on the top and asensor on the bottom of an SPA for different pressures. As the fascicle
is bent upwards from a flat position, the top sensor contracts, while thebottom sensor stretches, resulting in the diverging sensor responses observed
here. The mean sensor response stays relatively consistent throughout thebend, indicating that the overall length of the sensor is remaining the same
throughout the bending.

was fixed crossing the fascicle at mid-length. The actuator
was then inflated, and the bend angle was applied by raising
the free end in 1cm increments until a bend angle of 90◦
was reached. The bend angle was measured as the angle
between tangent lines drawn along each end of the fascicle.
As the actuator is bent, the sensor on the outside of thebend (bottom of the SPA) is stretched, while the sensor
on the inside of the bend (top of the SPA) is contracted,
resulting in mirrored sensor responses, as seen in Figure 6.
The sensor responses were normalized by subtracting theinitial value recorded while the actuator was unpressurized

In this paper, we have presented a soft pneumatic actuatorwith embedded strain sensors. By integrating two strain
sensors along opposing faces in the interior chamber ofan SPA, the extension and bending angle of the actuatorcan be ascertained by calculating the mean and differential
responses of the sensors. These measurements enable a moreaccurate reconstruction of the state of the sSPA fascicle,
which is particularly useful for applications of the sSPAs inenvironments where they will interact with its surroundings.
Future work will focus on further characterization of thesSPA’s behavior, improving the mechanical robustness of thesystem, exploring different designs of sSPAs, and performing feedback control of the actuators using proprioceptive
feedback from the sensors. In order to implement this in
an integrated robotic system, it would be beneficial to morethoroughly investigate the dynamic behavior of the sSPAs.
In particular, the bandwidth of the sensors and actuators,
the effects of inflation rate, and performance under many
cycles of operation will be relevant towards this goal. The
mechanical robustness of the interface between the sensor
body and the signal conditioning electronics was a limitationin this work. Because relative motion was allowed between
the signal conditioning boards and the sSPAs, a great dealof stress was placed on the junction between the sensor andthe copper strips. Some methods to potentially improve theinterface are to reinforce the end of the sensor with fabric or
to secure rigid plates around the interface. Additionally, theactuator robustness is sensitive to the tension applied to thefishing line as it is wound around the SPA. With uneventension, the alignment of the weave around the actuator
varied, allowing portions of the ElastoSil bladder to bubble
up between the fishing line, which could lead to poppingand failure of the actuator. Design of the sSPA can be tuned
to fit the geometric requirements, motion trajectories, andforce-displacement profiles needed by a given soft robotic
system. The fabrication methods presented here can be easily
scaled to accommodate various changes in geometry. An
extension of the dual-sensor system presented here would be
to incorporate three or more sensors to measure the full threedegrees of freedom of the free end relative to the interfaceend (extension, bending about two axes). A variety of othersilicone-based sensor types could also be incorporated on orin an SPA including torsional and exterior contact sensors.
Lastly, control strategies may be applied to the current systempresented here. Both position and force may be controlledusing the results of the characterization tests presented here.
In conclusion, the work presented here on embedding
a pair of sensors within a soft pneumatic actuator canadvance the field of soft robotics by enabling better state
reconstruction and control of a compliant actuator.
V. ACKNOWLEDGMENTS
The authors would like to thank Sagar D. Joshi for instruction
on manufacturing the soft pneumatic actuators. This work was
supported by the Swiss National Centre for Competence in Research(NCCR) Robotics and by the National Aeronautics and Space
Administration (NASA) through a Small Business Technology
Transfer Grant (Grant No. 80NSSC17C0030). MCY is supportedby the National Science Foundation Graduate Research Fellowship(Grant No. DGE-1333468).

R EFERENCES[1] J. C. Case, E. L. White, and R. K. Kramer, “Soft Material Characterization for Robotic Applications,” Soft Robotics, vol. 2, no. 2, pp.
80–87, June 2015.
[2] D. Rus and M. T. Tolley, “Design, fabrication and control of soft
robots,” Nature, vol. 521, no. 7553, pp. 467–475, May 2015.
[3] Y.-L. Park and R. J. Wood, “Smart pneumatic artificial muscle actuatorwith embedded microfluidic sensing,” in SENSORS, 2013 IEEE.
IEEE, 2013, pp. 1–4.
[4] Y. L. Park, B. r. Chen, C. Majidi, R. J. Wood, R. Nagpal, and
E. Goldfield, “Active modular elastomer sleeve for soft wearable
assistance robots,” in 2012 IEEE/RSJ International Conference onIntelligent Robots and Systems, Oct. 2012, pp. 1595–1602.
[5] L. O. Tiziani, T. W. Cahoon, and F. L. Hammond, “Sensorizedpneumatic muscle for force and stiffness control,” in 2017 IEEE
International Conference on Robotics and Automation (ICRA), May
2017, pp. 5545–5552.
[6] H. Kim, H. Park, J. Kim, K. J. Cho, and Y. L. Park, “Design ofanisotropic pneumatic artificial muscles and their applications to soft
wearable devices for text neck symptoms,” in 2017 39th Annual
International Conference of the IEEE Engineering in Medicine andBiology Society (EMBC), July 2017, pp. 4135–4138.
[7] R. A. Bilodeau, E. L. White, and R. K. Kramer, “Monolithic fabrication of sensors and actuators in a soft robotic gripper,” in Intelligent
Robots and Systems (IROS), 2015 IEEE/RSJ International Conference
on. IEEE, 2015, pp. 2324–2329.

[8] N. Farrow and N. Correll, “A soft pneumatic actuator that can sense
grasp and touch,” in 2015 IEEE/RSJ International Conference onIntelligent Robots and Systems (IROS), Sept. 2015, pp. 2317–2323.
[9] Y. Hao, T. Wang, Z. Xie, W. Sun, Z. Liu, X. Fang, M. Yang, and
L. Wen, “A eutectic-alloy-infused soft actuator with sensing, tunable
degrees of freedom, and stiffness properties,” J. Micromech. Microeng.,
2017.
[10] J. Morrow, H. S. Shin, C. Phillips-Grafflin, S. H. Jang, J. Torrey,
R. Larkins, S. Dang, Y. L. Park, and D. Berenson, “Improving
Soft Pneumatic Actuator fingers through integration of soft sensors,
position and force control, and rigid fingernails,” in 2016 IEEE
International Conference on Robotics and Automation (ICRA), May
2016, pp. 5024–5031.
[11] V. Wall, G. Zller, and O. Brock, “A method for sensorizing soft
actuators and its application to the RBO hand 2,” in 2017 IEEE
International Conference on Robotics and Automation (ICRA), May
2017, pp. 4965–4970.
[12] W. Felt, K. Y. Chin, and C. D. Remy, “Contraction Sensing With Smart
Braid McKibben Muscles,” IEEE/ASME Transactions on Mechatronics, vol. 21, no. 3, pp. 1201–1209, June 2016.
[13] W. Felt, M. Telleria, T. Allen, G. Hein, J. Pompa, K. Albert, and C. D.
Remy, “An Inductance-Based Sensing System for Bellows-Driven
Continuum Joints in Soft Robots,” in Proceedings of Robotics: Scienceand Systems, Cambridge, Massachusetts, 2017, oCLC: 853458128.
[14] J. C. Yeo, H. K. Yap, W. Xi, Z. Wang, C.-H. Yeow, and C. T. Lim,
“Flexible and Stretchable Strain Sensing Actuator for Wearable Soft
Robotic Applications,” Adv. Mater. Technol., vol. 1, no. 3, pp. n/a–n/a,June 2016.
[15] M. Luo, Y. Pan, E. H. Skorina, W. Tao, F. Chen, S. Ozel, andC. D. Onal, “Slithering towards autonomy: a self-contained soft robotic
snake platform with integrated curvature sensing,” Bioinspir. Biomim.,vol. 10, no. 5, p. 055001, 2015.
[16] S. Sareh, Y. Noh, M. Li, T. Ranzani, H. Liu, and K. Althoefer,“Macrobend optical sensing for pose measurement in soft robot arms,”
Smart Mater. Struct., vol. 24, no. 12, p. 125024, 2015.
[17] H. Zhao, K. OBrien, S. Li, and R. F. Shepherd, “Optoelectronicallyinnervated soft prosthetic hand via stretchable optical waveguides,”Science Robotics, vol. 1, no. 1, p. eaai7529, Dec. 2016.
[18] M. C. Yuen, H. Tonoyan, E. L. White, M. Telleria, and R. K. Kramer,“Fabric sensory sleeves for soft robot state estimation,” in 2017 IEEE
International Conference on Robotics and Automation (ICRA), May
2017, pp. 5511–5518.
[19] N. C. Goulbourne, S. Son, and J. W. Fox, “Self-sensing McKibben
actuators using dielectric elastomer sensors,” vol. 6524, 2007, pp.
652 414–652 414–12.
[20] H. Yang, Y. Chen, Y. Sun, and L. Hao, “A novel pneumatic soft sensor
for measuring contact force and curvature of a soft gripper,” Sensors
and Actuators A: Physical, vol. 266, no. Supplement C, pp. 318–327,
Oct. 2017.
[21] H. Zhao, R. Huang, and R. F. Shepherd, “Curvature control of soft
orthotics via low cost solid-state optics,” in 2016 IEEE International
Conference on Robotics and Automation (ICRA), May 2016, pp. 4008–
4013.
[22] K. Elgeneidy, N. Lohse, and M. Jackson, “Bending angle prediction
and control of soft pneumatic actuators with embedded flex sensors
A data-driven approach,” Mechatronics, Oct. 2017.
[23] G. Gerboni, A. Diodato, G. Ciuti, M. Cianchetti, and A. Menciassi,“Feedback control of soft robot actuators via commercial flex bend
sensors,” IEEE/ASME Transactions on Mechatronics, vol. PP, no. 99,
pp. 1–1, 2017.
[24] E. L. White, J. C. Case, and R. K. Kramer, “Multi-mode strain andcurvature sensors for soft robotic applications,” Sensors and Actuators
A: Physical, vol. 253, pp. 188–197, Jan. 2017.
[25] E. L. White, M. C. Yuen, J. C. Case, and R. K. Kramer, “Low-Cost,
Facile, and Scalable Manufacturing of Capacitive Sensors for Soft
Systems,” Adv. Mater. Technol., vol. 2, no. 9, pp. n/a–n/a, Sept. 2017.
[26] M. A. Robertson, H. Sadeghi, J. M. Florez, and J. Paik, “SoftPneumatic Actuator Fascicles for High Force and Reliability,” Soft
Robotics, Oct. 2016.