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A Reconfigurable Fabric Based Pneumatic Actuator with Button Fastened Constraint Modules for Multi Mode Actuation

Kentaro Kimura, Hiroki Ishizuka, Yusuke Sakaue, Sei Ikeda, Osamu Oshiro

arXiv:2610.11054v1cs.RO

TL;DR

Many soft robots are constrained by mechanisms and structures chosen at design time, and may not adapt to changing requirements. This paper uses attachable fabric constraints to switch a pneumatic actuator among four modes, demonstrating multi-mode actuation and reconfigurable grasping.

  • Problem

    Many robots’ actuation and target tasks are constrained by mechanisms and structures designed at the outset, and may not adapt to changing requirements or situations.

    Source: §I · p. 1

  • Method

    The actuator uses button-fastened, detachable low-stretch fabric constraints whose spatial arrangement determines its deformation mode.

    Source: §I · p. 2, A. PRINCIPLE OF ACTUATOR · p. 3

  • Results

    A single actuator demonstrated four modes, with elongation ratio 1.2, bending angle approximately 60 degrees, twisting angle approximately 90 degrees, and blocking forces exceeding 10 N at 24 kPa; a multi-actuator arm reconfigured grasping.

    Source: §VII · p. 10

  • Takeaways & Limitations

    In the demonstrated multi-actuator arm, changing attached constraint patterns reconfigured its grasping motion.

    Source: §VII · p. 10

    The maximum allowable pressure is limited by the silicone rubber and knitted fabric, so the actuator operates at lower pressure than other textile-based pneumatic actuators.

    Source: §VI · p. 9

Abstract

from arXiv · show

Soft pneumatic actuators are widely used in soft robotics. However, their actuation modes are typically fixed by internal chamber designs or reinforcements, making post fabrication reconfiguration difficult. This paper presents a reconfigurable fabric-based pneumatic actuator that enables rapid, tool free, and reusable switching among multiple actuation modes by attaching constraint fabric modules to a buttoned textile sleeve. By rearranging low-stretch constraint parts on a single actuator body, the proposed system realizes four actuation modes isotropic expansion, contraction, bending, and twisting without redesigning or disassembling the actuator.We further introduce an attachable capacitive fabric-based tactile sensor module that can be mounted at arbitrary locations on the actuator surface for task dependent contact sensing. Experiments demonstrated an elongation ratio of 1.2, a maximum bending angle of approximately 60 degrees, and a twisting angle of approximately 90 degrees at 24 kPa, while achieving blocking forces exceeding 10 N across all modes. The tactile sensor exhibited a monotonic, force-dependent increase in capacitance with low hysteresis (approximately 12%) and stable cyclic responses under preload. Finally, we constructed soft robotic arms composed of multiple actuators and demonstrated in situ motion reconfiguration for grasping by changing the attached constraint patterns. These results indicate that the proposed modular constraint and sensing framework improves the functional adaptability of fabric-based soft robots while preserving a simple, robust actuator structure.

I. INTRODUCTION

The paper addresses the limited, fabrication-fixed actuation modes of soft pneumatic actuators with reusable fabric constraint modules that reconfigure a single actuator body. It also introduces attachable tactile sensing and demonstrates motion reconfiguration in multi-actuator arms.

I. INTRODUCTION

  • Soft pneumatic actuators generally have deformation modes fixed by fabrication, while existing reconfiguration approaches can require specialized materials, reworking, disassembly, or replacement.The introduction identifies a need for a tool-free, reusable mechanism independent of the actuator body.Source: §I · pp. 1–2
  • Button-fastened fabric constraints enable reusable, tool-free switching of one actuator among expansion, contraction, bending, and twisting without redesign or disassembly.Different constraint patterns impose desired deformation modes while preserving a single actuator body.Source: §I · p. 2, Figure 1 · p. 2
  • The same attachment concept supports a soft tactile sensor module at arbitrary actuator-surface locations for task-dependent sensing.Informative contact regions can vary with task, configuration, and interaction conditions, so sensor placement can be adjusted.Source: §I · p. 2
  • Multi-actuator soft robotic arms demonstrate motion reconfiguration by changing their attached constraint patterns.The arms are composed of multiple soft pneumatic actuators.Source: §I · p. 2

II. METHOD · A. PRINCIPLE OF ACTUATOR

A buttoned fabric sleeve lets constraint parts be rearranged after fabrication to reconfigure one pneumatic actuator. Local constraints induce strain anisotropy, converting the actuator’s uniform radial expansion into task-oriented deformation.

A. PRINCIPLE OF ACTUATOR

  • An elastic bladder inside a stretchable, buttoned fabric sleeve supports rapid attachment, detachment, and rearrangement of constraint parts.The buttons mechanically fix the parts to the actuator surface.Source: A. PRINCIPLE OF ACTUATOR · p. 3
  • The arrangement of non-stretchable constraints creates local stiffness differences that convert uniform expansion into task-oriented deformation modes.The spatial placement of the constraints determines the resulting mode.Source: A. PRINCIPLE OF ACTUATOR · p. 3
  • Without attached constraints, the actuator’s isotropic cylindrical body expands nearly uniformly in the radial direction as internal pressure increases.Source: A. PRINCIPLE OF ACTUATOR · p. 3
  • Circumferential constraints produce contraction by limiting lateral surface length, so pressurized unconstrained regions bulge radially and reduce overall axial length.Constrained segments maintain their longitudinal length as the unconstrained segments expand.Source: A. PRINCIPLE OF ACTUATOR · p. 3
  • One-sided constraints perpendicular to the elongation direction inhibit axial elongation on that side, producing bending toward the constrained surface.Source: A. PRINCIPLE OF ACTUATOR · p. 3
  • Helical constraints suppress length changes along their path while unconstrained regions expand, generating rotation around the actuator axis.Twisting angle depends on input pressure and constraint density, set by helical turns per unit length.Source: A. PRINCIPLE OF ACTUATOR · p. 3

B. FABRICATION PROCESS OF ACTUATOR

The actuator is fabricated by combining a molded silicone pneumatic body with a stretchable textile skin and attachable low-stretch constraint parts.

B. FABRICATION PROCESS OF ACTUATOR

  • The silicone body’s cylindrical bladder and inlet were cast separately in 3D-printed resin molds, then bonded with uncured silicone to form an airtight assembly.Ecoflex 00-30 components were mixed at a 1:1 mass ratio and vacuum-degassed before casting.Source: B. FABRICATION PROCESS OF ACTUATOR · pp. 3–4, Figure 2 · p. 3
  • The actuator skin uses longitudinally oriented high-stretch knit, a sewn button grid, reinforced low-stretch ends, and a low-stretch top cap.Constraint strips use less-stretch satin fabric, measure 160 mm × 15 mm, and have 12 mm buttonholes at 24 mm intervals; twisting patches use 33 mm spacing.Source: B. FABRICATION PROCESS OF ACTUATOR · p. 4
  • The assembled cylindrical actuator is 160 mm long and 40 mm in outer diameter, with a 5 mm bladder wall; constraint arrangements can be changed in tens of seconds without tools.The shown arrangements support bending, contraction, and twisting.Source: B. FABRICATION PROCESS OF ACTUATOR · p. 4

C. DESIGN PRINCIPLE OF CAPACITIVE FABRIC-BASED TACTILE SENSOR

The tactile sensor detects force through capacitance changes caused by dielectric deformation. Its fabric electrodes and silicone dielectric form a button-attachable sensor whose capacitance increases under vertical load.

C. DESIGN PRINCIPLE OF CAPACITIVE FABRIC-BASED TACTILE SENSOR

  • The sensor uses conductive fabric electrodes sewn onto fabric with a silicone-rubber dielectric, and attaches to the actuator via buttons.Of its four electrodes, the outer pair reduces noise and the inner pair measures capacitance.Source: C. DESIGN PRINCIPLE OF CAPACITIVE… · p. 4
  • Vertical force compresses the silicone dielectric, reducing electrode spacing and increasing capacitance; because silicone is softer than fabric, its deformation chiefly drives the change.The sensor detects external loads through capacitance changes caused by dielectric deformation.Source: C. DESIGN PRINCIPLE OF CAPACITIVE… · p. 4
  • The model represents force-induced compression as silicone thickness changing from d0 to d1 and uses deformed capacitance C1 to calculate the theoretical capacitance-change ratio.The sensor is treated as a capacitor comprising two fabric layers and a silicone-rubber layer.Source: C. DESIGN PRINCIPLE OF CAPACITIVE… · pp. 4–5

D. FABRICATION PROCESS OF CAPACITIVE FABRIC-BASED TACTILE SENSOR

The sensor uses layered conductive fabric electrodes and a soft silicone dielectric, assembled into a flexible capacitive structure with an integrated shielding electrode.

D. FABRICATION PROCESS OF CAPACITIVE FABRIC-BASED TACTILE SENSOR

  • The sensor was assembled by sandwiching a 3 mm silicone dielectric between two conductive fabric-tape electrodes, each formed from Faraday Cloth Tape.The silicone was cured in a 3D-printed resin mold, and the sensor structure is shown in Fig. 4(a–c).Source: D. FABRICATION PROCESS OF CAPACITIVE… · p. 5
  • The 15 mm × 15 mm external shield electrode covers the sensing area to reduce external noise and parasitic capacitance.Source: D. FABRICATION PROCESS OF CAPACITIVE… · p. 5
  • The electrode area A is 225 mm2, silicone thickness ds is 3.0 mm with εs = 3.4, and fabric thickness df is 0.3 mm with εf = 1.5.The permittivity values were determined from previously reported measurements.Source: D. FABRICATION PROCESS OF CAPACITIVE… · p. 5

III. EXPERIMENTAL PROCEDURE · A. EXPERIMENT FOR ACTUATION

The experiments tested how constraint arrangements change actuator motion using controlled pneumatic actuation, video-based shape tracking, and repeated measurements across pressure conditions and actuators.

III. EXPERIMENTAL PROCEDURE

  • The procedure covered actuator and tactile-sensor evaluation, with actuator motion driven by regulated pneumatic pressure and recorded for image-based analysis.The actuator was mounted on a resin base; the setup used a compressor, regulator, solenoid valve, pressure sensor, microcontroller, and camera.Source: §III · p. 5, Figure 5 · p. 5, A. EXPERIMENT FOR ACTUATION · p. 5

A. EXPERIMENT FOR ACTUATION

  • The camera recorded actuator shape at 30 fps and 1920 × 1080 resolution, while markers tracked shape changes over time.Marker detection used Detectron2, and centroid coordinates provided the tracked marker positions.Source: A. EXPERIMENT FOR ACTUATION · p. 5
  • Relative positions of markers on the actuator’s top and bottom were used to calculate elongation ratio, contraction ratio, bending angle, and twisting angle for each constraint pattern.Source: A. EXPERIMENT FOR ACTUATION · p. 5
  • Actuation evaluation focused on no constraint, bending, twisting, and contracting, with pressure capped at 24 kPa and increased in 3 kPa increments.Pressure was held for 60 seconds at each condition to reach a stable actuation state and avoid excessive inflation.Source: A. EXPERIMENT FOR ACTUATION · p. 5
  • Five measurements were taken at each pressure condition, and three fabricated actuators were evaluated to assess actuator-to-actuator variability.Source: A. EXPERIMENT FOR ACTUATION · p. 5
  • Repeatability was assessed through 10 pressure-loading cycles, each applying 24 kPa for 15 seconds followed by 15 seconds of depressurization.Source: A. EXPERIMENT FOR ACTUATION · p. 5

B. EXPERIMENT FOR BLOCKING FORCE · C. EXPERIMENT FOR FABRIC-BASED TACTILE SENSOR

The sections describe experimental protocols for measuring blocking force across actuation modes and evaluating the capacitive tactile sensor’s force response, hysteresis, and repeatability.

B. EXPERIMENT FOR BLOCKING FORCE

C. EXPERIMENT FOR FABRIC-BASED TACTILE SENSOR

  • A three-axis table robot compressed the tactile sensor while a six-axis force sensor measured reaction force and an LCR meter recorded sensor output.A square probe with a 12 mm × 12 mm contact area was used; Fig. 7 depicts the setup.Source: C. EXPERIMENT FOR FABRIC-BASED TACTILE… · p. 6, Figure 7 · p. 6
  • Sensor output was compared with applied force during compression at 0.1 mm/s to 1 mm indentation, with a 2.5 N preload and 100 kHz, 0.5 V measurement settings.Output was sampled every 100 ms, and the no-load capacitance C0 was subtracted to calculate ∆C/C0.Source: C. EXPERIMENT FOR FABRIC-BASED TACTILE… · p. 6
  • Hysteresis was evaluated during loading and unloading, and repeatability was tested over 10 continuous loading-unloading cycles at 0.1 mm/s to 1 mm indentation.Capacitance was recorded throughout the cycles.Source: C. EXPERIMENT FOR FABRIC-BASED TACTILE… · p. 6

IV. EXPERIMENTAL RESULTS · A. EXPERIMENT FOR ACTUATION

Attaching localized constraint parts to the buttoned sleeve produced the intended actuator deformation modes, including expansion, contraction, bending, and twisting. The measured responses showed pressure-dependent deformation and generally stable repeated actuation.

A. EXPERIMENT FOR ACTUATION

  • At 24 kPa, the unconstrained actuator reached an elongation ratio of 1.2, while its maximum elongation tended to saturate above 12 kPa.The passage attributes saturation at higher pressure to tension-induced stiffening of the fabric skin.Source: A. EXPERIMENT FOR ACTUATION · p. 6, Figure 8 · p. 7
  • Across repeated cycles, expansion, contraction, and twisting showed no change, whereas bending showed a slight angle change during loading and unloading.The passage attributes the bending change to fabric anisotropy and reports small variation among actuators for bending and twisting.Source: A. EXPERIMENT FOR ACTUATION · pp. 6–8
  • Constraint patterns produced the intended deformation modes, as shown by the actuator shapes in Fig. 8.The results demonstrate that actuation can be modified by applying localized constraint parts.Source: A. EXPERIMENT FOR ACTUATION · p. 6, Figure 8 · p. 7
  • The contraction constraint reduced actuator length to approximately 96% of its initial length, with contraction remaining unchanged over repeated cycles.Some trials showed a slight initial extension, which the passage links to microscopic gaps and contact conditions that varied with fabrication and assembly.Source: Figure 8 · p. 7, A. EXPERIMENT FOR ACTUATION · p. 7
  • At 24 kPa, the bending constraint produced a maximum bending angle of approximately 60 degrees, increasing approximately linearly with pressure.The passage attributes the trend to the fabric’s anisotropic stretchability; variation among the three actuators was small.Source: Figure 8 · p. 7, A. EXPERIMENT FOR ACTUATION · p. 8
  • At 24 kPa, the helical constraint produced a twisting angle of approximately 90 degrees, with the angle tending to saturate above 18 kPa.The helical constraint parts converted expansion energy into rotational actuation.Source: Figure 8 · p. 7, A. EXPERIMENT FOR ACTUATION · p. 8

B. EXPERIMENT FOR BLOCKING FORCE · C. EXPERIMENT FOR FABRIC-BASED TACTILE

The actuator produced more than 10 N across its tested actuation modes at 24 kPa, while the attachable fabric tactile sensor showed force-dependent capacitance changes but was used for contact detection rather than quantitative force measurement.

B. EXPERIMENT FOR BLOCKING FORCE

  • At 24 kPa, all four tested actuation modes generated more than 10 N, with force increasing as pneumatic pressure rose.The reported blocking-force values were maxima from three trials, with standard deviations shown.Source: B. EXPERIMENT FOR BLOCKING FORCE · p. 8

SENSOR

  • The sensor’s capacitance change ratio ∆C/C0 increased monotonically with applied force, reflecting dielectric silicone deformation under small compression.The figure caption also reports high linearity and reproducibility.Source: SENSOR · p. 8, Figure 10 · p. 8
  • Approximately 12% hysteresis was observed, and repeated loading and unloading cycles showed no noticeable capacitance drift.Source: SENSOR · p. 8
  • Theoretical and experimental sensor responses both increased monotonically, but differed by approximately 50%, potentially because of material-property variation and insufficient modeling of fabric-layer gaps.Source: SENSOR · p. 8
  • The reported sensor results were idealized: the test eliminated the influence of the sensor’s layered structure and applied a preload.Source: SENSOR · p. 8
  • Because practical use requires a calibration curve accounting for the layered structure, the sensor was used only for contact detection, not quantitative force measurement.Source: SENSOR · p. 9

V. APPLICATION · VI. DISCUSSION

The robotic arms grasped objects at different positions after their surface constraint patterns were changed, without disassembly. The discussion identifies material, fabrication, and modeling limitations and outlines possible extensions to fabric-based soft robots.

V. APPLICATION

  • Each of two soft robotic arms used two actuators connected by fabric parts, with tactile sensors at the tips to confirm successful grasping.The arms’ motion was reconfigured by altering the actuators’ constraint patterns.Source: §V · p. 9, Figure 11 · p. 9
  • Changing constraints reconfigured grasping: contraction above and bending below reached an object beneath the arm, while all-bending reached an object in front, with both grasps confirmed by sensor outputs.The sensor responses reflected the grasping state in each configuration.Source: §V · p. 9, Figure 12 · p. 10, Figure 13 · p. 10
  • Constraint changes modified grasping without disassembling the arm, unlike approaches that change grasping behavior by replacing actuator modules.The proposed arm’s grasping position could be adjusted solely by changing surface constraint patterns.Source: §V · p. 9, Figure 12 · p. 10

VI. DISCUSSION

  • The maximum allowable pressure is limited by the silicone rubber and knitted fabric, so the actuator operates at lower pressure than other textile-based actuators,.Mitigating this limitation could improve achievable displacement and output force.Source: §VI · p. 9
  • The approach could extend to fabric-based pneumatic robots, humanoid inflatables, stretchable-material strain sensors, and varied actuator-connected morphologies,,.Button-based connections could link fabric actuators into different robot morphologies.Source: §VI · p. 9
  • Manual fabrication limited constraint placement; automation could increase button density, enable more complex combined motions, and reduce fabrication errors.The study’s manually fabricated actuator could accommodate only a limited number of constraints.Source: §VI · p. 9
  • Existing structures can guide simple bending and twisting patterns,,, but complex actuation needs design tools such as topology optimization,.The fabric-silicone thickness mismatch complicates finite-element modeling, so an approximate actuator model or structural redesign may be needed.Source: §VI · pp. 9–10

VII. CONCLUSION

The proposed system reconfigures a single fabric-based pneumatic actuator among four modes using reusable button-fastened constraint modules, and adds an attachable capacitive tactile sensor. Experiments demonstrated multi-mode actuation, force-dependent sensing, and reconfigurable grasping with a multi-actuator soft robotic arm.

VII. CONCLUSION

  • At 24 kPa, the actuator achieved an elongation ratio of 1.2, a bending angle of approximately 60 degrees, a twisting angle of approximately 90 degrees, and blocking forces exceeding 10 N across all modes.The four modes were isotropic expansion, contraction, bending, and twisting.Source: §VII · p. 10
  • Button-fastened low-stretch constraint parts let one actuator body switch among four deformation modes without modifying its internal chamber design or embedding reinforcements.The reusable modules attach to the fabric skin.Source: §VII · p. 10
  • The attachable capacitive fabric-based tactile sensor showed monotonic force-dependent output, approximately 12% hysteresis, and stable responses over repeated loading cycles.These responses support contact detection on the actuator surface.Source: §VII · p. 10
  • A soft robotic arm composed of multiple actuators reconfigured its grasping motion by changing the attached constraint patterns.Future work will improve allowable pressure and output through material and fabrication refinements, increase fastening-interface density, and develop computational constraint-layout design methods.Source: §VII · p. 10
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