A Soft, Asymmetric Pneumatic Pouch Actuator for
Providing Controlled Forces in Wearable Haptic Systems
Haptics | Soft Robotics | Human Robot Interaction
This project is in preparation to submit to the IEEE Robotics and Automation Letters. Project by the Human Augmentation for Physical Perception Interactions Lab, Cornell University.
2024
Wearable haptic devices have the potential to transform interactions in virtual and augmented reality environments, teleoperation, and social touch applications by providing precise and immersive force feedback. However, current wearable haptic devices (like vests) utilize symmetric or stacked pouches which deliver inconsistent force outputs and can have a poor fit across users, leading to suboptimal user experiences.
This work addresses these challenges by designing, fabricating, and testing asymmetric domed pouches capable of producing unidirectional force output with enhanced control over force distribution and contact area. This project involved constructing domed pouches with an LDPE bladder and a heat-sealable fabric constraint, modeling their inflation behavior using MATLAB, and testing their performance with precise control mechanisms. Simulations and experimental evaluations demonstrated how the domed geometry minimizes symmetric deformation enabling precise manipulation of the contact area. Results successfully demonstrate the functionality of asymmetric pneumatic pouch actuators. These findings highlight the potential of asymmetric domed pouches for wearable haptic devices. The enhanced control over force directionality and contact area achieved in this work paves the way for more effective and personalized haptic feedback solutions, addressing the limitations of current designs.
Symmetric Inflation
Asymmetric Inflation
To predict the behavior of the pouches during inflation, MATLAB simulations were developed to model the contact area and force output based on the pressure-volume relationship. The pouch was treated as a pair of elliptical domes (top and bottom). This formula accounts for the elliptical cross-section and approximates the three-dimensional volume of the inflated pouch. The total volume of the pouch was obtained by summing the volumes of the top and bottom domes. In addition to height calculations, the simulations included contact area visualization. Using the inflation height as a parameter, the contact area was visualized as an expanding ellipse. We are collecting data using a pressure grid to confirm our contact area simulated results.
See simulation code in progress here.
To ensure precise control over inflation dynamics, an Arduino Mega microcontroller connected to the pressure regulator, was programmed with a keyboard interface used to incrementally increase or decrease the pressure by 0.1 psi with each key press, allowing the operator to control the inflation process directly. This method provided flexibility to adjust the pressure in real time, ranging from 0 to 1 psi. Feedback from an MPX5100DP pressure sensor ensured consistent and accurate monitoring throughout the process.
Experimental setups were developed in order to analyse the pouch behavior. The pouch clamp (left) was designed to hold the pouch midair so that it was clear to visualize the symmetric vs. asymmetric inflation. This setup is used in all videos seen on this page.
The pressure grid consists of 16 taxels (tactile pixels) arranged in a 4x4 configuration (right). Each taxel is composed of four layers of pressure-sensitive sheets, sandwiched between copper tape on the top and bottom, which serve as the electrodes. When pressure is applied, the resistance of the pressure-sensitive sheet changes. A voltage divider circuit is employed, and by measuring the output voltage, we can determine the change in resistance and, consequently, the amount of force applied to the sensing sheet. A 3D-printed stand is used to hold the taxels in place. The stand has a two-layer structure, providing space to arrange and place the circuit beneath the taxels.
This project demonstrated the potential of asymmetric domed pouches to address longstanding challenges in wearable haptic devices. By leveraging a unique asymmetric design and domed geometry, the pouch allowed for unidirectional force output with enhanced control over force distribution and contact area. The integration of an LDPE bladder and a fabric constraint provided a practical and reliable solution for generating dynamic haptic feedback.