💻 computer science

A Wearable Stiffness-Rendering Haptic Device with a Honeycomb Jamming Mechanism for Bilateral Teleoperation

This paper presents the HJ-Haptic, a lightweight wearable haptic device utilizing a honeycomb jamming mechanism and vacuum pressure to render variable object stiffness (1.15–2.64 N/mm) for safe and effective bilateral teleoperation, demonstrating reliable stiffness perception and stable interaction through experimental validation.

Original authors: Thomas M. Kwok, Bohan Zhang, Wai Tuck Chow

Published 2026-08-05

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CC BY 4.0

Original authors: Thomas M. Kwok, Bohan Zhang, Wai Tuck Chow

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you are playing a video game where you control a robot arm on the other side of the world. You reach out to grab a virtual apple, but your screen shows the robot's hand closing, and you feel nothing. It's like trying to catch a ghost. To make remote work feel real, scientists use "haptics"—technology that gives your body a sense of touch. There are two main ways to do this. One is like a gentle buzz or a scratch on your skin, which tells you something is there. The other, called "kinesthetic" feedback, is like feeling the actual weight and resistance of an object pushing back against your muscles. This second type is crucial for delicate tasks, like a surgeon feeling the difference between soft tissue and hard bone, or a factory worker knowing if they are squeezing a fragile egg or a steel bolt. The big challenge has always been building a device that is light enough to wear, strong enough to feel real, and safe enough to use without breaking a sweat or a machine.

Enter the HJ-Haptic, a tiny, thumb-worn gadget designed to solve this puzzle. Think of it as a "smart glove" for just your thumb that can instantly change how hard it is to squeeze. Inside this 20-gram device (which is lighter than a standard AA battery) sits a secret ingredient: a honeycomb structure, similar to the wax cells a bee builds for its honey. Normally, this honeycomb is squishy and easy to bend. But the device has a vacuum pump attached to it. When the pump sucks air out, it creates a vacuum that presses the honeycomb layers together, making the whole structure lock up and become rigid, almost like turning a wet sponge into a rock-hard brick.

The researchers built this device to work in a "bilateral teleoperation" system. That's a fancy way of saying: you move your thumb, and a robot hand on the other side copies you. But here is the magic trick: as the robot hand squeezes a real object, the device on your thumb instantly changes its own stiffness to match that object. If the robot grabs a soft sponge, your thumb feels soft. If it grabs a hard box, your thumb feels hard. The team tested this with three items: a piece of tissue paper, a foam sponge, and a cardboard box. They found that the device could smoothly shift its stiffness from 1.15 N/mm to 2.64 N/mm using a vacuum pressure of just 30 kPa. The results were impressive; the movement of your thumb and the robot's hand stayed perfectly in sync, and the force you felt matched the force the robot applied with a very small error.

What makes this approach special is how it handles the "lag" or delay that often happens when signals travel long distances. Instead of trying to send separate messages about "how hard I'm pushing" and "how far I'm moving," which can get out of sync and feel weird, this device sends a single, unified message: "This is how stiff the object is." It's like the difference between trying to describe a song by listing the notes and the rhythm separately versus just humming the tune. By mimicking the stiffness directly, the system keeps the feeling natural even if there is a tiny delay in the connection.

The team also noted that using a vacuum (sucking air out) is much safer than using positive pressure (blowing air in). If a tube leaks in a blower system, it might pop or push unexpectedly. But if a vacuum tube leaks, the device just slowly loses its "rock-hard" feeling and becomes soft again, like a deflating balloon, which is much safer for the user. While the device worked well in their tests, the authors are careful to say that more studies are needed to see how comfortable it is to wear for hours and how well it feels to different people. They suggest this technology could eventually help not just in remote robotics, but also in virtual reality games where you want to feel the difference between a plastic sword and a wooden one. For now, the HJ-Haptic stands as a promising, lightweight step toward making the invisible world of remote robots feel as real as the objects in your own hands.

Technical Summary: A Wearable Stiffness-Rendering Haptic Device with a Honeycomb Jamming Mechanism for Bilateral Teleoperation

Problem Statement
Bilateral teleoperation relies heavily on effective haptic feedback to ensure intuitive and safe interaction between human operators and remote systems. While kinesthetic feedback (replicating direct forces) is crucial for tasks like object grasping, conventional devices face significant challenges. These include delayed force feedback leading to instability and sensation distortion, as well as joint misalignment in hand exoskeletons which causes unwanted shear forces and unreliable motion measurements. Furthermore, existing stiffness-rendering devices have not been sufficiently evaluated within teleoperation frameworks, and many current solutions separate stiffness perception into distinct force and motion components, compromising reliability due to synchronization issues caused by communication delays.

Methodology
The authors propose the HJ-Haptic, a wearable, lightweight (20 g), and compact device designed to render object stiffness directly through a honeycomb jamming mechanism.

Device Design: The core of the device is a sandwich structure comprising a Nomex® aramid paper honeycomb core (10 mm thick) and two jamming layers made from the loop side of Velcro strips. This assembly is enclosed in an airtight PVC membrane. A steel strip is integrated to provide elastic recovery. The device is worn on the operator's thumb tip, allowing free flexion of other fingers.
Stiffness Control Mechanism: The device utilizes a vacuum pressure system (up to 30 kPa) to induce the jamming effect. When vacuum is applied, the membrane compresses the jamming layers against the honeycomb core, increasing friction and constraining relative motion. This transforms the structure from a compliant state to a rigid state. The stiffness is controlled linearly via a PID controller managing a DC pump.
Sensing and Actuation: A strain gauge mounted on the steel strip measures the operator's fingertip deflection ( $\Delta x_h$ ), which commands the remote gripper's motion. Simultaneously, a load cell on the remote gripper measures interaction force ( $F_g$ ) to estimate object stiffness ( $k_o$ ).
Teleoperation Framework: The system implements a stiffness-rendering framework. Unlike traditional approaches that separate force and motion, this framework estimates the remote object's stiffness in real-time and maps it directly to the desired vacuum pressure ( $p_d$ ) for the HJ-Haptic. This ensures that the operator feels the stiffness of the remote object through the changing resistance of the wearable device, maintaining synchronization between the perceived stiffness and the gripper's interaction.

Key Contributions

Novel Wearable Mechanism: The integration of a honeycomb jamming mechanism into a haptic device, resulting in a 20 g wearable unit that can vary its stiffness by a factor of 2.3 (from 1.15 N/mm to 2.64 N/mm) using only 30 kPa of vacuum pressure.
Stiffness-Rendering Teleoperation: The development of a bilateral teleoperation framework that renders object stiffness directly. This approach avoids the signal asynchronization issues common in force-rendering systems by mapping estimated object stiffness directly to device stiffness.
Safety and Ergonomics: The use of vacuum pressure (negative pressure) rather than positive pneumatic pressure enhances operator safety by preventing dangerous outcomes in the event of gas leakage or material failure. The thumb-mounted design avoids joint misalignment issues associated with exoskeletons.

Experimental Results
The device and framework were evaluated through a three-point flexural test and teleoperated object-grasping tasks involving three objects of varying stiffness: tissue paper, foam sponge, and a carton box.

Device Characterization: The honeycomb structure demonstrated a linear relationship between vacuum pressure and stiffness ( $R^2 = 0.991$ ), achieving a stiffness range of 1.15 N/mm to 2.64 N/mm. The stiffness-changing ratio per kPa was 0.077, outperforming several existing pneumatic haptic devices.
Teleoperation Performance: Experiments showed small Root Mean Square Errors (RMSE) and strong correlations between the HJ-Haptic and the remote gripper across motion, stiffness, and interaction force.
- Motion: RMSE of 0.04 mm; Correlation $r = 0.68$ .
- Stiffness: RMSE of 0.09 N/mm; Correlation $r = 0.64$ .
- Force: RMSE of 0.15 N; Correlation $r = 0.62$ .
Stiffness and Force Rendering: A strong linear relationship was observed between the stiffness of the remote objects and the rendered stiffness of the device ( $R^2 = 0.998$ ), as well as between the operator's applied force and the gripper's force ( $R^2 = 0.985$ ). This indicates the operator could accurately gauge grip force and perceive object stiffness.

Significance and Claims
The paper claims that the HJ-Haptic effectively addresses the challenges of delayed feedback and joint misalignment in teleoperation. By directly rendering object stiffness, the device allows operators to adjust their grip force based on reliable kinesthetic feedback, mimicking the sensation of direct hand grasping. The authors highlight that the device's use of vacuum pressure ensures safety, and its lightweight, compact design facilitates unrestricted finger movement.

The study concludes that the honeycomb jamming mechanism holds significant potential for enhancing haptic feedback in teleoperation and extended-reality (XR) environments. While the current results demonstrate feasibility with constant stiffness objects, the authors note that future work will involve formal user studies to validate ergonomics and perception, as well as testing with objects of non-uniform stiffness and under significant communication delays. The paper maintains a modest tone, acknowledging limitations such as potential gas leakage at higher pressures and the need for further user validation before widespread application.

Technical Summary: A Wearable Stiffness-Rendering Haptic Device with a Honeycomb Jamming Mechanism for Bilateral Teleoperation

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