Source-linked AI summary
Cutaneous Force Feedback as a Sensory Subtraction Technique in Haptics
Domenico Prattichizzo, Claudio Pacchierotti, Giulio Rosati
TL;DR
Teleoperated needle insertion needs force information, but communication latency can compromise haptic-loop stability and transparency. The paper therefore tests wearable cutaneous-only feedback as sensory subtraction of complete haptic feedback. Experiments find better penetration performance than visual feedback, while the approach remains intrinsically stable, though interaction realism is weaker than with complete haptic feedback.
Problem
Teleoperated needle insertion requires force information for detecting tissue properties and abnormal resistance, while communication latency can compromise haptic stability and transparency.
Method
The paper uses wearable devices on the thumb and index finger to provide only the cutaneous component of complete haptic feedback during simulated teleoperated needle insertion.
Results
Sensory subtraction produced better penetration performance than visual feedback, with cutaneous-only modalities intermediate between visual and complete haptic feedback and no difference in task completion time.
Takeaways & Limitations
Cutaneous force feedback can substitute for complete cutaneous and kinesthetic feedback while intrinsically guaranteeing haptic-loop stability and simplifying actuator requirements.
Takeaways & Limitations
Interaction realism is weaker than with complete haptic feedback, and extending the approach to multi-degree-of-freedom tasks requires accounting for force-direction changes caused by hand repositioning.
Abstract
from arXiv · showhide
A novel sensory substitution technique is presented. Kinesthetic and cutaneous force feedback are substituted by cutaneous feedback (CF) only, provided by two wearable devices able to apply forces to the index finger and the thumb, while holding a handle during a teleoperation task. The force pattern, fed back to the user while using the cutaneous devices, is similar, in terms of intensity and area of application, to the cutaneous force pattern applied to the finger pad while interacting with a haptic device providing both cutaneous and kinesthetic force feedback. The pattern generated using the cutaneous devices can be thought as a subtraction between the complete haptic feedback (HF) and the kinesthetic part of it. For this reason, we refer to this approach as sensory subtraction instead of sensory substitution. A needle insertion scenario is considered to validate the approach. The haptic device is connected to a virtual environment simulating a needle insertion task. Experiments show that the perception of inserting a needle using the cutaneous-only force feedback is nearly indistinguishable from the one felt by the user while using both cutaneous and kinesthetic feedback. As most of the sensory substitution approaches, the proposed sensory subtraction technique also has the advantage of not suffering from stability issues of teleoperation systems due, for instance, to communication delays. Moreover, experiments show that the sensory subtraction technique outperforms sensory substitution with more conventional visual feedback (VF).
1 INTRODUCTION
The paper introduces cutaneous force feedback as a sensory-subtraction approach for teleoperated needle insertion, motivated by the importance of force information and the stability limitations of bilateral haptic teleoperation. It presents cutaneous-only feedback as a wearable alternative that preserves the cutaneous component while omitting kinesthetic feedback.
- Motivation: Force feedback helps surgical operators detect tissue properties and distinguish expected from abnormal resistance during needle advancement.This is particularly relevant for procedures involving critical areas where inaccurate insertion can cause serious injury.
- Motivation: Communication latency can reduce haptic-feedback effectiveness and affect stability and transparency, especially with stiff remote environments.Control, passivity, and wave-variable approaches can mitigate the problem, but the paper notes that control-based stability guarantees are not intrinsically safe.
- Related approach: Sensory substitution avoids master-side force actuators, making the haptic loop intrinsically stable while replacing kinesthetic feedback with vibrotactile, auditory, or visual feedback.The paper positions its cutaneous approach within this broader strategy for safer teleoperation.
- Proposed approach: The proposed sensory subtraction presents only the cutaneous component of complete haptic feedback, without the kinesthetic part.Wearable devices apply stresses to the finger pads in a pattern intended to correspond to the cutaneous stimuli produced by a haptic device.
- Study focus: The study evaluates the approach in a simulated teleoperated needle-insertion task using newly developed wearable cutaneous devices.The paper extends preliminary industrial results by testing sensory subtraction with new devices in the needle-insertion scenario.
2 SENSORY SUBTRACTION
Sensory subtraction presents only the cutaneous component of haptic feedback through wearable fingertip devices, omitting actuator-generated kinesthetic feedback while preserving similar stimulation at the finger pad. The approach is implemented and evaluated with a one-degree-of-freedom haptic handle and paired wearable devices.
- Sensory subtraction: Sensory subtraction provides cutaneous feedback alone instead of complete haptic feedback containing both cutaneous and kinesthetic components.The user’s natural hand and arm kinesthesia remains, but kinesthetic feedback generated by haptic-device actuators is removed.
- Sensory subtraction - a demonstrator: The proposed modality is compared with complete haptic feedback and visual substitution of contact-force feedback.This comparison tests the novel feedback modality against both conventional haptic feedback and a common sensory-substitution approach.
- Sensory subtraction: The approach uses the same finger-pad area and similar stimulus intensity as the cutaneous component perceived with an actuated haptic handle.It therefore delivers a subset of the stimuli normally provided by complete haptic feedback.
- The wearable fingertip cutaneous force feedback device: The wearable device presses a fingertip contact patch against the volar skin using cable lengths controlled by three small electrical motors.The prototype can simulate fingertip contact with an object or handle by generating forces normal to the fingertip.
- The wearable fingertip cutaneous force feedback device: Experiments place wearable devices on the thumb and index finger while a clamped Omega 3 haptic device restricts handle motion to the z-axis.A plastic handle permits the operator to grasp the device with two fingers, and additional devices are worn on the contralateral hand.
- Sensory subtraction - a demonstrator: Complete haptic feedback uses the Omega 3 with wearable devices off, producing mixed kinesthetic and cutaneous stimuli.In cutaneous-only feedback, the Omega 3 tracks hand motion without active force, while wearable devices reproduce task-associated cutaneous sensations.
3 A MEDICAL APPLICATION OF SENSORY SUB-
The paper evaluates cutaneous-only force feedback for teleoperated needle insertion in soft tissue with forbidden-region virtual fixtures. The setup compares haptic, visual, and cutaneous feedback while modeling needle–tissue interaction and monitoring stability.
- Experimental design: The sensory subtraction approach is intended to preserve intuitive motion feedback while avoiding kinesthetic force transmission and associated teleoperation stability concerns.The paper uses cutaneous force feedback alone as the substitute for complete haptic feedback.
- Setup: Virtual fixtures regulate needle motion by guiding it or forbidding entry into protected workspace regions.This study considers forbidden-region fixtures relevant to biopsies, deep brain stimulation, and functional neurosurgery.
- Setup: The task uses a one-degree-of-freedom haptic handle to teleoperate a needle through a simulated soft tissue with virtual fixtures.The virtual environment computes needle–tissue contact forces and returns them through haptic, cutaneous, or visual feedback.
- Scope and limitations: The tissue simulation is deliberately simple because the study aims to validate sensory subtraction rather than develop an accurate FEM-based tissue simulator.The limitation concerns model fidelity, not the evaluation objective.
- Soft tissue modeling: The tissue is modeled with spring, damping, viscous, and mass parameters, while the virtual fixture uses a much stiffer spring.The tissue parameters are Kt = 2 N/m, Bt = 5 Ns/m, Mt = 1 kg, and Vt = 0.7 Ns/m; the fixture spring is Kvf = 3000 N/m.
- Soft tissue modeling: The interaction model distinguishes no contact, contact without penetration, penetration within the safe area, and contact with the virtual fixture.Needle penetration begins only when the haptic force exceeds the threshold Fp = 0.1 N.
- Experimental design: Four modalities are compared: complete haptic feedback, visual substitution, and cutaneous-only feedback applied either to the handle-holding hand or the contralateral hand.The insertion task requires stopping at the perceived fixture, waiting for a beep after 5 s, and withdrawing the needle.
- Scope and limitations: Changing how the operator grasps the handle can change the perceived haptic force direction, so hand position must be monitored in future multi-degree-of-freedom extensions.This directional issue does not arise in the same way with cutaneous-only feedback.
4 EXPERIMENTAL RESULTS
Across three experiments, cutaneous-only feedback generally outperformed visual feedback, though complete haptic feedback often produced the best task performance. Removing kinesthetic feedback also improved stability under transmission delay and reduced unwanted needle motions.
- Experiment #1: Null penetration denotes the best accuracy or overshoot outcome, while positive penetration indicates overrunning the target and may damage tissue.The metrics quantify average penetration accuracy and maximum penetration overshoot during needle insertion.
- Experiment #1: Average and maximum penetration differed significantly among feedback modalities, with sensory subtraction producing intermediate performance between haptic and visual feedback.Average penetration: F3,45 = 106.5, P < 0.0001; maximum penetration: F3,45 = 81.89, P < 0.0001.
- Experiment #1: Contralateral cutaneous stimulation performed worse than fingertip stimulation on the acting hand, indicating that feedback localization is important for needle-control performance.The authors suggest that contralateral feedback may require additional transcallosal transmission before influencing the operating hand.
- Experiment #3: With a 50 ms delay, instability occurred only with complete haptic feedback, while cutaneous feedback maintained stable contact with the virtual fixture.Haptic feedback also required significantly more time to achieve stable contact than visual or cutaneous modalities under delay.
- Experiment #1: Visual feedback yielded the greatest penetration, whereas cutaneous-only feedback performed better than visual feedback but worse than complete haptic feedback.The same ordering held for both average and maximum penetration beyond the virtual fixture.
- Discussion: Cutaneous-only feedback reduced unwanted movements in guided tasks because eliminating kinesthetic feedback prevented active force transmission through the handle.This benefit is particularly relevant to robot-aided surgery, where unwanted hand movements could seriously harm the patient.
5 CONCLUSION AND FUTURE WORK
The proposed cutaneous force feedback approach can replace complete cutaneous and kinesthetic feedback during teleoperation while intrinsically guaranteeing haptic-loop stability. Its main trade-off is weaker realism, and future work targets improved wearability and broader device capabilities.
- Cutaneous force feedback on the thumb and index finger pads effectively substitutes complete cutaneous and kinesthetic feedback during handle manipulation.
- The cutaneous displays intrinsically guarantee haptic-loop stability, which is convenient for critical applications such as robotic surgery.
- Cutaneous displays usually require less power and are less bulky than complete haptic-feedback devices, simplifying mechanical design and reducing costs.
- The approach provides direct, co-located contact-force perception but offers weaker interaction realism than complete haptic feedback.
- Future work aims to improve device wearability, dynamic performance, psychophysical evaluation, scaled kinesthetic feedback, multimodal feedback, and comparisons with other substitution techniques.