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MiBOT: A head-worn robot that modulates cardiovascular responses through human-like soft massage
Alice Mylaeus, Stephanie Vogt, Berken Utku Demirel, Marcel Gort, Mirko Meboldt, Manuel Meier, Christian Holz
TL;DR
Existing massage robots have largely targeted the torso and limbs, leaving suitable head actuation for headache-related massage challenging. MiBOT addresses this gap with a wearable temple-massage robot using soft tactors, pressure feedback, and low-noise actuation. In a nine-participant evaluation, it reduced blood pressure and heart rate, with effects described as similar to human-administered massage.
Problem
Existing robotic massage systems have focused on the torso and limbs, while suitable actuation for human-like massage on the head remains challenging.
Method
MiBOT is a wearable temple-massage robot that uses soft tactors, pneumatic artificial muscles, pressure feedback, and hydraulic transmission to deliver human-like massage.
Results
MiBOT decreased participants’ blood pressure and heart rate; mean DBP fell from 67.8 to 66.1 mmHg, mean SBP from 119.8 to 117.0 mmHg, and mean HR by 3.4 bpm.
Takeaways & Limitations
The robotic massage modulated cardiovascular responses and showed a significant relaxation effect, with observed HR and BP effects similar to human-administered massage.
Takeaways & Limitations
The current system completes a full massage circle in about ten seconds because motor speed is limited by the force-producing transmission design.
Abstract
from arXiv · showhide
Massage therapy is helpful for the rehabilitation of various diseases, such as headaches caused by migraines and stress. Existing robotic systems have focused on massage therapy on the torso and limbs, but performing massage motions through suitable actuation on a person's head has been a challenge. In this paper, we present MiBOT, a head-worn massage robot that actuates two soft tactors to produce touch motions mimicking human massage. A key design principle behind MiBOT is its silent actuation, which we achieve through pneumatic artificial muscles in conjunction with a controller loop to respond to contact pressure. We evaluated the effectiveness of MiBOT in a controlled study and assessed subjects' blood pressure and heart rate levels while applying MiBOT. We found that our mechanical system generated positive and conclusive quantitative outcomes that are similar to the human-administered massage, decreasing participants' mean systolic and diastolic blood pressure by 2.8 mmHg and 1.7 mmHg, respectively, as well as calming their heart rate by 8-10% on average.
I. INTRODUCTION
MiBOT addresses the challenge of delivering human-like massage to the temple region, where existing massage robots have primarily targeted the torso and limbs. The wearable system combines adaptable soft-tactor actuation with cardiovascular evaluation in nine participants.
- Motivation: Massage may help prevent headaches, including migraines, while also relieving stress and improving well-being.The introduction describes massage as a possible alternative to medication for headache prevention and as a therapy associated with reduced stress, pain, anxiety, and depression.
- Design and contribution: MiBOT is a wearable robot with two symmetrically actuated soft tactors that produce human-like massage sensations on the temple regions.Its design uses pneumatic artificial muscles and sensor-driven pressure adaptation to conform to different head shapes and topologies.
- Motivation: Manual massage requires substantial labor and time, and therapists may fatigue while maintaining suitable force over extended periods.These constraints motivate automated, repeatable massage systems that can operate without fatigue.
- Research gap: Existing human-like massage robots have focused mainly on the back, shoulders, and arms rather than headache-related temple massage.The paper identifies the temple region as an underexplored target for robotic massage.
- Design and contribution: The feedback control loop enables defined massage trajectories with appropriate force despite naturally varying head topologies.Compliant mechanisms and pulleys transform actuator motion into circular massage motions approximating human touch.
- Evaluation: MiBOT’s effects on heart rate and blood pressure were evaluated with nine participants and compared with a commercially available head massage.The authors report cardiovascular modulation and a significant relaxation effect from the robotic massage.
A. Design Concept and Hardware Setup
MiBOT separates actuation from the head-mounted massage location and organizes the robot into functional blocks that support motion generation, transmission, and force transfer.
- A. Design Concept and Hardware Setup: The robot comprises actuation, actuation transmission, actuation output, and guidance-and-force-transfer blocks.These blocks divide drive generation, physical separation from the ear, massage-motion production, and motion transformation among system components.
- A. Design Concept and Hardware Setup: Stepper motors provide the drive, while a custom acrylic transmission uses gear reduction and rotary-to-linear conversion to compress syringes.The syringes function as fluidic cylinders connected to the massage device in a closed system.
- A. Design Concept and Hardware Setup: Separating the actuation unit from the headpiece helps keep the motor and transmission away from the wearer’s ear.This architecture supports the system’s effort to reduce noise and vibration at the massage location.
2) Actuation Transmission:
MiBOT uses a hydraulic transmission to reduce acoustic disturbance and vibration near the wearer’s head while delivering actuation from a separated unit.
- 2) Actuation Transmission:: 38 dB was the measured maximum actuation noise level, comparable to a soft whisper.The measurement was taken in a quiet environment at participants’ head height.
- 2) Actuation Transmission:: The final system uses hydraulic transmission because directly attaching the actuation unit to the headpiece was infeasible for noise and vibration reasons.The authors report that pneumatic transmission had high noise emissions, leading them to select hydraulics for the final design.
3) Actuation Output:
MiBOT uses flexible McKibben pneumatic artificial muscles for actuation, then combines their one-directional tension with compliant guidance elements to generate temple massage motions.
- 3) Actuation Output:: The McKibben actuator model relates tension force F to applied pressure P and knitting angle Θ.The paper describes force as linearly proportional to internal pressure and monotonic with knitting angle.
- 3) Actuation Output:: The actuator’s flexible driven part is suitable for use around people, but each McKibben muscle produces only unidirectional contractile tension.Additional guidance and force-transfer elements are therefore needed to create the desired massage motion and force at the temple.
- 3) Actuation Output:: 54.7° is the neutral knitting angle at which the exerted tension force reaches zero.The prototyped MiBOT actuators have resting knitting angles of 28°.
- 3) Actuation Output:: The force model Fm(P) uses applied pressure P, actuator area A, and knitting angle Θ to characterize actuator force under pressure.The passage explicitly defines A as the cross-sectional area of the McKibben actuators.
4) Guidance and Force Transfer:
MiBOT converts actuator motion into circular tactor massage through pulley-guided strings and discrete trajectory commands. Pressure feedback reduces oscillations and maintains contact pressure during massage.
- Mechanical guidance: Three McKibben actuators and compliant pulley mechanisms transform unidirectional actuator motion into limited circular tactor motion.The mechanism uses strings connected to the actuator ends and central tactor tube.
- Trajectory calculation: 24 discrete tactor positions determine string shortening or lengthening from shortest distances between pulley locations and the desired circular path.The pulley wheels are arranged at triangle vertices around the tactor axis.
- Pressure control: A feedback controller updates motor commands from the error between measured contact pressure and the 7.3 kPa setpoint during 0.1 Hz circular motion.The controller increases or decreases tactor inflation when contact pressure is too low or too high, with positional limits for safety.
- Pressure control: 25% lower and more unstable tactor pressure occurred without feedback control at a 2.5 kPa target during 3.5 circular motions.With feedback, pressure oscillations diminished significantly while reaching the desired pressure.
B. Participants
The study recruited nine participants without known diseases, comprising six males and three females with a mean age of 32 years.
- Participants: Nine participants without known diseases took part in the experiments.The sample included six males and three females, with a mean age of 32 years.
- Participants: All participants provided written informed consent, and the study followed the Declaration of Helsinki.
C. Experimental Protocol and Data Collection
The experiment measured blood pressure and heart rate during a standardized massage protocol using MiBOT and a commercial massage device. Measurements combined an oscillometric blood-pressure monitor with continuous carotid tonometry.
- Protocol: A 27-minute protocol comprised a 10-minute baseline, 12-minute massage intervention, and 5-minute post-intervention baseline.All participants received the same massage intervention and preparation procedure.
- Data collection: Blood pressure was recorded with an oscillometric cuff, while a carotid tonometer continuously recorded pulse pressure waveforms for heart-rate measurement.The tonometer was positioned over the carotid artery.
- Data collection: The custom tonometer used a silicone dome, tubing, and an analog pressure sensor sampled at 200 Hz to capture arterial pressure waves.The device had a 0–6 kPa measurement range and was positioned centrally over the carotid artery.
- Comparison condition: MiBOT was compared with a commercial scalp-massage device using air pressure and vibration at participant-selected intensity and temperature settings.The same experimental protocol was used for both devices.
D. Data processing
Heart rate was extracted from filtered carotid tonometry signals by detecting and smoothing heartbeats while removing motion-related artifacts. Blood-pressure values were used without additional external processing.
- Heart-rate processing: A third-order Butterworth bandpass filter from 3–15 Hz denoised the tonometry signal before heartbeat peak detection.Peak spacing was restricted to at least 300 ms, corresponding to a maximum heart rate of 180 beats per minute.
- Heart-rate processing: Heart-rate values were smoothed by averaging 10 adjacent beat-to-beat intervals after filtering motion-artifact peaks.Artifacts included transitions between massage sessions.
- Blood-pressure processing: Blood-pressure measurements received no additional processing because the device internally processed its output values.
III. RESULTS AND DISCUSSION
MiBOT reduced participants’ blood pressure and heart rate, with effects similar to human-administered massage, while its design emphasizes natural tactile motion and reduced noise. The study also identifies slower actuation and future personalization and sensing opportunities.
- Blood pressure: 2.8 mmHg and 1.7 mmHg: Mean SBP decreased from 119.8 to 117.0 mmHg, while mean DBP decreased from 67.8 to 66.1 mmHg after MiBOT massage.The maximum decreases were 11 mmHg for SBP and 5 mmHg for DBP; decreases were more pronounced at higher starting values.
- Heart rate: 7 of 9 participants experienced decreased HR, with an overall mean reduction of 3.4 bpm after robotic massage.The decrease reached 5 bpm for some participants and was close to a 10% average reduction in HR.
- Comparison with human massage: MiBOT’s observed HR and BP effects were similar to those reported for human-administered massage by nurses.Baseline-to-post-massage HR decreases were statistically significant for six participants using MiBOT.
- Comparison with commercial device: The commercial head-massage device produced no statistically significant relaxation effect and increased mean HR, unlike MiBOT’s average 8–10% HR reduction.The comparison used the same experimental procedure while varying the commercial device’s temperature and vibration intensity settings.
- System design: MiBOT uses tactor actuators to create multi-angle circular tactile sensations, while hydraulic transmission significantly reduces actuation noise.These design choices distinguish its sensations and transmission from the commercial device.
- Limitations and future work: A full circular massage currently takes about ten seconds because the system uses slow motor speeds and a 3:1 gear ratio to generate sufficient force.Lower-resistance fluidic cylinders or stronger motors could increase tactor-speed variability.
- Limitations and future work: Future improvements include tailoring tactor pressure and speed to individuals and integrating unobtrusive sensors for real-time cardiovascular monitoring.The authors propose adapting massage in response to observed HR and BP changes.
- Mechanical durability: The PLA compliant mechanism showed torsional stability during use, but aging may weaken high-stress regions and warrants further fatigue investigation.The base plate limits motion and helps prevent plastic deformation from excessive bending.
IV. CONCLUSION
MiBOT uses soft tactors at the temples to imitate human-like touch while addressing silent operation, pressure control, and head-shape conformance. In a nine-participant study, a 12-minute intervention decreased measured heart rate and blood pressure, indicating a massage-induced relaxation response.
- MiBOT actuates temple-region soft tactors to imitate human-like touch for alleviating migraines and tension.
- Near-silent operation, normal-pressure modulation, and adaptation to complex head topologies address key design challenges for head massage.
- A 12-minute MiBOT massage was evaluated with nine participants by measuring blood pressure and heart rate.
- Participants showed decreased heart rate and blood pressure values, indicating a massage-induced relaxation response.