In a paper recently published in the journal Scientific Reports, researchers from the US introduced a novel cable-driven robotic platform that enables six-degrees-of-freedom (DoF) natural head-neck movements. Their device could be utilized for various applications such as rehabilitation, sensory integration, and pain relief.
Human study task. Left: Labeled task GUI. The current time to target and average time to target is shown to the participant. The marker color changes from red to green as it approaches the target. The target number counts up to 30 to indicate how far along the participant is in the trial. The flexion-extension axis is flipped so that the GUI represents a top-down view of the head as the participants found that more intuitive. Center: Diagram of experiment setup including (from left to right) monitor, joystick, and chair-mounted robot. Right: Photograph of user study. Image Credit: https://www.nature.com/articles/s41598-024-59349-0
Background
The head-neck system provides the head with 6-DoF mobility relative to the trunk. This remarkable flexibility can be significantly compromised by neurological disorders, resulting in symptoms such as poor motor control, a dropped head posture, and a diminished quality of life.
Current treatments typically depend on static neck collars or rigid exoskeletons, which, unfortunately, impose restrictions instead of facilitating natural head-neck movements. Consequently, there is an urgent need for innovative devices that can enable and enhance these movements, effectively overcoming the constraints of existing treatments.
About the Research
In this study, the authors developed and validated a cable-driven robotic platform capable of measuring and controlling the 6-DoF of head-neck movements without enforcing rigid kinematic constraints. The system featured seven cables connected to a headpiece, which was securely attached to the user's head, and servo motors mounted on a frame that was affixed to a chair to actuate the cables.
The device employed a forward kinematics algorithm to calculate the head's orientation from the lengths of the cables and uses a tension distribution algorithm to exert a desired wrench (a combination of force and moment) on the head. This action can be directed either through user input or a predefined control law.
The robot was specifically optimized for high transmission efficiency of cable tensions, ensuring effective application of resultant moments on the head throughout the natural range of head-neck motion. Calibration processes were also carried out to ascertain the user’s neutral position and to achieve precise cable length measurements.
The effectiveness of the platform's forward kinematics and wrench output capabilities was confirmed through benchtop tests, which validated its accuracy in measuring head position and orientation and its efficacy in applying the desired wrench with both accuracy and repeatability.
Additionally, the researchers conducted a human experiment to demonstrate the device's potential in rehabilitation scenarios. Twelve healthy participants were recruited to perform a target-reaching activity that involved head rotations while using the device. The study also explored three control modes: a resistive force field mode, a torque control mode, and an orientation control mode. During these tests, head kinematics and the activation of four neck muscles were monitored using surface electromyography (EMG).
Research Findings
The outcomes indicated that the resistive force field mode increased the activation of the targeted neck muscles by an average of 19 %, whereas the assistive control modes reduced the activation by an average of 28-43 %. Additionally, the results revealed that the orientation control mode enhanced task performance (with a lower average time to reach the target) compared to the torque control mode.
Despite these advancements, the majority of participants expressed a preference for the torque control mode, citing its smoothness and ease of use.
Applications
The proposed device has various implications that require 6-DoF head–neck movements and force/moment application on the head. For example, it can treat patients with head-neck impairments, such as amyotrophic lateral sclerosis (ALS) or cerebral palsy (CP). Additionally, it can be utilized for pain relief and spinal alignment by applying traction forces on the head.
In sports training, athletes can utilize the new device to enhance reflexes, coordination, and neck strength, particularly in disciplines such as boxing or martial arts. The device can even be integrated with virtual reality (VR) systems to allow athletes to accurately track head movements and receive realistic force feedback.
In occupational therapy, individuals recovering from neck injuries or surgeries can incorporate the device into their rehabilitation programs to restore mobility and strength in neck muscles. Furthermore, it can be adapted into assistive devices for individuals with disabilities, enabling control of various electronic interfaces or devices through head movements.
Researchers in biomechanics, ergonomics, and neurology can leverage the device to study head and neck movements across different contexts, advancing the understanding of human physiology and facilitating the design of safer work environments. Lastly, in entertainment and media production, the device's capabilities can be used to capture lifelike head movements for creating realistic characters or special effects sequences.
Conclusion
In summary, the newly developed robotic platform proved highly effective in facilitating 6-DoF natural head-neck movements and applying force/moment on the head. Through optimization, validation, and human testing, the authors showcased its potential for rehabilitation and beyond.
The device exhibited commendable performance in measuring and controlling head-neck movements and regulating neck muscle activation. Its adaptability showed its ability to implement various control modes and adjust parameters according to user preference and capability.
Moving forward, the researchers acknowledged areas for improvement, including enhancing twist axis performance, reducing device size and weight, and exploring new design and control approaches for diverse applications.
Journal Reference
Bales, I., Zhang, H. A six degrees-of-freedom cable-driven robotic platform for head–neck movement. Sci Rep 14, 8750 (2024). https://doi.org/10.1038/s41598-024-59349-0, https://www.nature.com/articles/s41598-024-59349-0.
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