The Effect of Whole Body Horizontal Vibration in Position Sense and Dynamic Stability of the Spine

In many workplaces, workers are exposed to whole body vibration which involves multi-axis motion in fore-aft (x axis), lateral (y axis) and vertical (z axis) directions. In previous studies, our laboratory has found changes in biomechanical responses such as response time and position sense with exposure to vibration in single vertical direction. The objective of the current study was to investigate the effect of whole body, horizontal vibration on proprioception and sudden loading dynamics and to compare these results with the previously studied whole body vertical vibration experiment. Both position sense test and sudden loading test were performed in three conditions: a pre-exposure condition (pre), a post-washout condition (postw) and a post-vibration condition (postv). Subjects were exposed to the whole body horizontal vibration frequency of 5 Hz and constant acceleration of 0.284 RMS (m/s-2) for 30 minutes. Absolute reposition sense error increased slightly after vibration exposure (relative to after quiet sitting (postw)), although the results were not significant. Times to peak muscle response and flexion magnitude were also increased after horizontal vibration exposure, suggesting a decreased stability of the spine, but again these results were not significant. Compared to the previous study of vertical whole body vibration, the effects of horizontal vibration in this study were small and not significant. This may be due to differences in the transmissibility of vertical and horizontal vibrations at the 5 Hz frequency. These results would suggest that horizontal vibration may be less of a factor in whole-body vibration induced injuries. This work was supported by University of Kansas Transportation Research Institute Grant Program

Lumbar Position Sense with Extreme Lumbar Angle

Tasks involving flexed torso postures have a high incidence of low back injuries. Changes in the ability to sense and adequately control low back motion may play a role in these injuries. Previous studies examining position sense errors of the lumbar spine with torso flexion found significant increases in error with flexion. However, there has been little research on the effect of lumbar angle. In this study, the aim of the study was to examine how position sense errors would change with torso flexion as a function of the target lumbar angle. Fifteen healthy volunteers were asked to assume three different lumbar angles (maximum, minimum and mid-range) at three different torso flexion angles. A reposition sense protocol was used to determine a subject's ability to reproduce the target lumbar angles. Reposition sense error was found to increase 69% with increased torso flexion for mid-range target curvatures. With increasing torso flexion, the increase in reposition sense errors suggests a reduction in sensation and control in the lumbar spine that may increase risk of injury. However, the reposition error was smaller at high torso flexion angles in the extreme target curvatures. Higher sensory feedback at extreme lumbar angles would be important in preventing over-extension or over-flexion. These results suggest that proprioceptive elements in structures engaged at limits (such as the ligaments and facet joints), may provide a role in sensing position at extreme lumbar angles. Sensory elements in the muscles crossing the joint may also provide increased feedback at the edges of the range of motion

Whole body vibration alters proprioception in the trunk

Occupational whole body vibration has long been associated with low back injuries. However, the mechanism of these injuries is not well understood. In this paper, the effect of whole body vibration on proprioception and dynamic stability was examined. Subjects exposed to 20 minutes of vertical, seated, whole body vibration were found to have a 1.58 fold increase in position sense errors after vibration relative to controls exposed to 20 minutes of the same seated posture without vibration exposure. To understand the potential effect of a sensory loss on dynamic low back stability a lumped parameter model of the trunk and neuromotor response was created. Using this model, an increase in the threshold of the sensory system was predicted to increase trunk flexion and delay neuromotor response with a sudden, unexpected perturbation. These predictions were demonstrated in a second experiment where subjects exhibited both an 11.9% increase in trunk flexion and an 11.2% increase in time to peak paraspinal muscle response (measured using integrated electromyographic activity) after exposure to 20 minutes of vertical, seated, whole body vibration.This work was supported by a Whitaker Foundation Biomedical Engineering Research Grant (RG-03-0043)

Underactuated Robotic Fish Control: Maneuverability and Adaptability Through Proprioceptive Feedback

Bioinspired robotics is a promising technology for minimizing environmental disruption during underwater inspection, exploration, and monitoring. In this research, we propose a control strategy for an underactuated robotic fish that mimics the oscillatory movement of a real fish’s tail using only one DC motor. Our control strategy is bioinspired to Central Pattern Generators (CPGs) and integrates proprioceptive sensory feedback. Specifically, we introduced the angular position of the tail as an input control variable to integrate a feedback into CPG circuits. This makes the controller adaptive to changes in the tail structure, weight, or the environment in which the robotic fish swims, allowing it to change its swimming speed and steering performance. Our robotic fish can swim at a speed between 0.18 and 0.26 body lengths per second (BL/s), with a tail beating frequency between 1.7 and 2.3 Hz. It can also vary its steering angular speed in the range of 0.08 rad/s, with a relative change in the curvature radius of 0.25 m. With modifications to the modular design, we can further improve the speed and steering performance while maintaining the developed control strategy. This research highlights the potential of bioinspired robotics to address pressing environmental challenges while improving solutions efficiency, reliability and reducing development costs

Bio-inspired soft robotic systems: Exploiting environmental interactions using embodied mechanics and sensory coordination

Despite the widespread development of highly intelligent robotic systems exhibiting great precision, reliability, and dexterity, robots remain incapable of performing basic manipulation tasks that humans take for granted. Manipulation in unstructured environments continues to be acknowledged as a significant challenge. Soft robotics, the use of less rigid materials in robots, has been proposed as one means of addressing these limitations. The technique enables more compliant interactions with the environment, allowing for increasingly adaptive behaviours better suited to more human-centric applications. Embodied intelligence is a biologically inspired concept in which intelligence is a function of the entire system, not only the controller or `brain'. This thesis focuses on the use of embodied intelligence for the development of soft robots, with a particular focus on how it can aid both perception and adaptability. Two main hypotheses are raised: first, that the mechanical design and fabrication of soft-rigid hybrid robots can enable increasingly environmentally adaptive behaviours, and second, that sensing materials and morphology can provide intelligence that assists perception through embodiment. A number of approaches and frameworks for the design and development of embodied systems are presented that address these hypotheses. It is shown how embodiment in soft sensor morphology can be used to perform localised processing and thereby distribute the intelligence over the body of a system. Specifically in soft robots, sensor morphology utilises the directional deformations created by interactions with the environment to aid in perception. Building on and formalising these ideas, a number of morphology-based frameworks are proposed for detecting different stimuli. The multifaceted role of materials in soft robots is demonstrated through the development of materials capable of both sensing and changes in material property. Such materials provide additional functionality beyond their integral scaffolding and static mechanical characteristics. In particular, an integrated material has been created exhibiting both sensing capabilities and also variable stiffness and `tack’ force, thereby enabling complex single-point grasping. To maximise the intelligence that can be gained through embodiment, a design approach to soft robots, `soft-rigid hybrid' design is introduced. This approach exploits passive behaviours and body dynamics to provide environmentally adaptive behaviours and sensing. It is leveraged by multi-material 3D printing techniques and novel approaches and frameworks for designing mechanical structures. The findings in this thesis demonstrate that an embodied approach to soft robotics provides capabilities and behaviours that are not currently otherwise achievable. Utilising the concept of `embodiment' results in softer robots with an embodied intelligence that aids perception and adaptive behaviours, and has the potential to bring the physical abilities of robots one step closer to those of animals and humans.EPSR