Adaptive load feedback robustly signals force dynamics in robotic model of Carausius morosus stepping

Abstract

Animals utilize a number of neuronal systems to produce locomotion. One type of sensory organ that contributes in insects is the campaniform sensillum (CS) that measures the load on their legs. Groups of the receptors are found on high stress regions of the leg exoskeleton and they have significant effects in adapting walking behavior. Recording from these sensors in freely moving animals is limited by technical constraints. To better understand the load feedback signaled by CS to the nervous system, we have constructed a dynamically scaled robotic model of the Carausius morosus stick insect middle leg. The leg steps on a treadmill and supports weight during stance to simulate body weight. Strain gauges were mounted in the same positions and orientations as four key CS groups (Groups 3, 4, 6B, and 6A). Continuous data from the strain gauges were processed through a previously published dynamic computational model of CS discharge. Our experiments suggest that under different stepping conditions (e.g., changing “body” weight, phasic load stimuli, slipping foot), the CS sensory discharge robustly signals increases in force, such as at the beginning of stance, and decreases in force, such as at the end of stance or when the foot slips. Such signals would be crucial for an insect or robot to maintain intra- and inter-leg coordination while walking over extreme terrain.

Mechanosensory encoding of forces in walking uphill and downhill: force feedback can stabilize leg movements in stick insects

“…10 A ) or discharges ceased entirely. These findings reflect the finding that the joint torques occurring at the femoro-tibial joint in walking are largely dynamic in walking of freely moving animals: there is no prolonged hold phase ( 30 , 42 ). Many torque measurements in walking of vertebrates also never attain a constant level at distal leg joints ( 2 , 43 , 44 ).…”

A biomimetic fruit fly robot for studying the neuromechanics of legged locomotion

“…The robot can also serve as a data-collection platform for biomimetic sensory feedback. Several studies have previously used biologically-inspired robots to investigate sensory discharge from campaniform sensilla (CS), mechanoreceptors on the insect exoskeleton that encode strain [24], [76], [77], [78]. These studies primarily focus on single-leg stepping.…”

Mechanical modeling of mechanosensitive insect strain sensors as a tool to investigate exoskeletal interfaces

“…Each strain gauge was amplified using a Wheatstone bridge in the quarter-bridge configuration, whose output was amplified by an inverted operational amplifier circuit. During displacement, the strain gauges underwent a change in resistance, producing an analog voltage signal at the amplifier output that was proportional to the sensor strain [22]. In parallel, we used a manual hand wheeloperated test stand (FGS-250 W; Nidec-Shimpo Corp., Kyoto, Japan) equipped with a digital force gauge (1000 N ± 0.3% full scale accuracy; FG-3009; Nidec-Shimpo Corp.).…”

“…Due to the interplay of dynamic stresses and strains and the corresponding adaptive neuronal activity, CS mechanics and responses are highly complex, requiring interdisciplinary approaches to understand the mechanisms underlying their function (figure 1). Recent work integrating CS-like strain sensors in robotic legs modeled off of stick insect legs [22,23] demonstrated how the application of appropriate forces could evoke strain patterns similar to those measured in the insect leg itself [24]. Further work [23] showed how these artificial limbs could be used to answer questions that, to date, could not be answered using real animals, such as how speciesspecific CS locations determine the components of leg strain they can detect.…”

“…Many robots and robotic limbs use incorporated strain gauges for strain sensing, often mimicking leg CS or insect sensing [22,23,[62][63][64][65][66], together with models of sensory neuron firing [19]. These systems are capable of predicting cellular activity by processing changes in resistance caused by strain in a fashion similar to animal experiments.…”