AI News, Six-legged robots get closer to nature
- On Sunday, June 3, 2018
- By Read More
Six-legged robots get closer to nature
In the natural world, many species can walk over slopes and irregular surfaces, reaching places inaccessible even to the most advanced rover robots.
Now, researchers in Japan and Italy propose a new approach to walking pattern generation, based on a hierarchical network of electronic oscillators arranged over two levels, which they have demonstrated using an ant-like hexapod robot.
The lead author of the study, Ludovico Minati, who is also affiliated to the Polish Academy of Sciences in Krakow, Poland and invited to Tokyo Tech's Institute of Innovative Research (IIR) through the World Research Hub Initiative explains that insects can rapidly adapt their gait depending on a wide range of factors, but particularly their walking speed.
The proposed controller shows an extremely high level of versatility thanks to implementation based on field-programmable analog arrays (FPAAs), which allow on-the-fly reconfiguration and tuning of all circuit parameters.
Such emergent phenomena arise particularly as the network is realized with analog components and allows a certain degree of self-organization, representing an approach that vastly differs to conventional engineering, where everything is designed a-priori and fixed.
Because they can be changed dynamically, in the future it should be easy to vary them in real-time using a brain-computer interface, allowing the control of complex kinematics otherwise impossible to dominate with current approaches.'
And Natsue Yoshimura, also based at the IIR, says: 'As the controller responds gradually and embodies a biologically plausible approach to pattern generation, we think that it may be more seamless to drive compared to systems which decode discrete commands.
Closed-loop control of trunk posture improves locomotion through the regulation of leg proprioceptive feedback after spinal cord injury
We established a closed-loop robotic platform to enable precise, transparent actuation of trunk rotations in the mediolateral plane in rats with spinal cord injury (Fig.1).
We restricted the actuated rotations to those in the mediolateral plane in order to focus on the impact on lateral stability and sway, and we carefully chose miniaturized components to adjust the torque and precision to the specificities of experiments in rodents (~250–300 g).
To measure the absolute position of the motor, we employed a magnetic encoder (Faulhaber AESM-4096) combined with an elastic coupling to avoid any damage to the gearhead due to torsion, bending or impacts on the rotation axis.
To enable real-time control of posture based on the animal locomotor performance, we interfaced this application with a high-speed motion capture system (Vicon, Oxford, UK) that monitored leg movement in real-time (Fig.1b).
iliac crest, greater trochanter (hip joint), lateral condyle (knee joint), lateral malleolus (ankle) and distal end of the fifth metatarsophalangeal (MTP) joint.
Raw signals were filtered using adaptive filters (least mean squares), and processed online to account for missing data resulting from occlusions (interpolation from neighboring markers).
To align postural changes to the stepping rhythm of each animal, the real-time system continuously monitored bilateral hindlimb kinematics and extracted key gait events (foot-strikes and foot-off events) (Fig.5a and Fig.6a).
Foot-strikes were determined for each limb after the vertical displacement of the MTP marker crossed a predefined threshold (15 mm) and the limb length reached a maximum value (corresponding to the beginning of the loading phase).
At every foot-strike, the monitoring system extracted the mediolateral limb abduction angle for each limb and fed it to the controller, which computed the appropriate corrections based on the average of consecutive right and left angles.
At pre-defined events throughout the gait-cycle, the real-time system provided controlled rotations at constant speed of +/−5 degrees around the optimal trunk posture for each animal.
We fed the computer model with crest, hip, knee, ankle, and metatarsophalangeal joint angle traces recorded experimentally in rats under different postural conditions (n > 10 steps) and we calculated the corresponding muscle stretch and stretch velocity profiles through inverse kinematics for 3 pairs of antagonist muscles, i.e., Tibialis Anterior (TA) and Medial Gastrocnemius (GM) for the ankle joint, Vastus Lateralis (VL) and Semi Tendinosus (ST) for the knee joint, and Gluteus Medius (GMed) and Ilipsoas (IL) for the Hip joint (Fig.4a).
Although this model was originally established from cat electrophysiological recordings, dynamical relationships between muscle stretch and firing rate modulations are expected to be well preserved across mammals.
To derive the cumulative flexor- and extensor-related afferent input at footstrike for each postural condition (Fig.4c), we defined a window (10 ms) around each footstrike and calculated the mean firing rate (>10 gait cycles in each case) for each individual muscle.
Three animals received an incomplete lesion (lateral contusion at a mid-thoracic level, ~T8) and three additional animals received a complete spinal cord transection at the same level.
Hindlimb locomotion was enabled by epidural electrical stimulation applied at S1 and L2 spinal segments (Parameters: 0.2 ms, 40 Hz, 150–300 uA) and systemic administration of pharmacological neuromodulators (Quipazine, 0.2–0.3 mg per kg intra-peritoneal, and 8-OHDPAT 0.05–0.3 mg per kg subcutaneous)7.
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For example, the hexapod bot can walk with three legs straight out from its sides, like an ant, or with the legs spread more evenly around the body, like a cockroach.
The researchers developed a new biologically-inspired controller that uses a network of non-linear oscillators which enables a diverse number of postures and gaits using only a few high-level variables.
The controller has two levels, a pattern-generator circuit that controls the gait, and six local pattern generators that control the trajectories of the individual legs — each performs tasks based off of years of previous research.
According to the researchers, they have yet to crack how these complex movements are performed by such simple living creatures, but the study could eventually lead to new ways to control multi-legged robots and even a future that uses brain-computer interfaces.
While you won't find it in your local store's anytime soon, we must consider if/when restaurants will add meal-worm burgers and micro-algae buns to the menu.
Among the new grub is the Dogless Hotdog, which consists of dried and glazed carrots, beet and berry ketchup, mustard and turmeric cream, roasted onions, cucumber salad and an herb salad mix.
The non-profit is looking for $600k by April 13th to fund the next phase of R&D, and another $400k for the first community of 100 printed homes — that's 100 homes for what some people spend on a single house.
The children's book looks to inspire the next generation of tinkerers and big thinkers, and it just so happens to center around the tech industry's biggest draw.
Central Pattern Generator for Locomotion: Anatomical, Physiological, and Pathophysiological Considerations
Considering all the different CPGs located throughout the CNS that are involved in mediating various biological rhythms (e.g., sleep, mastication, ocular movement, breathing, deglutition, etc.), several signs, or pathological complications associated with rhythm-generator problems have been reported over the years.
For instance, nystagmus or involuntary rhythmic eye movement is an ocular problem that is associated with heredity problems, poor vision, cortical blindness, intracranial neoplasms, or cerebellar ataxia.
The latter, normally controlled by the swallowing CPG located in the bulbar area of the brain, has been shown to undergo dysfunctional activity when corticobulbar control becomes progressively impaired in ALS patients (Aydogdu et al., 2011).
Although no drug treatment exists for such swallowing rhythmic problems, NE reuptake inhibitors (e.g., desipramine) have been shown to reduce respiratory rhythmic problems in animal models of Rett Syndrome (Roux et al., 2007).
e.g., a patient suffering of a hemorrhagic lesion in that area was reported to display synchronous rather than rhythmic motor activities of the eye, tongue, mandible, pharynx, diaphragms, and other muscles in which myoclonus.
In contrast with most of these neurological problems where spontaneous and abnormal CPG activity have been proposed as one of the underlying mechanisms, a recently identified, rare and fascinating neurological condition described by Dr. Uner Tan has been instead associated with a entirely different and unique aspect of CPG malfunction.
In all cases, those individuals walk on their wrists and feet with straight legs and arms (Tan, 2006b) and display ataxia and cerebellar atrophy (e.g., vermial hypoplasia as shown by MRI and PET scans, Tan, 2008;
However, as interesting has it may sound, it is rather speculative and detailed mechanisms presumably underlying such abnormal (or primitive) CPG activities remain unclear and based largely upon behavioral observations and indirect associations with locomotion features in other species.
The locomotor network in lower vertebrates consists indeed of multiple spinal CPGs, with descending pathways activating individual CPGs for selective control of various segments in lampreys or joints and muscle groups in the case of terrestrial species.
During progression on a split-belt treadmill (velocity 3.5 km/h), short accelerations or decelerations were randomly applied to the right belt during the mid or end stance phase whereas trains of electrical stimuli were delivered to the right distal tibial nerve.
The results showed task-dependent and flexible neuronal coupling activities between lower and upper limb muscles in humans suggesting that several CPGs (e.g., for arms vs for leg rhythmic movements) for walking are still functional in the human lumbar and cervical spinal cord areas.
All in all, given these evidence and findings, it is not unreasonable to postulate that impaired equilibrium that may be directly attributed to cerebellar atrophy and deficits in UTS patients could have enabled the expression of more tightly coupled activities between the upper and lower CPGs for the development of quadrupedal walking instead of bipedal locomotion.
Therefore, in absence of sufficient drive to extensor muscles of the legs (prerequisite to weight-bearing stepping), corresponding sublesional plasticity changes may have occurred as a compensatory mechanism for preserving, at least, the expression of some form of CPG activation and walking capabilities.
Ancestral upper CPG activity, enabled or uncovered by this pathological condition, would not restore equilibrium but at least some descending drive (propriospinal instead of supraspinal) capable to support some leg movements during progression with all four extremities.
Another avenue to increase lower CPG drive and extensor activity may be based on electrical stimulation of ventrolateral tracts near thoracic segmental areas already known for reactivating the lumbar CPG in animal models (Cheng and Magnuson, 2011).
This will perhaps require additional adjustments and specific pharmacological aids to separately control spasticity and other peripheral input problems that can impair normal bipedal ambulation in some pathological conditions (Fung et al., 1990).
- On Saturday, March 23, 2019
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