Data-driven Tactile Sensing using Spatially Overlapping Signals

Providing robots with distributed, robust and accurate tactile feedback is a fundamental problem in robotics because of the large number of tasks that require physical interaction with objects. Tactile sensors can provide robots with information about the location of each point of contact with the manipulated object, an estimation of the contact forces applied (normal and shear) and even slip detection. Despite significant advances in touch and force transduction, tactile sensing is still far from ubiquitous in robotic manipulation. Existing methods for building touch sensors have proven difficult to integrate into robot fingers due to multiple challenges, including difficulty in covering multicurved surfaces, high wire count, or packaging constrains preventing their use in dexterous hands. In this dissertation, we focus on the development of soft tactile systems that can be deployed over complex, three-dimensional surfaces with a low wire count and using easily accessible manufacturing methods. To this effect, we present a general methodology called spatially overlapping signals. The key idea behind our method is to embed multiple sensing terminals in a volume of soft material which can be deployed over arbitrary, non-developable surfaces. Unlike a traditional taxel, these sensing terminals are not capable of measuring strain on their own. Instead, we take measurements across pairs of sensing terminals. Applying strain in the receptive field of this terminal pair should measurably affect the signal associated with it. As we embed multiple sensing terminals in this soft material, a significant overlap of these receptive fields occurs across the whole active sensing area, providing us with a very rich dataset characterizing the contact event. The use of an all-pairs approach, where all possible combinations of sensing terminals pairs are used, maximizes the number of signals extracted while reducing the total number of wires for the overall sensor, which in turn facilitates its integration. Building an analytical model for how this rich signal set relates to various contacts events can be very challenging. Further, any such model would depend on knowing the exact locations of the terminals in the sensor, thus requiring very precise manufacturing. Instead, we build forward models of our sensors from data. We collect training data using a dataset of controlled indentations of known characteristics, directly learning the mapping between our signals and the variables characterizing a contact event. This approach allows for accessible, cheap manufacturing while enabling extensive coverage of curved surfaces. The concept of spatially overlapping signals can be realized using various transduction methods; we demonstrate sensors using piezoresistance, pressure transducers and optics. With piezoresistivity we measure resistance values across various electrodes embedded in a carbon nanotubes infused elastomer to determine the location of touch. Using commercially available pressure transducers embedded in various configurations inside a soft volume of rubber, we show its possible to localize contacts across a curved surface. Finally, using optics, we measure light transport between LEDs and photodiodes inside a clear elastomer which makes up our sensor. Our optical sensors are able to detect both the location and depth of an indentation very accurately on both planar and multicurved surfaces. Our Distributed Interleaved Signals for Contact via Optics or D.I.S.C.O Finger is the culmination of this methodology: a fully integrated, sensorized robot finger, with a low wire count and designed for easy integration into dexterous manipulators. Our DISCO Finger can generally determine contact location with sub-millimeter accuracy, and contact force to within 10% (and often with 5%) of the true value without the need for analytical models. While our data-driven method requires training data representative of the final operational conditions that the system will encounter, we show our finger can be robust to novel contact scenarios where the shape of the indenter has not been seen during training. Moreover, the forward model that predicts contact locations and applied normal force can be transfered to new fingers with minimal loss of performance, eliminating the need to collect training data for each individual finger. We believe that rich tactile information, in a highly functional form with limited blind spots and a simple integration path into complete systems, like we demonstrate in this dissertation, will prove to be an important enabler for data-driven complex robotic motor skills, such as dexterous manipulation

Index to NASA Tech Briefs, 1975

This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs

The Histological Structure and Physiological Response of the Sensory Units in the Knee-Joint of the Cat

1. Using a 'single-fibre' technique, afferent discharges from single sensory units in the capsule of the knee-joint of the decerebrate cat have been recorded from the posterior articular nerve to this joint. 2. The responses are of two types - 'rapidly-adapting' and 'slowly-adapting'. 3. The rapidly-adapting responses consist of impulses during movement of the joint but not while the joint is stationary. Such responses were found on only a few occasions and are similar to those from the C organs of Matthews (1933), and also to those attributed by Gray & Matthews (1951) to Pacinian corpuscles. 4. The slowly-adapting responses were more frequently encountered. They are characterized by maintained steady discharges while the joint is stationary, with 'exaggerated' changes in frequency during movement. The degree of exaggeration depends on the rate of movement, and the exaggerated response is followed by adaptation to a new, steady impulse-frequency. 5. The steady, adapted impulse-frequency in any one position is independent of the rate, but not always of the direction, of the movement used to reach that position. If the movement is one which produces a decrease in the frequency of the impulses, the final steady value may he less than that in the same position following a movement in the direction producing an increase in impulse-frequency. The degree of this 'directional' effect varies from unit to unit. 6. The sensory units giving rise to both types of response can he made to discharge by direct pressure on the part of the capsule in which they lie. By locating them in this way, the slowly-adapting units have been found to he most numerous in the centre of the hack of the joint-capsule, whereas the rapidly-adapting units tend to lie towards the sides of the joint. 7. Using the Gairns (1930) gold chloride technique, two types of sensory unit have been demonstrated histologically in the posterior part of the knee-joint capsule, a 'spray' type and a 'lamellated' type. 8. By obtaining a single-fibre discharge from the articular nerve and, while still recording the discharge, excising the particular area of capsule containing the sensory unit responsible for the discharge, it has been possible to correlate the structure of the sensory units with their physiological response. 9. The sensory units of spray type consist of a number of sprays supplied by a single axon, and are situated in the fibrous layer of the joint-capsule; they are undoubtedly the 'typical Ruffini endings' described by Gardner (1944). They are definitely responsible for the slowly-adapting discharges in the posterior articular nerve. It is suggested that these spray sensory units are capable of providing accurate information about the relative position of the bones forming the joint. 10. The lamellated sensory units, which also lie in the fibrous capsule, are much scarcer than the spray type. They consist of several receptors supplied by a single axon. These receptors are double the length of the spray receptors, but are very much smaller, and relatively more elongated, than Pacinian corpuscles. The lamellated type of sensory unit is almost certainly responsible for the rapidly-adapting discharges in the posterior articular nerve. 11. It is doubtful if other types of organised nerve-ending exist in the capsule, but some free nerve-endings are present. On one occasion tendon-organs were found in a cruciate ligament. 12. It is suggested that the larger fibres in the articular nerve innervate tendon-organs in the ligaments of the joint, and that the response of these is similar to the response of the spray sensory units in the capsule. The possibility is discussed that the capsular spray units, the sensory units of spray type (tendon-organs) in ligaments and tendons, and the flower-spray units in muscle-spindles form a series of sensory units, graded in size, which are all basically similar in structure and in function

Impact of Homeostasis Disruption on the Structure and Function of Murine Articular Cartilage

Articular cartilage plays a vital role in facilitating pain-free movement and load distribution in synovial joints, such as the knee. Owing to its complex structure-functional requirements and limited regenerative capacity, articular cartilage is particularly vulnerable to deterioration triggered by intrinsic and extrinsic insults. For instance, abnormal loading, trauma and aging can disrupt cellular, anatomical, and functional homeostasis within the knee joint and/or articular cartilage microenvironment, contributing to the pathogenesis of tissue degradation and degenerative joint diseases, particularly osteoarthritis (OA). In this context, it is essential to understand how cartilage and the joint microenvironment respond to differential levels of tissue homeostatic disruption and the resulting implication on remodeling and repair outcomes. In this multifaceted study, I employed several transgenic mouse models in conjunction with histological, imaging, and mechanical testing modalities to deepen our understanding of structural and functional changes associated with degeneration and regeneration of murine articular cartilage

A critical review of the current state of forensic science knowledge and its integration in legal systems

Forensic science has a significant historical and contemporary relationship with the criminal justice system. It is a relationship between two disciplines whose origins stem from different backgrounds. It is trite that effective communication assist in resolving underlying problems in any given context. However, a lack of communication continues to characterise the intersection between law and science. As recently as 2019, a six-part symposium on the use of forensic science in the criminal justice system again posed the question on how the justice system could ensure the reliability of forensic science evidence presented during trials. As the law demands finality, science is always evolving and can never be considered finite or final. Legal systems do not always adapt to the nature of scientific knowledge, and are not willing to abandon finality when that scientific knowledge shifts. Advocacy plays an important role in the promotion of forensic science, particularly advocacy to the broader scientific community for financial support, much needed research and more testing. However, despite its important function, advocacy should not be conflated with science. The foundation of advocacy is a cause; whereas the foundation of science is fact. The objective of this research was to conduct a qualitative literature review of the field of forensic science; to identify gaps in the knowledge of forensic science and its integration in the criminal justice system. The literature review will provide researchers within the field of forensic science with suggested research topics requiring further examination and research. To achieve its objective, the study critically analysed the historical development of, and evaluated the use of forensic science evidence in legal systems generally, including its role regarding the admissibility or inadmissibility of the evidence in the courtroom. In conclusion, it was determined that the breadth of forensic scientific knowledge is comprehensive but scattered. The foundational underpinning of the four disciplines, discussed in this dissertation, has been put to the legal test on countless occasions. Some gaps still remain that require further research in order to strengthen the foundation of the disciplines. Human influence will always be present in examinations and interpretations and will lean towards subjective decision making.JurisprudenceD. Phil

Psr1p interacts with SUN/sad1p and EB1/mal3p to establish the bipolar spindle

Regular Abstracts - Sunday Poster Presentations: no. 382During mitosis, interpolar microtubules from two spindle pole bodies (SPBs) interdigitate to create an antiparallel microtubule array for accommodating numerous regulatory proteins. Among these proteins, the kinesin-5 cut7p/Eg5 is the key player responsible for sliding apart antiparallel microtubules and thus helps in establishing the bipolar spindle. At the onset of mitosis, two SPBs are adjacent to one another with most microtubules running nearly parallel toward the nuclear envelope, creating an unfavorable microtubule configuration for the kinesin-5 kinesins. Therefore, how the cell organizes the antiparallel microtubule array in the first place at mitotic onset remains enigmatic. Here, we show that a novel protein psrp1p localizes to the SPB and plays a key role in organizing the antiparallel microtubule array. The absence of psr1+ leads to a transient monopolar spindle and massive chromosome loss. Further functional characterization demonstrates that psr1p is recruited to the SPB through interaction with the conserved SUN protein sad1p and that psr1p physically interacts with the conserved microtubule plus tip protein mal3p/EB1. These results suggest a model that psr1p serves as a linking protein between sad1p/SUN and mal3p/EB1 to allow microtubule plus ends to be coupled to the SPBs for organization of an antiparallel microtubule array. Thus, we conclude that psr1p is involved in organizing the antiparallel microtubule array in the first place at mitosis onset by interaction with SUN/sad1p and EB1/mal3p, thereby establishing the bipolar spindle.postprin