Tactile sensors are essential for robotic systems to safely and effectively interact with the environment and humans. In particular, tri-axis tactile sensors are crucial for dexterous robotic manipulations by providing shear force, slip or contact angle information. The Soft Inductive Tactile Sensor (SITS) is a new type of tactile sensor that measures inductance variations caused by eddy-current effect. In this paper, we present a soft tri-axis tactile sensor using the configuration of four planar coils and a single conductive film with hyperelastic material in between them. The working principle is explained and design methods are outlined. A 3D finite element model was developed to characterize the tri-axis SITS and to optimize the target design through parameter study. Prototypes were fabricated, characterized and calibrated, and a force measurement resolution of 0.3 mN is achieved in each axis. Demonstrations show that the sensor can clearly measure light touch (a few mN normal force) and shear force pulses (10 to 30 mN) produced by a serrated leaf when it is moved across the sensor surface. The presented sensor is low cost, high performance, robust, durable, and easily customizable for a variety of robotic and healthcare applications.

Objective: This work aims to develop an integrated in-shoe measurement system to fully record plantar loading, including both pressure and shear stresses, across the full contact surface. These data are vital to help understand and prevent the development of complex conditions such as Diabetic Foot Ulcers (DFUs), a worldwide healthcare challenge. Currently no systems exist to reliably record these data. Methods: In this paper we report development of the SLIPS (‘Shear Load Inductive Plantar Sensing’) system which integrates 64 tri-axial force sensors into a flexible insole to measure plantar loading. SLIPS translates our multi-axis inductive load sensing technology into a full sensory array embedded within an insole and complete with communication and power bus. A pilot study evaluates the system in three healthy participants during walking. Results: Testing shows that the SLIPS system is well tolerated by participants and can operate under dynamic gait loading regimes. The pilot study reveals the complex nature of plantar loading. Regions of peak pressure loading align with anatomical landmarks and shear loading forms a significant component of the overall load. Notably, regions of peak shear and pressure are not necessarily collocated or present in unison. Conclusion: This work highlights the need for in-shoe plantar measurement systems like SLIPS capable of mapping both pressure and shear load, and their use to improve understanding of how these factors relate to clinical conditions like DFU. Significance: SLIPS represents the first in-shoe measurement system capable of measuring both pressure and shear across the whole plantar surface in unison.

Diabetic foot ulcers (DFUs) are a severe global public health issue. Plantar normal and shear load are believed to play an important role in the development of foot ulcers and could be a valuable indicator to improve assessment of DFUs. However, despite their promise, plantar load measurements currently have limited clinical application, primarily due to the lack of reliable measurement techniques particularly for shear load measurements. In this paper we report on the design and evaluation of a novel tri-axis force sensor to measure both normal and shear load on the foot’s plantar surface simultaneously. The sensor consists of a group of inductive sensing coils above which a conductive target is placed on a hyperelastic elastomer. Movement of the target under load affects the coil inductances which are measured and digitized by an embedded system. Using a computational finite element model, we investigated the influence of sensing coil form and configuration on sensor performance. A sensor configured with four-square coils and maximal turns provided the best performance for plantar load measurements. A prototype was fabricated and calibrated using a neural network to map the non-linear relationship between the sensor output and the applied tri-axis load. Experimental evaluation indicates that the tri-axis sensor can effectively detect shear load of ±16 N and normal load up to 105 N (RMS errors: 1.05 N and 1.73 N respectively) with a high performance. Overall, this sensor provides a promising basis for plantar normal and shear load measurement which are crucial for improved assessment of DFU.

Splinting techniques are widely used in medicine to inhibit the movement of arthritic joints. Studies into the effectiveness of splinting as a method of pain reduction have generally yielded positive results, however, no significant difference has been found in clinical outcomes between splinting types. Tactile sensing has shown great promise for the integration into splinting devices and may offer further information into applied forces to find the most effective methods of splinting. Hall effect-based tactile sensors are of particular interest in this application owing to their low-cost, small size, and high robustness. One complexity of the sensors is the relationship between the elastomer geometry and the measurement range. This paper investigates the design parameters of Hall effect tactile sensors for use in hand splinting. Finite element simulations are used to locate the areas in which sensitivity is high in order to optimise the deflection range of the sensor. Further simulations then investigate the mechanical response and force ranges of the elastomer layer under loading which are validated with experimental data. A 4 mm radius, 3 mm-thick sensor is identified as meeting defined sensing requirements for range and sensitivity. A prototype sensor is produced which exhibits a pressure range of 45 kPa normal and 6 kPa shear. A proof of principle prototype demonstrates how this can be integrated to form an instrumented splint with multi-axis sensing capability and has the potential to inform clinical practice for improved splinting.

Tactile sensors are essential for robotic systems to interact safely and effectively with the external world. In particular, tri-axis tactile sensors are crucial for dexterous robotic manipulations by providing shear force for slip and contact angle detection. In this paper, we present a soft tri-axis tactile sensors using flexible coils and conductive films based on eddy-current effect. Prototypes were developed, calibrated and evaluated, which achieved a force measurement resolution of 0.3 mN in each axis, with a bandwidth up to 1 kHz. The presented sensor is low-cost, robust, durable, and easily customizable for a variety of robotic and healthcare applications.

Soft sensors are essential for robotic systems to safely interact with humans and the environment. Although significant research has been carried out in the field of soft tactile sensing, most of these sensors are restricted to a predefined geometry and a fixed measurement range, hence limiting their application. This paper introduces a novel approach to soft sensing by proposing a soft load-sensing unit with an adjustable mechanical compliance achieved using an elastically inflatable fluidic dome. The sensor consists of a three-dimensional Hall-effect sensor, above which is a magnet whose movement is modulated by an intermediate elastomeric dome structure. Sensor configurations were designed and fabricated using three different silicone rubbers to cover ‘00–10’ and ‘20A’ durometer shore hardness scales. We demonstrated that the compliance of the sensor could be dynamically tuned by changing the internal pressure of the inflatable fluidic dome in all configurations. We performed finite element simulations to determine the reaction force of the sensor under load as well as the stresses within the internal structural behavior, which are not possible to capture experimentally. The proposed soft sensor has the potential to be readily adapted for use in various soft robotic applications of differing size, compliance range, and safety requirements.