Sensor development

Stiffness sensor

In our lab, we have created a novel optical-based soft-tipped force sensor capable of adjusting its range and sensitivity through pneumatic modulation. Results indicate that by increasing the pressure in the sensor, the sensing range can be increased and the sensitivity decreased. The dynamically adjustable range allows the sensor to preform well in operations where the load ranges may vary within or between tasks. Additionally, the ability of the sensor to measure angles allows it to be used in applications with diverse angles of contact and where knowing the angle of contact is beneficial, such as in palpation and object manipulation in grippers.

Stiffness sensor

We have made new findings concerning a novel hand-held stiffness probe for the medical diagnosis of abnormalities during the palpation of soft-tissue. Soft-tissue palpation is recognized by the medical community as an essential and low-cost method to detect and diagnose disease in soft-tissue. Providing clinicians with tools to more easily identify and classify tissue health and to obtain objective measurments is an area largely neglected. Variation of stiffness across the surface of tissue is central to obtaining a good understanding of the tissue characteristics, with tumorous tissue areas often having a higher stiffness than the the healthy ones. However, differences are often subtle and clinicians need to train for many years before they can conduct a realiable diagnosis.

The probe in the video fills this gap providing a means to easily obtain stiffness values of soft tissue during a palpation procedure. The probe incoporates a set of multiple spring-loaded sliding cylindrical indenters that are brought into contact with the surface of tissue to be examined and move depending on the spring constant and the stiffness of the tissue. A miniature camera integrated with the probe observes and logs the movements of the spring-loaded indenters. Employing springs with different spring constants, we can relate the movement of the indenters to tissue stiffness through image processing and mathematical modelling.

Tactile sensors

We have created tactile sensors taking inspiration from cucumber tendrils that have shown to be ideal tactile sensors for the plant that they are associated with providing useful environmental information during the plant’s growth.

Incorporating the sensing principles of cucumber tendrils, I have created miniature sensing elements that can be distributed across the surface of soft manipulators to form a sensor network capable of acquire tactile information. Each sensing element is a retractable hemispherical tactile measuring applied pressure. The actual sensing principle chosen for each tactile makes use of optic fibres that transfer light signals modulated by the applied pressure from the sensing element to the proximal end of the robot arm. Due to the simple structure of the proposed tactile sensor element, it is miniaturisable and suitable for MIS.

An important contribution of this work is that the developed sensor system can be ”loosely” integrated with a soft arm effectively operating independently of the arm and without affecting the arm’s motion during bending or elongation.

Force/torque sensors

Within STIFF-FLOP, I have looked into integrating a 3 DoF force/torque sensor into the STIFF-FLOP manipulator.

The video below shows the use of this sensor for reflex control.