What Is a Tactile Sensor?
A tactile sensor is a sensor that mimics the human sense of touch.
The sensing device used is a sensor that converts the pressure and vibration of a contact surface into an electrical signal, and various technological efforts, including those around sensor technology, are underway to mimic the function of this sensor to the human sense of touch. In addition, tactile sensors are integrated with multiple pieces of information, such as temperature sensitivity, to estimate the texture of sensitive objects.
The sense of touch is essential for the development of robotics technology because it plays an important role not only in evaluating the properties and texture of objects but also in basic human movements, such as grasping objects with appropriate force and writing with a pen in one’s hand.
Uses of Applications of Tactile Sensors
Tactile sensors are used in medical diagnostics, robotics, and industrial applications.
Recently, however, the application to the game space represented by VR (virtual reality) and the metaverse field is also highly expected under the generic name of haptics, a tactile technology.
1. Medical Applications of Tactile Sensors
The ability to evaluate the hardness of an object makes it possible to detect the presence of “lumps” originating from breast or prostate cancer with high sensitivity, contributing to the early detection of cancer. In addition, by evaluating roughness caused by surface roughness, it can be used for quantitative evaluation of dermatitis and xerosis.
2. Application of Tactile Sensors in Robotics
In robotics, the development of finger-mimicking sensors provides information for adjusting grip strength as sensors for robotic hands.
3. Industrial Application of Tactile Sensors
In industry, monitoring the texture of products can be useful for quality control.
4. Haptics for VR
In the world of VR (virtual reality), goggles for 3D have already been commercialized, and applications to reproduce a more realistic world in VR by attaching a suit or gloves to the VR and installing tactile sensors are being worked on.
Principle of Tactile Sensors
Tactile sensors use various physical phenomena to convert the force of contact with an object into an electrical quantity, and are composed mainly of conversion devices (sensors: elements). These electrical signals are analyzed via signal and information processing circuits. In principle, the sensor can employ a variety of detection modalities.
For example, one method is to detect the electrostatic capacitance resulting from changes caused by the application of pressure in a space sandwiched by conductive Depending on the application, piezoelectric ceramic elements (PZT: lead zirconate titanate) are generally used as the sensor element in many cases. Piezoelectric ceramic elements, also called piezoelectric elements, produce voltage changes when pressure is applied. This is called the piezoelectric effect.
The arrangement of ions in the solid crystal of a piezoelectric element changes when pressure is applied, causing a phenomenon called electric polarization, in which one end of the crystal is charged with positive electricity and the other with negative electricity. The pressure information and vibration frequency information are converted into electrical signals by the piezoelectric element, which can then be converted into tactile information through analog and digital processing circuits composed of ASICs and other devices.
In addition, as an optical principle, the contact position of an object on the sensor surface can be captured by detecting changes in the scattered light in the optical waveguide inside the sensor.
Other Information on Tactile Sensors
1. Tactile Sensor Market
The market size of tactile sensors is projected to reach $16,083.8 million by 2025 from $8,204.9 million in 2019.
Tactile sensors are one of the key elements supporting the development of robots that can work with humans. For example, a robot called RoCycle, which is being developed at MIT in the US, has a Tactile Sensor built into its hand that identifies materials so that it can recognize and sort paper, plastic, and metal.
At the Pohang University of Technology in Korea, a human fingerprint sensor is being developed using nano springs that can sense minute pressure and vibration. The results of the development include a machine learning analysis of the information obtained from the tactile sensor and the successful differentiation of eight types of fibers with an accuracy of 99.8%. As the accuracy of tactile sensors improves, demand for these sensors is expected to increase, especially in the robotics industry.
2. MEMS Tactile Sensor
MEMS (micro electromechanical systems) is a device in which sensors, electronic circuits, etc. are integrated on a substrate using micro-fabrication technology.
In recent years, ultra-sensitive tactile sensors using MEMS technology have been attracting attention.
3. Expansion Into the Field of Haptics
In addition to the world of VR, haptics is expanding its application to various familiar fields. Examples include home buttons on smartphone screens, navigation systems on the instrument panels of electric vehicles, styluses for electronic authentication, and PC keyboards.
In these fields, how small, lightweight, thin, and realistic tactile sensors can be realized is critical in terms of tactile technology. Therefore, manufacturers are working hard to develop cutting-edge MEMS technology, piezoelectric device technology, and application software.