Tactile sensing or touch sensing is one of the primary challenges in robot building and manipulation. The agile environment in which a robot works also requires pressure sensors to determine the careful operation of an object.

A robot skin is developed to mimic the touch senses perceived by human skin, integrating different types of tactile sensors. By doing so, a robot ‘feels’ many classes of objects – flexible, rigid, hard, soft, fragile, etc. This allows the robots to work in close proximity to humans while performing tasks of higher risk factors.

Building robots using tactile sensors

Cobots are robots that work hand-in-hand with humans in high-risk environments. The first cobot was built in 1996 for pick and place applications, which were communicated using motion resistance technology through computerized programs. Since then, cobots have come a long way in working with humans and detecting the environment around them with the help of vision and other types of sensors.

Modern cobots can take corrective actions with slight decision-making skills and sophisticated software. In addition, tactile sensors are now used to increase these cobots’ applicability and safety, especially in environments requiring delicate handling of objects, such as healthcare.

The use of tactile sensors

Piezoelectric, Pierzoresistive, capacitive, and electroresistive are the four types of tactile sensors in use today. A combination of all these types is used in building robots and cobots by transmitting their actions to a controller, thereby managing their sensitivity towards an object and their motion in different directions.

For some applications, detection sensors are placed outside the body of a collaborative robot which helps recognize human workers when they work closely. These sensors signal the robots to slow down or stop when an object is near.

Although collisions can take place to a certain extent, the impact of the collision can be minimized. However, tactile sensors are empowered with intelligent software technologies to improve the readability of these collaborative robots.

Precise object handling

Tactile or touch sensors are used in applications requiring precise object placements, like loading parts into a machine. The sensitive sensing technology provided by tactile sensors embedded in a robot’s body will help determine the exact location and the correct position to place the stock material with the help of insertion force.

Modern-day touch sensing technologies use tactile sensors to study the real-time parameters of an object like the shape, texture, size, etc. and determine highly accurate data of the object, which can also help determine defects and damages in an object. For example, cobots powered by tactile sensors can be used in surgery to interact with more fragile and deformable objects. However, multiple tactile sensors should be used to build empathetic robots, integrating them with AI and machine learning technologies.

The world of robotics is increasing by the second, and its applications have directly impacted the human world and how we process data. It is a no-brainer that robots use sensors to help them mimic human movements, to perform specific tasks. Although the integration of vision sensors, motion sensors, and many others had been introduced long back to the robotics world, the idea of touch sensors, also called tactile sensors, was often overlooked.

However, over the years, researchers started understanding the value of the sense of touch in robotic development. Having tactile sensors in robots enables the working of other sensors for power, machine vision, freedom of movement, and many more tasks.

Robotic touch technology and applications

One of the best touch sensor technology used in today’s robotics world is built by force torque sensors and the mechanism of low-resolution pressure sensors in the contact points of grippers. These tiny contact points act as the fingertips of a robot. Many of the present-generation robots use this technique for touch sensing. Integrating these sensors in the tips of robot fingers helps determine the system and object edges and results in close manipulation of the objects, just like the mechanism in a human body. This feature has also helped develop cobots, which work in sensitive environments close to humans.

Simple piezoresistive, capacitive, or piezoelectric technologies can be used to create such tactile sensors. However, the capacitive sensors have a higher advantage than the others, as they help the robots to solve their movements when they’re close to the object, avoiding wasting power and causing damage. In addition, a discrete set of temperature, moisture, and other sensors are attached to the gripper pads to provide a more human-like motion for these robotic hands.

Sensor fusion

Sensor fusion means integrating several sensors to build a versatile robot that can perform complex tasks, which helps determine an object’s physical properties. For instance, a robot with a capacitive tactile sensor cannot alone pick up metal and plastic objects as they have different capacitors.

Hence, when multiple sensors are overlapped in different detection areas, they can be relied on to produce data on critical scenarios. Also, having multiple sensors can help detect the robot’s safety and efficiency. For instance, a contradictory reading from two different tactile sensors indicates a problem in robot functioning, which also helps easily detect sensor failure.

Accurate feedback from the tactile sensor helps maintain the safety and efficiency of cobots- robots that work relatively efficiently with humans. Fortunately, modern machine learning and AI technologies are great at programming and integrating different sensors to make decisions. Hence, AI also plays a crucial role in robot touch sensing, giving a robot human-like skin with many embedded tactile sensors.

Tactile sensors measure forces in response to physical changes and environmental interactions. One of the leading human aspects of detecting a change in the environment is by touch. The same principle is also applied in robots to detect changes in the environment and statistically analyze sensor data.

Tactile sensors are modeled to a biological sense of human touch, which is further provoked by the mechanical stimulation of the skin. This working principle helps robots, security systems, and computer hardware to measure data and analyze it to determine results in various fields. One of the typical applications of tactile sensing technology is in robotic arms, also called robotic tactile sensing.

The importance of tactile sensors in robotic applications

One of the significant challenges facing the robotic industry is that the dexterity of fingers makes it difficult for the robotic systems to do 95% of manual jobs like preparing a drink, folding clothes, cleaning a chandelier, and others. Replacing these kinds of manual labor with robots includes high precision, flexibility, and object detection, which can be achieved by enhancing the accuracy of measuring and controlling robotic fingers. This ensures that an object’s fragility is well-determined and not crushed by the gripper, which is generally a semiconductor wafer handler. Although the load cells provide reliable hope in robots for performing such actions, they have been limited in use due to their bulk structure. Hence, multiple load button cells are used as tactile sensors in industrial robots to measure the force they produce when they are in contact with an object.

Working

Many research laboratories continue to explore the vastness of robotic tactile sensors, especially in developing high-precision robots to help test, measure, and produce quality data in the robotic tactile sensing space. The presence of miniature load buttons provides succession by one step in detecting the sensitivity and fragility of objects. Tiny load buttons on the robot’s fingertips are force sensors mounted on each robotic finger’s tip. The tactile sensors placed in the tips manage to calculate the force required to handle the objects with utmost precision. The entire tactile sensor system in a robot is connected to a USB solution, where the researchers can stem the force needed to be applied directly on a computer to which the USB is connected. Drawing a graph of the findings makes it easier for the researchers to calculate the force required to pick up an object.

One of the main applications of designing a robot with tactile touch capability is to develop prosthetics using artificial touch technologies. The functional requirements of developing such robots include the following:

• Contact detection of objects
• Lifting and replacement of an object
• Detection of size and shape for object recognition
• Detection of tangential forces to prevent object slip
• Estimation of grip forces
• Tracking all the contact points during manipulation
• Detection of all the dynamic and static forces around the object

Tactile sensors are an important part of any robot’s toolset. They provide information about an object’s surface properties, such as texture, hardness, and weight. This information can be used to improve a robot’s grip on an object or to help the robot avoid damaging fragile items.

Robotic sensors

Robotic sensors measure and detect physical parameters like temperature, pressure, speed, etc. They play an essential role in enhancing the performance of robots by allowing them to gather information about their surroundings and react accordingly.

There are many different types of robotic sensors available, each with its own unique set of capabilities. The most common type of sensor is the tactile sensor, which detects contact and pressure.

Force and touch

The sense of touch is especially important for robots, as it allows them to interact with their environment more naturally.

When choosing a sensor for your robot, consider the specific needs of your application. For example, if you need a sensor that can detect very light touches, you will want to choose a sensor with high sensitivity. On the other hand, if you need a sensor that can withstand heavy impacts, you will want to select a sensor with high durability.

In robotics, force sensors measure the interaction between a robot and its environment. This information can be used to control the robot’s behavior or movements.

Detecting the environment

A tactile sensor is a pressure-sensitive device that can detect the environment around it. By measuring the amount of pressure applied to the sensor, the robot can determine how far away objects are, what they are made of, and whether or not they are moving.

Temperature

Temperature sensors are used to measure the temperature of an object or environment. They are commonly used in robotic applications to track the temperature of the robot’s components and surroundings. Temperature sensors can be used to monitor the health of your robot and its environment and to optimize its performance.

Temperature sensors are typically classified by their operating principles, such as thermocouples, resistance temperature detectors (RTDs), or semiconductor-based sensors.

• Thermocouples are the most common type of temperature sensor used in industrial applications due to their high accuracy and wide operating range.
• RTDs offer greater accuracy than thermocouples but are limited to a narrower range of temperatures.
• Semiconductor-based sensors are often used in consumer electronics due to their small size and low cost.

Light

Tactile sensors can also determine the direction and intensity of the light. This information can be used to enhance your robot’s performance.

For example, if you are using a robot to navigate a dark room, you can use the tactile sensor to determine where the light is coming from and adjust your robot’s course accordingly. You can also use the tactile sensor to detect objects in your path and avoid them.

A tactile sensor is a great way to add an extra level of precision and control to your robot. With the right understanding of how they work and how to use them, you can take your robot’s performance to the next level.

A tactile sensor can help improve your robot’s performance by providing information about the surface it is touching.

Tactile sensors, also called touch sensors, help determine an object’s physical characteristics when they are close to the objects. They are also called transducers which are used in various applications worldwide.

Psychophysical studies have determined the importance of touch, which is used for interpretation, extraction, and manipulation of the object within our range that is registered in various types of receptors like thermoreceptors, nociceptors, mechanoreceptors, etc., which are connected to a system to scrape the necessary information.

Tactile sensor technologies

Tactile sensors are sensitive to static or dynamic forces, which can be used for proprioception or exteroception. These sensors measure the internal states of the robot, while the latter is used to measure physical characteristics like the sense of touch in the environment.

All tactile sensor technologies are classified based on the transduction method, which helps convert stimuli from the external environment into intelligent systems. The most widely used tactile sensors in robots are based on the following transduction methods:

• Capacitance
• Piezoresistivity
• Optics
• Magnetic
• Binary
• Piezoelectric

Capacitive sensors

These types of sensors measure the variations in capacitance from an applied load over a parallel plate capacitor in the sensor. Capacitive sensors are susceptible to the external field, which in robotics is called taxels mimic the operation of human fingers. Since these sensors can be fabricated in compact spaces, they are used at the fingertips of robots.

Piezoresistive sensors

These sensors detect the resistance of a contact when an external force is applied. These sensors are generally fabricated on conductive rubber made of piezoresistive ink. These sensors produce a wide dynamic range, good load tolerance, durability, and low-cost fabrication. These sensors are used in robots where high accuracy is not a prim criterion.

Optical sensors

These sensors transduce mechanical contact, movement, and pressure into changes in refractive index or light intensities, detected using state-of-the-art vision sensors. They provide robustness to electrical interference with the capability of resolving high-level problems. Due to this, they are used in dexterous object manipulation and various other robotic systems. It is also used as one of the primary sensors in a three-finger robot hand to grasp particular objects in close vicinity.

Piezoelectric sensors

They produce an electrical charge when a force, pressure, or deformation is applied to them. They are best used to measure vibrations and are widely used for their high-frequency response, sensitivity, and availability in various forms like ceramics, crystals, etc. They are also preferred for the fabrication of tactile sensors, given their workability, flexibility, and chemical stability. Recently, they were best used in integrating tactile sensors with robotic grippers in robotic hands. Along with binary sensors, they are the best choice for using them in five–finger robotic hands as well

Tactile sensors are based on a range of different technologies they are utilized in. They’re broadly defined as data acquisition devices designed to sense different properties via direct contact with the object. Robotic applications have expanded their horizon in agriculture, healthcare, and autonomous systems in various unstructured environments where tactile sensors are highly beneficial. Their deployment helps measure, detect, and convert information, mainly acquired by physical contact with the objects.

Although tactile sensing has expanded exponentially in recent years, they are still underdeveloped compared to vision sensing. Researchers predict that this underdevelopment is due to the complexity of the sense of touch.

Applications of robotic tactile sensors

In 1980, robotics was initially determined as the study of perception and action and their intelligent interaction with the environment. Today, touch sensors’ integration has played a significant role in the robust development of flexible and adaptable robots capable of exploring different environmental sectors and safely interacting with humans.

Various robotic platforms use tactile sensors in their developments, like fingerprints, hands, forearms, and torso. This has helped study embodied cognition, perception, recognition, learning, and interaction.

Robotic fingerprints

Robotic fingerprints built with tactile sensors are generally equipped with piezoelectric elements, which recognize objects’ properties like shape, texture, etc. Studying and understanding these properties are used to determine experimental procedures like pushing, squeezing, sliding, and tapping of different objects. The use of pressure and force sensors has also played a significant role in object detection and manipulation. For example, the use of tactile sensors in prosthetic hands helps in mimicking the natural motion of a human hand.

Object and shape exploration

Different perception and control approaches are used to determine the object and its shape in various tactile robotic platforms. For instance, the Puma robot is integrated with planar tactile sensors, which help extract object edges and their orientation based on the geometrical moments. A similar use of geometrical moments is used in the KUKA arm with planar tactile sensors, which can recognize the shape and texture of various objects in contact with its fingertips.

Rolling and enclosing exploration

Based on the kurtosis observed on the tactile fingerprint of a five-finger robotic hand, the rolling and enclosing features can be explored. For example, the iCub humanoid robot using tactile sensor information from hands and fingertips achieved higher accuracy in the enclosure procedure for an object recognition task. In recent years, the robotic hand developed by Barrett Hand Inc., which is covered by tactile sensors in its fingertips and palm, has been used to understand dexterous manipulations and study the perception of touch.

Conclusion

There are a plethora of benefits provided by the tactile or touch sensors to develop robots that mimic human tasks. A range of technologies has also been developed around these sensors, each with its advantages and limitations.

A tactile sensor is a small device that responds to stimuli and measures the information from interacting with its environment. These sensors are modeled to respond to physical environmental changes and can detect mechanical stimulation, temperature, and pain. They find their use in robotics, security systems, and computer hardware. A touchscreen device is one of the most common examples of tactile sensors.

There are different types of tactile sensors:

• Optical
• Capacitive
• Elastoresistive
• Piezoresistive
• Piezoelectric

Since the modification of sensors has come a long way, it is primarily used in robotics to control mechanical arms, aircraft, and other fields.

Uses of tactile sensors

Although there are innumerable applications of these sensors in different fields like medicine, robotics, aeronautics, etc., in this article, we will talk about their uses in designing robots.

Robots are machines designed to handle tasks involving precision, dexterity, or interaction with particular objects. A sensor can help a robot provide the necessary functionality, equivalent to human tactile ability. One of the main advantages of tactile sensors in robots involves complementing visual systems and providing additional information when the robot begins to get hold of an object. For example, since the mechanical properties of an object at grip cannot be determined visually, tactile sensors were introduced to measure its coefficient of friction, thermal conductivity, stiffness, center of mass, thermal conductivity, and other factors.

There are several classes of tactile sensors in robots, each performing different types of tasks advocated for monitoring and manipulation.

Optical–based tactile sensors

In recent years, several tactical sensors have been introduced in the market, which provide camera-like technologies to produce data with high resolution. For example, Samsung uses see through your skin sensor (STS), which uses a semi-transparent gel to provide precision imaging with high resolution.

Pressure array sensors

The tactle, an element of a tactical sensor, can detect regular forces. This means their interaction provides high-resolution images when the object comes in close contact with the sensors in a robot. With its spatial resolution and sensitivity to forcing, wiring and signal routing are also essential factors for system integration. Hence, pressure sensors are introduced into the robots, which helps manufacture R&D and can further be used in robotics.

Conclusion

Future robots are predicted to work closely with humans in the real world and are also predicted to be more efficient than humans in certain filed. The tactical data gathered by them using tactile sensors in them help in effectively managing robotic tasks. The right integration of a tactical sensor on a robot body is a prerequisite that helps in better utilization of the determined data. Due to their contribution and benefits, tactical sensors are considered one of the practical components of robotic platforms.

What image does the word “robot” conjure up for you? Do you envision a metallic machine? Robots are adaptable machines, demonstrated by the enormous range of their forms and capabilities. Fortunately, it appears more likely that robots would focus on performing dangerous or repetitive duties rather than acquiring absolute executive control. Let’s examine robotics and its tactile sensors.

Tactile sensors in robots

An instrument known as a tactile sensor detects the forces produced by physical interactions with the environment. Humans model their sense of touch after the biological sensation of touch that is triggered by mechanical compression and stimulation of the body and skin. Single touch sensors detect various details like the shape, size, and texture of an object during contact with its surface, and they then send an electronic signal to a nearby controller. The controller then gauges the object’s actual dimensions, form, and weight.

Tactile Sensor Types

Force/Torque Sensor

In order to provide the input for force control, force/torque sensors are employed in conjunction with a tactile array. These kinds of sensors have the same range of load sensing as a skin sensor and the proximal link of a manipulator.

Dynamic Sensor

Smaller accelerometers known as dynamic sensors are located on the robotic finger’s skin or on the finger strips. One or two skin accelerometers are sufficient for a whole finger because the overall function is similar to that of human Pacinian corpuscles and they have correspondingly large respective fields.

Heating Sensor

Although certain thermal sensors are utilized in robotics and are crucial to the human ability to determine the elements of the objects manufactured. The process of thermal sensing entails finding heat variations and gradients in the skin that correlate to an object’s temperature and thermal conductivity.

Uses of tactile sensors

Tactile sensors are frequently used in robotic fingers and hands. Robots need sensory equipment that is functionally similar to a human’s tactile capacity if they are to handle tasks that need accuracy, flexibility, or interaction with strange objects. For use with robots, tactile sensors play a major role.  When the robot starts to grasp an object, tactile sensors can supplement visual systems by adding further information. Eyesight is no longer appropriate at this point because vision alone cannot determine the mechanical characteristics of the object.

The importance of tactile sensors in robotic applications 

The fact that conventional robotic systems cannot perform approximately 95% of all manual tasks due to the dexterity and flexibility of the fingers is one of the biggest problems facing the robotics industry today. Extreme dexterity is needed to prepare a drink, fold a napkin, clean a chandelier, etc. Robots must be able to grasp objects with more dexterity and without crushing delicate objects, which requires precisely monitoring and adjusting the robot’s grasping force. Despite being trustworthy sensors for measuring force, load cells have typically been constrained by their heavy design.

Tactile sensors are also called touch sensors and are sensitive to factors like temperature, pressure, and touch. They are designed to collect data from humans and surroundings and generate the necessary information using measuring instruments attached to them. Over the last few years, these tactile sensors have shown immense improvement and use in various industries.

Wearable tactile sensors are wearable devices designed to accommodate hard surfaces without causing damage to the device. Due to their structure and their application, they are primarily used in the Internet Of Things.

What are tactile sensors?

Tactile sensors are novel data acquisition devices designed to detect the slightest of external factors like touch, pressure, vibration, temperature, etc. The information acquired can be translated into intelligent systems for analysis. Wearable tactile sensors have a higher advantage, as opposed to the regular sensors available in the market. Their rigidity and solid form prevent free movement and are fragile to external pressure. Hence, the consumers might not have to compromise on the following:

• Robustness
• Durability
• Rigidity

Many scientists and researchers in biomedical engineering addressed these challenges. They created an alternative sensor device that works on the liquid-based pressure sensing method, which is highly used in most tactile sensor devices.

Characteristics of wearable tactile sensors

• The use of diverse and user-friendly functional materials
• The sensitive sensing mechanism
• Used in diverse applications
• Used for various performance optimizing strategies
• Employs more than one sensing options
• Integration of the device to different other systems

Liquid-based pressure sensor

Most wearable tactile sensor devices today follow liquid-based pressure sensing technology. The micro-fields present in the sensors are fabricated on surfaces like silicone rubber that are incredibly flexible, and it also uses nanomaterial suspensions that are non-corrosive. For instance, graphene oxide is a good example which is also used to represent a pressure sensing element that recognizes even the slightest force applied.

These devices proved their versatility in the invention when they were subjected to various tests, including pressure, stretching, and bending. They were also subjected to multiple abusive forces like being placed under cars etc., and still proved their quality when unharmed.

The idea of wearables

Although tactile sensors were already in use in everyday household items, robotics, and biomedical industries, the introduction of wearables has opened a new spectrum of markets. Tactile sensor wearables are predominantly used in the biomedical industry, where the device may be subjected to human touch and skin.

Advantages of tactile sensor wearables

• Due to the gap in the market for wearables, the introduction of tactile sensors has also opened a new arena for users.
• Since these devices are flexible and durable, they are used mainly by the general public to monitor body movements.
• It is used in healthcare industries to micro-monitor patients in the hospital.

Tactile sensors are devices that are sensitive to touch, and they collect and document information when there is contact with objects in the environment. In general, tactile translates to “touch.” Hence a tactile sensor is also termed a touch sensor.

What are tactile sensors?

Tactile or touch sensors measure the intensity of touch with particular objects in the environment. They work when the sensor of a device comes close to a human or an object. They are designed to behave like switches when they are touched. Due to their inexpensive cost and simple design, mechanical switches often replace them.

There are three different types of touch sensors that are sensitive to contact, pressure, and force. They are:

• Force sensor
• Dynamic sensor
• Thermal sensor

Operating principle of touch sensors

The operating principle of tactile sensors is similar to that of mechanical switches. When the sensors come close to force, touch, or temperature, they behave like closed switches, and when the pressure is released, they behave like open switches. Different types of tactile sensors mainly function on the following principles:

• Piezoelectricity: When the magnitude of voltage generated during the deformation of crystal lattice changes, it changes the resistance in sensors.
• Capacitance: The pressure applied on the two conductive plates changes, and the capacitance in the parallel plate capacitors changes directly.
• Piezo- resistivity: The deformation of shape caused due to an applied force changes the resistance of a piezoresistivity sensor.

Working with a capacitive touch sensor

Capacitive tactile sensors are the simplest form of sensors. They consist of two metal plates that act as conductors and an insulator. The electrode at the end represents one of the conductor plates, and the second conductor plate is represented by the environment and a conductive object (human finger). Capacitance is directly proportional to surface area and inversely proportional to distance.

On one end, the sensor (electrode) is connected to a measuring device, and the capacitance is measured periodically. When an external object like a human finger approaches the sensor, the capacitance will increase, and the data is measured by a measuring device which converts it to a trigger signal.

Working with a resistive touch sensor

These sensors have a much longer duration than the capacitive sensors and work with non-conducting materials like plastic, stylus, etc. This sensor comprises two layers covered in the film, separated by spacer dots. The conductive layer is covered with a transparent metal layer and is subjected to voltage.

When an external pressure or force is applied on the other surface, the two layers come in contact and create a voltage drop, which is recorded in the measuring instrument. These types of sensors are used in harsh environments, and their response time is significantly greater. Hence they are being replaced by capacitive sensors.

Uses of tactile sensors

• Everyday household items
• Performance testing of various applications
• Medical imaging
• Robotics