Identifying Popular Sensors on Robots

Sensors are common yet very important devices thatperceive various measured quantities according to specified standards and convert them into useful signals according to certain rules. For sensors, depending on the input state, inputs can be divided into static quantities and dynamic quantities. We can obtain the static characteristics of a sensor based on the relationship between the output and input quantities under stable conditions of various values.

The main indicators of the static characteristics of a sensor include linearity, hysteresis, repeatability, sensitivity, and accuracy. The dynamic characteristics of a sensor refer to its response characteristics to input quantities that change over time. Dynamic characteristics are usually described using control models such as transfer functions. Generally, the signals received by the sensor contain weak low-frequency signals, and external interference sometimes exceeds the magnitude of the measured signals, thuseliminating the noise becomes a key sensor technology.

Physical Sensors

A physical sensor is a sensor that detects physical quantities. It utilizes certainphysical effects to convert the measured physical quantity into a signal in a form convenient for processing. The output signal has a definite relationship with the input signal. The main types of physical sensors includephotoelectric sensors, piezoelectric sensors, resistive sensors, electromagnetic sensors, thermoelectric sensors, and fiber optic sensors.

For example, let us look at the commonly usedphotoelectric sensor. This type of sensorconverts light signals into electrical signals, directly detecting radiation information from objects and can also convert other physical quantities into light signals. Its main principle is thephotoelectric effect: When light illuminates a material, the electrical effects on the material change, including electron emission, conductivity, and potential current.

Clearly, devices that can easily produce such effects become the main components of photoelectric sensors, such asphotoresistors. Thus, we know that the main workflow of a photoelectric sensor is to receive the corresponding light illumination, convert light energy into electrical energy through devices like photoresistors, and then through amplification and noise reduction processing, obtain the required output electrical signal. The output electrical signal here has a certain relationship with the original light signal, usually close to linear, making it not very complicated to calculate the original light signal. The principles of other physical sensors can be analogized to that of photoelectric sensors.

The application range of physical sensors is very wide. Let us look at the application of physical sensors from the perspective of biomedicine, and it is not difficult to infer that physical sensors also have important applications in other areas.

For instance,blood pressure measurement is the most routine type of medical measurement. Our usual blood pressure measurements are indirect, detecting the relationship between blood flow and pressure at the body surface to measure the blood pressure value in the vessels. The sensors needed for blood pressure measurement usually include aflexible diaphragm, whichconverts pressure signals into diaphragm deformation, and thenconverts this deformation into corresponding electrical signals based on the strain or displacement of the diaphragm. At the peak of the electrical signal, we can detect systolic pressure, and after passing through an inverter and peak detector, we can obtain diastolic pressure; by using an integrator, we can get the average pressure.

Let us look at respiratory measurement technology. Respiratory measurement is an important basis for clinical diagnosis of lung function and is essential in surgical operations and patient monitoring. For example, when using a thermoresistive sensor to measure respiratory frequency, the sensor’s resistance is mounted on the outer side of a clip that is clipped to the nostrils; when the respiratory airflow passes over the surface of the thermoresistor, it can measure the respiratory frequency and the state of the heated air through thethermoresistor.

Another common example is the process of measuring body surface temperature. Although it seems simple, it has a complex measurement mechanism. Body surface temperature is determined by multiple factors, including local blood flow, thermal conductivity of underlying tissues, and heat dissipation from the epidermis. Therefore, measuring skin temperature requires consideration of various influences.Thermocouple sensors are widely used for temperature measurement, typically includingrod thermocouples and thin-film thermocouples.

Due to the small size of thermocouples, and the ability to achieve high precision down to the micrometer level, they can accurately measure the temperature at a specific point. Coupled with later analysis and statistics, a comprehensive analysis result can be obtained. This is unmatched by traditional mercury thermometers and demonstrates the broad prospects brought by applying new technologies to scientific development.

From the above introduction, it can be seen that physical sensors have various applications, even just in biomedicine. The development direction of sensors is towards multifunctionality, imaging, and intelligence. As an important means of data acquisition, sensor measurement is essential in industrial production and even in household life, while physical sensors are the most common type in the sensor family. Flexibly utilizing physical sensors will inevitably create more products and better benefits.

Fiber Optic Sensors

In recent years, sensors have been developing towards sensitivity, precision, adaptability, compactness, and intelligence. In this process, fiber optic sensors, a new member of the sensor family, have gained much favor. Fiber optics have many excellent properties, such as:resistance to electromagnetic interference and atomic radiation, fine diameter, soft texture, lightweight mechanical properties, insulating, non-inductive electrical properties, water resistance, high-temperature resistance, and corrosion resistance, etc. They can serve as the eyes and ears of humans in places that are unreachable (such as high-temperature areas) or harmful to humans (such as nuclear radiation zones), and can even surpass human sensory limits to receive external information that cannot be perceived by human senses.

Fiber optic sensors are a new technology that has emerged in recent years and can be used to measure various physical quantities, such as sound fields, electric fields, pressure, temperature, angular velocity, and acceleration, and can accomplish measurement tasks that existing measurement technologies find difficult to achieve. In confined spaces, under strong electromagnetic interference and high voltage environments, fiber optic sensors have demonstrated unique capabilities. Currently, there are over 70 types of fiber optic sensors, roughly divided into fiber optic self-sensors and sensors utilizing fiber optics.

So-calledfiber optic self-sensors are those thatdirectly receive external measurements through the fiber optic itself. External physical quantities being measured can cause changes in thelength, refractive index, or diameter of the measurement arm, thereby causing changes in theamplitude, phase, frequency, or polarization of the light transmitted within the fiber. The light transmitted through the measurement arm interferes (compares) with the reference light from the reference arm, causing changes in the phase (or amplitude) of the output light. This high sensitivity to external influences allows for the detection of minute phase changes corresponding to physical quantities, on the order of 10 to the power of negative four radians. By utilizing the flexibility and low loss of fiber optics, long fibers can be coiled into small diameters to increase utilization length and achieve higher sensitivity.

Fiber optic acoustic sensors are one type of self-sensor that utilizes fiber optics. When a fiber optic experiences a very slight external force, it bends slightly, causing significant changes in its light transmission capability.Sound is a mechanical wave, and its effect on fiber optics is to exert force and cause bending, which can then be used to measure the strength of the sound.Fiber optic gyroscopes are also a type of self-sensor, which, compared to laser gyroscopes, have higher sensitivity, smaller size, and lower cost, making them suitable for high-performance inertial navigation systems in aircraft, ships, and other applications.

Another major category of fiber optic sensors issensors utilizing fiber optics. Their structure is roughly as follows:the sensor is located at the end of the fiber, and the fiber serves merely as a light transmission line, converting the measured physical quantity into variations in light amplitude, phase, or frequency. In this type of sensor system, traditional sensors are combined with fiber optics. The introduction of fiber optics provides the possibility of remote measurement through probing. This type of fiber optic transmission sensor has a wide range of applications, is easy to use, but has slightly lower precision than the first type of sensor.

Fiber optics are the latecomers in the sensor family, gaining widespread application due to their excellent properties, and they are a type of sensor that deserves attention in practical production.

Bionic Sensors

Bionic sensors are a new type of sensor that adopts new detection principles, utilizingimmobilized cells, enzymes, or other biologically active substances in combination with transducers to form sensors. This type of sensor has developed in recent years as a new information technology resulting from the intersection of biomedicine, electronics, and engineering. The characteristics of this sensor include high functionality and long lifespan. Among bionic sensors, bio-simulated sensors are commonly used.

Bionic sensors can be classified according to the medium used:enzyme sensors, microbial sensors, organelle sensors, tissue sensors, etc.. Bionic sensors are closely related to various aspects of biological theory and are a direct result of the development of biological theory. Among bio-simulated sensors, urea sensors are a recently developed type of sensor. Below, we will introduce the application of bionic sensors using urea sensors as an example.

Urea sensors are mainly composed ofbiological membranes and their ion channels. The biological membrane can sense external stimuli, while the ion channels can receive information from the biological membrane and amplify and transmit it. When the sensing part of the membrane is affected by external stimulants, the permeability of the membrane changes, allowing a large flow of ions into the cells, forming information transmission. The key role is played by the components of the biological membranemembrane proteins, which can produce conformational network changes, altering the permeability of the membrane to facilitate information transmission and amplification. The ion channels of the biological membrane are composed of polymerized amino acids, and can be replaced by easily synthesizedpolyurethane polymers (L-glutamic acid, PLG), which have better chemical stability than enzymes. PLG is water-soluble and not suitable for electrical modification, but PLG and polymers can be combined to form block copolymers, creating sensing membranes for sensor use.

The principle of the ion channels of the biological membrane is fundamentally similar to that of the biological membrane. When the block copolymer membrane is fixed on the electrode and a substance that induces changes in the PLG conformational network is added, the permeability of the membrane will change, leading to changes in current. By measuring the changes in current, it is possible to detect stimulatory substances.

Urea sensors have proven to be stable bio-simulated sensors with a detection limit on the order of 10 to the power of negative three, and can detect stimulatory substances, but are not yet suitable for in vivo measurements.

Currently, although many bionic sensors have been successfully developed, the stability, reproducibility, and mass production of bionic sensors are clearly insufficient, so bionic sensing technology is still in its infancy. Therefore, in addition to continuing to develop new series of bionic sensors and improving existing series, the immobilization technology of bioactive membranes and the solidification of bionic sensors deserve further research.

In the near future, bionic sensors simulating human olfactory, taste, auditory, and tactile functions will emerge, potentially surpassing human sensory capabilities and improving the current robots’ visual, taste, tactile functions, and their ability to manipulate objects. We can see the broad prospects for the application of bionic sensors, but all of this requires further development in biotechnology, and we await the arrival of that day.

Infrared Sensors

Infrared technology has developed to the point where it is well-known, and this technology has been widely applied in modern science and technology, national defense, and agriculture and industry.Infrared sensing systems are measurement systems that use infrared rays as the medium, which can be categorized into five types according to function: (1) Radiometers for measuring radiation and spectra; (2) Search and tracking systems for locating and tracking infrared targets, determining their spatial positions, and tracking their movements; (3) Thermal imaging systems that can generate images showing the distribution of infrared radiation from the entire target; (4) Infrared ranging and communication systems; and (5) Hybrid systems, which refer to combinations of two or more of the above types of systems.

The core of infrared systems is the infrared detector, which can be divided into two main categories based on detection mechanisms: thermal detectors and photon detectors. Below, we will analyze the principles of detectors using thermal detectors as an example.

Thermal detectors utilizeradiative thermal effects to causethe detection element to receive radiation energy, leading to a temperature rise, which in turn causes temperature-dependent properties of the detector to change. By detecting the change in one of these properties, radiation can be detected. Most often, this is done through thermoelectric changes. When the element receives radiation, causing non-electric physical changes, the corresponding electrical changes can be measured after appropriate transformations.

Electromagnetic Sensors

Magnetic sensors are the oldest type of sensor,with the compass being the earliest application of magnetic sensors. However, modern sensors require magnetic sensors to convert magnetic signals into electrical signals for easier signal processing. The earliest applications were magnetic-electric sensors made based onthe principle of electromagnetic induction. These magnetic-electric sensors made outstanding contributions in the field of industrial control, but today they have been replaced by new types of magnetic sensors primarily based on high-performance magnetic-sensitive materials.

Among the electromagnetic effect sensors used today, magnetic rotary sensors are an important category. Magnetic rotary sensors mainly consist ofsemiconductor magnetoresistive elements, permanent magnets, fixtures, and housings. A typical structure involves installing a pair of magnetoresistive elements on a permanent magnet’s stimulation, with the input and output terminals of the elements connected to the fixture, and then installed in a metal box and sealed with engineering plastics to form a closed structure, which provides good reliability. Magnetic rotary sensors have many advantages over semiconductor magnetoresistive elements in terms of shape. In addition to having high sensitivity and large output signals, they also have a strong rotational speed detection range, which results from advances in electronic technology. Moreover, this type of sensor can operate over a wide temperature range, has a long working life, and strong resistance to dust, water, and oil contamination, making it capable of withstanding various environmental conditions and external noise. Therefore, this type of sensor is widely valued in industrial applications.

Magnetic rotary sensors have widespread applications in factory automation systems due to their satisfactory characteristics and maintenance-free operation. Their main applications includedetecting the rotation of machine tool servo motors, positioning of robotic arms in factory automation, detecting hydraulic strokes, detecting the position of factory automation-related equipment, detecting units of rotary encoders, and various rotation detection units.

Modern magnetic rotary sensors mainly includefour-phase sensors and single-phase sensors. During operation, four-phase differential rotary sensors use a pair of detection units for differential detection while another pair performs inverse differential detection. This way, the detection capability of four-phase sensors is four times that of single units. The two-element single-phase rotary sensor also has its advantages, namely its compactness and reliability, and it provides large output signals, can detect low-speed motion, and has strong resistance to environmental influences and noise, making it cost-effective. Therefore, single-phase sensors also have good market potential.

Magnetic rotary sensors also have significant application potential in household appliances. In the changing mechanism of cassette tape recorders, magnetoresistive elements can be used to detect the endpoint of the tape. Most home video recorders with variable speed and high-speed playback functions can also use magnetic rotary sensors to detect spindle speed and control it to achieve high-quality images. The positive and negative rotation and high and low-speed rotation functions of motors in washing machines can also be detected and controlled using servo rotary sensors.

This switch can sense metallic objects entering its inspection area, controlling the internal circuitry to turn on or off. The switch generates its magnetic field, and when a metallic object enters the magnetic field, it causes a change in the magnetic field. This change can be converted into an electrical signal through the switch’s internal circuitry.

Furthermore, electromagnetic sensors represent a high-tech application with extensive applications, with both domestic and international research efforts being invested in this area. The application of such sensors is penetrating various fields of national economy, national defense construction, and daily life, and with the arrival of the information society, their status and role will undoubtedly continue to grow.

Magneto-Optical Effect Sensors

Modern electrical measurement technology is becoming increasingly mature. Due to its high precision and ease of connection to microcomputers for automatic real-time processing, it has been widely applied in both electrical and non-electrical measurements. However, electrical measurement methods are easily affected by interference, and during AC measurements, frequency response is not wide enough, and there are certain requirements for voltage resistance and insulation. With the rapid development of laser technology, these issues have been addressed.

Magneto-optical effect sensors are high-performance sensors developed using laser technology. Lasers are a new technology that rapidly developed in the early 1960s, marking a new stage in our ability to master and utilize light waves. Due to the low monochromaticity of ordinary light sources, many important applications were restricted, but the emergence of lasers has greatly advanced both radio and optical technologies, allowing them to penetrate and complement each other. Many sensors have been developed using lasers, solving many previously unsolvable technical challenges, making them suitable for hazardous and flammable environments such as coal mines, oil, and natural gas storage.

For example, fiber optic sensors made with lasers can measure parameters such as crude oil injection and the cracking of large oil tanks. At the actual measurement sites, no external power supply is needed, which is especially suitable for groups of petrochemical equipment that require strict safety and explosion-proof measures. They can also be used to achieve optical remote measurement techniques in certain processes of large steel mills.

The principle of magneto-optical effect sensors is primarily based onthe polarization state of light to realize the sensor’s function. When a beam of polarized light passes through a medium, if there is an external magnetic field in the direction of light propagation, the light will rotate at an angle through the polarization plane, which is known asthe magneto-optical effect. This means that the external magnetic field can be measured by the angle of rotation. Under specific experimental setups, the deflection angle is proportional to the output light intensity; by illuminating a laser diode (LD) with the output light, digitalized light intensity can be obtained to measure specific physical quantities.

Since the late 1960s, research reports on the magneto-optical effect have attracted attention. Countries like Japan and the Soviet Union have conducted research, and scholars in China have also explored this area. Magneto-optical effect sensors possess excellent electrical insulation performance, anti-interference, wide frequency response, fast response, and safety explosion-proof characteristics, making them uniquely effective for measuring electromagnetic parameters in special occasions, especially showing potential advantages in measuring high voltage and large current in power systems. Additionally, by developing software and hardware for processing systems, real-time automatic measurements can also be achieved in electric welding machines and robotic control systems. In the use of magneto-optical effect sensors, the most important aspect is the selection of magneto-optical media and lasers, as different devices have different capabilities in terms of sensitivity and working range. With the emergence of high-performance lasers and new types of magneto-optical media in recent decades, the performance of magneto-optical effect sensors has become increasingly powerful, and their applications are becoming broader.

As a specific-purpose sensor, magneto-optical effect sensors can perform their functions in specific environments and are also very important industrial sensors.

Pressure Sensors

Pressure sensors are the most commonly used type of sensor in industrial practice, and the pressure sensors we typically use are mainly made usingthe piezoelectric effect, and such sensors are also known as piezoelectric sensors.

We know thatcrystals are anisotropic, while amorphous materials are isotropic. Certain crystalline media, when subjected to mechanical forces in a specific direction, undergo deformation, resulting inpolarization effects; when the mechanical force is removed, they return to their uncharged state, meaning thatwhen pressure is applied, certain crystals may generate electrical effects, which is the so-called polarization effect. Scientists have developed pressure sensors based on this effect.

The main piezoelectric materials used in piezoelectric sensors include quartz, sodium tartrate, and diammonium phosphate.Quartz (silicon dioxide) is a natural crystal where the piezoelectric effect was discovered, and within a certain temperature range, the piezoelectric properties persist; however, beyond this range, the piezoelectric properties completely disappear (this high temperature is known as the “Curie point”). Because the electric field changes slightly with variations in stress (indicating a low piezoelectric coefficient), quartz has gradually been replaced by other piezoelectric crystals. Sodium tartrate has a high piezoelectric sensitivity and coefficient, but it can only be used at room temperature and low humidity conditions. Diammonium phosphate is a synthetic crystal that can withstand high temperatures and considerable humidity, thus it has been widely applied.

Currently, the piezoelectric effect is also applied to polycrystalline materials, such as today’s piezoelectric ceramics, includingbarium titanate piezoelectric ceramics, PZT, niobate piezoelectric ceramics, and lead magnesium niobate piezoelectric ceramics.

The piezoelectric effect is the main working principle of piezoelectric sensors, which cannot be used for static measurements because the electric charge generated after external force is only preserved when the circuit has infinite input impedance. This is not the case in practice, so this determines that piezoelectric sensors can only measure dynamic stress.

Piezoelectric sensors are mainly used for measuring acceleration, pressure, and force. Piezoelectric accelerometers are a commonly used type of accelerometer. They havea simple structure, small size, light weight, and long service life, making them widely used in measuring vibrations and impacts in aircraft, automobiles, ships, bridges, and buildings, particularly giving piezoelectric sensors a special status in aerospace.

Piezoelectric sensors can also be used to measure combustion pressure inside engines and vacuum levels. They can also be used in military applications, such as measuring the chamber pressure changes at the moment of firing in firearms and the shock wave pressure at the muzzle. They canmeasure both large pressures and tiny pressures.

Piezoelectric sensors are also widely used in biomedical measurements; for example, catheter microphones in ventricles are made from piezoelectric sensors. Due to the prevalence of dynamic pressure measurements, the applications of piezoelectric sensors are very extensive.

In addition to piezoelectric sensors, there are also resistive pressure sensors made usingthe piezoresistive effect and strain gauges, which utilize different effects and materials to serve unique purposes in various situations.

As robots continue to develop in traditional fields while expanding into non-traditional areas, they find new development directions, open up new markets, and gain new momentum. Sensor technology, as one of the foundations of robotics, is also evolving. Sensor technology is progressing from traditional sensory fields such as sight, touch, and smell towards non-contact methods, using brain waves to achieve sensing, allowing humans to truly enjoy the fruits of their labor. The future development of robotic sensor technology will undoubtedly lead to the establishment of a complete sensory system similar to that of humans, with robots serving as the unified carriers of these sensor technologies.

The reproduced content only represents the author’s views

and does not represent the position of the Institute of Physics, Chinese Academy of Sciences

For reprints, please contact the original public account

Original title: Sensors on Robots

Source: Sensor Technology

Editor: Garrett

Recent Popular Articles Top 10

↓ Click the title to view ↓

1. After sitting for six hours a day, this is what happens to your body

2. This organ, which is often removed, actually protected you throughout your childhood! (Not the appendix)

3. Can toilet paper be flushed down the toilet after use? Let’s do an experiment to show you

4. Just now, the first five photos of the hundred billion dollar “Webb Space Telescope” were officially released!

5. The Greatest Work, but the Second Middle School

6. Which is hotter, 100℃ water or 100℃ oil? | No.318

7. Which is the most real, your phone’s rear camera, front camera, or you in the mirror?

8. Why is it so hot this year?

9. Why can’t you peek through the door gap? It turns out that peeking through the door gap can see “ghosts”

10. Prohibited nesting of cauliflower, retina, and coffee pots

Click here to view all previous popular articles Identifying Popular Sensors on Robots

Related posts

Leave a Comment Cancel reply