Proximity sensors are characterized by long service life, reliable operation, high repeatability, no mechanical wear, no sparks, no noise, and strong vibration resistance. In automatic control systems, they can be used as limit switches, counters, positioning controls, and automatic protection components. They are widely used in industries such as machine tools, metallurgy, chemicals, textiles, and printing.
Before discussing the applications of proximity sensors, let's first understand some of their main functions: 1. Detecting distances and the stopping, starting, and passing positions of elevators and lifting equipment; detecting the position of vehicles to prevent collisions between two objects; detecting the set position of working machinery and the limit positions of moving machines or parts; detecting the stopping position of rotating bodies and the open or closed position of valves; detecting the piston movement position in cylinders or hydraulic cylinders.
2. Size control device for metal sheet punching and shearing; automatic selection and identification of metal part length; detection of stacking height during automatic loading and unloading; detection of the length, width, height and volume of items.
3. Detect the presence of objects: Check for product packaging boxes on the production and packaging line; check for product parts.
4. Speed and rotation speed control: Controls the speed of the conveyor belt; controls the rotation speed of rotating machinery; and controls the rotation speed and revolutions in conjunction with various pulse generators.
5. Counting and control of the number of products flowing through the production line; measurement of the number of revolutions of high-speed rotating shafts or discs; counting of parts.
6. Anomaly detection: Detecting the presence or absence of bottle caps; determining product qualification or non-qualification; detecting the absence or absence of metal products inside packaging boxes; distinguishing between metal and non-metal parts; detecting the presence or absence of product labels; alarm for dangerous areas on cranes; automatic start and stop of safety escalators.
7. Automatic measurement of products or parts; control of flow rate by detecting the pointer range of measuring instruments; control of flow rate by detecting buoy height and flow rate; detection of iron buoys in stainless steel barrels; control of upper or lower limits of instrument range; flow control and horizontal control.
8. The identification object is determined by the code on the carrier to determine whether it is true or false.
9. Information transmission: ASI (bus) connection equipment enables data transmission between sensors at various locations on the production line (50-100 meters).
Currently, proximity sensors are widely used in various industries such as aerospace, industrial production, transportation, and consumer electronics. Below are some typical application scenarios to help you develop ideas for proximity sensor application design.
Application of Human Proximity Sensors in ATM Monitoring: Human proximity sensors are control devices used to detect the approach of human bodies. They can accurately detect the approach of nearby individuals and are currently the best choice for alarm and status detection. Their sensing component has high sensitivity to the movement of nearby people and suppresses ambient sound signals, exhibiting strong anti-interference capabilities. Internally, they use microcircuit chips for programmable processing, resulting in high detection sensitivity and trigger reliability. The detection and control parts are integrated into one unit, with low power consumption and a switch signal output that directly triggers alarm recording.
Because the sensitivity to human movement is continuously adjustable, human proximity sensors can be used in many different situations. In terms of security and theft prevention, important locations such as archives, accounting firms, financial institutions, museums, and vaults are usually equipped with anti-theft devices composed of various proximity sensors.
Application of proximity sensors in aircraft landing gear systems
Aircraft power plant, landing gear system, and navigation system are the top three systems reported by airlines as causing difficulties in aircraft operation. Among them, landing gear system failures can easily cause abnormal events such as aircraft returning to their origin or making emergency landings, resulting in economic losses for the company and posing a threat to aviation safety.
In typical Airbus aircraft landing gear control systems, a digital fly-by-wire control system is usually used. Its basic principle is to send sensor signals to a control box (control computer), which then performs comprehensive calculations and comparisons before issuing commands to the actuators. This control mechanism is redundant.
Modern civil aircraft landing gear retraction and extension systems consist of two parts: normal retraction and extension, and emergency release. The landing gear control system is operated by fly-by-wire and is interconnected with other systems, widely employing inductive proximity sensors to detect the landing gear position.
Each landing gear unit has two main sensors: a retraction lock sensor and a landing gear lock sensor. These sensors are used to transmit position signals when the landing gear is retracted and locked, respectively. These sensors are magnetoresistive proximity sensors, mainly composed of two parts: the sensor body and the sensor excitation plate.
The sensor body converts electrical energy into a magnetic field, while the excitation plate primarily increases the magnetic permeability. When the landing gear approaches the excitation plate to a certain distance, the magnetic permeability increases, and the sensor sends a signal to the warning assembly indicating the landing gear position. The distance between them directly affects the accuracy of the indication, and the adjustment requirements are generally quite strict. Furthermore, there are slight differences between different aircraft models; the AMM manual for that specific aircraft model should be consulted for adjustment.
Using inductive proximity sensors to detect the landing gear position improves sensor lifespan. Furthermore, the control computer facilitates convenient information transmission and sharing with the avionics system.
Application of proximity sensors in railway track crossing monitoring
Train collisions account for a large proportion of all railway accidents, and often have serious consequences. Utilizing proximity sensors to monitor passing trains at level crossings has become a crucial element in improving railway safety.
In practical applications, leveraging the non-contact position measurement capabilities of proximity sensors, they can be symmetrically installed at both ends of the railway tracks at an intersection. When a train passes, the proximity sensors at both ends of the tracks can detect the changes caused by the passing wheels at their respective ends. The crossing monitoring microprocessor system analyzes the signals from each sensor to determine the direction of the vehicle's travel and its crossing status (whether it passes or stops). Finally, the information is transmitted to the traffic control center via cable or wireless communication for train dispatching.
The application of proximity sensors in automated packaging machinery: Mechanized manufacturing has spurred the demand for automated packaging technology, as manual packaging methods are far from meeting the needs of mass production. Automated packaging machinery, guided by a control system, can complete a series of packaging processes, improving product packaging efficiency and reducing packaging costs, but errors are still inevitable. Therefore, automated packaging inspection has become a crucial link in ensuring packaging quality. For cases involving ferromagnetic materials during packaging, non-contact detection using proximity sensors is a commonly employed method.
A proximity sensor contains a coil that generates an alternating magnetic field. When a ferromagnetic object is placed in this environment, eddy currents are induced within it due to electromagnetic induction. When the magnetic field generated by these eddy currents is sufficiently strong, it alters the original circuit parameters of the proximity sensor, thereby producing a signal output. Therefore, proximity sensors can be used to identify the presence of magnetic or easily magnetized substances within a certain range. In some automated packaging processes, such as the metal foil packaging of chocolates, the detection of magnetic substances by proximity sensors can determine whether there are packaging errors or missed processes, thus improving packaging quality.
Applications of Proximity Sensors in Robotic Grippers: A robotic gripper is a mechanical component with multiple degrees of freedom, capable of dexterously grasping objects. It can be used in various industrial automated production, assembly, and operations, and can perform tasks such as information detection, object collection and reconnaissance, and bomb disposal in high-risk environments. Robotic grippers generally employ a clamp-like structure, grasping objects by opening and closing. Therefore, the precise measurement and control of the opening degree of the "jaws" is a key factor directly affecting the success of the gripping process.
Because proximity sensors can detect changes in distance and position, they are commonly used in robot grippers to measure opening and closing. They utilize changes in the magnetic field and the relative position of the metal part being measured. Typically, the sensor is mounted on one of the grippers' clamps. When gripping an object, the proximity sensor determines the distance between the gripper and the clamp by sensing changes in the magnitude of the magnetic field. This information can then be compared with a set value to adjust the gripper's opening, preventing missed grips or damage to the object.
Applications of Capacitive Proximity Sensors in Automotive Electronics: The demand for proximity detection sensors in automotive electronics applications has been steadily increasing. The potential applications of proximity detection in the automotive electronics industry are limitless, for example:
• Car access control: Detects a hand approaching the door handle to initiate the unlocking process. • Illuminates and wakes the touchscreen when the palm approaches the screen surface. • Turns interior lights on/off when the palm approaches the sensor. • Opens/closes devices by detecting simple hand movements in the air. • Detects large obstacles around the car while it is parked.
Various proximity detection methods exist to meet the diverse needs of automotive electronic applications, such as capacitive sensing, infrared, ultrasonic, and optical methods. For proximity detection in the range of 5mm to 300mm, capacitive sensing technology offers several advantages over other technologies: excellent reliability, simple mechanical design, low power consumption, and low cost.
An example of capacitive proximity detection is its application in a car access control system (see figure below). A proximity sensor that detects a person's hand approaching is located inside the door handle (1). Once an object is detected, the main control unit (2) sends a wake-up signal via a low-frequency antenna (3); this signal activates the car key transmitter (4). The car key transmitter then exchanges information with an RFID receiver (5); if the encoded information matches that of the main control unit (2), the car door lock is opened. The entire process of proximity detection and ID recognition takes approximately a fraction of a second. This means that when the hand pulls the door handle, the door lock is already open.
Compared to touch detection, the advantage of using proximity detection in car access control systems is that it can identify the car owner in advance, resulting in the door lock being open before the door is even pulled.
Detecting spatial gestures to turn devices on or off is a common application in automotive electronics. Using two or more capacitive proximity sensors simultaneously, devices can be turned on or off by detecting simple hand movements in the air, such as waving in front of the device. The image below shows a simple example of using such a system to turn interior lighting on/off. Waving in one direction towards the light turns it on, and waving in the opposite direction turns it off. The system analyzes the signals from the proximity sensors to determine whether the gesture indicates turning the light on or off. There are many different methods for designing sensing electrodes within the light bulb, ranging from using thin copper wires to employing conductive polymers that can be directly attached to plastic.
The application of proximity switch sensors in platform screen doors: For safety reasons, platform screen doors are increasingly being used in subway stations. Proximity switch sensors will be widely used in the technology of platform screen doors, and subway accidents will be minimized through the application of sensors.
Currently, the common solution for detecting opening and closing in platform screen door systems generally uses two proximity switches. Because proximity sensors can perform detection in a non-contact manner, they do not wear down or damage the object being detected. This is a major reason why they are suitable for installation in subways. As the performance of proximity sensors further improves, they will be applied to more applications, and in the future, they will be widely used not only in subway doors but also in other platform screen doors such as those on buses.
The application of proximity sensors in touchscreen phones: Proximity sensors utilize MEMS technology and have become widespread in smartphones.
When touchscreen phones first became popular, users noticed a drawback: when answering a call in the most common way, the face often touches the screen, accidentally pressing the hang-up or hands-free button, causing unnecessary embarrassment. Therefore, phone manufacturers utilized MEMS technology, incorporating MEMS proximity sensors into touchscreen phones to automatically lock the screen when a call is answered, preventing accidental triggering. Additionally, locking the screen also turns off the backlight, effectively saving energy and extending standby time.
Smartphones utilize MEMS ambient light sensors and proximity sensors: ambient light detection (judging the surrounding brightness by measuring the amount of light detected by the sensor's illumination) and proximity detection (judging the distance to the object by measuring the amount of light reflected from the sensor's light source). Ambient light sensors can optimize the LED backlight, allowing the phone to automatically adjust to a suitable brightness in any environment, whether it's a dimly lit movie theater or a brightly lit outdoor setting. Proximity sensors can disable the touchscreen during calls, preventing accidental disconnections or unauthorized access to other functions.
Conclusion:
Technological innovations have transformed proximity sensors. Widely used in industrial automation control, proximity sensors are now being applied to a wider range of fields through upgrades in intelligence, miniaturization, and integration.
