As the name implies, a proximity sensor detects objects in its vicinity. The sensor measures the target object without touching it, thus there is no physical contact. It generally emits electromagnetic radiation (e.g. infrared) and then detects the object proximate to it by getting a return signal and measuring the time delay.
Proximity sensors are of different types and there are over a dozen different types available. To name a few: inductive sensors, capacitive sensors and magnetic sensors are the ones used extensively. Inductive technology is used to detect metallic objects while capacitive sensors would be used to detect other materials. Magnetic sensors are robust and operate very efficiently in dirty or damp conditions, and are thus used primarily in cranes and heavy vehicles. Thus, the type of technology used in the sensor depends on the target object that needs to be detected. In short, wherever an object’s proximity is important to report, proximity sensors are the indispensable tools to make use of.
Most proximity sensors have industrial uses; e.g. they are extensively used in conveyor belts in the assembly lines. Besides, one particular use brings them very close to the consumer: the use of proximity sensors in automobiles to assist in car parking is of prime importance in today’s traffic cluttered cities. They detect objects (sense other automobiles or car park curbs) from the bumper and assist in proper parking. They are especially useful in automatic parking systems installed on automobiles. This type of sensors used in automobiles is ultrasonic sensor. Ultrasonic, by definition is just sound but at a higher than audible frequency and thus ultrasonic cannot be heard by the human ear.
Another consumer related usage of the proximity sensor is in a smartphone whereby it is used to detect proximity to ear while calling and enables the phone to negate any touch by any part of the ear of the smartphone touchscreen.
Furthermore, another sensor usage directly affecting the safety of airline passengers is in the ground proximity warning systems that are extremely important for the aviation industry. They enable aircraft to dodge protruding peaks and cliffs of hills or mountains near to the airport or when they are flying at a low altitude.
As mentioned earlier, over a dozen types of proximity sensors are available, each using a different type of technology. Sensors of various nominal ranges are available in different shapes and sizes depending on their applications. Proximity sensors comprise six main groups, according to principles of operation: optical, capacitive, resistive, magnetic, ultrasound, and air pressure. Each of these sensors can measure numerous physical properties and are extensively used in various applications including robotics.
Proximity sensors have great application in Space Robotics as well. Robust collision avoidance control is not just for automobiles and the aviation industry, it is an indispensable field of study for space robotics industry as well. Sensors and sensor technologies are selected after evaluating them individually against the requirements of these space based rugged applications. In space sciences, the selection of proximity sensors for manipulator collision avoidance during space applications is of prime concern. Usually, the important factors involved in proximity sensing in this field are: intensity of reflection (photoelectric sensor technology used to detect and monitor objects and predict / prevent collisions), triangulation (optical sensing technique ideally suited for soft objects which can otherwise be damaged by probes), time of flight sensing (ToF: provides accurate distance measurement even if target has high reflectance), capacitance and inductance etc.
Future of Proximity sensors
Proximity sensing is the next inevitable step in the future of portable, consumer, industrial, and medical electronics. Multiple sensors would be utilized simultaneously to increase the performance of consumer devices to predict how users want to use them and to provide for the desired intuitive user experience. Capacitive proximity sensing can also be used continuously to provide approach-to-wake functionality (as in smartphones or tablets). This would, of course, eliminate the need for mechanical buttons.
In this fast pace world of today, the graph depicting the uses of proximity sensors can only go one way. With the development of robotics, the use of proximity sensors in robots would enable the intelligent machines to maneuver their way through objects and avoid or target the ones in proximity to them. Driverless cars would be using these sensors to navigate through traffic in order to reach their destination. Thus, the future is bright for these sensors regardless of whichever technology they employ. Similarly, their use in space applications and collision avoidance system will be both mandatory and extensive. Proximity sensors would always be a part of any closed loop object detection and control system in the future, regardless of the technology used. Their advancement and further refinement would ensure a safer, more secure environment for human endeavor in all spheres of life, and they will prove to be very valuable and indispensable companions for decades to come.