Proximity sensing usually means detecting:
a, the presence or absence of an object.
b, The size or simple shape of the object.
Proximity sensors can be further classified in operation as contact or non-contact, and analog or digital. The choice of sensor depends on physical, environmental and control conditions. These include:
Mechanical:
Any suitable mechanical/electrical switch can be used, but micro-switches are usually used because of the force required to operate mechanical switches.
Pneumatic:
These proximity sensors work by disrupting or disturbing airflow. Pneumatic proximity sensors are examples of contact sensors. However, they cannot be used on lightweight parts that may be blown away.
Optical:
In their simplest form, optical proximity sensors fall by disconnecting a light beam that falls on a photosensitive device such as a photocell. These are examples of non-contact sensors.
It is important to note that extra care must be taken with the lighting environment of these sensors; for example, optical sensors may be obscured by flashes of light from the arc welding process, airborne dust and smoke clouds may impede light transmission, etc.
Electrical:
Electrical proximity sensors can be either contact or non-contact. Simple contact sensors operate by making the sensor and components form a complete circuit. Non-contact electrical proximity sensors rely on the inductive principle to detect metals or on capacitance to detect non-metals.
Range Sensing:
Range sensing involves detecting how close or far the component is from the sensing location, although they can also be used as proximity sensors. Distance or proximity sensors use non-contact analog technology. Capacitive, inductive and magnetic technologies are used to sense short distances between a few millimeters and several hundred millimeters. Longer range sensing is performed using various types of emitted energy waves (e.g., radio waves, sound waves, and lasers).
Force Sensing
There are six types of forces that may need to be sensed. In each case, the force applied can be static (at rest) or dynamic. Force is vectorial in the sense that it must be specified both in magnitude and direction. Therefore, force sensors operate analogically and are sensitive to the direction in which they act. The six forces are:
①, tensile force
②, compression force
③, shear force
④, torsion force
⑤, bending force
⑥,Friction force
A variety of techniques exist for sensing forces, some direct and some indirect.
Tensile force:
They can be determined by strain gauges, which show a change in their resistance as the length increases. The change in resistance measured by these gauges can be converted into a force and hence are indirect devices.
Pressure:
Can be determined by devices called load cells, which can be loaded "by detecting a change in cell size under a compressive load, or by detecting an increase in pressure within the cell under a load, or by operating with a change in resistance under a compressive load."
Torsional force:
Can be viewed as a combination of tensile and compressive forces, so a combination of the above techniques can be used.
Friction forces:
These relate to situations where motion is to be restricted and therefore "friction is detected indirectly by using a combination of force and motion sensors. Example:
Haptic Sensing
Haptic sensing refers to sensing by touch. The simplest type of tactile sensor uses arrays of simple touch sensors arranged in rows and columns, these are often called matrix sensors.
Each individual sensor is activated when it comes into contact with an object. By detecting which sensors are active (digital) or the size of the output signal (analog), an imprint of the component can be determined. The imprint is then compared to previously stored imprint information to determine the size or shape of the component.
Mechanical, optical and electronic tactile sensors have been implemented.
Thermal Sensing
Thermal sensing may be required as part of process control or as a means of safety control. There are a variety of methods available and the choice of these methods depends largely on the temperature to be detected.
Some common methods are: bimetal strips, thermocouples, resistance thermometers or thermistors. For more complex systems involving low level heat sources, infrared cameras may be used.
Acoustic sensing (hearing)
Acoustic sensors can detect and sometimes distinguish between different sounds. They can be used for speech recognition to give verbal commands or to recognize unusual sounds, such as explosions. The most common type of acoustic sensor is a microphone.
The obvious problem with acoustic sensors in an industrial environment is the large amount of background noise.
Of course, it is possible to simply tune acoustic sensors to respond only to certain frequencies, thus allowing them to distinguish between different noises.
Gas sensing (odor)
Gas or smoke sensors that are sensitive to specific gases rely on a chemical change in the material contained in the sensor, which either creates a physical expansion or generates enough heat to trigger a switching device.
Robotvision (sight)
Vision is probably the most active area of current research in robotic sensory feedback.
Robot vision involves capturing an image in real time with some sort of camera and converting that image into a form that can be analyzed by a computer system. This conversion usually means converting the image into a digital field that can be understood by the computer. The entire process of image capture, digitization, and data analysis should be fast enough to allow the robotic system to respond to the analyzed image and take appropriate action during the execution of the task set.
The refinement of robot vision will allow the full potential of artificial intelligence to be realized in industrial robots. Its uses include detecting presence, position and movement, recognizing and identifying different components, styles and features.
However, even the simplest vision techniques require large amounts of computer memory and can take considerable processing time.