Linear position sensors are also referred to as encoders, transducers or redheads. The alternative type is a relative sensor and provides 360 degree measurements. Position sensing is the process of monitoring the movement of a component and providing an analog or digital signal to a motion controller. A patent application for the device was first filed in 1996 by Nartron Corporation. The inventors responsible are Ko, Munch, Shank and Strom. Since that time, many uses have been found for the device.
Any industry that relies on the precise position of an object, including scientific, industrial or military projects, make use of these devices. More specifically, they are commonly used in scanners, calipers and high precision machining tools, like robotics.
The types of sensors or encoders include optical, magnetic and other, more complex types. Optical linear encoders are primarily used in products with high resolution and shuttering. The light sources used include infrared and visible LEDs, miniature light-bulbs and laser diodes, also called injection laser diodes. Magnetic linear encoders use either magnetic or passive scales. They do not produce the minute scales of optical encoders, and are used in industries that do not require extreme detail. They work by monitoring the movement of a nearby magnet or series of magnets.
Such delicate instrumentation requires the encoder to be enclosed if it is to be used in dirty or dangerous environments like in a tool shop. Excessive dust, dirt or rough handling can affect their accuracy. This type of encoder is called enclosed because it is contained within a protective housing. Open instruments provide better accuracy but must be used in a safe, clean environment where it is less likely to be damaged.
The type of scale used depends on what is being monitored. It is typically glass, for use in scanners, or reflective scales. Scale materials include chrome, metal, ceramics and plastics. It can be self supporting, glued to the substrate or mounted on a track.
If space is a problem, sensors are available in very small sizes and can provide resolutions of less than . 001 mm. The accuracy is perfect for highly precise applications. If the project undertaken involves large products, the size of the measuring device is larger.
There are a many types of position sensors. For example, capacitive type, which is a non-contact method of measurement, providing extremely accurate electrical sensing technology. Hall effect transducers change their output voltage in response to changes in the magnetic field. They are applicable for proximity switching, positioning and speed detection.
Inductive sensors are non-contact and can measure the change in the effective resistance of a coil. It does not require physical contact between the device providing the signal and the sensing element. Ultrasonic systems act as transmitters or receivers and transform electrical energy into acoustic energy. It works through air or water.
The configuration used depends on what is to be measured. If extended position sensing is required, multiple bridges are lined nest to a magnet that slides past them. Linear position sensors have aided in the development of many technologically advanced devices.
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