Ultra-accurate position sensor

Illuminating an optical matrix by a collimated light beam

The next step in position sensor technology

Position sensors are used in all kind of movable equipment to facilitate a measurement of a mechanical position. 

From the simplest type as limit switches and potentiometers that represent contact position sensors, manufacturers have employed a much wider variety of approaches and technologies to develop non-contact position sensors. Those sensors does not wear out because of no physical contact.

Modern position sensors today consist of optical and magnetic encoders as well as magneto resistive sensors (AMR)

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Today’s positional sensors are pretty accurate, but some types are large in size.

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Use of Collimated light and an Optical matrix as a positional sensor. 

By directing a micron sized light beam from a collimator to an optical matrix, the positional relationship between the collimator and the optical matrix can be decided.

Pinhole elements are available down to 1µm and can efficiently utilize todays micron size optical pixels and both the high numbers of pixels on modern matrices and the accuracy each pixel can offer.  An ADC accuracy of 10 bit offers 1024 levels on each pixel, from no light to fully saturated.

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The solution can be used in a wide area of equipment where positional sensors are needed.

  • Robot technology

  • CNC machines

  • Joysticks

  • Computer roller balls

  • Inclinometers

  • Autonomous vehicles

A setup example with:
Image sensor – Samsung ISOCELL HMX (S5KHMX)   ADC accuracy 10-bit.  Collimator with light ray 1 µm in diameter.

                    

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By utilize a circular area with dia. = 9000 pixels on the image sensor for to detect a rotational movement.

9000x3,14=28260 pixels represented on the circle.

ADC = 10 bit = 1024 levels/pixel

28260 x 1024 = 28 938 240 measured positions

 

This equals an accuracy of ≈ 0,045 arc second as an absolute measurement.

 

This is more than 40 times better than the best rotational encoders on the market today and the accuracy can be improved by use of ADC with higher bit rate.                               

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A high-quality rotational encoder on the market today has a typical accuracy of ± 1 arc second. The size of the encoder could be 100mm in diameter.

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A setup example for a rotational encoder designed based on optical sensors and a collimated light ray:

Made by arranging optical sensors in a 100 mm circle with 1 µm sized optical sensors, ADC accuracy =10 bit. (1024)

 

This could give 321 536 000 measured positions.

This equals an accuracy of 0,0040 arc second, and as an absolute measurement.

This is 200-300 times better accuracy than encoders in use today.

Use of collimated light and optical sensor as linear position sensor.

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The light ray for this set up could be shaped as a slit to increase the tolerances for horizontal un-linearity.

 

The solution is also tolerant to variation in height between collimator and optical sensor.

 

Pinhole slit units are available products today.

 

By use of an optical sensor with 1 µm pixel size and ADC accuracy = 10 bit:

The accuracy could be 1 µm / 1024 ≈ 1 nm.

The measurement is absolute.

High resolution optical sensors are today small, and collimator housings with light source can also be small. The LED as the light source would be the larger component in a set up with collimator and sensor.


High resolution positional sensors with small dimensions could be made.

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A joystick may be equipped with collimator and an optical matrix.

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Benefits by use of collimated light ray and optical matrix:

  • Non-contact solution – high reliability

  •  High resolution

  •  100% repeatability

  • Tolerant to external magnetic fields, and so opens for to use magnets for centring joystick or use magnets for to incorporate a new and innovative type of force – feedback.