FIELD OF INVENTION
The present invention relates to an angular position sensor device comprising: variable aperture to pass light. Angle position sensors are used for converting angular position to a voltage signal so that the information can used to know the position of a rotating member.
BACKGROUND OF PRESENT INVENTION
Common sensors for angular position include variable resistors (potentiometers) encoders, sensors based on non contact sensors viz. Hall effect sensors etc. Whilst, potentiometers have mechanical contacts and have limited life. Encoders are expensive. The current invention addresses a solution for a reliable solid-state sensing of angular position since is non contact.
PRIOR ART
There are many sensors in the market and few of patented. But all them have there own advantages and disadvantages. Most relevant patent application is listed below.
US Patent Number: 5,671,043 Title: "Optical position detector for determining the angular position of a rotatable element" by Cambridge Technology, Inc. This document provides an angle detection method and system for a rotating member. This document has a light emitting source and a photo sensitive device to help in determining the angle of rotation. Even in instant invention uses same apparatus to determine the angle of rotating element. But the different lies in that, this patent uses two light sources and 4 light detectors to perform the task when compare to just one light source and on light detector in instant invention. In addition this makes this patent more expensive and complex compare to instant invention which is far simple in its construction. Furthermore, no were in this patent there is a mention of an aperture with a variable opening.
US Patent Number: 5,523,561 Title: "Enhanced position signals in optical torque sensors" by Lucas Industries Public Limited Company.

This document provides an angle detection method and system for a rotating member. This document has a light emitting source and a photo sensitive device to help in determining the angle of rotation. Even instant invention uses same apparatus to determine the angle of rotating element. But the different lies in that, patent uses more than one light source and 2 light detectors to perform the task when compare to just one light source and on light detector in instant invention. In addition this makes this patent more expensive and complex compare to instant invention which is far simple in its construction. Further the mask used in the construction is completely different from what is been used in instant invention. Furthermore, no were in patent there is a mention of an aperture with a variable opening.
US Patent Number: 5,076,249, Title: "Angular position detector apparatus" by Mitsubishi Denki Kabushiki Kaisha.
This document provides an angle detection method and system for a rotating member. This document has a light emitting source and a photo sensitive device to help in determining the angle of rotation. Even instant invention uses same apparatus to determine the angle of rotating element. But the different lies in that, this patent uses two light source and 2 light detectors to perform the task when compare to just one light source and on light detector in instant invention. In addition this makes this patent more expensive and complex compare to instant invention which is far simple in its construction. Further the mask used in the construction is completely different from what is been used in instant invention. Furthermore, no were in this patent there is a mention of an aperture with a variable opening.
A few other Patents in the area of instant invention are given below. But, none of them disclose the instant invention.
1. US Patent 4,851,749 Title: "Automatic positioner with nonlinear drive" by General Dynamics Corp., Pomona Div.

2. US 6,868,392 Title: "System and method for electronic shopping using an interactive shopping agent by Fujitsu Limited.
3. http://www.freepatentsonline.com/5844673.html
4. W09954688; and
5. DE10143662.
OBJECTS OF INVENTION
The primary objective of the invention is to develop an angular position sensor device.
Another objective of the invention is to develop an angular position sensor device
comprising: variable aperture to pass light.
Another objective of the instant invention is to develop a method for determining angular
position.
Still another objective of the present invention is passing light through variable aperture,
Still another objective of the present invention is detecting the light by photo-detector(s)
and determining the angular position using the detected light.
Yet another objective of the present invention is to develop a system to determine angular
position comprising: an angular position sensor having variable aperture to pass light.
STATEMENT OF INVENTION
The present invention is related to an angular position sensor device comprising: variable aperture to pass light; a method for determining angular position comprising steps of: passing light through variable aperture, detecting the light by photo-detector(s) and determining the angular position using the detected light; and a system to determine angular position comprising: an angular position sensor having variable aperture to pass light.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Figure 1(a) shows side view of angular position sensor with variable aperture, slit and
shaft.
Figure 1(b) shows front view of angular position sensor

Figure 2 shows photo-transistor sensor circuit.
Figure 3 shows angular position sensor performance graph
DETAILED DESCRIPTION OF THE INVENTION
The primary embodiment of the invention is an angular position sensor device comprising: variable aperture to pass light.
In yet another embodiment of the present invention the aperture has a variable opening with respect to the angular position.
In still another embodiment of the present invention it has at least one light source. In still another embodiment of the present invention the light source is LED.
In still another embodiment of the present invention it has at least one photo-detector to detect the light.
In still another embodiment of the present invention the photo-detector is phototransistor.
In still another embodiment of the present invention position of slit is in alignment with that of the photo-detector for passing the light through said slit.
In still another embodiment of the present invention position of the light source is in alignment with that of said photo-detector.
In still another embodiment of the present invention the aperture is fixed to rotating shaft.
In still another embodiment of the present invention size of the opening varies as the shaft rotates.

Another main embodiment of the present invention is a method for determining angular position comprising steps of: passing light through variable aperture, detecting the light by photo-detector(s) and determining the angular position using the detected light.
In yet another embodiment of the present invention is fixing the variable aperture to a rotating shaft.
In still another embodiment of the present invention the detected light varies as the shaft rotates.
Another main embodiment of the present invention is a system to determine angular position comprising: an angular position sensor having variable aperture to pass light.
In yet another embodiment of the present invention is means to determine angular position using the light.
In still another embodiment of the present invention the aperture has a variable opening with respect to the angular position.
In still another embodiment of the present invention it as least one light source to emit light.
In still another embodiment of the present invention the light source is LED.
In still another embodiment of the present invention is at least one photo-detector to detect the light.
In still another embodiment of the present invention the photo-detector is phototransistor.
In still another embodiment of the present invention position of slit is in alignment with that of the photo-detector for passing the light through said slit.

In still another embodiment of the present invention position of the light source is in alignment with that of said photo-detector.
In still another embodiment of the present invention the aperture is fixed to rotating shaft.
In still another embodiment of the present invention size of the opening varies as the shaft rotates.
In still another embodiment of the present invention a circuit determines the angle depending on the amount of light falling on said photo-detector.
Angle position sensors are used for converting angular position to a voltage signal so that the information can used to know the position of a rotating member. Common sensors include variable resistors (potentiometers) encoders etc.
Whilst, potentiometers have mechanical contacts and have limited life. Encoders are expensive.
The current invention addresses a solution for a reliable solid-state sensing of angular position.
The sensor consists of a LED (Light emitting diode) (8), a Photo transistor (5), a slit (7) and a variable aperture disk (6) fitted into a rotating shaft (9). The shaft is suitably attached to the rotating member whose angular position needs to be sensed. The arrangement housed in a sealed enclosure as shown in Fig-1(a) and Fig- 1(b) were it also has Housing (Bottom) [1], Housing (Top) [2], P.C. Board Assembly [3] and Connector [4]. The aperture disk (6) has variable opening (10).
The LED (8) is lit using a power source and the light passes through the slit (7) & aperture of aperture disk (6) and falls on to the Phototransistor (5). The amount of light

falling on to the transistor depends on the angular position of the aperture disk (6) with respect to the slit (7) as the aperture disk has a variable opening (10) with respect to angle.
The output voltage of figure 2 depends on the amount of light falling onto the photo transistor PT which in turn depend on the angular position of the aperture and hence the output voltage correspond to the angular position of the shaft. The output voltage can be measured using the circuit as shown in Fig - 2 wherein Dl is LED and Rl &R2 are resistors.
The shaft is connected by suitable means to the member whose angular position need to be measured. As the shaft is made to rotate, the voltage VCE changes which can be detected by suitable circuit for indication / control purposes. The output voltage vs angle performance as measured using the setup is given in Fig -3.