1. Field of the Invention
The present invention is generally related to a photoelectric sensor that senses the light passing through a movable aperture and, more particularly, to a light sensor which has a light sensitive area that is shaped to provide a generally linear output even though the intensity of light impinging on the light sensor can vary as a function of the position of a movable object in which an aperture is formed.
2. Description of the Prior Art
Many different types of light sensors are known to those skilled in the art. One type of known photoelectric sensor incorporates a light source, a pair of light sensors and a movable object that comprises an aperture formed therethrough. The plane of the movable object is generally parallel to the plane in which the two light sensors are disposed. The total power of the light impinging on each of the light sensors is restricted to the light which passes through the aperture formed in the movable object. A light sensor of this type can be incorporated in a switch of which the plunger is attached to the movable object. The light impinging on the two light sensors can be compared to determine the precise position of the movable object.
A problem that exists in light sensors such as that described immediately above is that the position of the movable object and its aperture changes the intensity of light passing through the aperture and impinging on the light sensors. If the output signal of one light sensor is subtracted from the output signal of the other light sensor, a decrease in the light intensity passing through the aperture can adversely affect the linearity and accuracy of the device. Since, in normal operation, movement of the movable object causes the lighted portion of one light sensor to be larger than the lighted portion of the other light sensor, and the light intensity impinging on the light sensors is decreased, the algebraic difference between the two output signals can be nonlinear. It would therefore be significantly beneficial if a light sensor of this general type could be improved in a way which increases the linearity of an output signal that is formed by subtracting the output signal of one light sensor from the output signal of the other light sensor. Although devices such as these described above can compare the two light sensor signals from each other, it should be clearly understood that other means of signal comparison are also possible. For example, a ratio of the two light sensor signals can be used to compare their relative magnitudes.