Annular photodiode for use in an optical rotary encoder

• US 5,428,217 A
• Filed: 10/04/1993
• Issued: 06/27/1995
• Est. Priority Date: 11/27/1992
• Status: Expired due to Term

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Nakajima, Hajime, Shikai, Masahiro
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): NICHOLS, STEVEN
• Application Number:
  US08/130,874
• Time in Patent Office: 631 Days
• Field of Search: 250/214.1, 250/214 PR, 250/338.4, 250/370.01, 250/370.08, 250/370.11, 250/332, 250/231.13, 257/465
• US Class Current: 250/214.1
• CPC Class Codes: G01D 5/38 by diffraction gratings

Abstract

The present invention relates to an optical rotary encoder for detecting a position optically. In the optical rotary encoder of the invention, a light beam reflected by a half mirror enters a deflector, whereby it is reflected while being deflected in a certain direction. The reflected light beam again enters the half mirror. Transmitted light from the half mirror enters a position detector, in which a light spot is formed on an annular photodiode. The path of the reflected light from the deflector forms a cone having a vertical angle which is twice the angle of deflection of the deflector. The position detector is disposed perpendicularly to the optical axis of the reflected light in the case of the deflection angle being 0° and with the center of the annular photodiode made coincident with the said optical axis. A suitable distance between the deflector and the photodiode is selected so that a light spot is radiated onto the photodiode. The position of the light spot formed on the annular photodiode is in a corresponding relation to a rotational angle of a rotating shaft. The position detector detects the position of the light spot to detect such rotational angle.

Claims

1. A position detector comprising:

a flat plate-like photodiode formed in the shape of a ring;

a resistor disposed along the outer periphery of said photodiode and concentrically with the photodiode;

at least two output electrodes attached to said resistor at equal angular intervals; and

fine narrow electrically conductive layers projecting from said resistor onto said photodiode radially at equal angular intervals so as to subdivide the angular spacing between adjacent said output electrodes, said electrically conductive layers being provided in a larger number than said output electrodes.

2. A position detecting method for detecting the position of a light spot incident on a flat plate-like photodiode formed in the shape of a ring, using a position detector comprising said photodiode, a resistor disposed concentrically along the outer periphery of said photodiode, output electrodes attached to said resistor at equal angular intervals, said output electrodes being provided in a number corresponding to a multiple of 4, and a plurality of fine narrow electrically conductive layers projecting from said resistor radially at equal angular intervals onto said photodiode, said method comprising the steps of:

selecting a pair of opposed output electrodes and a pair of output electrodes opposed to said paired output electrodes at an angle of 90 degrees, from among said output electrodes of said position detector;

measuring an electric current value based on the incidence of said light spot in each of the selected output electrodes;

dividing a difference between the measured current values in each said pair of output electrodes by the sum of both current values; and

detecting an incident position of said light spot on the basis of the resulting two quotients.

3. A position detecting method for detecting the position of a light spot incident on a flat plate-like photodiode formed in the shape of a ring, using a position detector comprising said photodiode, a resistor disposed concentrically along the outer periphery of said photodiode, output electrodes attached to said resistor at equal angular intervals, said output electrodes being provided in a number corresponding to a multiple of 4 and not less than 8, and a plurality of fine narrow electrically conductive layers projecting from said resistor radially at equal angular intervals onto said photodiode, said method comprising the steps of:

selecting a pair of opposed output electrodes and a pair of output electrodes opposed to said paired output electrodes at an angle of 90 degrees, from among said output electrodes of said position detector;

measuring an electric current value based on the incidence of said light spot in each of the selected output electrodes;

dividing a difference between the measured current values in each said pair of output electrodes by the sum of both current values;

determining a rough incident position of said light spot on the basis of the resulting two quotients;

then, with respect to one of said output electrodes closest to said rough position, selecting a pair of said output electrodes disposed on both sides of said closest output electrode;

measuring an electric current value based on the incidence of said light spot in each of said selected output electrodes;

dividing a difference between the measured current values in said selected output electrodes by the sum of both current values; and

detecting an incident position of said light spot on the basis of the resulting quotient.

4. An optical rotary encoder comprising:

a rotary member for deflecting light emitted from a light source and forming a light spot which moves on an annular path in correspondence to a rotational angle of said rotary member;

a position detector disposed so that the light spot formed by said rotary member moves on a flat plate-like photodiode formed in the shape of a ring, said position detector comprising said photodiode, a resistor disposed concentrically along the outer periphery of said photodiode, output electrodes attached to said resistor at equal angular intervals, said output electrodes being provided in a number corresponding to a multiple of 4, and a plurality of fine narrow electrically conductive layers projecting from said resistor onto said photodiode radially at equal angular intervals; and

a position detecting means which selects two pairs of output electrodes opposed to each other at an angle of 90 degrees from among the output electrodes of said position detector, measures an electric current value generated in each of the selected output electrodes upon incidence of the light spot on said photodiode and detects an incident position of the light spot on the basis of the measured values.