KR19980033766A - Optical encoder and coded optical signal reading method - Google Patents

Abstract

A method of reading an encoded optical signal comprises the steps of: i) driving a light source for calculating a light beam; ii) focusing the light beam derived from the light source using a lens to the receiving surface of the crystal of the phototransistor; And iii) cutting out the light energy from the light beam exceeding the rated operating voltage of the phototransistor, and ignoring the potential of the light beam below a predetermined threshold level in the determination to obtain a waveform substantially equal to the square wave.

Description

Optical encoder and method of reading encoded optical signal

1 is a circuit block diagram of an encoded optical signal reading apparatus according to the prior art.

FIG. 2 is a plan view showing the positions of the optical transistor crystals of the optical encoder of the apparatus for reading the encoded optical signal shown in FIG.

3 is a schematic diagram showing one state of light beam projection onto a light receiving surface of a phototransistor crystal according to the prior art

Figure 4 is a curve showing the output waveform of the phototransistor according to the prior art

5 is a schematic diagram showing another state of light beam projection onto the light receiving surface of the phototransistor crystal according to the prior art.

6 is a curve showing another output waveform of the phototransistor according to the prior art.

7 is a curve showing waveforms obtained from two crystals of an optical transistor of an optical encoder of a device for reading an encoded signal according to the prior art.

8 is a circuit block diagram of an optical encoder according to the present invention.

9 shows a light beam projected onto the crystal of the phototransistor of the optical encoder according to the invention.

10 is a schematic view showing a light beam projected onto a crystal through a lens according to the present invention

11 is a view showing one state of light beam projection onto one light receiving surface of the optical transistor of the optical encoder according to the present invention.

12 is a waveform diagram obtained from FIG.

13 is a waveform diagram showing the difference between waveforms obtained from an optical encoder with a lens and an optical encoder without a lens according to the present invention.

14 is a schematic diagram showing the projection of light rays through a lens of a phototransistor of an optical encoder according to the invention onto one crystal;

15 shows another state of projection of a light beam onto one light receiving surface of an optical transistor of the optical encoder according to the present invention.

FIG. 16 is a waveform diagram obtained from FIG. 15

17 is a waveform diagram showing two other waveforms obtained from an optical encoder with a lens and an optical encoder without a lens according to the present invention.

18 is a waveform diagram showing one waveform of an output signal of the optical encoder according to the present invention, and

19 is a waveform diagram showing another waveform of an output signal of the optical encoder according to the present invention.

* Description of the symbols for the main parts of the drawings *

1: light source 2: wheel

3: first lens 4: second lens

80: light encoder 81: light source

82: wheel 83: phototransistor

84: potential circuit 90: judgment circuit

831, 831 ': phototransistor crystal

The present invention uses a lens that focuses a light beam passing from the light source through the wheel to the light receiving surface of the phototransistor crystal, chops off the light energy from the light beam exceeding the rated operating voltage of the phototransistor. And a method of reading the encoded optical signal by ignoring the potential of the light beam that is below a predetermined threshold level in the determination.

1 and 2 show an apparatus for reading an encoded optical signal according to the prior art, which includes an optical encoder 80 and a determination circuit 90. The optical encoder 80 includes a light source 81, a wheel 82 (transparent or grating), an optical transistor 83, and a potential circuit 84. Light originating from the light source 81 is projected through the wheel 82 to the light receiving surface of the crystal 831 or 831 'of the phototransistor 83, and causes the phototransistor 83 to correspond to the optical signal. To increase the potential at the same time. The obtained potential signal is transmitted to the judging circuit 90 through the potential circuit 84, so that the judging circuit 90 can read the output signal of the optical encoder 80. The change of the light beam encountering the phototransistor 83 is measured when the width of the light beam is smaller than the width of the crystals (FIGS. 3 and 4), where C and D are the widths of the light beams, and A and B are The width of the crystal, T1 ~ T4 is the time the light beam travels. When the light beam encounters the crystal's receiving surface, the following changes occur:

1. When the width D of the light beam moves to T1, it is projected to 1/2 of the width A of the light beam, and the potential energy of the light beam rises from 0 volts a1 to level a2:

2. When the width D of the light beam moves to T2, the light beam is projected over the entire surface of the width A, and the potential energy of the light beam rises from level a2 to level a3:

3. When the width D of the light beam moves to T3, the light beam is projected on one half of the width A, and the potential energy of the light beam drops from level a3 to level a4:

4. When the width D of the light beam moves to T4, the light beam is prohibited from being projected to the width A, and the potential of the light beam drops from level a4 to level a5. Drawing the line connecting all points a1-a5 to each other, the curve shown in FIG. 4 is obtained. If the width D of the light beam is the width A of the crystal and the width C of the light beam is the width B of the crystal, the potential points a1 to a5 do not change.

On the contrary, if the width C of the light beam is the width B of the crystal, the positions of a2, a3 and a4 relatively change on the time axis, the positions of a1 and a5 do not change on the time axis, and the waveform shown in FIG. 6 is obtained.

As noted above, in order to obtain the same waveform from the two crystals 831 and 831 'of the phototransistor 83, the sizes of the crystals 831 and 831' must be equal. As shown in Fig. 7, the phases of the crystals are staggered so that the desired waveform is obtained.

However, the already mentioned structure of the encoded optical signal reading device is not satisfactory in function. Due to manufacturing tolerances, a small difference in the size between the crystals of the phototransistor 83 is unavoidable. This difference makes the cycle and magnitude of the output signal of the phototransistor 83 unstable (because the magnitude of the output signal of the phototransistor 83 is directly proportional to the area of the receiving surface of the crystal). Therefore, the decision circuit 90 may make a wrong decision. To eliminate this problem, the optical encoder 80 must be adjusted through a series of tests. However, this complex test significantly increases the manufacturing cost of the optical encoder 80. Furthermore, the structure of the optical encoder 80 requires a large installation space.

The present invention is accomplished by providing an optical encoder suitable for the encoded optical signal reading method and such a method for eliminating the above-mentioned problem. A method of reading an encoded optical signal according to the present invention comprises the steps of: i) driving a light source for calculating a light beam, ii) focusing a light beam derived from the light source using a lens to a receiving surface of a crystal of an optical transistor, and iii) cutting off the light energy from the light beam that exceeds the rated operating voltage of the phototransistor, and ignoring the potential of the light beam below a predetermined threshold level in the judgment to obtain a waveform substantially equivalent to the square wave. Encoders suitable for the method of reading such encoded optical signals include a lens installed in the optical transistor between the wheel and the light receiving surface of the corresponding crystal to cut out the energy of the light beam exceeding the rated operating voltage of the phototransistor and to a predetermined threshold level. By ignoring the following potential of the light beam in the judgment, a square wave digital signal can be obtained.

With reference to FIG. 8, an optical encoder according to the invention generally comprises a light source 1, a wheel 2, a first lens 3, a second lens 3 ′, and a phototransistor 4. have. The lenses 3, 3 ′ are arranged between the wheel 3 and the phototransistor 4 and are inherently enclosed with the phototransistor by the light shielding material.

The circle 2 may be a transparent or lattice wheel. The lenses 3 and 3 'may be plano-convex lenses or biconvex lenses.

9 and 10 and 8 again, the wheel 2 encodes the light originating from the light source 1 into a uniform cycle of light beam, and converts the encoded light beam signal into a light beam signal. The lenses 3 and 3 'are output to the phototransistor 4 while allowing the light to be focused on the light receiving surfaces of the crystals 41 and 41' of the phototransistor 4.

11 and 12, at time T1, the light beam energy rapidly rises from 0 volt a1 to point a2 (critical level), and immediately rises to the rated operating voltage. At time T2 the light beam energy reaches the highest point a3. At time T3 the light beam energy drops rapidly to point a4, and at time T4 the light beam energy drops from point a4 to the zero volt level a5.

FIG. 13 is a waveform comparison table showing the difference between the waveform H1 obtained from the optical encoder with a lens and the waveform H2 obtained from the optical encoder without a lens. As shown, when the light beam width C is smaller than the light beam width B, the potential of the light beam may increase rapidly, but the amount of light beam energy received by the crystal does not change, and the diagonal area at H1 is equal to the diagonal area at H2.

The figures of FIGS. 14-16 show the change in the projection of the light beam to the crystal, which is focused on the crystal within the light beam width B when the light beam width C crystal width B. FIG. The change is as follows:

1. Before moving to time T1, the light beam energy is concentrated and rises to a2 above the rated operating voltage;

2. When time T2, light beam energy reaches up to peak a3;

3. At time T3, the light beam energy is maintained at a4 above the rated operating voltage;

4. Moving to the time T4, the light beam energy drops rapidly below the threshold level and drops to the zero voltage level at the point a5 when the time T4 is reached.

FIG. 17 is a waveform diagram showing two other waveforms obtained from an optical encoder with a lens and an optical encoder without a lens according to the present invention, in which the diagonal area is the sum of the light beam energies output when the lens is installed. ; The diagonal area in H4 is the sum of the light beam energies output when no lens is installed. As pointed out, when the lens is installed, the light beam energy can be increased relatively.

18 and 19, light beam energy above the operating voltage and light beam energy below the threshold level are excluded from the judgment, and a signal almost the same as a square wave is obtained for reading.

It is to be understood that the drawings are designed for illustrative purposes only and are not intended to limit or define the scope of the invention.

Claims (4)

A method of reading an encoded optical signal, i) driving a light source for producing a light beam; ii) focusing the light beam derived from the light source using a lens to the receiving surface of the crystal of the phototransistor; And iii) cutting the light energy from the light beam exceeding the rated operating voltage of the phototransistor, and ignoring the potential of the light beam below a predetermined threshold level in the judgment to obtain a waveform substantially equal to the square wave. Signal reading method An optical encoder for reading an encoded optical signal, A light source suitable for producing a light beam; A wheel suitable for encoding the light beam of the light source and outputting a corresponding light beam signal in uniform cycles; A lens mounted to the wheel, the lens adapted to focus the light beam signal obtained from the light source through the wheel; And An optical transistor suitable for receiving the light beam from the lens, increasing the potential of the light beam signal, causing light above the rated operating voltage of the phototransistor to be cut out of the light beam and for potential below a predetermined threshold level to be ignored in the determination; And an optical encoder for reading the encoded optical signal. The method of claim 2, And the lens is a flat iron lens. The method of claim 2, And said lens is a convex lens on both sides.