JPH0478931B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a photoelectric rotary encoder that detects rotational information such as the rotational speed and rotational direction of a rotating body using light-emitting/light-receiving elements.

<Prior art> Conventionally, as a device for detecting the speed and direction of a rotating body such as a motor, a rotating body with slits formed at a constant pitch is placed between a light emitting element and a light receiving element, and an optical path between these elements is established. A photoelectric rotary encoder has been developed that generates rotational information based on an optical signal detected by a light receiving element by rotating the rotating body so as to block the rotation.

FIG. 8 is a partially enlarged view of a conventional photoelectric rotary encoder, showing the relationship between the light receiving element and the slit formed in the rotating body as seen from the light emitting side. As shown in FIG. 8, four light-receiving elements Pd ₁ to Pd ₄ are provided in slits 11, .
The four light-receiving elements Pd ₁ to Pd ₄ are arranged at 1/4 pitch intervals in the direction in which the slits 11, .

When the rotating body 12 rotates in either direction,
When light passes through the slit 11 and is irradiated onto each of the light receiving elements Pd ₁ to Pd ₄ , these light receiving elements Pd ₁ to Pd ₄
are shifted by 1/4 pitch from each other, so the light receiving state for the incident light between them is also 1/4
For example, a phase difference of 90° occurs between the light receiving element Pd ₁ and the light receiving element Pd ₂ , and a phase difference of 180° occurs between the light receiving element Pd ₃ .

That is, conventionally, _four groups of light-receiving elements Pd ₁ to Pd for detecting light passing through the slit are arranged in the same direction as the arrangement direction of the slit 11, and each element Pd ₁ to Pd ₄ is arranged one at a time with respect to the pitch P of the slit 11. The positional relationship was shifted by /4 pitch, and the rotation information of the rotating body 12 was obtained by comparing the output signals between the elements.

<Problems to be Solved by the Invention> However, in the above-mentioned conventional structure, there are four light receiving elements Pd ₁ to _{Pd 4} in one pitch of the slit of the rotating body 12.
optical S/N.
Considering (the ratio when the value of the photocurrent when the optical path is not blocked by the object to be detected is defined as S and the value of the photocurrent when the optical path is blocked by the object to be detected is defined as N), 1
The limit for pitch was around 0.8mm. Moreover, when the arrangement of the light receiving elements Pd ₁ to Pd ₄ is set at a constant pitch,
In order to improve the resolution, it was necessary to increase the diameter of the rotating body 12.

Therefore, in the photoelectric rotary encoder having the above structure, it has been extremely difficult to achieve high resolution while at the same time reducing the size and cost.

The present invention was made in view of the above circumstances, and
The object of the present invention is to provide a photoelectric rotary encoder that has a simple structure, can achieve high resolution, and can also be made smaller and lower in price.

<Means for Solving the Problems> The present invention provides a photoelectric rotary encoder that detects rotational information by passing a rotating body in which a slit is formed between a light emitting element and a light receiving element that are arranged to face each other. , radial rotating body slits bored at a constant pitch in the rotational direction, and radial rotating body slits bored at the same pitch as the rotating body slits and angled with respect to the rotating body slits so as to form moire fringes with the rotating body slits. radial fixed slits arranged in the same direction, and a plurality of electrically independent light receiving elements that detect the light emitted from the light emitting element through both of these slits, and the light receiving elements are formed by overlapping the rotating body slits and the fixed slits. It is arranged so as to match the pitch of the moire fringes generated by the alignment, and is configured to read the movement of the moire fringes to form rotation information.

By the way, FIGS. 3 and 4 are diagrams showing the appearance of moiré fringes caused by the overlapping of the rotating body slit and the fixed slit.

FIG. 3 is an example of a combination of equally spaced slits and radial slits.

Usually, moiré fringes 4 appear as a group of lines connecting pairs of obtuse intersecting angles of two superimposed grids, but in reality, moiré fringes 4 are a collection of irregular quadrilaterals shown in the shaded area as shown in Figure 3. I can see it. As the spacing between the slits of this irregular quadrilateral becomes narrower, the area difference between the quadrilaterals adjacent to the left and right increases, and the shape also changes. When attempting to obtain a sufficient amount of light to detect rotational information, it is desirable to have a slit shape in which a plurality of quadrilaterals can be obtained in the horizontal direction.

FIG. 4 is an example of a combination of two radial slits having the same pitch.

In FIG. 4, the squares are distributed symmetrically about the perpendicular bisector of the line segment AB connecting the rotating slit center A and the stationary slit center B. Furthermore, the area difference and shape change between the left and right adjacent quadrilaterals are smaller than in the case of FIG. 3.

Therefore, in the present invention, the rotating body slit and the fixed slit are both radial slits, and are arranged at angles that are symmetrical to each other with respect to the arrangement direction of the light-receiving element group for reading Moiré fringes.

<Function> In the photoelectric rotary encoder of the present invention, rotation information is formed by reading moiré fringes generated by overlapping a rotating body slit and a fixed slit, and the bright and dark pitches of the moire fringes are determined by the rotational slit and the fixed slit. Since it can be enlarged arbitrarily by changing the inclination of the slit, the pitch of the light receiving element is no longer subject to the conventional restrictions on high resolution. Furthermore, the fixed slits and the rotating body slits are radially bored at the same pitch, and the plurality of light receiving elements for these slits are placed on the perpendicular bisector of the line connecting the center lines of the rotating body slits and the fixed slits. Since they are arranged in a line, the moiré fringes on the photodetectors have a substantially symmetrical shape on the perpendicular bisector, and accurate rotational information can be obtained by multiple photodetectors arranged in a line. .

With such a simple configuration, the photoelectric rotary encoder can achieve high resolution, detect accurate rotational information, and at the same time realize miniaturization and cost reduction.

<Example> Hereinafter, an example of the photoelectric rotary encoder according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a main part of an embodiment of the present invention, and FIG. 2 is a partially enlarged view of FIG. The positional relationship between the shaded area) and the light receiving element is shown.

The photoelectric rotary encoder according to the present invention includes:
As shown in FIGS. 1 and 2, a rotating body slit 1 with a constant pitch is bored in the rotating direction, a fixed slit 2 is arranged at an angle θ with respect to the rotating body slit 1, and a rotating body Each electrically independent light receiving element PD ₁ detects the emitted light from the light emitting element (not shown) through the slit 1 and the fixed slit 2.
~ PD ₄ , and the light receiving elements PD ₁ ~ _{PD 4} are equipped with moiré fringes 4 generated by overlapping the rotating body slit 1 and the fixed slit 2 in the direction that bisects the angle θ.
It is arranged so as to match the pitch W of.

In this embodiment, the rotating body slit 1 and the stationary slit 2 are both radial slits, and a combination of two radial slits as shown in FIG. 4 described above is used.

In FIG. 4, when the rotary slit 1 is rotated by the slit interval (1 pitch) ω with the center A of the rotating slit 1 as the rotation center, the hatched portion of the quadrilateral moves by its own length W (1 pitch of the moiré fringes). Rotation information can be generated by optically reading the movement of this quadrilateral.

_As clearly shown in FIG _{. 1} , this quadrilateral shape (moiré fringes)
and PD ₃ so that their areas are substantially the same. Even when the moire fringes move from the timing of the shape shown in FIG. 1, the moire fringes on each photodetector become substantially symmetrical in the longitudinal direction, and the multiple photodetectors PD ₁ lined up in a row become substantially symmetrical in the longitudinal direction.
Accurate rotation information can be obtained from PD4 to _PD4 .

Generally, as shown in Fig. 5, the moiré fringe period (actually, the length W of the longer diagonal of a quadrilateral) obtained when two slits 5 and 6 with the same period (period: ω) are superimposed is The relationship is W=ω/2sinθ/2, where θ is the inclination angle of the two slits 5 and 6. Here, the meaning of the relationship in the equation is that the moiré fringes 7 generated by overlapping the two equally spaced slits 5 and 6 are 1/2 sin θ/2 times the slit pitch ω, and the direction of movement of the moire fringes 7 is the same as that between the two slits 5 and 6. This means that it is on the bisector of the inclination angle of .

Using this relationship, determine the positional relationship between the rotating body slit 1 and the fixed slit 2 so that a quadrilateral (one of the dark or bright parts of the moiré fringes) can be arranged as shown in Figure 1. For the shape of 2, slits equally spaced (with the same pitch) as the rotating slit 1 may be used.

FIG. 6 is a diagram showing the relationship between the shape of the fixed slit 2 formed in the actual mask 8, the rotating body slit, and its center position.

In FIG. 6, the intersection of the X-X' axis and the Y-Y' axis is the center of the light receiving section (the center of the four photodiodes), and the center of the fixed slit 2 and the rotating body slit 1. Point A indicates the position of the rotation axis of the rotating body slit 1, and point B is the virtual center point of the fixed slit 2. Pitch of fixed slit 2 (deg)
Then, at the slit center, ω = 2πR / 360.If the inclination angle of rotating body slit 1 and fixed slit 2 at the center of the light receiving part (center of 4 photodiodes) is θ, then from the formula, W = 1/2 sin θ / 2 × 2πR / 360 Also, d=Rsinθ/2.

In the embodiment shown in FIG. 1, the photodetector PD ₁
~ PD ₄ is arranged to correspond to only one moiré (or one fixed slit),
As shown in Figure 7, a shape that spans multiple moirés (or multiple fixed slits), including the left and right ones,
It may be the size. The moire 4a at the center in FIG. 7 corresponds to the moire 4 in FIG.

With such a configuration, the light receiving elements PD ₁ to _{PD 4}
The positioning of the fixed slits 1,... with respect to the first
Since it does not require as high precision as the case shown in the figure, positioning is easy, and the output can be increased due to the large light-receiving area.

Incidentally, the present invention may employ an OPIC light-receiving element and have the circuit configuration shown in FIG. 9. For example, the 9th
The one shown has an infrared light emitting diode GP, four photodiodes PD ₁ to PD ₄ , and a signal processing circuit.
It consists of an OPIC light receiving element and a fixed mask 8 in which slits are formed at pitches for applying moire fringes. The applied OPIC light-receiving element includes a light-receiving section consisting of four photodiodes PD ₁ to _{PD 4} , an amplifier circuit that amplifies the optical signal detected by the light-receiving section, and a waveform shaping circuit that compares the amplified signal and converts it into a digital waveform. and an output circuit.

In the above configuration, each photodiode PD ₁ ~
The photocurrent output from PD ₄ is applied to each input terminal of operational amplifiers AMP.1 to AMP.4 of the signal processing circuit shown in Fig. 9 and is amplified.
The outputs V _A , V _B , V _A , V _B of AMP.1 to AMP.4 are
Outputs V _A and V _A and V _B and V _B , whose phases are inverted, are paired to form a comparator Comp.1, or
Cnmp.2, and the levels of each input signal are compared. In the comparator Comp.1, for example, the output V _A is compared with the output V _A as a reference signal, and the output V _A
A high level comparator output is derived when
A low level comparator output is derived when the output V _A becomes lower than the output V _A , and eventually V _A , V _A , V _B , V
Output V _OA (A output) and V _OB (B output) corresponding to _B
is formed, and two signals with a 90° phase difference are obtained. Rotation information of the rotating body can be obtained from these output signals V _OA and V _OB .

The photoelectric rotary encoder with the above structure has 1
By adopting an optical push-pull method with two photodiodes for output, it has a function to correct the decrease in the output of the light emitting diode due to temperature rise and the change over time of the light emitting diode.
In addition, by using an OPIC element, it is easy to reduce the size and weight. Furthermore, high resolution can be achieved by applying Moire fringes in combination with a rotating body having slits of the same pitch as the fixed mask.

<Effects of the Invention> As described above, according to the present invention, a light receiving element and a processing circuit, which are generally used in a photoelectric rotary encoder, are provided on the same semiconductor substrate.
By using OPIC (optical integrated circuit) elements,
In addition, the tilt angle θ in the above equation is designed to match the pitch of the moire fringes to the pitch of the OPIC photodetector, and the shape of the moire fringes on the photodetector is substantially symmetrical in the longitudinal direction. As a result, accurate rotation information can be obtained, and the encoder can be easily realized at the same time with higher resolution, smaller size, and lower cost.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the main part of an embodiment of the present invention, Fig. 2 is a partially enlarged view of Fig. 1, and Figs. FIG. 5 is a diagram showing the relationship between two slits with the same period and moire fringes, FIG. 6 is a diagram showing an example of the shape of a fixed slit, and FIG. 7 is a diagram showing the shape of a fixed slit. Figure 8 is a partially enlarged view of the conventional example; Figure 9 is a diagram showing the main parts of another embodiment;
The figure is a basic configuration diagram of an embodiment of the present invention. 1: Rotating body slit, 2: Fixed slit, PD ₁
~PD ₄ : Photodetector, 3: Rotating body, 4: Moire fringe.

Claims (1)

[Claims] 1. In a photoelectric rotary encoder that detects rotational information by passing a rotating body having a slit between a light-emitting element and a light-receiving element that are arranged opposite to each other, The radial rotating body slits are bored at the same pitch as the rotating body slits, and are arranged to intersect at an angle to the rotating body slits so as to form moire fringes with the rotating body slits. It comprises a radial fixed slit and a plurality of electrically independent light receiving elements that detect the emitted light from the light emitting element through both of these slits, and the plurality of light receiving elements are arranged at the center point of the radial rotating body slit. and arranged in a line on the perpendicular bisector of the line segment connecting the center points of the radial fixed slits so as to match the pitch of moire fringes generated by the superposition of the rotating body slits and the fixed slits. Features a photoelectric rotary encoder.