JPH02268227A - Encoder - Google Patents

Abstract

PURPOSE: To obtain an inexpensive encoder by eliminating the need of any tracking servo mechanism from the encoder by forming the pits of a scale board carrying a large number of pits on its surface as scale divisions longer in the direction perpendicular to the scanning direction of a laser spot. CONSTITUTION: A scale board 4 on the surface of which a large number of pits 5 are formed as scale divisions is irradiated with a laser spot 3 and reading signals of the pits 5 corresponding to the brightness of reflected light are obtained. The pits 5 are formed longer in the direction perpendicular to the scanning direction of the laser spot 3. Therefore, even when a read head is deviated from the scale board 4 in the direction perpendicular to the moving direction of the head, the pits 5 can be read surely, because the pits 5 can be surely irradiated with the spot 3. Therefore, an inexpensive encoder can be obtained, because no tracking servo mechanism is required.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical encoder, and particularly to a reflective encoder using a laser.

[Conventional technology]

Conventionally, as an optical rotary encoder, a large number of slits are formed as graduations on a circular scale plate attached to a rotating body, and the scale plate is irradiated with a parallel beam of light using a light emitting diode as a light source to transmit through the slits. There is a device that receives light using a light receiving element placed on a fixed side.

According to this low-resolution encoder, as the scale plate rotates, light transmission through the slits and light blocking between the slits are repeated, and a change in the amount of light is given to the light receiving element. signal is obtained,
The rotation angle of the rotating body was detected.

However, in the conventional low-resolution encoder, when the spacing between the slits is narrowed, the projected image of the slits becomes blurred due to the influence of light diffraction, making it difficult to achieve high resolution.

On the other hand, in recent years, laser disc technology has been provided as a technology for recording and reproducing sound and image information. In other words, when pit rows are formed spirally on a disc to record sound and image information, and a laser spot is irradiated onto the pit rows (tracks), light interference and diffraction occur between areas with and without pits. Since this causes variations in the strength of the reflected light, a method of reading it as a 0/1 signal is known.

According to this method, the density of pits can be increased, and high-density signals can be recorded.

Therefore, the inventor of the present invention came up with the idea of applying the laser disc technology to provide a high-resolution encoder.

However, as shown in Figure 6, the pit row is formed in a spiral shape on the disk (1), and each pit (2
) is formed vertically in the circumferential direction of the disk (1), so it is necessary to make the laser spot follow the pit row (track) with high precision, and for this purpose, a so-called tracking servo mechanism is indispensable. . therefore,
If the laser disk technology is directly applied to an encoder, a tracking servo mechanism must be provided in the read head, resulting in an expensive disadvantage.

[Problem to be solved by the invention]

The present invention has been made in view of the above-mentioned prior art, and aims to provide an inexpensive encoder that can obtain high resolution by applying the laser disk technology and does not require a tracking servo mechanism. .

[Means to solve the problem]

In order to solve the above problems, the present invention provides a scale plate on which a large number of pits are formed as graduations, and a reading head that irradiates the scale plate with a laser spot and obtains a read signal of the pits corresponding to the intensity of the reflected light. The configuration includes the following. Each of the pits is formed vertically in a direction perpendicular to the scanning direction of the laser spot due to the relative movement of the scale plate and the reading head.

The read head may be configured to irradiate a plurality of laser spots and obtain read signals of pits having mutually different phases.

[For production]

According to the present invention, one of the scale plate and the reading head is attached to the movable body and the other to the fixed side. The movable body may be one that rotates or one that moves linearly, and accordingly, the encoder according to the present invention can be configured as a rotary encoder or a linear encoder.

The present invention includes a scale plate on which a large number of pits are formed as graduations, and a reading head that irradiates a laser spot on the scale plate and obtains a read signal of the pits corresponding to the intensity of the reflected light. Therefore, as the moving body moves, the scale plate and the reading head move relative to each other, and the laser spot scans the pits formed as a scale.The reading head sequentially scans the bits using the same principle as in the case of conventional laser discs. is read, a number of signals corresponding to the amount of movement of the moving object are obtained, and the amount of movement of the moving object is detected. As described above, the present invention uses pits and a read head that reads the pits with a laser spot, similar to conventional laser disc technology, so that the pits can be densely packed and the resolution can be increased. can.

In the present invention, pits are formed vertically in a direction perpendicular to the scanning direction of the laser spot due to the relative movement of the scale plate and the reading head. Even if a deviation occurs in the direction perpendicular to the intended direction of movement, the pits will be reliably read. Therefore, the present invention does not require a tracking servo mechanism like the conventional laser disk technology, and can be provided at low cost.

In addition, if the reading head is configured to irradiate a plurality of laser spots on the scale plate and obtain read signals of pits with different phases, the movement direction can be determined by processing these read signals with different phases as appropriate. It is also possible to increase the resolution of the encoder to several times that of the pit itself. In this case, in the present invention, since the pits are vertically formed in a direction perpendicular to the scanning direction of the laser spot, by irradiating a plurality of laser spots so as to scan different positions in the longitudinal direction of the pit, The read signals having different phases can be easily obtained.

〔Example〕

The present invention will be described below based on embodiments shown in the drawings.

Figure 1 is a schematic diagram of the encoder according to the present invention, and Figure 2 is a scale plate (3) showing the relationship with the laser spot (3).
4) is an enlarged view of the main part, which in this embodiment is configured as a rotary encoder.

In the drawing, (4) is a large number of pits (5) as a scale.
The scale plate (6) is formed with the scale plate (4).
This is a read head that irradiates the entire laser spot (3) and obtains a read signal of the pit (5) corresponding to the intensity of the reflected light.

In the case of the illustrated embodiment, since it is configured as a rotary encoder, the scale plate (4) is configured in a disk shape. Note that the scale plate (4) is constructed in the same manner as a laser disc, and has a large number of pits (5) formed therein. However, each pit (5) is formed at equal intervals in the circumferential direction.

In addition, in the case of the drawing embodiment, the reading head (6) is
Laser diode (7), beam splitter (8),
It is composed of a lens (9) and a photodiode α0), and the laser light emitted from the laser diode (7) passes through the beam splitter (8) and enters the lens (9).
) focuses the light onto the scale plate (4), and the light reflected here passes through the lens (9) again, is reflected by the beam splitter (8), and is received by the photodiode 0ω. .

The reading head (6) is equipped with a focus servo, which is already known in laser disk technology, so that the laser beam is always focused on the scale plate (4) even if the scale plate (4) is undulated. It is desirable to provide a mechanism (not shown).

In the present invention, each of the pits (5) is formed vertically in a direction perpendicular to the scanning direction of the laser spot (3) by the relative movement of the scale plate (4) and the reading head (6). be done.

In the case of the embodiment shown in the drawing, since it is configured as a rotary encoder, each pit (5
) is formed vertically in the radial direction of a scale plate (4) configured in a disk shape.

According to the rotary encoder according to the present invention having the above configuration, one of the scale plate (4) and the reading head (6) is attached to the rotating body (not shown), and the other is attached to the fixed side.

Therefore, as the rotating body rotates, the scale plate (4) and the reading head (6) move relative to each other, and the laser spot (3) scans the pit (5) as shown in the second figure. Pit as well as technology (
Since the intensity of the reflected light varies due to interference and diffraction of light between the portions with and without 5), a read signal of the pit (5) can be obtained from the photodiode noise. For this reason,
The rotation angle of the rotating body can be detected by appropriately waveform-shaping the output signal of the photodiode (10) and counting the number of pulses. Furthermore, the rotational speed of the rotating body can also be detected by counting the number of pulses per unit time.

Note that, as is known in conventional laser disc technology, the pits (5) are adjusted so that the difference in strength of reflected light between areas with and without pits (5) is maximized.
It is desirable to set the width of the beam spot (3) to approximately % of the diameter of the beam spot (3).

And, in the present invention, as in the conventional laser disc technology, a pit (5) and a reading head (6) that reads the pit (5) with a laser spot (3) are used, so that the pit (5) can be read. High density can be achieved and resolution can be improved.

Further, in the present invention, the scale plate (4) and the reading head (
Due to the relative movement of the scale plate (4) and the reading head (6), the pit (5) is formed vertically in the direction perpendicular to the scanning direction of the laser spot (3). The pits (5) can be reliably read even if there is a deviation K in the direction perpendicular to the intended movement direction (radial direction of the scale plate (4) in the case of the embodiment shown in the drawings). Become.

Therefore, the present invention does not require a tracking servo motor mechanism like the conventional laser disk, and can be provided at low cost.

The reading head (6) may be configured to irradiate the scale plate (4) with a plurality of laser spots 01) α2 to obtain read signals of pits (5) having mutually different phases.

In that case, although not shown in the drawings, specifically, for example, a diffraction grating may be inserted into the irradiation optical path of the laser beam emitted from the laser diode (7) in Figure 1 to convert the laser beam into zero-order, It is divided into three beams of +1st order and -1st order, and two laser spots (Ill(
12e spear 3 As shown in the figure, irradiate with a phase shift of 90 degrees, and
Two photodiodes corresponding to the photodiodes (101) in the figure may be provided, and the two photodiodes may each receive the reflected light based on the two laser spots σ2.

The signal obtained by waveform shaping the output signals of the two photodiodes is shown in FIG. 5 (al). As shown in FIG. It is.

In this example, the intervals between each pit (5) are appropriately determined,
The duty of the waveform-shaped signal is 50%. Therefore, if the circuit is processed so that pulses are generated at the rising and falling parts of the signal shown in Figure 5 (α) and (b) above, each cycle will be generated as shown in Figure 5 (C). 4 pulses are obtained, and the resolution of the encoder is reduced to pit (
5) The resolution can be increased to four times its own resolution. Further, as described above, if two signals having a phase difference of 90 degrees are appropriately processed, the direction of rotation can also be detected.

In addition, as shown in Figure 4, only one pit (5) is formed longer than the other pits (5), and the above-mentioned 0-order, +1-order
1 based on the remaining 1 beam among the 3 beams of next and -1st order
The laser spot α3 is set to scan only the one pit (5), and the laser spot (131
By adding a photodiode that receives reflected light based on , it is also possible to obtain an origin signal.

In the above description, an example in which the present invention is applied to a rotary encoder has been described, but it goes without saying that the present invention can also be applied to a linear encoder.

〔Effect of the invention〕

According to the present invention, high resolution can be obtained, and a tracking servo mechanism is not required, making it possible to provide the device at low cost.

In addition, if the reading head is configured to irradiate a plurality of laser spots on the scale plate and obtain reading signals of pits with mutually different phases, the direction of movement can be detected,
This has the effect of increasing the resolution of the encoder to several times the resolution of the pit itself.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention. Fig. 1 is a schematic configuration diagram, Fig. 2 is an enlarged view of the main part of a scale plate showing the relationship with the laser spot, and Fig. 3 is a laser in another embodiment. Figure 4 is an enlarged view of the main part of the scale plate showing the relationship with the laser spot, Figure 4 is an enlarged view of the main part of the scale plate showing the relationship with the laser spot in another embodiment, Figure 5 is a signal waveform diagram, Figure 6 is Figure 6. is an enlarged view of the main parts of a conventional laser disc. (3)...O laser spot, (4)...Φ scale plate, (5)...pit, f6)--reading head,
Old 1 (121 (131...laser spot).

Claims (2)

[Claims] (1) It comprises a scale plate on which a large number of pits are formed as graduations, and a reading head that irradiates the scale plate with a laser spot and obtains a read signal of the pits corresponding to the intensity of the reflected light. An encoder characterized in that the pits are formed vertically in a direction perpendicular to the scanning direction of the laser spot due to relative movement of the scale plate and the reading head. (2) The encoder according to claim 1, wherein the read head irradiates the scale plate with a plurality of laser spots to obtain read signals of pits having mutually different phases.