JP2007024793A - Rotary encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide inexpensively a small-sized rotary encoder capable of performing speed measurement with high resolution and high accuracy, even when the speed of a rotated measuring object is low. <P>SOLUTION: This rotary encoder 15 includes a rotary disk 16 mounted rotatably in a body on a motor shaft 11 (rotated measuring object), a laser diode 17 for irradiating one side face of the rotary disk 16 with light, and a built-in photosensor PD on the back side of the laser diode 17. The photosensor PD receives emitted light from the rear end face of the laser diode 17 subjected to self-mixing modulation by return of a part of reflected scattered light from the rotary disk 16 to the laser diode 17. The rotational speed or rotation angle displacement of the motor shaft 11 is measured highly precisely by a beat signal detected by the photosensor PD. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rotary encoder, and more particularly to a rotary encoder that can measure the rotational speed (angular speed) and rotational angular displacement of a measurement object such as a motor with high accuracy.

  Conventionally, when measuring the speed of a rotating body such as a motor, an optical rotary encoder or a tachometer is generally used. For example, as shown in FIG. 5, the optical rotary encoder 1 includes a rotating slit plate 2 in which a plurality of slits 2a are formed at equal intervals in the circumferential direction, and the rotating shaft 3 of the rotating slit plate 2 has a cup Via a ring 4, it is connected to a shaft 6 on the motor 5 side so as to be integrally rotatable. Further, a light emitting element (LED) 7 and a pair of two photodetectors 8 are arranged on both sides of the rotary slit plate 2, and two slits are provided between the photodetector 8 and the rotary slit plate 2. A fixed slit plate 9 having 9a is provided.

When the encoder-side rotating shaft 3 rotates integrally with the motor-side shaft 6, the light L from the light emitting element 7 passes through the slit 2a of the rotating slit plate 2 and the slit 9a of the fixed slit plate 9, and then detects light. The light is received by the device 8. As a result, a pulse train corresponding to the rotation state of the rotating shaft 3 is electrically output from the detection unit of the photodetector 8, and the rotational angular displacement of the motor side shaft 6 is measured. Furthermore, the rotational speed (angular speed) of the motor side shaft 6 is obtained by differentiating the rotational angular displacement with time (see, for example, Patent Document 1). An example of the pulse signal waveform 10 detected by the photodetector 8 is shown in FIG.
JP 01-318526 A

  However, according to the conventional optical rotary encoder, when the rotational speed of the shaft 6 of the motor 5 that is the object to be rotated is lowered to a certain value or less, the measurement accuracy of the rotational speed is remarkably lowered. That is, when measuring the rotational speed with the optical rotary encoder, it is necessary to perform differential (difference) processing after detecting the rotational angular displacement. In particular, the rotational speed of the motor side shaft 6 becomes very low. In this case, there is a time when the light L does not pass through the slit 2a of the rotary slit plate 2 even if the rotary shaft 3 is rotating, so that it is difficult to avoid the disadvantage that the measurement error of the rotational angular displacement and the rotational speed becomes large. .

  Here, in order to reduce the measurement error, for example, it is conceivable to increase the number of slits 2a to be engraved on the rotary slit plate 2, but in this case, if the number of slits 2a is increased, processing with considerably high accuracy is possible. Requires technology and increases costs.

  On the other hand, the tacho generator is a very accurate speed detector. However, since it uses electromagnetic induction in principle, the noise in the low speed rotation region is large and it is difficult to improve the S / N ratio. Therefore, the tachometer generator has a problem that the measurement accuracy and resolution in the low-speed rotation region are lowered, as in the optical rotary encoder.

Therefore, even when the object to be rotated is at a low speed, a technical problem to be solved in order to enable measurement with high measurement accuracy and resolution arises, and the present invention aims to solve the problem. To do.

  The present invention has been proposed in order to achieve the above object, and the invention according to claim 1 is a rotating body attached to a rotating measurement object so as to be integrally rotatable, and a laser beam is applied to one side surface of the rotating body. A laser light emitting element for irradiating; and a laser light receiving element for receiving the emitted light from the laser light emitting element and the reflected scattered light from the rotating body. The laser light receiving element is based on a beat signal output by the laser light receiving element. A rotary encoder configured to measure the rotational speed of a rotational measurement object is provided.

  According to this configuration, the laser light is irradiated from the laser light emitting element to the rotating body and the laser light receiving element, and the light irradiated to the rotating body is scattered on the surface of the rotating body, and one of the scattered lights. The part returns to the laser light emitting element side. The scattered light returning to the laser light emitting element side causes a self-mixing effect of the laser light emitting element, and the laser emission light is modulated. On the other hand, irradiation light from the laser light emitting element is directly incident on the laser light receiving element. For this reason, a beat signal waveform having a beat frequency corresponding to the speed of the rotating body is output to the detector of the laser light receiving element due to the self-mixing effect of the laser. Based on this beat frequency, the rotation speed of the object to be rotated is measured.

  According to a second aspect of the present invention, there is provided the rotary encoder according to the first aspect, wherein the rotating body is attached to a rotating shaft connected to the object to be rotated via a coupling.

  According to this configuration, the rotating body is attached to the rotating shaft, and the rotating shaft is connected to the measurement object such as the motor shaft via the coupling. That is, the rotary encoder can be attached to and detached from the measurement object to be rotated freely through the coupling, and can be flexibly adapted to various types of measurement objects to be rotated.

  According to a third aspect of the present invention, there is provided the rotary encoder according to the first aspect, wherein the rotating body is directly attached to the object to be rotated.

  According to this configuration, since the rotating body is directly attached to the measured object to be rotated, there is no need to provide a connecting member between the rotating object and the measured object to be rotated.

  According to a fourth aspect of the present invention, there is provided the rotary encoder according to the first, second or third aspect, wherein the laser light receiving element is built in the back side of the laser light emitting element.

  According to this configuration, the laser light emitting element LD in which the laser light receiving element PD is disposed on the back side is used. Accordingly, part of the light scattered and reflected on the surface of the rotating body is feedback-mixed by the laser light emitting element LD, and the frequency (light wavelength) changes. That is, the scattered light is frequency-shifted by the Doppler effect of light, and a frequency difference between the emitted light and the scattered light is generated, and the difference generates a beat frequency inside the laser light emitting element LD.

  The invention described in claim 1 has an excellent effect of being able to detect speed and displacement with higher accuracy and higher resolution than in the prior art. That is, unlike the conventional rotating slit plate or the one using electromagnetic induction, the Doppler effect of the laser is used, so that the rotational speed of the rotational measurement object is rotated even when the rotational measurement object is rotating at a very low speed. In addition, the rotational angular displacement can be measured accurately and stably. In addition, since it is not necessary to engrave a large number of slits in the rotating body, high-precision slit machining technology is not required and production cost is reduced. In particular, since the measurement is performed using the self-mixing effect, the optical system becomes very simple.

  In the invention described in claim 2, since the rotary encoder is attached to and detached from the measurement object to be rotated through the coupling, in addition to the effect of the invention described in claim 1, even when the measurement object to be rotated is changed, The rotary encoder can be attached and detached easily and quickly.

  According to the invention described in claim 3, since it is not necessary to separately attach a special connecting member between the rotating body and the object to be rotated, in addition to the effect of the invention described in claim 1, the number of parts is reduced. Therefore, it is possible to simplify the configuration, reduce the size, and reduce the cost.

  In the invention described in claim 4, since the scattered reflected light is feedback mixed by the laser light emitting element, in addition to the effect of the invention described in claim 1, 2 or 3, the optical system can be simplified. Has merit.

  The best mode according to the present invention is a rotating body attached to a rotating measurement object so as to be integrally rotatable in order to achieve the object of ensuring high measurement accuracy and resolution even when the rotation speed of the rotating measurement object is low. A laser light emitting element that irradiates one side surface of the rotating body with laser light, and a laser light receiving element that receives light emitted from the laser light emitting element and reflected / scattered light from the rotating body. The rotational speed of the object to be rotated is measured based on the beat signal output by the element.

  The rotary body of the rotary encoder includes a direct connection system in which the rotary body is directly coupled to the measurement object to be rotated and an indirect connection system in which the rotation body is coupled to a rotation shaft coupled to the measurement object to be rotated. In the former, since it is not necessary to provide a connecting member between the rotating body and the object to be rotated, a simple compact structure is possible. In the latter case, since the rotary encoder is attached to and detached from the rotating measurement object using a coupling, for example, when the rotary encoder is replaced with a rotating measurement object of a different size, it can be easily handled only by the coupling, and the specifications are different. There is no need to prepare many types of rotating bodies.

An embodiment of the present invention will be described below with reference to FIGS. In this embodiment, the rotational speed and rotational angular displacement of the object to be rotated are measured by the self-mixing effect of the semiconductor laser based on the Doppler effect of light using the laser diode LD with a built-in photosensor PD. In this case, the irradiation angle of the laser to the rotating body and the distance from the rotation center of the rotating body to the laser spot are fixed as design values in order to perform highly accurate measurement even when the speed of the object to be rotated is low. . In addition, although the rotating shaft of a motor is mentioned as an example as a to-be-rotated measurement object, if a rotary body can be connected so that integral rotation is possible, it will not be limited to this but all are applicable.

  1 and 2 are explanatory views showing the configuration of the rotary encoder according to the present embodiment, and FIG. 2 is a front view showing an attached state of the rotary encoder of FIG. In FIG. 2, reference numeral 11 denotes a rotating shaft (hereinafter referred to as a motor shaft) of a motor 12 that is an object to be rotated. A rotating shaft 14 is integrated with one end of the motor shaft 11 via a coupling 13. It is mounted for rotation.

  A laser Doppler velocimeter (or laser Doppler velocimeter) LDV 15 measures the rotational angular displacement and rotational speed of the rotating shaft 14 and the motor shaft 11. The rotary encoder 15 includes a rotating disk 16 that is a rotating body, and the rotating disk 16 is attached to an intermediate portion of the rotating shaft 14 on the same core. One surface of the rotating disk 16 is made of a material having a required light reflectance, for example, a plastic material such as polycarbonate resin, or a metal material such as aluminum, and the rotating disk 16 has one slit. Absent.

  As shown in FIG. 1, a laser diode (laser light emitting element LD) in which a photosensor (photodetector) PD is built in the back side at a predetermined position on one side (left side in FIG. 2) of the rotating disk 16. 17 is provided, and the laser diode 17 is fixed to an optical element mounting member 18 disposed on the side of the rotating shaft 14. The laser diode 17 is mounted so as to form a predetermined relative angle (irradiation angle θ ≠ 0) with respect to the vertical line 19 on the surface of the rotating disk 16, and the laser light L emitted from the laser diode 17 is rotated. It is configured to irradiate a predetermined position on the outer peripheral edge side of the disk 16.

  The rotational center of the rotating disk 16, that is, the distance r between the axis C of the rotating shaft 14 and the laser irradiation point P is set to a predetermined constant value. The photosensor PD described above is built in the rotating disk 16 and the other surface side (left side in FIG. 2) of the laser diode 17. The photosensor PD receives light emitted from the rear end face side of the laser diode 17. The emitted light from the rear end face side is modulated by the self-mixing effect of the laser diode 17 and the reflected light emitted from the front end face side of the laser diode 17 and scattered by the surface of the rotating disk 16 and the emitted light from the laser diode 17. Light. The irradiation angle θ is set to 10 ° to 15 ° here, but is not particularly limited as long as the scattered light reflected from the surface of the rotating disk 16 can be efficiently received by the photosensor PD.

  Next, the measurement principle of the embodiment will be described. Here, it is assumed that the laser light L having the wavelength λ is emitted from both end faces of the laser diode 17 with a built-in photosensor PD. Now, when the motor shaft 11 rotates, the rotating shaft 14 and the rotating disk 16 rotate integrally through the coupling 13. Then, the laser light L from the laser diode 17 is irradiated at a predetermined angle on the one side surface of the rotating rotating disk 16, that is, a position P separated from the rotation center C by a distance r at an irradiation angle θ.

  A part of the light irradiated to the predetermined position P of the rotating disk 16 returns to the laser diode 17 side, and the laser light is modulated by the self-mixing effect. The modulated light is received by the photosensor PD built in the rear end face side of the laser diode 17. In this case, the light emitted from the rear end face of the laser diode 17 also directly enters the photosensor PD.

As a result, a small beat signal 20 as shown in FIG. 3 appears in the AC output of the detection unit of the photosensor PD due to the self-mixing effect of the semiconductor laser. The beat frequency f _d of the beat signal waveform 20, the angular velocity ω of the rotating disk 16, and the velocity V on the predetermined position P are expressed by (Equation 1), (Equation 2), and (Equation 3). In FIG. 3, the symbol T indicates a cycle.

(Formula 1): f _d = (2 V · sin θ) / λ
(Formula 2): ω = f _d · λ / (2r · sin θ)
(Formula 3): V = r · ω
Therefore, by detecting the beat frequency f _d , the rotational speed (angular speed) of the rotating shaft 14, that is, the motor shaft 11 is measured. Further, by counting the number of beat signals per unit time, the rotational angular displacement (relative displacement) of the motor shaft 11 is also measured with high accuracy.

  Here, the self-mixing effect of a semiconductor laser means that when a moving object (rotating body) is irradiated with a semiconductor laser, part of the light scattered by the moving object returns to the semiconductor laser and a beat (swell) signal is output to the laser output. Appears. The frequency of the beat signal is equal to the Doppler shift frequency due to the moving object. This makes it possible to measure a Doppler-shifted beat signal without configuring a complicated optical system.

  As described above, in this embodiment, the rotating disk 16 is irradiated with the laser light from the laser diode 17, and at this time, part of the light scattered on the surface of the rotating disk 16 returns to the laser diode 17, and the photosensor PD. By detecting the beat signal appearing at, the speed of the rotating shaft 14 and the motor shaft 11 can be measured with high accuracy and optical resolution. Further, by counting the number of beat signals per unit time, it is possible to measure the rotational angular displacement with high accuracy. Furthermore, by utilizing the self-mixing effect of the semiconductor laser, the optical system components are very simple, and the rotary encoder can be reduced in size and cost.

In the above-described embodiment, the rotary shaft 14 is connected to the motor shaft 11 via the coupling 13, and the rotary encoder 15 is attached to the rotary shaft 14 to measure the rotational speed or the like of an object to be rotated such as a motor. Although an external type measuring method is given as an example, the present invention can also be used by incorporating the rotary encoder 15 in a measurement object to be rotated.

  FIG. 4 shows another embodiment in which, for example, the rotary encoder 15 of the present invention is built in the DC servo motor 21. In the figure, reference numeral 22 denotes a rotor provided inside the stator side magnet 23, and the rotary encoder 15 of the present invention is attached to one end side portion of the rotating shaft (measurement object) 24 of the rotor 22. Yes. Since the configuration of the rotary encoder 15 is the same as that of the above embodiment, the same components as those in FIG.

  In this embodiment, since the rotary disk 16 of the rotary encoder 15 is directly attached to the rotary shaft 24 of the rotor 22, no coupling is required, thereby further simplifying the structure or reducing the size and size. Can be planned.

  The present invention can be widely applied to fields where current optical rotary encoders or tachometers are used, for example, factory automation fields where industrial robots are installed. The rotary encoder 15 of the present invention can be used.

  It should be noted that the present invention can be variously modified without departing from the spirit of the present invention, and the present invention naturally extends to the modified ones.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows one Example of this invention and shows the structure of a rotary encoder. The front view which shows the attachment state of the rotary encoder of FIG. The wave form diagram which shows an example of the beat signal output from the photosensor which concerns on the rotary encoder of FIG. The front view which shows the other Example of this invention and shows the attachment state of a rotary encoder. Explanatory drawing which shows a prior art example and shows the structure of an optical rotary encoder. The front view which shows the attachment state of the optical rotary encoder of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical rotary encoder 2 Rotating slit board 2a Slit 3 Rotating shaft 4 Coupling 5 Motor 6 Shaft 7 Light emitting element (LED)
8 Photodetector 9 Fixed slit plate 9a Slit 10 Pulse signal waveform 11 Motor shaft (object to be rotated)
12 Motor 13 Coupling 14 Rotating shaft 15 Rotary encoder 16 Rotating disk (Rotating body)
17 Laser diode (PD built-in type laser light emitting element LD)
18 Optical element mounting member 19 Vertical line 20 Beat signal 21 DC servo motor 22 Rotor 23 Magnet 24 Rotating shaft (measurement object to be rotated)
θ Irradiation angle L Light (laser)
V Rotational speed (angular speed)
C Axis core P Irradiation position (laser spot)
r Distance (radius)
PD photo sensor (laser photo detector)

Claims (4)

  A rotating body that reflects laser light, a laser light emitting element that irradiates laser light to one side surface of the rotating body, and a laser light receiving element that receives light emitted from the laser light emitting element and reflected and scattered light from the rotating body And the rotating body measures the rotation of the laser light emitting element in a state where the irradiation angle of the laser beam to the rotating body and the irradiation distance from the rotation axis of the rotating body are fixed to a predetermined constant value. A rotary encoder, wherein the rotary encoder is configured to measure the rotational speed of the object to be rotated on the basis of a beat signal that is attached to an object and rotated integrally and output by the laser light receiving element.   2. The rotary encoder according to claim 1, wherein the rotating body is attached to a rotating shaft connected to the measurement object to be rotated through a coupling.   The rotary encoder according to claim 1, wherein the rotating body is directly attached to the object to be rotated.   4. The rotary encoder according to claim 1, wherein the laser light receiving element is built in the back side of the laser light emitting element.

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