JPH0723692Y2 - Optical encoder index signal generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an optical encoder, and more particularly to a device for generating an index signal as an origin signal in an optical encoder of an increment system.

[Prior Art] As is well known, in the case of a rotary encoder, an increment type optical encoder is composed of a rotary slit plate, a fixed slit plate, a driving device, a light emitting / receiving device, and a signal processing circuit. On the rotary slit plate, as many light transmitting portions as necessary to obtain a required resolution are formed on the entire circumference at equiangular positions. The fixed slit plate is provided so that its surface is parallel to the rotary slit plate, and is set at right angles to the light emitting and receiving axis so that the respective light transmitting portions are on the light emitting and receiving axis.

The light projected on the rotary slit plate side passes through both the rotary slit plate and the fixed slit plate when the positions of the rotary slit plate and the fixed slit plate are aligned on the optical axis. Enters the light receiving device and is converted into an electric pulse. Therefore, the number of transmission parts of the rotary slit plate passing between the light projecting device and the fixed slit plate in accordance with the rotation angle given to the rotary slit plate is equal to the number of electric pulses obtained by the light receiving device. The rotation angle can be obtained from the number of pulses.

In order to obtain the origin, in the conventional method, a transparent portion is provided on the rotary slit plate at one location, and a transparent portion is provided at a position opposite to the fixed slit plate to obtain an index pulse. Further, in order to determine the rotation direction, the transmission part of the fixed slit plate is composed of both the A-phase and B-phase transmission parts whose positions are displaced from each other in the rotation direction of the rotation slit plate, and two output waveforms with phase shifts are provided. Was obtained.
Therefore, at least three trucks were required.

[Problems to be Solved by the Invention] Not only is the three sets of tracks required in the above-mentioned conventional technique disadvantageous in terms of space for forming the transmitting portions of the rotary slit plate and the fixed slit plate, but this also results in a number of parts. However, it also required space for its installation.

In particular, by dedicating the index track and its light emitting / receiving device, a mounting error, a temperature characteristic of the light emitting / light receiving element, and a phase shift due to variations in responsiveness occur, which directly affect the measurement accuracy.

Therefore, the present invention reduces the number of elements and space,
An object of the present invention is to provide an index signal generation device for an optical encoder having improved characteristics.

[Means for Solving the Problems] The index signal generator of the increment type optical encoder according to the present invention does not use a dedicated index track and element, but the area of one optical slit of the movable slit plate is Optical slits are formed on the fixed slit plate so that they can be different from each other and the light transmitted through the optical slits can be detected. With the combination of the movable slit plate and the fixed slit plate, a part of the increment waveform is transformed from the others, and the obtained signal is calculated to obtain the index signal.

[Operation] When the movable slit plate travels and the optical slit thereof coincides with the optical slit of the fixed slit plate, an increment waveform is output from the light emitting and receiving device. As the movable slit plate travels, when the optical slits having different areas come to the positions corresponding to the optical slits of the fixed slit plate, the corresponding portions of the increment waveform are deformed. This modification is identified and calculated by the signal processing circuit to obtain the index signal.

[Embodiment] An embodiment of an index signal generating device of an optical encoder according to the present invention will be described in detail with reference to the accompanying drawings. First, referring to FIG. 6, the illustrated embodiment is one in which the present invention is applied to an increment type optical encoder. This encoder is a rotary encoder,
It has a movable slit plate, that is, a rotary slit plate 10. The rotary slit plate 10 includes a shaft 50 connected to a drive device (not shown).
It is supported by and can rotate around this. Facing the rotary slit plate 10, the fixed slit plate 18 as shown
Is provided.

The rotary slit plate 10 is composed of an optically opaque circular flat plate, and has a number of optical slits or light transmitting portions (first optical slits) 14 and (second optical slits) necessary to obtain a required resolution.
Optical slits) 16 (see FIG. 1) are formed at equal angular positions over the entire circumference. The fixed slit plate 18 is provided so that its main surface is parallel to the rotary slit plate 10, and the light transmission parts 20, 22, 24, 26, 28 (FIG. 2) of the fixed slit plate 18 are on the light emitting / receiving axis 52. As described above, the light emitting and receiving axis 52 is set substantially at right angles.

A light projecting / receiving device is arranged on the light projecting / receiving shaft 52, and this light projecting / receiving device comprises a light projecting device 54 and a light receiving device 56, which are arranged for both slit plates 10 and 18, as shown in the drawing. Projector 54
The light projected from the rotary slit plate 10 to the rotary slit plate 10 is transmitted through the rotary slit plate 10 and the fixed slit plate 18 through the optical axis.
When the two coincide with each other on 52, the light passes through both transmitting parts and enters the light receiving device 56, and the latter generates an electric pulse corresponding thereto. Therefore, depending on the rotation angle given to the rotary slit plate 10, the optical axis 52
The number of transmission parts of the rotary slit plate 10 passing above corresponds to the number of electric pulses obtained by the light receiving device 56, and the rotation angle can be obtained by using this electric pulse. The light projecting device 54 may be arranged on the fixed slit plate 18 side, and the light receiving device 56 may be arranged on the movable slit plate 10 side.

In FIG. 6, in order to avoid complication of the drawing, the light transmitting portions of the slit plates 10 and 18 are only partially illustrated in a conceptual manner. Therefore, the rotary slit plate 10 is shown in FIG.
As shown in a partially enlarged view, the rotary slit plate 10 is optically opaque, and has optically transparent openings, that is, light transmitting portions 14 and 16 formed in a part thereof. The transparent portion 14 is
They have the same size and shape and are provided on the entire circumference of the rotary slit plate 10 at the same angle (equal distance) with respect to the drive shaft 50. A transmission portion 16 for an index pulse track, which is wider than the slit 14, is formed at one position on the entire circumference in the radial direction toward the rotation axis 50 and / or in the opposite radial direction. The other portions form the non-transmissive portion 12. In the present embodiment, the width of the transmissive portions 14 and 16 in the circumferential direction of the rotary slit plate 10 is substantially half the arrangement pitch in the circumferential direction.

FIG. 2 shows the fixed slit plate 18 in this embodiment. The fixed slit plate 18 is also formed of a material that does not optically transmit light as a whole, and has light transmitting portions 20, 22, 24, 26 and 28 arranged as shown in the drawing. As can be seen, the encoder of this embodiment has four phases, that is, A ,,
B and phase pulses are generated and their respective transmissive parts 20,
The width of the transmissive portion (third optical slit) 20 of only one phase of 22, 24, 26 and 28, for example, the A phase, extends to the b portion in addition to the a portion. Further, regarding the c portion 22 and the d portion 24 which are the phase portions that generate the inverted waveform of the A phase, the area increase of the A phase, that is, the d portion 24 having substantially the same area as the b portion is transmitted to the same phase as the A phase. It is provided as a section. The height from the upper end of the transmission part 20 to the lower end of the transmission part 24 in the figure is substantially equal to that of the index pulse generation transmission part 16 of the rotary slit plate 10.

The fixed slit plate 18 is also provided with A, phase-shifted B, and phase light transmission parts 26 and 28, as shown in the figure. The other portion 30 of the fixed slit plate 18 forms a non-transmissive portion. The height from the upper end of the transmission part 26 to the lower end of the transmission part 28 is substantially equal to that of the encoder pulse generation transmission part 14 of the rotary slit plate 10. Also, fixed slit plate
The horizontal arrangement pitch in the figure between the transmission parts 20 or 24 and 22 of 18 is substantially equal to half the arrangement pitch in the circumferential direction of the transmission parts 14 of the rotary slit plate 10, which is equal to the transmission pitch. The same applies to parts 26 and 28.

Returning to FIG. 6, the light-receiving device 56 has light-receiving elements 56A, 56, 56B and 56, which are fixed slit plates 18 respectively.
The optical axis corresponding to the positions of the transmission parts 20, 22, 24, 26 and 28 of
It is arranged near 52. These light receiving elements 56A, 56
, 56B and 56 are transparent portions 14 and 16 of the rotary slit plate 10 and transparent portions 20, 22, 24 of the fixed slit plate 18, respectively.
When the positions of 26 and 28 are aligned on the optical axis 52, the projector 54
Receives the light from and outputs the corresponding electric signal output Ain,
Generates in, Bin and in. These outputs are connected to the index pulse generation circuit 60 shown in FIG.
The circuit 60 is configured by connecting three comparators 32, 34 and 40 and two adders 36 and 38 as shown in the figure,
Finally, it is an electronic circuit that generates the differential outputs Aout and Bout of both phases and the index pulse Zout (Fig. 5).

FIG. 3 shows A, B, and phase currents induced in the light receiving device 56. As you can see, the A-phase current Ain is
When the transmitting portion 14 of the rotary slit plate 10 is on the optical axis 52, the waveform of the dotted line 70 is taken. However, when the transmissive portion 16 having a large area of the optical aperture comes on the optical axis 52, the light receiving element 56A receives the light transmitted through the entire optical aperture area of the transmissive portion 20, and thus outputs the waveform of the solid line 72. This shows the maximum value of the amplitude at one location.

On the other hand, in the vicinity of the transmissive portion 16, the phase current in is always incident on the light receiving element 56 that has passed through either of the transmissive portions 22 and 24 due to its presence. Therefore its output in
Changes from the waveform of the dashed-dotted line 74 to the waveform 76 of the solid line, which is a waveform lacking one peak. Regarding B and phase, since the transmitting portions 26 and 28 of the fixed slit plate 18 have the same size, there is no influence by the transmitting portion 16, and the maximum 72 or flat waveform 76 as in A and phase does not occur. When these output waveforms are processed by the index pulse generation circuit 60, the waveforms shown in FIG. 5 are obtained.

The consulting currents Bin and in of B and B do not change even in the vicinity of the wide transparent portion 16.

In the index pulse generation circuit 60, the comparator 32 and
34, A, phase and B, differential output of each phase Aout, Bo
ut are obtained, and these are 1/4 as shown in Fig. 5 (1).
It is an output waveform of a normal increment method with different pitch phases. The adders 36 and 38 and the comparator 40 shown in FIG.
It is a signal processing circuit for generating an index pulse.
The adders 36 and 38 obtain the index waveform Zin and the reference waveform in shown in FIG. 5 (2) by adding the outputs Ain, in and Bin, in of the respective phases. Further, these two outputs are converted into differential outputs by the comparator 46, and FIG. 5 (3)
The waveform Zout shown in is obtained. This Z-phase final waveform is used as a normal index pulse.

Although the invention has been described with reference to particular embodiments, the invention is not limited thereto. For example, not only the rotary encoder as in this embodiment but also the linear encoder can be effectively applied. Further, although the light transmissive slit plate is used in the embodiment, a reflective slit may be used, for example. Further, although the index pulse transmission part is one in the embodiment, a plurality of index pulse transmission parts may be provided.

As described above, in the present embodiment, the index signal generating track and the phase output generating track of either the A phase or the B phase have the same mechanical position, so that the displacement of the origin at the time of mounting the element is minimized. can do. Further, by sharing the optics for the phase output of either the A or B phase, it is possible to prevent the phase shift of the origin due to the variations in the temperature characteristics and the responsiveness of the light emitting / receiving elements. Further, the space for the optical system dedicated to generating the index pulse is unnecessary, so that the entire encoder can be downsized.

[Advantage of the Invention] According to the present invention, the index pulse of the optical encoder can be generated without using a dedicated index track and element, thereby reducing the space,
Cost is reduced. In addition, since the index pulse is generated from the encoder waveform itself, phase shift due to element mounting error and phase shift due to the difference in temperature characteristics and responsiveness due to separate elements are eliminated, resulting in a highly accurate waveform. can get.

[Brief description of drawings]

FIG. 1 is an enlarged partial plan view showing a part of a rotary slit plate in the embodiment of the present invention shown in FIG. 6, and FIG. 2 is a plan view of a fixed slit plate in the embodiment, and FIG. Is a waveform diagram showing a current waveform of each phase output obtained in the light receiving device in the same embodiment, FIG. 4 is a block diagram showing a configuration example of an index pulse generation circuit in the same embodiment, and FIG. FIG. 4 is a diagram showing a mutual relationship of outputs, and FIG. 6 is an explanatory perspective view of an embodiment in which the present invention is applied to an index signal generating device of an optical encoder. Explanation of symbols of main parts 10 …… Rotating slit plate 12,30 …… Non-transmissive part 14,16 …… Transmissive part 18 …… Fixed slit plate 20,26 …… Transmissive part 32,34 …… Comparator 36,38 …… Adder 40 …… Comparator

Claims (1)

[Scope of utility model registration request] 1. An array of a plurality of first optical slits is formed, and a light transmission area different from that of the first optical slits included in the array and having the same width in the moving direction with respect to the first optical slits. A movable slit plate having a second optical slit extending in a direction perpendicular to the moving direction, and third and fourth optical slits formed at positions partially corresponding to the array, A third optical slit in which a portion for detecting the optical slit row and an optical slit for detecting a portion corresponding to the extended portion of the second optical slit are formed on the same straight line.
Optical slit and a portion for detecting the first optical slit row are displaced from each other by a half pitch with respect to the third optical slit, and an optical slit for detecting a portion corresponding to the extended portion of the second optical slit. A fixed slit plate having a fourth optical slit formed on the same straight line as the third optical slit, and light that passes through a part of the array and the third optical slit, and the received light And a second electric signal corresponding to the received light, which receives light passing through a part of the array and the fourth optical slit. An index signal generating device for an optical encoder, comprising: a second light receiving unit that outputs the signal, and a signal processing circuit that calculates the first and second electric signals to generate an index signal.