JP2699542B2 - Code plate and read head for 1-track type absolute encoder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a code plate for a one-track absolute encoder and a read head.

[Prior Art] Japanese Patent Application Laid-Open No. 54-118259 discloses a code plate having tracks of two or more magnetic patterns, and a magnetoresistive element (Magn.
A magnetic absolute encoder combined with a read head using an etoresistive element (hereinafter referred to as an MR element) as a sensor is shown.

Generally in order to obtain a resolution of 2 ^N in this type of absolute encoder requires minimum N of tracks as absolute pattern, the code disc if the disc type, a plurality of tracks are arranged in concentric circles. For example, when N = 4, four circular tracks are provided concentrically on the disk-shaped code plate, and absolute patterns of binary codes "0" and "1" are formed on these tracks according to the direction of magnetization. Is done. A sensor composed of an MR element is assigned to each track, and as the code plate rotates relative to the sensor around its center, the output of each sensor obtained at an arbitrary rotation position of the code plate is obtained. The combination is a code signal that gives the absolute rotational position of the code plate.

On the other hand, JP-A-57-175211, or JP-A-60-1529
In Japanese Patent Application Publication No. 16-216, two types of minimum reading units corresponding to the "0" signal and the "1" signal, that is, a minimum reading unit having magnetism and a minimum reading unit having no magnetism in the case of the magnetic type are arranged in a predetermined arrangement. And a read head comprising a plurality of sensors which are relatively movable with respect to the code plate and are arranged in the track length direction. A signal train output from each sensor is represented by a binary code. 1 shows a magnetic or optical one-track type absolute encoder that detects an absolute position.

In such a one-track type absolute encoder, when reading a plurality of corresponding minimum reading units (codes) simultaneously with a plurality of sensors, whether magnetic or optical, it is assumed that “0” is included in those codes. Assuming that two or more codes have just changed from “1” or “1” to “0”, the pattern accuracy of the code plate or the sensor arrangement pattern accuracy of the reading head is low (conversely, a high-precision code plate or Since the read head is difficult to manufacture and not practical), a plurality of sensors do not always read the changed code simultaneously. That is, one sensor reads the code before the change, and the other sensor reads the sensor after the change.

Then, if there is one reading error in the read binary code, in the case of the one-track type, there is no regularity between the change in the absolute position and the change in the binary code. An unexpected absolute position will be detected.
As a result, the reading accuracy decreases.

As one solution to this problem, the present inventors have previously provided a track of an incremental pattern on the same or an adjacent code plate in parallel with a one-track absolute pattern, and provided a clock signal generated using this incremental track. By operating the latch circuit using the strobe signal as the strobe signal, a system was obtained in which a plurality of sensors were simultaneously read at the time when they were almost at the center of the minimum reading unit to obtain an absolute output (binary code). 63-177072). In addition, in principle, a plurality of minimum reading units are read in chronological order by one sensor instead of the plurality of sensors, and then serial / parallel data conversion is performed, thereby obtaining the same absolute output as in the previous invention. A method (Japanese Patent Application No. 63-171922) was invented.

As an example, the outline of the former method is shown in FIGS. 8 (a) and (b).
Shown in

Examples of the FIG. 8 (a) is the number of scale graduation 2 ⁴ = 16 (N
= 4) In a pulse type optical example, a track 102 having a one-track absolute pattern and an incremental track 103 are manufactured on a disk-shaped code plate 101. The absolute pattern of the track 102 is “0000110101111001”. Reference numerals 104 _{-1 to} 104 _-4 denote optical sensors for reading the track 102, which obtain an absolute signal consisting of a 4-bit binary code. The incremental track 103 is read by another optical sensor 105. still,
Reference numeral 106 denotes a rotation axis of the code plate 1.

Figure 8 (b) is a drawing showing an example of an output circuit for processing the results read by these sensors, the incremental signal from the sensor 105, and the absolute signal from the sensor 104 _-1 to 104 _-4, respectively Pulse shaping circuit 110, 110 _-1 ~
At 110 _-4 , the waveform is shaped into a rectangular wave, then the absolute signal is directly input to the latch circuit 114, and the incremental pulse is input to the one-shot circuit 112 to generate a clock pulse at both the rising and falling points. ,
This is used as a strobe signal for the latch circuit 114. In this case, the clock pulse rises at substantially the center of the pulse width of the unit pulse constituting the absolute signal (when the sensor is positioned at the center of the minimum reading unit). Each time a clock pulse arrives, the latch circuit 114 reads the high / low level of the pulse of the absolute signal (the high and low levels of this level correspond to one and the other of the "0" and "1" signals), and the next clock is output. entering until latches that value, continues to output to the output terminal 116 _-1 -116 _-4.

[Problems to be Solved by the Invention] Although the above-described latch system avoids the decrease in the reading accuracy of the output of the one-track absolute encoder described above, this time, the track of the incremental pattern necessary to obtain the clock signal for synchronization is used. Must be provided separately from the tracks of the absolute pattern,
At the time of assembling the encoder, it is necessary to perform a highly accurate phase adjustment between the two, which causes a problem that the assembling becomes difficult and the manufacturing cost is increased. In addition, when two tracks are provided on the same code plate, there is a second problem that the size of the code plate cannot be reduced.

[Means for Solving the Problems] Accordingly, the present invention relates to such a code plate, in which at least one of the two minimum reading units, the signal determination part thereof is set to a part instead of the entire length of the unit, A read mark of a constant pitch for a synchronizing signal is formed on the same track by utilizing a gap between them.

[Operation] In the present invention, the signal determination unit in the absolute signal indicates an area (range) for determining whether the unit represents a “0” signal or a “1” signal.
For example, in the case of an optical system, as shown in FIG. 1A corresponding to the embodiment, as shown in FIG. 1A, one of the plurality of minimum reading units arranged at a constant pitch represents one signal representing a "1" signal. Has a dark area (shaded area) only in a part thereof, whereas the other unit representing the "0" signal has no dark area at all. The partial dark area portion of the one unit is the signal determination unit that determines the unit as a “1” signal.

On the other hand, in the conventional code plate, as shown in FIG. 2, the entire area of one unit representing the "1" signal is occupied by a dark area (shaded area), and the entire unit is a signal determining section. I was

In the code plate of the present invention, since the signal determination section is provided only in a partial area of the unit, it is necessary to perform reading in the dark area of the partial area when reading the unit. It should be noted that, for each reading unit, it is desirable that the signal determination unit exists at a substantially central position in the unit area. Then, the length λ of the minimum reading unit can be reduced.

In the code plate of the present invention, since the minimum reading unit is read by the signal determining unit, a clock signal for setting a timing at the time of reading is separately required. In order to obtain this clock signal, the code plate of the present invention utilizes a gap between the signal determining portions in the track of the absolute pattern to make a constant pitch, that is, a pitch equal to the length λ of the minimum reading unit. An incremental pattern consisting of a plurality of reading unit marks (see FIG. 1A) arranged in the above manner is provided, and this can be read by another sensor to obtain a clock signal. The reading unit mark is a mark for generating a clock signal used as a synchronization signal for reading an absolute pattern.

In general, the synchronization varies slightly due to the characteristics of the clock signal processing system, and the range of this variation is calculated from the relative speed between the code plate and the reading head, and the variation range of the reading position in the track length direction for each unit is determined in advance. It is preferable that the minimum length range of the signal determining portion of the absolute pattern be wider than the fluctuation range so as to cover the fluctuation range.

The signal determination unit is preferably provided substantially at the center of the minimum reading unit.

As a characteristic feature of the code plate of the present invention, a reading unit mark for an incremental signal exists outside a signal determining portion for an absolute signal, but both need to be read separately and simultaneously. Thus, the readhead requires at least two sensors and those sensors are
It is necessary to arrange them at an interval substantially equal to the interval between the signal determination section and the reading unit mark (see FIG. 1B).

The signal determination unit is provided substantially at the center of the minimum reading unit,
When the reading unit mark is provided near the boundary of the minimum reading unit, the interval between the two sensors is substantially (m + 1/2)
λ.

Here, λ is the length of the minimum reading unit of the code plate, and m is 0 or a positive integer.

Accordingly, the present invention provides, as a second invention, a "read head provided with at least two sensors arranged along the track longitudinal direction of the code plate, wherein one of the sensors is used for an incremental signal and the other is used for an absolute signal. And a distance between the two is substantially separated by (m + 1/2) λ.

The sensor for the absolute signal and the sensor for the incremental signal must be able to distinguish and detect the signal determination section A and the read unit mark B for the synchronization signal, respectively. Therefore, A and B preferably have different physical properties.

However, from the viewpoint of manufacturing, it is preferable that the physical properties of A and B are the same because the cost can be reduced. For example, two minute regions having the same physical properties as the minimum reading unit corresponding to “0” and “1” of the absolute pattern are formed adjacent to each other as a reading unit mark, and a clock signal is obtained at the boundary between both regions. (See Fig. 1C).

For example, in the case of an optical system, as shown in FIG. 1C, it is preferable that an adjacent pair of two kinds of minute regions (a transparent portion and a dark portion) having different light transmittances be used as the reading unit mark. The read unit marks are arranged at a constant pitch λ in the gap between the absolute pattern signal defining portions to form an incremental pattern in the same track.However, the read unit marks of these synchronization signals are not necessarily between the minimum read unit of the absolute pattern. There is no need to match the boundaries.

However, in the case of FIG. 1C, the absolute signal sensor and the incremental signal sensor cannot read the signal determination portion A and the reading unit mark B separately. Therefore, as shown in FIG. 1D, within the same minimum reading unit,
When the signal determination section A is in the dark area, the reading unit mark B
The transparent portion between the dark minute area and the signal determination section A (dark area) is similarly defined as a dark area, and is set as one large dark area.

In this way, the clock signal is generated only when the incremental signal sensor detects a change (change from 0 to 1) from the transparent minute area to the dark minute area, and synchronized with this clock signal, the absolute signal sensor generates a clock signal. Is read.

Then, if the track moves in the direction of arrow Y,
Since a change from 0 to 1 is detected when the incremental signal sensor starts passing the reading unit mark, a clock signal is generated at this time, and then the incremental signal sensor passes through the signal determination section in the same minimum reading unit. At the end of the operation, a change from 1 to 0 is detected. At this time, since the change is not from 0 to 1, no clock signal is generated. In this case, no clock signal is generated in the signal determination unit.

In the case of FIG. 1D, the reading unit mark B is
(Within the same minimum reading unit), in which case the portion located between them is darkened. In this case, a clock signal is generated only when a change (a change from 1 to 0) from a dark minute area to a transparent minute area of the reading unit mark A is detected.

Incidentally, as in the present invention, if the signal defining portion of the absolute pattern is formed as a part of the area of the minimum reading unit and the reading unit mark for the incremental pattern is provided in the same track, for example, using lithography technology By manufacturing a code plate, a code plate with extremely high phase accuracy between both patterns can be obtained, and assembly and adjustment of an absolute encoder are facilitated.

In the absolute encoder using the code plate of the present invention, for example, a plurality of sensors that are relatively movable in the longitudinal direction of the track with respect to the code plate of the present invention are provided, and one of them reads an incremental pattern to obtain a clock signal. At the same time, when reading a predetermined number of units simultaneously by a plurality of remaining sensors to read each high and low level of the pulse of the absolute signal, only the determined portion shorter than the minimum reading unit length λ is synchronized with the clock signal. Thus, reading is performed at a point within the width of the corresponding pulse.

The absolute pattern may be read in time series with one sensor without using a plurality of sensors. In this case, the pulse train extracted from the sensor is serial data corresponding to a digital code array according to a certain unit pitch of the absolute pulse.Therefore, the high / low level of the unit pulse constituting the pulse train is converted into the clock signal for each unit. Read sequentially in synchronization. Also in this case, the sensor output for the absolute signal is read at a stable time apart from the rise and fall of each unit pulse of the pulse train based on the clock signal, so that an error in the encoder output is prevented from occurring. It becomes possible to make it extremely small.

In the present invention, since the signal determination unit for determining whether the minimum reading unit in the absolute pattern is “0” or “1” is formed smaller than the unit length λ, the adjacent signal determination unit Has an advantage that mutual influence is reduced.

Further, since the clock signal is obtained from a reading result of an incremental pattern provided together in the same track on which the absolute pattern of the code plate is formed, for example, the clock signal is obtained from an incremental pattern of another track of the same code plate. It is not necessary to take into account the relative accuracy of the tracks or the torsion of the shaft connecting the code plates, as compared to that obtained from the incremental pattern of the It is also possible to improve the resolution of the encoder by making the size of the section in the track length direction extremely short.

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment FIG. 3 is a schematic plan view of a code plate for a rotary encoder according to the present embodiment, showing sensor positions superimposed.

In FIG. 3, the code plate 1 is formed with one circular track 2 centered on its rotation axis 6.

Here, the track 2 is a track having an absolute pattern, and the track is divided into 2 ⁿ = 8 (n = 3 bits) to form eight minimum reading units.

Here, the transparent area is “0”, and the dark area is “1”.
When this absolute pattern is counted counterclockwise from the position of the arrow X in FIG. 3, it becomes 00011101.

Here, the reading unit mark B is provided at the start end of the minimum reading unit (length λ) when viewed counterclockwise, and the start end of the mark B coincides with the start end of the unit. And
In the case of the minimum reading unit of the code “1”, the space between the signal determining portion A and the mark B is painted dark (corresponding to FIG. 1D).

Next, the reading head will be described. The read head is not shown in the drawing, but only the relative position of the sensor is important, so that only the read head is shown in FIG.

The sensors are 3-1 for absolute signals, 3-2, 3
-3, 3-4, and one incremental signal 4B. The sensor for the absolute signal here is n
= 3 bits, so it is sufficient to use three bits. However, three bits 3-1 and 3-2 and 3-1 are used in the counterclockwise direction, and 3-4, 3-3 and 3-2 in the clockwise direction. I decided to use three. In this way, the absolute position can be detected in both forward and reverse rotations.

When the length (pitch) of the minimum reading unit is λ, the sensor 4b is separated from the nearest sensor 3-1 by approximately λλ. The mutual spacing is λ. This is because the reading unit mark is provided at the start end of the minimum reading unit, while the signal determination unit is provided at the center of the minimum reading end area, and each sensor must come to a corresponding position. is there.

Sensors 4a and 4
b is provided, and the sensor 4b is also used for an incremental signal.

Each of these sensors comprises a pair of a light source (eg, an LED) and a photoelectric conversion element (eg, a photodiode), and a track of a code plate is located between the two. When the transparent area of the track crosses the sensor, the sensor output goes high, and when the dark area crosses the sensor, the sensor output goes low.

FIG. 4 schematically shows an example of a signal processing circuit for processing each sensor output of the read head.

FIG. 5 shows the output (pulse waveform) of the incremental signal sensor 4b when the code plate 1 is rotated once clockwise from the position of arrow X in FIG. 3 by the encoder including the code plate and the reading head. .

The falling edge of this pulse (at the time of change from 0 to 1) coincides with the beginning of the read unit mark (change from 0 to 1) provided for each minimum read unit of the track. Therefore,
Only when this fall is detected, a clock signal is output from the one-shot circuit and latched, and the absolute signal sensors 3-1, 3-2 and 3-3 are turned on and the minimum reading unit corresponding to each sensor is turned on. Of each signal determination unit is read. For example, in the position of FIG. 5, the sensors 3-1, 3-2,
Both 3-3 detect 0 and the binary code at this position is "000".

Since the binary code (here, 3 bits) read by the absolute signal sensor is patterned so as not to have the same one, the absolute position can be known by the above method. For any natural number N, 2 ^K-1 <N ≦ 2 ^K
Is a natural number K, and for N columns of “0” and “1”,
Since it is known that there are no patterns where the continuous K binary codes are identical everywhere in the pattern, the one-track absolute pattern can have a larger pulse number. .

As mentioned above, the rotary encoder is explained as an example,
The present invention can be applied to a linear encoder and an encoder of a magnetic type or any other detection method.

[Reference] The absolute pattern arrangement is determined as follows.

That is, when the number of graduations is small, it may be sequentially performed by trial and error, but when the number of graduations is large, it is necessary to calculate by a computer.

In the case of the above-described four scales, for example, when each scale is “0”, there is always a case, so a series of four “0” s “0,0,0,0” is considered first. Then, if five “0” s are consecutive, the same combination will occur, so “0”
It is assumed that "1" always comes after four consecutive characters. In this way, “0” or “1” is sequentially added so that the same combination of contents does not occur when shifting one division at a time by four divisions.

The result of the computation performed by the computer in this way is the sixth.
Figures (a), (b), (c) and (d) show.

FIG. 6 (a) shows an absolute pattern in the case of 32 graduations, ie, N = 5 bits, and FIG. 6 (b) shows a 64 graduation, ie, N
FIG. 6 (c) shows an absolute pattern in the case of N = 8 bits, and FIG. 6 (d) shows an absolute pattern in the case of 1024 scales, ie, N = 10 bits. Patterns.

The absolute patterns in FIGS. 6 (b), (c) and (d) are configured as a series of patterns in which the scale at the end of the line is connected to the scale at the beginning of the next (lower) line.

When the absolute pattern shown in FIG. 6 is used for a rotary encoder, the last graduation in the lowermost row is connected to the first graduation in the first row so as to be endlessly continuous.

In the example of FIG. 6, the code arrangement when the absolute signal sensors are continuously arranged at intervals (λ) corresponding to one scale of the absolute pattern is shown. In the case where it is physically difficult to continuously arrange the scales at the scale intervals, it is possible to arrange the sensors at intervals of 2λ, for example, every other scale of the code array by devising the code arrangement of the absolute pattern. FIG. 7 shows an absolute pattern when N = 10 as one example. In this case N =
Ten, so ten sensors are placed on one scale, that is, the interval 2
λ.

Of course, it is possible to appropriately determine the absolute code for other intervals as well, and generally, an absolute code can be created for an interval that is an integral multiple of λ.

According to such an absolute pattern, since an absolute pattern can be realized in one track, it is possible to obtain an absolute encoder whose size is almost the same as that of a so-called incremental encoder.

[Effects of the Invention] As described above, according to the present invention, the signal determining portion in the absolute pattern of the code plate is formed smaller than the minimum reading unit, and the reading mark for the incremental pattern is formed in the gap. Therefore, a code plate including both an absolute pattern and an incremental pattern can be obtained in a single track, and the influence of adjacent reading units is reduced for the absolute pattern, so that reading accuracy is improved, and the code plate itself and the code plate itself are improved. It also contributes to downsizing of the combined detector. Further, there is an advantage that the formation of the absolute pattern and the incremental pattern of the code plate and the assembling and adjustment of the encoder are facilitated. That is, since the absolute signal is read based on the clock signal obtained from the same track, the high and low levels of the pulse signals detected from the individual sensors can be read simultaneously at a stable point in time, and there is no possibility that an error occurs in the output. A highly accurate absolute encoder can be obtained.

[Brief description of the drawings]

1A to 1D are schematic partial plan views showing an example of a code plate of the present invention, FIG. 2 is a schematic partial plan view of a conventional example, and FIG. 3 is a diagram relating to an embodiment of the present invention for an optical absolute encoder. FIG. 4 is a schematic circuit diagram showing an example of a signal processing circuit, FIG. 5 is an explanatory diagram of a detected waveform, and FIG.
To (d) are explanatory diagrams showing some examples of absolute patterns for obtaining absolute signals having different numbers of scales, FIG. 7 is an explanatory diagram showing another example of an absolute pattern, and FIG. FIG. 1B is a schematic plan view of a code plate for an optical absolute encoder according to an example, and FIG. 2B is a circuit diagram showing a signal processing circuit thereof. (Explanation of reference numerals of main parts) 1: Code plate 2: Track 3-1: Sensor for absolute signal 3-2: Sensor for absolute signal 3-3: Sensor for absolute signal 3-4: Sensor for absolute signal 4b: Incremental Signal sensor 5: (missing number) 6: Rotary axis

Claims (3)

(57) [Claims] 1. A one-track type absolute encoder code plate in which two types of minimum reading units corresponding to a "0" signal and a "1" signal are arranged on one track in a predetermined arrangement, wherein at least one of the types The minimum reading unit has a signal determining portion shorter than the unit length, and a synchronization signal reading unit mark is provided at a constant pitch corresponding to the unit length in a gap between the signal determining portions on the same track. A code plate for a one-track type absolute encoder, characterized in that: 2. A code plate according to claim 1, wherein: (a) a reading unit mark in the same minimum reading unit; and (b) a signal determining unit in said minimum reading unit of “1”.
(C) the area between the two has the same physical properties, and (d) the signal determination section of the minimum reading unit of “0”, and (e) all remaining areas on the track. Has a physical property different from the physical property described above. 3. A read head having at least two sensors arranged along the longitudinal direction of a track of a code plate, wherein one of said sensors is used for an incremental signal, the other is used for an absolute signal, and the distance between the two is set. A read head characterized in that the read heads are separated by substantially (m + 1/2) λ (where λ is the minimum read unit length of the code plate, and m is 0 or a positive integer).