JP2011154005A - Encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an encoder which can improve reliability when operating at high temperatures. <P>SOLUTION: The encoder (1) includes a code disk (10) having a pattern, a light source (20) for irradiating the code disk (10) with light, a sensor (30) having a plurality of light receiving elements for detecting the pattern, and an arithmetic processing part (90) using a first sensor signal obtained from the sensor (30) in a first state when at least part of the plurality of light receiving elements do not receive the light to correct a second sensor signal obtained from the sensor (30) in a second state when the light receiving elements detect the pattern. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an encoder that performs position detection.

  In an optical encoder that optically detects a moving position of a moving body and a rotation angle position of a rotating body, the position is detected using a photo IC or an image sensor having a photodiode array. The encoder detects the temperature of the operating environment by a temperature sensor provided in the encoder in order to ensure the detection accuracy of the position. In particular, the temperature sensor is applied to a high-temperature operating environment or detects an abnormal temperature rise to prevent an encoder failure and a decrease in detection accuracy (see, for example, Patent Document 1). ).

JP 2006-50710 A

By the way, in recent years, the encoders as described above are desired to be further downsized due to the expansion of their applications.
However, when a temperature sensor is provided inside the encoder to manage the temperature of the operating environment as in Patent Document 1, for example, the temperature sensor may be a limiting condition for downsizing the encoder. . On the other hand, when the temperature sensor is not provided, the encoder cannot identify that it is within the operating temperature range, cannot detect the occurrence of abnormal temperature rise, and ensures the reliability of the encoder body and detected position information. There is a problem that it may not be possible.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an encoder capable of improving the reliability within the operating temperature range.

  In order to solve the above problems, an embodiment of the present invention includes a code plate having a pattern, a light source that irradiates light to the code plate, a plurality of light receiving elements, a sensor that detects the pattern, and the plurality From the sensor in the second state in which the light receiving element detects the pattern using a first sensor signal obtained from the sensor in a first state in which at least some of the light receiving elements are not receiving the light. An encoder comprising: an arithmetic processing unit that performs correction on the obtained second sensor signal.

  According to the present invention, it is possible to improve the reliability within the operating temperature range.

It is a block diagram which shows the structure of the encoder by one Embodiment of this invention. It is a figure which shows one form of the pattern provided in the code | symbol plate 10 by one Embodiment of this invention. It is a side view which shows arrangement | positioning of the code | symbol board 10, the light source 20, and the sensor 30 by one Embodiment of this invention. It is a top view which shows the light-receiving surface 31 of the sensor 30 by one Embodiment of this invention. It is an enlarged view which shows the light-receiving surface 31 of the sensor 30 by one Embodiment of this invention. It is sectional drawing of the code | symbol plate 10, the light source 20, and the sensor 30 by one Embodiment of this invention. It is sectional drawing of the code | symbol plate 10, the light source 20, and the sensor 30 by one Embodiment of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In the optical encoder shown in the present embodiment, the temperature change of the image sensor can be detected by monitoring the dark current of the image sensor. Accordingly, the encoder can prevent erroneous determination of the detected optical signal, and can improve the reliability of the detected position information.

(First embodiment)
FIG. 1 is a block diagram showing the configuration of the encoder according to the present embodiment.
The encoder 1 shown in this figure includes a code plate 10, a light source 20, a sensor 30 (image sensor), a light source drive unit 40, a sensor drive unit 50, an amplification unit 60, a storage unit (memory) 70, and an arithmetic processing unit 90. Is provided. The encoder 1 shown in this embodiment shows an aspect for detecting angular position information of the rotating shaft of the rotating body.
The code plate 10 is fixed to the rotating shaft of the rotating body and is provided so as to be rotatable together with the rotating body. On the code plate 10, a pattern that is an index indicating the position of the rotation angle is arranged. At least one of an absolute track in which an absolute angular position pattern for detecting an absolute angular position is arranged and an incremental track in which a relative angular position pattern for detecting a relative angular position is arranged in the arrangement of the pattern. One track is provided. The tracks provided on the code plate 10 are arranged at a fixed distance with respect to the rotation axis, that is, provided on the circumferences having different radii.

FIG. 2 is a diagram illustrating one form of a pattern provided on the code plate 10.
The code plate 10 shown in FIG. 2 includes both an absolute track including the pattern 11 and an incremental track including the pattern 12. The pattern 11 included in the absolute track is obtained by encoding position information indicating the positional relationship between the sensor 30 and the code plate 10 as an absolute position. Further, the pattern 12 included in the incremental track is obtained by arranging indexes of the same shape at equal intervals.
Patterns 11 and 12 provided on each track of the code plate 10 are reflective patterns that reflect light from the light source 20. The patterns 11 and 12 are subjected to surface treatment, for example, in a state having different reflectances so that the amount of reflection differs according to the information indicated by the patterns. In this figure, regions with low reflectivity are shown in dark colors, and regions with high reflectivity are shown in white.
In addition, the patterns 11 and 12 are provided side by side on the code plate 10, and each pattern is provided on the same circumference having different radii with reference to the rotation axis. The width of each pattern and the radius from the rotation axis are appropriately provided, and a gap is provided so that the two patterns do not overlap.

Returning to FIG. 1, the light source 20 emits light necessary for detecting a pattern provided on the track of the code plate 10. The lighting state of the light source 20 is controlled according to a control signal supplied from the light source driving unit 40.
The sensor 30 detects a pattern provided on the track of the code plate 10. The light receiving surface of the sensor 30 is disposed to face the surface of the code plate 10 on which the tracks are provided. The light receiving surface of the sensor 30 is provided with a light detecting element (light receiving element) arranged on a two-dimensional lattice. The light detection element is provided so as to be parallel to the tangential direction of the track provided on the code plate 10 or to face the position where the track of the code plate 10 is arranged along the track. As the sensor 30, for example, a charge coupled device (CCD), a complementary metal oxide semiconductor (C-MOS) sensor, or the like can be applied.
Each light detection element of the sensor 30 performs photoelectric conversion according to the amount of received light, and converts it into an analog signal indicated by a voltage corresponding to each light quantity. For example, a C-MOS (Complementary Metal Oxide Semiconductor) sensor can be applied to each light detection element. In the case of the C-MOS sensor, the light detection element includes a photodiode, a charge voltage conversion unit, a selector switch, and the like. Each light detection element of the sensor 30 is selected according to a control signal supplied from the light source driving unit 40, and can detect the amount of light received from information output from the selected light detection element.

The light source driving unit 40 supplies a control signal for causing the light source 20 to emit light necessary for detecting a pattern provided on the track of the code plate 10.
The sensor driving unit 50 supplies the sensor 30 with a control signal and a timing signal for detecting the amount of light received by the photodetecting elements included in the selected region on the light receiving surface of the sensor 30 in accordance with an instruction from the arithmetic processing unit 90. .
The sensor driving unit 50 sequentially outputs a signal voltage corresponding to the amount of charge accumulated according to the amount of received light to the light detection elements included in the range corresponding to the selected region.
The amplifying unit 60 amplifies a signal corresponding to the amount of received light detected by the light detection element in the sensor 30. The amplification unit 60 adjusts the amplification factor according to the signal level output from the sensor 30 so as to obtain an appropriate signal level.

The storage unit (memory) 70 stores operation mode designation information supplied from the outside, a reference value used for determination processing, setting information according to the state of the sensor 30, and the like in a variable area. The storage unit 70 is not limited to a semiconductor memory element, and may be a latch circuit that stores a state.
The arithmetic processing unit 90 performs various settings in the encoder 1, outputs a control instruction to each unit during operation, and generates and outputs position information detected based on the amount of light detected by the sensor 30. The arithmetic processing unit 90 includes an input / output unit 91, a light source control unit 92, a sensor control unit 93, a signal detection unit 94, and a position detection unit 95.
The input / output unit 91 receives setting information such as an initial value and a threshold for determining the operation of the encoder 1 according to setting information supplied from the outside, and records it in the memory 70. Further, when an instruction to refer to a setting state or the like is supplied from the outside, the input / output unit 91 refers to and outputs corresponding information.
The light source control unit 92 supplies a control signal for controlling the light emission state of the light source 20 to the light source driving unit 40 based on an instruction from the input / output unit 91.
The sensor control unit 93 supplies a control signal for selecting information to be output from the sensor 30 to the sensor driving unit 50 based on an instruction from the input / output unit 91.
The signal detection unit 94 is supplied with information based on the signal detected by the sensor 30 via the amplification unit 60. The signal detection unit 94 performs signal conversion processing on the information. Examples of signal conversion processing include filtering processing and analog-digital conversion processing.
The position detection unit 95 performs determination processing based on the result processed by the signal processing unit 94. Examples of the determination process include a determination process for comparing with a predetermined reference value.

Next, with reference to the drawings, the arrangement of each component described above will be described.
FIG. 3 is a side view showing the arrangement of the code plate 10, the light source 20 and the sensor 30.
The code plate 10 shown in FIG. 3 is provided with a track provided with the patterns 11 and 12 shown in FIG. 2 on the lower surface. The light receiving surface 31 of the sensor 30 is arranged in a state parallel to and facing the surface on which the patterns 11 and 12 are arranged. The light source 20 is disposed on the light receiving surface 31 of the sensor 30 with the optical axis directed toward the code plate 10. Light emitted from the light source 20 is irradiated toward the code plate 10, and each reflected light through the patterns 11 and 12 of the code plate 10 is applied to the light receiving surface 31 of the sensor 30.

FIG. 4 is a top view showing the light receiving surface 31 of the sensor 30.
FIG. 4 schematically shows the change in the amount of light caused by the light irradiated on the light receiving surface 31 and the regions 32 and 33 where the light detection elements for detecting the reflected light from the patterns 11 and 12 are selected. Show.
For example, light reflected by a portion having a low reflectance is absorbed by the patterns 11 and 12 provided on the code plate 10, and the amount of light irradiated on the light receiving surface 31 by the reflected light is reduced. In FIG. 4, a shadow indicated by a square area is formed in accordance with a pattern having a low reflectance.
The patterns 11 and 12 are parallel patterns on the code plate 10 by providing each pattern on the same circumference with different radii with the rotation axis of the code plate 10 as a reference. The light source 20 is disposed on the light receiving surface 31 that faces the gap formed between the pattern 11 and the pattern 12. The optical axis of the light source 20 is parallel to the rotation axis of the code plate 10 and is provided so as to pass through a gap formed between the pattern 11 and the pattern 12. That is, the light source 20 is provided at a position facing the gap between the pattern 11 and the pattern 12 provided in parallel. When the light source 20 is arranged at such a position, as shown in the figure, the shadow of the pattern 11 and the pattern 12 is projected on the light receiving surface 31 with the light source 20 interposed therebetween.

FIG. 5 is an enlarged view showing the light receiving surface 31 of the sensor 30 in the present embodiment.
FIG. 6 is a cross-sectional view of the code plate 10, the light source 20, and the sensor 30. A state in which the light source 20 emits light is shown.
On the light receiving surface 31 of the sensor 30, the light detection elements are two-dimensionally arranged.
In addition, the light receiving surface 31 in the present embodiment includes a light shielding region 310 where light cannot be received and a region 320 where light can be received. The light shielding region 310 can be formed by providing a light-shielding film that does not transmit light on the light receiving surface 31 of the sensor 30. As a result, among the light detecting elements arranged on the light receiving surface 31 of the sensor 30, the light detecting element 311 that cannot receive light and the light detecting element 321 that can receive light can be provided on the light receiving surface 31. The light detection element 311 and the light detection element 312 have the same characteristics formed as the same sensor 30, but are shielded by the light shielding film of the light shielding region 310 provided on the light receiving surface 31. No is different.
The light source 20 is disposed between the light shielding region 310 and the region 320 that can receive light. With such an arrangement, it is possible to provide a wiring for supplying power to the light source 20 on the light shielding region. The place where the light source 20 is arranged is a light shielding region 310.

The sensor 30 generates a dark current even when the light detection element receives light (second state) and does not receive light (first state), and the level of the detection signal changes due to the dark current. . The magnitude of the dark current depends on the temperature of the sensor 30 and increases as the temperature increases. When the change rate of the dark current is expressed by a temperature coefficient (temperature gradient), for example, in the case of a CCD, when the temperature changes by 8 ° C., the value of the dark current is doubled, and in the case of a CMOS sensor, the temperature is 5 to 6 When the temperature changes, the dark current value doubles. When the applicable temperature range is wide, the value of dark current changes greatly.
The encoder 1 needs to avoid the influence of such dark current and correctly determine the state of receiving light (second state) and the state of not receiving light (first state).
Therefore, in order to adapt to a wide temperature range, if the signal from the sensor 30 is determined by a method of comparing with a predetermined reference value, the noise margin decreases and the probability of erroneous detection increases. Therefore, by performing correction by subtracting the offset voltage due to the dark current that varies with temperature from the signal generated by the sensor 30, it is possible to reduce the influence of the dark current at that temperature and obtain a detection signal. That is, the encoder 1 in the present embodiment performs correction based on the offset voltage generated by the dark current, and obtains a detection signal that is detected according to the amount of received light. Therefore, the encoder 1 according to the present embodiment uses the first sensor signal obtained from the sensor 30 in the first state where at least some of the plurality of light detection elements (light receiving elements) are not receiving light. The second sensor signal obtained from the sensor 30 is corrected in the second state in which the light detection element 321 detects the pattern.

Also, by detecting the dark current of the sensor 30 and comparing the detected value with the standard dark current value at the standard temperature, the value of the standard dark current is subtracted from the dark current value according to the temperature. The obtained dark current difference is defined as dark current deviation. The temperature difference from the standard temperature can be calculated from the dark current deviation value. An estimated operating temperature is calculated based on the temperature difference calculated by this calculation process.
The process of calculating the temperature difference from the standard temperature based on the obtained dark current deviation can be performed with reference to an arithmetic expression defined by a linear operation or a table in which a correspondence relationship is determined. A table that defines the correspondence between the dark current deviation and the temperature difference from the standard temperature is stored in the memory 70 in advance, and the arithmetic processing unit 90 refers to the value of the dark current deviation as a key to determine the temperature. Get the difference value.

  Through the processing described above, the encoder 1 can detect the dark current in the sensor 30 and reduce the influence of the dark current that changes according to the operating temperature. Further, since the operating temperature at that time can be derived based on the value of the dark current, the temperature can be detected without providing a separate temperature sensor. The encoder 1 can detect an abnormal state such as a state exceeding the operating temperature range, and can improve reliability during high-temperature operation.

(Second Embodiment)
Next, another embodiment of the dark current detection method will be described with reference to the drawings. The same components as those in FIGS. 1 to 6 are denoted by the same reference numerals.
FIG. 7 is a cross-sectional view of the code plate 10, the light source 20, and the sensor 30, and shows a state where the light source 20 is turned off. That is, each light detection element provided on the light receiving surface of the sensor 30 is in a state (first state) in which no light is received without covering the light receiving surface with a light shielding film or the like.
The encoder 1 in the present embodiment can detect the dark current by detecting the output signal (first sensor signal) of the sensor 30 during the period when the light source is turned off.
The light source 20 is driven to repeat intermittent lighting from the light source driving unit 40 based on an instruction from the light source control unit 92. Therefore, the arithmetic processing unit 90 detects the signal of the sensor 30 during the period when the light source 20 is turned off, and corrects the signal (second sensor signal) of the sensor 30 detected during the period when the light source 20 is caused to emit light. Do.
The arithmetic processing unit 90 can detect the value of the dark current by detecting the signal of the sensor 30 during the period when the light source 20 is turned off. Further, the light detection element 321 of the sensor 30 used for detecting the state where the light source 20 emits light (second state) can also be used for detecting the dark current. Since the dark current can be measured using the same light detection element 321, detection errors due to differences in elements can be reduced.

Note that the light source 20 can be used by repeatedly operating light emission and extinction to provide a period for detecting a dark current within the extinction period, and can be implemented without performing special processing on the sensor 30.
By setting the dark current detection period t _dc to the same length as the light emission time t _ON of the light source 20 (t _dc = t _ON ), the amount of dark current affected by the light emission time of the light source 20 can be offset. it can.

(Third embodiment)
Next, another embodiment of the dark current detection method will be described. The same components as those in FIGS. 1 to 7 are denoted by the same reference numerals.
By shortening the emission time t _ON of the light source 20, because it can reduce the amount of blur due to the movement of the code plate 10 to the sensor 30, the light emission period t _ON is sufficiently short time is selected for the light-off period t _OFF The The dark current detection period t _{dc is set} to a length of N times the light emission time t _ON of the light source 20 (where N is (N × t _ON ) <t _OFF ), and the detected dark current value is set. By multiplying by 1 / N, the influence of dark current corresponding to the same time as the light emission period can be calculated. The calculated value can be used to offset the amount of dark current that is affected by the light emission time of the light source 20. By performing such processing, the influence of noise mixed in the dark current detection period can be reduced. However, even if the dark current detection period t _dc and the light emission time t _ON of the light source 20 are set to N times as long, saturation on the circuit does not occur.

(Fourth embodiment)
Next, another embodiment of the dark current detection method will be described. The same components as those in FIGS. 1 to 7 are denoted by the same reference numerals.
The light source driving unit 40 changes the lengths of the period during which the light source 20 is turned on and the period during which the light source 20 is turned off in synchronization with the cycle of the detection cycle for detecting the position information of each pattern in accordance with the control from the arithmetic processing unit 90. To do. Thereby, since the detection cycle of each pattern performed repeatedly and the light extinction period for dark current determination do not interfere, it can carry out continuously without interrupting a detection cycle. And according to the timing which switches a detection cycle, the period of light emission and light extinction of the light source 20 can be changed.

  The present invention is not limited to the above embodiments, and can be modified without departing from the spirit of the present invention.

  Note that the arithmetic processing unit 90 of the encoder 1 according to the present embodiment has a first state obtained from the sensor 30 in a first state where at least some of the plurality of light detection elements (light receiving elements) are not receiving light. Using the sensor signal, the second sensor signal obtained from the sensor 30 is corrected in the second state in which the light detection element 321 detects the pattern.

  In the encoder 1 according to this embodiment, the plurality of light detection elements are formed on the same substrate as the light detection element 311 that is shielded as the first state, and detects the pattern as the second state. And a photodetecting element 321.

  In the encoder 1 according to this embodiment, the light source 20 is disposed between the light detection element 311 and the light detection element 312.

  In addition, in the encoder 1 according to the present embodiment, the arithmetic processing unit 90 detects the first sensor signal during the period when the light source 20 is turned off, and the second sensor signal detected during the period during which the light source 10 is caused to emit light. Perform the correction.

  In the encoder 1 of the present embodiment, the light source driving unit that repeats light emission and extinction of the light source 20 changes the period of light emission and extinction of the light source in synchronization with pattern detection.

  In the encoder 1 according to the present embodiment, the pattern is a first pattern that is arranged at equal intervals, and a second pattern that is encoded position information that indicates the positional relationship between the sensor 30 and the code plate 10 as an absolute position. And formed.

  In the encoder 1 according to the present embodiment, the light source 20 is provided at a position facing the first pattern and the second pattern provided in parallel.

  In the encoder 1 according to the present embodiment, the light source 20 is disposed on the light receiving surface 31 of the sensor 30.

  In the encoder 1 according to the present embodiment, the arithmetic processing unit 90 detects a change in the ambient temperature based on the change amount of the first sensor signal.

  In the encoder 1 according to the present embodiment, the arithmetic processing unit 90 subtracts the dark current component included in the second sensor signal based on the first sensor signal.

  In the encoder 1 according to the present embodiment, the arithmetic processing unit 90 increases the amplification factor for the second sensor signal in accordance with the increase in the first sensor signal.

  In the encoder 1 according to the present embodiment, the threshold level for determining the second sensor signal is a value that increases as the first sensor signal increases.

In addition, the encoder 1 in the present embodiment outputs abnormality information based on the first sensor signal and the second sensor signal.
The optical encoder shown in this embodiment uses an image sensor as a sensor for detecting light, for example. By monitoring the dark current of some or all of the pixels in the image sensor, erroneous detection during high temperature operation of the optical encoder is prevented, and abnormal operation leading to failure is avoided.
In addition, the temperature sensor that has been generally provided so far is not used for temperature detection in the present embodiment, and thus can be deleted. The number of parts to be mounted on the encoder body can be reduced and the size can be reduced, and the reliability can be improved by reducing the number of parts.

DESCRIPTION OF SYMBOLS 1 Encoder 10 Code | symbol plate 20 Light source 30 Sensor 90 Arithmetic processing part

Claims (13)

A sign plate having a pattern;
A light source for irradiating the code plate with light;
A sensor having a plurality of light receiving elements and detecting the pattern;
In a second state in which the light receiving element detects the pattern using a first sensor signal obtained from the sensor in a first state in which at least some of the plurality of light receiving elements do not receive the light. An encoder comprising: an arithmetic processing unit that performs correction on a second sensor signal obtained from the sensor. The encoder according to claim 1, wherein
The plurality of light receiving elements are:
A first light-receiving element that is shielded from light as the first state; a second light-receiving element that is formed on the same substrate as the first light-receiving element and detects the pattern as the second state;
An encoder comprising: The encoder according to claim 2, wherein
The encoder is characterized in that the light source is disposed between the first light receiving element and the second light receiving element. The encoder according to any one of claims 1 to 3,
The arithmetic processing unit includes:
An encoder that detects the first sensor signal during a period when the light source is turned off and corrects the second sensor signal detected during a period when the light source is caused to emit light. The encoder according to any one of claims 1 to 4,
A light source driving unit that repeats light emission and extinction of the light source,
The light source driving unit is
An encoder that changes a period of light emission and extinction of the light source in synchronization with detection of the pattern. An encoder according to any one of claims 1 to 5,
The pattern is
An encoder comprising: a first pattern arranged at equal intervals; and a second pattern encoded with position information indicating a positional relationship between the sensor and the code plate as an absolute position. . The encoder according to claim 6, wherein
The light source is
An encoder, wherein the encoder is provided at a position facing the first pattern and the second pattern provided in parallel. The encoder according to any one of claims 1 to 7,
The encoder, wherein the light source is disposed on a light receiving surface of the sensor. The encoder according to any one of claims 1 to 8,
The arithmetic processing unit includes:
An encoder that detects a change in ambient temperature based on a change amount of the first sensor signal. An encoder according to any one of claims 1 to 9,
The arithmetic processing unit includes:
An encoder characterized by subtracting a dark current component contained in the second sensor signal based on the first sensor signal. The encoder according to any one of claims 1 to 10,
The arithmetic processing unit includes:
An encoder that increases an amplification factor for the second sensor signal in accordance with an increase in the first sensor signal. The encoder according to any one of claims 1 to 11,
The threshold level for determining the second sensor signal is a value that increases with an increase in the first sensor signal. The encoder according to any one of claims 1 to 12,
An encoder that outputs abnormality information based on the first sensor signal and the second sensor signal.

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