An absolute optical encoder signal processing method

Abstract

This invention relates to a signal processing method for an absolute photoelectric encoder, comprising: illuminating incremental and absolute code tracks on an encoding medium with light emitted from a light source; wherein the incremental code track is composed of periodically interlaced dark lines, and the absolute code track is composed of specific lines containing absolute position information; the light signals transmitted or reflected by the two code tracks contain position information; the light-receiving device array corresponding to the incremental code track includes an incremental light-receiving device array and a reference light-receiving device array; the incremental light-receiving device array converts the light signal into a sinusoidal incremental current signal with the same amplitude and a 90° phase difference; the reference light-receiving device array converts the light signal into a reference photocurrent approximately equal to DC; a reference level is obtained after amplification by a certain ratio; a set of absolute codes is obtained; and the position information is further determined by further subdividing the absolute codes based on the relationship between the widths of the incremental and absolute code track lines.

Description

Technical Field

[0001] This invention belongs to the field of photoelectric encoders and relates to a signal processing method for an absolute photoelectric encoder. Background Technology

[0002] An optical encoder is a precision optical instrument that converts mechanical geometric displacement into electrical signals using photoelectric conversion technology. Based on their working principle and encoding method, photoelectric encoders can be divided into incremental and absolute types. Incremental encoders obtain relative position information using the output signal, while absolute encoders obtain absolute position information through digital encoding. An absolute encoder's code disk can simultaneously have incremental and absolute code tracks. The absolute code track signal is amplified and compared with a reference level to output a square wave, providing absolute position information. The incremental code track signal is amplified and outputs a sine wave, which is then used for angle subdivision via analog-to-digital conversion (ADC). Absolute photoelectric encoders can achieve high resolution while being miniaturized. However, this design has the following drawbacks: when conditions such as temperature and light intensity change, the photocurrent changes. With a constant reference level, the duty cycle of the absolute code track signal will change, easily leading to bit errors. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a signal processing method for an absolute photoelectric encoder. This method obtains the reference level of the absolute signal by processing a reference signal derived from the incremental code channel, resulting in lower cost, wider application environments, and a lower bit error rate. The technical solution is as follows:

[0004] A signal processing method for an absolute photoelectric encoder, characterized by comprising the following steps:

[0005] 1) The light emitted by the light source illuminates the incremental code track and the absolute code track of the encoding medium. The incremental code track is composed of periodic etched lines with dark interlacing, and the absolute code track is composed of specific etched lines containing absolute position information. The encoding of each position is uniquely determined, and the light signal transmitted or reflected by the two code tracks contains position information.

[0006] 2) The light-receiving device array corresponding to the incremental code track includes an incremental light-receiving device array and a reference light-receiving device array. The incremental light-receiving device array converts the optical signal into four sinusoidal incremental current signals with the same amplitude and a 90° phase difference. The reference light-receiving device array converts the optical signal into a reference photocurrent that is approximately DC. The N light-receiving devices in the reference light-receiving device array are arranged in an even number of cycles with the optical signal width corresponding to one incremental code track scribe line as the period.

[0007] 3) The reference photocurrent is amplified by a certain ratio to obtain the reference level;

[0008] 4) The n light-receiving devices corresponding to the absolute code channel convert the optical signal into a set of current signals. After the current signals are amplified, they are compared with the reference level to obtain a set of absolute codes. The absolute codes are uniquely associated with the position of the encoding medium and are used for coarse position division.

[0009] 5) The four sinusoidal incremental current signals are amplified by the circuit and then converted from analog to digital to obtain the specific position represented by a pair of bright and dark lines in the incremental code track within the cycle, that is, the relative position information based on the absolute code. Combining the relationship between the width of the incremental code track lines and the width of the absolute code track lines, the position information is further subdivided based on the absolute code.

[0010] Furthermore, let the reference photocurrent be I. D0 Four-channel sinusoidal incremental current signal I D1 I D2 I D3 and I D4 , then I D0 =NI0+I A sin(2πft+α1)+I A sin(2πft+α2)+…+I A sin(2πft+α N ) = NI0, where I0 is the common-mode current of a single photodetector, I A denoted as ν, where ν is the current amplitude and f is the optical signal frequency.

[0011] Furthermore, the amplification factor of the reference photocurrent is:

[0012]

[0013] Among them, A M P is the amplification factor of the current signal corresponding to the absolute code track. M P represents the incident light power received by a single light-receiving device corresponding to an absolute code channel. D0 The total incident light power received by the N light-receiving devices that generate the reference photocurrent.

[0014] Furthermore, the signal processing is implemented using an absolute photoelectric encoder, which includes an encoding medium, a detection element, a light source, and a lens. The encoding medium contains incremental code tracks and absolute code tracks. The incremental code tracks are composed of periodic etched lines with alternating light and dark areas, and the absolute code tracks are composed of specific etched lines containing absolute position information. The detection element includes an incremental light-receiving device array, a reference light-receiving device array, an absolute light-receiving device array, an incremental signal readout circuit, an absolute signal readout circuit, and a reference level generation circuit.

[0015] Furthermore, the detection element and the light source are disposed on both sides of the code disk; the lens is disposed between the light source and the encoding medium to convert the light emitted by the light source into parallel light; the incremental light receiving device array and the reference light receiving device array are both disposed on one side of the detection element for detecting the light signal from the incremental code track of the code disk;

[0016] The absolute light-receiving device array is disposed on one side of the detection element and is used to detect the optical signal from the absolute code track of the code disk;

[0017] The incremental signal readout circuit is used to process the photocurrent signal of the incremental signal receiving device;

[0018] The absolute signal readout circuit is used to process the photocurrent signal generated by the absolute photodetector array;

[0019] The reference level generation circuit is a DC amplifier circuit used to process the photocurrent signal of the reference light-receiving device.

[0020] Compared with the prior art, the beneficial effects of the technical solution of the embodiments of the present invention are:

[0021] This invention proposes a method for generating a reference level that adapts to environmental changes. In the array of light-receiving devices corresponding to the incremental code channel, a portion is used as a reference light-receiving device. After its output is amplified by a certain proportion, it is used as a reference level in the absolute signal processing process, so that it can change synchronously with the absolute signal as temperature and light intensity change, thereby achieving more accurate absolute code output. Attached Figure Description

[0022] Figure 1 This is a cross-sectional view of an absolute photoelectric encoder according to the first embodiment of the present invention;

[0023] Figure 2 This is a cross-sectional view of an absolute photoelectric encoder according to a second embodiment of the present invention;

[0024] Figure 3 This is a partial schematic diagram of the encoding media of the present invention;

[0025] Figure 4 This invention relates to the correspondence between incremental code channels and light-receiving devices, as well as the arrangement of light-receiving devices.

[0026] Figure 5 This is a schematic diagram of the detection element scheme of the present invention;

[0027] Explanation of reference numerals in the attached figures

[0028] 100, 200 Absolute Photoelectric Encoders

[0029] 11, 21 Detection elements

[0030] 111, 24 light sources

[0031] The light-receiving device arrays corresponding to incremental code channels 112 and 211

[0032] 113, 212 Absolute photodetector array

[0033] 12, 22 Encoded Media

[0034] Incremental code channels 121 and 221

[0035] 122, 222 Absolute Code Track

[0036] 23 Lenses

[0037] I D1 I D2 I D3 I D4 Incremental photocurrent

[0038] I D0 Reference photocurrent

[0039] V ref_TIA Transimpedance amplifier reference level

[0040] V ref Reference level Detailed Implementation

[0041] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0042] The absolute photoelectric encoder of this invention can operate within a certain range of light intensity and temperature, and has a low bit error rate.

[0043] Please refer to Figure 1 The image shown is a cross-sectional view of a photoelectric encoder according to a first embodiment of the present invention. The optical encoder 100 includes an encoding medium 12 and a detection element 11. The encoding medium 12 is, for example, a code disk or codetrip, which rotates or performs linear motion relative to the detection element, depending on the application.

[0044] The encoding medium 12 includes incremental code channels 121 and absolute code channels 122. The absolute code channel 122 generates a specific reflection pattern that determines the absolute position to ascertain the current position or angle of the encoding medium 12. The incremental code channel 121 generates a periodic reflection pattern with alternating bright and dark areas to facilitate subdivision of the position or angle and provide a reference level. In this embodiment, one bright-dark cycle of the incremental code channel corresponds to twelve light-receiving devices in the detection element. In this invention, there are no specific limitations on the number and shape of the slits or reflective strips included in the incremental and absolute code channels, nor on the number of light-receiving devices in the detection element corresponding to one bright-dark cycle of the incremental code channel.

[0045] Figure 1 In this context, the detection element 11 refers to the package or chip located below the encoding medium 12. The detection element includes a light source 111, a light-receiving device array 112 corresponding to the incremental code track, an absolute light-receiving device array 113, an incremental signal readout circuit, an absolute signal readout circuit, and a reference level generation circuit.

[0046] Please refer to Figure 2 The image shown is a cross-sectional view of a photoelectric encoder according to a second embodiment of the present invention. The optical encoder 200 includes a detection element 21, an encoding medium 22, a lens 23, and a light source 24. The encoding medium 22 is, for example, an encoding disk or encoding tape, which rotates or performs linear motion relative to the detection element, depending on the application. The detection element includes an array of light-receiving devices 211 corresponding to the incremental code track, an array of absolute light-receiving devices 212, an incremental signal readout circuit, an absolute signal readout circuit, and a reference level generation circuit. The light emitted by the light source 24 is converted into parallel light after passing through the lens 23, passes through the code track slits of the encoding medium 22, reaches the array of light-receiving devices in the detection element 21, and is output after processing by the incremental signal readout circuit, the absolute signal readout circuit, and the reference level generation circuit. In this embodiment, one cycle of the incremental code track corresponds to twelve light-receiving devices in the detection element.

[0047] Figure 3 The structure of the incremental and absolute code channels in any of the aforementioned embodiments is illustrated using a circular encoding medium comprising one incremental code channel and one absolute code channel as an example. In this invention, there are no specific limitations on the shape of the encoding medium or the number of code channels it contains. Figure 3 As shown, the incremental code track consists of periodic etched lines with alternating light and dark areas, while the absolute code track consists of specific etched lines containing absolute position information.

[0048] Figure 4The arrangement of the light-receiving device array corresponding to the incremental code track in any of the aforementioned embodiments is illustrated using a linear code disk and a rectangular light-receiving device as examples. In this invention, the shape of the light-receiving device is not specifically limited. In any of the aforementioned embodiments, each pair of bright and dark etched lines in the incremental code track corresponds to twelve light-receiving devices after imaging. The light-receiving device array corresponding to the incremental code track has five outputs as shown in the figure. Four incremental signal light-receiving devices output sinusoidal signals with a 90° phase difference. The final output of the reference light-receiving device D0 is a signal with low phase correlation and approximate to DC. To obtain a larger signal output, multiple interleaved light-receiving devices are connected in parallel to provide one signal output. Let I0 represent the common-mode current of a single light-receiving device, I... A Let f represent the current amplitude and f represent the output signal frequency. Then, the five output signals of the incremental light-receiving device corresponding to a pair of bright and dark scribed lines can be expressed as follows:

[0049]

[0050]

[0051]

[0052]

[0053]

[0054] The total output of the reference light-receiving device is an approximate DC current independent of phase. In this invention, there is no absolute limit to the number of light-receiving devices in the detection element corresponding to one cycle of the incremental code track, and there is no absolute limit to the position of the reference light-receiving device in the incremental light-receiving device array; only the total output of the reference light-receiving device is limited to an approximate DC current.

[0055] The common-mode current of the reference photodetector in the photodetector array corresponding to the incremental code channel has a certain proportional relationship with the common-mode current of the absolute photodetector. This proportional relationship is related to the area of ​​the photodetector and the light distribution of the light source. This proportional relationship can be determined by theoretical analysis combined with test results. Therefore, the photocurrent of the reference photodetector can be amplified by a certain ratio and used as the reference level of the absolute signal. The amplification factor of the reference photocurrent is:

[0056]

[0057] Among them, A M P is the amplification factor of the current signal corresponding to the absolute code track. M P represents the incident light power received by a single light-receiving device corresponding to an absolute code channel. D0 The total incident light power received by the N light-receiving devices that generate the reference photocurrent.

[0058] like Figure 5As shown, the photocurrent of the reference light-receiving device is amplified by DC and used as the reference level for the absolute signal. The photocurrent of the absolute code is first converted from current to voltage by a transimpedance amplifier (TIA) and amplified in one stage. Then, it enters a comparator and is compared with the aforementioned reference level, converting the analog signal into a square wave signal corresponding to the absolute code element, thus obtaining the coarse position information for determining the absolute code. The photocurrent of the incremental code is first converted from current to voltage by a transimpedance amplifier (TIA) and amplified in one stage. Then, it is converted from single-ended signal to differential signal by an operational amplifier (OPA) and amplified in two stages. The relative position information based on the absolute code is obtained through analog-to-digital conversion. Combining the relationship between the width of the incremental code track and the width of the absolute code track, the absolute code can be further subdivided to obtain the final position information.

[0059] In summary, traditional absolute photoelectric encoders, due to the fixed reference level of the absolute signal, experience changes in the common-mode level of the absolute signal when conditions such as light intensity and temperature change. For a fixed reference level, the duty cycle of the comparator output square wave will change, easily leading to misjudgments. Therefore, this invention provides a method for generating a reference level. This method involves setting a reference photodetector at a specific position corresponding to the incremental code track, ensuring that the photocurrent output by the reference photodetector is DC. After amplification by a certain ratio, this photocurrent serves as the reference level for the absolute signal. Because this reference level, like the absolute signal, originates from the photodetector, it changes synchronously with conditions such as light intensity and temperature, i.e., it adapts to environmental changes, thereby stabilizing the duty cycle of the absolute signal output square wave and reducing its bit error rate.

[0060] While the present invention has been disclosed through the foregoing examples, it is not intended to limit the invention. Anyone skilled in the art to which this invention pertains can make various modifications and alterations without departing from the spirit and scope of the invention. Therefore, the scope of protection of this invention shall be determined by the appended claims.

Claims

1. A signal processing method for an absolute photoelectric encoder, characterized in that, Includes the following steps: 1) The light emitted by the light source illuminates the incremental code track and the absolute code track of the encoding medium. The incremental code track is composed of periodic etched lines with alternating light and dark, and the absolute code track is composed of specific etched lines containing absolute position information. The encoding of each position is uniquely determined, and the light signal transmitted or reflected by the two code tracks contains position information. 2) The light-receiving device array corresponding to the incremental code track includes an incremental light-receiving device array and a reference light-receiving device array. The incremental light-receiving device array converts the optical signal into four sinusoidal incremental current signals with the same amplitude and a 90° phase difference. The reference light-receiving device array converts the optical signal into a reference photocurrent that is approximately DC. The N light-receiving devices in the reference light-receiving device array are arranged in an even number of cycles with the optical signal width corresponding to one incremental code track scribe line as the period. 3) The reference photocurrent is amplified by a certain ratio to obtain the reference level; 4) The n light-receiving devices corresponding to the absolute code channel convert the optical signal into a set of current signals. After the current signals are amplified, they are compared with the reference level to obtain a set of absolute codes. The absolute codes are uniquely associated with the position of the encoding medium and are used for coarse position division. 5) The four sinusoidal incremental current signals are amplified by the circuit and then converted from analog to digital to obtain the specific position represented by a pair of bright and dark lines in the incremental code track within the cycle, that is, the relative position information based on the absolute code. Combining the relationship between the width of the incremental code track lines and the width of the absolute code track lines, the position information is further subdivided based on the absolute code.

2. The signal processing method for an absolute photoelectric encoder according to claim 1, characterized in that, ... The reference photocurrent is I D0 Four-channel sinusoidal incremental current signal I D1 I D2 I D3 and I D4 , then I D0 =NI0+I A sin(2πft+α1)+I A sin(2πft+α2)+…+I A sin(2πft+α N ) = NI0, where I0 is the common-mode current of a single photodetector, I A denoted as ν, where ν is the current amplitude and f is the optical signal frequency.

3. The signal processing method for an absolute photoelectric encoder according to claim 2, characterized in that, The amplification factor of the reference photocurrent is: Among them, A M P is the amplification factor of the current signal corresponding to the absolute code track. M P represents the incident light power received by a single light-receiving device corresponding to an absolute code channel. D0 The total incident light power received by the N light-receiving devices that generate the reference photocurrent.

4. The signal processing method for an absolute photoelectric encoder according to any one of claims 1 to 3, characterized in that, The signal processing is achieved using an absolute photoelectric encoder, which includes an encoding medium, a detection element, a light source, and a lens. The encoding medium contains incremental code tracks and absolute code tracks. The incremental code tracks are composed of periodic etched lines with alternating light and dark areas, and the absolute code tracks are composed of specific etched lines containing absolute position information. The detection element includes an incremental light-receiving device array, a reference light-receiving device array, an absolute light-receiving device array, an incremental signal readout circuit, an absolute signal readout circuit, and a reference level generation circuit.

5. The signal processing method for an absolute photoelectric encoder according to claim 4, characterized in that, The detection element and the light source are disposed on both sides of the code disk; the lens is disposed between the light source and the encoding medium to convert the light emitted by the light source into parallel light; the incremental light receiving device array and the reference light receiving device array are both disposed on one side of the detection element for detecting the light signal from the incremental code track of the code disk; The absolute light-receiving device array is disposed on one side of the detection element and is used to detect the optical signal from the absolute code track of the code disk; The incremental signal readout circuit is used to process the photocurrent signal of the incremental signal receiving device; The absolute signal readout circuit is used to process the photocurrent signal generated by the absolute photodetector array; The reference level generation circuit is a DC amplifier circuit used to process the photocurrent signal of the reference light-receiving device.

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