JPH05296791A - Signal interpolation circuit and displacement measuring device therewith - Google Patents

Abstract

PURPOSE:To make displacement information extending over a wide range detectable so accurately in getting a high resolution even at a low frequency domain by inputting a sine wave signal and a cosine wave signal into two comparators and an integral type analog-to-digital converter, and adding the output thereto. CONSTITUTION:Two comparators 13 and 14 detect a time range between a sine wave signal (a) based on displacement (position) information and a zero-cross point of a cosine wave signal, outputting a double waveform frequency signal (c) from an XOR circuit 15. An integrating means 16 counts pulse numbers of the signal (c), and resolution outputs a 1/4 periodic signal (d) of these signals (a) and (b). This signal (d) is not varied as far as both these signals (a) and (b) are not varied at the 1/4 period. integrating type analog-to-digital converters 18 and 19 measures these signals (a) and (b) into a high resolution through a voltage level, but when these signals (a) and (b) are not changed as long as the 1/4 period within the specified time, so far as during the while yet smaller signal is outputted from an adding means 21 by means of a digital signal (position information) to be outputted from a signal processing circuit 20 by control over a connecting means 17, so displacement information on a moving body is detectable at a high resolution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal interpolating circuit and a displacement measuring apparatus using the signal interpolating circuit. For example, in an incremental type rotary encoder or linear encoder, a predetermined phase difference detected by two light receiving means is provided. From the two sets of sinusoidal signals, other signals with different phases are interpolated to obtain a plurality of signals with different phase differences, from which the resolution such as detectable angular displacement is increased. The present invention relates to an insertion circuit and a displacement measuring device using the insertion circuit.

[0002]

2. Description of the Related Art Conventionally, in an incremental type rotary encoder or the like, two sine wave signals having different phases obtained from two light receiving means are used to detect a rotational displacement amount and a rotational direction of a rotating object.

At this time, a plurality of signals having a phase difference corresponding to a division unit with respect to the original signal are produced, a zero point of the waveform is detected to obtain a division pulse, and the detection resolution is increased. Insertion circuit is used.

FIG. 5 is a schematic view of a main part of a conventional signal interpolation circuit. In the figure, reference numerals 1 and 2 respectively denote input terminals, and two sine wave signals having different phases (the signal from the input terminal 2 is deviated by 90 degrees from the signal from the input terminal 1) are input. Will be done. The buffers 3 and 4 and the inverting buffer 5 are connected to the input signal at this time, and sine wave signals having different phases of 45 degrees and 135 degrees are generated through the resistor network.

From this, the phases are 0 °, 45 °, 90 °, 1
4 sine wave signals different from 35 degrees are converters 6-9
Is converted into a rectangular shape by. Then, it is inputted to the pulse signal processing circuit 10 via the exclusive logic circuit. Then, the pulse signal processing circuit 10 outputs an UP pulse or a DOWN pulse according to the phase relationship of the input signal. In the signal interpolating circuit in the figure, an interpolating signal obtained by dividing one cycle of the input sine wave signal into eight can be obtained.

FIG. 6 is an explanatory diagram showing output signal waveforms (a to L) from the respective parts at this time. Then, by counting the number of pulses output from the pulse signal processing circuit 10, the angular displacement amount of the rotating object to be inspected and the like are detected.

Regarding the function of the pulse signal processing circuit 10, for example, "Advancement of digital type angle transducer" (Precision Machine, Vol. 44, No. 5, P12 to P18, 197).
May, 1998, Makoto Kajitani).

[0008]

In the conventional signal interpolation method, a sine wave and a cosine wave whose phase is 90 degrees different from that of the sine wave are divided by using a plurality of set resistors, and a zero cross of the divided value is obtained by a comparator. I used a digitizer. The resolution at this time depends on the number of resistors and comparators and their accuracy.

If an attempt is made to improve the resolution by the signal interpolation method, a highly accurate resistor and a comparator are required, and the circuit configuration becomes complicated and the capacitance value of each node mounted becomes large, resulting in a poor frequency characteristic. Moreover, there is a problem that matching of resistors and comparators in a high frequency region becomes necessary.

On the other hand, the applicant of the present invention discloses the Japanese Patent Laid-Open No. 3-115.
In Japanese Patent Laid-Open No. 921, a circuit is provided that directly integrates the zero crosses of the sine wave and the cosine wave, and the circuit configuration is simplified by switching to the circuit according to the frequency of the input signal, thereby increasing the capacitance value in mounting each node. We have proposed a signal interpolator circuit that prevents the noise and improves the matching of resistors and comparators in the high frequency range.

Generally, the object to be measured by the encoder is a moving object having a certain weight, and the moving object itself has inertia in position measurement, position control (servo) and the like. Therefore, highly accurate measurement is required at the time of relatively gentle movement, at which time the frequency of the output signal from the encoder is low.

The present invention is an improvement of the signal interpolation circuit proposed by the applicant of the present application, and by utilizing a predetermined comparator and a resistor, high resolution is obtained when the output signal is in a low frequency region, It is an object of the present invention to provide a signal interpolation circuit which can obtain a maximum band when a signal is in a high frequency region and can detect displacement information of a moving object with high accuracy over a wide range, and a displacement measuring device using the signal interpolation circuit.

[0013]

The signal interpolating circuit of the present invention comprises: (a) measuring means for measuring information on the time width of the zero crossing points of the input sine wave signal and cosine wave signal; And an integration type A / D converter having a cosine wave signal as an input signal, a signal processing circuit for processing the signal from the integration type A / D converter and outputting it as a digital signal, depending on the signal from the measuring means. Control means for controlling driving of the integration type A / D converter and the signal processing circuit, integrating means for integrating signals from the measuring means, and signal from the integrating means and digital signal from the signal processing circuit It is characterized in that a digital output signal is obtained from the input signal by using an adding means for outputting a signal to which is added.

(B) Measuring means for measuring the information regarding the time width of the zero-cross point of the input sine wave signal and cosine wave signal, and the sine wave signal and the cosine wave signal as input signals 1
Δ with bit A / D converter and digital filter
Σ-type A / D converter, signal processing circuit for processing the signal from the ΔΣ-type A / D converter and outputting as a digital signal, the digital filter and the signal processing circuit according to the signal from the measuring means A driving means for controlling the driving of the measuring means, an integrating means for integrating the signals from the measuring means, and an adding means for outputting a signal obtained by adding the signal from the integrating means and the digital signal from the signal processing circuit. Then, a digital output signal is obtained from the input signal.

The displacement measuring device according to the present invention comprises: (c) a reading means for reading a scale provided on a moving object,
When detecting the displacement information of the moving object using the signal from the reading means, a measuring means for measuring the information regarding the time width of the zero-cross point of the sine wave signal and the cosine wave signal input from the reading means, An integrating A / D converter having the sine wave signal and the cosine wave signal as input signals, a signal processing circuit for processing the signal from the integrating A / D converter and outputting the digital signal, and the measuring means The integration type A / D depending on the signal
Control means for controlling driving of the converter and the signal processing circuit,
Displacement information of the moving object using an integrating means for integrating the signals from the measuring means and an adding means for outputting a signal obtained by adding the signal from the integrating means and the digital signal from the signal processing circuit. Is detected.

(D) A sine wave signal input from the reading means when the scale provided on the moving object is read by the reading means and the displacement information of the moving object is detected by using the signal from the reading means. And a measuring means for measuring information on the time width of the zero-cross point of the cosine wave signal, a ΔΣ type A / D converter having a 1-bit A / D converter using the sine wave signal and the cosine wave signal as input signals and a digital filter. Vessel, the ΔΣ
Signal processing circuit for processing the signal from the A / D converter and outputting it as a digital signal, control means for controlling the driving of the digital filter and the signal processing circuit according to the signal from the measuring means, and the measuring Displacement information of the moving object is detected by using accumulating means for accumulating signals from the means and adding means for outputting a signal obtained by adding the signal from the accumulating means and the digital signal from the signal processing circuit. It is characterized by doing.

[0017]

1 is a block diagram of the essential parts of a first embodiment of a signal interpolation circuit of the present invention.

In the figure, 11 and 12 are input terminals. Of these, a sine wave signal a based on displacement information (positional information) is input from the input terminal 11 from, for example, an encoder as a displacement measuring device to be described later, and the input terminal 12 is 90 degrees out of phase with the signal a. A cosine wave signal b is input.

Reference numerals 13 and 14 are comparators as measuring means, respectively, which detect information relating to the time width of the zero cross points of the signals a and b from the input terminals 11 and 12. 1
Reference numeral 5 is an exclusive logic circuit (XOR circuit), which uses the signals from the comparators 13 and 14 to output a digital signal c having a frequency twice that of the waveforms of the signals a and b.

Reference numeral 16 denotes an integrating means, which is composed of an asynchronous counter and integrates the number of edges of the signal c from the exclusive logic circuit 15 and counts the number of pulses. Then, the digital signal d whose count value changes by 1 is output in four divisions of one cycle of the waveforms of the original input signals a and b.

That is, the resolution of the signal d obtained by the integrating means 16 is 1/4 cycle of the input signals a and b, and the output value does not change unless the input signals a and b change 1/4 cycle.

In this embodiment, since the input signals a and b are directly input to the two comparators 13 and 14, the mounting capacitance value is small and the comparator itself has a very high accuracy. Since it is not required, detection is possible in a wide band up to high frequencies.

Reference numerals 18 and 19 denote integrating A / D converters, respectively, which measure the input signals a and b at a voltage level with high resolution. Reference numeral 20 denotes a signal processing circuit, which converts the output signal from the integrating A / D converter (18, 19) into a digital signal and obtains the phase angle between the signals a and b. Reference numeral 17 denotes a control means, which is composed of, for example, a time interval counter (time width counter), measures the time width between the edges of the output signal c from the exclusive logic circuit 15, and responds to the signal at that time by integrating type A / The drive of the D converter (18, 19) and the signal processing circuit 20 is controlled.

Reference numeral 21 is an adding means. The output signal d from the integrating means 16 has a resolution of 1/4 cycle of the signals a and b, and the output value does not change unless the original signals a and b change by 1/4 cycle. That is, it is a coarse signal. The adding means 21 outputs a further finer signal based on the phase angle information from the signal processing circuit 20 during the time when it does not change.

In this embodiment, the signal obtained from the adding means 21 at this time is used to detect the displacement information about the moving object with high resolution.

The integral type A / D converter (18, 1) of this embodiment
In 9), the input signals a and b are integrated and measured for a certain period of time. Therefore, it is necessary that the signals a and b input during a fixed time do not change significantly. Therefore, from the frequency of the input signal c measured by the control means 17, the input signal (a, a,
It is detected whether or not b) is changing by 1/4 cycle.

Only when it has not changed, the signal processing circuit 20 outputs the digital signal e to the adding means 21. Then, the adding means 21 outputs the signal d from the integrating means 16.
Using the signal e from the signal processing circuit 20, high-resolution displacement information is obtained.

FIG. 2 is a block diagram of the essential parts of a second embodiment of the signal interpolation circuit of the present invention. In this embodiment, the same elements as those in the first embodiment shown in FIG. 1 are designated by the same reference numerals.

This embodiment is different from the first embodiment shown in FIG. 1 in that a ΔΣ type A / D converter 30 is used instead of the integrating type A / D converters (18, 19). Have the same configuration.

The ΔΣ type A / D converter 30 of this embodiment is 1b.
It has an it A / D converter (31, 32) and a digital filter 33.

The 1-bit A / D converter (31, 32) converts the signals a, b from the input terminals (11, 12) into digital signals, and the digital filter 33 obtains the phase angles of the signals a, b. The input signal is integrated by the digital filter 33 for a certain period of time and measured. It is necessary that the input signals a and b do not change significantly within this fixed time.

The integration time of the digital filter 33 is proportional to the resolution of the output signal. Therefore, according to the present embodiment, by changing the integration time (time constant) of the digital filter 33, the higher the frequency of the input signals a and b, the higher the resolution of the signal obtained.

In this embodiment, the control means 17 inputs the input signal a,
By selecting the time constant of the digital filter 33 having an integration time corresponding to the time width in accordance with the time width information in which b changes by ¼ cycle, it is possible to detect a high resolution in a signal with a gentle signal change. ..

FIG. 3 is a schematic view of a main part of one embodiment when applied to an encoder as a displacement measuring device using the signal interpolation circuit of the present invention.

In this embodiment, the coherent light beam from the laser 71 is made into a substantially parallel light beam by the collimator lens 72, and is made incident on the polarization beam splitter 79 into two light beams of a linearly polarized transmitted light beam and a linearly polarized reflected light beam. It is divided. At this time, the mounting position of the laser 71 is adjusted so that the linear polarization azimuth of the emitted light beam of the laser 71 is 45 degrees with respect to the polarization beam splitter 79. As a result, the intensity ratio of the transmitted light flux and the reflected light flux from the polarization beam splitter 79 is set to approximately 1: 1.

The reflected light beam and the transmitted light beam from the polarization beam splitter 79 are circularly polarized through the quarter-wave plates 75 ₁ and 75 _{2 and} are reflected by the reflecting mirrors 80 ₁ and 80 ₂ to be diffracted on the moving object. When entering the grating 73, the m-th order diffracted light from the target diffraction grating 73 is entered so as to be reflected from the diffraction grating 73 substantially vertically.

That is, when the grating pitch of the diffraction grating 73 is P, the wavelength of the coherent light beam is λ, m is an integer, and the incident angle of the coherent light beam to the diffraction grating 73 is θ _m , θ _m = sin ^-1 (mλ / P) .....

The m-th order diffracted light emitted substantially vertically from the diffraction grating 73 is made incident on the optical member 81 of the condensing system 90. Since the reflection film 82 is provided in the vicinity of the focal plane of the optical member 81, the incident light flux is reflected by the reflection film 82 as shown in FIG. It enters the diffraction grating 73.

The m-th order reflected diffracted light diffracted again by the diffraction grating 73 returns to the original optical path and is reflected by the reflecting mirrors 80 ₁ , 80 _2.
It is reflected by the laser beam, is transmitted through the quarter-wave plates 75 ₁ and 75 _2, and is incident on the polarization beam splitter 79 again.

At this time, the re-diffracted light is a quarter wavelength plate 75 ₁ ,
Since back and forth 75 _2, a polarizing beam splitter 7
When the light beam first reflected at 9 is re-incident, the light beam is transmitted because the polarization direction is different by 90 degrees with respect to the polarization beam splitter 79. On the contrary, the light beam first transmitted by the polarization beam splitter 79 is reflected when it is incident again.

In this way, the polarization beam splitter 79
The two diffracted lights are overlapped and passed through the quarter-wave plate 75 ₃ to be circularly polarized light, split into two light beams by the beam splitter 76, passed through the polarizing plates 77 ₁ and 77 _{2, and} are linearly polarized light to be a light receiving element. They are made incident on 78 ₁ and 78 ₂ , respectively.

The signals from the light receiving elements 78 ₁ and 78 ₂ are input to the reading means 92. The reading means 92 has the signal interpolating circuit shown in FIGS. 1 and 2, and input signals are input to its input terminals 11 and 12, respectively. Then, the displacement information of the moving object provided with the diffraction grating 73 is obtained by performing the above-described signal processing.

It is to be noted that the angle θ _{m in the} equation (1) has only to be within a range in which the diffracted light can enter the focusing system 90 and enter the diffraction grating 73 again.

In this embodiment, the phase of the m-th order diffracted light changes by 2 mπ when the diffraction grating moves by one pitch.

Therefore, since the light receiving elements 78 ₁ and 78 ₂ receive the interference of the light beams that have undergone the positive and negative m-th order diffractions twice respectively, when the diffraction grating 73 moves by one pitch of the grating, it becomes 4
m sinusoidal signals are obtained.

For example, the pitch of the diffraction grating 73 is 3.2 μm,
If the first order (m = 1) is used as the diffracted light, the light receiving elements 78 ₁ , 78 when the diffraction grating 73 moves by 3.2 μm.
Four sinusoidal signals are obtained from ₂ . That is, 1/4 of the pitch of the diffraction grating 73, that is, 3.2 / 4 = 0.8 μm is obtained as the resolution per one sine wave.

Also, the quarter wave plates 75 ₁ , 75 ₂ , 75 ₃
And a combination of the polarizing plates 77 ₁ and 77 ₂ provides a 90 ° phase difference between the output signals from the light receiving elements 78 ₁ and 78 ₂ and inputs the signals to the signal interpolating circuit of the reading means 92. As described above, in the signal interpolation circuit, the signal a having a sine waveform is input to the input terminal 11 and the signal b having a cosine waveform is input to the input terminal 12. As a result, the signal is interpolated and the diffraction grating 7
3, that is, the displacement information of the moving object is detected with high resolution.

In the present embodiment, the time interval counter as the control means is only required to be able to measure the cycle of the output signal from the encoder. For example, the comparator (1
Alternatively, the output signal from (3, 14) may be directly input.

Although the case where the input signal is divided into 1/4 by the comparator and the exclusive logic circuit is shown, the number of divisions may be increased by increasing the number of comparators.

The integration type A / D converter has one integration time, which is divided into two modes of high resolution and low resolution. In addition, the integration time is set to two or more, and the mode is output by the time interval counter accordingly. You may use the method of switching. Any number of time constants can be switched for the digital filter.

[0051]

According to the present invention, by setting each element as described above, that is, by utilizing a predetermined comparator and resistor, high resolution can be obtained when the output signal is in the low frequency region, It is possible to achieve a signal interpolating circuit and a displacement measuring apparatus using the signal interpolating circuit, which can obtain the maximum band when the signal is in the high frequency region and can detect the displacement information of the moving object with high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of a first embodiment of a signal interpolation circuit of the present invention.

FIG. 2 is a block diagram of a main part of a second embodiment of a signal interpolation circuit of the present invention.

FIG. 3 is a schematic view of a main part of a displacement measuring device using the signal interpolation circuit of the present invention.

4 is an explanatory view of a part of FIG.

FIG. 5 is a block diagram of a main part of a conventional signal interpolation circuit.

6 is an explanatory diagram of an output signal waveform in each part of FIG.

[Explanation of symbols]

 11, 12 Input Terminals 13, 14 Comparator 15 Exclusive Logic Circuit 16 Accumulating Means 17 Controlling Means 18, 19 Integrating A / D Converter 20 Signal Processing Circuit 21 Adding Means 30 ΔΣ A / D Converter 31, 32 1bitA / D converter 33 Digital filter

Claims (4)

[Claims] 1. A measuring means for measuring information about a time width of a zero-cross point of an input sine wave signal and a cosine wave signal, and an integral type A / D converter using the sine wave signal and the cosine wave signal as input signals. A signal processing circuit for processing the signal from the integrating A / D converter and outputting it as a digital signal, and driving the integrating A / D converter and the signal processing circuit according to the signal from the measuring means. Using a control means for controlling, a integrating means for integrating the signals from the measuring means, and an adding means for outputting a signal obtained by adding the signal from the integrating means and the digital signal from the signal processing circuit, A signal interpolating circuit, wherein a digital output signal is obtained from the input signal. 2. A measuring means for measuring information about a time width of a zero-cross point of an input sine wave signal and a cosine wave signal, and 1bi having the sine wave signal and the cosine wave signal as input signals.
A ΔΣ type A / D converter having a tA / D converter and a digital filter, a signal processing circuit for processing a signal from the ΔΣ type A / D converter and outputting it as a digital signal, and a signal from the measuring means. Accordingly, a control means for controlling driving of the digital filter and the signal processing circuit, an integrating means for integrating the signals from the measuring means, and a signal from the integrating means and a digital signal from the signal processing circuit are added. A signal interpolating circuit, wherein a digital output signal is obtained from the input signal by using an adding means that outputs the signal. 3. A sine wave signal input from the reading means when the scale provided on the moving object is read by the reading means and the displacement information of the moving object is detected using the signal from the reading means. Measuring means for measuring information on the time width of the zero-cross point of the cosine wave signal, integral type A / D converter using the sine wave signal and the cosine wave signal as input signals, and the integral type A / D
A signal processing circuit for processing a signal from the converter and outputting it as a digital signal; a control means for controlling driving of the integration type A / D converter and the signal processing circuit according to the signal from the measuring means; Displacement information of the moving object is calculated by using accumulating means for accumulating signals from the measuring means and adding means for outputting a signal obtained by adding the signal from the accumulating means and the digital signal from the signal processing circuit. Displacement measuring device characterized by being detected. 4. A sine wave signal input from the reading means when the scale provided on the moving object is read by the reading means and the displacement information of the moving object is detected using the signal from the reading means. Measuring means for measuring information on the time width of the zero-cross point of the cosine wave signal, a ΔΣ type A / D converter having a 1-bit A / D converter having the sine wave signal and the cosine wave signal as input signals, and a digital filter, ΔΣ type A / D
A signal processing circuit for processing the signal from the converter and outputting it as a digital signal, a control means for controlling the driving of the digital filter and the signal processing circuit according to the signal from the measuring means, and a signal from the measuring means. Displacement information of the moving object is detected by using an integrating unit that integrates the moving object and an adding unit that outputs a signal obtained by adding the signal from the integrating unit and the digital signal from the signal processing circuit. Displacement measuring device.