WO2022186386A1

WO2022186386A1 - Position sensor

Info

Publication number: WO2022186386A1
Application number: PCT/JP2022/009496
Authority: WO
Inventors: 正之三木; 良介高間; 佳嗣川村
Original assignee: 株式会社リベックス
Priority date: 2021-03-05
Filing date: 2022-03-04
Publication date: 2022-09-09
Also published as: JPWO2022186386A1

Abstract

[Problem] The objective of the present invention is to provide a position sensor which is capable of high-speed position detection, and which has a low cost and can be miniaturized. [Solution] This position sensor is provided with a sensor unit including an exciting coil and a detecting coil, and a control unit including a CPU, a DAC, and an ADC. The CPU, the DAC and the ADC operate synchronously by means of an identical clock signal, and an excitation signal generated by the DAC is applied to the exciting coil. The CPU detects an output signal from the detecting coil by means of the ADC, in synchronism with a prescribed timing of the excitation signal, and calculates a distance between the sensor unit and an object being measured, from the synchronously detected output signal and the excitation signal.

Description

position sensor

The present invention relates to position sensors.

Magnetic position sensors are known which have an excitation coil and a detection coil. The mutual inductance between the excitation coil and the detection coil changes depending on the distance between the position sensor and the object, so that the distance between the object and the position sensor can be measured.
In such a position sensor, a sinusoidal alternating current signal is input as an excitation signal for exciting the excitation coil, and the amplitude change of the output signal as a sinusoidal wave from the detection coil is detected.
In order to detect the amplitude of the output signal, a rectifier circuit is used to convert it into a DC voltage, and a peak hold circuit using a capacitor and a resistor or an integration circuit is used to detect the maximum amplitude width of the output waveform. In addition, the influence of external noise can be reduced by integrating the output waveform with the integrating circuit.

JP-A-2002-169614 JP 2020-173232 A JP 2019-15657 A

Since the conventional position sensor needs to measure the amplitude of the sinusoidal signal output from the detection coil as described above, high-speed position detection is difficult.
Position sensors are often incorporated into various manufacturing equipment, and miniaturization is sometimes desired. However, since the position sensor requires a complicated circuit for detecting the amplitude of the output signal in addition to the circuit for generating the sine wave of the excitation signal, it is expensive and difficult to miniaturize.

An object of the present invention is to provide a position sensor capable of high-speed, high-performance position detection, low cost, and miniaturization.

A position sensor according to the present invention includes:
A position sensor comprising a sensor unit having an excitation coil and a detection coil and a control unit,
The control unit includes a control device having an arithmetic processing unit, a digital-to-analog converter, and a first analog-to-digital converter,
The arithmetic processing unit, the digital-to-analog converter, and the first analog-to-digital converter all operate in synchronization with the same clock signal,
An excitation signal generated by the digital-to-analog converter is applied to the excitation coil,
The arithmetic processing unit detects an output signal from the detection coil by the first analog-to-digital converter in synchronization with a predetermined timing of the excitation signal,
The distance between the sensor unit and the object to be measured is calculated from the synchronously detected output signal and the excitation signal.

Further, the position sensor according to the present invention is
The output signal is detected at a timing when the excitation signal reaches a peak.

By accurately synchronizing with the excitation signal and detecting the output signal of the detection coil, the position sensor can detect the position of the object to be measured at high speed with as little influence of noise as possible.
A position sensor can be configured with a simple circuit configuration, and miniaturization and cost reduction can be achieved.
The position can be detected at the timing when the excitation signal peaks, ie, becomes maximum or minimum.

Further, the position sensor according to the present invention is
The excitation signal is a triangular wave having a step function.

　Since the triangular wave consisting of the step function generated by the digital-analog converter is used as the excitation signal, the output signal of the detection coil is detected without phase shift, enabling accurate and high-speed position detection.

Further, the position sensor according to the present invention is
The output signal is averaged in a step region including the peak of the excitation signal.

Further, the position sensor according to the present invention is
The output signal is averaged in the vicinity of the timing at which the excitation signal peaks.

Further, the position sensor according to the present invention is
The output signal is averaged at a plurality of timings at which the excitation signal peaks.

Special various averaging techniques for noise reduction in the output signal of the detection coil, because a special excitation signal generated by the digital-to-analog converter can be used to detect the output signal synchronously with the excitation signal. becomes possible.

Further, the position sensor according to the present invention is
The control device controls an electric motor that drives the object to be measured,
Calculation of the distance between the object to be measured and the sensor unit is eliminated based on the output signal from the first analog-to-digital converter in synchronization with the noise generated by the electric motor.

The position sensor controls the drive of the electric motor by its control device, can accurately recognize the generation period of noise from the drive motor, and can detect the position of the object to be measured while avoiding the noise. .

Further, the position sensor according to the present invention is
the position sensor comprises a noise sensor,
the control device comprises a second analog-to-digital converter operating in synchronization with the clock signal;
The noise sensor is provided in a power supply line of an electric motor that drives the object to be measured,
The arithmetic processing unit detects timing of occurrence of noise in the power supply line from a signal from the noise sensor input via a second analog-to-digital converter,
The output signal from the detection coil is removed in synchronization with the noise generation timing.

The position sensor can detect the occurrence of noise from the electric motor, making it possible to detect the position of the object to be measured while avoiding noise.

According to the present invention, it is possible to provide a position sensor that is capable of high-speed, high-performance position detection, low cost, and can be miniaturized.

FIG. 1(a) is a configuration diagram showing the main configuration of the position sensor (position detection device) 1 of Embodiment 1, and FIGS. It is a schematic diagram showing. FIG. 2 is a graph showing an example of the excitation signal output from the DAC 42. As shown in FIG. FIG. 2(a) is a graph showing an example in which the excitation signal is a triangular wave, FIG. 2(b) is a partially enlarged graph, and FIG. 2(c) is an example in which the excitation signal is a sawtooth wave. It is a graph showing. FIG. 3 is a graph showing measured values of the excitation signal applied to the excitation coil 2 and the output signal output from the detection coil 3. In FIG. FIG. 3(a) shows an example in which the frequency of the excitation signal is 1 kHz, and FIG. 3(b) shows an example in which the frequency of the excitation signal is 2 kHz. 4 is a graph showing a stepped excitation signal near the peak position P. FIG. FIG. 5 is a graph for explaining the averaging method 3, showing the correspondence between the excitation signal of the excitation coil 2 having multiple peaks and the output signal of the detection coil 3, and the peak-to-peak interval. FIG. 6 is a graph showing noise generated in the power supply line when the electric motor 9 is driven. FIG. 7 is a schematic diagram showing the configuration of the position sensor 1 of Embodiment 2 that can eliminate the influence of noise from the electric motor 9. As shown in FIG. FIG. 8 is a schematic diagram showing the main configuration of the position sensor 1 of Embodiment 3 that can eliminate the influence of noise from the electric motor 9. As shown in FIG.

(Embodiment 1)
FIG. 1(a) is a configuration diagram showing the main configuration of the position sensor (position detection device) 1 of Embodiment 1, and FIGS. It is a schematic diagram showing.
The position sensor 1 will be described below with reference to FIG.

The position sensor 1 comprises a sensor section 5 having an excitation coil 2 and a detection coil 3 .
Moreover, as shown in FIGS. FIG. 1(b) shows an example in which the excitation coil 2 and the detection coil 3 are arranged in series, and FIGS. . Any arrangement may be used for the excitation coil 2 and the detection coil 3 . Further, as shown in FIG. 1(c), the detection coil 3 may be arranged so that the longitudinal axis of the detection coil 3 is perpendicular to the object 6 to be measured, or FIG. 1(d). , the longitudinal axes may be arranged in parallel so that at least a portion of the object to be measured 6 is inserted inside the detection coil 3 . The arrangement of the excitation coil 2 and the detection coil 3 can be appropriately selected according to the place where the sensor unit 5 is installed and the application.
The sensor unit 5 may be configured without a capacitor (capacitance), or may be configured with an RL circuit.
The control device 4 supplies an input signal to the excitation coil 2 and also receives an output signal from the detection coil 3 to generate a distance between the sensor unit 5 and the object to be measured 6, that is, positional information or an electric current reflecting the positional information. Convert to a signal and output to the outside.

The control device 4 is a single semiconductor device including a CPU (arithmetic processing unit) 41, a DAC (digital-to-analog converter) 42, an ADC (analog-to-digital converter) 43, a storage device 44, and an IO (input/output unit) 45. The CPU 41, the DAC 42, and the ADC 43 are all synchronously operated by the same clock signal.

The clock signal may be generated using a signal generated by an oscillator built in the control device 4 as a clock source, or may be generated using a signal generated by an external oscillator such as a crystal oscillator as a clock source. good.
As long as the CPU 41, the DAC 42, and the ADC 43 operate synchronously with the same clock signal, any known circuit may be used as the clock signal generating circuit. From the viewpoint of size reduction of the position sensor 1, it is preferable to use a built-in oscillator.

The CPU 41 can operate the DAC 42 and the ADC 43 according to a program stored in the storage device 44 , process the signal output from the ADC 43 , and store the processing result in the storage device 44 .
Communication with the outside is possible via the IO 45 of the control device 4, measurement results and the like can be output to the outside, and instructions (starting, ending, etc. of measurement) can be input to the CPU 41 from the outside.
Power is supplied to the control device 4 from a power source (not shown). For the power supply, for example, a battery, a converter for converting commercial AC power into DC power, or the like can be used.

The control device 4 can use the DAC 42 to generate an excitation signal to be input to the excitation coil 2 by digital processing.
In addition, the position sensor 1 may include an input signal amplifier 7 for amplifying the excitation signal, if necessary. Since the input signal amplifier 7 amplifies the excitation signal while maintaining the waveform as it is without integrating the excitation signal, no phase shift occurs. If the excitation signal generated by the DAC 42 does not have the power required to excite the excitation coil 2 , the input signal amplifier 7 increases the excitation signal generated by the DAC 42 to a sufficient power to excite the excitation coil 2 . can be amplified to an excitation signal with sufficient power.
Therefore, if the excitation coil 2 can be excited by the excitation signal output from the DAC 42, the input signal amplifier 7 may be omitted.

Since the output of the DAC 42 is generally a voltage output, an example of the voltage output will be described below. good too.

When an excitation signal is applied to the excitation coil 2, an output signal is induced in the detection coil 3 by electromagnetic coupling. An output signal output from the detection coil 3 is input to the ADC 43 of the control device 4 .
The position sensor 1 may be provided with an output signal amplifier 8 as required. For example, when the output signal output from the detection coil 3 is weak, it can be amplified by the output signal amplifier 8 according to the input range of the ADC 43 . The output signal amplifying device 8 amplifies the output signal while maintaining the waveform of the output signal as it is, so that no phase shift occurs.
The installation positions of the input signal amplification device 7 and the output signal amplification device 8 can be appropriately set according to the sensor section 5 and the control device 4 .

The object 6 to be measured of the position sensor 1 is a magnetically responsive member, and is made of magnetic metal or non-magnetic metal. An output signal from the detection coil 3 depends on mutual inductance between the excitation coil 2 and the detection coil 3 . The mutual inductance changes depending on the relative distance d between the sensor section 5 and the object 6 to be measured. The position sensor 1 can detect the distance d between the sensor unit 5 and the object to be measured 6 from changes in mutual inductance, and the position of the object to be measured 6 can be determined from the known positional information of the position sensor 1. It is possible to detect

The mutual inductance can be calculated from the relationship between the excitation signal, which is the input signal applied to the excitation coil 2, and the output signal output from the detection coil 3, for example, the intensity ratio.
The position sensor 1 can synchronize the generation of the excitation signal and the detection of the output signal by the DAC 42 and the ADC 43 operating with the same clock signal. Therefore, the position sensor 1 can detect the output signal at any timing.
The position sensor 1 detects an output signal at a predetermined timing, specifically at the timing when the excitation signal reaches its peak, and measures the distance d from the relationship between the excitation signal and the output signal.

In the case of the conventional position sensor, since the distance d is calculated from the amplitude of the excitation signal and the amplitude of the output signal, it is necessary to measure the amplitude of the output signal every predetermined period. Therefore, it takes time to measure the amplitude of the output signal, making high-speed position detection difficult. In addition, the probability of noise mixing during measurement also increases.
However, since the position sensor 1 acquires an output signal at a specific timing of the excitation signal, specifically, at each peak moment, and calculates the distance d, high-speed position detection is possible, and noise is reduced. small impact.

The detection timing by the position sensor 1 may be the peak position at which the excitation signal is maximized as described above, or the bottom (trough) at which the excitation signal is minimized.
An example of detection of the output signal from the detection coil 3 at the peak position will be described below, but the same applies to detection of the output signal from the detection coil 3 at the bottom position of the excitation signal.
The position where the excitation signal exhibits the extreme value or the position where the sign of the slope of the time change of the excitation signal changes from positive to negative or from negative to positive is referred to as the peak position, and the peak is limited to the maximum. Instead, it includes the local minimum and indicates the position of the extreme value.

The control device 4 can measure the voltage value of the output signal by digitizing the output signal of the detection coil 3 using the ADC 43 . Since the excitation signal is generated by the DAC 42, the control device 4 also recognizes the voltage value of the input signal, which is the excitation signal at the timing when the output signal is measured. Therefore, at a predetermined timing, it is possible to calculate a measured value that reflects the inductance change from the relationship between the excitation signal and the output signal.

The storage device 44 of the control device 4 stores in advance the correlation data between the measured value and the distance d, for example, as a data table or a relational expression.
The CPU 41 of the control device 4 can calculate the distance d from the correlation data and the measured value, and can output the distance d or an electric signal reflecting the distance d to the outside via the IO 45 . The electric signal reflecting the distance d may be either a digital signal or an analog signal.

Conventionally, a sine wave generated by a separately provided oscillator has been used as an excitation signal for exciting the excitation coil 2 . However, as will be explained below, the controller 4 of the position sensor 1 can generate the excitation signal as a triangular wave or a sawtooth wave without the need for a separate oscillator.
In order for the controller 4 to generate the excitation signal, a table (referred to as an excitation signal generation table) specifying the relationship between the count number of the clock signal and the voltage of the excitation signal is stored in the storage device 44 . The excitation signal generation table specifies the relationship between the number of clock counts in a half cycle and the voltage of the excitation signal.
The CPU 41 reads the excitation signal generation table from the storage device 44, controls the DAC 42, and generates the voltage specified in the excitation signal generation table as the excitation signal according to the count number of the clock signal.
In this manner, the DAC 42 of the control device 4 can generate an excitation signal with a predetermined frequency through software.

The excitation signal generation table, for example, sets the clock count number in the initial state to 0, sets the voltage of the excitation signal to 0 V, and outputs from the DAC 42 every predetermined clock count number (clock unit number ΔC), for example, every 10 counts from the initial state. The excitation signal voltage is increased by a constant voltage (output change amount ΔV), and the clock count number (Cp) of the peak position P at which the voltage of the excitation signal reaches the maximum value Vmax, for example, 500 (=Cp=50*ΔC) When it exceeds, the voltage of the excitation signal is reduced by a constant voltage (the number of units Δ) every predetermined number of clock counts, and the voltage of the excitation signal is set to the initial state of 0 V at the last clock count number of the half cycle, for example, 1000. It is
Here, the clock unit number ΔC is a natural number, and the output change amount (ΔV) is a natural number times the resolution of the DAC 42 .

The excitation signal generation table is, for example, a two-dimensional array (0, 0), (ΔC, ΔV), (2ΔC, 2ΔV) . . . can be stored in the storage device 44 as (2Cp, 0).
Instead of the excitation signal generation table, a linear expression representing the relationship between the voltage of the excitation signal and the number of clock counts may be stored in units of half cycles. However, by storing it as a table, the output process of the excitation signal can be executed at high speed.

FIG. 2 is a graph showing an example of the excitation signal output from the DAC42. FIG. 2(a) is a graph showing an example in which the excitation signal is a triangular wave, FIG. 2(b) is a partially enlarged graph, and FIG. 2(c) is an example in which the excitation signal is a sawtooth wave. It is a graph showing. In FIG. 2, the horizontal axis is the clock count number and the vertical axis is the voltage.

As shown in FIGS. 2A and 2C, the signal waveform directly output by the DAC 42 through digital processing is a triangular wave or a sawtooth wave. Macroscopically, the signal voltage increases linearly with the clock count number up to a peak position indicated by P in the figure, and then linearly decreases with the clock count number.
FIG. 2(b) shows the excitation signal waveform near the peak position (P). As indicated by the dotted line in FIG. 2B, the macroscopic slope of the signal waveform changes from positive to negative at the peak position (P). The excitation signal waveform discretely changes with the clock count number up to the peak position indicated by P in FIG.

The clock count number of the flat portion of each staircase (referred to as a step area) is the number of clock units ΔC, which is 1 or more. By setting the number of clock units ΔC to a value of 2 or more, a special noise elimination method becomes possible, as will be described later.

Thus, the excitation signal is a triangular wave or sawtooth wave composed of a step function, and as shown in FIGS. As shown in FIG. 2(b), it has a stepped waveform microscopically, and is a stepped triangular wave or sawtooth wave. The excitation signal macroscopically increases while repeating microscopic boosting and holding, and after exceeding the peak, macroscopically decreases while microscopically repeating stepping down and holding.

Since the signal waveform is formed according to the number of clock counts, the peak position of the waveform is clearly determined. Further, when the excitation signal is generated from the excitation signal generation table, the load on the CPU is reduced, the peak position does not shift, and the excitation signal generation process can be executed at high speed.

As shown in FIG. 2(c), the excitation signal may be a sawtooth wave instead of a triangular wave. In the case of the sawtooth wave, when the peak position (P) is exceeded, the voltage of the excitation signal becomes 0 V, and the voltage of the excitation signal increases again with the clock count.
Note that the sawtooth wave is considered to be a triangular wave having different tilt angles before and after the peak, so the term "triangular wave" includes the sawtooth wave.

The stepwise triangular excitation signal generated by the DAC 42 is input to the excitation coil 2 without being smoothed. Therefore, the signal generated by the DAC 42 is input to the exciting coil 2 without any phase shift. An output signal is output from the detection coil 3 and input to the ADC 43 while being electromagnetically induced by the microscopically stepped excitation signal.

The CPU 41 drives the ADC 43 at a predetermined timing and digitizes the output signal of the detection coil 3 . For example, at the peak position P of the output signal of the DAC 42, the ADC 43 is driven and the output signal of the detection coil 3 is digitally converted into numerical data. Data of the digitized output signal is stored in the storage device 44 .
The CPU 41 of the control device 4 can digitize and measure the output signal from the detection coil 3 input to the ADC 43 at the same clock count as the peak position of the excitation signal generated from the DAC 42 . Since the sensor section 5 and the control device 4 do not use a phase-shifting capacitor, it is possible to accurately recognize and calculate the relationship (for example, the ratio) between the excitation signal and the output signal at the peak position.

FIG. 3 is a graph showing an output signal output from the detection coil 3 when a triangular wave excitation signal generated by the DAC 42 is input to the excitation coil 2 in the position sensor 1 . Vi is an excitation signal, Vo is an output signal, and each is measured data. FIG. 3(a) shows an example in which the frequency of the excitation signal is 1 kHz, and FIG. 3(b) shows an example in which the frequency of the excitation signal is 2 kHz.

As shown in FIGS. 3A and 3B, the output signal also peaks at the position P where the excitation signal peaks, and it can be understood that no phase shift occurs in either case.
Thus, it was demonstrated that the value of the output signal can be accurately detected by the ADC 43 at the peak position P of the excitation signal designated by the DAC 42 and quantified.

As shown in FIG. 3(a), the output signal for the 1 KHz excitation signal has a substantially flat region before the peak position P. On the other hand, as shown in FIG. 3(b), the output signal with respect to the excitation signal of 2 kHz does not have a flat region, and the response of the output signal to the excitation signal is high. Therefore, by increasing the frequency of the excitation signal, high-speed and highly accurate measurement is possible.

Even with such a high-frequency excitation signal, the DAC 42 and ADC 43 operate with the same clock, so the output signal can be accurately synchronized with the excitation signal and measured.
As shown in FIG. 3(a), when the time from the position where the output signal is minimum to the peak position P (hereinafter referred to as the peak period) is five times or more the time constant, In the region, the signal waveform becomes a substantially flat saturation region. However, by determining the frequency of the excitation signal so that the output signal peak period is 3.5 times or less, preferably 3 times or less, the time constant as shown in FIG. 3(b), the output signal becomes large. , a high S/N ratio can be obtained, and highly accurate position detection is possible.

As shown in FIG. 3, the timing of detecting the output signal of the detection coil 3 is part (instantaneous), and most of the output signals are not digitized by the ADC 43 .
Therefore, the probability of noise input is very low. Also, the time for driving the ADC 43 is short, which contributes to the reduction of the energy consumption of the position sensor 1 .

The frequency of the excitation signal is not limited to the example shown in FIG. As a frequency, for example, 100 kHz to 0.1 kHz can be adopted. The frequency can be appropriately set according to the installation state of the sensor section 5, the distance between the sensor section 5 and the control device 4, the responsiveness to the object 6 to be measured, and the like. For example, a high frequency is adopted when high speed is required, and a low frequency is adopted when the distance between the sensor section 5 and the control device 4 is long.

The control device 4 can detect the excitation signal and the output signal for each clock count (or for each predetermined number of clock units for increasing or decreasing the voltage of the excitation signal) and calculate the distance d. Therefore, noise can be removed by digital processing such as moving average.
An averaging technique for noise reduction will be described below.
Each average value obtained by the following averaging process has random noise reduced and can be used to calculate the distance d to the object 6 to be measured.
In addition, below, although the average value is calculated by the simple moving average, you may calculate an average value by a weighted moving average suitably. For example, at each timing, a value obtained by dividing the output signal by the excitation signal may be used.

(Averaging method 1)
4 is a graph showing a stepped excitation signal near the peak position P. FIG.
The excitation signal generated by the DAC 42 is stepped up or stepped down every clock unit number ΔC.
Since the excitation signal is composed of a stepped triangular wave, the voltage of the excitation signal is kept constant at the peak position P for the number of clock units ΔC. The period during which this voltage is kept constant corresponds to the step region.
When the number of clock units ΔC is 2 or more, since a plurality of clock counts (the state in which the clock signal is "H (high)") are included, the output signal is averaged at each clock count of the number of clock units ΔC. can be
Let Vo(C) be the voltage of the output signal at the count number C at the peak position, and let <Vo(Cp)> be the average value of the output signal at the peak position Cp.
As shown in FIG. 4, <Vo(Cp)> is defined by the following equation, where Cp is the first clock count at the peak position.
<Vo(Cp)>=ΣVo(C) (Formula-1)
Integration range C=Cp to Cp+ΔC.

In this way, in the step region having the peak position P, by detecting all or at least part of the output signals in a plurality of clock counts and averaging them, random noise can be reduced.

(Averaging method 2)
A continuous clock count of clock unit numbers ΔC can be treated as one group (group), and an output signal averaging process can be performed on a group of a plurality of clock unit numbers ΔC near the peak position P. FIG.
Specifically, as shown in FIG. 4, an output signal n clock units .DELTA.C, for example, 5.DELTA.C before the clock count position of the peak position P is detected for each group of clock units .DELTA.C and averaged. good. That is, when the count number at the peak position is Cp, the output signal of the detection coil may be detected within the range of the count number from Cp−n*ΔC to Cp, and the obtained output signals may be averaged.
The average value <Vo> of the output signal Vo is defined by the following equation.
<Vo>=ΣVo(Cp−k*ΔC)/(n+1) (Formula-2)
The integration range k=0 to n, where n is a natural number such as 2 to 10.
Note that the averaging process 1 and the averaging process 2 are combined to obtain Vo(Cp-k*ΔC), and the averaging process 1 averages <Vo(Cp-k*ΔC) within the group range of the number of clock units ΔC )> may be used.

The voltage of the excitation signal generated by the DAC 42 is designated by, for example, an excitation signal generation table. The specified value of the excitation signal may be averaged in the count range from Cp-n to Cp and used as the average value <Vi> of the excitation signal to calculate the distance d to the object 6 to be measured. The voltage of the excitation signal at the clock count Cp-k*ΔC is defined as Vi(Cp-k*ΔC), and instead of Vo(Cp-k*ΔC), the intensity ratio between the excitation signal and the output signal Vo( Cp−k*ΔC)/Vi(Cp−k*ΔC) may be used to calculate the average value of the intensity ratio. In this case, a weighted moving average is calculated.

In the above, the count number is averaged in the range from Cp-n*ΔC to Cp. Well, the averaging process may be performed in the range of the count number from Cp−n*ΔC to Cp+n*ΔC.
For example, in case of the output signal shown in FIG. In this case, the averaging process may be performed in any range. The averaging range may be set according to the waveform of the output signal.

Averaging method 2 averages the output signal from the detection coil 3 in the vicinity of the timing at which the excitation signal peaks, that is, in a period of a predetermined number of clock counts including the peak. Although the average value for the period is calculated, since the distance d is calculated using only part of the output signal, high-speed distance calculation (position detection) is possible.

(Averaging method 3)
FIG. 5 is a graph showing the correspondence between the excitation signal of the excitation coil 2 having a plurality of peaks and the output signal of the detection coil 3, and the peak-to-peak interval.
As shown in FIG. 5, the voltage of the output signal at a plurality of consecutive peak positions P can be averaged. Let Cf be the number of clock counts from one peak position P to the next peak position (interval between peak positions). Assuming that the count number at one peak position is Cp and the voltage of the output signal at the count number C is Vo(C), the voltage average value <Vo> of the output signal is defined by the following equation.
<Vo>=ΣVo(Cp+k*Cf)/(n+1) (Formula-3)
The integration range k=0 to n, where n is a natural number such as 2 to 10.
Averaging method 3 averages the output signal at a plurality of timings when the excitation signal reaches its peak.

A combination of the averaging

methods

1 and 2 and the averaging method 3 is also possible.
That is, at a plurality of continuous peak positions, the average value <Vo> of the voltage of the output signal is calculated by averaging

methods

1 and 2, respectively, and the obtained plural average values <Vo> are averaged by averaging method 3. may
For example, if the average value <Vo> obtained by averaging

methods

1 and 2 at the first peak position is <Vo> ₁ , and the average value <Vo> at the m-th peak position is <Vo> _m , <Vo> is averaged. The average value <<Vo>> using method 3 is determined by the following formula.
<<Vo>>=Σ<Vo> _k /m (Formula-8)
The integration range k=1 to m, where m is a natural number such as 2 to 10.

Although the output signal was averaged, the distance d was calculated for each detected output signal, the above averaging methods 1 to 3 were applied to the distance d, and the noise of the distance d was removed. may be reduced.

In this way, the position sensor 1 is capable of accurate and highly accurate position detection while having a simple configuration.
A commercially available microcomputer equipped with a DAC and an ADC can be used for the control device 4, which is a main component, making it possible to manufacture the position sensor 1 in a small size and at a low cost.
Furthermore, since the measurement of the output signal from the detection coil 3 is performed intermittently, power consumption can be suppressed. Therefore, the position sensor 1 can be battery-driven, and can be easily incorporated into various devices without requiring a separate power supply.
Furthermore, since the output signal can be detected at the same time as the excitation signal for each clock count or each clock unit number ΔC, noise reduction countermeasures by various averaging processes can be applied.

(Embodiment 2)
The position sensor 1 can be suitably used even when the object to be measured 6 is driven by an electric motor.
In general, an electric motor generates electromagnetic noise at the timing of exciting the electromagnetic coil of the motor and the switching timing of the magnet unit. When noise is generated from the electric motor, it may be superimposed on the output signal of the detection coil 3 of the sensor section 5 .
In this embodiment, the distance d between the sensor unit 5 and the object to be measured 6 is measured by detecting the output signal from the detection coil 3 while avoiding the time when the noise generated by the electric motor occurs. can be done.

FIG. 6 is a graph showing an example of noise generated in the power supply line when the electric motor 9 is driven. The horizontal axis represents time, and the vertical axis represents power supply voltage. FIG. 6 shows an example in which a direct current is used as the power source for the electric motor, but the same applies when an alternating current is used.
As indicated by arrows in FIG. 6, noise with a constant period is observed as a peak.
The period of noise can be obtained by detecting the timing when the power supply voltage becomes equal to or higher than a predetermined threshold.
Therefore, by measuring this period in advance and storing it in the storage device 44 of the control device 4, the distance between the object 6 to be measured and the sensor section 5 can be calculated while eliminating the influence of noise from the electric motor. d can be measured.

FIG. 7 is a schematic diagram showing the configuration of the position sensor 1 of Embodiment 2 that can eliminate the influence of noise from the electric motor 9. As shown in FIG.
The power of the electric motor 9 is transmitted to the object to be measured 6 by a transmission mechanism 10 (power transmission mechanism) to move the object to be measured 6 in a desired direction at a desired speed.
Electric power for driving the electric motor 9 is supplied from a power control device 11 .

The control device 4 controls the power control device 11 by the CPU 41 via the IO 45 . The control device 4 controls driving of the electric motor 9 via the power control device 11 .
The noise period of the electric motor 9 is stored in the storage device 44 . The CPU 41 can recognize the timing at which the noise is generated by the electric motor 9 from the driving start time of the electric motor 9 and the noise generation period.

The CPU 41 of the control device 4 controls the ADC 43 so as not to drive at the time when the noise of the electric motor 9 occurs. Alternatively, the CPU 41 can stop the calculation of the distance d at the time when the noise of the electric motor 9 occurs, and can control not to use the data of the output signal of the detection coil 3 acquired via the ADC 43 .
In any case, the CPU 41 is configured to digitally eliminate the output signal from the detection coil 3 in synchronization with the period of the noise of the electric motor 9 in relation to the calculation of the distance d.
As a result, the control device 4 can accurately obtain the distance d while avoiding noise from the electric motor 9 .

The position sensor 1 can be effectively applied particularly to stepping motors, switched reluctance motors, servo motors, and linear DC motors whose rotation can be controlled by pulse signals. The control device 4 can generate a control pulse signal for the electric motor 9, and the noise generation timing can be predicted more accurately. As a result, the influence of noise can be eliminated particularly effectively in calculating the distance d.

(Embodiment 3)
FIG. 8 is a schematic diagram showing the main configuration of the position sensor 1 of Embodiment 3 that can eliminate the influence of noise from the electric motor 9. As shown in FIG.
The control device 4 comprises a first ADC 43a and a second ADC 43b.
The first ADC 43a and the second ADC 43b operate in synchronization with the same clock signal as the CPU 41 of the control device 4, etc., as described above.
A first ADC 43a shown in FIG. 8 corresponds to the ADC 43 that detects the output signal from the detection coil 3 as described in the first embodiment.

As shown in FIG. 8, the electric motor 9 is supplied with power from the power control device 11 via the power line L11.
A non-contact noise sensor 12 is provided on a portion of the power supply line L11. The noise sensor 12 can use, for example, a clamp meter, a non-contact ammeter such as a loop antenna, or a non-contact voltmeter. Noise in the current or voltage of the power supply line L11 can be detected as a pulse (high frequency signal). When a non-contact ammeter is used as the noise sensor 12, for example, it can be converted into voltage by a resistive load and input to the second ADC 43b.
As the clamp meter, a known clamp meter using electromagnetic induction can be used. The power supply line L11 is used as a supply source of an excitation signal, and an output signal is generated by electromagnetic induction in a detection coil built into the clamp meter. to detect

The output signal (noise detection signal) of the noise sensor 12 is input to the second ADC 43b and digitized. The CPU 41 detects a noise generation timing or period by detecting a signal (pulse) equal to or greater than a preset threshold in the digitized output of the noise sensor 12 . The CPU 41 can also store the detected noise generation timing or period in the storage device 44 .

The CPU 41 can stop the detection of the output signal of the detection coil 3 by the first ADC 43a in accordance with the noise generation timing. Alternatively, the CPU 41 can be configured to stop calculating the distance d at the noise generation timing or not to output the calculated distance d from the IO 45 at the noise generation timing.
In other words, the CPU 41 is configured to digitally eliminate the output signal from the detection coil 3 in synchronization with the timing or cycle of noise generated by the electric motor 9 when calculating the distance d.
As a result, the control device 4 can accurately obtain the distance d while avoiding noise from the electric motor 9 .

The position sensor according to the present invention has a simple configuration and can accurately measure the distance to the object to be measured at high speed. The configuration is simple, and it is possible to manufacture a position sensor that is smaller and less costly than conventional ones. This position sensor can be applied to various uses and situations, and has great industrial applicability.

1 position sensor (position detection device)
2 excitation coil 3 detection coil 4 control device 41 CPU (arithmetic processing unit)
42 DAC (Digital to Analog Converter)
43 ADC (Analog Digital Converter)
43a first ADC
43b Second ADC
44 storage device 45 IO (input/output unit)
5 sensor unit 6 object to be measured 7 input signal amplifier 8 output signal amplifier 9 electric motor 10 transmission mechanism (power transmission mechanism)
11 power control device 12 noise sensor L11 power supply line

Claims

A position sensor comprising a sensor unit having an excitation coil and a detection coil and a control unit,
The control unit includes a control device having an arithmetic processing unit, a digital-to-analog converter, and a first analog-to-digital converter,
The arithmetic processing unit, the digital-to-analog converter, and the first analog-to-digital converter all operate in synchronization with the same clock signal,
An excitation signal generated by the digital-to-analog converter is applied to the excitation coil,
The arithmetic processing unit detects an output signal from the detection coil by the first analog-to-digital converter in synchronization with a predetermined timing of the excitation signal,
A position sensor that calculates a distance between the sensor unit and an object to be measured from the output signal and the excitation signal detected synchronously.
The position sensor according to claim 1, wherein the output signal is detected at a timing when the excitation signal reaches a peak.
The position sensor according to claim 2, wherein the excitation signal is a triangular wave consisting of a step function.
4. The position sensor according to claim 3, wherein said output signal is averaged in a step region including a peak of said excitation signal.
The position sensor according to claim 3, wherein the output signal is averaged in the vicinity of the timing at which the excitation signal peaks.
4. The position sensor according to claim 3, wherein said output signal is averaged at a plurality of timings when said excitation signal reaches a peak.
The control device controls an electric motor that drives the object to be measured,
4. The method of claim 1, wherein calculation of the distance between the object to be measured and the sensor section is eliminated based on the output signal from the first analog-to-digital converter in synchronization with noise generated by the electric motor. 2. The position sensor of claim 1.
the position sensor comprises a noise sensor,
the control device comprises a second analog-to-digital converter operating in synchronization with the clock signal;
The noise sensor is provided in a power supply line of an electric motor that drives the object to be measured,
The arithmetic processing unit detects timing of occurrence of noise in the power supply line from a signal from the noise sensor input via a second analog-to-digital converter,
2. The position sensor according to claim 1, wherein the output signal from the detection coil is eliminated in synchronization with the noise generation timing.