JP2001255109A - Position-measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption associated with the detection of errors in a position-measuring apparatus, such as an electronic caliper. SOLUTION: In an electronic caliper, the displacement of a grid is detected with respect to a scale with a detection circuit 12, based on a signal of a transducer 10. A CPU14 displays the position detected on a display device 24. The CPU14 executes detection of errors in the transducer, only when the relative speed of the grip with respect to the scale is zero or lower than a prescribed value. Since the detection of errors is performed only at a prescribed timing, thereby reducing the power consumption.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position measuring device, and more particularly to a method for detecting a displacement between two members, which reduces power consumption of the position measuring device.

[0002]

2. Description of the Related Art Measuring instruments, such as electronic calipers, are widely used in the manufacturing industry to measure the thickness and other physical dimensions of objects, and transducers are used as a major component of the measuring instruments.

[0003] As transducers, a capacitive transducer and an inductive transducer are known. In a capacitive transducer, a transmission electrode and a reception electrode are provided on a grid (slider), and a signal electrode is provided on a scale facing the grid. The transmitting and receiving electrodes on the grid are capacitively coupled to the signal electrodes on the scale. A drive signal is supplied to the transmission electrode, and a detection signal generated at the reception electrode is processed by a processing circuit in accordance with a relative position between the grid and the scale to detect a movement or a position of the grid with respect to the scale.

On the other hand, in an inductive transducer, a relative position is detected based on electromagnetic induction between a grid and a scale. For example, an excitation coil is provided on the grid to generate magnetic flux, and an induced current is generated in the scale coil. The induced current generates a magnetic flux, and an induced current (induced voltage) is generated in a detection coil provided on the grid. Since the induced voltage generated in the detection coil changes according to the displacement between the grid and the scale, the displacement can be detected based on the induced voltage signal.

[0005] In order to ensure that the transducer is operating reliably, in a conventional measuring instrument,
At each sampling timing, the signal from the transducer is monitored by the CPU to determine whether the signal is normal.

[0006]

However, in the configuration in which the CPU is operated at each sampling timing to detect an error as to whether the transducer is normal or not,
The power consumption increases, and for example, when a battery is used as a power supply, there is a problem that the battery life is shortened.

In particular, when an inductive transducer is used as a transducer, there is an advantage that it can be used in an environment with a high degree of contamination as compared with the capacitive coupling type, but there is a problem that power consumption is larger than that of the capacitive coupling type. An increase in power consumption is not desirable.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the related art, and an object of the present invention is to provide a position measuring device which can detect a transducer error and consumes low power.

[0009]

In order to achieve the above object, the present invention is a position measuring device for detecting a displacement between two members, and outputs the displacement between the two members as an electric signal. It has a transducer and a detecting means for detecting a malfunction of the transducer when a relative speed between the two members is equal to or less than a predetermined value.
The power consumption associated with the malfunction detection can be reduced by performing the malfunction detection when the relative speed is equal to or less than a predetermined value, instead of performing the malfunction detection (error detection) of the transducer every predetermined time. .

Here, it is preferable that the malfunction is detected when the relative speed between the two members is zero. Especially when the relative velocity is zero, it is necessary to detect the position with high accuracy.Detecting the malfunction of the transducer at that position enables efficient malfunction detection and improves the position detection accuracy. Secure.

[0011] The transducer may be, for example, an inductive transducer. Since the power consumption of the inductive transducer itself is relatively large, the usability of the inductive transducer is improved by reducing the power consumption due to the malfunction detection. In addition, when driven by a battery, it is possible to extend the battery life.

Further, the transducer may be an absolute type electronic caliper transducer for detecting a displacement from a predetermined reference position, that is, an absolute position. In the incremental type electronic caliper, the displacement amount is sequentially detected, but in the case of the absolute type electronic caliper, the absolute position of the grid is measured with the grid stationary with respect to the scale in many cases. Therefore, when the relative speed of the grid becomes equal to or less than the predetermined speed or when the relative speed becomes zero, the malfunction detection of the transducer is detected, so that the position detection timing and the malfunction detection timing can be synchronized, Efficient processing becomes possible.

Preferably, the detecting means detects the malfunction by using an amplitude ratio of an electric signal for detecting the displacement to a normal state. If a failure of the transducer itself, a change in the interval between the scale and the grid, or the intrusion of foreign matter occurs, the amplitude of the detection signal changes from the normal amplitude. Therefore, by using the ratio between the amplitude of the detection signal and the amplitude at the normal time, it is possible to reliably detect the malfunction of the transducer.

[0014]

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

FIG. 1 is a block diagram showing the configuration of an absolute position detecting (absolute type) electronic caliper according to this embodiment. Transducer 10 as detector
And a detection circuit 12, and a CPU 14, a ROM 16, a RAM 18, a switch 20,
A jumper 22 and a display 24 are provided.

The transducer 10 is, for example, an inductive transducer, and outputs a displacement of a grid (slider) with respect to a scale to a detection circuit 12 as an electric signal. To detect a displacement from a predetermined reference position (zero position), the wavelength (pitch) is different from λ1 and λ2.
It is sufficient to provide two scale coils and detect the intensity difference between the induced voltage signals having wavelengths λ1 and λ2 generated by the induced currents of these scale coils, respectively. The detection circuit 12
An induced voltage signal from the transducer 10 is input, an absolute position is detected using the intensity difference described above, and the absolute position is output to the CPU 14.

The CPU 14 displays the detection data supplied from the detection circuit 12 on a display 24 such as an LCD. R
The OM 16 stores processing programs or data necessary for the operation of the CPU 14. In the RAM 18,
The detection data is stored. When an error is detected in the transducer 10, data in a normal state is stored in the RAM 18 and compared with the detected data. The switch 20 is a switch for setting a reference position, and the jumper 22 is
The PU 14 is used to determine a timing at which the error detection of the transducer 10 is performed.

FIG. 2 shows a flowchart of the overall processing in this embodiment. First, an error detection timing is determined based on the state of the jumper 22 set in advance or reset by the user (S101).
In the present embodiment, when the grid is stationary with respect to the scale, that is, when the relative speed between the scale and the grid becomes zero, it is determined whether or not the grid is stationary with the jumper 22 in order to detect an error of the transducer 10. Set parameters for determination. This parameter α specifically defines the number of times that it is determined that there is no change in the absolute position of the grid detected by the transducer 10 and the detection circuit 12, and the number of times that there is no change in the absolute position of the grid is α. When it reaches, it is determined that the grid is stationary and error detection is performed.

After setting the jumpers, each variable is initialized (S102). Here, the X direction is the direction in which the grid is displaced with respect to the scale, X0 is a predetermined reference position (zero position), Xa is the detected absolute position, n is the number variable for determining the stationary state, Origin Flag
Is a flag for setting a predetermined reference point. Also,
The error flag is a flag that is set to 1 when an error of the transducer 10 is detected.

After initializing each variable, the detected values MA0 and MB0, which are references when detecting an error of the transducer 10, are measured (S103). MA0 and MB0
Is the amplitude value of the induced voltage signal of the wavelengths λ1 and λ2 immediately after the power is turned on. When the transducer 10 operates normally, the amplitude value is constant. On the other hand, when an error occurs, such as when a foreign substance enters between the grid and the scale, when the distance (air gap) between the grid and the scale changes, or when the transducer 10 itself breaks down, the amplitude value Changes compared to the normal value. Therefore, in this embodiment, the reference amplitude value is measured immediately after the power is turned on, and the measured value is stored in the RAM 18 (S104).

Next, a watchdog timer for bringing the CPU 14 into a sleep state is reset (S105), and
It is determined whether or not the iin Flag is 1 (S10).
6). Since it is set to 0 in the initial state, the current grid position Xa + 1 is further measured (S10).
7). The measured position is stored in the RAM 18,
The CPU 14 determines whether or not the previous position Xa and the current position Xa + 1 are the same (S108). If they are the same, it is determined whether or not n is 0 (S109).
If not, n is reduced by 1 (S110), and it is determined whether or not n is 0 (S111). When the number of times the previous position and the current position are the same reaches α (it can be said that the stationary state has continued for a certain period of time), n becomes 0, and when it has not yet reached n> 0. Become. If n> 0, then Xa-X0 is calculated as an absolute position and displayed on the display 24 (S119), and it is determined whether or not the Origin switch 20 has been operated (S120).
Here, when the Origin switch 20 is not operated, the CPU 14 is set to the sleep state (S121). The pause state continues for a predetermined time t. Power consumption can be suppressed by setting the CPU 14 to a sleep state instead of operating the CPU 14 for each sampling as in the related art.

On the other hand, when the Origin switch 20 is operated, the Origin Flag is set to 1 (S123), and the process returns to S106. In this process, since the flag is set from 0 to 1, the reference values (reference amplitude values) MA0 and MB0 used for error detection are input again (S112). This processing will be described later. After resetting the reference value, the watchdog timer is reset, and it is again determined whether or not the previous position is the same as the current position, that is, whether or not the grid has been stationary for a certain period of time.

Further, in the determination processing of S108, the previous position Xa and the current position Xa + 1 are not the same, that is, if the grid is moving with respect to the scale, 0 if the error flag is 1. (If the error flag is 0, it is maintained as it is) (S11)
4) Then, n is incremented by 1 (S115), and the current position is stored in the RAM 18 as Xa (S116) (S117). In the processing of S115, n is set to α
May be reset.

If the number of times the previous position and the current position have become the same has reached α (or if the stationary state has continued for a certain period of time), n = 0, and the CPU 14 issues a predetermined error only in this case. Execute detection processing (S11
3).

If an error in the transducer 10 is detected as a result of the error detection processing, the error flag is set to 1
Therefore, when the processing after S105 is repeated again after the error is detected, the determination in S118 is YES, and the error display is performed without displaying the current position on the display 24 (the processing in S119 is not performed). Is performed (S1
22). After the error is displayed, the CPU 14 is put into a sleep state (S121).

FIG. 3 is a detailed flowchart of the reference value input process (S113) in FIG. O
When the regin switch 20 is operated, the detection circuit 12
Calculates the amplitude values of the induced voltage signals of the wavelengths λ1 and λ2 at that time (S201) and stores them in the RAM 18 (S20).
2). The reference value calculated at power-on and stored in the RAM 18 may be overwritten and stored. And switch 2
The position when 0 is operated is stored in the RAM 18 as X0 (S203, S204). After storing the new reference position (zero position) and the reference amplitude values MA0 and MB0, Or
The iin Flag is set to 0 again (S20).
5).

FIG. 4 is a detailed flowchart of the error detection (S113) in FIG. First, the CPU 14 calculates the ratios MA / MA0 and MB / MB0 between the amplitude values MA0 and MB0 in the normal state and the current amplitude values MA and MB. Then, the ratio of these amplitude ratios (MA / MA
0) / (MB / MB0) is further calculated (S30).
1). Then, it is determined whether or not this ratio is within a predetermined range including 1, specifically, whether or not the calculated value is between Za and 1 / Za with Za being a predetermined value smaller than 1 (S30).
2). When the transducer 10 is operating normally, MA and MA0 are almost equal, and MB and MB0
Are approximately equal, the calculated value is close to 1, and the calculated value is within the above range. Therefore, if the calculated value is out of the above range, either the MA or the MB is not normal, and it is determined that an error has occurred in the transducer 10 and the CPU 14 displays an error on the display 24 (S
303).

Then, the error flag is set from 0 to 1 (S304). When the error flag is set to 1, the error display is maintained in S122 of FIG. 2 as described above. When the error flag is set to 1, n is returned to α (S309), and S105 in FIG.
It returns to the subsequent processing.

On the other hand, when the calculated value is within the above range, it can be determined to be normal. However, there is a possibility that the amplitude values of both MA and MB have changed by the same degree. Therefore, in order to confirm the degree of change between MA and MB, CPU 1
4 calculates (MA * MB) / (MA0 * MB0) (S305). When MA and MB change by the same degree, the value is away from 1 because MA * MB is multiplied by the degree of change and expanded. Therefore, this value falls within a predetermined range, specifically, a predetermined value Z smaller than 1.
It is determined whether or not b is between Zb and 1 / Zb (S306). If it is outside the range, the CPU 14 determines that an error has occurred in the transducer 10 and displays an error on the display 24 (S303). . Then, also at this time, the error flag is set from 0 to 1 (S304). If this value is within the predetermined range, the CPU 14 determines that the transducer 10 is normal, and displays a normal display on the display 24 (S307). Specifically, the current absolute position Xa + 1-X0 is displayed on the display 24 to notify the user of normal operation. If it is determined that the status is normal, the error flag is set to 0 (S30).
8). After setting the error flag to 0, n is returned to α (S309), and the process returns to S105 and subsequent steps in FIG.

As described above, in the present embodiment, the error detection of the transducer 10 is performed only when the grid is in a stationary state, so that the power consumption accompanying the error detection can be reduced. Further, in the electronic caliper for detecting the absolute position as in the present embodiment, when the grid is stopped, the position is to be detected for the user. By doing so, efficient error detection becomes possible.

In the process of FIG. 2, it is also possible to execute the error detection process (S113) immediately when α is 1, that is, when the previous position and the current position become the same. Further, in order to prevent the error detection processing from being executed a plurality of times when the stationary state continues for a long time, S
If n = 0 (that is, n = α is not reset) in 309, the error detection process is executed only once in the stationary state, and the power consumption can be further reduced.

Further, in the processing of FIG.
After calculating 0 and MB / MB0, it is determined whether or not each value is within a predetermined range including 1, and if both MA / MA0 and MB / MB0 are within the predetermined range, it is normal,
Otherwise, an error may be determined.

FIG. 5 shows a processing flowchart of another embodiment. In the present embodiment, the error detection of the transducer 10 is not performed when the grid is stationary with respect to the scale, but the error is detected when the relative speed of the grid is equal to or less than a predetermined value and it is expected that the grid will eventually stop.

In the drawing, the processing of S401 to S407 is the same as that of S101 to S107 of FIG. Is determined (S408). If the relative speed of the grid with respect to the scale is equal to or less than a predetermined value, the difference value between the current position Xa + 1 and the previous position Xa is equal to or less than a predetermined value a, and if the relative speed exceeds the predetermined value, the difference value is equal to a predetermined value. Value will be exceeded. Therefore, when the difference value exceeds the predetermined value a, the measured position is displayed on the display 24, and the CPU 14 is set to the rest state (S
409-S415). Since the relative speed is equal to or higher than the predetermined value, the position does not have to be displayed on the display 24 in S411. The value of a is, for example, 10 to 20 μm when the position measurement period (sampling period) is 0.1 second.
m is preferable.

On the other hand, when the relative speed of the grid with respect to the scale is equal to or less than the predetermined value a (NO in S408), it is next determined whether or not the position is the same as the previous position (S408).
416).

When the speed of the grid decreases and falls below a predetermined value, the current value and the previous value are not the same, and NO
Is determined and the current value is stored in the RAM (S419, S
420), an error detection process is performed after the current absolute position is displayed on the display 24 (S422). The error detection processing is the same as the processing shown in FIG. However, in the present embodiment, since the variable n is unnecessary, the processing in S309 can be omitted. Here, instead of displaying the absolute position in S421, error detection is performed in S422, and when it is determined that the transducer 10 is normal, 4
It is also preferable to display the absolute position calculated at 21 on the display 24. Also, while the difference value is equal to or less than the predetermined value a,
The error detection process is repeatedly performed, but by making the predetermined value a sufficiently small, the error detection process is performed once.
Alternatively, it can be limited to about several times.

If the grid is stationary with respect to the scale, YES is determined in S416, and an error flag is confirmed (S417). The error flag is set to 1 when it is determined that an error has occurred in the error detection processing, and is set to 0 when it is determined that the error is normal. If the error flag is 1, the error display is continuously performed (S418). If the error flag is 0, the current position is displayed because it is normal (S4).
11).

As described above, in the present embodiment, the error detection of the transducer 10 is executed only when the relative speed with respect to the scale becomes equal to or less than the predetermined value, so that the power consumption accompanying the error detection processing can be reduced.

In this embodiment, the difference between the current position and the previous position is compared with a predetermined value to determine whether or not the relative speed of the grid with respect to the scale is equal to or less than a predetermined value. In such a case, error detection is performed. However, whether or not the relative speed is equal to or less than a predetermined value is detected by another method, for example, by providing a speed sensor and directly detecting the relative speed.
Alternatively, a method of estimating the relative speed from the pattern of the induced voltage signal is also possible.

[0040]

As described above, according to the present invention,
Power consumption due to error detection can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of an embodiment.

FIG. 2 is an overall processing flowchart of the embodiment.

FIG. 3 is a flowchart of a reference value input process in FIG. 2;

FIG. 4 is a flowchart of an error detection process in FIG. 2;

FIG. 5 is an overall processing flowchart of another embodiment.

[Explanation of symbols]

10 transducer, 12 detection circuit, 14 CP
U, 16 ROM, 18 RAM, 20 switches, 2
2 jumpers, 24 indicators.

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshiaki Shiraishi 1-20-1 Sakado, Takatsu-ku, Kawasaki-shi, Kanagawa F-term (reference) 2F063 AA02 CA02 CA15 DA09 DA23 DD02 EA05 GA23 KA03 LA10 LA23 LA24 LA25 LA29 MA04 MA10

Claims (5)

[Claims] 1. A position measuring device for detecting a displacement between two members, wherein the transducer outputs a displacement between the two members as an electric signal, and a relative speed between the two members is equal to or less than a predetermined value. And a detecting means for detecting a malfunction of the transducer in such a case. 2. The position measuring device according to claim 1, wherein the detecting means detects the malfunction when the relative speed between the two members is zero. 3. The position measuring device according to claim 1, wherein the transducer is an inductive transducer. 4. The position measuring device according to claim 1, wherein the transducer is an electronic caliper transducer for detecting a displacement from a predetermined reference position. 5. The position measuring apparatus according to claim 4, wherein said detecting means detects said malfunction by using an amplitude ratio of an electric signal for detecting said displacement to a normal state. .