JPH0626850A - Displacement measuring apparatus - Google Patents

Abstract

PURPOSE:To obtain an absolute type displacement measuring apparatus, which can perform the measuring operation to the lower level of the output of a power supply. CONSTITUTION:A solar battery 5 for supplying electric power into a system, an absolute type displacement sensor 1, a signal processing circuit 2, which processes the output signal of the displacement sensor 1 and measures the absolute displacement amount, and a control circuit 3, which controls the signal processing circuit 2 and intermittently performs the measuring operation, are provided. A voltage detecting circuit 4, which detects the output voltage of the solar battery 5, is provided. The control circuit 3 has the function, which variably controls the measuring time per unit time of the intermittent measuring operations in response to the output voltage of the solar battery 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement measuring device applied to a small measuring instrument such as a digital caliper, and more particularly to an absolute displacement amount of a movable element with respect to a fixed element of a displacement sensor. The present invention relates to a so-called absolute type displacement measuring device.

[0002]

2. Description of the Related Art As a small measuring instrument such as a digital caliper, a digital micrometer or a height gauge for displaying a measured value on a liquid crystal display device or the like, it is promising to use a capacitance type displacement sensor. In a capacitance type displacement sensor, a large number of electrodes are arranged on a fixed element such as a main scale and a movable element such as a slider which moves relative to the fixed element, and the electrodes are moved along with the movement of the movable element with respect to the fixed element. The displacement amount is detected by extracting a signal of periodic capacitance change generated between patterns.

Such displacement sensors are classified into two types, an incremental type and an absolute type, depending on the form of the output signal. The former measures the displacement amount by continuously measuring the periodic signal generated by the movement of the slider from the reference position. The latter is capable of obtaining the absolute displacement amount (position) of the movable element with respect to the fixed element without performing the continuous counting operation. For example, depending on the shape of the electrode pattern, a coarse pitch, an intermediate pitch, or a fine pitch can be obtained. By making it possible to output a periodic signal of a pitch and combining the phase information of these periodic signals of each pitch, it is possible to detect the absolute displacement amount of the movable element.

When these displacement sensor devices use a solar cell (solar cell) as the main power source, the usable power source current is determined by the illuminance. With the incremental type, it is necessary to continuously measure the amount of slider movement from an arbitrarily set origin, and measurement must be stopped when the battery output current becomes low due to low illuminance. I have to. On the other hand, the absolute displacement sensor
Since the absolute position can be known in a short time measurement, intermittent measurement is possible and the measurement cycle can be set by the control circuit. For example, with a digital caliper using an absolute displacement sensor, a measurement time of 40 msec.
Intermittent operation of 10 times in sec. By performing such an intermittent operation, the average current consumption can be reduced as compared with the case of the incremental type.

[0005]

However, even with an absolute displacement sensor using a solar cell, if the illuminance falls below a certain level, the power supplied to the system will be insufficient and measurement will not be possible. . The present invention has been made in view of such circumstances, and an object of the present invention is to provide an absolute displacement measuring device capable of performing a measuring operation even at a lower power output level.

[0006]

According to the present invention, a DC power source for supplying electric power to a system, a displacement sensor for outputting an output signal according to a relative positional relationship of a movable element to a fixed element, and an output signal of the displacement sensor are processed. In the displacement measuring device having signal processing means for measuring the absolute displacement amount of the movable element with respect to the fixed element, and control means for intermittently performing the measuring operation by controlling the signal processing means, the output voltage of the DC power source The control means has a function of variably controlling the measurement time per unit time of the intermittent measurement operation according to the output voltage of the DC power supply.

[0007]

According to the present invention, the measurement time per unit time of the intermittent measurement operation using the absolute displacement sensor, that is, the duty ratio is variably controlled according to the power supply output. Specifically, for example, when the power supply output becomes lower than a certain set level, control is performed to lengthen the measurement cycle (that is, increase the measurement interval). As a result, the average current consumption of the system under a low power supply voltage is reduced, and a displacement measuring device that guarantees the measurement operation up to a low power supply voltage can be obtained.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system configuration of a displacement measuring device according to an embodiment of the present invention. Reference numeral 1 is an absolute capacitance displacement sensor (hereinafter referred to as ABS sensor), 2 is a signal processing circuit for calculating the output signal of the ABS sensor 1 to obtain an absolute displacement amount, and 3 is controlling them. This is a control circuit for performing measurement by intermittent operation. In this embodiment, the solar cell 5 is used as a DC power supply that supplies power to the entire system. The output portion of the solar cell 5 is provided with a voltage detection circuit 4 that detects the output voltage.

The specific configuration of the system is shown in FIGS. 4 and 5. The ABS sensor 1 is configured, for example, as shown in FIG. Slider 21 which is a movable element
Are arranged to face the main scale 22, which is a fixed element, with a slight gap therebetween, and are movable in the measurement axis x direction. Transmission electrodes 23 are arranged on the slider 21 at a predetermined pitch Pt0. The transmitting electrode 23 is capacitively coupled to the first receiving electrode 24a and the second receiving electrode 24b arranged on the main scale 22 at the pitch Pr.
The reception electrodes 24a and 24b are connected to the first transmission electrodes 25a and the second transmission electrodes 25b having the pitches Pt1 and Pt2, which are adjacent to each other in the arrangement direction, in a one-to-one correspondence. Transmission electrode 2
5a and 25b are the first detection electrodes 26a and 26b and the second detection electrode 27, which are provided on the main scale 21 side, respectively.
It is capacitively coupled with a and 27b.

The transmitting electrodes 23 are commonly connected to every other seven electrodes to form a plurality of eight electrode groups. In the measurement mode, the eight-phase periodic signals a, b, ...
Is being supplied as. More specifically, these drive signals Sd are signals chopped with high frequency pulses, and are generated and output from the transmission waveform generating circuit 11 in FIG.

The pitch Wt of the electric field pattern generated by supplying the drive signal Sd to the transmitting electrode 23 is eight times the pitch Pt0 of the transmitting electrode 23, and this pitch Wt is
It is set to N times the pitch Pr of the receiving electrodes 24a and 24b. Here, N is preferably an odd number such as 1, 3, 5 or the like, and is set to 3 in this embodiment. Therefore, three to four receiving electrodes 24a and 24b are always capacitively coupled to the eight continuous transmitting electrodes 23. The receiving electrodes 24a and 24b are formed by sandwiching triangular or sinusoidal electrode pieces. The phase of the signal received by each of the receiving electrodes 24a and 24b is determined by the capacitive coupling area between the transmitting electrode 23 and the receiving electrodes 24a and 24b, which changes depending on the relative position between the slider 21 and the main scale 22. .

Receiving electrodes 24a, 24b and transmitting electrode 25
If a and 25b are formed at the same pitch, the detection electrodes 26a, 26b, 27a, and 27b simply detect a periodic signal that is repeated each time the position of the main scale 21 in the x direction changes by the pitch Pr. However, in the ABS sensor 1 of this embodiment, a coarse displacement amount (coarse scale),
In order to detect the displacement amount of three levels of the intermediate displacement amount (medium scale) and the fine displacement amount (fine scale), the transmission electrodes 25a and 25b are actually the reception electrodes 24a and 24b.
On the other hand, the pitch is changed to deviate by D1 and D2 respectively. The deviation amounts D1 and D2 are functions of the distance x in the measuring direction from the reference position x0, and can be expressed as in the following formula 1.

[0013]

## EQU1 ## D1 (x) = (Pr-Pt1) x / Pr D2 (x) = (Pr-Pt2) x / Pr

The transmitting electrodes 25a and 25b are thus displaced relative to the receiving electrodes 24a and 24b, and the detecting electrode 26
a, 26b, 27a, 27b with a pitch Wr1 (= 3Pt
1) and Wr2 (= 3Pt2), the deviation amounts D1 (x) and D2 from the detection electrodes 26 and 27 are set.
Detection signals B1, B2, C1 in which a small period of the detection electrodes 25a, 25b is superimposed on a large period corresponding to (x)
, C2 can be obtained. The signals B1 and B2 have a large period in opposite phase and a small period in phase. Therefore, a signal with a large period can be obtained from the difference between both signals, and a signal with a small period can be obtained from the sum of both signals. The same applies to the detection signals C1 and C2. Here, the electrode pattern is set so that the large cycle of the detection signals B1 and B2 is several tens of times the small cycle and the large cycle of the detection signals C1 and C2 is tens of times the large cycle of the detection signals B1 and B2. Thus, the displacement of each level can be obtained by the calculation of the following Expression 2.

[0015]

[Equation 2] C1-C2 (coarse scale) B1-B2 (medium scale) (B1 + B2)-(C1 + C2) (fine scale)

These operation output signals C1-C2, B1-
B2, (B1 + B2)-(C1 + C2) are respectively a coarse scale demodulation circuit 121, a medium scale demodulation circuit 122,
Fine scale demodulation circuit 123 and phase detection circuit 131,
It is processed at 132 and 133. Specifically, demodulation is performed by generating a rectangular wave phase signal CMP having phase information at the edge through processing such as sampling at the chop frequency of the transmission waveform, mixing, low-pass filtering, and binarization. Be seen. The 0 ° drive signal Sd output from the transmission waveform generation circuit 11 is output from the phase detection circuits 131, 132, 133.
Is used as a reference signal, and the phase of each input signal is output as a digital value.

The digital values output from these phase detection circuits 131 to 133 are weighted and synthesized by the synthesis circuit 14. The synthesis circuit 14 is also supplied with an offset value stored in an offset storage unit such as an EEPROM so that the offset amount of the synthesis value can be adjusted. The output of the synthesizing circuit 14 is converted in the arithmetic circuit 16 into, for example, the electrode array pitch into the actual dimension value. The arithmetic circuit 16 is connected to a control circuit such as a microcomputer via an interface (not shown). The actual size value obtained by the arithmetic circuit 16 is displayed on the LCD display unit 17.

In this embodiment, the power supply voltage at which the system operates is, for example, 1.5 V or higher, whereas the voltage detection circuit 4 has three voltages of 1.5 V, 1.4 V and 1.3 V.
The output voltage of the solar cell 5 is checked with one threshold value. Then, the control circuit 3 variably controls the measurement time per unit time of the intermittent measurement operation according to the output voltage. Specifically, in the case of this embodiment, the measurement cycle is controlled. As shown in FIG. 3, when the output voltage is 1.5 V or more, the measurement cycle is 100 msec (that is, 10 seconds per second).
When the output voltage is 1.5 V or less, the measurement cycle is doubled to 200 msec (that is, 5 times per second). The measurement time is 40 msec in each case. In addition to the above control of the measurement cycle, the control circuit 3 supplies an ON / OFF signal, a reset signal, a clock signal, etc. to each circuit to control the operation of the entire system.

FIG. 2 is a state transition diagram of control in this embodiment. The measurement cycle is changed at the boundary of 1.5 V as described above. Further, in this embodiment, below 1.4V, only the control circuit is kept in the ON state to stop the measurement operation,
Further, when the voltage becomes 1.3 V or less, the operation of the entire system is stopped. Here, the operation of the entire system is not stopped at 1.4V or less, and only the control circuit is kept in the ON state in the range of 1.3V to 1.4V because the measurement operation is immediately performed after the power output is restored. This is to keep the control circuit in the standby state as much as possible so that it can be restarted.

According to this embodiment, A using a solar cell is used.
In the BS sensor system, the average current consumption of the system under low illuminance can be reduced, and it is possible to measure even lower illuminance than before. In addition, it is possible to display a warning of low illuminance by using the detection result of the solar cell output voltage.

The present invention is not limited to the above embodiment. For example, in the embodiment, the measurement cycle of the intermittent measurement operation is controlled in two steps according to the illuminance, but it may be controlled in three steps or more, or in some cases, the measurement cycle may be continuously variably controlled. Further, in the embodiment, the measurement cycle was controlled while the measurement time was kept constant, but conversely, the measurement time may be kept constant and the measurement time may be variably controlled. This also variably controls the measurement time per unit time. As a result, power consumption can be saved as well. Furthermore, although the case where the solar cell is used has been described in the embodiment, the present invention is also effective when another DC power source is used.

[0022]

As described above, according to the present invention, in an absolute displacement measuring device for intermittent operation, the system under a low power supply voltage is controlled by variably controlling the measurement time per unit time according to the power supply output. It is possible to reduce the average current consumption of, and to guarantee the measurement operation up to a lower power supply voltage than before.

[Brief description of drawings]

FIG. 1 is a diagram showing a block configuration of a capacitance type displacement measuring device according to an embodiment of the present invention.

FIG. 2 is a control state transition diagram of the embodiment.

FIG. 3 is a timing diagram of a measurement operation of the same example.

FIG. 4 is a diagram showing a configuration of a signal processing circuit unit of the embodiment.

FIG. 5 is a diagram showing a configuration of an ABS sensor of the example.

[Explanation of symbols]

1 ... ABS sensor, 2 ... signal processing circuit, 3 ... control circuit,
4 ... Voltage detection circuit, 5 ... Solar cell.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Yaku Toru 20-1 Sakado, Takatsu-ku, Kawasaki-shi, Kanagawa Mitutoyo Development Laboratory Co., Ltd.

Claims (1)

[Claims] 1. A direct current power supply for supplying power to a system, a voltage detecting means for detecting an output voltage of the direct current power supply, a displacement sensor for outputting an output signal according to a relative positional relationship of a movable element with respect to a fixed element, Signal processing means for processing the output signal of the displacement sensor to measure the absolute displacement amount of the movable element with respect to the fixed element, and controlling the signal processing means to perform the measurement operation intermittently, A displacement measuring device comprising: a control unit that variably controls a measuring time per unit time of an intermittent measuring operation according to an output.