JPS6131804B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a length measurement signal detector, and more particularly to a length measurement signal detector that electrically detects the amount of movement of a probe using changes in capacitance.

In a length measuring device such as a micrometer, caliper, three-dimensional measuring device, or coordinate position measuring device, the probe is moved in accordance with the length of the object to be measured, and the amount of movement is electrically detected and displayed digitally. Measuring devices that perform this are well known and have the advantage of providing accurate measuring action without reading errors.

Conventionally, photoelectric detectors or electromagnetic detectors have been used as the above-mentioned electrical length measurement signal detectors, but each of these conventional devices has several drawbacks, limiting their range of use. There was a problem. In other words, a photoelectric detector has a configuration in which a slit plate moves between a light emitting and receiving device and electrically detects light transmission and light shielding. A current must be supplied to produce the light emitting action, and for this reason the current consumption of the detector is extremely large, and especially in small measuring instruments that use batteries as a driving source, the battery life limits the usage time of the measuring instrument. This caused a problem. In particular, recent electronic circuits for measuring instruments use C-MOS integrated circuits with low current consumption, and the current consumption of the electronic circuit itself has been significantly reduced, so the current consumption of the photoelectric detector mentioned above has become a major problem. Ta. Furthermore, electromagnetic detectors have a configuration that electrically detects changes in magnetic flux.
This method has the disadvantage that the detection accuracy is significantly reduced due to noise introduced by the external magnetic field around the detector, and it is difficult to shield the external magnetic field, making it impossible to obtain a high-precision detector.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to provide a highly accurate length measurement signal detector with low current consumption.

To achieve the above object, the present invention provides a fixed electrode plate having a plurality of slit electrodes arranged in an array on its surface, and a fixed electrode plate having a plurality of slit electrodes arranged in an arrangement on a surface facing the slit electrode, which moves with the movement of a probe. A variable capacitor is formed by the two slit electrodes, and a dielectric layer is provided between the two slit electrodes.

According to the present invention, an accurate length measurement signal can be detected by moving one electrode of the variable capacitor along with the movement of the measuring head, and detecting an accurate length measurement signal based on the change in capacitance at this time. Since the dielectric layer is provided between the electrodes, the capacitance value can be significantly increased compared to the case where there is air between the electrodes, and this has the advantage that the detection sensitivity can be significantly improved.

Preferred embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows an embodiment in which the length measurement signal detector according to the present invention is applied to a rotary measuring device, such as a micrometer, in which a fixed electrode plate 12 fixed to a micrometer substrate with fixed legs 10 and It includes a movable electrode plate 14 in sliding contact with the electrode plate 12, the shaft 16 of the movable electrode plate 14 being connected directly or indirectly to a micrometer spindle (not shown). Therefore, the movable electrode plate 14 can be rotated relative to the fixed electrode plate 12 as the micrometer spindle, which is the measuring point of the measuring instrument, moves.

FIG. 2 shows the electrode structures of the electrode plates 12 and 14, in which a plurality of slit electrodes 12a are arranged in alignment on one surface of the fixed electrode plate 12, and similarly, the fixed electrode plate 12 of the movable electrode plate 14 and A plurality of slit electrodes 14a are arranged in alignment on the opposing surfaces. The detector in the embodiment detects the amount of movement of the probe as two types of signals with different phases, and for this purpose, the slit electrode 1 provided on the fixed electrode plate 12
2a is separated into an upper half and a lower half in FIG. A sine wave signal and a cosine wave signal are output. As is clear from FIG. 2, the slit electrode group 12a has a substantially comb-like shape, and is electrically connected in common by a half-moon ring-shaped common electrode portion 12b provided on the outer side of the fixed electrode plate 12. . The fixed electrode plate 12 in this embodiment is made of a plastic substrate, and the slit electrode 12a and the common electrode portion 12b are formed by a well-known printed circuit board method.

Similarly, a comb-like slit electrode 14a is formed on the surface of the movable electrode plate 14 by a printed circuit board method.
are arranged at equal pitches in the circumferential direction. The slit electrode 14a is electrically connected to the common electrode part 14b, and the common electrode part 14b is arranged to extend to the back surface of the movable electrode plate 14, as shown in FIG. It is in electrical sliding contact with a slit ring 22 provided near the terminal 14, and an electrical signal from the terminal 24 is transmitted to the slit electrode 1 of the movable electrode plate 14 via the slit ring 22.
4a.

As is clear from FIG. 2, when the slit electrode 14a of the movable electrode plate 14 is overlapped with the slit electrode 12a of the fixed electrode plate 12, the capacitance value between the two electrodes becomes maximum, and this amount of overlap is By electrically detecting the capacitance change that changes with the rotational movement of the electrode plate 14 and that occurs during this movement, it is possible to electrically detect the amount of movement of the movable electrode plate 14, that is, the measuring head. Become.

FIG. 3 shows the electrode structure of FIGS. 1 and 2, and by providing a dielectric layer between both electrodes 12a and 14a, the capacitance value between the electrodes is increased, and the capacitance is increased. Fluctuation errors due to changes in external conditions such as temperature or humidity are removed. In FIG. 3, the interelectrode dielectric layer consists of dielectric layers 26 and 28 coated on the surfaces of the electrode plates 12 and 14 on which both electrodes 12a and 14a are provided, and the dielectric layers 26 and 28 in the embodiment are Made from Teflon coating. As is well known, Teflon has a significantly higher dielectric constant than air, is extremely stable against external conditions, and has a small coefficient of friction. Therefore, as shown in FIG. 3, even when the electrode plates 12 and 14 are brought into sliding contact with each other, the sliding resistance is small and wear due to friction is small, resulting in stable characteristics and durability. It is possible to form a variable capacitor with a certain value.

FIG. 4 shows an electrode arrangement suitable for the present invention,
In the embodiment shown in FIG. 2, electrodes 12a and 14 having different phases are provided in the upper and lower halves of the electrode plates 12 and 14 to obtain two types of detection signals with different phase differences.
In the embodiment shown in FIG. 4, the electrode plate 12 is divided into six equal parts along its circumference, and one
A slit electrode is provided in every other area 101, 102, and 103 to detect a sine wave signal, and a slit electrode is provided in every other area 201, 202, and 203 to detect a cosine wave signal having a different phase. It is provided. According to the embodiment shown in FIG. 4, each slit electrode can detect a sine wave signal and a cosine wave signal even if an axis misalignment or roundness error occurs during processing or assembly of the electrode plate and shutter plate. are distributed along the circumference of the electrode plate, so the overall averaged output is always a constant output value regardless of the error, making it possible to improve detection accuracy.

FIG. 5 shows an electronic circuit suitable for the present invention,
An alternating current electrical signal is supplied from an oscillator 30 to the slit electrodes 14a for detecting sine wave signals and cosine wave signals provided on the electrode plate 14, and this alternating current wave has an oscillation frequency of 1 MHZ in the embodiment. The detector according to the present invention itself forms a variable capacitor, and as a result, a modulation signal corresponding to the movement of the movable electrode plate 14 is output from the slit electrode 12a side, and this modulation signal is transmitted to the detection circuits 32 and 34. Envelope detection is performed, and the output thereof is further level-converted by level converters 36 and 38. As a result of the above, a cosine wave signal is output from the level converter 36 and a sine wave signal is output from the level converter 38.
By supplying both output signals to the well-known dividing circuit 40, a digital length measurement signal corresponding to the amount of movement of the movable electrode plate 14 can be obtained, and by counting this length measurement signal, the movable electrode The amount of movement of the plate 14, that is, the measuring tip, is determined as a digital value.

FIG. 6 shows an embodiment in which the detector according to the present invention is configured as a cylindrical measuring device, and the same reference numerals are given to the members corresponding to those in the above-described embodiment, and the explanation thereof will be omitted. In the embodiment shown in FIG. 6 as well, since dielectric layers 26 and 28 are provided between the electrode plates 12 and 14, changes in capacitance can be detected with high precision.

Furthermore, FIG. 7 shows an embodiment of the present invention in which a flat movable electrode plate 14 moves back and forth along a long fixed electrode plate 12, and the linear movement of the probe fixed to the movable electrode plate 14 is shown in FIG. The amount can be reliably detected electrically.

FIG. 8 shows still another embodiment of the present invention,
In each of the embodiments described above, a slip ring 22 is provided to supply an electrical signal to the movable electrode plate 14, but in the embodiment of FIG. 8, the movable electrode plate 14 is
It is characterized in that an electric signal can be supplied to the slit electrode 14a without contact. That is, an auxiliary electrode 42 is provided on the opposite side of the movable electrode plate 14 from the slit electrode.
A signal supply electrode plate 46 having a signal supply electrode 44 facing the auxiliary electrode 42 is fixed to the substrate. Auxiliary electrode 42 and signal supply electrode 4
4 is approximately ring-shaped, and both electrodes 42, 44
A signal supply capacitor is formed.

The equivalent circuit of FIG. 8 is shown in FIG. 9. A signal supply capacitor composed of an auxiliary electrode 42 and a signal supply electrode 44 is connected in series to a variable capacitor composed of slit electrodes 12a and 14a. An electrical signal is supplied from the connected terminal 24. The capacitance of the signal supply capacitor does not change even when the movable electrode plate 14 rotates.
Therefore, the composite capacitance obtained from the equivalent circuit of FIG. 9 is obtained only from the relative movement of both slit electrodes 12a, 14a when the movable electrode plate 14 moves. That is, the signal supply capacitor is provided only to electrostatically supply an electric signal, and as a result, there is no need for electrical connection to the movable electrode plate 14, and resistance changes at the sliding contact portion are prevented. It becomes possible to eliminate error factors such as The capacitance of the signal supply capacitor is preferably as large as possible, and in the embodiment, both electrodes 4
It is preferable to increase the area of electrodes 2 and 44 and to reduce the gap therebetween, and it is also preferable to provide a dielectric layer between both electrodes 42 and 44.

FIG. 10 shows still another embodiment of the electrode structure suitable for the embodiment, in which slit electrodes 12a and 14a formed on the surfaces of both electrode plates 12 and 14 are made of aluminum electrodes. The surfaces of both aluminum electrodes 12a, 14a are chemically oxidized, and aluminum oxide films 48, 5 are formed on the surfaces.
0 is formed. As is well known, an aluminum oxide film has a high dielectric constant and can be used as a good dielectric layer. In the embodiment, plastic thin films 52 and 54 are further coated on the surfaces of the aluminum oxide films 48 and 50, and the dielectric layer of the present invention is formed from the aluminum oxide films 48 and 50 and the plastic thin films 52 and 54. ing. FIG. 11 shows an enlarged view of the aluminum oxide film 50, in which, as a result of the chemical treatment, a number of depressions 50a with widening bottoms are formed on its surface, so that when coating the plastic film 54, The aluminum oxide film 50 and the plastic thin film 54 are tightly bonded, making it possible to obtain a strong coating of the plastic thin film 54.

As described above, according to the embodiments shown in FIGS. 10 and 11, a dielectric layer having a good dielectric constant is obtained from the oxide film and the plastic thin film, and the electrode surface is made of a plastic thin film with low frictional resistance, such as Teflon, etc. Since both electrode plates 12,1
It becomes possible to perform the sliding contact of No. 4 with low resistance.

As explained above, according to the present invention, the space between the two electrodes forming the variable capacitor is filled with a dielectric layer, and measurement errors due to intervening air etc. can be removed, so stable detection sensitivity can be achieved. It becomes possible to provide a good length measurement signal detector.

Since the detector according to the present invention is of a capacitance type, its current consumption is extremely small, making it possible to significantly extend battery life, especially in battery-powered measuring instruments, and making it possible to significantly extend the battery life of small portable measuring instruments. It is extremely suitable as Further, the detector of the present invention needs only to be inserted into a simple metal case in order to shield external electric fields, and it is an object to provide a high-precision measuring instrument with less intrusion of external noise compared to conventional electromagnetic types. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing a preferred embodiment of the length measurement signal detector according to the present invention, FIG. 2 is an exploded plan view showing the electrode arrangement of FIG. 1, and FIG. 3 is the same as that of FIGS. An enlarged sectional view showing the electrode structure in detail, FIG. 4 is an explanatory diagram showing another configuration of the electrode arrangement of the detector according to the present invention, and FIG. 5 is an explanatory diagram showing a detection circuit suitable for the present invention and its waveform diagram. 6, 7, and 8 are perspective views of main parts showing other embodiments of the detector according to the present invention, FIG. 9 is an equivalent circuit diagram of FIG. 8, and FIG. FIG. 11 is an enlarged sectional view of the main part of FIG. 10, showing another embodiment of the electrode structure. 10...Fixed foot, 12...Fixed electrode plate, 14...
...Movable electrode plate, 12a, 14a...Slit electrode, 26, 28...Dielectric layer, 48, 50...Aluminum oxide film, 52, 54...Plastic thin film.

Claims (1)

[Scope of Claims] 1. A fixed electrode plate with a plurality of slit electrodes arranged on its surface; a movable electrode plate with a plurality of slit electrodes arranged on its surface opposite to the slit electrodes, which moves with the movement of the probe. , the two slit electrodes form a variable capacitor, the surfaces of the two slit electrodes are each covered with a dielectric layer, and the two opposing dielectric layers slide when the movable electrode plate moves. contact,
the slit electrode is made of an aluminum electrode,
Further, each of the dielectric layers is formed from an oxide film applied to a corresponding aluminum electrode and a plastic thin film covering the oxide film, and sliding contact between both dielectric layers is made by the plastic thin film. A length measurement signal detector characterized by: