JP2015087179A - Air micrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air micrometer capable of suppressing the deterioration of a measurement accuracy caused by the fluctuation of the supply pressure of an air source.SOLUTION: A meter main body 1 of an air micrometer includes: an air pipe 13; pressure sensors 15, 17; and a measurement arithmetic processing unit 20. The air pipe 13 is interposed in an airflow passage from an air source to a nozzle 22a of a measuring head 3, and an orifice 14 is formed at a part of the air pipe. The pressure sensor 15 detects a supply pressure PH which is a pressure of the air available at the side of the air source with respect to the orifice 14 in the interior of the air pipe 13. The pressure sensor 17 detects a back pressure PL which is the pressure of the air available at the side of the nozzle 22a with respect to the office 14 in the interior of the air pipe 13. The measurement arithmetic processing unit 20 performs a process of calculating a gap dimension Z between an inner wall of a work W and the nozzle 22a on the basis of the supply pressure PH and the back pressure PL of the air source.

Description

  The present invention relates to an air micrometer that measures the dimensions such as the inner diameter of a workpiece with high accuracy by ejecting air from a nozzle provided in a measuring head.

Conventionally, as an air micrometer for measuring an inner diameter dimension of a cylindrical workpiece, the back pressure method shown in the following Non-Patent Document 1, the back pressure / differential pressure method shown in Patent Document 1, and Patent Document 2 are shown. An air micrometer such as a back pressure control system has been proposed.
The back pressure type air micrometer described in Non-Patent Literature 1 stabilizes the pressure of air supplied from an air source by a regulator (regulating valve), and then defines a flow path partitioned by an orifice (orifice). The nozzle is ejected from the nozzle to the work, and the back pressure of the nozzle is measured.

  The back pressure / differential pressure type air air micrometer described in Patent Document 1 supplies air supplied from an air source to two channels with a fixed throttle, and one channel is used for a measurement head. A flow path is provided, and another fixed throttle is provided in the other flow path to form an exhaust flow path, and a structure for measuring a differential pressure between the measurement head flow path and the exhaust flow path is provided.

  An air micrometer of a back pressure control system described in Patent Document 2 passes air supplied from an air source from a nozzle of a measurement head through a flow path partitioned by a porous member after passing through a control valve. A structure for measuring the air pressure in the flow path from the control valve to the porous member and the back pressure of the nozzle is provided. Then, the measurement calculation unit detects the pressure difference between the input and output flow paths to the porous member in a state in which the back pressure becomes a constant value by the valve control means for controlling the opening of the control valve, and the back of the nozzle. Based on the pressure and the temperature of the air, the inner diameter of the workpiece is calculated based on a linear expression or table data indicating the relationship between the air flow rate per unit time ejected from the nozzle of the measuring head and the inner diameter of the workpiece.

JP 2005-114511 A JP 2012-58213 A

Yoshio Fujinuma and 2 others, “Research on In-process Measurement”, Ibaraki Prefectural Industrial Technology Center, 1990 Research Report, No. 19, p. 1-6

  By the way, the air micrometer is generally composed of an air circuit portion and an electric circuit portion. With respect to the air circuit portion, Non-Patent Document 1 obtains a theoretical formula indicating the flow rate of air passing through an orifice (throttle) and a nozzle based on fluid dynamics, and as shown in FIG. The values indicate that they are almost the same.

  However, as will be described later, there is a problem in that the gap size is greatly influenced by fluctuations in absolute pressure and atmospheric pressure at the orifice inlet. In addition, there are very few portions where the gap size and the absolute back pressure are proportional, and there is a problem that the range in which the gap size can be accurately measured is extremely narrow.

  A similar problem occurs when measuring a gauge back pressure (differential pressure between absolute back pressure and atmospheric pressure) instead of absolute back pressure with a conventional back pressure type air micrometer. As described in Non-Patent Document 1, even if the throttle inlet pressure is stabilized by the adjustment valve, the gap size is affected by fluctuations in atmospheric pressure and air temperature, as shown by the theoretical formula. There was a problem that high-precision measurement could not be performed for a long time.

  In the back pressure / differential pressure type air micrometer described in Patent Document 1, the influence of fluctuations in the air source pressure is reduced in order to measure the differential pressure, but it is described in FIG. 2 of Patent Document 1. In addition, the measurement accuracy deteriorates when the linear range is narrow and the nonlinear range is used. Moreover, the sensor characteristic (for example, temperature characteristic) of the pressure sensor which measures a differential pressure has a direct influence on a measurement result, and there existed a subject that a highly accurate measurement was not made.

  A back pressure type or back pressure / differential pressure type air micrometer is available on the market that can adjust sensitivity by manual knob adjustment or zero adjustment during measurement so that the linear range can be adjusted. There are many problems to use for in-process measurement of machining lines.

  In the back pressure control type air micrometer described in Patent Document 2, the control valve is moved by the valve control means of the measurement calculation unit constituted by an electric circuit so that the back pressure becomes constant, and then the flow rate is calculated. In order to measure the dimension of the workpiece by the means and the dimension calculating means, there is a problem that the measurement time becomes long.

  The present invention has been made in view of the above reasons, and can suppress a decrease in measurement accuracy due to fluctuations in supply pressure of the air source and fluctuations in atmospheric pressure, and in particular, in-process measurement in a machining line. The purpose of the present invention is to provide an air macrometer that is easy to handle, has a short measurement time, and can perform high-accuracy measurement over a long period of time.

(1) An air micrometer according to the present invention ejects air supplied from an air source from a nozzle of a measurement head toward a measurement object, and measures the dimension of a gap between the nozzle and the measurement object. A micrometer, an air pipe interposed in an air flow path from an air source to a nozzle of a measurement head and partially provided with a throttle part; and inside the air pipe, closer to the nozzle side than the throttle part A ratio of a first pressure sensor that detects pressure, a second pressure sensor that detects pressure on the air source side of the throttle, and a first detection value of the first pressure sensor and a second detection value of the second pressure sensor And a measurement calculation processing device that performs a process of calculating a gap dimension based on the calculated value.

  According to this configuration, the dimension of the measurement object is calculated based on the calculated value corresponding to the ratio between the first detection value of the first pressure sensor and the second detection value of the second pressure sensor. Compared to a configuration in which the gap size is calculated without considering the supply pressure fluctuation and the atmospheric pressure fluctuation, it is possible to suppress a decrease in measurement accuracy of the gap dimension due to the supply pressure fluctuation of the air source and the atmospheric pressure fluctuation.

(2) In the air micrometer according to the present invention, the calculated value is a ratio between the first detection value and the second detection value.
According to this configuration, the same effect as the above (1) can be obtained.

(3) In the air micrometer according to the present invention, the calculated value may be a ratio between a differential pressure between the first detection value and the second detection value and the second detection value.
According to this configuration, since the ratio between the second detection value and the differential pressure between the first detection value and the second detection value is employed as the calculated value, only the first detection value (back pressure) is used. Compared to the configuration in which the above dimensions are calculated based on the above, it is less susceptible to fluctuations in the supply pressure of the air source and fluctuations in the atmospheric pressure. In addition, it is less susceptible to changes in sensitivity of the pressure sensor due to fluctuations in power supply voltage and temperature. Therefore, highly accurate measurement can be performed for a long time.

(4) In the air micrometer according to the present invention, the measurement calculation processing device may calculate the gap size from table data indicating a relationship between the calculated value and the gap size.

  According to this configuration, the measurement calculation processing device can reduce the processing load of the measurement calculation processing device by using the table data.

(5) Further, in the air micrometer according to the present invention, the first detection value is a gauge pressure on the nozzle side of the throttle portion in the air pipe, and the second detection value is the air pressure. The gauge pressure on the air source side with respect to the throttle portion in the pipe may be used.

  According to this configuration, since the calculated value is a value corresponding to the pressure ratio between the gauge pressure on the air source side and the gauge pressure on the nozzle side, the gap size is calculated based only on the pressure on the nozzle side. Compared to the configuration, it is less susceptible to atmospheric pressure fluctuations. Therefore, highly accurate measurement can be performed.

  According to the air micrometer of the present invention, the measurement calculation processing device calculates the size of the gap between the measurement object and the nozzle based on the pressure ratio. Therefore, compared to a configuration in which the gap size is calculated without using the supply pressure of the air source, it is possible to suppress a decrease in measurement accuracy of the gap size due to fluctuations in the supply pressure of the air source and fluctuations in atmospheric pressure. Less susceptible to changes in pressure sensor sensitivity due to changes in temperature and power supply voltage. Furthermore, since there are no adjustment points, handling is easy, measurement time is short, and highly stable measurement can be performed for a long time, it is suitable for in-process measurement in a machining line.

It is the schematic of the air micrometer main body and measurement head which concern on embodiment. It is a block diagram of the measurement calculation processing apparatus which concerns on embodiment. A graph showing how the gap dimension Z and the rate of change change with respect to the gauge back pressure PL when the supply pressure ps fluctuates 10% for the back pressure type air micrometer. It is. About the air micrometer concerning an embodiment, it summarizes the graph showing how the standardization gap size (Z / Zo) and its change rate change to the 1st pressure ratio. . The air micrometer which concerns on embodiment summarizes the graph showing how the standardization clearance dimension (Z / Zo) and its change rate change with respect to a 2nd pressure ratio. . It is the graph which showed the relationship between the calibration data memorize | stored as table data and registration data about an air micrometer in embodiment. It is a flowchart which shows registration setting operation | movement about the air micrometer which concerns on embodiment.

<Embodiment>
<1> Configuration FIG. 1 shows a schematic diagram of an air micrometer according to the present embodiment.
The air micrometer according to the present embodiment directs air supplied from an air source (not shown) such as an air compressor or an adjustment valve from a nozzle 22a of the measurement head 3 described later to an inner wall of a cylindrical workpiece W. Erupt. The air micrometer measures the size of the gap between the nozzle 22a and the inner wall of the workpiece W.

  This air micrometer includes a meter main body 1 and a measurement head 3. The meter body 1 includes an air circuit unit 10, pressure sensors 15 and 17, and a measurement calculation processing device 20.

  The air circuit unit 10 is for obtaining a pressure value necessary for calculating the dimension of the gap between the nozzle 22a and the inner wall of the workpiece W. The air circuit unit 10 is connected to the measurement head 3 via a tube P12 and is connected to an air source via a tube P11. Air is supplied to the air circuit unit 10 from an air source through a tube P11 through an adjustment valve (not shown). And the air circuit part 10 supplies the air supplied from the air source to the measurement head 3 through the tube P12. The air circuit unit 10 is provided with pressure sensors 15 and 17, and these pressure sensors are connected to the measurement calculation processing device 20 via signal lines.

The air circuit unit 10 includes an air pipe 13 and an orifice (throttle unit) 14. The air pipe 13 is provided with two pressure sensors 15 and 17.
The air pipe 13 is interposed in an air flow path from the air source to the nozzle 22a of the measuring head 3.

  The orifice 14 is provided at a substantially central portion in the tube axis direction of the air pipe 13. The orifice 14 is made of, for example, a member made of a metal plate and partially provided with a through hole 14a penetrating in the thickness direction. Here, the air that has flowed from the air source into the air pipe 13 through the adjustment valve flows into the measurement head 3 through the through hole 14a of the orifice 14 (white arrows A1, A2, A3 in FIG. 1). (Refer to A4 and A5).

  The pressure sensor 15 detects the gauge pressure PH of air on the upstream side (air source side) of the orifice 14. Further, the pressure sensor 17 detects a gauge back pressure PL that is a gauge pressure of air downstream of the orifice 14 in the air pipe 13 (on the nozzle 22a side of the measurement head 3).

FIG. 2 shows a configuration diagram of the measurement calculation processing device 20.
The measurement calculation processing device 20 includes an analog / digital converter 24, a storage unit 25, a calculation processing unit 26, and an input / output unit 27.

The analog-digital converter 24 converts analog signals output from the two pressure sensors 15 and 17 into digital signals.
The storage unit 25 stores calibration data indicating the relationship between the pressure ratio and the gap size, and registration data such as a nozzle cross-sectional area as table data.

The arithmetic processing unit 26 has a function of calculating a pressure ratio from a digital signal input from the analog-digital converter 24. The arithmetic processing unit 26 has a function of storing the calibration data and registration data input from the input / output unit 27 in the storage unit 25 as table data.
Further, the arithmetic processing unit 26 has a function of calculating a workpiece size from data indicating the calculated pressure ratio, calibration data and registration data stored as table data, and the calculated result to the input / output unit 27. Output function.

  The input / output unit 27 has a function of inputting calibration data and registration data as table data to the arithmetic processing unit 26 and inputting an operation command signal. The input / output unit 27 also has a function of outputting the workpiece dimensions calculated by the arithmetic processing unit 26 as an analog signal or a digital signal.

  The measurement arithmetic processing unit 20 may be configured by an individual IC such as an analog / digital converter, ROM, RAM, MPU, digital / analog converter, or a one-chip microcomputer in which these functions are integrated. It may be a thing.

  Further, the measurement arithmetic processing device 20 is connected to the pressure sensors 15 and 17 through signal lines. The measurement calculation processing device 20 is connected to a user interface 101 such as an LED display, a switch, or a liquid crystal panel with a touch panel via an input / output unit 27.

  Note that the measurement calculation processing device 20 may not be connected to the user interface 101 but may only output an analog signal or a digital signal indicating the workpiece size via the input / output unit 27. Furthermore, the measurement calculation processing device 20 may be connected to a network (not shown) via the input / output unit 27.

  Returning to FIG. 1, the measuring head 3 includes a nozzle 22a. The measuring head 3 is connected to the air pipe 13 via the tube P12. As shown in FIG. 1, the air discharged from the nozzle 22a of the measuring head 3 passes through the gap between the nozzle 22a and the inner wall of the workpiece W (see white arrow A5 in FIG. 1).

<2> Relationship between air flow rate and gap size in air micrometer In order to clarify the problems of the conventional air micrometer and solve the problems, the inventor has developed a continuous formula and compressibility in hydrodynamics. Based on Bernoulli's equation for the fluid, a theoretical equation for the air flow rate with changes in the channel cross-sectional area was derived.

Assuming that the cross-sectional area of the flow path is A, the flow coefficient for correcting flow loss, etc. is α, the absolute pressure and absolute temperature at the inlet are po and To, respectively, and the absolute pressure at the outlet is p, It is represented by the formula (1).

Here, ρ is the density of air, γ is a specific heat ratio, R is a gas constant, and α is a flow coefficient. Formula (1) became a theoretical formula equivalent to the theoretical formula described in Non-Patent Document 1.

If the diameter of the through hole 14a of the orifice 14 of the back pressure system of the air micrometer and d _1, the flow path cross-sectional area becomes (πd ₁ ²⁾ / 4. Further, the hole diameter of the nozzle 22a of the measuring head 3 and d _2, if the gap dimension between the nozzle 22a and the object to be measured is Z, the flow path cross-sectional area of the nozzle 22a and the measurement object is formed [pi] d ₂ Z. The flow rate of air passing through the orifice 14 by applying the equation (1) where the absolute pressure at the throttle inlet is ps, the absolute pressure at the throttle outlet (absolute back pressure of the nozzle) is pn (= PL), and the atmospheric pressure is pa. Since the flow rates passing through the nozzle 22a and the nozzle 22a are equal, the following equation (2) representing the gap dimension between the nozzle 22a and the measurement object can be derived.

Here, Zo (α ₁ , α ₂ , d ₁ , d ₂ ), Q (ρn, ρa, Ts, Tn), and P (ps, pn, pa) are expressed by the following equations (3) to (5). And can be described by dividing into a function by the shape of the orifice 14 and the nozzle 22a, a function by the absolute temperature of air, and a function by the absolute pressure of air.

Here, α ₁ and α ₂ are flow coefficients of the orifice 14 portion and the nozzle 22a portion, respectively.

Here, ρn and ρa are the air densities of the back pressure portion and the atmospheric pressure portion, respectively.

Equation (2) indicates that the gap size depends on the absolute pressure at the inlet of the orifice 14, the absolute back pressure of the nozzle 22a, the atmospheric pressure, the absolute temperature of the air, and the like. That is, when measuring only absolute back pressure with a conventional back pressure type air micrometer, the gap size calculated from the absolute back pressure is affected by fluctuations in the absolute pressure and atmospheric pressure at the orifice inlet. ing.

  In order to clarify the extent of these influences, the nozzle back pressure (absolute back pressure) pn and gap dimension Z when ps and pa fluctuate by 10%, respectively, based on the equation (2) A graph representing the relationship was calculated.

  FIG. 3 shows the relationship between the gap size Z and the rate of change with respect to the gauge back pressure PL when the supply pressure (absolute supply pressure) ps and the atmospheric pressure pa fluctuate by 10% for the back pressure type air micrometer. This is a summary of graphs that show how they change. Here, the gauge back pressure PL is a pressure corresponding to a differential pressure (pn−pa) between the absolute back pressure pn and the atmospheric pressure pa.

3A and 3B, the supply pressure (absolute supply pressure) ps was fixed at 0.30 MPa, and the atmospheric pressure pa was changed to 0.09, 0.10, 0.11 [MPa]. It is a graph showing the gap | interval dimension Z with respect to the gauge back pressure PL in the case, and its change rate ((DELTA) Z / (DELTA) PL).
3 (c) and 3 (d) show gauges when the atmospheric pressure pa is fixed at 0.10 MPa and the supply pressure ps is changed to 0.27, 0.30, 0.33 [MPa]. It is a graph showing the gap dimension Z with respect to the back pressure PL and its change rate.

  From FIG. 3, it is clear that there is a problem that the gap dimension Z is greatly influenced by fluctuations in absolute pressure and atmospheric pressure at the inlet of the orifice 14. It is also clear that there are very few parts where the gap size and the absolute back pressure are proportional, and there is a problem that the range in which the gap size can be accurately measured is extremely narrow. There is a similar problem even when a conventional back pressure type air micrometer measures gauge back pressure (differential pressure between absolute back pressure and atmospheric pressure) instead of absolute back pressure.

  As described in Non-Patent Document 1, even if the adjustment valve is used to stabilize the throttle inlet pressure, the gap size is affected by fluctuations in atmospheric pressure and air temperature. It is clear from the theoretical formula that there is a problem that measurement is not possible.

  As shown in the above formulas (2) to (5), the inventor found that the formula (2) regarding the gap dimension Z is the diameter of the through hole 14a of the orifice 14 of the air circuit unit 10 and the hole of the nozzle 22a of the measurement head 3. It is found that it can be decomposed into an equation (3) depending on the diameter, an equation (4) depending on the specific weight and temperature of air, and an equation (5) depending on the absolute supply pressure ps, the absolute back pressure pn, and the atmospheric pressure pa. ing.

In the equation (4), the air weight is substantially the same inside and outside the air pipe 13. Further, assuming that the temperature is substantially constant over the entire inside of the air pipe 13, the formula (4) becomes a constant C. Further, since the expression (3) is a shape function Zo determined by the orifice 14 and the nozzle 22a of the air circuit unit 10, the expression (2) can be modified as the following expression (6).

Here, since the specific heat ratio γ of air is constant (γ = 1, 40307), the expression (6) normalized by Zo depends only on the absolute supply pressure ps, the absolute back pressure pn, and the atmospheric pressure pa. I understand that. It is possible to measure these three pressure values and calculate the gap size based on equation (6). However, since the theoretical value and the actually measured value do not completely coincide with each other, it is preferable to calibrate based on the actually measured value. In this case, the calibration data is obtained by using three pressure values as parameters, and the amount of data is enormous. Therefore, it is necessary to create a method capable of calibration with a small number of parameters.

<3> Examination of parameters for calculating gap size Here, in addition to absolute pressure (first pressure, second pressure) ps, pn, gauge pressure (first gauge pressure, The concept of the second gauge pressure) is introduced, the gauge pressure of the supply pressure, that is, the gauge supply pressure (second detection value) is PH (= ps-pa), the gauge pressure of the back pressure, ie, the gauge back pressure (first 1 detection value) is PL (= pn-pa).
The inventor has calculated the gap size Z for absolute back pressure pn, gauge back pressure (first detection value) PL (= pn-pa), differential pressure (ps-pn, PH-PL), and several pressure ratios. We examined the validity as a parameter to calculate.
As a result, it was found that the first pressure ratio (calculated value) [PL / PH] and the second pressure ratio (calculated value) [(PH-PL) / PH] are optimum parameters. Hereinafter, this process will be described in detail.

  FIG. 4 summarizes a graph showing how the standardized gap dimension (Z / Zo) and the rate of change thereof change with respect to the first pressure ratio for the air micrometer according to the embodiment. It is a thing.

FIGS. 4A and 4B show the first case where the supply pressure ps is fixed at 0.30 MPa and the atmospheric pressure pa is changed to 0.09, 0.10, 0.11 [MPa]. It is a graph showing the normalization gap dimension with respect to a pressure ratio, and its change rate.
FIGS. 4C and 4D show the first pressure ratio when the atmospheric pressure pa = 0.10 MPa is fixed and ps = 0.27, 0.30, 0.33 MPa. It is a graph showing the normalization gap dimension and its change rate.

  Comparing FIG. 4 with FIG. 3, it can be seen that if the pressure ratio [PL / PH] is used as a parameter, it is difficult to be influenced by fluctuations in absolute supply pressure and atmospheric pressure. Also, the rate of change of the normalized gap dimension with respect to the first pressure ratio is substantially flat when [PL / PH] is in the range of 0.3 to 0.9, that is, the normalized gap with respect to the pressure ratio in this range. The dimension becomes substantially linear. This substantially linear range is sufficiently wider than that of FIG.

FIG. 5 summarizes a graph showing how the normalized gap dimension (Z / Zo) and the rate of change thereof change with respect to the second pressure ratio for the air micrometer according to the embodiment. It is a thing.
FIGS. 5A and 5B show the case where the supply pressure ps is fixed at 0.30 [MPa] and the atmospheric pressure pa is changed to 0.09, 0.10, 0.11 [MPa]. It is a graph showing the normalized clearance dimension with respect to a 2nd pressure ratio, and its change rate. 5C and 5D, the atmospheric pressure pa is fixed at 0.10 [MPa], and the supply pressure ps is changed to 0.27, 0.30, 0.33 [MPa]. It is a graph showing the normalized clearance gap dimension with respect to the 2nd pressure ratio in the case, and its change rate.

Comparing FIG. 5 with FIG. 3, it can be seen that if the second pressure ratio is used as a parameter, it is difficult to be influenced by fluctuations in absolute supply pressure and atmospheric pressure. Further, the change rate of the normalized gap dimension with respect to the second pressure ratio is substantially flat when [(PH−PL) / PH] is in the range of 0.15 to 0.7, that is, with respect to the pressure ratio in this range. Therefore, the standardized gap dimension is substantially linear. This substantially linear range is sufficiently wider than that of FIG.
From the comparison between FIG. 4 and FIG. 5 and FIG. 3, if the first pressure ratio or the second pressure ratio is used as a parameter, only one parameter related to calibration data is required. As a result, the amount of calibration data is small. This makes it easier to generate calibration data.

<4> Calibration Data and Registration Data Regarding calibration data and registration data stored in advance as table data in the storage unit 25 of the measurement calculation processing unit 20 when the first pressure ratio [PL / PH] is used as a parameter, explain. The same can be said for the case where the second pressure ratio is used as a parameter.

FIG. 6 is a graph showing the relationship between calibration data stored as table data and registration data for the air micrometer according to the present embodiment.
The calibration data shows the relationship of the normalized gap dimension (Z / Zo) to the pressure ratio (PL / PH) with the absolute supply pressure (ps = 0.30 MPa) and the atmospheric pressure (pa = 0.10 MPa) being constant. Measured relationship between pressure ratio (PL / PH) and standardized gap dimension (Z / Zo) over a wider range, not limited to the substantially linear range of the graph (see FIG. 6, ○ mark) Is actually measured value) and is stored in advance by the storage unit 25. That is, the calibration data is obtained by actually measuring the relationship represented by the equation (6) when the supply pressure (ps = 0.30 MPa) and the atmospheric pressure (pa = 0.10 MPa) are fixed to a constant value. As will be described later, the measurement range of the air micrometer is not limited to a substantially linear range, and can be applied to a wider measurement range. Further, since the standardized gap size Z / Zo is used instead of the gap size Z when Zo is different, the amount of calibration data is small.

  As the registration data, the hole diameter of the orifice 14 as a reference of the air circuit section and the hole diameter of the nozzle of the reference measurement head as a reference are stored in advance in the storage section 25. Thereby, even when the orifice 14 and the measurement head 3 are replaced, that is, even when Zo is changed, the gap dimension Z can be easily calculated from the relationship of the expression (3). FIG. 1 shows a case where there is one nozzle. However, when there are a plurality of nozzles, equation (3) may be corrected according to the concept of the flow path cross-sectional area. For example, if the nozzle hole diameter is d and there are two nozzles, d2 in equation (3) may be (d + d).

  From the conclusion of the study of the parameters for calculating the <3> gap size in the previous section, if the first pressure ratio or the second pressure ratio is used as a parameter, the relationship between the air flow rate and the gap size in section <2> air micrometer Although it is possible to calculate the approximate gap size by applying the formulas (2) to (5) described in the above, the dimensional tolerance of the air circuit unit 10 (for example, the tolerance of the hole diameter of the orifice 14) Since there are variations in the sensitivity of the pressure sensor, it is preferable to previously measure calibration data for each air micrometer.

Therefore, the meter main body 1 of the air micrometer according to the present embodiment includes pressure sensors 15 and 17 and a measurement calculation processing device 20. Here, the pressure sensor 17 detects the gauge pressure PL on the nozzle 22 a side of the orifice (throttle portion) 14 in the air pipe 13. The pressure sensor 15 detects the gauge pressure PH closer to the air source than the orifice 14. The measurement calculation processing device 20 obtains a first pressure ratio (calculated value) between the gauge back pressure (first detected value) PL of the pressure sensor 17 and the gauge supply pressure (second detected value) PH of the pressure sensor 15. Then, a process of calculating the gap dimension Z based on the pressure ratio is performed.
In the measurement calculation processing device 20 according to the present embodiment, for example, the first difference between the gauge supply pressure (second gauge pressure) PH and the differential pressure (PH-PL) between the gauge supply pressure PH and the gauge back pressure PL is obtained. The pressure ratio of 2 may be calculated, and the process of calculating the gap dimension Z based on the calculated ratio may be performed.

  By the way, the calculated value corresponding to the ratio (pressure ratio) between the gauge back pressure (first detection value) PL of the pressure sensor 17 and the gauge supply pressure (second detection value) PH of the pressure sensor 15 is the aforementioned first value. It is not limited to a pressure ratio [PL / PH] of 1 and a second pressure ratio [(PH-PL) / PH]. This calculated value includes any calculated value calculated by a predetermined relational expression including the first pressure ratio [PL / PH]. This calculated value may be, for example, [(PH + PL) / PH].

<5> Operation The measurement calculation processing device 20 according to the present embodiment uses the gap dimension Z from the table data indicating the relationship between the pressure ratio (PL / PH) between the gauge supply pressure PH and the gauge back pressure PL and the gap dimension Z. Is calculated.

Therefore, a registration setting operation in which the measurement calculation processing device 20 performs registration setting using registration data as table data for the air micrometer according to the present embodiment will be described.
FIG. 7 shows a flowchart of the setting operation of the measurement calculation processing device 20.
First, the measurement calculation processing device 20 performs master gauge dimension setting (step S101). The master gauge is a cylindrical measuring master. Here, a case where two types of master gauges having different inner diameters are used will be described. Hereinafter, these two types of master gauges are referred to as a large master gauge and a small master gauge. Here, the measurement calculation processing device 20 inputs the actual measurement dimension (X1) of the large master gauge and the actual measurement dimension (X2) of the small master gauge input by the user via the input / output unit 27, and stores them. The data is stored as registration data by the unit 25 (see step 101, FIG. 6).

  As the large master gauge and the small master gauge, those whose measured dimensions correspond to the upper limit value and the lower limit value of the actually measured dimension allowed for the workpiece W may be selected. For example, it is assumed that the design dimension of the inner diameter of the workpiece W is 20.000 mm and the allowable dimensional tolerance is ± 0.01 mm. In this case, a master gauge having an actually measured inner diameter of X1 = 20.01 mm may be selected as the large master gauge, and a master gauge having an actually measured inner diameter of X2 = 19.99 mm may be selected as the small master gauge.

  Next, the measurement arithmetic processing device 20 measures a master gauge (step S102). Here, for each of the large master gauge and the small master gauge, the analog-digital converter 24 acquires information indicating the gauge supply pressure PH and the gauge back pressure PL based on the signals output from the pressure sensors 15 and 17. The analog / digital converter 24 converts the acquired information into digital values corresponding to the gauge supply pressure PH and the gauge back pressure PL.

  Thereafter, the measurement calculation processing unit 20 calculates a pressure ratio (P1) for the large master gauge and a pressure ratio (P2) for the small master gauge by the calculation processing means, and P1 and P2 are calculated by the storage unit 25. Stored as registered data (step S103, see FIG. 6).

  Finally, the measurement calculation processing unit 20 uses the calculation processing means to measure the normalized gap dimension (Z1) corresponding to the pressure ratio obtained by measuring the large master gauge and the pressure ratio obtained by measuring the small master gauge. Is calculated from the calibration data, and Z1 and Z2 are stored as registration data in the storage unit 25 (see step S104, FIG. 6). In order to calculate Z1 and Z2 from calibration data, a straight line passing through two adjacent calibration data values may be obtained and calculated from the straight line, or a curve approximating a plurality of adjacent calibration data values may be calculated. It may be obtained and calculated from the curve.

<6> Summary After all, in the air micrometer according to the present embodiment, the gap size between the workpiece W and the nozzle 22a is calculated based on the pressure ratio, so the supply pressure of the air source (second pressure) ps. Compared with the configuration in which the above dimensions are calculated without taking into account the fluctuations in the air pressure and the atmospheric pressure pa, it is possible to suppress a decrease in the measurement accuracy of the dimensions due to the fluctuation in the supply pressure ps of the air source and the fluctuation in the atmospheric pressure pa.

  In addition, the air micrometer according to the present embodiment has a pressure ratio of the air pressure on the nozzle side (first pressure) to the air pressure on the air source side of the throttle unit as the pressure ratio, or the air source of the throttle unit. Since the pressure ratio between the air source side of the throttle and the differential pressure on the nozzle side relative to the air pressure (second pressure) on the side can be calculated, the air source can be compared with a configuration that calculates the above dimensions based only on the back pressure ps. Are not easily affected by fluctuations in supply pressure and atmospheric pressure. In addition, it is less susceptible to changes in sensitivity of the pressure sensor due to fluctuations in power supply voltage and temperature. Therefore, highly accurate measurement can be performed for a long time.

  Furthermore, according to the air micrometer according to the present embodiment, the relational expression indicating the relationship between the pressure ratio and the gap size is not easily affected by fluctuations in the supply pressure of the air source and fluctuations in the atmospheric pressure. The pressure ratio is not easily affected by changes in sensitivity of the pressure sensor due to changes in temperature and power supply voltage. Therefore, highly accurate measurement can be performed for a long time.

<Modification>
(1) In the embodiment, the example in which the air circuit unit 10 includes the orifice 14 as the throttle unit has been described. However, the present invention is not limited to this. For example, a laminar flow element may be used instead of the orifice 14. . As a laminar flow element, a porous member, a mesh, etc. are mentioned, for example. Examples of the porous member include a porous body formed by sintering a powder of metal, ceramic, glass, or the like, or a porous body formed of a porous polymer such as a fluororesin.

(2) In the embodiment, the example in which the measurement calculation processing device 20 calculates the pressure ratio without performing any signal processing on the measurement data input from the pressure sensors 15 and 17 has been described. The measurement data may be processed by combining digital signal processing such as moving average processing for improving the S / N ratio and preceding prediction signal processing for shortening the measurement time.

(3) The measurement processing unit 20 according to the embodiment includes a LAN connection port (for example, RS485 port) and can be connected to an external device (for example, a personal computer) via the LAN. May be.
According to this configuration, the measurement arithmetic processing device 20 can acquire setting data from an external device, and can transmit numerical data indicating the dimension of the inner diameter of the workpiece W obtained by measurement to the external device.

(4) In the embodiment, an example in which two types of master gauges are used has been described. However, the types of master gauges to be used are not limited to two types. For example, three or more types of master gauges may be used.
According to this configuration, the measurement calculation processing device 20 uses the least square method, and the measurement data obtained by measuring each of three or more types of master gauges among the theoretical curves represented by the above equation (6). A curve passing through is calculated. Therefore, since the calculated curve reflects the actual measurement data more than when two types of master gauges are used, it is possible to improve the dimensional measurement accuracy.

(5) In the embodiment, the method for calculating the gap size by creating the registration data using the master gauge has been described. However, the gap size may be calculated directly from the calibration data without using the master gauge.
According to this configuration, a master gauge is not required, and it is not necessary to perform registration setting. Therefore, the gap dimension can be calculated easily. That is, the measurement arithmetic processing unit 20 measures Px for the workpiece W, obtains the normalized gap dimension Zx from the calibration data, and calculates the gap dimension Z from the formula: Z = Zx · Zo (see FIG. 6). In this case, the measurement calculation processing device 20 needs to obtain Zo in advance and store it in the storage unit 25.

(6) In the embodiment, the configuration using the table data indicating the relationship between the pressure ratio of the gauge back pressure (first gauge pressure) PL to the gauge supply pressure (second gauge pressure) PH and the gap size has been described. The table data is not limited to this. For example, table data indicating the relationship between the pressure ratio of the first pressure P detected by the pressure sensor (first pressure sensor) 17 to the second pressure detected by the pressure sensor (second pressure sensor) 15 and the gap dimension Z is obtained. It may be used. Further, table data indicating the relationship between the pressure ratio of the differential pressure (PH-PL) between the gauge back pressure PL and the gauge supply pressure PH to the gauge supply pressure PH and the gap dimension Z may be used. .

DESCRIPTION OF SYMBOLS 1 Meter main body 3 Measuring head 10 Air circuit part 13 Air piping 14 Orifice (throttle part)
15, 17 Pressure sensor 20 Measurement calculation processing device 22a Nozzle

Claims (5)

An air micrometer that measures the size of a gap between the nozzle and the measurement object by ejecting air supplied from an air source toward the measurement object from a nozzle of the measurement head,
An air pipe interposed in the air flow path from the air source to the nozzle of the measurement head and partially provided with a throttle part;
A first pressure sensor for detecting a pressure on the nozzle side with respect to the throttle portion inside the air pipe;
A second pressure sensor for detecting a pressure on the air source side with respect to the throttle portion;
A measurement calculation process for obtaining a calculated value corresponding to a ratio between the first detected value of the first pressure sensor and the second detected value of the second pressure sensor, and calculating the gap dimension based on the calculated value And an air micrometer. The air micrometer according to claim 1, wherein the calculated value is a ratio between the first detection value and the second detection value. The air micrometer according to claim 1, wherein the calculated value is a ratio between a differential pressure between the first detection value and the second detection value and the second detection value. The air micrometer according to claim 1, wherein the measurement calculation processing device calculates the gap size from table data indicating a relationship between the calculated value and the gap size. . The first detection value is a gauge pressure on the nozzle side with respect to the throttle portion inside the air pipe,
The air micrometer according to any one of claims 1 to 4, wherein the second detection value is a gauge pressure on the air source side with respect to the throttle portion inside the air pipe.