JP2012058213A - Air micrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air micrometer capable of highly accurately measuring dimensions by a simple operation.SOLUTION: The air micrometer includes: a measurement part 1 configured by partitioning the upstream side and downstream side of an air channel 11 by a porous member 12; a first pressure sensor 3 for detecting the first pressure of air on the upstream side of the measurement part 1 and outputting the signal; a second pressure sensor 4 for detecting the second pressure of the air on the downstream side of the measurement part 1 and outputting the signal; and a temperature sensor 5 for detecting the temperature of the air inside the measurement part 1 and outputting the signal. The signals output from the first pressure sensor and the second pressure sensor are fetched, the opening of the control valve 6 of the air channel 11 is controlled so as to turn the second pressure of the second pressure sensor to a fixed value. A mass flow rate per unit time of the air jetted from a jetting hole 22 of a measurement head 2 is calculated on the basis of a pressure difference between the first pressure and the second pressure, the second pressure and the temperature of the air, and the dimension of a work is calculated on the basis of the mass flow rate.

Description

  The present invention relates to an air micrometer that measures air and other dimensions with high accuracy by ejecting air from an ejection hole provided in a measurement head.

  2. Description of the Related Art Conventionally, a back pressure / differential pressure type air micrometer shown in Patent Document 1 is known as an air micrometer for measuring an inner diameter of a workpiece.

  This air micrometer supplies air supplied from an air source to two systems of pipes with fixed orifices, one pipe serving as a measuring head pipe, and the other pipe having another fixed orifice. Is used as an exhaust pipe, and the measurement head pipe and the exhaust pipe are connected by a sensor pipe provided with a differential pressure sensor, and the measurement head pipe is provided with a nozzle hole. Connected.

JP 2005-114511 A

  For example, when measuring the inner diameter of a workpiece hole, this air micrometer inserts a cylindrical measuring head into the hole for measuring the inner diameter of the workpiece and ejects air from the nozzle hole of the measuring head. The change in the back pressure of the air (change in the flow rate) is measured by a differential pressure sensor that detects the differential pressure between the pressure of the pipe for the measurement head on the workpiece side and the pressure of the exhaust pipe. Based on the graph data indicating the relationship between the differential pressure data and the inner diameter dimension (measuring gap dimension), the inner diameter dimension of the workpiece is calculated.

  However, this type of conventional back pressure / differential pressure type air micrometer detects the differential pressure between the pressure of the pipe for the measuring head on the workpiece side and the pressure of the exhaust pipe using a differential pressure sensor, and the differential pressure sensor. Based on the graph data showing the relationship between the differential pressure data obtained from the above and the inner diameter, the inner diameter of the work (measuring gap dimension) is calculated. Therefore, it is necessary to perform complicated operations such as sensitivity adjustment and zero adjustment by manual knob adjustment at the time of measurement.In addition, the measurement data of the differential pressure sensor detected as back pressure and the As shown in FIG. 2 of Patent Document 1, the relationship with the measurement gap dimension is such that the linear range is very narrow and the measurement accuracy deteriorates when used in a non-linear range.

  For this reason, in order to perform measurements in a small range where the relationship between the back pressure data and the gap to be measured is linear, it is necessary to prepare measuring heads of various sizes according to the dimensions of the workpiece. Needed to be changed to match the workpiece dimensions.

  In addition, when using an air micrometer with the measurement head replaced, the pressure loss of the air ejected from the nozzle of the measurement head inevitably changes, and the relationship between the differential pressure and the size also varies with changes in the air temperature. There has been a problem that the measurement accuracy is lowered.

  The present invention solves the above-mentioned problems, and makes the differential pressure constant, calculates the air flow rate at that time, calculates the dimensions based on the flow rate, and provides high-precision dimensions with a simple operation. An object is to provide an air micrometer capable of performing measurement.

The air micrometer according to the present invention is:
In an air micrometer that measures the dimension of the workpiece by ejecting air supplied from an air source toward the workpiece from the ejection hole of the measurement head,
Air from the air source is supplied to an air flow path through a control valve, and a measurement unit configured by partitioning an upstream side and a downstream side of the air flow path by a porous member;
A first pressure sensor that detects a first pressure of air upstream of the measurement unit and outputs a signal thereof;
A second pressure sensor for detecting a second pressure of the air downstream of the measuring unit and outputting a signal thereof;
Valve control means for taking in a signal output from the second pressure sensor and controlling the opening of the control valve so that the second pressure of the second pressure sensor becomes a constant value;
A temperature sensor that detects the temperature of the air in the measurement unit and outputs a signal;
A flow rate calculation means for calculating a mass flow rate per unit time of air ejected from the ejection hole of the measurement head based on a pressure difference between the first pressure and the second pressure, a second pressure, and an air temperature;
Based on the mass flow rate calculated by the flow rate calculation means, a dimension calculation means for calculating the dimensions of the workpiece;
It is provided with.

  According to this invention, the air ejected from the ejection hole of the measurement head based on the pressure difference between the first pressure on the upstream side of the porous member of the measurement unit, the downstream side and the second pressure, the second pressure, and the temperature of the air. The mass flow rate per unit time is calculated, and the workpiece dimensions are calculated based on the mass flow rate. Therefore, a relatively wide range of workpiece dimensions can be measured with high accuracy by one measuring head.

Here, the flow rate calculation means calculates the mass flow rate Qm as follows:
αQm * Qm + βQm = A * ΔP * (ΔP + 2 * P2 + B) * C / (C + TS−Tm)
(Where ΔP is the pressure difference between the first pressure P1 and the second pressure P2, A is the shape factor of the porous member, B is the correction value for the air compressibility, C is the correction value for the temperature, Ts is the reference temperature, Tm is air temperature, α is a coefficient depending on air molecular weight, β is a coefficient depending on air viscosity)
It is preferable to calculate from the following equation.

  According to the present invention, since the air flow rate ejected from the measuring head is corrected by the air temperature and pressure and is calculated as the mass flow rate, the dimension value of the workpiece can be accurately calculated from the accurate air flow rate data.

  Pressure loss data indicating the relationship between the pressure loss generated in the flow path and the ejection hole in the measurement head and the mass flow rate is stored in advance in the set value storage means, and the flow rate calculation means is based on the pressure loss data. It is preferable to correct the control value of the second pressure.

  According to the present invention, since the pressure loss generated in the flow path and the ejection hole in the measurement head is corrected so as to be subtracted, the error due to the pressure loss such as the ejection hole can be eliminated.

  The set value storage means stores in advance the master gauge of the master gauge having different outer diameter or inner diameter and at least two dimensions of the measurement head as a dimensional reference value in the master measurement value storage means. Preferably, the mass flow rate is measured in advance using the measuring head, and data indicating the relationship between the master gauge dimension reference value and the mass flow rate is preferably stored in the master measured value storage means.

  According to the present invention, when measuring the dimensions of the workpiece, the dimension calculation means for calculating the dimensions uses the mass flow rate calculated by the flow rate calculation means, and uses the dimension reference for each master gauge stored in the master measurement value storage means. The workpiece dimensions can be calculated easily and accurately from a linear expression or table data indicating the relationship between the value and the mass flow rate of the master measurement value.

  In addition, when the dimensional reference value of the workpiece and the tolerance thereof are (A ± a), a large master gauge having a dimension (A + a) and a small master gauge having a dimension (A−a) are prepared, and the dimensions of the large master gauge are prepared. The dimension (A + a) as the reference value and the dimension (A-a) as the dimension reference value of the small master gauge are stored in the set value storage means, and the mass flow rate is measured for the large master gauge and the small master gauge. The dimension reference value of the master gauge can be stored in the master measurement value storage means.

  According to the present invention, when measuring the dimensions of the workpiece, it is possible to quickly and accurately determine whether or not the dimensions are within the dimension tolerance of the workpiece.

  According to the air micrometer of the present invention, it is possible to perform highly accurate dimension measurement with a simple operation by calculating the air flow rate at that time and calculating the dimensions based on the flow rate at a constant differential pressure. it can.

It is a block diagram which shows the basic composition of the air micrometer of this invention. 1 is an external perspective view of an air micrometer according to an embodiment of the present invention. It is a block diagram of the flow measurement part of the air micrometer. It is a block diagram of the configuration of the measurement calculation unit. It is a flowchart of the setting process of an air micrometer. It is a flowchart of the measurement process of a large master gauge. It is a flowchart of the measurement process of a small master gauge. It is a flowchart of a workpiece dimension measurement process. It is a graph which shows the relationship between a flow volume and a pressure loss. It is a graph which shows the relationship between a flow volume and a dimension (%).

  Hereinafter, an air micrometer and one embodiment of the present invention will be described with reference to the drawings. In the air micrometer of the present invention, as shown in the block diagram of FIG. 1, air from an air source (not shown) is supplied to the air flow path 11 through the control valve 6, and the upstream and downstream sides of the air flow path 11 are porous members. 12, a measurement unit 1 that is partitioned by 12, a first pressure sensor 3 that detects a first pressure P1 of air upstream of the measurement unit 1 and outputs a signal thereof, and air downstream of the measurement unit 1 The second pressure sensor 4 for detecting the second pressure P2 and outputting the signal, the temperature sensor 5 for detecting the temperature of the air in the measuring unit 1 and outputting the signal, and the measurement calculation for calculating the dimensions from the mass flow rate Unit 10.

  The measurement calculation unit 10 takes in the signals output from the first pressure sensor 3 and the second pressure sensor 4, and the value obtained by adding the correction value to the second pressure P2 of the second pressure sensor 4 is a constant value. Based on the valve control means for controlling the opening degree of the control valve 6, the differential pressure ΔP between the first pressure P 1 and the second pressure P 2, the second pressure P 2, and the air temperature Tm, the air is ejected from the ejection hole 22 of the measuring head 2. A flow rate calculating means for calculating a mass flow rate of air per unit time, a dimension calculating means for calculating a workpiece size based on the mass flow rate calculated by the flow rate calculating means, a flow path and a jet hole in the measuring head 2 Set value storage means for storing pressure loss data indicating the relationship between the pressure loss caused by the mass flow and the mass flow rate.

The flow rate calculation means calculates the mass flow rate Qm, for example,
αQm * Qm + βQm = A * ΔP * (ΔP + 2 * P2 + B) * C / (C + TS−Tm)
It is calculated from the following equation. Here, A is the shape factor of the porous member 12, B is the correction value for the air compressibility, C is the correction value for the temperature, Ts is the reference temperature, Tm is the air temperature, α is the coefficient depending on the air molecular weight, β Is a coefficient depending on the air viscosity.

  The dimension calculating means is configured to calculate the dimension of the workpiece using the approximate straight line correction data or the table data stored in advance based on the calculated mass flow rate Qm.

The calculation formula for calculating the mass flow rate Qm does not use the coefficient α depending on the air molecular weight and the coefficient β depending on the air viscosity,
Qm = A * ΔP * (ΔP + 2 * P2 + B) * C / (C + TS−Tm)
The mass flow rate Qm can also be calculated from the following equation.

  As shown in FIGS. 2 to 4, the air micrometer stores the flow rate measuring device 36 and the measurement calculation unit 10 of the measuring unit 1 in the main body case 30, and the flow rate in the lower part of the main body case 30. A measuring device 36 is arranged, an air input connector 34 for connecting an air line from an air source is provided on the lower back side of the main body case 30, and an air line of the measuring head 2 is connected to the lower front side of the main body case 30. An air output connector 35 is provided. Further, on the front surface of the main body case 30, there are provided a bar graph display unit 31 for displaying dimension% when measuring the dimension of the workpiece (measured gap dimension) and a character indicator 32 for displaying the workpiece dimension and the like in characters. Below that, an input panel switch 33 is provided.

  The flow rate measuring device 36 is configured by connecting the air flow path 11 of the measurement unit 1 having the above configuration between the air input connector 34 and the air output connector 35, and air from the air source is passed through the control valve 6 to the air flow path 11. To supply. The air flow path 11 is partitioned by the porous member 12 at the upstream side and the downstream side. The porous member 12 is composed of a member formed by sintering a powder of metal, ceramic, glass or the like, or a member formed by forming a porous body made of a porous polymer such as a fluororesin into a disk shape, It becomes a laminar flow element.

  That is, as shown in FIG. 1, the measuring unit 1 is composed of an air flow path 11 formed of a pipe line, and the control valve 6 is connected to the air supply side of the air flow path 11, while the inside of the air flow path 11 is The upstream side and the downstream side are separated by the porous member 12, the upstream chamber 13 is formed on the upstream side, and the downstream chamber 14 is formed on the downstream side. The first pressure sensor 3 is provided in the upstream chamber 13, and the pressure detected by the first pressure sensor 3 is output as the first pressure P1. Moreover, the 2nd pressure sensor 4 is provided in the downstream chamber 14, and the pressure detected by the 2nd pressure sensor 4 is output as 2nd pressure P2.

  Further, a temperature sensor 5 is provided for detecting the air temperature in the upstream chamber 13 and outputs a detection signal indicating the temperature. The temperature sensor 5 may be installed so as to detect the temperature of the downstream chamber 14, or the temperature sensor 5 is installed outside the air flow path 11 to indirectly detect the air temperature in the flow path. You may do it.

  The control valve 6 operates as a proportional control valve and is configured to control the flow rate of air flowing through the air flow path 11. A value obtained by adding a correction value to the second pressure P2 of the second pressure sensor 4 is determined in advance. The opening degree of the control valve 6 is controlled by the valve control means so as to be a constant value.

  On the other hand, as shown in FIG. 3, the measurement head 2 is connected to the air output connector 35 via a connection tube. The measuring head 2 is for measuring the inner diameter of the hole of the workpiece W, and is formed, for example, in a cylindrical shape. As shown in FIG. 1, an air flow path 21 is formed on the central axis, and both sides are formed. Are provided on the outer peripheral portion of the nozzle. The jet holes 22 are connected to the air flow path 21 and are jetted from the jet holes 22 and 22 to the inner peripheral portion of the hole of the workpiece W to measure the inner diameter (measured). Measure the gap dimension.

  The measuring head 2 of this embodiment has a shape for measuring the inner diameter of the workpiece W. However, when the workpiece is in a columnar shape or a pipe shape and the outer diameter is measured, the measuring head is larger than the outer diameter of the workpiece. It can be an annular head having a hole with a slightly larger inner diameter, or it can be formed in a bifurcated shape that is set so as to sandwich the outer periphery of a cylindrical or pipe-shaped workpiece. Any of the measurement heads has a structure in which ejection holes are provided on both sides or both inner sides of the inner peripheral surface, and air is ejected from the ejection holes on both sides.

  As described above, the measurement calculation unit 10 constituting the valve control unit, the flow rate calculation unit, the dimension calculation unit, and the set value storage unit includes a CPU 40, a ROM 41, a RAM 42, and an input / output unit 43 as shown in FIG. The main part is a microcomputer. The input / output unit 43 is connected to the first pressure sensor 3, the second pressure sensor 4, and the temperature sensor 5 so as to capture detection signals from the respective sensors, while being connected to the control valve 6, and the second pressure sensor The control valve 6 is proportionally controlled by the CPU 40 so that a value obtained by adding a correction value to the second pressure P2 of the sensor 4 becomes a predetermined constant value.

  Based on the program data stored in the ROM 41 in advance, the CPU 40 uses the work area set in the RAM 42 to capture signals output from the first pressure sensor 3 and the second pressure sensor 4, and sets the second pressure P2. The opening degree of the control valve 6 is controlled so that the control value including the correction value becomes a constant value, and the differential pressure ΔP between the first pressure P1 and the second pressure P2, the second pressure P2, and the air temperature Tm are controlled. Based on this, the mass flow rate per unit time of the air ejected from the ejection holes 22 of the measuring head 2 is calculated, and the process of calculating the dimensions of the workpiece is performed based on the calculated mass flow rate. In the ROM 41, an arithmetic expression for calculating the above-described mass flow rate Qm, αQm * Qm + βQm = A * ΔP * (ΔP + 2 * P2 + B) * C / (C + TS−Tm), shape factor A of the porous member 12, air Fixed data such as a correction value B for the compression ratio, a correction value C for the temperature, a reference temperature Ts, an air temperature Tm, a coefficient α depending on the air molecular weight, and a coefficient β depending on the air viscosity are stored in advance.

  Further, the CPU 40 of the measurement calculation unit 10 measures the pressure loss of the measurement head 2 in the measurement setting process of the master gauge, which is performed before measuring the actual workpiece, as will be described in the setting process described later. The RAM 42 stores and sets pressure loss data indicating the relationship between the pressure loss and the mass flow rate generated in the flow paths and the ejection holes in the RAM 42. In addition, the RAM 42 is provided with an area for presetting and storing a reference dimension of a workpiece, a dimensional tolerance thereof, a dimension of a large master gauge, a dimension of a small master gauge, and the like as the set value storage means. As the setting means, when measuring the dimensions of the large master gauge and the small master gauge, an area for storing graph data or table data indicating the relationship between the flow rate and the dimension measurement value is set.

  That is, when measuring the dimension of the workpiece W, based on the calculated mass flow rate Qm, a linear expression indicating the relationship between the mass flow data and the dimension value of the master gauge when the dimension measurement is performed on the master gauge, or The dimensions of the workpiece W are calculated from the table data. The set dimensions of the master gauge used at that time and the data of the mass flow rate Qm at the time of the dimension measurement are stored in the RAM 42 as a linear expression or table data based on the graph data. The

  The vertically long bar graph display unit 31 installed on the front surface (FIG. 1) of the main body case 30 is configured to display the workpiece size as a percentage of the size of the large master gauge and the small master gauge, and has a set tolerance. When the measurement dimension is within the tolerance, for example, a normal color is displayed. When the measurement dimension is out of the tolerance, the display is displayed in red, for example. Further, for example, a 7-segment display is used as the character display 32 provided on the lower side of the bar graph display unit 31, and the standard dimensions and measurement dimensions of the workpiece, the set dimensions and measurement dimensions of the large master gauge, and the small master gauge. In addition to displaying the set dimensions, measurement dimensions, tolerances, etc., the characters at various settings are displayed. The panel switch 33 provided in the lower part is configured as a function switch including an arrow switch, and is used for mode switching at the time of setting, setting input, and the like.

  The microcomputer (measurement calculation unit 10) is provided with a LAN connection port (for example, RS485 port), and the measurement calculation unit 10 is connected to an external personal computer via the LAN. Can be input to the measurement calculation unit 10, and measured dimension data, tolerance determination results, and the like can be sent from the measurement calculation unit 10 to an external personal computer.

  Next, the operation of the air micrometer having the above configuration will be described with reference to the flowcharts of FIGS. When measuring the dimensions of a workpiece with an air micrometer, first, various setting processes including measurement of a master gauge as shown in FIG. 5 are performed.

  When performing the setting process, the measurement operation unit 10 is set to the setting mode. First, in step 100, the reference dimension of the workpiece W to be measured (for example, the workpiece W has holes as shown in FIGS. When measuring the inner diameter of the hole, the exact inner diameter design dimension) is input using the panel switch 33 and the character display 32. The CPU 40 of the measurement calculation unit 10 stores the input reference dimension data in the RAM 42.

  Further, in step 110, the CPU 40 performs storage setting for the dimension width. The dimension width is a value indicating the dimension range displayed on the bar graph display unit 31. For example, when the dimension width is set and input as 0.0200 mm, the bar graph display unit 31 sets the center to 0% and 50% above and below the center. In order to display 50%, +0.0100 mm is the upper dimension width of the bar graph display unit 31, and −0.0100 mm is the lower dimension width of the bar graph display unit 31. The input dimension width is stored in the RAM 42.

  Similarly, in steps 120 and 130, the dimensions of the large master gauge (large) are set, and the dimensions of the small master gauge (small) are set. The large master gauge and the small master gauge are masters of the workpiece W, have holes having the same shape as the workpiece W, and are formed with accurate reference dimensions. When the reference dimension of the inner diameter of the hole of the workpiece W is 20.000 mm and the tolerance is ± 0.0250 mm, for example, the inner diameter of the large master gauge is formed to 20.0250 mm, and the inner diameter of the small master gauge is 1.9750 mm It is formed.

  In this master gauge setting process, in step 120, 20.0250 mm is input as the inner diameter of the large master gauge, and in step 130, 1.9750 mm is input as the inner diameter of the small master gauge. The CPU 40 stores the input data of the large master gauge and the small master gauge in the RAM 42.

  As described above, the inner diameter dimensions of the large master gauge and the small master gauge are formed according to the upper and lower limits of the dimensional tolerance of the workpiece W, and the dimension values are set. The inner diameter of the gauge is independent of the tolerance. For example, the inner diameter of the large master gauge is slightly larger than the design dimension value of the inner diameter of the hole of the workpiece W, and the inner diameter of the small master gauge is It is also possible to set the dimension value slightly smaller than the designed dimension value of the inner diameter of the W hole.

  That is, when the size of the workpiece W is measured, the large and small master gauge obtains the linear expression or table data of the graph of FIG. 10 used when converting the size (inner diameter) of the workpiece W from the calculated flow rate Qm data. As long as the dimensions are about the upper limit and the lower limit of the tolerance, for example, there are three large master gauges, medium master gauges, and small master gauges. You can also make a master gauge and set its dimensions. In that case, the inner diameter of the medium master gauge is set so as to substantially match the reference dimension (20.000 mm) of the inner diameter of the hole of the workpiece W.

  Next, in steps 140 and 150, the tolerance of the workpiece W is set and inputted. The tolerance is used as a reference when determining the quality of the workpiece W. For example, when the workpiece W has a reference dimension of 20.000 mm and a positive-side allowable dimension of 20.000, +0.0020 is defined as + tolerance. If the allowable dimension on the-side is 19.9980, enter -0.0020 as the -tolerance. The input + tolerance and −tolerance are stored in the RAM 42.

  Next, in step 160, zero point adjustment of the first pressure sensor 3 and the second pressure sensor 4 is performed. The zero point adjustment of the first pressure sensor 3 and the second pressure sensor 4 is to adjust the zero point of each pressure sensor (a circuit in which strain gauges are bridge-connected). The supply pressure of air supplied to the air flow path 11 In this state, the panel switch 33 is operated to adjust the zero point.

  Next, in steps 170 and 180, the pressure loss of the measuring head 2 connected to the air flow path 11 of the measuring unit 1 is measured, and the correction value P2s and the flow rate Qt of the correction second pressure obtained at that time are measured. Store the data. The measurement of the pressure loss of the measuring head 2 is a data conversion of the relationship between the air flow rate Qt depending on the shape of the measuring head 2 and the temperature T and the correction value P2s of the second pressure. The air is supplied to the measurement head 2 through the air flow path 11 and the air flow rate Qt, temperature T, and correction value P2s of the second pressure at that time are measured and calculated at a plurality of calibration points. The flow rate Qt calculated at each calibration point is corrected by the temperature T detected by the temperature sensor 5, and the correction value P2s of the second pressure and the data of the flow rate Qt are stored as table data.

  That is, the measurement of the pressure loss of the measuring head 2 is automatically performed by the CPU 40 of the measurement calculation unit 10, and the opening degree of the control valve 6 is automatically changed, for example, in increments of 5% to 10%. The first pressure P1 from the first pressure sensor 3, the second pressure P2 from the second pressure sensor 4, and the temperature T from the temperature sensor 5 are each automatically measured. Further, the CPU 40 calculates the flow rate Qt using the above arithmetic expression for calculating the mass flow rate Qm, and data of the correction flow rate Qt and the correction value P2s of the second pressure measured at each calibration point. Are stored in the RAM 42 as table data or a multipoint broken line system. The relationship between the flow rate Qt and the second pressure correction value P2s is approximated by a multipoint broken line as shown in the graph of FIG. 9, and the multipoint of the flow rate Qt and the second pressure correction value P2s changing as shown in this graph. Based on the broken line or the table data, the second pressure P2 is corrected when measuring the dimensions of the large master gauge and the small master gauge described later and when measuring the actual dimensions of the workpiece W.

  Next, in step 200, the dimensions of the large master gauge are measured, and the flow rate Qtl is calculated and stored for the large master gauge. The measurement of the large master gauge is performed in the same manner as when measuring the dimension of the workpiece W, with the measurement head 2 inserted into the hole of the large master gauge, and air from the air source through the air flow path 11 of the measurement unit 1. This is carried out as shown in the flowchart of FIG. 6 by ejecting into the holes from the two ejection holes 22 and 22.

  In the large master gauge dimension measurement process of FIG. 6, the CPU 40 first proceeds from step 210 to step 220, where the first pressure P <b> 1 of the first pressure sensor 3 and the second pressure P <b> 2 of the second pressure sensor 4 at that time. , And the detection data of the temperature T of the temperature sensor 5, and then, in steps 230 and 240, the CPU 40 is a value obtained by adding the correction value P2s to the second pressure P2 detected by the second pressure sensor 4, here Then, the opening degree of the control valve 6 is adjusted so that a value obtained by subtracting the correction value P2s from the second pressure P2 becomes a preset constant value.

  Next, when the value obtained by subtracting the correction value P2s from the second pressure P2 becomes a predetermined constant value, the CPU 40 takes in the second pressure P2 and the temperature T at that time, and takes the mass flow rate Qm. The mass flow rate Qtl of the large master gauge is calculated using the arithmetic expression {αQm * Qm + βQm = A * ΔP * (ΔP + 2 * P2 + B) * C / (C + TS−Tm)}. In step 260, the calculated data is stored as the large master gauge size set in step 120, that is, the mass flow rate Qtl of the large master gauge corresponding to, for example, 20.0250 mm.

  Next, in step 300 of FIG. 5, similarly, the dimensions of the small master gauge are measured, and the flow rate Qts is calculated and stored for the small master gauge. The dimension measurement of the small master gauge is performed in the same manner as described above, with the measurement head 2 inserted into the hole of the small master gauge, and the air from the air source is ejected through the air flow path 11 of the measurement unit 1. This is carried out as shown in the flowchart of FIG.

  In the small master gauge dimension measurement process of FIG. 7, the CPU 40 first proceeds from step 310 to step 320, where the first pressure P1 of the first pressure sensor 3 and the second pressure P2 of the second pressure sensor 4 at that time. , And the temperature T detection data of the temperature sensor 5, and then in steps 330 and 340, the control valve is set so that the value obtained by subtracting the correction value P2s from the second pressure P2 becomes a preset constant value. Adjust the opening of 6.

  Then, when the value obtained by subtracting the correction value P2s from the second pressure P2 becomes a predetermined constant value, the CPU 40 takes in the second pressure P2 and the temperature T at that time, and calculates the mass flow rate Qm. The mass flow rate Qts of the small master gauge is calculated using an arithmetic expression {αQm * Qm + βQm = A * ΔP * (ΔP + 2 * P2 + B) * C / (C + TS−Tm)} for calculation. In step 360, the calculated data is stored as the small master gauge size set in step 130, that is, the mass flow rate Qts of the small master gauge corresponding to, for example, 19.9750 mm.

  Next, in step 400 of the flowchart of FIG. 5, the mass flow rate Qtl of the large master gauge obtained in steps 200 and 300 (corresponding to the size of the large master gauge of 20.0250 mm) and the mass flow rate Qts of the small master gauge (small From the flow rate data and dimension data of the master gauge dimension (19.99750 mm), as shown in FIG. 10, a straight line connecting the two points of the large master gauge and the small master gauge (straight line indicating the relationship between the flow rate Q and the dimension) Formula or table data) is calculated, and the linear formula or table data is stored in the RAM. As shown in FIG. 10, the dimension of the vertical axis of the graph is displayed in%. This is because the display on the bar graph display unit 31 is displayed in%. Here, the dimension of the large master gauge is + 50%, the size of the small master gauge is set to -50%. Thereby, the setting process before measurement is completed.

  On the other hand, the dimension measurement of the workpiece W is performed as shown in the flowchart of FIG. 8 in a state where the setting process of FIG. 5 is completed.

  When measuring the dimension of the workpiece W, air from the air source is supplied to the measuring unit 1 in a state where the measuring head 2 is inserted into the hole of the workpiece W, as in the dimension measurement of the master gauge. Air is ejected from the ejection holes 22, 22 of the measuring head 2 into the hole of the workpiece W through the air flow path 11, and the dimensions are measured as shown in the flowchart of FIG.

  When entering the dimension measurement process of the workpiece W in FIG. 8, the CPU 40 first proceeds from step 500 to step 510, where the first pressure P1 of the first pressure sensor 3 and the second pressure P2, of the second pressure sensor 4 at that time. Then, each detection data of the temperature T of the temperature sensor 5 is fetched, and then in steps 520 and 530, the control valve 6 is controlled so that the value obtained by subtracting the correction value P2s from the second pressure P2 becomes a predetermined constant value. Adjust the opening.

  Next, when the value obtained by subtracting the correction value P2s from the second pressure P2 becomes a predetermined constant value, the CPU 40 takes in the second pressure P2 and the temperature T at that time and in step 540, the mass flow rate Qm The mass flow rate Qtw of the workpiece W is calculated using the arithmetic expression {αQm * Qm + βQm = A * ΔP * (ΔP + 2 * P2 + B) * C / (C + TS−Tm)}.

  Next, in step 550, based on the calculated mass flow rate Qtw, the dimensions of the workpiece W are calculated using data indicating the relationship between the dimensions of the master gauge and the mass flow rate Qt. In other words, the table data indicating the relationship between the linear flow of FIG. 10 connecting the two points of the large master gauge and the small master gauge or the size of the large and small master gauges and the mass flow rate Qt stored in the setting process of step 400 and the calculated mass Using the flow rate Qtw, a dimension measurement value of the workpiece W is calculated. In step 560, the calculated dimension measurement value of the workpiece W is displayed on the character display 32, and the dimension measurement value of the workpiece W is displayed on the bar graph display unit 31 in% display.

  Thus, according to the air micrometer, the pressure difference between the first pressure P1 on the upstream side of the porous member 12 of the measuring unit 1 and the downstream side and the second pressure P2, the second pressure P2, and the temperature T of the air Based on the above, the mass flow rate per unit time of the air ejected from the ejection holes 22, 22 of the measurement head 2 is calculated, and the dimensions of the workpiece W are calculated based on the mass flow rate. It is possible to measure workpiece dimensions in a significantly wider range with high accuracy. Furthermore, when measuring the dimensions of the workpiece W, based on the calculated mass flow rate, from a linear equation or table data indicating the relationship between the master flow size reference value measured and stored in advance and the master measurement value mass flow rate, The dimensions of the workpiece W can be calculated easily and accurately.

DESCRIPTION OF SYMBOLS 1 Measuring part 2 Measuring head 3 1st pressure sensor 4 2nd pressure sensor 5 Temperature sensor 6 Control valve 10 Measurement calculating part 11 Air flow path 12 Porous member 13 Upstream chamber 14 Downstream chamber 21 Air flow path 22 Ejection hole 30 Main body case 31 Bar graph display section 32 Character display 33 Panel switch 34 Air input connector 35 Air output connector 36 Flow rate measuring device 40 CPU
41 ROM
42 RAM
43 Input / output section

Claims (5)

In an air micrometer that measures the dimension of the workpiece by ejecting air supplied from an air source toward the workpiece from the ejection hole of the measurement head,
Air from the air source is supplied to an air flow path through a control valve, and a measurement unit configured by partitioning an upstream side and a downstream side of the air flow path by a porous member;
A first pressure sensor that detects a first pressure of air upstream of the measurement unit and outputs a signal thereof;
A second pressure sensor for detecting a second pressure of the air downstream of the measuring unit and outputting a signal thereof;
Valve control means for taking in a signal output from the second pressure sensor and controlling the opening of the control valve so that the second pressure of the second pressure sensor becomes a constant value;
A temperature sensor that detects the temperature of the air in the measurement unit and outputs a signal;
A flow rate calculation means for calculating a mass flow rate per unit time of air ejected from the ejection hole of the measurement head based on a pressure difference between the first pressure and the second pressure, a second pressure, and an air temperature;
Based on the mass flow rate calculated by the flow rate calculation means, a dimension calculation means for calculating the dimensions of the workpiece;
An air micrometer characterized by comprising: The flow rate calculation means calculates the mass flow rate Qm,
αQm * Qm + βQm = A * ΔP * (ΔP + 2 * P2 + B) * C / (C + TS−Tm)
(Where ΔP is the pressure difference between the first pressure P1 and the second pressure P2, A is the shape factor of the porous member, B is the correction value for the air compressibility, C is the correction value for the temperature, Ts is the reference temperature, Tm is air temperature, α is a coefficient depending on air molecular weight, β is a coefficient depending on air viscosity)
The air micrometer according to claim 1, wherein the air micrometer is calculated from an arithmetic expression:   Pressure loss data indicating the relationship between the pressure loss generated in the flow path and the ejection hole in the measuring head and the mass flow rate is stored in advance in the set value storage means, and based on the pressure loss data, the flow rate calculation means determines the second flow rate calculation means. 3. The air micrometer according to claim 1, wherein the control value of pressure is corrected.   The set value storage means stores an outer diameter or an inner diameter of the measuring head and master dimensions of at least two different master gauges as dimension reference values, and stores in advance as master measurement values of the master gauge. Measurement value storage means is provided, and for each master gauge, the mass flow is measured in advance using the measurement head, and data indicating the relationship between the dimensional reference value of the master gauge and the mass flow is the master measurement value storage means. The air micrometer according to claim 3, wherein the air micrometer is stored in the air micrometer.   When the dimensional standard value of the workpiece and its tolerance is (A ± a), a large master gauge of dimension (A + a) and a small master gauge of dimension (A-a) are prepared, and the dimensional standard value of the large master gauge Dimension (A + a) and Dimension (A-a) as the dimensional reference value of the small master gauge are stored in the set value storage means, and the mass flow rate is measured for the large master gauge and the small master gauge. 5. The air micrometer according to claim 4, wherein data indicating a relationship between the master gauge and a dimension reference value of the master gauge is stored in the master measurement value storage means.

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