JP2012088138A - Outside diameter measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an outside diameter measuring apparatus capable of obtaining high measurement accuracy even when measuring the outside diameter of a bar steel, a linear material, or a steel pipe which is a material having a circular cross section and high temperature, and capable of preventing attachment of scales and dust to a light projection part and a light receiving part.SOLUTION: An outside diameter measuring apparatus 1 includes an outside diameter measuring instrument 2 for measuring the outside diameter of a bar steel W and an insertion member 3 for inserting the bar steel W. The outside diameter measuring instrument 2 includes a light projection part 21 for projecting light L to the bar steel W, a light receiving part 22 for receiving the light L and a control calculation part 23 for calculating the outside diameter of the bar steel W. The insertion member 3 has an insertion port 31 for inserting the bar steel W, and the insertion port 31 is formed so as to be opposed to an optical path from the light projection part 21 to the light receiving part 22. The insertion member 3 has an annular vent 32 surrounding the insertion port 31, and the vent 32 forms an air curtain A on the outer periphery of the bar steel W in the diameter direction of the bar steel W by sending air F in the axial direction of the bar steel W. There is no shelter in the sending direction of air F sent from the vent 32.

Description

  The present invention relates to an outer diameter measuring device that measures the outer diameter of a circular cross-sectional material. In particular, the present invention relates to an outer diameter measuring apparatus that has a good outer diameter measurement accuracy and that scales and dust are less likely to adhere to a light projecting part and a light receiving part.

Conventionally, for example, in the measurement of the outer diameter of a steel bar (cross-sectional circular material), a wire (cross-sectional circular material), a steel pipe (cross-sectional circular material) in a high temperature state after hot rolling, the steel bar, the wire, and the steel pipe are hot. Therefore, an outer diameter measuring device that optically captures the contour from multiple directions and optically measures the outer diameter is known.
However, in such an outer diameter measuring device, scales and dusts peeled off from the surface of high-temperature steel bars, wires, and steel pipes adhere to the light projecting part and the light receiving part, and the surfaces of the light projecting part and the light receiving part are soiled. Therefore, there is a problem that measurement cannot be performed.
For this reason, there is an outer diameter measuring device that prevents the scale and dust from adhering to the surface of the light projecting unit and the light receiving unit by blowing off the scale and dust with air.

An example of an outer diameter measuring device that blows off scales and dust with such air will be described with reference to FIG. FIG. 1A is a partial cross-sectional view of the side surface of the outer diameter measuring device, and FIG. 1B is a front view of the light projecting unit and the light receiving unit viewed from the direction D in FIG.
The outer diameter measuring device 101 includes an outer diameter measuring instrument 102 that measures the outer diameter of the steel bar W, and an insertion member 103 that allows the steel bar W to pass therethrough. The outer diameter measuring device 102 includes a light projecting unit 121 that projects light L onto the steel bar W, and a light receiving unit 122 that receives the light L projected by the light projecting unit 121. The outer diameter measuring instrument 102 has three sets of a light projecting unit 121 and a light receiving unit 122 (in FIG. 1A, only one set of the light projecting unit 121 and the light receiving unit 122 is shown).
The insertion member 103 has an insertion port 131 through which the steel bar W is inserted, and the insertion port 131 is provided so as to face the optical path from the light projecting unit 121 to the light receiving unit 122.
Further, the insertion member 103 has a blower port 132 that blows air F from the outer periphery in the radial direction of the steel bar W on the side surface of the steel bar W, and the blower port 132 communicates with the suction port 133 that performs intake. Yes. The intake port 133 is connected to a blower (not shown).

The light projecting unit 121 is, for example, an LED or a halogen lamp, and projects light L onto the outer peripheral edge of the steel bar W. The light receiving unit 122 is, for example, a CCD line sensor, and a light receiving element that receives the light L projected on the outer peripheral edge of the steel bar W, and a light receiving unit that does not receive the light L projected in the shadow of the steel bar W. From the position of the boundary with the element, the outer diameter of the steel bar W is calculated.
The three sets of the light projecting unit 121 and the light receiving unit 122 are arranged so that the optical paths from the respective light projecting units 121 to the light receiving unit 122 intersect each other at an angle of 120 degrees at the radial center O of the insertion port 131. ing.
The light projecting unit 121 and the light receiving unit 122 are rotatable in the circumferential direction of the steel bar W starting from the radial center O of the insertion port 131, and the outer diameter of the steel bar W is set to all the circumferential direction of the steel bar W. Measure from position.

However, a high temperature air layer is formed on the surface of the steel bar W, and in such an outer diameter measuring device 101, the air layer is disturbed by the air F from the air blowing port 132. There is a problem that the refraction direction of the light L projected from the portion 121 to the vicinity of the surface of the steel bar W is disturbed, and the measured value of the outer diameter varies.
The measurement result of the steel bar W by the outer diameter measuring device 101 is shown in FIG. Each of the three sets of the light projecting part 121 and the light receiving part 122 is measured from all positions in the circumferential direction of the steel bar W. A distance from the straight line passing through the center O in the radial direction of the insertion opening 131 to the periphery of the steel bar W from the straight line parallel to the light L (hereinafter, this distance is referred to as a virtual radius) is measured, and a reference value (20 mm in this case) is obtained. It is expressed by the difference between The average value of the virtual radius measured from the entire circumference of the steel bar W is taken as the virtual radius average value, and twice the virtual radius average value is taken as the outer diameter of the steel bar W.

  However, the lines indicating the measured values R101, R102, and R103 of the virtual radius by the three sets of the light projecting unit 121 and the light receiving unit 122 are separated from each other as shown in FIG. 2, and the virtual radius average value varies. Among the virtual radius average values of the steel bars W by the three sets of the light projecting part 121 and the light receiving part 122, the minimum value is 19.90 mm, the maximum value is 20.10 mm, and the difference between the maximum value and the minimum value is 0.20 mm. Yes, measurement accuracy is not enough.

Also known is an outer diameter measuring device that blows air in the axial direction of the steel bar W (for example, see Patent Document 1).
However, in the outer diameter measuring apparatus of Patent Document 1, since there is a shield in the air blowing direction, there is a possibility that air abuts on the shield and the scale and dust rise. Further, since the light projecting unit and the light receiving unit are not separated from the air, the scales and dust that have risen may adhere to the light projecting unit and the light receiving unit.

Japanese Utility Model Publication No. 54-123856

  The present invention has been made to solve such problems of the prior art, and has high measurement accuracy even when measuring the outer diameter of high-temperature steel bars, wire rods, and steel pipes, which are circular cross-sectional materials, and has a scale, It is an object of the present invention to provide an outer diameter measuring device in which dust hardly adheres to the light projecting unit and the light receiving unit.

  In order to solve the above-mentioned problems, the present inventor examined the air blowing direction and the like. As a result, air is blown in the axial direction of the cross-section circular material to form an annular air curtain around the outer periphery in the radial direction of the cross-section circular material, and if there is no shielding in the air blowing direction, the outer diameter We obtained the knowledge that the measurement accuracy is improved.

  The present invention has been completed based on the knowledge of the present inventors. That is, in order to solve the above-mentioned problem, the present invention is an outer diameter measuring device for measuring an outer diameter of a circular cross-sectional material, and is directed from a direction perpendicular to the axial direction of the circular cross-sectional material toward a side surface of the circular cross-sectional material. An outer diameter measuring instrument comprising: a light projecting unit that projects light; and a light receiving unit that is provided on the opposite side of the light projecting unit across the circular member in cross section and receives the light projected by the light projecting unit And an insertion member having an insertion port through which the circular cross-sectional material is inserted, and the insertion member is provided so that the insertion port faces an optical path from the light projecting unit to the light receiving unit, and the insertion member Has an annular air outlet surrounding the insertion opening, and the air outlet blows air around the radially outer side of the circular cross-section member in the axial direction of the circular cross-section member. The light projecting portion and the light receiving portion are separated from the circular cross-sectional material that is inserted through the insertion opening. Than said annular air curtain provided radially outward of said circular section material, to provide an outer diameter measuring device, characterized in that no shielding the blowing direction of the air.

According to the present invention, even if the cross-sectional circular material is a high-temperature steel bar, wire, or steel pipe, air is blown in the axial direction of the circular cross-sectional material around the radial outer periphery of the circular cross-sectional material from the air outlet. Since the air curtain is formed, the layered high-temperature air layer on the surface of the circular cross-section material is not easily disturbed, so the refraction direction of the light projected from the light projecting portion to the vicinity of the surface of the circular cross-section material is not easily disturbed. In addition, the measurement accuracy of the outer diameter is good.
In addition, the light projecting unit and the light receiving unit are separated from the circular cross-sectional material, and there is an annular air curtain between the light projecting unit and the light receiving unit and the circular cross-sectional material, and there is a shield in the air blowing direction. By not doing so, the scale and dust peeled off from the circular cross-sectional material are discharged outside in a state of being confined in an annular air curtain. Therefore, the scale and dust are less likely to adhere to the light projecting portion and the light receiving portion provided radially outward of the annular air curtain, so that there is little possibility that the outer diameter cannot be measured due to dirt due to the scale or dust.

  Preferably, the outer diameter measuring device covers the light projecting part and the light receiving part, and has a cover part having an opening facing the annular air curtain, and an inside and an outside of the cover part provided in the cover part. The cover portion is provided on the downstream side of the air blowing direction with respect to the air blowing direction, and the opening portion is located in the vicinity of the annular air curtain.

  According to such a preferable method, the air inside the cover part is sucked and discharged outside the cover part due to the ejector effect by the annular air curtain, so even if scales or dust enter the inside of the cover part. Those scales and dust are sucked and discharged outside the cover part, and are difficult to adhere to the light projecting part and the light receiving part.

  Preferably, the cover portion is provided on the upstream side in the air blowing direction with respect to the light projecting portion and the light receiving portion, and a first cover member provided in an annular shape around a radially outer side of the circular cross-section member; A second cover member provided annularly around the radially outer side of the cross-sectional circular material, on the downstream side in the air blowing direction with respect to the light projecting unit and the light receiving unit, and the light projecting unit and the light receiving unit On the other hand, a third cover member that is annularly provided around the radially outer side of the circular cross-section member and is interposed between the first cover member and the second cover member and connects the first cover member and the second cover member. And having

  According to the present invention, even when the cross-sectional circular material is a high-temperature steel bar, wire rod, or steel pipe, the measurement accuracy of the outer diameter is good. In addition, scale and dust are less likely to adhere to the light projecting unit and the light receiving unit.

FIG. 1A is a partial cross-sectional view of a side surface of a conventional outer diameter measuring device, and FIG. 1B is a front view of a light projecting unit and a light receiving unit viewed from the direction D in FIG. is there. FIG. 2 is a measurement result of the virtual radius of the steel bar measured by the outer diameter measuring device. FIG. 3A is a partial cross-sectional view of the side surface of the outer diameter measuring apparatus according to the first embodiment, and FIG. 3B is a perspective view when a steel bar is inserted into the insertion member, FIG. 3C is a diagram illustrating a state in which the light receiving unit receives light from the light projecting unit. FIG. 3D illustrates the light projecting unit and the light receiving unit viewed from the direction D in FIG. FIG. FIG. 4A is a diagram for explaining a method of plotting the obtained value of the virtual radius on the measurement result diagram, and FIG. 4B is a diagram of the virtual radius of the steel bar measured by the outer diameter measuring device. It is a measurement result. Fig.5 (a) is a partial cross section figure of the side surface of the outer diameter measuring apparatus which concerns on 2nd Embodiment, FIG.5 (b) is a perspective view of a cover part.

(First embodiment)
The outer diameter measuring apparatus according to the first embodiment of the present invention will be described with reference to FIG. 3 (a) is a partial cross-sectional view of the side surface of the outer diameter measuring device, and FIG. 3 (b) is a perspective view when a steel bar is inserted into the insertion member of the outer diameter measuring device. (C) is a figure which shows the state which a light-receiving part receives the light from a light projection part, FIG.3 (d) is the front which looked at the light projection part and the light-receiving part from the D direction in Fig.3 (a). FIG.
The outer diameter measuring device 1 includes an outer diameter measuring device 2 that measures the outer diameter of the steel bar W, and an insertion member 3 through which the steel bar W is inserted.
The outer diameter measuring device 2 includes a light projecting unit 21 that projects light L onto the steel bar W, and a light receiving unit 22 that receives the light L projected by the light projecting unit 21 and transmits an electrical signal corresponding to the light L. In addition, the light projecting unit 21 projects light L, and the control calculating unit 23 calculates the outer diameter of the steel bar W based on the electrical signal transmitted by the light receiving unit 22.
The outer diameter measuring device 2 has three sets of the light projecting unit 21 and the light receiving unit 22 (in FIG. 3A, only one set of the light projecting unit 21 and the light receiving unit 22 is shown).
The insertion member 3 has an insertion port 31 through which the steel bar W is inserted, and the insertion port 31 is provided so as to face the optical path from the light projecting unit 21 to the light receiving unit 22. The insertion member 3 has an annular air blowing port 32 that surrounds the insertion port 31, and the air blowing port 32 communicates with an air intake port 33 that performs intake. The intake port 33 is connected to a blower (not shown).
The air blowing port 32 blows air F around the radially outer periphery of the steel bar W in the axial direction of the steel bar W to form an annular air curtain A. There is no obstruction in the blowing direction of the air F blown from the blowing port 32. If the thickness of the annular portion of the air curtain A is too thin, it becomes difficult for scale and dust peeled off from the circular cross-section material to be trapped in the air curtain A. On the other hand, if the air curtain A is too thick, the air F hits the steel bar W. The layered high-temperature air layer is disturbed and the measurement accuracy of the outer diameter is deteriorated. Therefore, the thickness of the annular portion of the air curtain A is preferably 10 to 15 mm at the blowing position of the air blowing port 32, and is 10 mm in the present embodiment. If the air volume of the air F is too small, the scale and dust peeled off from the circular cross-section material will be difficult to be discharged to the outside while confined in the air curtain A. On the other hand, if the air volume is too large, the air F will hit the steel bar W. The layered high-temperature air layer is disturbed, and the measurement accuracy of the outer diameter is deteriorated. Therefore, the air volume of the air F is a balloon position of the air blowing port 32 is preferably 0.30~0.50Nm ³ / ^cm 2 · min, in the present embodiment is a 0.37Nm ³ / ^cm 2 · min.

The light projecting unit 21 is, for example, an LED or a halogen lamp, and projects light L onto the peripheral edge in the radial direction of the steel bar W. The light receiving unit 22 is a CCD line sensor, for example, and has a plurality of light receiving elements 221 in a line shape in a direction parallel to the outer diameter direction of the steel bar W. The control calculation unit 23 is a boundary between the light receiving element 221 that receives the light L projected on the peripheral edge in the radial direction of the steel bar W and the light receiving element 221 that does not receive the light L projected in the shadow of the steel bar W. The outer diameter of the steel bar W is calculated based on the position.
The three sets of the light projecting unit 21 and the light receiving unit 22 are arranged so that their optical paths intersect each other at an angle of 120 degrees at the radial center O of the insertion port 31. The light projecting unit 21 and the light receiving unit 22 are separated from the steel bar W inserted through the insertion port 31 and are provided radially outward of the steel bar W from the annular air curtain A.
The light projecting unit 21 and the light receiving unit 22 are rotatable in the circumferential direction of the steel bar W starting from the radial center O of the insertion port 31. The control calculation unit 23 rotates the light projecting unit 21 and the light receiving unit 22 in the circumferential direction of the steel bar W by a rotation driving unit (not shown), and measures the outer diameter of the steel bar W from the position of the entire circumference around the steel bar W. To do.

  A distance from the straight line M passing through the center O in the radial direction of the insertion port 31 and parallel to the light L to the peripheral edge of the steel bar W (hereinafter, this distance is referred to as a virtual radius) is measured. In the example of FIG. 3C, x1 and x2 are measured as virtual radii. The average value of the virtual radius measured from the entire circumference of the steel bar W is taken as the virtual radius average value, and twice the virtual radius average value is taken as the outer diameter of the steel bar W.

Next, a method for measuring the outer diameter of the steel bar W will be described.
In a state where the blower is driven and the air F is blown to the intake port 33, the steel bar W is inserted into the center of the insertion port 31 in the radial direction. Air F is blown in the axial direction of the steel bar W around the radially outer periphery of the steel bar W from the blower opening 32, and an annular air curtain A is formed around the radially outer side of the steel bar W.
The control calculation unit 23 causes the light projecting unit 21 and the light receiving unit 22 to rotate in the circumferential direction of the steel bar W by the rotation driving unit, causes the light projecting unit 21 to project the light L, and based on the electrical signal from the light receiving unit 22. The outer diameter of the steel bar W is calculated.

The measurement result of the steel bar W by the outer diameter measuring device 1 is shown in FIG. Each of the three sets of the light projecting portion 21 and the light receiving portion 22 is measured from all positions in the circumferential direction of the steel bar W. The virtual radius is represented by the difference from the reference value (20 mm in this measurement). When the virtual radii measured from the horizontal direction are x1 and x2 as in the example of FIG. 3C, as shown in FIG. 4A, x1 and x2 are on a straight line passing through the center of the coordinates vertically. Is plotted based on the difference from the reference value. FIG. 4B shows the measurement result in which the virtual radius is plotted over the entire circumference.
The measurement results R1, R2, and R3 by the three sets of the light projecting unit 21 and the light receiving unit 22 are shown, and the lines indicating the measured values R1, R2, and R3 are close to each other. The variation is smaller than the measured value.
Among the virtual radius average values of the steel bars W by the three sets of the light projecting unit 21 and the light receiving unit 22, the minimum value is 19.85 mm, the maximum value is 19.98 mm, and the difference between the maximum value and the minimum value is 0.13 mm. Yes Measurement accuracy is good.

Thus, even if the steel bar W is hot, the air F is blown from the air outlet 32 in the axial direction of the steel bar W around the radially outer side of the steel bar W to form the annular air curtain A. Since the layered high-temperature air layer on the surface of the steel bar W is not easily disturbed, the refraction direction of the light L projected from the light projecting portion 21 to the vicinity of the surface of the steel bar W is not easily disturbed, and the outer diameter measurement accuracy is improved.
In addition, the light projecting unit 21 and the light receiving unit 22 are separated from the steel bar W, the annular air curtain A is present between the light projecting unit 21 and the light receiving unit 22, and the steel bar W, and the air blowing direction. Therefore, the scale and dust peeled off from the steel bar W are discharged to the outside while being confined in the annular air curtain. Therefore, the scale and dust are less likely to adhere to the light projecting unit 21 and the light receiving unit 22 provided radially outward of the annular air curtain A, and there is a possibility that the outer diameter cannot be measured due to dirt due to the scale or dust. Few.

Further, the light projecting unit 21 and the light receiving unit 22 may be configured as follows. The light projecting unit 21 is a laser scanning device (for example, a combination of a laser light source and a polygon mirror), and the light receiving unit 22 is a photodetector such as a photomultiplier tube.
For example, in the case of using a configuration in which a laser light source and a polygon mirror are combined as a laser scanning device, the polygon mirror is rotationally driven at a constant speed around the axis of the shaft provided in parallel with the axial direction of the steel bar W, and the laser light source The laser beam is scanned along the outer diameter direction of the steel bar W by reflecting the laser beam emitted from the reflecting surface.
The light receiving range of the light detector is wider than the outer diameter of the steel bar W, and the light detector receives the laser light scanned on the steel bar W and transmits an electric signal corresponding to the received light to the control calculation unit 23. . The control calculation unit 23 calculates the outer diameter of the bar W from the length of time that the scanned laser beam hits the bar W and the photodetector does not detect the laser beam.
With this configuration, the outer diameter of the steel bar W can be measured as in the case where the light projecting unit 21 is an LED or a halogen lamp and the light receiving unit 22 is a CCD line sensor.

(Second Embodiment)
Next, the outer diameter measuring apparatus 1 according to the second embodiment will be described with reference to FIG. FIG. 5A is a partial cross-sectional view of the side surface of the outer diameter measuring device, and FIG. 5B is a perspective view of the cover portion.
The outer diameter measuring apparatus 1 according to the present embodiment has a cover part 4 that covers the light projecting part 21 and the light receiving part 22 in addition to the configuration of the outer diameter measuring apparatus 1 according to the first embodiment.
The cover unit 4 includes a first cover member 41 provided in an annular shape around the radially outer side of the steel bar W on the upstream side in the air blowing direction of the air F with respect to the light projecting unit 21 and the light receiving unit 22, and the light projecting unit The second cover member 42 provided annularly around the radially outer side of the steel bar W on the downstream side in the air blowing direction with respect to the light guide 21 and the light receiving part 22, and the steel bar with respect to the light projecting part 21 and the light receiving part 22 A third cover member 43 provided in a ring around the radially outer side of W and interposed between the first cover member 41 and the second cover member 42 and connecting the first cover member 41 and the second cover member 42; Have. Moreover, the cover part 4 has the opening part 44 which opposes the cyclic | annular air curtain A, and the communicating port 45 which connects the inside and the exterior of the cover part 4. As shown in FIG. The opening 44 is located in the vicinity of the annular air curtain A.

In such a configuration, when the air F is blown from the air blowing port 32, the opening 44 is in the vicinity of the annular air curtain A, so that the air inside the cover 4 is opened by the ejector effect due to the flow of the air F. The part 44 is sucked outside the cover part 4. Then, since the communication port 45 is provided in the cover part 4, as indicated by an arrow F 1, new air is supplied from the communication port 45 to the cover unit 4, and the air inside the cover unit 4 continues to cover the cover unit 4. 4 Sucked outside and discharged.
Thus, even if scales and dust enter the inside of the cover part 4 because the air inside the cover part 4 is sucked and discharged outside the cover part 4, those scales and dust are sucked outside the cover part 4 It is difficult to adhere to the light projecting unit 21 and the light receiving unit 22.

  The opening 44 is preferably as close as possible to the annular air curtain A, but it is desirable to leave a gap between the opening 44 and the annular air curtain A so that the air F does not contact the first cover member 41. . Further, the communication port 45 is preferably provided in the vicinity of the light projecting unit 21 and the light receiving unit 22 apart from the opening 44. Further, although it is desirable to provide the communication port 45 for each of the light projecting unit 21 and the light receiving unit 22, only one communication port 45 may be provided.

Moreover, although the outer diameter measuring apparatus 1 which covers all the light projection parts 21 and the light-receiving parts 22 by one cover part 4 as an example of this embodiment was shown, all the light projection parts are shown by several cover parts 4. 21 and the light receiving unit 22 may be separately covered. For example, the light projecting unit 21 and the light receiving unit 22 may be covered by the individual cover unit 4.
Moreover, the shape of the cover part 4 is not limited to the shape using the 1st cover member 41, the 2nd cover member 42, and the 3rd cover member 43, What is necessary is just to have the opening part 44 and the communication port 45. FIG. .

In addition, this invention is not restricted to the structure of the said embodiment, A various deformation | transformation is possible in the range which does not change the meaning of invention. For example, in the first embodiment and the second embodiment, the number of sets of the light projecting unit 21 and the light receiving unit 22 may be any number, for example, one set.
Further, the outer diameter of the steel bar W may be measured while moving the steel bar W in the axial direction of the steel bar W relative to the outer diameter measuring device 1. By measuring in this way, the outer diameter distribution of the steel bar W along the axial direction of the steel bar W can be measured.

DESCRIPTION OF SYMBOLS 1 ... Outer diameter measuring device 2 ... Outer diameter measuring device 21 ... Light projection part 22 ... Light receiving part 3 ... Insertion member 31 ... Insertion port 32 ... Blower port 4 .... -Cover part 41 ... 1st cover member 42 ... 2nd cover member 43 ... 3rd cover member 44 ... Opening part 45 ... Communication port A ... Air curtain L ... Light W ... Steel bar (circular cross section)

Claims (3)

An outer diameter measuring device for measuring the outer diameter of a circular cross-section material,
A light projecting portion for projecting light from a direction perpendicular to the axial direction of the cross-sectional circular material toward a side surface of the circular cross-sectional material; and a light projecting portion provided on the opposite side of the light projecting unit with the circular cross-sectional material interposed therebetween. An outer diameter measuring instrument comprising a light receiving part for receiving the light projected by the light part;
An insertion member having an insertion port through which the circular cross-sectional material is inserted;
The insertion member is provided so that the insertion port faces an optical path from the light projecting unit to the light receiving unit,
The insertion member has an annular air outlet that surrounds the insertion opening,
The blower port blows air in the axial direction of the circular cross-sectional material around the radially outer periphery of the circular cross-sectional material to form an annular air curtain,
The light projecting portion and the light receiving portion are spaced apart from the circular cross-sectional material that is inserted through the insertion port, and are provided radially outward of the circular cross-sectional material from the annular air curtain.
An outer diameter measuring apparatus having no shielding object in the air blowing direction. A cover portion that covers the light projecting portion and the light receiving portion and has an opening facing the annular air curtain;
A communication port provided in the cover portion and communicating with the inside and the outside of the cover portion;
The cover part is provided on the downstream side of the air blowing direction from the air blowing port,
The outer diameter measuring device according to claim 1, wherein the opening is located in the vicinity of the annular air curtain. The cover portion is provided on the upstream side in the air blowing direction with respect to the light projecting portion and the light receiving portion, and a first cover member provided annularly around the radially outer side of the circular cross-section member;
A second cover member provided annularly around the radially outer side of the circular cross-sectional material on the downstream side in the air blowing direction with respect to the light projecting unit and the light receiving unit;
The first cover member and the second cover are provided between the first cover member and the second cover member, and are annularly provided around the radially outer portion of the circular section member with respect to the light projecting unit and the light receiving unit. The outer diameter measuring apparatus according to claim 2, further comprising a third cover member that connects the members.

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