Bar steel inspection device

Abstract

To provide a device that can detect whether a bar steel has a flaw without a determination made by human.SOLUTION: A bar steel inspection device is to inspect a bar steel having a symmetrical shape relative to an axis while conveying the bar steel in a direction of the axis, and comprises: a pair of optical displacement meters that are arranged symmetrically to each other relative to the axis and each directed to the bar steel; a noise removal unit that removes a noise from outputs from the pair, and that includes a synthesis unit adding the outputs from the pair to each other to synthesize the outputs; and a determination unit that stores a threshold and determines the presence or absence of a flaw on the basis of a result of operation performed by the noise removal unit and the threshold.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The following disclosure relates to an apparatus for optically detecting the presence or absence of defects in steel bars such as round bars, and in particular to an apparatus that can detect the presence or absence of defects without human judgment. [Background technology]

[0002] The quality standards acceptable by customers for many steel products, including steel bars, are becoming stricter every year. For example, a steel bar with a diameter of 150 mm may be deemed defective if it has a dent of just 0.5 mm in depth. This is something that a skilled inspector can only detect with extreme care. However, due to personnel shortages and prohibitions on long working hours, it is not possible to place an excessive burden on inspectors.

[0003] Various devices have been considered for mechanically detecting surface defects. For example, technologies using eddy current sensors and ultrasonic sensors have been considered. The former is only effective for detecting defects with specific characteristics that obstruct the flow of eddy currents, while the latter is not sensitive enough to detect minute defects.

[0004] A technique has been proposed in which an object is photographed with a camera and inspected by image analysis. Patent Document 1 discloses a related technique. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special table number 2006-510876 Summary of the Invention [Problem to be solved by the invention]

[0006] Even image analysis is not free from the effects of noise contained in the original data, and problems arise when automatically determining whether or not there are defects. Ultimately, a final check by a skilled inspector is required, and this does not necessarily contribute to labor savings. There is a demand for a device that can detect the presence or absence of defects without human judgment. [Means for solving the problem]

[0007] A steel bar inspection device that inspects a steel bar having a symmetrical shape with respect to an axis while transporting the steel bar in the direction of the axis comprises a pair of optical displacement meters that are arranged symmetrically with respect to the axis and each directed toward the steel bar, a noise removal unit that removes noise from the outputs of the pair, the noise removal unit including a synthesis unit that combines the outputs of the pair by addition, and a judgment unit that stores a threshold value and determines whether or not there is a defect based on the calculation result by the noise removal unit and the threshold value.

[0008] Preferably, the steel bar inspection device further includes one or more pairs of other optical displacement meters, each arranged symmetrically with respect to the axis and directed toward the steel bar, and the plurality of pairs of optical displacement meters are arranged at equal intervals around the axis. Alternatively, preferably, the noise removal unit further includes a difference calculation unit that calculates a difference between two points of the combined output. Also preferably, the steel bar inspection device further includes a data conversion unit that divides each of the paired outputs into a plurality of parts in the width direction with respect to the axis, selects the maximum or minimum value from the plurality of outputs, arranges them in the direction of the axis, and outputs them to the combination unit. [Effects of the Invention]

[0009] To provide a device capable of detecting whether or not a steel bar has a defect without human judgment. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view of a steel bar according to an example. [Figure 2] FIG. 2 is a partial elevational view of the steel bar, showing in particular the defect from the side and in enlarged view. [Figure 3] FIG. 3 is a schematic elevational view of an inspection device according to one embodiment. [Figure 4] FIG. 4 is an elevation view of the flaw detection device as viewed in the axial direction. [Figure 5] FIG. 5 is a block diagram of the inspection device. [Figure 6] FIG. 6 is a flowchart of a process for determining the presence or absence of a flaw. [Figure 7] FIG. 7 is a schematic perspective view illustrating the process of converting the read data. [Figure 8] FIG. 8 is a graph that schematically shows data at each stage in the noise removal process. DETAILED DESCRIPTION OF THE INVENTION

[0011] Several exemplary embodiments will be described below with reference to the accompanying drawings. It should be particularly noted that the drawings are not necessarily drawn to scale, and therefore the dimensional relationships between the drawings are not limited to those shown. Throughout the following description and the appended claims, unless otherwise specified, the terms "upstream" and "downstream" are used for convenience to mean above and below, respectively, in relation to the direction in which the steel bars are transported, although embodiments in which the transport direction is reversed are also possible.

[0012] The inspection device disclosed below can be used to determine whether or not there are defects such as scratches on the surface of a steel bar, and one example of the steel bar is a round steel bar 1 shown in Figure 1. Of course, what is shown in Figure 1 is merely an example, and the device can be used to inspect not only round bars but also steel products with shapes symmetrical with respect to axis X, such as square bars, polygonal columns, elliptical columns, or semi-circular columns.

[0013] Although rare, various defects occur on the surface of steel bar 1 for various reasons. One example is a shallow, wide depression called a dent 3. This occurs, for example, when steel bar 1 interferes with hot rolling equipment or when steel bars are pressed against each other by their own weight when stacked after forming. Referring to FIG. 2(a) in combination with FIG. 1, the diameter D1 of steel bar 1 is in the range of, for example, 60 to 165 mm, while the depth d3 of dent 3 can be very shallow, less than 1 mm. On the other hand, the width w3 can range up to several tens of mm, making it wide and shallow, making it difficult to detect using conventional flaw detection methods.

[0014] Also, flaws 5 with extremely large aspect ratios are often seen. Such flaws are presumed to be caused by unintentional strikes or by burrs being pushed in, and are called C flaws or similar based on their orientation. Referring to Figure 2(b), when the width w5 and depth d5 ​​of C flaw 5 are less than 1 mm, it becomes difficult to distinguish it from noise in the measurement data.

[0015] The inspection device according to this embodiment generally uses a pair of optical displacement meters to effectively remove noise from measurement data and clarify defects, thereby facilitating their determination.

[0016] Referring primarily to FIG. 3, the inspection device 11 generally inspects a steel bar 1 while transporting it in the direction of axis X. It includes a flaw detection device 13 equipped with one or more optical displacement sensors, a transport device 15, and a computer 21 that controls these devices and removes noise from acquired data to determine the presence or absence of flaws. The inspection device 11 may include other inspection devices, or the flaw detection device 13 may be installed as an add-on to an existing inspection device. An existing inspection device is, for example, a line including a length measuring device, an outer diameter measuring device, an ultrasonic flaw detector, etc., and the flaw detection device 13 may be added, for example, to the most upstream of these devices. Alternatively, the inspection device 11 may include a marker 19, which can be used, for example, in conjunction with the flaw detection device 13 and the computer 21 to mark flaw locations.

[0017] Referring to FIG. 4 in combination with FIG. 3, the flaw detection device 13 includes at least a pair of optical displacement meters 23a, 23b. The optical displacement meters 23a, 23b are devices that measure the position and shape of an optically opaque object surface by triangulation using, for example, laser light, and any commercially available devices can be used. In this embodiment, since the steel bar 1 is measured while being transported, a so-called two-dimensional laser displacement meter can be suitably used. The two-dimensional laser displacement meter is, for example, a device that uses a cylindrical lens to expand laser light in the width direction and forms an image of the reflected light on a CMOS sensor, but is not necessarily limited to this. Of course, a three-dimensional laser displacement meter may also be used.

[0018] In this embodiment, a pair of optical displacement gauges 23a and 23b are used. The optical displacement gauges 23a and 23b are fixed to, for example, a circular frame 25 that surrounds the steel bar 1 and are arranged symmetrically with respect to the center of the frame. The steel bar 1 is passed through the center of the frame 25, and the optical displacement gauges 23a and 23b are each directed toward the steel bar 1, thereby enabling thorough measurement of the entire peripheral surface of the steel bar 1. Needless to say, the optical displacement gauges 23a and 23b are each connected to the computer 21, and their measurement data is extracted. Using a pair of symmetrically arranged optical displacement gauges is not only useful for measuring the entire surface of the steel bar 1, but is also significantly useful for noise reduction, as will be described in detail later.

[0019] The flaw detection device 13 is not limited to the pair of optical displacement gauges 23a and 23b, but may also include other pairs of optical displacement gauges 23c and 23d, or even other pairs. While the more pairs, the higher the measurement accuracy, the fewer pairs are preferred in terms of cost and maintenance. While five pairs are shown in the example of FIG. 4, the number may be four or fewer, or even six or more. These pairs are preferably arranged at equal intervals around the axis X, but are not necessarily required to be spaced at equal intervals.

[0020] The conveying device 15 is a device that conveys the steel bar 1 horizontally in a constant direction, such as a roller table. Alternatively, other devices such as a belt conveyor or a series of pinch rollers may be used. In any case, the conveying device 15 is capable of conveying the steel bar 1 at a constant speed in a conveying direction 17 parallel to the axis X under the control of a computer 21. By combining two-dimensional displacement measurement perpendicular to the axis X with constant-speed conveyance parallel to the axis X, it becomes possible to measure the three-dimensional shape of the steel bar 1.

[0021] Referring to Figure 5 in combination with Figure 3, the computer 21 can be a general factory computer equipped with a temporary memory element such as a DRAM, storage such as a hard disk, a central processing element, and a display. Of course, a general office PC or a mainframe computer can also be used. Furthermore, instead of a single computer, multiple computers interconnected via a network can also be used.

[0022] The computer 21 is connected to each displacement gauge via an interface or controller, and reads position data at each point on the surface of the steel bar 1. The computer 21 is also connected to actuators, for example via an appropriate programmable logic controller (PLC), to adjust the height and focus of each displacement gauge and to control the overall operation of the conveying device 15, marker 19, and inspection device 11. Needless to say, some of these controls may be performed by another computer on the network. In addition, the temporary or permanent storage and use of measured data may also be performed by another computer.

[0023] The data processing procedure will be described with reference to Figure 6 in combination with Figures 3 and 5. The computer 21 is programmed to execute the processing according to the flowchart shown in Figure 6 and the following description. For ease of explanation, only the processing of data from a pair of optical displacement gauges will be described below, but the processing is essentially the same even if two or more pairs are used.

[0024] The computer 21 controls the conveying device 15 via the PLC, and while conveying the steel bar 1 in the direction 17, reads data from the optical displacement meter via the controller (step S1). The read data is in the form of three-dimensional position data, for example, as schematically shown by the dashed line in Fig. 7.

[0025] The computer 21 may process the data in this three-dimensional format, or may convert the data as appropriate (step S3). For example, the computer 21 may convert the three-dimensional data into a two-dimensional format in which the data is divided into multiple parts in the width direction relative to each of the axes. The divided data is as shown schematically by the solid lines in Figure 7. Furthermore, the maximum or minimum value can be selected from these multiple outputs. The converted data is output to the next noise removal step S5.

[0026] As shown in Figure 8(a), the data obtained by the processing up to this point contains a lot of noise that is not directly related to the surface shape of the steel bar 1. Even if there is a flaw less than 1 mm in height, its signal is buried in the noise, making it impossible to determine its presence or absence. One cause of the significant noise is presumed to be the vibration or rocking of the steel bar 1 on the conveying device 15. Noise caused by the vibration or rocking should appear in opposite phases in the paired outputs from the pair of optical displacement gauges 23a, 23b (the upper and lower waveforms in Figure 8(a)). Therefore, the computer 21 combines the paired outputs by adding them together (step S5-1). The combined result is shown, for example, in Figure 8(b).

[0027] Even after combining, significant noise may still be mixed in. Therefore, the computer 21 may further perform noise removal. One example is a two-point difference calculation (step S5-2). That is, in a series of data, noise is removed by sequentially calculating the difference between a numerical value at one point and a numerical value at another point that is a small distance away from the first point. Of course, the difference may be calculated by referring to three or more points. The result of the difference calculation is, for example, as shown in FIG. 8(c).

[0028] In addition to or instead of the difference calculation, the computer 21 may perform appropriate filtering (step S5-3). Examples of such filtering include low-pass filtering, which removes frequency components above a certain level, high-pass filtering, which removes frequency components below a certain level, or band-pass filtering, which passes only components within a certain frequency range. Of course, other filtering may be performed instead of or in addition to this.

[0029] Needless to say, the computer 21 can execute steps S5-1 to S5-3 in any order, not just in this order. One or more of these steps may be omitted, or other noise removal means may be further applied.

[0030] The noise-removed data is then subjected to a determination step in which it is determined whether or not there is a defect (step S7). In the determination step, the computer 21 can make the determination using various criteria, one example of which is using a threshold value. For example, if there is a point in the noise-removed data that exceeds the threshold value, it can be determined that there is a defect. For example, if the threshold value is set to ±0.3 mm, there are no points that exceed the threshold value in the example of Figure 8(c), so it can be determined that there is no defect in that range. The threshold value can be stored in storage in advance and read out each time, or it can be read out from another computer on the network, or it can be manually input by the operator each time.

[0031] Of course, the threshold value may be set not only for height but also for length, or height and length may be related to each other. This makes it possible to automatically distinguish between dents and burrs from the waveform. Also, instead of or in addition to these, threshold values ​​may be set for information other than height and length, or other criteria may be adopted.

[0032] According to this embodiment, a pair of optical displacement meters is used to cancel out the main noises, thereby effectively removing noise and revealing signals derived from flaws, making it possible to detect the presence or absence of flaws without human judgment.

[0033] Although several embodiments have been described, modifications or variations of the embodiments can be made based on the above disclosure. [Industrial Applicability]

[0034] To provide a device capable of detecting whether or not a steel bar has a defect without human judgment. [Explanation of symbols]

[0035] 1 steel bar 3 Dents 5 C flaw 11 Inspection equipment 13 Defect detection device 15. Conveying equipment 17 Conveying direction 19 Marker 21 Computer 23a, 23b, 23c, 23d Optical displacement gauge D1 diameter d3,d5 depth w3,w5 width X-axis S1, S3, S5, S7 steps

Claims

1. A steel bar inspection device that inspects a steel bar having a symmetrical shape with respect to an axis while transporting it in the direction of the axis, a pair of optical displacement gauges arranged symmetrically with respect to the axis and each directed toward the steel bar; a noise removal unit that removes noise from the pair of outputs and includes a combining unit that combines the pair of outputs by addition; a determination unit that stores a threshold value and determines whether or not a flaw exists based on the calculation result by the noise removal unit and the threshold value; A steel bar inspection device equipped with the above.

2. Further comprising one or more pairs of other optical displacement gauges each arranged symmetrically with respect to the axis and directed toward the steel bar; 2. The steel bar inspection device according to claim 1, wherein the plurality of pairs of optical displacement gauges are arranged at equal intervals around the axis.

3. The steel bar inspection device according to claim 1 , wherein the noise removal unit further includes a difference calculation unit that calculates a difference between two points of the combined output.

4. a data conversion unit that divides each of the paired outputs into a plurality of parts in the width direction of the axis, selects a maximum value or a minimum value from the plurality of outputs, arranges them in the direction of the axis, and outputs them to the synthesis unit; The steel bar inspection device of claim 1 further comprising:

Images