JP2005118837A - Method and apparatus for controlled cooling of hot rolled steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for controlled cooling of a hot rolled steel which can secure uniformity in both shape characteristics and material characteristics in the transverse direction, through enhancement of accuracy of cooling control by estimating an internal temperature distribution (temperature distribution through the thickness) of a heavy steel plate highly accurately, when the controlled cooling is performed by jetting a coolant on the hot rolled steel, and apparatus therefor. <P>SOLUTION: In the controlled cooling apparatus for the steel which comprises a group of nozzles to jet the coolant, a supply control means of the coolant jetted from the group of nozzles, and a conveying speed control means, ultrasonic waves are transmitted and propagated by an ultrasonic sensor into the steel being cooled. Based on a relationship between a propagation speed of the ultrasonic wave and the temperature of steel, the internal temperature distribution (temperature distribution through the thickness) of the steel is estimated highly accurately. Based on the estimation result, the internal temperature of the steel (average temperature) is obtained and the jetting coolant quantity from the group of nozzles or both of the jetting coolant quantity and the conveying speed are controlled so as to match a target average temperature or cooling speed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to controlled cooling of a hot steel material obtained by, for example, hot rolling, and more specifically, a controlled cooling method of a hot steel material applied to obtain a steel material having good shape characteristics and a uniform material, and The present invention relates to a control cooling device.

For example, when producing a thick steel plate by hot rolling, the hot rolled steel plate is cooled when transported to a winding or pickling process, and in this case, uniform material properties and shape Since it is important to ensure the characteristics (flatness), it is necessary to perform the controlled cooling so that the temperature distribution in the sheet width direction is uniform.
As a cooling device for performing such controlled cooling, for example, in Patent Document 1, a plurality of steel plates are arranged so as to be directed to the upper and lower surfaces of the steel sheet while transferring the hot-rolled steel sheet in the longitudinal direction. In the method of controlling and supplying the cooling water to the steel plate from the nozzles of each of the steel plates, each temperature is measured by detecting the temperature before starting water cooling, at the middle of water cooling, and after the end of water cooling at the center and side edges in the vertical direction and width direction of the steel plate. Find the temperature and temperature difference of the hot spot, predict and calculate the amount of change in the normal temperature range of the steel sheet based on the relational expression corresponding to the temperature difference between each temperature measuring point and the temperature point, It is disclosed that the amount of cooling water supplied to the plurality of nozzles is controlled so that the predicted value falls within the allowable range of the target value.

Patent Document 2 includes (a) a step of measuring the surface temperature distribution of a steel plate after hot rolling, (b) a step of measuring the shape of the steel plate with ultrasonic waves during the latter half of the control cooling, c) A method for cooling a steel sheet comprising a step of controlling control cooling water based on the measurement result of the surface temperature distribution and the measurement result of the surface shape of the steel sheet is disclosed.
Moreover, as a control cooling device for that purpose, (a) a temperature measuring device for measuring the surface temperature distribution of the steel plate immediately after rolling, and (b) for measuring the plate shape of the steel plate installed in the cooling header or the cooling water distribution pipe. An ultrasonic sensor; (c) a cooling device including a cooling header, a means for controlling the cooling water amount, and a nozzle for supplying laminar cooling water connected thereto; and (d) the temperature measuring device for a steel plate. And a control apparatus for cooling water that receives and stores signals from the ultrasonic sensor, flattens the steel sheet according to a predetermined calculation program, and controls the cooling water amount so as to make the surface temperature distribution of the steel sheet uniform. Has been.

However, in the cooling methods of Patent Document 1 and Patent Document 2, a non-contact surface thermometer or a radiation thermometer that measures electromagnetic waves generated by thermal radiation is used for temperature measurement. It is possible to estimate the internal temperature of the steel sheet by introducing it into the calculation formula, but in order to obtain sufficient accuracy, it is necessary to accurately grasp the cooling process of the steel sheet.
In addition, in the temperature measurement method using thermal radiation, the measurement accuracy decreases when cooling water or steam is interposed between the steel plate and the thermometer, especially when a scale exists on the steel plate surface. Only the layer suddenly drops in temperature, and the thickness of this scale and the generation distribution are non-uniform, resulting in a significant reduction in measurement accuracy.
Therefore, since there is a problem in the reliability of the measurement value itself as a base, there is a problem that it is difficult to ensure stable control accuracy when performing control cooling based on the surface temperature.
Japanese Patent Laid-Open No. 62-158825 (claim, FIG. 1) JP-A-8-294717 (claim, FIG. 1) JP-A-57-24834 (Claims, FIGS. 1 to 3)

  The present invention predicts and controls the internal temperature distribution (thickness direction temperature distribution) of steel with high accuracy during cooling even when hot steel with a scale, refrigerant, steam, etc. on its surface is cooled by an injection refrigerant. It is an object of the present invention to provide a control cooling method and a control cooling device for hot steel that can improve accuracy and in particular ensure uniformity of shape characteristics and material characteristics in the width direction of the hot steel.

The present invention is summarized as the following (1) to (8) in order to solve the above problems.
(1) While cooling the steel material with the jet refrigerant from the nozzle group, the ultrasonic wave is incident and propagated inside the steel material by the ultrasonic sensor, the propagated ultrasonic wave is received, and the relationship between the propagation speed and the steel material internal temperature A method for controlling cooling of hot steel, which predicts a steel material internal temperature distribution and controls the amount of refrigerant injected based on the steel material internal temperature (average temperature) obtained from the prediction result.
(2) While the steel material is being cooled by the jet refrigerant from the nozzle group, the surface temperature of the steel material is measured, and ultrasonic waves are incident and propagated by an ultrasonic sensor inside the steel material, and the propagated ultrasonic wave is received and propagated. Predicts the steel internal temperature distribution from the speed and the steel surface temperature, and controls the amount of refrigerant injected based on the measured steel internal temperature (average temperature) and the steel surface temperature obtained from this prediction result. Controlled cooling method for steel.
(3) In (1) or (2), when cooling the steel material in the conveying state, the amount of the injected refrigerant and the conveying speed are controlled based on the steel material internal temperature (average temperature) obtained from the prediction result of the steel material internal temperature distribution. A method for controlling and cooling hot steel material.

(4) In a cooling apparatus for steel material provided with a nozzle group for injecting refrigerant, supply control means for the injection refrigerant from this nozzle group, and a conveyance speed control means, ultrasonic waves are incident and propagated inside the steel material being cooled. The internal temperature of the steel material (average temperature) is calculated by predicting the internal temperature distribution of the steel material from the relationship between the ultrasonic sensor to receive, the ultrasonic wave propagation speed from the ultrasonic sensor and the internal temperature of the steel material, and the injected refrigerant amount and the conveyance speed A control cooling device for hot steel, comprising: an arithmetic control device for calculating and controlling the above.
(5) Nozzle group for injecting refrigerant, supply control means for jetting refrigerant from this nozzle group, and a steel material cooling device provided with a conveying speed control means, and a temperature measuring device for measuring the steel surface temperature during cooling, The temperature inside the steel is estimated by predicting the internal temperature distribution of the steel based on the ultrasonic sensor that receives and propagates ultrasonic waves inside the steel, and the ultrasonic propagation velocity from the ultrasonic sensor and the surface temperature of the steel from the temperature measuring device. And an arithmetic control device for calculating and controlling the amount of refrigerant injected and the conveyance speed from the internal temperature (average temperature) of the steel material and the measured value of the steel surface temperature from the surface temperature measuring device. Controlled cooling device for hot steel.

(6) A controlled cooling device for hot steel, wherein an electromagnetic ultrasonic sensor is used as the ultrasonic sensor in (4) or (5).
(7) In (6), in the case where steel material is restrained and restrained between restraining rolls, an electromagnetic ultrasonic sensor is provided on the outer peripheral portion of the restraining roll, and the control cooling device for hot steel materials.
(8) The controlled cooling device for hot steel according to claim 4 or 5, wherein a water column ultrasonic sensor is used as the ultrasonic sensor in (4) or (5).

  In the present invention, when a hot steel plate, for example, a hot thick steel plate having a scale, cooling water, steam, or the like on its surface is controlled and cooled by spray cooling water from a spray nozzle group, an ultrasonic sensor is also used during cooling. In addition, the internal temperature distribution (thickness direction temperature distribution) of steel can be predicted with high accuracy using an ultrasonic sensor and a surface temperature measuring device, and the amount of jet cooling water or the amount of jet cooling water adapted to this internal temperature distribution The cooling speed can be increased by controlling the conveying speed, and in particular, the uniformity of the shape characteristics and material characteristics in the width direction of the hot thick steel plate can be secured stably.

In the present invention, a hot steel material, for example, a thick steel plate 3 having a temperature of 800 to 1000 ° C. obtained by hot rolling with a hot rolling mill 2 as shown in FIG. It can be applied to a case where controlled cooling is performed at 450 to 200 ° C. with a refrigerant, for example, jet cooling water, from the control cooling device 1 having a spray nozzle group between the restraining rolls 4 a and 4 b disposed in the subsequent stage of the machine 2. .
The present invention conceptually uses an ultrasonic sensor that is not easily affected by the generation scale, cooling water, steam, or the like during the cooling with the jet cooling water in the control cooling device 1, or the ultrasonic sensor and the surface temperature. The internal temperature distribution (temperature distribution in the thickness direction) of the thick steel plate 3 is predicted with high accuracy by using the measuring device together, and based on the average temperature of the thick steel plate 3 obtained from this prediction result, for example, It is possible to stably ensure the uniformity of the shape characteristics and material characteristics of the hot thick steel plate by ensuring stable control accuracy of the jet cooling water amount and the conveyance speed so that the average temperature or the cooling rate is within the target range.

In addition, when controlling and cooling the thick steel plate 3 in the transport state, there are a method of controlling the jet cooling water amount with a constant transport speed and a method of controlling the transport speed with a constant jet cooling water amount. In order to realize controlled cooling, it is effective to control both the amount of jet cooling water and the conveyance speed. When the steel plate 3 is controlled and cooled in a non-conveyance state, only the amount of jet cooling water is controlled.
In the present invention, ultrasonic waves are incident / propagated from an ultrasonic sensor inside a steel material, and the propagation speed is measured to predict the steel material internal temperature distribution. Therefore, the application of the present invention has an internal temperature distribution prediction portion of at least 3 mm. This is particularly effective when a hot steel material having the above thickness and a temperature of 800 to 1000 ° C. is to be cooled.

Below, as shown in FIG. 2, this invention is demonstrated concretely based on the structural example of the control cooling apparatus of the hot thick steel plate which has arrange | positioned three cooling rows in the conveyance direction.
The control cooling device 1 basically includes a group of spray nozzles 5 that are connected to header pipes 6 arranged above and below the thick steel plate 3 and injects cooling water, and a cooling water supply control device from the spray nozzles 5 group. 11 and a control cooling device provided with a transport speed control device 12, sprayed on the upper surface side and the lower surface side with respect to the thick steel plate 3 in the cooling state, restrained between the restraining rolls 4 a and 4 b, respectively. Cooling water is jetted from the nozzle 5 group, the cooling water jet 5a is made to collide, and the thick steel plate 3 is controlled and cooled.

In this controlled cooling device 1, spray nozzles 5 are arranged on the upper surface side and the lower surface side of the thick steel plate 3 so as to cool the upper and lower surfaces of the thick steel plate 3, and simultaneously cool the upper surface side and the lower surface side. Yes, basically, the spray nozzles 5 group are arranged in the same manner as the upper surface side, and the cooling plate or the steel plate temperature (average temperature) or the cooling rate is in the target range (closer), respectively, The amount of cooling water injected for the next (subsequent) thick steel plate is controlled (in the case of the entire cooling train, the control of the conveyance speed is also taken into consideration).
However, since the behavior of the cooling water jet flow is different on the lower surface side and there is no cooling water flow like the cooling water on the plate like the upper surface side, the amount of injected cooling water on the lower surface side ensures a favorable cooling balance with the cooling on the upper surface side. Control is performed under separate conditions. Here, the cooling on the upper surface side will be mainly described.
The spray nozzle group 5 used here is a known flat nozzle, which is connected to the header pipe 6 in a plurality of units, and is arranged in a plurality of rows in the width direction and the transport direction of the thick steel plate 3 in each cooling row. Five groups are formed so that the cooling conditions can be changed in units of six header tubes. Here, the amount of injected cooling water can be changed at the center portion and both sides in the width direction of each cooling row unit and the thick steel plate 3. The conveyance speed is controlled in the entire cooling row.

  In this controlled cooling device 1, a water column ultrasonic sensor 8 is provided in front of the restraining roll 4b on the rear side of the intermediate cooling row, and the steel plate 3 being cooled or cooled by the water column ultrasonic sensor 8 is cooled. The ultrasonic wave is incident and propagated inside, the propagated ultrasonic wave is received and the propagation velocity is measured, and the measured value is input to the arithmetic unit 10, and the internal temperature distribution (thickness direction) of the measured value of the propagation velocity is calculated. (Temperature distribution) is calculated and predicted, and compared with the target steel plate internal temperature distribution range after cooling from this prediction result. If it is outside the target steel plate internal temperature distribution range, The amount of jet cooling water from the nozzle 5 group is controlled (corrected) via the cooling water supply control device 11 so as to achieve an appropriate cooling speed within the temperature distribution range, and the conveyance speed is controlled via the conveyance speed control device 12. Configure as you can There.

  In addition, the electromagnetic ultrasonic sensor 7 is disposed with a device that is always disposed in the vicinity of the thick steel plate 3 or is always in contact with the thick steel plate 3 between the front restraint roll 4a and the rear restraint roll 4b. This is arranged on the outer peripheral part of the restraining roll 4b on the rear side, makes ultrasonic waves enter and propagate inside the thick steel plate 3 during or after cooling, receives the propagated ultrasonic waves, measures the propagation velocity, and measures this measured value. Is input to the arithmetic unit 10 to calculate / predict the steel plate internal temperature distribution (thickness direction temperature distribution) from the measured value of the propagation speed, and from this prediction result, the cooling rate to obtain a preset target thick steel plate internal temperature distribution Thus, the jet cooling water amount from the nozzle 5 group is controlled (corrected) via the cooling water supply control device 11, and the transport speed is controlled via the transport speed control device 12.

The water column ultrasonic sensor 8 as an ultrasonic sensor used in the present invention is a jet flaw detector that makes ultrasonic waves from a probe incident and propagate through a laminar or jet water flow on a thick steel plate and receives the propagated ultrasonic waves. The principle of the method of measuring the internal temperature of the thick steel plate is as follows. As shown in FIG. 3, the ultrasonic wave is applied to the thick steel plate 3 under a plurality of oblique incidence conditions (for example, θ1 to θ4). Incidence and propagation of sound waves, ultrasonic propagation time (T1, T2, T3, T4) and distances X1, X2, X3, X4 between generation point and detection points 1, 2, 3, 4 are measured. Calculate the propagation velocity (m / sec) v1, v2, v3, v4 at the thicknesses d1, d2, d3, d4 of the thick steel plate 3 from the equation, and obtain the sound velocity distribution in the thickness direction of the thick steel plate based on the following equation. Can do.
Tj = Fj (v1, v2, v3, v4)
Xj = Gj (v1, v2, v3, v4)
Where j: detection points 1, 2, 3, 4
F: Relation between sound speed and temperature
G: Relational expression between sound velocity and propagation distance Based on the knowledge that this propagation velocity has a close correlation with the temperature (° C.) of the thick steel plate, this is applied to the measurement of the internal temperature (thickness direction temperature distribution) of the thick steel plate.
As described above, when using a method in which ultrasonic waves are incident and propagated on the thick steel plate 3 under a plurality of oblique incidence conditions (for example, θ1 to θ4), the internal temperature measurement of the thick steel plate is not indispensable. The surface temperature measuring device 13 is arranged near the position, the surface temperature of the thick steel plate 3 is measured, this measured value is processed by the signal processor 9 and input to the arithmetic device 10, and the propagation velocity (m / second) Reflecting (adding correction) to the internal temperature distribution of the thick steel plate 3 calculated from (2) is effective in predicting the internal temperature distribution of the thick steel plate with higher accuracy.

Further, as a method for easily predicting the internal temperature of the thick steel plate, ultrasonic waves are incident and propagated perpendicularly to the thick steel plate 3, and the average propagation inside the thick steel plate is determined from the ultrasonic propagation time and the thickness of the thick steel plate 3 measured in advance. There is a method of calculating the velocity and predicting the average temperature inside the thick steel plate from the average propagation velocity based on the relationship between the propagation velocity and the internal temperature of the thick steel plate. Especially when this method is used, the surface temperature measuring device 13 is arranged. Then, the surface temperature of the thick steel plate 3 is measured, and the internal temperature distribution of the thick steel plate 3 is set to 2 by using together the average temperature inside the thick steel plate measured by incident and propagating ultrasonic waves perpendicularly to this measured value. Predicting by quadratic curve approximation is effective.
When the surface temperature of the thick steel plate 3 is actually measured, it is preferable to carry out under the condition that cooling water, steam and scale are not interposed as much as possible between the thick steel plate and the temperature measuring device. For example, when actually measuring in the cooling water injection region, it is also considered to temporarily stop the injection of cooling water.
When the surface temperature is measured simultaneously with the internal temperature measurement of the thick steel plate by the water column ultrasonic sensor 8, the surface temperature measuring device 13 is used to prevent the surface temperature measurement accuracy from being deteriorated by the water flow of the water column ultrasonic sensor 8. It is desirable to install on the upstream side of the sonic sensor 8.

The electromagnetic ultrasonic sensor 7 is basically as disclosed in Patent Document 3, and in principle, ultrasonic waves are incident and propagated electromagnetically to the thick steel plate 3 and propagated. This is based on the principle of electromagnetic ultrasonic flaw detection method for receiving water, and the water column ultrasonic sensor 8 is different in ultrasonic transmission / reception method. Basically, the water column ultrasonic sensor 8 has almost the same contents, and the internal temperature distribution (thickness direction temperature distribution) of the thick steel plate 3 can be predicted with high accuracy in the same manner. The combined effect of the actual measured value of the surface temperature of the thick steel plate 3 by the surface temperature measuring device 13 is also the same as when the water column ultrasonic sensor 8 is used.
Since this electromagnetic ultrasonic sensor 7 can perform non-contact measurement and does not need to pass through a water column, the measurement accuracy does not deteriorate even when a fast-flowing cooling medium is present or a vapor film is present on the surface of a thick steel plate. It is effective for measurement during cooling and when the temperature of the steel plate surface is high. However, since it is necessary to place the sensor itself in the very vicinity of the steel plate 3, the sensor always in the vicinity of the steel plate is used here. It arrange | positions to the outer peripheral part of the restraint roll 4b of the rear part side which always contacts the apparatus which can be arrange | positioned, and the thick steel plate 3. FIG.

The water column ultrasonic sensor 8, electromagnetic ultrasonic sensor 7, and surface temperature measuring device 13 used in the present invention are selected and used in combination, and a plurality of temperature management positions in the width direction are used. Cooling conditions can also be controlled in the width direction.
Moreover, when there is a size change of the thick steel plate, it is necessary to change the arrangement position of the thick steel plate 3 in the width direction. Therefore, it is considered to be displaceable with respect to the surface of the thick steel plate 3 and to be displaceable symmetrically about the width center line in the width direction of the thick steel plate 3. In addition, it is considered that the spray nozzle group 5 can be similarly displaced.

In this example, the thickness variation in the thickness when the internal temperature measurement of the thick steel plate by the electromagnetic ultrasonic sensor and the water column ultrasonic sensor according to the present invention is used as an index and the surface temperature measurement value by the conventional optical thermometer is used as an index. This is a comparison of the fluctuation range of the stop temperature caused by this by numerical simulation.
Here, using a rolled steel sheet SM490 for welded structure with a thickness of 20 mm uniformly heated to 900 ° C. as a model, those with and without a 50 μm thickness were each cooled with water, and the surface temperature was used as an indicator of the end of cooling. The one using the internal average temperature was compared with the one using the internal average temperature. The comparison results are shown in Table 1.

As can be seen from Table 1, when scale exists on the surface, the temperature of only the scale layer with low thermal conductivity is lowered. A variation of about 100 ° C. occurs in the later thick steel plate temperature. However, when the cooling condition is determined using the internal average temperature as an index, the variation in the temperature of the thick steel plate after cooling is about 10 ° C.
This means that when the internal average temperature is used as an index compared to the case where the surface temperature is used as an index, the variation in the temperature of the thick steel plate after cooling is reduced. It shows the effectiveness of measuring temperature.

In addition, this invention is not limited to said content. For example, in the above example, the cooling target is described as a thick steel plate in a transport state, but the cooling target can be applied to other steel materials, and can be applied to a steel material in a non-transport state.
Also, types of ultrasonic sensors, surface temperature measuring devices, combinations thereof, arrangement conditions, cooling row arrangements, types of nozzles forming nozzle groups, structure, arrangement conditions, types of refrigerants such as cooling water, and injection conditions thereof Is within the range that satisfies the above claims, depending on the steel conditions (material, shape, size, temperature) to be cooled, the cooling conditions set in consideration of the shape characteristics and material characteristics required for the steel materials, etc. There are some changes.

The conceptual explanatory drawing which shows the example of arrangement | positioning of the hot rolling line which applies the control cooling apparatus of the hot thick steel plate of this invention. Side surface explanatory drawing which shows the structural example of the control cooling apparatus of the hot thick steel plate of this invention. The principle explanatory drawing of the incidence and propagation of the ultrasonic wave by the water column ultrasonic sensor used in the present invention and the prediction of the internal temperature distribution of the thick steel plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control cooling device 2 Hot finishing rolling mill 3 Thick steel plate 4a, 4b Restraining roll 5 Spray nozzle 5a Cooling water jet 6 Header pipe 7 Electromagnetic ultrasonic sensor 8 Water column ultrasonic sensor 9 Signal processor 10 Arithmetic control device 11 Cooling water supply Control device 12 Transport speed control device 13 Surface temperature measurement device

Claims (8)

  While cooling the steel with the jet refrigerant from the nozzle group, ultrasonic waves are incident and propagated inside the steel by an ultrasonic sensor, and the propagated ultrasonic waves are received and the internal temperature distribution of the steel from the relationship between the propagation speed and the steel temperature. A control cooling method for hot steel, characterized in that the amount of refrigerant injected is controlled based on the internal temperature (average temperature) of the steel obtained from this prediction result.   While the steel material is being cooled by the jet refrigerant from the nozzle group, the surface temperature of the steel material is measured, and ultrasonic waves are incident and propagated by the ultrasonic sensor inside the steel material. Predicting the steel internal temperature distribution from the relationship with the temperature, and controlling the amount of injected refrigerant based on the measured steel internal temperature (average temperature) and the steel surface temperature obtained from this prediction result Controlled cooling method for steel.   The cooling medium amount and the conveying speed are controlled based on the steel material internal temperature (average temperature) obtained from the prediction result of the steel material internal temperature distribution when cooling the steel material in the conveying state. The control cooling method of hot steel materials as described.   In a steel material cooling device equipped with a nozzle group for injecting refrigerant, a supply control means for the refrigerant injected from the nozzle group, and a conveyance speed control means, ultrasonic waves are incident and propagated inside the steel material being cooled, and received. Predicts the internal temperature distribution of the steel material from the relationship between the ultrasonic sensor and the ultrasonic wave propagation speed from the ultrasonic sensor and the steel material temperature, calculates the steel material internal temperature (average temperature), and controls the injection refrigerant amount and the conveyance speed. A control cooling device for hot steel, comprising an arithmetic control device.   Nozzle group for injecting refrigerant, supply control means for jetting refrigerant from this nozzle group, and steel material cooling device provided with transport speed control means, temperature measuring device for measuring steel surface temperature during cooling, and internal steel material Calculates the internal temperature (average temperature) of the steel material by predicting the ultrasonic wave velocity and the internal temperature distribution of the ultrasonic material that is incident / propagated to and received by the ultrasonic sensor. A control and cooling device for hot steel material, comprising: an arithmetic control device for calculating and controlling the amount of refrigerant injected and the conveying speed from the average temperature) and the measured value of the steel material surface temperature from the surface temperature measuring device.   The controlled cooling device for hot steel according to claim 4 or 5, wherein an electromagnetic ultrasonic sensor is used as the ultrasonic sensor.   The apparatus for controlling and cooling hot steel material according to claim 6, wherein an electromagnetic ultrasonic sensor is provided on an outer peripheral portion of the restraining roll when the steel material is restrained between the restraining rolls for cooling.   The controlled cooling device for hot steel materials according to claim 4 or 5, wherein a water column ultrasonic sensor is used as the ultrasonic sensor.

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