JP2007071551A - Ultrasonic snow sensor and snow melting device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic snow sensor suitable to be used for a snow melting device, capable of detecting fallen snow with high reliability by avoiding wrong detection caused by an influence of the quality of the fallen snow. <P>SOLUTION: In addition to the first snow determination means for determining that snow has fallen when a measuring distance becomes short, compared with a reference distance in the state of no snow, the second snow determination means for determining that snow has fallen when a measuring distance becomes long is adopted. In order to stabilize furthermore snow determination, a wave receiving filter means wherein a recognition lower limit of an ultrasonic received signal level is set and a low-level received signal is not taken into consideration is adopted. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an ultrasonic snow sensor for detecting snow on an outdoor parking lot, a roof, and the like, and a snow melting device using the same.

  Snowfall can be a problem in outdoor parking lots, roadways, sidewalks, gardens, and even roofs of buildings. Therefore, conventionally, a snow cover sensor that can automatically detect the presence or absence of snow has been proposed. There has also been proposed a snow melting device that uses a detection signal from a snow accumulation sensor to detect whether there is snow or not and automatically melts snow.

  By the way, as a conventional snow accumulation sensor, what detects snowfall using a water droplet sensor and a heater is known, for example as described in patent document 1 (Unexamined-Japanese-Patent No. 06-3462). In addition, as another snow accumulation sensor, for example, as described in Patent Document 2 (Japanese Patent Laid-Open No. 10-142352), one that detects snow accumulation using reflection of an ultrasonic snow accumulation surface is also known. .

  However, the former snow sensor with a water drop sensor cannot detect the degree of snow but also has many problems such as many malfunctions due to water drops and dust, and does not satisfy the performance required at a practical level. It was. In addition, the snow sensor by the latter ultrasonic sensor cannot detect the level of snow because it only determines the presence or absence of snow from the reception level of the ultrasonic wave reflected from the snow surface. Since the reception level of the ultrasonic wave greatly changes depending on the quality and the presence or absence of freezing, the error is large and practical application is difficult.

  In Patent Document 3 (Japanese Patent Laid-Open No. 09-269257), the distance from the reference position to the snow cover surface is obtained using ultrasonic waves reflected from the snow cover surface, so that not only the presence or absence of snow but also the snow cover depth. A snow depth gauge to detect is disclosed.

  However, when the present inventors have examined such a snow depth meter, the snow depth of the fresh snow, particularly in a powder snow state or a sleet snow state, may cause a malfunction because the detected snow depth is a negative value or a zero value. It became clear that there was. Such a malfunction is considered to be caused by the fact that the snow cover has a porous structure and absorbs sound, making it difficult to perform effective distance measurement. Moreover, with such a snow depth gauge, it is extremely difficult to detect that the surface is a thin ice layer such as road surface freezing. This is because the ultrasonic distance sensor generally has a measurement error of about 1 to 2 cm when measuring a distance of several meters, and it is difficult to detect an ice layer of about several millimeters.

Japanese Patent Laid-Open No. 06-3462 Japanese Patent Laid-Open No. 10-142352 JP 09-269257 A

  Here, the present invention has been made in the background as described above, and the problem to be solved is a novel structure capable of detecting snow accumulation in a parking lot, road, roof, etc. with high accuracy. It is to provide an ultrasonic snow cover sensor.

It is another object of the present invention to provide a snow melting apparatus having a novel structure using such an ultrasonic snow accumulation sensor.

  Hereinafter, embodiments of the present invention made to solve the above-described problems will be described. In addition, the component employ | adopted in each aspect as described below is employable by arbitrary combinations as much as possible. In addition, aspects or technical features of the present invention are not limited to those described below, but are based on the entire specification and drawings, or based on the inventive concept that can be grasped by those skilled in the art from these descriptions. It should be understood that

(The present invention relating to an ultrasonic snow sensor)
The feature of the present invention relating to the ultrasonic snow cover sensor is that it includes the following configurations (a) to (h).
(A) A transmitting means that is disposed to face and separate from the detection target surface of snow and that transmits ultrasonic waves toward the detection target surface;
(B) A wave receiving means that receives the reflected wave from the detection target surface of the ultrasonic wave that is disposed to face the detection target surface and is spaced apart upward.
(C) a calculation means for measuring a time from transmission of the ultrasonic wave by the wave transmission means to reception by the wave reception means, and obtaining measurement distance information of the propagation path of the ultrasonic wave from the obtained time measurement result;
(D) The measurement means obtains the measurement distance information of the propagation path of the ultrasonic wave between the transmission means and the reception means and the detection target surface in a state where there is no snow on the detection target surface. Reference value storage means for storing the obtained measurement distance information as reference distance information;
(E) first snow determination means for determining whether or not there is snow based on a difference between the measurement distance information and the reference distance information when the measurement distance information is smaller than the reference distance information;
(F) a receiving filter means for setting a lower limit level of the magnitude of the ultrasonic wave received by the receiving means so as not to consider receiving the ultrasonic wave having a magnitude equal to or lower than the lower limit level;
(G) A second snow cover judgment for judging that there is snow when the measured distance information is larger than the reference distance information because the received wave cannot be confirmed by the action of the wave receiving filter means. means,
(H) Output means for outputting the judgment result of the presence or absence of snow by the first and second snow accumulation judgment means

  In such an ultrasonic snow cover sensor structured according to the present invention, the first snow cover judging means and the second snow cover judging means judge the presence or absence of snow on different standards. That is, when the quality of the accumulated snow is tight or frozen (including those whose surface is solidified or rough snow), the reflectance of the ultrasonic waves is relatively high. Therefore, it is possible to detect the presence or absence of snow with sufficient accuracy by the first snow cover judging means. On the other hand, when the quality of the accumulated snow is sloppy or sherbet-like, or in the case of powdered snow, the reflectance of ultrasonic waves becomes small. In that case, the snow cover can be detected by the second snow cover judging means.

  In addition, in the present invention, since the wave receiving filter means is provided, when the reflectance of the ultrasonic wave is small, a malfunction due to the ultrasonic wave detected at a slight level is avoided, and the first and second It is possible to stably determine the presence or absence of snow by the snow determination means.

  Also, in the present invention, since the presence or absence of snow is determined based on distance information detected using ultrasonic waves, there is an error caused by dust or water droplets compared to a snow sensor using a conventional water droplet sensor. Operation is also prevented.

  Note that the measurement distance information and the reference distance information may be information related to the distance of the ultrasonic propagation path between the transmitting and receiving means and the detection target surface, and may be based on the ultrasonic propagation timing result. Information. That is, it may be a calculated value that can be directly recognized as distance information, but may be time information, for example. The measurement distance information and the reference distance information are information in the same unit so that they can be compared with each other.

  Further, in the present invention relating to such an ultrasonic snow sensor, when calculating the measurement distance information of the ultrasonic propagation path in the calculation means, correction is performed in consideration of changes in the ultrasonic propagation velocity due to the temperature. Is desirable.

  By the way, in the present invention relating to such an ultrasonic snow cover sensor, the following configuration can be suitably employed.

  That is, in the first snow cover judging means, the ON side operation value and the OFF side operation value as absolute values of the difference between the measurement distance information and the reference distance information are adopted as the determination reference values, respectively, and the ON side operation value Is set to be larger than the OFF-side operating value, and there is snow when the absolute value of the difference between the measured distance information and the reference distance information exceeds the ON-side operating value in a state where no snow is detected on the detection target surface. On the other hand, in the state where snow cover on the detection target surface is detected, it is determined that there is no snow cover when the absolute value of the difference between the measured distance information and the reference distance information falls below the OFF side operating value. Is preferably employed.

  By adopting the first snow accumulation determining means having such a configuration, it is possible to determine the presence or absence of snow by the first snow accumulation determining means with higher accuracy. The OFF-side operation value: H0 is preferably set to a value in the range of 0 cm <H0 <5 cm in consideration of a distance measurement error by the ultrasonic sensor. The ON side operation value: H1 is preferably set to a value in the range of 1 cm <H1 <10 cm in consideration of avoiding malfunction due to foreign matters such as fallen leaves.

  Furthermore, in the ultrasonic snow sensor according to the present invention, the measurement distance information obtained by the computing means based on the reception of ultrasonic waves larger than the lower limit level set in the receiving filter means, When the distance is larger than the reference distance information, it is desirable to provide a dead zone processing means that does not employ the obtained measurement distance information.

  By adopting such a dead zone processing means, it is possible to obtain a more stable determination result of the presence or absence of snow in the ultrasonic snow sensor. That is, for example, when there is little snow (for example, 1 cm to several centimeters) in a state where there is no snow, or when the snow is carried slightly from the place by the wind, the calculation means In some cases, the measurement distance information obtained by the above becomes larger than the reference distance information. This phenomenon is caused by the fact that the snow covered with powdered snow has a porous structure, so that the ultrasonic waves that enter it are reflected after passing through a large propagation path within the snow and are detected by the receiving means. It is thought to be caused by.

  Here, by adopting the dead zone processing means as described above, it is possible to avoid a decrease in reliability due to detection of measurement distance information larger than the reference distance information due to snow accumulation such as powder snow. It becomes possible.

  Preferably, in the dead zone processing means, an upper limit value of the delay time of the ultrasonic wave detected by the wave receiving means is set. That is, even when the upper limit value is reached, if the ultrasonic wave is still not detected by the wave receiving means, it can be determined that there is snow by the second snow accumulation determining means, as the wave reception has not been confirmed. . As a result, it is not necessary to wait for the detection of the ultrasonic wave by the wave receiving means at any time, and early determination is possible, and adverse effects due to external noise and the like can be avoided as much as possible.

  As such an upper limit value, for example, an upper limit distance in the atmosphere that can be measured by ultrasonic waves or a value close thereto is suitably employed. In addition, in this dead zone processing means, when the measurement distance information is not adopted, the judgment result of the presence / absence of snow is the result of the previous judgment (for example, the one judged effectively by the first or second snow accumulation judgment means). It is desirable that the immediately preceding determination result is maintained.

(The present invention relating to a snow melting device)
The feature of the present invention relating to the snow melting device is that it includes the following configurations (i) to (k).
(I) a heating means for heating the surface to be detected;
(J) an ultrasonic snow sensor constructed according to the present invention as described above;
(K) Heating operation control means for controlling the heating operation in the heating means based on the determination result of the presence / absence of snow output from the ultrasonic snow sensor.

  In such a snow melting device constructed according to the present invention, the operation of the heating means is controlled according to the result of the snow accumulation determination by the above-described ultrasonic snow accumulation sensor capable of detecting snow accumulation with high accuracy and stability. The snow melting operation can be efficiently performed for the presence or absence of snow. As a result, it is possible to quickly eliminate snow accumulation and prevent problems caused by snow accumulation, and to avoid useless operation of the snow melting device in the absence of snow accumulation, thereby realizing energy saving.

  As the heating means, for example, an electric heater is disposed directly below the detection target surface, and a water pipe is laid below the detection target surface, and heating means such as oil, gas, or electricity is used. Any configuration that allows the obtained warm water to flow therethrough can be employed.

  The operation mode of the snow melting device is not particularly limited. For example, when snow is detected, the operation is performed for a predetermined time set in advance, or the operation is performed until it is determined that the snow has disappeared. Any aspect can be adopted.

  Further, when water is passed through the water pipe, it is desirable to circulate the water at least during the daytime even in a situation where the heating means is not operated. Cover and make the temperature rise due to the solar heat of the water in the water flow pipes arranged in the sun to the shaded area, and make the snow melting state uniform throughout the water pipe installation area Etc. are possible. As a result, snow melting unevenness can be reduced.

  By the way, in this invention regarding such a snow melting apparatus, the following structure can be employ | adopted suitably.

  That is, in the heating operation control means, a freezing detection mode is provided in which the heating means is operated to heat the detection target surface even under a situation where it is determined that there is no snow by the ultrasonic snow accumulation sensor, Based on the determination of the presence or absence of snow by the second snow accumulation determination means during operation of the freeze detection mode, the presence or absence of freezing of the detection target surface is determined, and the determination result of the presence or absence of such freezing is output by the output means. In addition, in the heating operation control means, a configuration in which the heating means is heated based on the determination result of the presence of freezing by the output means so as to eliminate the freezing of the detection target surface is preferably used. Adopted.

  By adopting such a freeze detection mode, etc., even if a frozen layer that is so thin as to be difficult to detect by the first and second snow cover judging means is generated on the detection target surface, the presence or absence of such freezing Can be detected effectively. Then, it is possible to detect the occurrence of freezing and quickly eliminate the freezing.

  However, as a result of many experiments, researches, and examinations by the present inventor, when there is freezing on the road surface or the like, water vapor can be generated by heating the road surface with a heating means. Then, by generating water vapor in the area where the ultrasonic snow cover sensor is installed, a phenomenon like disturbance occurs with respect to the ultrasonic wave transmitted there. As a result, the ultrasonic waves are in a state of irregular reflection or scattering on the path, and it is impossible to receive a sufficiently large ultrasonic wave. Therefore, as described above, based on the fact that the second snow accumulation judging means cannot confirm the reception of the wave by the action of the wave receiving filter means, the second snow accumulation judging means judges that there is snow.

  The determination result with snow that is output in such a situation can be determined as a freeze detection signal. That is, before heating the surface to be detected by the heating means, the result of determining that there is no snow is being output, and as a result of heating the surface to be detected by the heating means, the determination result is that there is snow. Under the changed situation, the determination result of the presence of snow indicates that the detection target surface is frozen.

  And based on this determination result, it becomes possible to cancel freezing of a detection object surface by operating a heating means.

  In particular, in this embodiment, a temperature sensor for detecting the outside air temperature is provided, and a heating means capable of heating to a temperature 30 degrees or more higher than the outside air temperature, preferably 40 degrees to 50 degrees higher is preferable. It has been confirmed by the present inventor that steam is more efficiently generated from the detection target surface by setting such a temperature difference from the outside air temperature in the heating means. Specifically, in the type of heating device that passes hot water through the buried pipeline, the second snow judgment means detects the frozen state when freezing occurs by passing hot water that is 40 ° C higher than the outside air temperature. It is possible to produce a sufficient amount of steam.

  In the present invention, it is necessary to operate the heating means even under a situation where snow is not detected due to some trigger. The trigger for such operation is not particularly limited, and for example, it is conceivable to operate the heating means at a preset time or time interval, or to operate when the outside air temperature becomes a predetermined value or less.

  Furthermore, in the snow melting apparatus having the structure according to the present invention, the following modes can be suitably employed. That is, the determination result output by the output unit of the ultrasonic snow sensor is that there is snow and the determination is performed under the condition that the heating operation of the heating unit is performed by the heating operation control unit. An off-delay that performs an off-delay operation by continuing the heating operation of the heating means by the heating control means for a predetermined off-delay time set in advance when the result reaches a judgment result of no snow accumulation In addition to providing an operating means, a signal with snowfall continues as the judgment result again for a predetermined time only during a preset monitoring time from the time when the judgment result reaches the judgment result without snowfall. An off-delay count monitoring means is provided for monitoring whether or not a signal with a snow cover is again transmitted for a predetermined time by the off-delay count monitoring means. If the result of the determination is not confirmed, the time point when the determination result reaches the determination result indicating that there is no snow is used as the start point for counting the duration of the off-delay operation in the off-delay operation means. If the count monitoring means again confirms that there is a snow cover signal over a predetermined time, the off-delay operation in the off-delay operation means is canceled and the heating means by the heating operation control means The aspect which returned to the said heating operation | movement of is suitably employ | adopted.

  According to such an aspect, complete snow melting can be realized by continuing the heating operation for a predetermined time even after it is determined that the snow has melted by the off-delay operating means. In particular, when a heating means for passing warm water is adopted, it is possible to achieve complete snow melting by efficiently using warm water energy. The time for the off-delay operation can be set appropriately, and can be set and changed within an appropriate range such as 30 minutes to 6 hours.

  In addition, in this aspect, by adopting the off-delay count monitoring means, snow is melted under the snowfall condition, and snow melting is performed faster than snow accumulation. Is repeated at short time intervals, it can be avoided that the heating means is repeatedly turned on and off, resulting in an unstable operation state. For example, about 1 minute is preferably used as the time reference (predetermined time value) at which it is determined by the off-delay count monitoring means that the snowy signal has been continuously confirmed again. The value of can also be set appropriately according to the snowfall condition, environment, and the like.

Even when it is determined that there is snow by the output means of the ultrasonic snow sensor from the state where there is no snow, for a similar purpose, a predetermined on-delay time is set rather than immediately turning on the heating means. The heating means may be turned ON on condition that it is determined that there is still snow even after the on-delay time has elapsed. As described above, even when the heating means is turned ON, for example, by setting an on-delay time of 1 minute or the like, it is sensitive to useless operation of the heating means due to erroneous detection of snow accumulation or snowfall to the extent that natural snow melts. It is possible to prevent the heating means from operating wastefully in response to the above. Of course, such setting of the on-delay time is not essential in the present invention.

  As is clear from the above description, in the ultrasonic snow cover sensor structured according to the present invention, the first and second snow cover judging means determine the presence or absence of snow on the basis of different criteria, so that the state of snow cover Regardless of this, the presence or absence of snow can be determined stably with high accuracy.

Further, in the snow melting device having the structure according to the present invention using such an ultrasonic snow accumulation sensor, it is possible to realize an energy saving and efficient snow melting operation by detecting the snow accumulation with high accuracy and melting the snow.

  In order to clarify the present invention more specifically, embodiments of the present invention will be described in detail with reference to the drawings.

  First, FIG. 1 shows an overall schematic structure of a snow melting device 10 as an embodiment of the present invention. The snow melting device 10 is configured by using an ultrasonic snow accumulation sensor 12 as one embodiment of the present invention. That is, the snow melting device 10 is an equipment of an outdoor parking lot road surface 14 as a snow detection target surface, an ultrasonic snow sensor 12 for detecting the presence or absence of snow on the road surface 14, and avoiding snow on the road surface 14. Or it comprises the warm water type heater 16 as a heating means to eliminate.

  More specifically, the ultrasonic snow sensor 12 is an ultrasonic transmitter / receiver composed of a transmitter as a transmitter for transmitting ultrasonic waves and a receiver as a receiver for receiving ultrasonic waves. 18 is provided. And the ultrasonic transmitter / receiver 18 is attached to the tip of the support pole 20 fixedly standing at an appropriate place in the outdoor parking lot. As the transmitter and receiver, those having directivity are employed, both of which are separated from each other in the substantially vertical direction and are directly opposed to each other.

  Thereby, in the ultrasonic transmitter / receiver 18, the ultrasonic wave transmitted from the transmitter is reflected by the road surface 14, sent back to the receiver, and detected by the receiver. In order to adjust the reflection efficiency of ultrasonic waves, the ease of snow accumulation, etc., a snow plate such as a stainless plate having high thermal conductivity may be installed at the ultrasonic wave reflection portion on the road surface 14.

  Note that the transmitter of the ultrasonic transmitter / receiver 18 according to the present embodiment is operated by a high-frequency driving voltage and transmits ultrasonic waves in a burst (front) within a predetermined viewing angle (downward). Is for receiving ultrasonic waves arriving at a predetermined viewing angle in the front (downward) and converting them into corresponding high-frequency electrical signals. In the present invention, ultrasonic transmitters and receivers having various known configurations are employed. obtain. For example, a transmitter and a receiver may be integrated as a transmitter / receiver by concentrically arranging or juxtaposing them, or a transmitter / receiver having both functions of a transmitter and a receiver. It is also possible to automatically switch the function using an overvoltage protection circuit or the like by using a detector, or switch the function at a cycle twice the sampling frequency. In addition, when adopting separate transmitters and receivers, it is desirable that the separation distance (installation height: H) from the road surface 14 is made uniform to have the same reference height. And the receiver may be installed at different heights.

  Such an ultrasonic transmitter / receiver 18 is connected to the processing device 22 and is operated by the processing device 22. A block diagram showing the overall configuration of the ultrasonic snow sensor 12 including the processing device 22 is shown in FIG.

  As shown in FIG. 2, the transmission system in the processing device 22 shown in FIG. 1 includes an oscillation drive circuit 24 that oscillates at a high frequency to generate ultrasonic waves to be transmitted. The high frequency signal obtained by the circuit 24 is amplified by the booster circuit 26 and supplied to the ultrasonic transmitter / receiver 18, thereby driving the transmitter of the ultrasonic transmitter / receiver 18 and sending out the ultrasonic wave.

  On the other hand, the reception system of the processing device 22 first passes the high-frequency signal received by the receiver of the ultrasonic transmitter / receiver 18 through the overvoltage protection circuit 28 to obtain a voltage-adjusted high-frequency signal. The overvoltage protection circuit 28 is not essential in the present invention. Further, after the high frequency signal is amplified and detected by the receiving circuit 30, it is passed through a reception level filter circuit 32 comprising a voltage comparator or the like, and only a high frequency signal having a signal level of a predetermined magnitude or more is taken out. A received wave input to the arithmetic processing unit 34 is obtained. In such a receiving system, frequency filter means or the like may be employed in order to remove noise from the obtained signal.

  The processing device 22 controls the operation of the above-described transmission system and reception system, and the time until the ultrasonic wave transmitted by the transmitter is reflected by the road surface 14 and detected by the receiver. Further, an arithmetic processing unit (CPU) 34 is provided as arithmetic means for obtaining the ultrasonic transmission path length from the obtained count time value: T with reference to a known ultrasonic propagation velocity. Yes. That is, the arithmetic processing unit 34 obtains a separation distance (installation height: H) between the ultrasonic transmitter / receiver 18 and the road surface 14 in accordance with a known lower formula.

H (m) = T (seconds) / 2 × V (m / second)
V is the propagation speed of ultrasonic waves in the air.

In this embodiment, the installation height of the transmitter and the receiver is the same: H (m). For example, the separation distance between the transmitter and the detection target surface: H ₁ and the receiver And the separation distance of the detection target surface: H ₂ is different from each other, the total value of the separation distances: H ₁ + H ₂ is used for calculation. Such H ₁ + H ₂ is the ultrasonic transmission path length from when the ultrasonic wave is transmitted from the wave transmitting means to the detection target surface and when the reflected wave from the ultrasonic detection target surface is received by the wave receiving means. Yes, if the transmission time of the ultrasonic wave in such a transmission path is T (seconds) and the propagation speed of the ultrasonic wave is V (m / second), the above calculation formula is as follows.
H ₁ + H ₂ (m) = T (second) · V (m / second)

Note that the value of the ultrasonic velocity V in the above equation changes as shown in the following equation depending on the temperature of the air serving as the medium: t.
V (m / sec) = 340 + 0.6t
Therefore, in this embodiment, for example, an outside air temperature measuring device 36 configured by a temperature sensor such as a thermistor is provided, and the value of the ultrasonic velocity: V is changed and set according to the value of the outside air temperature: t. It has become. As a result, temperature correction is performed on an arithmetic expression of installation height: H in the arithmetic processing unit 34.

  That is, in such an ultrasonic snow cover sensor 12, as shown in FIG. 4, the counted time value T and the outside air temperature detected by the ultrasonic handset 18 in a situation where there is no snow on the road surface 14. Based on the outside air temperature: t detected by the measuring instrument 36, the arithmetic processing unit 34 detects the installation height H of the ultrasonic transmitter / receiver 18 with respect to the road surface 14. This is stored as reference distance (teaching data) as reference distance information in the arithmetic processing unit 34 as reference value storage means. The storage element of the arithmetic processing unit 34 is constituted by a built-in RAM or the like, but an appropriate storage medium may be provided outside the arithmetic processing unit 34 as reference value storage means. The teaching data storage process (teaching) is performed by operating a teaching unit 35 connected to the arithmetic processing unit 34. Accordingly, the reference distance can be updated by operating the teaching unit 35 when, for example, replacing the ultrasonic handset 18 or changing the installation height. Further, when the reference value storage element is composed of RAM, the record is erased every time the ultrasonic snow sensor 12 (arithmetic processing unit 34) is turned off. Will be. However, it is also possible to keep the memory of the reference distance by continuing to energize the memory element by using a built-in battery or the like.

  On the other hand, as shown in FIG. 5, when there is snow with a height of h on the road surface 14, the ultrasonic waves sent from the transmitter toward the road surface 14 are reflected by the snow surface 48. It will be detected by returning to the receiver. Therefore, in this case, the installation height: Hh of the ultrasonic transmitter / receiver 18 with respect to the snow surface 48 instead of the road surface 14 is detected. This is a measurement distance as measurement distance information.

  Further, although not specifically shown in the drawing, the arithmetic processing unit 34 includes a digital sampling filter. The digital sampling filter is a known digital filter, and controls the frequency when collecting a discrete signal from a received wave input obtained by a receiving system of the processing device 22. Thereby, for example, a high-frequency signal or the like due to disturbance such as electromagnetic noise or noise noise is cut so that it is not used in the calculation of the measurement distance by the arithmetic processing unit 34. The arithmetic processing unit 34 obtains the measurement distance based on the received wave input obtained through the digital sampling filter. Then, the comparison means provided additionally calculates and determines whether or not the measurement distance obtained as a result of the calculation processing is smaller than the reference distance.

  Note that in the ultrasonic handset 18 of the present embodiment, ultrasonic waves of 10 to 100 kHz, which is a relatively low frequency region among ultrasonic waves, and more preferably, ultrasonic waves of about 40 kHz are employed. Further, the booster circuit 26 boosts the voltage as high as possible within a range that the transmitter can withstand, and feeds the high-frequency signal to the transmitter. As a result, the ultrasonic transmitter / receiver 18 is installed at a ground height of several meters or more (for example, about 5 m) while suppressing measurement errors of several centimeters or less (particularly about ± 1 cm when ultrasonic waves of 40 kHz are employed). It is possible to do.

  The processing device 22 is connected to a power source 38 such as a household 100V power source to obtain operating power, and is equipped with a remote control type operation panel 40. For example, an operation panel in a house is provided. 40 can be installed. The operation panel 40 is provided with, for example, a manual operation switch, an operation monitor lamp using an LED, and the like as necessary, in addition to ON / OFF of operation.

  On the other hand, water pipes 42 are embedded at appropriate intervals on the road surface 14 of the outdoor parking lot. Such water pipes 42 are arranged at substantially uniform intervals over substantially the entire area of the road surface 14 to be melted by being meandered appropriately.

  A kerosene-type water heater 44 is connected to the water pipe 42, and both ends of the water pipe 42 are connected to the outlet and return hot water outlet of the water heater 44, thereby The hot water heated by the vessel 44 can be circulated through the water pipe 42. In addition, the water pipe 42 can be configured by a plurality of divided pipes with an appropriate length in consideration of the size of the laying region and the like. In this embodiment, it is comprised from four independent division | segmentation pipe lines 42a, 42b, 42c, and 42d. In this way, by adopting the divided pipe structure, the length of each water pipe 42 can be set short, the temperature drop due to the hot water flow can be suppressed, and the response to the accident etc. and the maintenance become easy. .

  As is clear from this, in this embodiment, a hot water heater (load heating) 16 as a heating means is configured by a circulation pump (not shown) including the water pipe 42 and the water heater 44. ing. Further, the load heating 16 includes a temperature controller as a heating operation control means (not shown). And the warm water of the set temperature can be circulated at the set flow rate. The flow rate adjustment of the circulating water is performed manually by a valve, but may be automatically performed using a circulating hot water controller.

  By circulating the warm water through the water pipe 42 in this way, the road surface 14 is warmed, so that the snow on the road surface 14 can be melted.

  In particular, in this embodiment, the circulation pump can operate independently of the water heater 44. Thereby, even if it is a cold water state, the inside of the water flow pipe 42 can be circulated through. By circulating the cold water through the water pipe 42 in this way, not only can the freezing of the enclosed water be prevented, but, for example, during the daytime, the temperature rise in the part irradiated with sunlight is spread over the entire road surface 14. It is also possible to achieve a uniform temperature increase over the entire road surface 14 by dispersing. Thereby, snow melting by solar heat in the daytime is promoted, and it is also possible to avoid partial snow accumulation during daytime snowmelt on the road surface 14, for example. Note that an antifreeze liquid is preferably used as the enclosed water that is circulated through the load heating 16.

  The operation of the snow melting apparatus 10 having the above-described structure is shown in a block diagram in FIG. That is, first, the teaching operation as described above is performed in a state where there is no snow, and the reference distance: H is stored. Under such circumstances, ultrasonic transmission (ultrasonic transmission processing) and reception (ultrasonic reception processing) of ultrasonic waves are performed in the ultrasonic handset 18 of the ultrasonic snow sensor 12. The transmission and reception may be performed, for example, by a single pulse-like execution value, but transmission and reception are performed sequentially over a plurality of times to determine the majority theory or average. The result value of the distance calculation may be determined by value theory or the like.

  Then, based on the received wave input obtained by the ultrasonic transmitter / receiver 18, the arithmetic processing unit 34 performs distance calculation while considering correction of the outside air temperature obtained by the outside air temperature measuring device 36, and the above-described measurement distance is obtained. Ask for.

  By comparing the measurement distance obtained in this way with a reference distance: H obtained in advance by teaching, the presence or absence of snow on the road surface 14 is determined, and the result is output. Based on the output result, the operation of the road heating 16 is controlled. For example, when it is determined that there is snow, the semiconductor switch 46 is turned on and the load heating operation is started. Hot water is circulated through 42 to start or continue the snow melting operation. In addition, although the specific aspect of this snow melting operation | movement is not limited, For example, in addition to performing circulating water flow of warm water over the preset predetermined time, there is no snow accumulation by the above-mentioned ultrasonic snow accumulation sensor 12 You may carry out continuously until it determines with. As is clear from the above description, the output means for outputting the determination result of the presence or absence of snow is configured including the arithmetic processing unit 34.

  Particularly preferably, the ON-side operation value and the OFF-side operation value are set for the snow cover height: h obtained from the difference between the measurement distance and the reference distance. At that time, for example, snow height: h1 as the ON side operation value: h1, snow height: h2 as the OFF side operation value, and h1> h2. The specific values of h1 and h2 are set in consideration of the wavelength of the ultrasonic wave to be used, the calculation processing accuracy of the sensor, and the like. Preferably, the value of h1 to h2 is in the range of 1 to 5 cm. And 0 <h2 ≦ 10 cm.

  And when the snowfall is detected when the measurement distance is substantially equal to the reference distance and the measurement is continued under the condition that there is no snowfall, when the snowfall height: h is h ≧ h1, An ON signal is output to the semiconductor switch 46, the operation of the snow melting device 10 is started, and hot water is circulated through the water conduit 42 to start the snow melting operation.

  On the other hand, when the measurement distance is smaller than the reference distance and there is snow, and the snow is not substantially detected when measurement is continued under the condition where the snow melting device 10 is operating, the snow height: h is When h ≦ h2, an OFF signal is output to the semiconductor switch 46, the snow melting device 10 is stopped, and heating by the water heater 44 for circulating water through the water pipe 42 is stopped.

  Here, the ultrasonic snow sensor 12 in this embodiment is specially equipped with (I) a configuration that avoids malfunction due to a difference in accumulated snow quality, and (II) a configuration that detects freezing of the road surface 14. Has been.

  That is, as shown in FIG. 5 described above, when there is snow with a height of h, since the ultrasonic reflection surface becomes the snow surface 48, the measurement distance is considered to be Hh. It is done. However, as a result of examination by the present inventor, it has been found that the measurement distance error by the ultrasonic snow sensor 12 is very large depending on the quality of the accumulated snow. As a result of further investigation, in the case of a rough snow or a snow solidified on the surface, the reflectance of the ultrasonic wave on the snow surface 48 is high as shown in FIG. Therefore, the measurement distance can be detected relatively accurately, and the presence or absence of snow can be easily determined.

  In short, when determining the snow cover, it is determined whether the measurement distance is the same or smaller than the reference distance. If the measurement distance and the reference distance are substantially the same, there is no snow, and the measurement distance is greater than the reference distance. If it is small, the presence or absence of snow is determined based on the criterion that there is snow. As is apparent from this, the snow accumulation determining step is the first snow accumulation determining means.

  However, for example, in the case of snow accumulation in a sleet snow state or the like, as shown in FIG. 6, it becomes porous to the surface, which acts like a sound absorbing material, and the irradiated ultrasonic waves are converted into snow. It was found that the light was absorbed or diffusely reflected by the surface 48 and dispersed, resulting in a very low reflection efficiency. For this reason, the ultrasonic wave reflected by the snow surface 48 cannot be stably captured by the receiver, and as a result, the problem that the reliability of determining the presence or absence of snow becomes very low has been found. It was.

  Therefore, in the present embodiment, the above-described received wave level filter circuit 32 is provided in the ultrasonic wave receiving system so that the presence or absence of snow can be determined with high reliability even in the case of snow accumulation in the sleet snow state. At the same time, a new criterion was adopted as a criterion for determining the presence or absence of snow based on the calculation result of the arithmetic processing unit 34. The reference is the second snow cover judging means for determining whether or not the measurement distance is substantially larger than the reference distance. If the measurement distance is substantially the same as the reference distance, there is no snow. The presence / absence of snow is determined on the basis that snow is present if the measurement distance is greater than the reference distance.

  In snow cover such as sleet and sleet snow, the level of ultrasonic waves reflected by the snow surface 48 and received by the receiver is low, but it is not always a constant low level, and the fluctuation is large. Accordingly, since the ultrasonic snow sensor 12 of the present embodiment includes the reception level filter circuit 32, even if there is a certain reception level, it is set in the reception level filter circuit 32. When the value falls below the lower limit level, it is prevented from being intercepted by the received wave level filter circuit 32 and used for calculation of the measurement distance by the arithmetic processing unit 34.

  As a result, when the level of the received signal is further smaller than a preset lower limit level, the time until the ultrasonic wave transmitted by the transmitter is reflected by the road surface 14 and detected by the receiver. Count value: T becomes larger than the reference state shown in FIG. As a result, it is recognized that the measurement distance obtained by the arithmetic processing unit 34 exceeds the reference distance. As is clear from this, the reception filter means includes the reception level filter circuit 32. Further, the measurement distance and the reference distance are compared by comparing the reference distance stored in the RAM provided in the arithmetic processing unit 34 and the measurement distance obtained based on the arithmetic processing according to the program stored in the RAM. This can be performed by performing a comparison operation in a comparison process according to a program stored in the RAM. Of course, the arithmetic means realized by software by such a program can also be configured by hardware.

  Therefore, in the snow cover determination process, even if the measurement distance by the first snow cover determination unit is not smaller than the reference distance, if the measurement distance by the second snow cover determination unit becomes larger than the reference distance, It will be determined that there is. As a result, it is possible to detect snow accumulation such as sleet snow, and the snow melting operation as described above is performed even when snow accumulation is detected by the second snow accumulation determining means.

  Furthermore, in the present embodiment, it is possible to determine whether or not the road surface 14 is frozen by using the above-described snow cover determination process, particularly by using the determination process by the second snow cover determination means. .

  That is, when the thin frozen layer 50 is formed on the road surface 14, the frozen layer 50 is substantially impossible to detect with the snow cover height: h by the first snow cover judging means. In layer 50, there is no surface sound absorption, and detection at the received wave level by the second snow accumulation judging means is substantially impossible.

  Therefore, in the present embodiment, a freeze determination mode is set as a freeze detection mode using the snow melting device 10 and the second snow accumulation determination means so that the frozen layer 50 can also be determined with sufficient reliability.

  Specifically, in this freezing determination mode, the load heating operation of the hot water heater 16 is intentionally started under the condition that no snow cover is detected by any of the first and second snow cover determination means. Warm water is circulated through the water pipe 42 and the heating operation is started. The starting condition for the heating operation is not particularly limited, and may be a predetermined time or a preset time, or when the outside air temperature measured by the outside air temperature measuring device 36 is below freezing point. It may be.

  If the frozen layer 50 does not exist on the road surface 14, even if the load heating operation is performed, the measurement distance is maintained at a value substantially equal to the reference distance and does not change in consideration of necessary temperature correction. .

  On the other hand, when the frozen layer 50 exists on the road surface 14, as shown in FIG. 7, the road surface 14 is heated by the hot water flowing through the water pipe 42 embedded in the road surface 14 and frozen. Layer 50 melts. In particular, when it is heated to a temperature sufficiently higher than the outside air temperature, a considerable amount of steam is generated from the road surface 14 and diffuses into the atmosphere. As a result, a state such as disturbance or scattering occurs in the ultrasonic wave propagation path in the ultrasonic snow cover sensor 12, and the ultrasonic wave reception level by the wave receiver is greatly reduced.

  Accordingly, the reception level of the ultrasonic wave by the receiver is lowered, and the second snow accumulation judging means outputs a judgment result that there is snow. This is the determination result of the existence of the frozen layer 50.

  When it is determined that the frozen layer 50 is present in this way, an ON signal is output to the semiconductor switch 46, the operation of the snow melting device 10 is continued, and hot water is circulated through the water conduit 42 to freeze. The elimination of the layer 50 is performed. In this case, as described above or by the on-delay operation shown in FIG. 8, an appropriate time (1 minute in FIG. 8) set in advance from the time when it is determined that the frozen layer 50 (or snow cover) is present. For example, an on-delay operation in which the semiconductor switch 46 is turned on after being delayed by a certain amount may be employed.

  Therefore, in the snow melting device 10 according to the present embodiment as described above, snow can be detected with high reliability and high accuracy regardless of the quality of the accumulated snow. Moreover, even if there is a frozen layer 50 that could not be detected by a conventional snow cover sensor, it can be detected with sufficient accuracy by skillfully utilizing the structure of the snow cover sensor without adding a special device. It becomes.

  Further, in the present embodiment, even if the reception level due to disturbance such as noise noise and electromagnetic noise is recognized by the reception circuit 30 and the reception level filter circuit 32 via the receiver, it is calculated. By passing through the digital sampling filter of the device 34, it is removed based on the frequency filter function and is not used for the calculation of the measurement distance. As a result, the measurement distance based on the predetermined reception level is stably obtained, and the snow accumulation determination by the first and second snow accumulation determination means is performed stably.

  Further, in the present embodiment, the first snow cover judging means judges the presence or absence of snow based on the measured distance obtained by averaging the measured distances obtained a plurality of times. As a result, even when the snow surface 48 is undulated due to, for example, walking or puddles, variations in measurement distance are suppressed, and it is possible to efficiently determine the presence or absence of snow on the detection target surface. Note that, instead of averaging a plurality of measurement distances set in advance, averaging of a plurality of measurement distances over a predetermined time may be employed.

  In particular, in this embodiment, the value of the distance (measurement distance) obtained from the time signal transmitted by the transmitter and received by the receiver is the reference height (reference distance) without snow. ): If it is larger than H, it is as described above that the second snow accumulation judging means for judging that there is snow in a sleet state as having not been received, but in addition, As shown in FIG. 9, a dead zone region that does not reflect the measurement result in the specific measurement distance region (ignoring it without adopting it) is set.

  That is, even when the ultrasonic wave signal of a predetermined level or higher can be confirmed by the receiver through the reception level filter circuit 32, the measurement distance by the calculation result exceeds the reference distance. Would be strange in theory. However, such a detection result occurs in fact. The reason for this is thought to be due to the action of increasing the transmission path of ultrasonic waves in the snow covered with a porous structure such as powder snow, as described in the section of “Means for Solving the Problems” described above. However, if such a measurement distance is obtained, for example, it may be determined that there is snow, but in this embodiment, the measurement result itself is not adopted, and the control of the heating means is The control state based on the previous measurement results was maintained.

  As a result, unstable snow detection due to powder snow, for example, frequent ON / OFF operation (chattering) of the heating means due to temporary snow accumulation due to snow accumulation, etc. can be avoided, and the operation can be stabilized. Become.

  In the present embodiment, the detection by the receiver is set to continuously monitor the time until the measurement distance reaches the predetermined distance: H ′ beyond the time when the measurement distance becomes the reference distance. is doing. In other words, when the time corresponding to the predetermined distance: H ′ is reached from the transmission by the transmitter, the waiting for reception by the receiver is set to be stopped. As a result, an unstable operation that waits for detection of a received wave at any time is avoided.

  Note that the value of H ′ is set to a value that substantially corresponds to a measurable distance according to the intensity and frequency of the ultrasonic wave to be employed. Specifically, for example, when a general 40 kHz ultrasonic transmitter / receiver for distance measurement is employed, H ′ = 5 m, H = 2 m, and the like are set. In this case, the dead zone distance: H′−H = α = 3 m. If the dead zone distance is about this level, it has been confirmed that it is only about 1 cm of snow in terms of powder snow.

  If the ultrasonic wave is not detected by the receiver even after a time corresponding to the time H ′, it is determined that there is snow by the second snow cover judgment as described above.

  In short, by adopting such a snow cover determination process that employs the dead zone, when the measurement distance is in the non-detection area: α, the arithmetic processing unit 34 does not output the determination result of the presence or absence of snow. The road heating operation is controlled based on the output result of the distance measured last time, and the previous snow melting operation ON / OFF state is continued.

  Thereby, for example, even when soft snow is piled up on the hard snow piled up on the road surface 14 and the measurement distance smaller than the reference distance H is equal to or larger than the reference distance H. Therefore, it is determined that there is no snow immediately, and it is determined that there is snow based on the detection result of the hard snow before the soft snow is accumulated, thereby preventing erroneous determination of no snow. In addition, for example, small snow flickering on the road surface 14 melts faster than snow newly accumulated due to residual heat on the road surface 14 or road heating, and the measurement distance is equal to or larger than the reference distance or less than the reference distance. Is repeated often, until the measurement distance exceeds the non-detection region: α, the determination of snow accumulation based on the measurement distance measured last time is continued. The so-called chattering phenomenon that is frequently switched and input is prevented. Therefore, snow accumulation on the road surface 14 can be reliably detected, and an energy-saving and efficient snow melting operation can be realized.

  Furthermore, in this embodiment, as shown in FIG. 8 described above, an off-delay operation means is employed. This off-delay operation means continues the heating operation for a predetermined time when the snow accumulation signal changes from the presence state to the absence state, that is, after the snow melting is completed.

  Therefore, in this embodiment, off-delay count monitoring means is also employed. As shown in FIG. 8, the off-delay count monitoring means sets a predetermined monitoring time such as 1 minute, and the snow cover continues for a predetermined time (eg 1 minute) again during the monitoring time. It monitors whether a presence signal has been detected again.

  If it is determined that there is a continued snowfall during the monitoring time, the timing of the off-delay operation is canceled. That is, the off-delay operation started when it is determined that there is no snow accumulation is stopped, and the warming operation for normal snow melting is resumed. Thereafter, when it is determined that there is no snow accumulation again, the off-delay operation is started from that point. Of course, the off-delay count monitoring means is also started together with the start of the off-delay operation.

  By adopting such an off-delay operation and off-delay count monitoring means together, unstable control of the snow melting operation due to frequent fluctuations in the presence / absence determination of snow melting before and after the completion of snow melting is avoided.

  In the embodiment shown in FIG. 8, the above-described on-delay operation is also employed. Therefore, as shown in the “supplement” column of FIG. 8, when a signal with snow is output from a state without snow, and when a signal without snow is output after that, the judgment result with snow is continued. Depending on the time, the count start point of the off-delay operation is different.

  As mentioned above, although one Embodiment of this invention has been explained in full detail, this invention is not interpreted limitedly by this description. For example, in the above-described embodiment, the first snow cover determination unit, the second snow cover determination unit, and the freeze determination unit (freeze determination mode) are all configured to share one ultrasonic handset 18. However, a different ultrasonic transmitter / receiver 18 may be employed for each determination unit. Further, when the ultrasonic transmitter / receiver 18 is shared, the shared ultrasonic transmitter / receiver 18 may be installed at a plurality of locations on the road surface 14.

  Further, the shape, size, structure, number, arrangement and the like of the ultrasonic transmitter / receiver 18 attached to the support pole 20 are not limited to the forms shown in the drawing.

  Moreover, in the said embodiment, although the ultrasonic handset 18 was attached to the support pole 20, the support pole 20 is not an essential member, For example, the ultrasonic handset 18 is attached to the outer wall of a building, the eaves, etc. Also good.

  Further, when the first snow cover judging means determines the presence or absence of snow, it is possible to set an effective upper limit value of the detected snow cover height: h. For example, if an upper limit effective value of 50 cm or 100 cm is set, erroneous determination of snow accumulation can be prevented even when a car or a person enters the ultrasonic wave propagation path in the ultrasonic handset 18. To avoid such erroneous determination, for example, the change rate of the snow height: h is monitored, and when the snow height: h becomes larger at a speed higher than a preset change rate, the snow detection is canceled. This can also be realized by doing so.

  In the embodiment, the non-detection area: α is provided as a dead zone in the snow accumulation determination process. However, this is provided according to the intended snow melting operation and is not essential.

  Furthermore, it goes without saying that the present invention can be installed in various places requiring snow detection, such as roads and sidewalks, as well as outdoor parking lots as illustrated. In particular, since it is energy-saving and efficient, it can be suitably used for a small-scale parking lot for general households and a snow melting device in a road, a garden, a roof, and the like. In the above embodiment, a household 100V power source is connected, but various known power sources such as a solar cell and a battery can be suitably employed.

In addition, although not enumerated one by one, the present invention can be carried out in a mode to which various changes, modifications, improvements and the like are added based on the knowledge of those skilled in the art. It goes without saying that all are included in the scope of the present invention without departing from the spirit of the present invention.

It is explanatory drawing which shows roughly the whole structure of the snow melting apparatus which is one Embodiment of this invention provided with the ultrasonic snow accumulation sensor as one Embodiment of this invention. It is a block diagram which shows the whole structure of the ultrasonic snow accumulation sensor especially in the snow melting apparatus shown by FIG. It is an operation | movement block diagram for demonstrating the processing operation | movement of the snow cover detection in the snow melting apparatus shown by FIG. It is explanatory drawing which shows the measurement operation | movement of the reference distance by the ultrasonic snow cover in the snow melting apparatus shown by FIG. It is explanatory drawing which shows the action | operation of the 1st snow accumulation judgment means by the ultrasonic snow cover in the snow melting apparatus shown by FIG. It is explanatory drawing which shows the action | operation of the 2nd snow accumulation judgment means by the ultrasonic snow cover in the snow melting apparatus shown by FIG. It is explanatory drawing which shows the action | operation of the freezing determination mode by the ultrasonic snow cover in the snow melting apparatus shown by FIG. It is explanatory drawing for demonstrating a specific example of the on-delay operation | movement and off-delay operation | movement employ | adopted in the snow melting apparatus shown by FIG. It is explanatory drawing which shows the snow accumulation determination process employ | adopted in the ultrasonic snow accumulation sensor of the snow melting apparatus shown by FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Snow melting apparatus 12 Ultrasonic-type snow accumulation sensor 14 Road surface 16 Hot water type heater 18 Ultrasonic transmitter / receiver 22 Processing apparatus 30 Reception circuit 34 Arithmetic processing apparatus 36 Outdoor temperature measuring instrument 42 Water pipe 44 Water heater 48 Snow surface 50 Freezing layer

Claims (6)

A transmitting means for transmitting ultrasonic waves toward the detection target surface, arranged to be opposed to the detection target surface of the snow;
Receiving means for receiving a reflected wave of the ultrasonic wave transmitted from the wave transmitting means by the detection target surface, spaced apart from the detection target surface and opposed to the detection target surface;
A calculation means for measuring a time from transmission of the ultrasonic wave by the wave transmission means to reception by the wave reception means, and obtaining measurement distance information of the propagation path of the ultrasonic wave from the obtained time measurement result;
The measurement means obtains the measurement distance information of the propagation path of the ultrasonic wave between the transmission means and the reception means and the detection target surface in a state where there is no snow on the detection target surface. Reference value storage means for storing the measured distance information as reference distance information;
First snow determination means for determining the presence or absence of snow based on the difference between the measurement distance information and the reference distance information when the measurement distance information is smaller than the reference distance information;
A receiving filter means for setting a lower limit level of the magnitude of the ultrasonic wave received by the receiving means and not allowing the ultrasonic wave having a magnitude equal to or lower than the lower limit level to be considered;
A second snow cover judging means for judging that there is snow when the measurement distance information is larger than the reference distance information because the wave cannot be confirmed by the action of the wave receiving filter means;
An ultrasonic snow sensor, comprising: output means for outputting a judgment result of the presence or absence of snow by the first and second snow accumulation judgment means.   In the first snow accumulation determination means, the ON side operation value and the OFF side operation value as absolute values of the difference between the measurement distance information and the reference distance information are adopted as the determination reference values, respectively, and the ON side operation value Is set to be larger than the OFF-side operating value, and the absolute value of the difference between the measured distance information and the reference distance information exceeds the ON-side operating value in a state in which snow on the detection target surface is not detected. In the case where there is snow on the detection target surface, there is no snow when the absolute value of the measurement distance information and the reference distance information is lower than the OFF-side operating value in a state where snow is detected on the detection target surface. The ultrasonic snow cover sensor according to claim 1, which is determined as follows.   Obtained when the measurement distance information obtained by the calculation means based on the reception of ultrasonic waves larger than the lower limit level set in the reception filter means is larger than the reference distance information. The ultrasonic snow sensor according to claim 1, further comprising a dead zone processing unit that does not employ the measurement distance information. Heating means for heating the detection target surface;
The ultrasonic snow cover sensor according to any one of claims 1 to 3,
A heating operation control means for controlling a heating operation in the heating means based on a determination result of the presence or absence of snow output from the ultrasonic snow accumulation sensor is provided, and the heating operation of the heating means is provided. A snow melting device characterized in that the surface to be detected is melted. In the heating operation control means, a freezing detection mode is provided in which the heating means is operated to heat the detection target surface even under a situation where it is determined that there is no snow by the ultrasonic snow accumulation sensor,
Determining the presence or absence of freezing of the detection target surface based on the determination of the presence or absence of snow by the second snow accumulation determination means during operation of the freeze detection mode;
While outputting the determination result of the presence or absence of such freezing by the output means,
The snow melting according to claim 4, wherein the heating operation control unit is configured to cause the heating unit to perform a heating operation based on a determination result of the presence of freezing by the output unit to eliminate freezing of the detection target surface. apparatus. The determination result output by the output means of the ultrasonic snow sensor is the presence of snow, and the determination result is obtained when the heating operation of the heating means is performed by the heating operation control means. When it reaches the judgment result that there is no snow,
Providing an off-delay operation means for performing an off-delay operation by continuing the heating operation of the heating means by the heating control means for a predetermined off-delay time set in advance;
A signal with snow cover may be continuously output again for a predetermined time as the determination result only during a preset monitoring time from the time when the determination result has reached the determination result with no snow cover. Provide an off-delay count monitoring means to monitor whether
When the off-delay count monitoring means has not been able to confirm again that there is a snow cover for a predetermined time, the off-delay operation is performed when the judgment result reaches the judgment result of snow cover without snow cover. While the count start point of the duration of the off-delay operation in the means,
When the off-delay count monitoring means continuously confirms a signal with snow again over a predetermined time, the off-delay operation in the off-delay operation means is canceled and the heating operation control means The snow melting device according to claim 4 or 5, wherein the heating operation is returned to the heating operation.