Cold storage pipe evaporator defrosting robot

Abstract

The present invention relates to a defrosting robot for a cold storage pipe-type evaporator. The defrosting system includes a defrosting ring bracket rotating mechanism, a defrosting ring bracket installed on the defrosting ring bracket rotating mechanism, three pairs of brush motors arranged on the defrosting ring bracket, defrosting brushes arranged on the brush motor, a frost-dropping bucket bracket arranged on the central axis of the defrosting robot body, and two frost-dropping buckets located on both sides of the frost-dropping bucket bracket; the defrosting ring bracket rotating mechanism is connected to the lifting arm in the obstacle crossing system; when the obstacle sensor detects a steel frame obstacle, the track motor and the brush motor are both stopped, the defrosting ring bracket rotates from a vertical state to a horizontal state, the spur gear drive group is started, the lifting arm drives the defrosting system to rise as a whole, and the track motor is started to cross the obstacle. After crossing the obstacle, it returns to the defrosting working state in sequence to realize continuous defrosting operation. The present invention has the characteristics of simple and reasonable structure, suitable for repeated operations, high efficiency, safety and reliability, economical and practical, and remote control.

Description

Technical Field

[0001] The present invention relates to a cold storage tube-type evaporator defrosting robot, in particular to a device for removing frost on the surface of a cold storage tube-type evaporator instead of manual work, belonging to the field of refrigeration and air-conditioning equipment manufacturing and special operation robot manufacturing, and realizing fast and efficient removal of frost on the surface of a cold storage tube. Background Art

[0002] With the development of our society, the demand for large cold storage is also increasing. Since the temperature of large cold storage is very low (<-15℃), the relative humidity in the cold storage is very high, which makes it easy for frost to form on the cold storage pipes (the surface temperature of the pipes is <-25℃). The loose structure of the frost causes its thermal conductivity to be extremely low, which seriously reduces the heat exchange efficiency of the pipes, causing the performance of the refrigeration system to decline and unnecessary energy consumption to increase, thereby increasing the operating cost of the cold storage.

[0003] In order to solve the adverse effects caused by frosting, the cold storage pipes are generally defrosted regularly. At present, the main defrosting methods are manual defrosting and thermal defrosting. Manual defrosting is to manually sweep away the frost layer on the surface of the pipes, and workers use brooms and other long-pole cleaning tools to clean. Although this method is simple to operate, it is time-consuming and labor-intensive, the degree of cleaning is not high, and the labor cost is high. Thermal defrosting is to use a solenoid valve or a conversion device to use the high-temperature superheated refrigerant vapor discharged by the compressor as a heat source to melt the frost layer on the surface of the pipes. This method will cause the temperature of the cold storage to fluctuate greatly, which is not conducive to the storage of items in the cold storage, and will consume a lot of electricity. In addition, some emerging cold storage defrosting devices have emerged, but they are mainly for defrosting the cold storage bare pipes, and cannot defrost the pipe-type evaporator with wings.

[0004] In summary, there is currently no efficient fully automatic cold storage exhaust pipe evaporator defrosting equipment. The present invention aims to invent a fully automatic cold storage exhaust pipe defrosting robot to replace manual removal of frost on the cold storage exhaust pipe and its fins. Summary of the invention

[0005] The present invention provides a cold storage pipe defrosting robot, which aims to replace manual removal of frost on the cold storage pipe. The cold storage pipe defrosting robot can move back and forth on a guide rail parallel to the cold storage pipe, and remove frost on the pipe during the reciprocating movement; it can cross the steel frame obstacle during the movement, so that the pipe defrosting process is carried out continuously to ensure the stable refrigeration performance of the cold storage pipe.

[0006] The technical solution of the present invention is: a cold storage exhaust pipe evaporator defrosting robot, including a defrost system, a motion system, an obstacle crossing system, and a control system. The defrost system includes a defrost ring bracket rotating mechanism, a defrost ring bracket installed on the defrost ring bracket rotating mechanism, three pairs of brush motors arranged at 120° arranged on the defrost ring bracket, a defrost brush arranged on each brush motor, a frost bucket bracket arranged on the central axis of the defrost robot body, and two frost buckets located on both sides of the frost bucket bracket. The frost bucket is tightly installed and connected to the frost bucket bracket through a lock, and the lock sensor sends a lock installation signal to the control system. A weight sensor is installed between the frost bucket and the frost bucket bracket to detect whether the frost in the frost bucket is full and needs to be cleared; the defrost ring bracket rotating mechanism is connected to the lifting arm in the obstacle crossing system; during defrosting, the brush motor drives the defrost brush to rotate at high speed to defrost the cold storage exhaust pipe and wing blades, and the cleared frost falls into the frost bucket The motion system comprises a crawler motor, a transmission mechanism, a crawler and a guide rail. The crawler is arranged on a guide rail parallel to the cold storage exhaust pipe and is located on both sides of the defrost robot body. The crawler motor is connected to the crawler through a transmission mechanism installed in the defrost robot body. The crawler motor drives the crawler to move back and forth on the guide rail through the transmission mechanism to achieve defrosting of different positions of the exhaust pipe; the obstacle crossing system comprises an obstacle sensor, a lifting arm, and a spur gear drive group. The obstacle sensor is arranged on the defrost ring bracket, and the lifting arm is installed on the defrost robot body and connected to the spur gear drive group; the control system is respectively connected to three pairs of brush motors, crawler motors, spur gear drive groups, defrost ring bracket rotation mechanisms, obstacle sensors, weight sensors, and lock sensors, which are used to control the defrost robot to switch between the defrost working state, the obstacle crossing state, and the frost removal state to achieve continuous defrosting operation.

[0007] Furthermore, there is a 120° opening arc directly below the defrost ring bracket, which facilitates the defrost system to cross the steel frame obstacle.

[0008] Furthermore, the spacing between a pair of brush motors is slightly wider than the exhaust pipe fins, and the length of the defrost brush is longer than the height of the exhaust pipe fins.

[0009] Furthermore, the obstacle sensor is an obstacle sensor with limiting functions in both forward and backward directions, and the limit detection length of the obstacle sensor is longer than the length of the defrost ring bracket, so as to ensure that when the defrost robot encounters a steel frame obstacle during its forward and backward movement, the defrost ring bracket will not collide with the steel frame obstacle when the defrost ring bracket is driven by the defrost ring bracket rotating mechanism to rotate to a horizontal state and restore to a vertical state.

[0010] Furthermore, the wireless communication module in the control system is connected to a computer or mobile phone terminal via a wireless network to achieve remote monitoring.

[0011] Furthermore, when the cleared frost fills the frost bucket, the weight sensor sends a signal to the control system. On the one hand, the control system outputs a control to make the defrost robot suspend the defrosting work, and on the other hand, it alarms through the built-in alarm speaker of the defrost robot and simultaneously sends an alarm signal to the monitoring terminal through the wireless network.

[0012] Furthermore, the guide rail is completely parallel to the cold storage pipes and slightly longer than the pipes. On the one hand, it serves as a support for the forward and backward movement of the defrost robot's tracks; on the other hand, it supplies power to the defrost robot and maintains contact with the power supply end of the defrost robot through the built-in wiring terminal of the guide rail to continuously supply power.

[0013] Furthermore, when the frost bucket is full of frost and enters the frost clearing state, the weight sensor between the frost bucket bracket and the bottom of the frost bucket sends a full box signal to the control system, and the brush motor and the track motor are both shut down to remind the staff to clear the frost in the frost bucket. After clearing and correctly installing the frost bucket, the lock sensor sends a locked installation signal to the control system and returns to the defrosting working state.

[0014] Furthermore, when the defrost robot encounters a steel frame obstacle supporting the exhaust pipes while walking and enters the obstacle crossing state, the obstacle sensor of the obstacle crossing system detects the obstacle; the brush motor and the track motor are both stopped, the defrost ring bracket rotating mechanism rotates 90°, and the defrost ring bracket is rotated from a vertical state to a horizontal state, parallel to the exhaust pipes of the cold storage; the spur gear drive group works to make the lifting arm rise, drive the defrost system to move upward as a whole, so that the defrost system is above the exhaust pipes of the cold storage, the track motor is turned on, and the defrost robot continues to walk, thereby crossing the steel frame obstacle; after crossing the obstacle, the control system controls the track motor to suspend work, at this time, the obstacle sensor detects that there are no obstacles in front and behind, the spur gear drive group works in reverse, the lifting arm descends, the defrost ring bracket rotating mechanism rotates 90° in the opposite direction, and the defrost ring bracket is rotated from a horizontal state to a vertical state, entering the defrost working state, and the brush motor and the track motor are both restarted to achieve continuous defrosting operation.

[0015] Compared with the prior art, the present invention has the following beneficial effects: the cold storage pipe defrosting robot of the present invention is composed of four parts: a motion system, an obstacle crossing system, a defrosting system and a control system. The present invention enables the defrosting robot to move forward and backward on a guide rail parallel to the cold storage pipe through the crawler movement, and mechanically defrosts the cold storage pipe and its fins through three pairs of defrosting brushes arranged on the defrosting ring bracket. When the defrosting robot encounters an obstacle of the pipe steel frame, the control system controls the defrosting ring bracket rotating mechanism to rotate 90°, so that the defrosting system is parallel to the cold storage pipe, and then controls the spur gear drive group to work, so that the lifting arm rises, and the defrosting system is slightly higher than the cold storage pipe, and the crawler continues to move forward, so that the defrosting robot crosses the obstacle. After passing the obstacle, each component is controlled to return to the defrosting working state in sequence to achieve continuous defrosting.

[0016] Therefore, the present invention can overcome the shortcomings of low manual defrosting efficiency, complicated and dangerous operation, frost falling on stored items and contaminating the items, and high labor costs; at the same time, the present invention has a simple and reasonable structure, is suitable for repeated operations, has high efficiency, is safe and reliable, and is economical and practical. It can last for a long time by directly taking power from the power supply, and plays an important role in defrosting the cold storage pipes. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a structural schematic diagram of the cold storage pipe defrosting robot of the present invention;

[0018] Figure 2 It is a partial top view of the cold storage pipe defrosting robot of the present invention;

[0019] Figure 3 It is a three-dimensional schematic diagram of the cold storage pipe defrosting robot of the present invention;

[0020] Figure 4 A three-dimensional schematic diagram of the internal structure of the cold storage pipe defrosting robot of the present invention;

[0021] In the figure: 1-obstacle sensor, 2-defrost ring bracket, 3-defrost brush, 4-brush motor, 5-lifting arm, 6-track motor, 7-control system, 8-spur gear drive group, 9-transmission mechanism, 10-track, 11-defrost ring bracket rotation mechanism, 12-guide rail, 13-frost bucket, 14-frost bucket bracket, 15-weight sensor, 16-lock sensor. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0023] like Figures 1 to 4 As shown, a cold storage pipe defrosting robot is composed of four parts: a motion system, an obstacle crossing system, a defrosting system and a control system.

[0024] The defrost system includes a defrost ring bracket rotating mechanism 11, and a defrost ring bracket 2 installed thereon, the bracket has an arc of 240°, and an arc of 120° directly below is an opening, so that the defrost system can cross the steel frame obstacle; three pairs of brush motors 4 are arranged on the defrost ring bracket 2, and are arranged at 120°. The spacing between a pair of brush motors 4 is slightly wider than the pipe fins, and a defrost brush 3 is arranged on each brush motor 4, and the length of the defrost brush 3 is longer than the height of the pipe fins; a frost bucket bracket 14 is arranged on the central axis of the defrost robot and two frost buckets 13 are located on both sides of the frost bucket bracket 14. The frost bucket 13 is tightly installed with the frost bucket bracket 14 through a lock, and the lock sensor 16 sends a lock installation signal to the control system 7, and a weight sensor 15 is installed between the frost bucket 13 and the frost bucket bracket 14 to detect whether the frost in the frost bucket 13 is full and needs to be cleared. During defrosting, the brush motor 4 drives the defrosting brush 3 to rotate at high speed to defrost the cold storage pipes and wings, and the removed frost falls into the frost bucket 13. When the frost bucket is full of frost, it enters the frost removal state, and the weight sensor between the frost bucket bracket 14 and the bottom of the frost bucket 13 sends a full box signal to the control system 7, and the brush motor 4 and the crawler motor 6 are both stopped to remind the staff to remove the frost in the frost bucket. After the frost bucket is removed and correctly installed, the lock sensor 16 sends a lock installation signal to the control system 7.

[0025] The motion system includes a crawler motor 6, a transmission mechanism 9, a crawler 10 and a guide rail 12. The crawler 10 is arranged on the guide rail 12 parallel to the cold storage pipe. The crawler motor 6 drives the transmission mechanism 9, and the transmission mechanism 9 drives the crawler 10 to move forward and backward on the guide rail 12 to achieve defrosting of different positions of the pipe.

[0026] The obstacle crossing system includes an obstacle sensor 1, a lifting arm 5, a spur gear drive group 8 and a defrost ring bracket rotating mechanism 11. When the defrost robot encounters a steel frame obstacle supporting the pipes while walking, it enters the obstacle crossing state, and the obstacle sensor 1 of the obstacle crossing system detects the obstacle; the brush motor 4 and the track motor 6 are both stopped, and the defrost ring bracket rotating mechanism 11 rotates 90°, rotating the defrost ring bracket 2 from a vertical state to a horizontal state, parallel to the cold storage pipes; the spur gear drive group 8 works, causing the lifting arm 5 to rise, driving the defrost system to move upward as a whole, so that the defrost system is above the cold storage pipes, the track motor 6 is turned on, and the defrost robot continues to walk, thereby crossing the steel frame obstacle. After crossing the obstacle, the control system 7 controls the track motor 6 to stop working. At this time, the obstacle sensor 1 detects that there are no obstacles in front and behind, the spur gear drive group 8 works in reverse, the lifting arm 5 descends, and the defrost ring bracket rotation mechanism 11 rotates in reverse 90°, rotating the defrost ring bracket 2 from a horizontal state to a vertical state, entering the defrost working state, and the brush motor 4 and the track motor 6 are restarted to achieve continuous defrosting operation.

[0027] The control system 7 includes the control of three pairs of brush motors 4, track motors 6, spur gear drive groups 8, defrosting ring bracket rotating mechanisms 11, obstacle sensors 1, weight sensors 15, lock sensors 16 and remote monitoring. The functions of the control system 7 mainly include controlling the defrosting robot to switch accurately and efficiently between the defrosting working state, obstacle crossing state and frost removal state to achieve continuous defrosting operation. In addition, the wireless communication module of the control system 7 can be linked to a computer or mobile phone terminal through a wireless network to achieve remote monitoring, including the working state of the defrosting robot, the degree of brush wear, the weight of the defrosted frost in the frost bucket, and the robot defrosting start and stop and defrosting working timing settings.

[0028] The obstacle sensor 1 has a limiting function in both the front and rear directions, and the limit detection length of the obstacle sensor is longer than the length of the defrost ring bracket 2, to ensure that when the defrost robot encounters a steel frame obstacle during its forward and backward movement, the defrost ring bracket rotating mechanism 11 drives the defrost ring bracket 2 to rotate to a horizontal state and restore to a vertical state without colliding with the steel frame obstacle.

[0029] The frost bucket 13 has a frost weight sensor and is connected to the control system 7. When the removed frost fills up the frost bucket, the frost weight sensor sends a signal to the control system 7. The control system 7, on the one hand, makes the defrosting robot suspend the defrosting work, and on the other hand, sends an alarm through the built-in alarm speaker and alarm of the defrosting robot, and at the same time sends an alarm signal to the monitoring terminal through the wireless network. After the staff removes the frost bucket and removes the frost, puts the frost bucket back and locks it, the defrosting robot automatically detects and resumes the defrosting work.

[0030] The guide rail 12 is completely parallel to the cold storage pipe and slightly longer than the pipe. On the one hand, it supports the defrosting robot's crawler to move forward and backward; on the other hand, it also has the function of supplying power to the defrosting robot, and the built-in wiring terminal of the guide rail 12 keeps in contact with the power supply terminal of the defrosting robot to continuously supply power.

[0031] The specific working process of the present invention is as follows:

[0032] In the defrosting working state, the crawler motor 6 drives the transmission mechanism 9, the transmission mechanism 9 drives the crawler 10, and the crawler 10 drives the entire cold storage pipe defrosting robot forward or backward. The defrosting ring bracket is a 240° arc shape, in a vertical state, covering the cold storage pipe, and 3 groups of defrosting brushes 3 and brush motors 4 are set at equal angles of 120°. The defrosting brushes 3 rotate under the drive of the brush motor 4 to defrost the cold storage pipe and wing. In the obstacle crossing state, when the cold storage pipe defrosting robot encounters a steel frame obstacle supporting the pipes while walking, the obstacle sensor 1 detects the obstacle and transmits it to the control system 7. The control system 7 controls the track motor 6 and the brush motor 4 to stop, and controls the defrosting ring bracket rotating mechanism 11 to rotate 90° to be in a horizontal state and parallel to the cold storage pipes; then, the control system 7 controls the spur gear drive group 8 to work, and the lifting arm 5 drives the defrosting robot to rise, so that the defrosting ring bracket 2 is slightly higher than the cold storage pipes; the track 10 is controlled to continue to move forward; when the obstacle sensor 1 detects that there are no obstacles in both the front and rear directions, the steel frame obstacle has been crossed and transmitted to the control system 7; the control system 7 controls the defrosting ring bracket rotating mechanism 11 to rotate 90° in the opposite direction, so that the defrosting ring bracket returns to a vertical state; the spur gear drive group 8 is controlled to work, and the lifting arm 5 drives the defrosting robot to descend and return to the height of the defrosting working state; the track motor 6 and the brush motor 4 resume operation, and the cold storage pipe defrosting robot continues to move forward and defrost. In the frost removal state, when the box of frost swept from the frost bucket 13 is full, the weight sensor 15 sends a full box signal to the control system 7, the defrost robot stops the defrosting operation, and sends a full box alarm to the remote monitoring mobile phone and computer through the defrost robot's onboard alarm light and alarm horn and the wireless communication system, reminding the staff to clear the frost in the frost bucket 13. After the frost in the frost bucket 13 is cleared and put back into the frost bucket bracket 14, it is tightly installed through the lock, and the defrost robot automatically detects whether the lock sensor 16 is normal and returns to the defrosting working state. In summary, the present invention can realize fully automatic obstacle crossing, frost collection, full box reminder, automatic detection and continuous defrosting operations.

[0033] The protection scope of the present invention is not limited to the above-mentioned embodiments. As long as the structure is the same as the structural schematic diagram of a cold storage defrosting device of the present invention, it falls within the protection scope of the present invention.

Claims

1. A cold storage pipe evaporator defrosting robot, comprising a defrosting system, a motion system, an obstacle crossing system, and a control system, characterized in that: The defrost system comprises a defrost ring bracket rotating mechanism (11), a defrost ring bracket (2) mounted on the defrost ring bracket rotating mechanism (11), three pairs of brush motors (4) arranged at 120 degrees and arranged on the defrost ring bracket (2), a defrost brush (3) arranged on each brush motor (4), a frost bucket bracket (14) arranged on the central axis of the defrost robot body, and two frost buckets (13) located on both sides of the frost bucket bracket (14), wherein the frost bucket (13) is tightly installed and connected to the frost bucket bracket (14) through a lock, and the lock is used to lock the frost bucket bracket (14). The sensor (16) sends a lock installation signal to the control system (7). A weight sensor (15) is installed between the frost bucket (13) and the frost bucket bracket (14) to detect whether the frost in the frost bucket (13) is full and needs to be cleared. The defrosting ring bracket rotating mechanism (11) is connected to the lifting arm (5) in the obstacle crossing system. During defrosting, the brush motor (4) drives the defrosting brush (3) to rotate at high speed to defrost the cold storage exhaust pipe and wing blades, and the cleared frost falls into the frost bucket (13). The motion system includes a crawler motor (6), a transmission mechanism (9 ), a crawler (10) and a guide rail (12), wherein the crawler (10) is arranged on the guide rail (12) parallel to the cold storage pipe and is located on both sides of the defrosting robot body, the crawler motor (6) is connected to the crawler (10) via a transmission mechanism (9) installed in the defrosting robot body, and the crawler motor (6) drives the crawler (10) to move forward and backward on the guide rail (12) via the transmission mechanism (9), thereby achieving defrosting of different positions of the pipe; the obstacle crossing system comprises an obstacle sensor (1), a lifting arm (5), and a spur gear drive group (8), wherein the obstacle The sensor (1) is arranged on the defrosting ring bracket (2); the lifting arm (5) is installed on the defrosting robot body and connected to the spur gear drive group (8); the control system (7) is respectively connected to three pairs of brush motors (4), a crawler motor (6), a spur gear drive group (8), a defrosting ring bracket rotating mechanism (11), an obstacle sensor (1), a weight sensor (15), and a lock sensor (16), and is used to control the defrosting robot to switch between a defrosting working state, an obstacle crossing state, and a frost removal state, so as to realize continuous defrosting operation.

2. The cold storage pipe-type evaporator defrosting robot according to claim 1 is characterized in that: There is a 120° opening arc directly below the defrosting annular bracket (2), so as to facilitate the defrosting system to cross the steel frame obstacle.

3. The cold storage pipe-type evaporator defrosting robot according to claim 1 is characterized in that: The distance between the pair of brush motors (4) is slightly wider than the exhaust pipe fins, and the length of the defrosting brush (3) is longer than the height of the exhaust pipe fins.

4. The cold storage pipe-type evaporator defrosting robot according to claim 1 is characterized in that: The obstacle sensor (1) is an obstacle sensor with limit functions in both the front and rear directions, and the limit detection length of the obstacle sensor is longer than the length of the defrost ring bracket (2), so as to ensure that when the defrost robot encounters a steel frame obstacle during its front and rear movement, the defrost ring bracket (2) driven by the defrost ring bracket rotating mechanism (11) to rotate to a horizontal state and restore to a vertical state will not collide with the steel frame obstacle.

5. The cold storage pipe-type evaporator defrosting robot according to claim 1 is characterized in that: The wireless communication module in the control system (7) is connected to a computer or mobile phone terminal via a wireless network to achieve remote monitoring.

6. The cold storage pipe-type evaporator defrosting robot according to claim 1 is characterized in that: When the cleared frost fills up the frost bucket, the weight sensor (15) sends a signal to the control system (7). The control system (7) outputs a control to cause the defrosting robot to suspend defrosting work, and on the other hand, sends an alarm through the built-in alarm speaker of the defrosting robot and simultaneously sends an alarm signal to the monitoring terminal through the wireless network.

7. The cold storage pipe-type evaporator defrosting robot according to claim 1 is characterized in that: The guide rail (12) is completely parallel to the cold storage pipe and slightly longer than the pipe. On the one hand, it serves as a support for the defrosting robot's crawler to move forward and backward; on the other hand, it supplies power to the defrosting robot and maintains contact with the power supply terminal of the defrosting robot through the built-in wiring terminal of the guide rail (12) to continuously supply power.

8. The cold storage pipe-type evaporator defrosting robot according to claim 1 is characterized in that: When the frost bucket is full of frost and enters the frost removal state, the weight sensor between the frost bucket bracket (14) and the bottom of the frost bucket (13) sends a full box signal to the control system (7), and the brush motor (4) and the crawler motor (6) are both stopped to remind the staff to remove the frost in the frost bucket. After the frost is removed and the frost bucket is correctly installed, the lock sensor (16) sends a lock installation signal to the control system (7) to restore to the defrosting working state.

9. The cold storage pipe-type evaporator defrosting robot according to claim 1, characterized in that: When the defrosting robot encounters a steel frame obstacle supporting the pipes while walking and enters the obstacle crossing state, the obstacle sensor (1) of the obstacle crossing system detects the obstacle; the brush motor (4) and the crawler motor (6) are both stopped, the defrosting ring bracket rotating mechanism (11) rotates 90 degrees, and the defrosting ring bracket (2) is rotated from a vertical state to a horizontal state, parallel to the cold storage pipes; the spur gear drive group (8) works, so that the lifting arm (5) rises, driving the defrosting system as a whole to move upward, so that the defrosting system is above the cold storage pipes, and the crawler motor (6) is turned on. The defrosting robot continues to move, thereby crossing the steel frame obstacle; after crossing the obstacle, the control system (7) controls the crawler motor (6) to stop working. At this time, the obstacle sensor (1) detects that there are no obstacles in front and behind, the spur gear drive group (8) works in reverse, the lifting arm (5) descends, the defrosting ring bracket rotating mechanism (11) rotates in reverse by 90 degrees, and rotates the defrosting ring bracket (2) from a horizontal state to a vertical state, entering the defrosting working state, and the brush motor (4) and the crawler motor (6) are restarted to achieve continuous defrosting operation.

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