Golf mat

Abstract

Provided is a golf mat comprising: a mat base providing an installation space having a predetermined area; a grass part formed in a mat shape composed of a plurality of individual grass blades, installed on the mat base, and providing a bottom surface on which a golf ball is placed; a color-changing part formed on at least a portion of the individual grass blades constituting the grass part, the color-changing part providing a color-changed region on the bottom surface of the grass part by changing to a predetermined color when reaching a predetermined temperature; and a temperature control part installed under the grass part, disposed under the color-changing part, and controlling a temperature of the color-changing part by providing heat of a predetermined temperature.

Description

Golf mat

[0001] Embodiments disclosed herein relate to a golf mat, and more particularly, to a golf mat that provides a bottom surface on which a golf ball is placed for a golf swing.

[0002] In general, golf is mainly played on golf courses, but it is also played at indoor practice ranges and indoor practice ranges. Recently, screen golf, which provides a virtual golf environment through a screen instead of playing golf outdoors, has become popular.

[0003] In the case of indoor practice ranges or screen golf, as disclosed in Korean Patent Publication No. 10-2257321, a golf ball can be placed on a golf mat made of artificial grass and a golf club can be swinged.

[0004] These golf mats can typically be produced in three types: fairway, rough, and bunker.

[0005] Here, when hitting a golf ball through a golf swing, a divot, a mark called a dent in the front of the golf ball, often occurs depending on the type of golf club used.

[0006] At this time, on a golf course with actual natural grass, you can check the creation of a divot by looking at the grass being dug up, whereas on a conventional golf mat, there was a problem in that there was no divot mark left, so information about the club path (the direction at the moment the golf club hits the ball) after impact could not be known.

[0007] For example, when hitting the back of the golf ball or when the direction of the golf club is wrong, there was a problem with conventional golf mats in that they did not provide accurate and intuitive feedback on the club path.

[0008] Accordingly, a golf practice device equipped with a color-changing member has been proposed recently, as disclosed in Korean Patent Publication No. 10-0942630.

[0009] The above prior art is a technology that indicates the occurrence of a divot by causing a color change member bonded to the upper surface of a golf mat to change color due to heat generated by impact or frictional contact with a golf club.

[0010] However, the above prior art has a limitation in that it can only display a divot caused by a golf club swing, as the color-changing member is configured to change color only by friction of the golf club.

[0011] In addition, the prior art has a problem in that discoloration of the color-changing member does not occur even due to friction of a golf club when the indoor temperature environment inside the store where the golf mat is installed is significantly lower than room temperature.

[0012] That is, the prior art has a problem in that discoloration does not occur because the color-changing member does not reach a temperature at which the color changes even when the indoor temperature inside the store is lower than room temperature due to friction from a golf club.

[0013] Therefore, a technology to solve the above-mentioned problems became necessary.

[0014] Meanwhile, the background technology described above is technical information that the inventor possessed for the purpose of deriving the present invention or acquired during the process of deriving the present invention, and cannot necessarily be said to be publicly known technology disclosed to the general public prior to the application for the present invention.

[0015] The embodiments disclosed herein aim to provide a golf mat that can indicate a divot through a discolored portion that changes color through frictional heat from a golf club while providing a bottom surface on which a golf ball is placed for a golf swing, and can provide other visual effects in addition to the divot through the discolored portion.

[0016] In addition, the embodiments disclosed in this specification aim to present a golf mat that can discolor a discolored portion regardless of the indoor temperature within a store where the golf mat is installed.

[0017] In addition, the embodiments disclosed herein aim to provide a golf mat that can not only passively discolor a discolored portion through the frictional heat of a golf club, but also actively discolor a discolored portion.

[0018] In addition, the embodiments disclosed in this specification aim to present a golf mat that can actively discolor a discoloration area by controlling the temperature of the discoloration area by providing heat of a predetermined temperature from the lower portion of the discoloration area.

[0019] In addition, the embodiments disclosed in this specification aim to present a golf mat that can provide various information through a discoloration line having a predetermined pattern on a grass portion by discoloring the discoloration portion in a pattern set as needed.

[0020] In addition, the embodiments disclosed in this specification aim to provide a golf mat that can provide more diverse information by providing a plurality of discoloration lines through a discoloration part and allowing the plurality of discoloration lines to discolor individually.

[0021] Additionally, the embodiments disclosed herein aim to provide a golf mat capable of providing information through different colors by causing a plurality of discoloration lines to change color to different colors.

[0022] As a technical means for achieving the above-described technical problem, a golf mat according to one embodiment may include a mat base providing an installation space of a set area; a grass portion formed in the form of a mat composed of a plurality of individual grass pieces and installed on the mat base to provide a bottom surface on which a golf ball is placed; a discoloration portion formed on at least a portion of the individual grass pieces constituting the grass portion and providing a discoloration area on the bottom surface of the grass portion while changing to a set color when a set temperature is reached; and a temperature control portion installed under the grass portion and arranged under the discoloration portion to provide heat of a set temperature while controlling the temperature of the discoloration portion.

[0023] Additionally, the discoloration portion may be formed by a thermosensitive dye that is coated on the surface of the individual grasses or dyed into the yarn forming the individual grasses.

[0024] In addition, the thermochromic dye can change color when it reaches the set temperature when a temperature change of 2 to 3°C occurs.

[0025] In addition, the temperature control unit may include at least one heating element that is installed on the mat base and is positioned below the discoloration unit and operates by power to provide heat; and a temperature control unit that controls the operation of the heating element and maintains the heating element at a set temperature.

[0026] In addition, the temperature control unit may further include a temperature sensor installed on the mat base and detecting the temperature of the discoloration unit or the heating wire and applying the temperature to the temperature control unit.

[0027] In addition, the heating wire may be extended in a predetermined pattern while being positioned at the lower portion of the discoloration section and may be operated by the temperature control section to form at least one discoloration line having a predetermined pattern in the discoloration section.

[0028] In addition, the above heating wires may be configured in multiple numbers and each may be operated individually by the temperature control unit to form the above discoloration line.

[0029] Additionally, the discoloration portion can be formed in a pattern corresponding to the discoloration line.

[0030] In addition, the temperature control unit controls each of the plurality of heating wires to a different temperature, and the discoloration unit is formed in a pattern corresponding to each of the plurality of discoloration lines by the plurality of heating wires, and can be formed so that each of the plurality of heating wires changes color at a temperature corresponding to each of the plurality of heating wires and changes color to a different color.

[0031] In addition, the temperature control unit can maintain the temperature of the discoloration unit at a temperature 2 to 3°C lower than the set temperature.

[0032] According to any one of the aforementioned problem solving means, a golf mat can be proposed that provides a bottom surface on which a golf ball is placed for a golf swing, and that a divot can be indicated through a discolored portion that is discolored by frictional heat from a golf club, and that other visual effects can be provided in addition to the divot through the discolored portion.

[0033] In addition, according to any one of the aforementioned problem solving means, a golf mat can be proposed that can provide information on a divot or a club path after impact during a swing of a golf club by passively discoloring the discoloring part through the frictional heat of the golf club, and can provide various information other than the divot by actively discoloring the discoloring part through a temperature control part.

[0034] In addition, according to any one of the aforementioned problem solving means, the temperature of the discoloration part can be maintained at a temperature at which discoloration can occur due to frictional heat through a temperature control unit, so that a golf mat can be proposed that can uniformly discolor the discoloration part regardless of the indoor temperature of the store where the golf mat is installed.

[0035] In addition, according to any one of the aforementioned problem solving means, a golf mat can be proposed that can provide guideline information, such as a putting line, during a golf swing through a discoloration line by discoloring a discoloration part in a pattern set as needed through a temperature control part to form a discoloration line having a predetermined pattern on a grass part.

[0036] In addition, according to any one of the aforementioned problem solving means, a golf mat capable of providing more diverse information can be proposed by providing multiple discoloration lines through a discoloration part and allowing the multiple discoloration lines to change color individually.

[0037] In addition, according to any one of the aforementioned problem solving means, a golf mat can be proposed that can provide various types of information through different colors by causing a plurality of discoloration lines to discolor into different colors.

[0038] The effects that can be obtained from the disclosed embodiments are not limited to the effects mentioned above, and other effects that are not mentioned can be clearly understood by a person having ordinary skill in the art to which the disclosed embodiments belong from the description below.

[0039] FIG. 1 is a perspective view showing a golf mat according to one embodiment.

[0040] Figure 2 is an exploded perspective view showing a golf mat according to one embodiment.

[0041] Fig. 3 is a longitudinal cross-sectional view showing a golf mat according to one embodiment.

[0042] Fig. 4 is a schematic diagram showing a discoloration portion of a golf mat according to one embodiment.

[0043] Fig. 5 is a schematic diagram showing a discolored portion of a golf mat according to another embodiment.

[0044] Figures 6 and 7 are schematic diagrams showing a discolored portion of a golf mat according to another embodiment.

[0045] Below, various embodiments are described in detail with reference to the attached drawings. The embodiments described below may be modified and implemented in various different forms. To more clearly explain the features of the embodiments, detailed descriptions of matters widely known to those skilled in the art to which the embodiments pertain below have been omitted. In addition, parts of the drawings that are not related to the description of the embodiments have been omitted, and similar parts have been designated with similar drawing reference numerals throughout the specification.

[0046] Throughout the specification, when a component is said to be "connected" to another component, this includes not only the "direct connection" but also the "connection with other components in between." Furthermore, when a component is said to "include" another component, this does not exclude other components, but rather implies that other components may be included, unless otherwise specifically stated.

[0047] FIG. 1 is a perspective view showing a golf mat according to one embodiment, FIG. 2 is an exploded perspective view showing a golf mat according to one embodiment, and FIG. 3 is a longitudinal cross-sectional view showing a golf mat according to one embodiment. In addition, FIG. 4 is a schematic diagram showing a discoloration portion of a golf mat according to one embodiment, FIG. 5 is a schematic diagram showing a discoloration portion of a golf mat according to another embodiment, and FIGS. 6 and 7 are schematic diagrams showing a discoloration portion of a golf mat according to still another embodiment.

[0048] A golf mat (10) according to one embodiment provides a floor surface on which a golf ball (B) is placed for a golf swing, and is a device that displays a divot (D) on a part where a golf club has made contact through frictional heat generated by the golf club or visually provides information on the club path after impact.

[0049] Here, divot (D) refers to the mark made on the ground in front of the golf ball (B) on natural grass, and club path refers to the direction of the golf club at the moment it hits the ball.

[0050] In particular, a golf mat (10) according to one embodiment is a device that can actively provide other visual effects in addition to indicating a divot (D).

[0051] Referring to FIGS. 1 and 2, a golf mat (10) according to one embodiment may be configured to include a mat base (100), a grass portion (200), a discoloration portion (300), and a temperature control portion (400).

[0052] The above mat base (100) is a member that forms the body of a golf mat (10) and provides an installation space of a set area, and can provide an installation space in which the grass portion (200), the discoloration portion (300), and the temperature control portion (400) described below can be installed.

[0053] It is preferable that this mat base (100) be made of a material having rigidity, such as metal, but it is not limited to the above material.

[0054] In addition, the mat base (100) is manufactured in a standardized size so that it can be installed in multiple pieces at the installation location, and alternatively, it can be manufactured in a shape and area corresponding to the installation location.

[0055] The above-mentioned grass mat (200) is intended to provide a floor surface on which a golf ball (B) is placed for a golf swing, and is formed in the form of a single mat by fixing a plurality of artificial individual grasses planted therein and installed on a mat base (100).

[0056] For example, a grass mat (200) can be manufactured by fixing a plurality of individual grasses to a mesh plate having an area corresponding to the mat base (100).

[0057] These grass mats (200) can be manufactured to function as fairways, roughs, or bunkers of a golf course depending on the length and shape of each individual grass.

[0058] Here, individual lawns can be made from synthetic resin or can be made by weaving yarn.

[0059] The above discoloration part (300) is intended to provide a discoloration area such as a divot (D) on the bottom surface of the lawn part (200) by discoloring to a set color when a set temperature is reached, and is formed on at least a portion of the individual grasses constituting the lawn part (200) and can provide a discoloration area by discoloring to a set color when a set temperature is reached.

[0060] Such discoloration portion (300) may be formed in a block shape in an area close to the entire area of ​​the grass portion (200) as illustrated in FIG. 4, and may also be formed as at least one discoloration line (310) in a line shape in a portion of the area of ​​the grass portion (200) as illustrated in FIG. 5. In addition, as illustrated in FIG. 6, it may be formed in a combined shape of a block shape and a discoloration line (310).

[0061] Here, the discoloration part (300) may be composed of a thermosensitive dye that is coated on the surface of individual grasses forming the grass part (200) or dyed into the yarn forming the individual grasses.

[0062] Thermochromic dyes are pigments that change color depending on temperature. When a certain temperature is reached, a color different from the original color appears or the original color disappears.

[0063] These thermochromic dyes may be composed of reversible pigments that change to a different color as the temperature rises and then return to their original color as the temperature decreases, or they may be composed of pigments that are colorless at low temperatures but appear colored when a certain temperature is reached.

[0064] Here, the thermochromic dye is composed of a microcapsule powder type and a liquid slurry type, and can be coated on the surface of individual grass and dyed into the yarn that makes up the individual grass.

[0065] Meanwhile, when individual grasses forming the discolored area (300) are struck with a golf club, the temperature change due to the frictional heat of the golf club is approximately 2 to 3°C.

[0066] Accordingly, the thermochromic dye forming the discoloration portion (300) can be formed to be discolored when a temperature change of 2 to 3°C occurs based on the temperature at the installation location, reaching a set temperature at which the discoloration can occur.

[0067] For example, if the temperature of the grass part (200) and the discoloration part (300) is 28 to 29°C at the installation site of the golf mat (10), the temperature of the friction part caused by the golf club is 30 to 32°C, so a thermochromic dye that changes color at 30 to 32°C can be applied to the discoloration part (300).

[0068] Accordingly, when a golf club is struck by a golf swing, the discoloration part (300) can visually display and provide information on the divot (D) or club path by changing the color of the friction part as shown in FIGS. 1 and 2.

[0069] The above temperature control unit (400) is a component that is installed at the bottom of the grass unit (200) and positioned at the bottom of the discoloration unit (300) to provide heat at a set temperature to control the temperature of the discoloration unit (300), thereby actively changing the color of the discoloration unit (300). In addition, it is a component that allows the discoloration unit (300) to maintain the same temperature in all environments and to smoothly express the color.

[0070] This temperature control unit (400) may be configured to include a heating wire (410), a temperature control unit (420), and a temperature sensor (430) as shown in FIG. 2.

[0071] The above heating wire (410) operates by power controlled by a temperature control unit (420) to provide heat, and is configured to be at least one and is installed on the mat base (100) and placed under the discoloration unit (300) to provide heat of a predetermined temperature.

[0072] These heating wires (410) can be installed on the mat base (100) in a state where they are arranged on the surface of an insulating block (411) having a block shape as shown in FIGS. 2 and 3, or alternatively, the configuration of the insulating block (411) can be omitted.

[0073] The above temperature control unit (420) is a component that controls the operation of the heating wire (410) and maintains the heating wire (410) at a set temperature.

[0074] This temperature control unit (420) controls the power supplied to the heating wire and maintains the heating wire (410) at a predetermined temperature, thereby heating the discoloration unit (300) to a predetermined temperature and discoloring it to a color corresponding to the temperature.

[0075] This temperature control unit (420) operates through a command input from a user and can heat the temperature of the heating wire (410) to a temperature that can change the color of the discoloration part (300) to a set color, and after the discoloration is completed, the heating of the heating wire (410) can be stopped to return the discoloration part (300) to its original color.

[0076] For example, the temperature control unit (420) may be provided in a controller that performs golf simulation such as screen golf, and may be composed of a microprocessor, memory, display, etc. that performs input of data input from a user or execution of commands.

[0077] The above temperature sensor (430) is a component that detects the temperature of the discoloration part (300) or the heating wire (410) and applies it to the temperature control part (420). It is installed together with the heating wire (410) to detect the temperature of the discoloration part (300) or the temperature of the heating wire (410) and can apply the detected temperature value to the temperature control part (420).

[0078] Here, the temperature sensor (430) is shown as being positioned between the temperature control unit (420) and the heating wire (410) in FIG. 2 and connected to each of the temperature control unit (420) and the heating wire (410), but this is not limited thereto and may be installed at a location capable of detecting the temperature of the discoloration unit (300) or the temperature of the heating wire (410).

[0079] Accordingly, the temperature control unit (420) can control the operation of the heating wire (410) based on the temperature of the discoloration unit (300) or the heating wire (410) applied from the temperature sensor (430) to maintain the discoloration unit (300) at a predetermined temperature or cool the temperature of the discoloration unit (300) to the original temperature.

[0080] Meanwhile, as illustrated in FIG. 4, the heating wire (410) is configured as one and extends in a zigzag shape with a relatively narrow interval, and is arranged in an area corresponding to the discoloration portion (300), thereby allowing the entire area of ​​the discoloration portion (300) to be discolored.

[0081] In this case, the heating wire (410) operates by the temperature control unit (420) to heat and discolor the entire discoloring unit (300), thereby discoloring the color of the entire grass unit (200), thereby providing a visual field feel.

[0082] In addition, the temperature control unit (420) can maintain the temperature of the discoloration unit (300) at a temperature at which the discoloration can be smoothly performed regardless of the indoor temperature environment of the installation location through the heating wire (410).

[0083] That is, the temperature control unit (400) can maintain the temperature of the discoloration unit (300) at a temperature 2 to 3°C lower than the temperature set to cause the discoloration unit (300) to discolor.

[0084] For example, when the discoloration temperature of the thermochromic dye forming the discoloration part (300) is 30 to 32°C, the temperature change due to frictional heat from the golf club is 2 to 3°C, so the temperature control part (420) can maintain the temperature of the discoloration part at 28 to 29°C.

[0085] Accordingly, the discoloration part (300) can be smoothly discolored through friction of the golf club in any temperature environment.

[0086] In addition, the heating wire (410) can be extended in a pattern set in a state of being arranged at the bottom of the discoloration part (300) and operated by the temperature control part (420) to form at least one discoloration line (310) having a pattern set in the discoloration part (300).

[0087] For example, as shown in FIG. 5, the heating wire (410) can be extended in the form of a plurality of mat lines extending at equal intervals on the grass part (200) and operated by the temperature control part (420) to discolor the discoloration part (300).

[0088] Accordingly, the grass part (200) is normally a plain pattern, but when the heating wire (410) is operated, multiple mat lines appear through the discoloration lines (310) of the discoloration part (300), so that it can be used according to the difficulty setting, for example.

[0089] Here, the heating wire (410) illustrated in FIG. 5 may be configured in multiple pieces and each may be individually operated by the temperature control unit (420) to form multiple discoloration lines (310) in the discoloration section (300). Unlike the illustration, the heating wire (410) may be configured in one piece and may extend in a zigzag shape at relatively wide intervals to form multiple discoloration lines (310).

[0090] At this time, the discoloration part (300) can be formed in a pattern corresponding to a plurality of discoloration lines (310) formed by the heating wire (410).

[0091] In addition, as shown in Fig. 6, the heating wire (410) is not arranged at the striking position of the golf ball, but is arranged in a radial manner in front of the striking position of the golf ball while being composed of multiple pieces, thereby forming multiple discoloration lines (310) that guide the striking (putting) direction of the golf ball.

[0092] Meanwhile, multiple heating wires (410) are individually controlled through a temperature control unit (420), so that only one discoloration line (310) appears depending on the type or direction of the golf swing.

[0093] In addition, the color changing lines (310) corresponding to each of the plurality of heating wires (410) may be composed of the same thermochromic dye so as to change to the same color, or alternatively, the color changing lines (310) may be composed of different thermochromic dyes so as to change to different colors.

[0094] In addition, the plurality of heating wires (410) can be controlled to different temperatures through the temperature control unit (420). In this case, at least one of the discoloration lines (310) can be discolored at different temperatures, and for example, can be composed of a thermochromic dye that is green at a temperature of 10 degrees or more and less than 20 degrees and changes to red at a temperature of 20 degrees or more. Meanwhile, the plurality of heating wires (410) can be installed so that the discoloration line appears while maintaining the temperature of the entire area of ​​the discoloration section (300), as illustrated in FIG. 7.

[0095] That is, one of the plurality of heating wires (410) is arranged over the entire area of ​​the discoloration portion (300) and the temperature of the discoloration portion (300) is maintained at a temperature 2 to 3°C lower than the temperature at which discoloration occurs by the temperature control unit (420), thereby indicating a divot (D) during a golf swing. In addition, at least one other of the plurality of heating wires (410) can be operated at a different temperature by the temperature control unit (420) to cause a discoloration line such as a putting line to appear.

[0096] A method of using a golf mat (10) according to one embodiment including the above components is described.

[0097] The temperature control unit (420) can control the heating wires (410) according to the type or direction of the golf swing during a golf swing to heat the discoloration part (300) to a predetermined temperature, thereby causing discoloration lines (310) to appear.

[0098] Accordingly, the discoloration part (300) can provide an actual field feel through color discoloration by the heating wire (410), and can provide various information such as putting direction, swing type, and difficulty through the number or color of discoloration of the discoloration lines (310).

[0099] In addition, when a golf swing is made, the discoloration part (300) can indicate the divot (D) position or club path through the discoloration part by discoloring the striking part through the frictional heat generated by the striking of the golf club.

[0100] At this time, the temperature control unit (420) can maintain the temperature of the discoloration part (300) at a temperature 2 to 3°C lower than the discoloration temperature. Accordingly, the discoloration part (300) can smoothly discolor while rising by 2 to 3°C when friction of the golf club occurs, regardless of the temperature environment of the installation location.

[0101] Accordingly, the user can check the swing information and inspect the swing through the divot (D) of the discoloration part (300).

[0102] As described above, according to one embodiment of the golf mat (10), a divot (D) can be indicated through a discoloration part (300) that is discolored by frictional heat from a golf club while providing a floor surface on which a golf ball (B) is placed for a golf swing, and other visual effects can be provided in addition to the divot (D) through a discoloration line (310) forming the discoloration part (300).

[0103] The embodiments described above are provided for illustrative purposes only, and those skilled in the art will readily appreciate that the embodiments described above can be readily modified into other specific forms without altering the technical concepts or essential characteristics of the embodiments described above. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, components described as being single may be implemented in a distributed manner, and similarly, components described as being distributed may be implemented in a combined manner.

[0104] The scope of protection sought through this specification is indicated by the claims described below rather than the detailed description above, and should be interpreted to include all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts.

Claims

1. For golf mats, A mat base that provides installation space of a set area; A grass portion formed in the form of a mat made of multiple individual grasses and installed on the mat base to provide a floor surface on which a golf ball is placed; A discoloration portion formed on at least a portion of the individual grasses constituting the lawn portion, and discoloring to a set color when a set temperature is reached, thereby providing a discoloration area on the bottom surface of the lawn portion; and A golf mat, comprising a temperature control unit installed under the grass portion and positioned under the discoloration portion to provide heat at a set temperature while controlling the temperature of the discoloration portion.

2. In paragraph 1, The above discolored part is, A golf mat comprising a thermosensitive dye coated on the surface of the individual grasses or dyed in the yarn forming the individual grasses.

3. In paragraph 2, The above thermochromic dye is, A golf mat characterized in that it discolors when it reaches the set temperature when a temperature change of 2 to 3℃ occurs.

4. In paragraph 1, The above temperature control unit, At least one heating wire that is installed on the mat base and is positioned at the bottom of the discoloration part and provides heat while being operated by power; and A golf mat comprising a temperature control unit that controls the operation of the heating wire and maintains the heating wire at a set temperature.

5. In paragraph 4, The above temperature control unit, A golf mat further comprising a temperature sensor installed on the mat base and detecting the temperature of the discoloration part or the heating wire and applying the temperature to the temperature control part.

6. In paragraph 4, The above heating wire is, A golf mat, which is extended in a predetermined pattern while being positioned at the lower portion of the discoloration portion and is operated by the temperature control portion to form at least one discoloration line having a predetermined pattern in the discoloration portion.

7. In paragraph 6, The above heating wire is, A golf mat, which is composed of multiple parts, each of which operates independently by the temperature control unit to form the discoloration line.

8. In paragraph 6, The above discolored part is, A golf mat formed with a pattern corresponding to the above discoloration line.

9. In paragraph 7, The above temperature control unit, Each of the above plurality of heating wires is controlled to a different temperature, The above discolored part is, A golf mat formed in a pattern corresponding to each of the plurality of discoloration lines by the plurality of heating wires, and formed so as to change color into different colors at a temperature corresponding to each of the plurality of heating wires.

10. In paragraph 1, The above temperature control unit, A golf mat that maintains the temperature of the discolored area at a temperature 2 to 3℃ lower than the set temperature.

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