Metal plate polishing machine and control method therefor

Abstract

The present invention discloses a metal plate polishing machine and a control method therefor. The metal plate polishing machine comprises a work base, the work base is provided with a conveyor belt, a feed motor for driving the conveyor belt, a polishing roller located above the conveyor belt, a main motor for driving the polishing roller, a lifting mechanism for driving the polishing roller to move up and down, and a chassis with a controller inside, the feed motor and the main motor are electrically connected with the controller respectively, the conveyor belt is arranged at a front position of the work base, the feed motor is arranged behind the conveyor belt and is in transmission connection with a drive shaft on a feed end of the conveyor belt, the main motor is located behind the conveyor belt and is in transmission connection with the polishing roller.

Claims

1. A metal plate polishing machine, comprising a work base (1), wherein the work base (1) is provided with a conveyor belt (3) for conveying a metal plate (2), a feed motor (4) for driving the conveyor belt (3), a polishing roller (5) located above the conveyor belt (3), a main motor (6) for driving the polishing roller (5), a lifting mechanism (7) for driving the polishing roller (5) to move up and down, and a chassis (8) with a controller (9) inside, a panel of the chassis (8) is provided with a plurality of buttons (10), the feed motor (4) and the main motor (6) are electrically connected with the controller (9) respectively, the conveyor belt (3) is arranged at a front position of the work base (1), the feed motor (4) is arranged behind the conveyor belt (3), the feed motor (4) is in transmission connection with a drive shaft (3.1) on the conveyor belt (3), the main motor (6) is located behind the conveyor belt (3), the main motor (6) is in transmission connection with the polishing roller (5), and the chassis (8) is arranged in a width direction on one side of the main motor (6) away from the feed motor (4).

2. The metal plate polishing machine according to claim 1, wherein the lifting mechanism (7) comprises a lead screw (7.1), a lead screw nut (7.2) and a hand wheel (7.3), the lead screw (7.1) is installed on the chassis (8) in a vertical direction, the lead screw nut (7.2) is in threaded transmission with the lead screw (7.1), a casing of the main motor (6) is fixedly connected with the lead screw nut (7.2), an upper end of the lead screw (7.1) is exposed outside the chassis (8), and the hand wheel (7.3) is connected with the upper end of the lead screw (7.1).

3. The metal plate polishing machine according to claim 1, wherein a vertical mounting plate (11) is arranged between the main motor (6) and the polishing roller (5), the casing of the main motor (6) is fixed to the vertical mounting plate (11), a rotating shaft of the main motor (6) penetrates through the vertical mounting plate (11), and an end of the rotating shaft is connected with a central shaft (5.1) of the polishing roller (5).

4. The metal plate polishing machine according to claim 3, wherein the vertical mounting plate (11) is provided with a dust cover (12), the dust cover (12) is placed over the polishing roller (5), and a spacing is reserved between the dust cover (12) and the conveyor belt (3) to allow passage of the metal plate (2).

5. The metal plate polishing machine according to claim 3, wherein both sides of the polishing roller (5) in a width direction are respectively provided with a press roller, rear ends of the two press rollers are connected with the vertical mounting plate (11), and the press rollers are arranged to be able to be rotatably matched with the vertical mounting plate (11) around axes thereof.

6. The metal plate polishing machine according to claim 5, wherein the vertical mounting plate (11) is provided with slide rails (13) extending in a vertical direction respectively at positions corresponding to the rear ends of the two press rollers, each slide rail (13) is provided with a slide block (14) slidably matched with the slide rail (13), the rear ends of the two press rollers are connected with the corresponding slide blocks (14), the vertical mounting plate (11) is provided with a thrust spring (15), and the thrust spring (15) is arranged to apply a downward thrust to the slide blocks (14).

7. The metal plate polishing machine according to claim 5, wherein the press rollers comprise a front press roller (16) and a rear press roller (17) located on both sides of the polishing roller (5), the front press roller (16) is located on one side of the polishing roller (5) close to a feed end, an overrun clutch (18) is arranged in the front press roller (16) and/or the rear press roller (17), and the overrun clutch (18) is arranged to be in a locked state when a rotational speed exceeds a set value and in an active state when the rotational speed is less than or equal to the set value; when the overrun clutch (18) is in the locked state, the press roller corresponding to the overrun clutch (18) can only be rotated in a reverse direction; when the overrun clutch (18) is in the active state, the press roller corresponding to the overrun clutch (18) can be rotated in a forward or reverse direction.

8. The metal plate polishing machine according to claim 7, wherein the overrun clutch (18) comprises an inner barrel (18.1) and an outer barrel (18.2) sleeved outside the inner barrel (18.1), an inside wall of the outer barrel (18.2) is provided with a plurality of inverted tooth grooves (18.3) uniformly arranged in a circumferential direction, a plurality of movable pieces (18.4) uniformly arranged in the circumferential direction are arranged between the inner barrel (18.1) and the outer barrel (18.2), one end of each movable piece (18.4) is hinged with the inner barrel (18.1), the other end of the movable piece (18.4) is provided with a tooth (18.5) matched with the inverted tooth groove (18.3), the inner barrel (18.1) is provided with a tension spring (18.6) at a position corresponding to each movable piece (18.4), one end of the tension spring (18.6) is fixed to the inner barrel (18.1), the other end of the tension spring (18.6) is connected with the movable piece (18.4), and the movable piece (18.4) is disengaged from the inverted tooth groove (18.3) under the action of a tensile force of the tension spring (18.6) or rotated outward when a centrifugal force is larger than the tensile force of the tension spring (18.6) until the tooth (18.5) of the movable piece (18.4) is abutted against the inverted tooth groove (18.3).

9. The metal plate polishing machine according to claim 8, wherein a pressure sensor for detecting a pressure value between the press rollers and the metal plate (2) is arranged in the front press roller (16) and the rear press roller (17) respectively, and the two pressure sensors are respectively communicated with the controller (9).

10. A control method for a metal plate polishing machine, comprising the metal plate polishing machine of claim 9, wherein the panel of the chassis (8) of the metal plate polishing machine is provided with an indicator light (21); after the feed motor (4) and the main motor (6) are started, if a pressure value detected by a first pressure sensor (19) in the front press roller (16) is within a set range S1 after the metal plate (2) comes into contact with the front press roller (16), a first detection qualified signal will be sent, otherwise a suspension signal will be sent, and the controller (9) shuts down the feed motor (4) based on the received suspension signal; with time of the first detection qualified signal obtained by the controller (9) as initial time T0, transmission time t of the metal plate (2) between the two press rollers is calculated according to a transmission speed v of the conveyor belt (3) and a distance between the two press rollers; if a second pressure sensor (20) in the rear press roller (17) does not obtain a detection signal within a time interval t+C after the initial time T0, or if a pressure value detected by the second pressure sensor (20) is less than a set range S2, a termination signal will be sent, and the controller (9) shuts down the main motor (6) and the feed motor (4) based on the termination signal, otherwise a second detection qualified signal will be sent, wherein C is a set time constant; and the controller (9) controls the indicator light (21) to give different light indications respectively when the controller (9) receives the first detection qualified signal, the second detection qualified signal, the suspension signal and the termination signal.

Description

DESCRIPTION OF DRAWINGS

[0020] FIG. 1 is an axonometric schematic diagram of a metal plate polishing machine of the present invention.

[0021] FIG. 2 is an exploded schematic diagram of a metal plate polishing machine in FIG. 1.

[0022] FIG. 3 is a left schematic diagram of a metal plate polishing machine of the present invention.

[0023] FIG. 4 is a front schematic diagram of a metal plate polishing machine of the present invention.

[0024] FIG. 5 is a local amplified schematic diagram of area A in FIG. 4.

[0025] FIG. 6 is a control logic block diagram of a metal plate polishing machine of the present invention.

[0026] FIGS. 7 and 8 show polishing barrels of two structures in the present invention.

[0027] In the figures: 1. work base; 2. metal plate; 3. conveyor belt; 3.1. drive shaft; 4. feed motor; 5. polishing roller; 5.1. central shaft; 5.2. polishing barrel; 6. main motor; 7. lifting mechanism; 7.1. lead screw; 7.2. lead screw nut; 7.3. hand wheel; 8. chassis; 9. controller; 10. button; 11. vertical mounting plate; 12. dust cover; 13. slide rail; 14. slide block; 15. thrust spring; 16. front press roller; 17. rear press roller; 18. overrun clutch; 18.1. inner barrel; 18.2. outer barrel; 18.3. inverted tooth groove; 18.4. movable piece; 18.5. tooth; 18.6. tension spring; 18.7. rubber layer; 19. first pressure sensor; 20. second pressure sensor; and 21. indicator light.

DETAILED DESCRIPTION

[0028] Embodiments of the present invention will be described below in detail. Examples of the embodiments are shown in drawings, wherein same or similar reference signs refer to same or similar elements or elements having same or similar functions from beginning to end. Embodiments described below by reference to the drawings are exemplary embodiments, and are used for explaining the present invention, and shall not be understood as a limitation to the present invention.

[0029] The metal plate polishing machine and the control method therefor according to the embodiments of the present invention will be described below in detail by reference to the drawings.

[0030] The present invention provides a metal plate polishing machine and a control method therefor, as shown in the figures, comprising a work base 1. The work base 1 is provided with a conveyor belt 3, a feed motor 4, a polishing roller 5, a main motor 6, a lifting mechanism 7 and a chassis 8. The conveyor belt 3 is arranged at a front position of the work base 1 close to operators, a feed end of the conveyor belt 3 is located on a left side in a width direction of the work base 1, a discharge end is located on a right side in the width direction of the work base 1, and the entire conveyor belt 3 is arranged by extending from left to right in a horizontal direction. The feed motor 4 is located behind the conveyor belt 3, a casing of the feed motor 4 is fixedly connected with the work base 1, an output shaft of the feed motor 4 is in transmission connection with a drive shaft 3.1 on the feed end of the conveyor belt 3, and preferably, the output shaft of the feed motor 4 is fixedly connected with the drive shaft 3.1 through a coupling. The polishing roller 5 is located above the conveyor belt 3 for polishing a metal plate on the conveyor belt 3, the main motor 6 is located behind the polishing roller 5, and an output shaft of the main motor is in transmission connection with a central shaft of the polishing roller 5. Preferably, the output shaft of the main motor is fixedly connected with the central shaft of the polishing roller 5 through a coupling. Further, the main motor is installed on the lifting mechanism 7, and the lifting mechanism 7 is fixedly installed on the work base 1. Therefore, the main motor 6 can be driven to move up and down together with the polishing roller 5 on the main motor 6 through the lifting mechanism 7. A controller 9 and a power module electrically connected with the controller 9 are arranged in the chassis 8, a panel of the chassis 8 is provided with a plurality of buttons 10 electrically connected with the controller 9, and the feed motor 4 and the main motor 6 are electrically connected with the controller 9 respectively.

[0031] Preferably, the chassis 8 is arranged on one side of the main motor 6 away from the feed motor 4 in a width direction.

[0032] Preferably, the work base 1 has a sheet-like flat structure, and the work base 1 is provided with a plurality of lightening holes. Therefore, the weight of the entire work base 1 is greatly reduced.

Embodiment 2

[0033] Based on one of preferred examples of the lifting mechanism 7 in the above embodiment: as shown in the figures, the chassis 8 is arranged at an upper right corner of the work base 1, so the chassis 8 is adjacent to the main motor 6. Therefore, the chassis 8 can be used as a carrier of the lifting mechanism 7, enhancing the stability of the lifting mechanism 7. Specifically, the lifting mechanism 7 comprises a lead screw 7.1 installed on the chassis 8 in a vertical direction and a lead screw nut 7.2 in threaded transmission with the lead screw 7.1, both ends of the lead screw are rotatably matched with bearing holes on the chassis 8, the lead screw nut 7.2 is sleeved on the lead screw 7.1 and can move up and down along with the rotation of the lead screw 7.1, a casing of the main motor 6 is fixedly connected with the lead screw nut 7.2, and an upper end of the lead screw 7.1 is exposed outside the chassis 8 and connected with a hand wheel 7.3 at a top of the chassis 8. Therefore, the height adjustment of the main motor 6 and the polishing roller 5 can be achieved by hand operation in the present embodiment. The manual adjustment method is more inconvenient than electric or hydraulic methods, but can greatly reduce the weight of the lifting mechanism 7, which is conducive to the lightweighting of the polishing machine of the present embodiment.

Embodiment 3

[0034] Based on one of preferred examples of the lifting mechanism 7 in the above embodiment: the lifting mechanism 7 comprises a linear motor installed on a side wall of the chassis 8 in a vertical direction, and the linear motor is an existing commercially available product. Therefore, the structure of the linear motor will not be elaborated. The casing of the main motor 6 is fixedly connected with moving parts on the linear motor, and thus the main motor 6 is driven by the linear motor for lifting adjustment.

[0035] Preferably, the lifting mechanism 7 can also be other conventional lifting mechanisms commercially available at present that have a lifting function and a height adjustment function.

Embodiment 4

[0036] As shown in FIG. 2, based on a preferred example in the above embodiment, a vertical mounting plate 11 is arranged between the main motor 6 and the polishing roller 5, the casing of the main motor 6 is fixed to the vertical mounting plate 11, and a rotating shaft of the main motor 6 penetrates through the vertical mounting plate 11 and is connected with a central shaft 5.1 of the polishing roller 5 to drive the polishing roller 5 to rotate.

[0037] Preferably, the vertical mounting plate 11 is provided with a dust cover 12 placed over the polishing roller 5, an opening is reserved at a bottom of the dust cover 12, and a spacing reserved between the dust cover 12 and the conveyor belt 3 located below shall be larger than the thickness of the metal plate when the dust cover 12 is driven by the vertical mounting plate 11 to move down to a limit position, so that the metal plate on the conveyor belt 3 can smoothly pass through the spacing between the dust cover 12 and the conveyor belt 3. It should be understood that due to different thicknesses of metal plates, under the condition of meeting dust-proof requirements, a left side plate and a right side plate of the dust cover in a feed direction are arranged at higher positions, so that the spacing between the dust cover and the conveyor belt 3 below can meet the passage requirements of most metal plates.

[0038] Further, a spacing between the side plate on one side of the dust cover 12 close to the feed end and the conveyor belt 3 below is larger than that between the side plate on one side of the dust cover 12 close to the discharge end and the conveyor belt 3 below.

[0039] As shown in FIG. 2, FIGS. 7 and 8, the polishing roller 5 comprises a central shaft 5.1 and a polishing barrel 5.2 sleeved outside the central shaft 5.1, and the polishing barrel 5.2 is detachably connected with the central shaft 5.1. According to the type of a metal plate 2 to be polished, any existing type of conventional polishing barrel can be selected, including but not limited to two types of sandpaper wheels shown in FIGS. 7 and 8, and a central hole of each polishing barrel 5.2 is matched with the central shaft 5.1.

Embodiment 5

[0040] Based on a preferred example in the above embodiment, both sides of the polishing roller 5 in a width direction are respectively provided with a press roller, the two press rollers comprise a front press roller 16 arranged on a left side of the polishing roller 5 in a feed direction of the metal plate conveyed by the conveyor belt 3 and a rear press roller 17 arranged on a right side of the polishing roller, rear ends of the two press rollers are connected with the vertical mounting plate 11, and the press rollers are arranged to be able to be rotatably matched with the vertical mounting plate 11 around axes thereof.

[0041] Specifically, the press rollers are sleeved outside respective corresponding core shafts, rear ends of the core shafts are fixed to the vertical mounting plate 11, and the press rollers are rotatably matched with the core shafts.

Embodiment 6

[0042] Based on a preferred example in embodiment 5, as shown in FIG. 2 and FIG. 4, the vertical mounting plate 11 is provided with slide rails 13 extending in a vertical direction respectively at positions corresponding to the rear ends of the two press rollers, each slide rail 13 is provided with a slide block 14 slidably matched with the slide rail 13, the slide block 14 has a strip structure, the rear ends of the two press rollers are connected with the respective corresponding slide blocks 14, and the vertical mounting plate 11 is provided with a thrust spring 15 for driving the slide blocks 14 and the press rollers on the slide blocks 14 to move downward. An upper end of the thrust spring 15 is provided with a transverse rod, one end of the transverse rod is fixed to the vertical mounting plate 11, the upper end of the thrust spring 15 is fixed to the transverse rod, and a lower end of the thrust spring 15 is fixed to the slide blocks 14. Therefore, under a vertical downward elastic force of the thrust spring 15, the slide blocks have a motion tendency to move downward, and when the press roller is driven to move upward after the metal plate passes through a position of the press roller, the press roller can apply pressure from top to bottom to the metal plate under a force of the thrust spring 15, increasing static friction between the metal plate and the conveyor belt.

Embodiment 7

[0043] Based on a preferred example in embodiment 5, as shown in FIG. 4 and FIG. 5, the press rollers comprise a front press roller 16 located on one side of the polishing roller 5 close to the feed end and a rear press roller 17 located on the other side, an overrun clutch 18 is arranged in the front press roller 16, and the overrun clutch 18 is arranged to be in a locked state when a rotational speed exceeds a set value and in an active state when the rotational speed is less than or equal to the set value; when the overrun clutch 18 is in the locked state, the press roller can only be rotated in a reverse direction; and when the overrun clutch 18 is in the active state, the press roller can be rotated in a forward or reverse direction.

[0044] And/or, an overrun clutch 18 is arranged in the rear press roller 17, and the overrun clutch 18 is arranged to be in a locked state when a rotational speed exceeds a set value and in an active state when the rotational speed is less than or equal to the set value; when the overrun clutch 18 is in the locked state, the press roller can only be rotated in a reverse direction; and when the overrun clutch 18 is in the active state, the press roller can be rotated in a forward or reverse direction.

[0045] Since the overrun clutch 18 is arranged in the press roller, when the metal plate is driven by the conveyor belt to move forward at a constant speed and is polished, the rotational speeds of the two press rollers are also constant and within a set normal range. At this time, the overrun clutch 18 is in the active state, so the press rollers can freely rotate in a circumferential direction. When the thickness of the metal plate is uneven, or foreign objects on the conveyor belt lead to situations such as the metal plate being elevated, a force between the metal plate and the polishing roller 5 will be increased instantaneously, a larger force will push the metal plate to have a larger thrust to move forward in the feed direction, and such thrust will overcome friction on the conveyor belt, causing the metal plate to be ejected forward at a high speed, which easily causes damage to people or objects in front of the feed direction. In the present embodiment, the instantaneous high-speed forward motion tendency of the metal plate will drive the instantaneous increase in the rotational speeds of the press rollers. At this time, when the rotational speeds of the press rollers exceed the set value, the overrun clutch 18 can be switched from the active state to the locked state, and the overrun clutch 18 locks the press rollers, limiting the forward rotation direction of the press rollers. Therefore, rolling friction between the press rollers and the metal plate will be transformed into sliding friction or static friction, greatly reducing the speed of the metal plate.

[0046] In the present embodiment, the forward rotation direction of the press rollers refers to a direction in which the press rollers rotate synchronously when the press rollers come into contact with the metal plate and the metal plate is moved in the feed direction, as shown in FIGS. 4 and 5, the forward rotation direction is a counterclockwise direction of the two press rollers, and the reverse rotation direction is a clockwise direction.

[0047] It should be understood that the set value can be obtained through a finite number of tests, and the detailed set value data will not be elaborated one by one in the present embodiment.

Embodiment 8

[0048] Based on a preferred example of the overrun clutch 18 in embodiment 7, as shown in FIG. 5, the overrun clutch 18 comprises an inner barrel 18.1 and an outer barrel 18.2 sleeved outside the inner barrel 18.1, an inside wall of the outer barrel 18.2 is provided with a plurality of inverted tooth grooves 18.3 uniformly arranged in a circumferential direction, a plurality of movable pieces 18.4 uniformly arranged in the circumferential direction are arranged between the inner barrel 18.1 and the outer barrel 18.2, one end of each movable piece 18.4 is hinged with the inner barrel 18.1, the other end of the movable piece 18.4 is provided with a tooth 18.5 matched with the inverted tooth groove 18.3, the inner barrel 18.1 is provided with a tension spring 18.6 at a position corresponding to each movable piece 18.4, one end of the tension spring 18.6 is fixed to the inner barrel 18.1, the other end of the tension spring 18.6 is connected with the movable piece 18.4, and the movable piece 18.4 is disengaged from the inverted tooth groove 18.3 under the action of a tensile force of the tension spring 18.6 or rotated outward when a centrifugal force is larger than the tensile force of the tension spring 18.6 until the tooth 18.5 of the movable piece 18.4 is abutted against the inverted tooth groove 18.3. That is, when a rotational speed of the overrun clutch 18 driven by the press rollers is less than or equal to a set rotational speed, the tensile force of the tension spring 18.6 can overcome the centrifugal force so that the movable piece 18.4 is kept at a position disengaged from the inverted tooth groove 18.3. On the contrary, when the rotational speed of the overrun clutch 18 driven by the press rollers is larger than the set rotational speed, the centrifugal force increases and exceeds the tensile force of the tension spring 18.6. As a result, one end of the movable piece 18.4 with the teeth 18.5 is moved radially outward until the end is abutted against the inverted tooth groove 18.3. At this time, the forward rotation direction of the outer barrel 18.2 is limited.

[0049] Preferably, a rubber layer 18.7 covering an outside wall of the outer barrel 18.2 is arranged outside the outer barrel 18.2, and the rubber layer 18.7 not only can be used as a buffer layer to reduce indentation of the press rollers on the metal plate, but also can increase static friction and sliding friction between the press rollers and the metal plate.

Embodiment 9

[0050] In embodiment 8, although the existence of the overrun clutch 18 can greatly reduce the damage to people and objects caused by the instantaneous high-speed flying out of the metal plate, a large amount of debris generated in the polishing process may get stuck between the slide rails 13 and the slide blocks 14 in the above embodiment, thereby causing the slide blocks 14 to get stuck. When the thickness of a previous metal plate to be processed is relatively large, the press rollers are located at a higher position. At this time, if the slide blocks 14 get stuck, the thickness of a next metal plate to be processed will be smaller, which will result in failure of the press rollers to be compacted well on the metal plate. If the press rollers are disengaged from the metal plate when the metal plate is ejected at a high speed, the metal plate will not drive the press rollers to rotate. Therefore, the overrun clutch 18 may fail, especially the slide rails 13 and the slide blocks 14 on the rear press roller 17 may get stuck. For this purpose, the present embodiment is improved in that: a pressure sensor for detecting a pressure value between the press rollers and the metal plate 2 is arranged in the front press roller 16 and the rear press roller 17 respectively, and the two pressure sensors are respectively communicated with the controller 9. The pressure sensors can adopt a variety of existing conventional pressure sensors, such as strain gauge pressure sensors, whose strain gauges can be arranged between the outside wall of the outer barrel 18.2 of the press roller and the outer rubber layer.

[0051] In the present embodiment, among the two pressure sensors, a pressure sensor located in the front press roller 16 is a first pressure sensor 19, and a pressure sensor located in the rear press roller 17 is a second pressure sensor 20.

Embodiment 10

[0052] Based on a control method for the metal plate polishing machine in embodiment 9, comprising the metal plate polishing machine, the panel of the chassis 8 of the metal plate polishing machine is provided with an indicator light 21;

[0053] First, the feed motor 4 and the main motor 6 are started;

[0054] Then, the metal plate 2 is placed on the feed end of the conveyor belt 3, and the conveyor belt 3 drives the metal plate to move forward with the operation of the conveyor belt 3; after the metal plate 2 comes into contact with the front press roller 16, the first pressure sensor 19 in the front press roller 16 will obtain a pressure detection value; and if a pressure value detected by the first pressure sensor 19 in the front press roller 16 is within a set range S1, the first pressure sensor 19 will send a first detection qualified signal, and the controller receives the first detection qualified signal and keeps the feed motor 4 and the main motor 6 in operation, otherwise the first pressure sensor 19 will send a suspension signal, and the controller 9 shuts down the feed motor 4 based on the received suspension signal;

[0055] With time of the first detection qualified signal obtained by the controller 9 as initial time T0, transmission time t of the metal plate 2 between the two press rollers is calculated by a calculation module in the controller according to a transmission speed v of the conveyor belt 3 and a distance between the two press rollers, the transmission speed v can be a fixed parameter input manually in advance, or the transmission speed v of the conveyor belt can be calculated according to a rotational speed of the feed motor detected by a speed sensor, or a more accurate transmission speed can be obtained by adding a speed sensor on the conveyor belt 3; if a second pressure sensor 20 in the rear press roller 17 does not obtain a detection signal within a time interval t+C after the initial time T0, or if a pressure value detected by the second pressure sensor 20 within the time interval t+C is less than a set range S2, a termination signal will be sent, and the controller 9 shuts down the main motor 6 and the feed motor 4 based on the termination signal, otherwise the second pressure sensor 20 will send a second detection qualified signal,

[0056] Wherein C is a set time constant;

[0057] Finally, the controller 9 controls the indicator light 21 to give different light indications respectively when the controller 9 receives the first detection qualified signal, the second detection qualified signal, the suspension signal and the termination signal. The light indications include but are not limited to the color change or flashing change of the indicator light 21.

[0058] Although the embodiments of the present invention have been shown and described above, it will be appreciated that the above embodiments are exemplary and shall not be understood as limitations to the present invention. Those ordinary skilled in the art can make changes, amendments, replacements and variations to the above embodiments within the scope of the present invention.

[0059] Various changes and corrections will undoubtedly be apparent to those skilled in the art who have read the above description. Therefore, the attached claims shall be regarded as covering all changes and corrections to the true intent and scope of the present invention. Any and all equivalent scopes and contents within the scope of the claims shall be considered to fall within the intent and scope of the present invention.