DESCRIPTION

Title of the Invention DUST COLLECTOR

Technical Field

[0001] The present invention relates to a dust collector which sucks dust produced by an electric tool, together with water.

Background Art [0002] A dust collector collects dust produced by cutting or grinding with an electric tool.

[0003] Some electric tools are of a type which drops water on a cutting place and a type which rinses a member to be cut with water to prevent scattering of dust and cool the blade. Accordingly, some dust collectors are of a wet and dry type capable of sucking both dry dust and water-containing dust. The wet and dry type dust collector has a filter which separates sucked dust from water, and a tank which stores the separated water. The filter may be clogged when soaked in water. In this respect, the wet and dry type dust collector has a water level detector to detect the water level in the tank. The water level detector stops the suction unit when a voltage is applied between a pair of electrodes, disposed under the filter, and the current between the electrodes becomes equal to or greater than a preset value.

[0004] The dust collector with the foregoing structure has a problem that water in the tank waves to let the current flow between the electrodes for only a short period of time, so that the dust collector may halt. Accordingly, the conventional wet and dry type dust collector is configured to stop the suction unit when the current flows for around a second or longer, and prevent the suction unit from operating thereafter unless the ON/OFF switch of the dust collector is set OFF once.

[0005] In the conventional wet and dry type dust collector, however, when the ON/OFF switch is set OFF even after the water level detector detects the water level reaching a given level, and is then switched ON from the OFF state, the suction unit is in operation for about one second. If switching of the ON/OFF switch between the OFF state and the ON state is repeated, therefore, the suction unit is kept operating to gradually suck water into the tank, so that the filter is soaked in the water.

[0006] When the suction unit stops due to water collected in the tank, the user does not understand what causes the stopping of the suction unit and may not therefore carry out an adequate recovery process. [0007] Patent Document 1 discloses a wet and dry type dust cleaner having a mechanism of preventing a float switch from malfunctioning. Patent Document 2 discloses a dust collector which automatically operates a dust catcher when the filter is clogged, thereby removing dust from the filter.

However, neither technique disclosed cannot inhibit water from being collected in the tank, so that the filter is soaked in the water. [0008]

Patent Document 1 : Unexamined Japanese Patent Application KOKAI Publication No. H05-228076

Patent Document 2: Unexamined Japanese Patent Application KOKAI Publication No. 2007-245019

Summary of Invention

[0009] The present invention has been made in consideration of the foregoing problems, and it is an object of the invention to provide a dust collector capable of solving the problem that the filter is soaked in water.

It is another object of the invention to provide a dust collector which inhibits a suction unit from being in operation even when an ON/OFF switch is switched ON from

an OFF state, until water which has been collected up to an allowable amount in a tank is removed therefrom.

[0010] To achieve the objects, a dust collector according to the invention includes: a suction unit that sucks dust; a tank that stores the dust sucked from an inlet port by the suction unit; a water level detecting unit that detects a water level in the tank; an ON/OFF switch that instructs operation/stopping of the suction unit; and a control unit that controls an operation of the suction unit based on a status of the ON/OFF switch and the water level detected by the water level detecting unit, and further controls the suction unit in such a way that the suction unit does not come to an operational when the water level in the tank detected by the water level detecting unit exceeds a threshold value with the ON/OFF switch being set ON; wherein when the water level detecting unit detects that the water level in the tank exceeding the threshold value while the ON/OFF switch is ON and the suction unit is in operation, the control unit stops the suction unit after a given time elapses since the detection.

[0011] The dust collectors with the foregoing structures can prevent water from being collected in the tank to a level equal to or higher than a predetermined threshold value, thus solving the problem that the suction unit is kept operating to gradually suck water into the tank to cause the filter to be soaked in the water.

Brief Description of Drawings

[0012] FIG. 1 is an outline diagram of a dust collector according to an embodiment of the invention; " FIG. 2 is a side cross-sectional view of the main body of the dust collector according to an embodiment of the invention;

FIG. 3 is a block diagram showing the configuration of a controller of the dust

collector according to an embodiment of the invention;

FIG. 4 is a circuit diagram showing one example of a water level detecting circuit of the dust collector according to an embodiment of the invention; and

FIGS. 5 A to 5 C are flowcharts illustrating the control operation of the dust 5 collector according to an embodiment of the invention.

Description of Embodiment

[0013] A dust collector according to an embodiment of the present invention will be described below with reference to the accompanying drawings. 10 [0014] The dust collector according to the embodiment serves to clean a floor or so in a work area where electric tools for cutting wood, such as a circular saw and jigsaw, and electric tools, such as a hammer drill and a stone cutter, which are used in drilling, cutting, grinding or the like concrete or stone, are used.

[0015] As shown in FIG. 1, a dust collector 100 has a main body 1 and a suction port 15 101. The dust collector 100 sucks dust on a floor together with ambient air and water through the suction port 101 inside the main body 1 via a hose 102 and an inlet port 3.

An operation panel 15 is arranged on the upper front side of the main body 1. The operation panel 15 has a main switch 17, a mode switch 29, an alarm indicator 20, etc. arranged thereon. 20 [0016] As shown in a cross-sectional view of FIG. 2, the main body 1 has a cylindrical tank 2 to store dust. The inlet port 3 is formed in a side portion of the tank 2. A motor base 4, a motor cover 5 and a head cover 6, which are formed integral with one another, are clamped to the upper opening portion of the tank 2. A suction unit 7 is disposed between the motor base 4 and the motor cover 5. 25 [0017] The suction unit 7 comprises a suction fan 8, and a motor 9 which rotates the suction fan 8. The motor base 4, the motor cover 5 and the head cover 6 form a discharge path to discharge air, sucked through an intake port 4a, provided at the lower

portion of the motor base 4, to a discharge port 4b.

[0018] A control board 14, the operation panel 15 and an insulation transformer 23 are provided at that portion of the motor cover 5 which is located above the inlet port 3. A water level detecting circuit 28 which detects the position (water level) of the top surface 5 of water collected in the tank 2 is formed at the control board 14. The water level detecting circuit 28 will be described later referring to FIG. 3.

A pair of contacts 25a, 25b are provided at the lower portion of the motor base 4. A pair of lead wires connected to a pair of input terminals of the water level detecting circuit 28 at the control board 14 are respective connected to the pair of contacts 25a, 25b

10 through the motor base 4.

[0019] A filter housing 11 is fixed and secured between the upper end of the side wall of the tank 2 and the motor base 4. A filter 13 which filters out dust and passes air alone, and a filter cover 12 which holds the filter 13 in such a way that the filter 13 does not collapse due to internal negative pressure are mounted to the filter housing 11. The filter

15 13 and the filter cover 12 constitute a filter device 10.

[0020] The filter housing 11 is provided with a pair of contacts 26a, 26b. The pair of contacts 25a, 25b face contacting the pair of contacts 26a, 26b.

A pair of electrodes 27a, 27b for detecting the water surface (water level) in the tank 2 are disposed at the lower end of the filter 13. The electrodes 27a, 27b have distal

20 ends disposed to be positioned under the filter 13. The distal ends of the electrodes 27a, 27b are disposed to be positioned at the position of the upper limit of the allowable range of water collected in the tank 2. The pair of electrodes 27a, 27b are respectively connected to the pair of contacts 25a, 25b provided at the filter housing 11 on the filter 13 side via the pair of contacts 26a, 26b on the motor base 4 side. Accordingly, the pair of

25 electrodes 27a, 27b are electrically connected to the input terminals of the water level detecting circuit 28 at the control board 14. [0021] Next, the electric configuration of the dust collector 100 will be described

referring to FIGS: 3 and 4.

First, the configuration of a water level detecting circuit 28 formed on the control board 14 will be described referring to FIG. 3.

[0022] As shown in FIG. 3, the water level detecting circuit 28 includes a comparator CM, resistors Rl, R2, R3, R4, R5, R6, R7, and capacitors Cl ₃ C2, C3. The resistor and capacitor comprise, for example, a chip resistor and a chip capacitor, respectively.

[0023] A voltage of +5 V is supplied to the power supply terminal of the comparator CM from a DC power supply 24. The capacitor C2 connected between the anode and cathode of the DC power supply 24 serves to reduce power supply noise. The voltage of +5 V is applied to one electrode 27a via the resistor Rl, the contact 25a and the contact

26a from the DC power supply 24. The other electrode 27b is connected to the ground terminal of the DC power supply 24 via the contact 26b, the contact 25b and the resistor

R2.

[0024] A current which flows between the electrodes 27a, 27b is converted to a voltage Vin expressed by the following equation. The voltage Vin is input to the +

(non-inverting) input terminal of the comparator CM.

Vin = (5 V - (resistance of resistor Rl) x (value of the current I flowing between the electrodes 27a, 27b)

Note that the resistor R3 and the capacitor Cl serve to reduce noise. [0025] Meanwhile, a reference voltage Vr obtained by dividing +5V, supplied from the

DC power supply 24, by the resistors R4 and R5 is input to the - (inverting) input terminal of the comparator CM. The reference voltage Vr is given by the following equation.

Vr = 5-R5/(R4 + R5) [0026] The output (water-level detection signal) of the comparator CM is input to a digital input port P02 of a microcomputer 22. The resistor R6 pulls up the output terminal of the comparator CM. The resistor R7 and the capacitor C3 serve to reduce

noise.

[0027] When the electrodes 27a, 27b are not soaked in water, the electrodes 27a, 27b are insulated from each other by an insulator, such as air or plastics. This causes the current to hardly flow between the electrodes 27a, 27b. Therefore, the voltage Vin becomes approximately 5 V from the above equations.

[0028] When the electrodes 27a, 27b are soaked in water, on the other hand, the current flows between the electrodes 27a, 27b due to the conduciveness of water. In the embodiment, the intervals or the like between the resistors Rl, R2, and the electrodes 27a, 27b are set in such a way that when the electrodes 27a, 27b are soaked in water, the current flows therebetween becomes 1 to 2 μA.

[0029] The reference voltage Vr for determining whether the electrodes 27a, 27b are soaked in water is set in such a way as to be, for example, Vin (= 5 V - Rl [ω] x 3.3 [μA]) when the current I flowing between the electrodes 27a, 27b is 3.3 μA. [0030] That is, the resistances (ratio) of the resistors Rl, R2, R4 and R5 are set in such a way that when the current I flowing between the electrodes 27a, 27b is smaller than 3.3 μA, the output (water-level detection signal) of the comparator CM becomes substantially 0 V (low level), and when the current I flowing between the electrodes 27a, 27b is larger than 3.3 μA, the output of the comparator CM becomes 5 V (high level). [0031] Next, the general electric configuration of the dust collector 100 will be described referring to FIG. 4.

As illustrated, the dust collector 100 has the motor 9, the control board 14, a power supply plug 16, the alarm indicator 20, the insulation transformer 23, the contacts 25a, 25b, 26a, 26b, the electrodes 27a, 27b, and so forth. [0032] As illustrated, a capacitor 33 is connected between the two input terminals of the aforementioned water level detecting circuit 28. A capacitor 34 is connected between the positive input terminal of the water level detecting circuit 28 and the plus electrode of the DC power supply 24. Further, a capacitor 35 is connected between the negative

input terminal of the water level detecting circuit 28 and the minus electrode (ground) of the DC power supply 24.

[0033] The pair of electrodes 27a, 27b for detecting the water level are exposed from the filter device 10. Therefore, there may be a case where a worker touches the electrodes 5 27a, 27b at the time of removing the suction unit 7, the filter device 10, etc. from the tank 2 to dispose of dust or clean the filter 13.

[0034] For prevention of static buildup caused by dry dust, the tank 2, the inlet port 3, the hose 102 and so forth are made of a conductive material and are connected to the ground. Therefore, there may be a case where when a worker touches the electrodes 27a,

10 27b, static electricity charged on the worker is discharged to the ground from the electrodes 27a, 27b through the water level detecting circuit 28. If the three capacitors 33, 34, 35 are not present on the input side of the water level detecting circuit 28, electrostatic discharge to the electrodes 27a, 27b produces a pulse current which flows to the DC power supply 24 through the resistor Rl, the resistor R2 and the comparator CM.

15 Accordingly, the resistor Rl or the resistor R2 is deteriorated by electrostatic-discharge oriented migration, and its resistance may change, thus impairing the water-level detecting function. In addition, dielectric breakdown or the like may occur to cause an internal damage on the comparator CM. [0035] With the configuration in FIG. 4, when electrostatic discharge to the water-level

20 detecting electrode 27a occurs, part of the electrostatic originated pulse current flows to the DC power supply 24 through the capacitor 34 and the plus electrode, while another part of the current flows to the DC power supply 24 through the capacitors 33 and 35 and the minus electrode. This allows only a slight current to flow to the water level detecting circuit 28. Therefore, the electrostatic discharge does not cause malfunction of

25 the water level detecting circuit 28.

[0036] The main switch 17 is formed by an ON/OFF switch to enable or disable power supply to the motor 9 of the dust collector 100.

The mode switch 29 changes the operation mode of the dust collector 100 between an individual operation mode and a sequential operation mode.

A switch state detecting circuit 18, a motor drive circuit 19, an alarm indicator drive circuit 21, the microcomputer 22, the DC power supply 24, the water level detecting circuit 28, and a receptacle current detecting circuit 31 are disposed on the control board 14.

[0037] The power supply plug 16 connected to an AC power supply (commercially available power supply) is connected to the motor 9, the motor drive circuit 19 and the insulation transformer 23. [0038] The switch state detecting circuit 18 detects the ON/OFF action of the main switch 17, and the operation mode specified by the mode switch 29, and outputs data indicating the states of the switches 17 and 29 to digital ports POO and POl of the microcomputer 22.

The motor drive circuit 19 turns on or off (rotates or stops) the motor 9 using the AC voltage supplied through the power supply plug 16 under the control of the microcomputer 22. The power control element of the motor drive circuit 19 is electrically insulated from a signal system (circuit which operates on the power from the DC power supply 24) by a photo insulating coupler called photo-triac coupler or photocoupler. The alarm indicator drive circuit 21 turns on or off the alarm indicator 20 under the control of the microcomputer 22.

[0039] An AC voltage supplied from the commercially available power supply via the power supply plug 16 is applied to the primary winding of the insulation transformer 23. The DC power supply 24 is connected to the secondary winding of the insulation transformer 23. The DC power supply 24 has a rectifying circuit and a smoothing circuit to convert an AC voltage to a DC voltage, and supplies the DC voltage to the individual circuits on the control board 14. Therefore, the individual circuits

(microcomputer 22, water level detecting circuit 28, switch state detecting circuit 18, etc.) which are supplied with the power from the DC power supply 24 are insulated from an external power supply by the insulation transformer 23.

[0040] As described above, the pair of electrodes 27a, 27b for detecting the water level are connected to the water level detecting circuit 28 via the pair of contacts 26a, 26b and the pair of contacts 25a, 25b.

[0041] The receptacle 32 is attached to the operation panel 15, and is applied with the AC voltage through the power supply plug 16. The plug of another electric device may be plugged into the receptacle 32 to acquire power. The receptacle current detecting circuit 31 measures the current flowing to the receptacle 32 through a current detector (current transformer) 30 or the like. The receptacle current detecting circuit 31 supplies a voltage signal indicating the measured current value to an analog input port Ainl of the microcomputer 22. [0042] The microcomputer 22 incorporates a CPU (Central Processing Unit) and a memory, and operates according to a program stored. The microcomputer 22 has an individual operation mode and sequential operation mode. The operation mode is changed over by the mode switch 29.

[0043] In individual operation mode, the microcomputer 22 controls the motor drive circuit 19 according to the ON/OFF action of the main switch 17 to change between the operation and the halting of the motor 9.

[0044] In sequential operation mode, when detecting that an electric tool which gains power through the receptacle 32, the microcomputer 22 automatically operates the motor 9, whereas when detecting that the electric tool has stopped, the microcomputer 22 automatically stops the motor 9. Switching between the sequential operation mode and the individual operation mode is done by the mode switch 29.

[0045] Next, the operation of the dust collector 100 will be described referring to flowcharts illustrated in FIGS. 5Ato 5C.

[0046] When the power supply plug 16 of the dust collector 100 is connected to the commercially available power supply, the AC voltage is applied to the receptacle 32. This makes it possible to connect the plug of another electric tool to the receptacle 32 to drive this electric tool. Further, the AC voltage is applied to the DC power supply 24 through the insulation transformer 23. As a result, the DC power supply 24 starts operating to start supplying the DC operational power to the individual circuits on the control board 14. In response to the start of power supply, the microcomputer 22 starts processes shown in FIG. 5A. First, the microcomputer 22 executes an initialization process to initialize resistors, RAM, input/output ports, etc. (step SlOO). [0047] Next, the microcomputer 22 executes an instruction-standby input scan process starting at reference symbol "A" (step SIlO). In the instruction-standby input scan process (step SIlO), the microcomputer 22 first determines the state of the main switch 17 through the switch state detecting circuit 18 (step Sill). When the main switch 17 is OFF (step Sill; OFF), the dust collector 100 is not in an operational state. Therefore, the microcomputer 22 repeats the determination in step Sill until the main switch 17 is set ON.

[0048] When the microcomputer 22 determines that the main switch 17 is ON (step Sill; ON), the microcomputer 22 determines whether a water-level detection signal is at a low level (step Sl 12). hi other words, the microcomputer 22 determines whether or not water collected in the tank 2 has reached a threshold level, the electrodes 27a, 27b are soaked in water, and the current I flowing between the electrodes 27a, 27b is larger than a threshold value.

When determining that the water-level detection signal is at a high level (step Sl 12; NO), the electrodes 27a, 27b are not soaked in water. Therefore, dust collection by the dust collector 100 is possible. The microcomputer 22 determines through the switch state detecting circuit 18 whether the mode switch 29 indicates the individual operation mode or the sequential operation mode (step S 114).

When the mode switch 29 indicates the individual operation mode (step S 114; INDIVIDUAL OPERATION MODE) ₅ the microcomputer 22 executes an individual operation process starting at reference symbol "B" illustrated in FIG. 5B. That is, as the main switch 17 is set ON when the water in the tank 2 has not reached the threshold level in individual operation mode, the microcomputer 22 initiates the individual operation process starting at reference symbol "B".

In this individual operation process, the microcomputer 22 controls the motor drive circuit 19 to rotate the motor 9 (step S 121). As a result, the suction unit 7 starts air intake and the dust collector 100 starts collecting dust. [0049] When the mode switch 29 indicates the sequential operation mode (FIG. 5 A, step S 114; SEQUENTIAL OPERATION MODE), the microcomputer 22 acquires the value of the current (receptacle current) flowing to an external electric tool from the receptacle 32 through the receptacle current detecting circuit 31. Next, the microcomputer 22 determines whether the receptacle current is larger than the threshold value (step Sl 15). When the microcomputer 22 determines that the receptacle current is larger than the threshold value (step Sl 15; YES), the microcomputer 22 initiates the sequential operation process starting at reference symbol "C" illustrated in FIG. 5C. In other words, when the main switch 17 is set ON and the electric tool connected to the receptacle 32 is ON in sequential operation mode, the microcomputer 22 initiates the sequential operation process starting at reference symbol "C" illustrated in FIG. 5C.

[0050] When determining in step S 112 that the water-level detection signal is at a low level (step S112; YES), on the other hand, the microcomputer 22 determines whether the water-level detection signal keeps the low-level state for one second or longer (step S 113). In other words, the microcomputer 22 determines whether the electrodes 27a and 27b are. continuously soaked in water for one second or longer. Even if only a slight amount of water is collected in the tank 2, the water may wave to contact the electrodes 27a and 27b, so that a current temporarily flows therebetween. It is possible to determine that the

electrodes 27a and 27b are surely soaked in water by discriminating that the current continuously flows for one second.

The scheme of measuring that the low level of the water-level detection signal has continued for one second is optional. For example, the following scheme i) or ii) can be employed.

[0051] i) When it is determined YES in step S112, i.e., that the water-level detection signal output from the water level detecting circuit 28 is at a low level, the microcomputer 22 determines whether a measurement-in-progress flag is set. When the measurement-in-progress flag is OFF, the measurement-in-progress flag is set and a timer is activated. When the measurement-in-progress flag is ON, on the other hand, the microcomputer 22 acquires the time measured by the timer, and determines whether the time has reached one second. When the time has reached one second, the microcomputer 22 shifts the control to a water-level detection process indicated by reference symbol "Dl". When the time has not reached one second yet, on the other hand, the microcomputer 22 returns the control to the top (reference symbol "A") in the instruction-standby input scan process. In this case, when it is determined OFF in step Sill and NO in step Sl 12, the measurement-in-progress flag is set OFF. ii) When it is determined YES in step S 112, the microcomputer 22 activates the internal timer to measure one second. When the internal timer measures one second, the microcomputer 22 determines whether the water-level detection signal output from the water level detecting circuit 28 is at a low level, and shifts the control to the water-level detection process indicated by reference symbol "Dl" if the signal is at the low level, and returns the control to the top of the instruction-standby input scan process SIlO if the signal is at the high level. [0052] In the individual operation process starting at reference symbol "B", as shown in FIG. 5B, the microcomputer 22 first controls the motor drive circuit 19 to rotate the motor 9. This causes the suction unit 7 to start air intake and causes the dust collector 100 to

start collecting dust. Subsequently, the microcomputer 22 initiates an individual-operation input scan process S 120 starting at reference symbol "Bl". [0053] In the individual-operation input scan process S120, the microcomputer 22 scans the statuses of the main switch 17, the water level detecting circuit 28, the mode switch 29 and the receptacle current detecting circuit 31.

The microcomputer 22 first determines whether the main switch 17 is ON or OFF (step S 122). When the main switch 17 is ON, the microcomputer 22 determines whether the low-level state of the water-level detection signal output from the water level detecting circuit 28 continues for one second or longer (step S123). The scheme of checking if the low-level state of the water-level detection signal continues for one second or longer is optional, and schemes similar to the those used in the processes of the steps S 112 and S 113 can be adopted.

[0054] When it is determined NO in step S 123, i.e., when the water in the tank 2 has not reached the threshold level, the microcomputer 22 discriminates the operation mode indicated by the mode switch 29 (step S 124). When the mode switch 29 indicates the individual operation mode (step S 124; INDIVIDUAL OPERATION MODE), the control goes to step S 122 to keep the individual operation, whereas when the mode switch 29 indicates the sequential operation mode (step S 124; SEQUENTIAL OPERATION MODE), the control goes to step S 125. In step S 125, the microcomputer 22 determines whether the receptacle current is larger than the threshold value (step S 125).

When it is determined in step S 125 that the receptacle current is larger than the threshold value (step S 125; YES), i.e., when the main switch 17 is ON, the water collected in the tank 2 is at or below the threshold level, the main switch 17 indicates the sequential operation mode, and the electric tool connected to the receptacle 32 is in operation, the microcomputer 22 initiates the sequential operation process starting at reference symbol "Cl" shown in FIG. 5C.

[0055] On the other hand, when it is determined OFF in step S 122 and it is determined in step S 125 that the receptacle current is smaller than the threshold value, the microcomputer 22 sets the motor 9 OFF to stop the rotation thereof (step S 126). That is, when the main switch 17 of the dust collector 100 is set OFF or when the operation of the electric tool connected to the receptacle 32 is stopped in sequential operation mode, the motor 9 is set OFF. Thereafter, the microcomputer 22 initiates the instruction-standby input scan process SIlO starting at reference symbol "A" in FIG. 5 A.

When it is determined in step S 123 that the low-level state of the water-level detection signal output from the water level detecting circuit 28 continues for one second or longer, i.e., when water is collected to or above the threshold level in the tank 2, the microcomputer 22 initiates the water-level detection process starting at reference symbol "D" in FIG. 5A.

[0056] In the sequential operation process starting at reference symbol "C" in FIG. 5C, the microcomputer 22 sets the motor 9 ON first (step S131). Accordingly, the dust collector 100 starts dust collection. Then, the microcomputer 22 initiates the sequential-operation input scan process (step S130) starting at reference symbol "Cl". [0057] In the sequential-operation input scan process (step S 130), the microcomputer 22 scans the statuses of the main switch 17, the water level detecting circuit 28, the mode switch 29 and the receptacle current detecting circuit 31. The microcomputer 22 first determines whether the main switch 17 is ON or

OFF (step S 132). When the main switch 17 is OFF, the microcomputer 22 sets the motor 9 OFF (step S 147), and then initiates the instruction-standby input scan process (step SIlO) starting at reference symbol "A" in FIG. 5 A.

When it is determined that the main switch 17 is ON (step S 132; ON), the microcomputer 22 determines whether the low-level state of the water-level detection signal output from the water level detecting circuit 28 continues for one second or longer, i.e., whether the electrodes 27a, 27b are soaked in water (step S133). The scheme of

checking if the low-level state of the water-level detection signal continues for one second or longer may be the same as employed in the processes of the steps Sl 12 and Sl 13. [0058] When the low-level state of the water-level detection signal is less than one second (step S 133; NO), the microcomputer 22 discriminates the operation mode indicated by the mode switch 29 (step S 134). When the mode switch 29 indicates the individual operation mode, the process progresses to the individual-operation input scan process (S 120) starting at reference symbol "Bl". When the mode switch 29 indicates the sequential operation mode (step S 134; SEQUENTIAL OPERATION MODE), on the other hand, the process progresses to the step S 135 to determine whether the receptacle current is larger than the threshold value.

When it is determined in step S 135 that the receptacle current is larger than the threshold value, the process returns to step S 132.

[0059] When it is determined that the receptacle current is equal to or smaller than the threshold value, a 5-second timer is activated (step S141), after which a 5-second operation input scan process (step S140) starting at reference symbol "C2" is initiated.

In the 5-second operation input scan process (step S 140), first, it is determined whether the 5-second timer has overflowed, i.e., whether five seconds have passed (step S142).

When it is determined that the 5-second timer has overflowed (step S 142; YES), the microcomputer 22 sets the motor 9 OFF (step S 147), and then initiates the instruction-standby input scan process (step SIlO) starting at reference symbol "A". [0060] When it is determined that the 5-second timer does not overflow (step S 142; NO), the microcomputer 22 first determines whether the main switch 17 is ON or OFF (step S 143). When the main switch 17 is OFF, the microcomputer 22 sets the motor 9 OFF (step S 147), and then initiates the instruction-standby input scan process (step SIlO) starting at reference symbol "A".

When it is determined that the main switch 17 is ON (step S 143; ON), the

microcomputer 22 determines whether the low-level state of the output signal of the water level detecting circuit 28 continues for one second or longer, i.e., whether the electrodes 27a, 27b are soaked in water (step S 144). The scheme of checking if such a state continues for one second or longer is similar to the scheme employed in the processes of the steps S112 and S113.

[0061] When the duration of the low-level state of the water-level detection signal is less than one second (step S 144; NO) ₅ the microcomputer 22 discriminates the operation mode indicated by the mode switch 29 (step S145). When the mode switch 29 indicates the individual operation mode (step S 145; INDIVIDUAL OPERATION MODE), the process progresses to the individual-operation input scan process (step S 120) starting at reference symbol "Bl" in FIG. 5B. When the mode switch 29 indicates the sequential operation mode (step S 145; SEQUENTIAL OPERATION MODE), on the other hand, the microcomputer 22 determines whether the receptacle current is larger than the threshold value (step S146). When it is determined in step S 146 that the receptacle current is larger than the threshold value (step S 146; YES), i.e., when it is determined that the electric tool connected to the receptacle 32 is in operation, the process goes to the sequential-operation input scan process (step S 130).

On the other hand, when it is determined that the receptacle current is equal to or smaller than the threshold value, i.e., when it is determined that the electric tool connected to the receptacle 32 is stopped (step S 146; NO), the process returns to step S 142.

[0062] On the other hand, when it is determined YES in step S 123 in FIG. 5B and steps S133 and S144 in FIG. 5C, i.e., when it is determined that the electrodes 27a, 27b are soaked in water, the microcomputer 22 initiates the water-level detection process starting at reference symbol "D" in FIG. 5A and stops the motor 9 through the motor drive circuit 19.

After the motor 9 is stopped in step Sl 51 and when it is determined YES in step S 113, the microcomputer 22 turns on the alarm indicator 20 (step S 152), and initiates a water-level detection key scan process S 150.

[0063] In the water-level detection key scan process S 150, the microcomputer 22 repeats the process of detecting the ON/OFF action of the main switch 17 until the OFF state of the main switch 17 is detected (step S 153). After water is collected in the tank 2 and above the threshold value, therefore, the dust collector 100 cannot be operated unless the main switch 17 is turned OFF once. [0064] When detecting that the main switch 17 is turned OFF, the microcomputer 22 turns off the alarm indicator 20 (step S 154), and then initiates instruction-standby input scan process SIlO starting at reference symbol "A".

[0065] As described above, as the processes described referring to FIGS. 5A to 5C are executed, in a case where the water-level detecting electrodes 27a, 27b are not soaked in water and the state where the current flowing between the electrodes 27a and 27b is larger than the water-level detection threshold value does not continue for one second or longer, when the power supply plug 16 is connected to the power supply and the main switch 17 is set ON with the mode switch 29 indicating the individual operation mode, the motor 9 is turned on (step S121), thus rendering the dust collector 100 in an operational state. [0066] . When the electric tool connected to the receptacle 32 operates with the main switch 17 being ON and the mode switch 29 indicating the sequential operation mode, the motor 9 is set ON (step S131), bringing the dust collector 100 to an operational state. When the operation of the electric tool is stopped thereafter, the motor 9 is stopped after being operated for about 5 seconds (step S 147). [0067] Further, when the low-level state of the water-level detection signal continues for one second or longer with the motor 9 being ON, the motor 9 is set OFF. That is, when water equal to or greater than the allowable amount is collected in the tank 2 and the current flowing between the water-level detecting electrodes 27a and 27b becomes larger

than the water-level detection threshold value for more than one second, the motor 9 is set OFF to render the suction unit 7 in a halt state. At this time, the alarm indicator 20. is turned on, and the dust collector 100 cannot be brought into an operational state unless the main switch 17 is turned OFF once.

5 [0068] When the main switch 17 is switched ON from the OFF state with the electrodes 27a, 27b being soaked in water, it is detected that the low-level state of the water-level detection signal has continued for one second or longer (steps Sl 12, S 113), the alarm indicator 20 is turned on, and the water-level detection key scan process S 150 is repeated. Therefore, the dust collector 100 does not become an operational state even when the

10 main switch 17 is set ON with the water-level detecting electrodes 27a, 27b being soaked in water.

Even if water in the tank 2 waves so that the water-level detecting electrodes 27a, 27b are soaked in water in instantaneously, the state does not continue for one second or longer, so that the operation of the dust collector 100 is not affected.

15 [0069] According to the embodiment, as described above, even when the main switch 17 is set ON with the electrodes 27a, 27b being soaked in water and the current flowing between the electrodes 27a, 27b exceeding the threshold value in the wet and dry type dust collector 100, the dust collector 100 does not come to an operational state. This prevents occurrence of the state where the repetitive ON/OFF action of the main switch

20 17 causes water to be gradually sucked into the tank 2 to soak the filter 13.

[0070] Even when water in the tank 2 waves so that the water-level detecting electrodes 27a, 27b are soaked in water instantaneously, the operation of the dust collector 100 is not affected.

In the case of the sequential operation, as a given time (five seconds) is provided

25 for the suction unit 7 to halt after the electric tool connected to the dust collector 100 is stopped, it is possible to surely suck dust or the like produced by the electric tool. [0071] In addition, the use of the water level detecting circuit 28 using a pair of

electrodes has an advantage of being capable of suppressing occurrence of malfunction originated by dust or the like, over the mechanical water-level detecting system, such as float type detection.

[0072] Providing a pair of electrodes under the filter can inhibit the filter from being wet with water.

[0073] It is unnecessary to provide mechanical a control unit, so that the dust collector can be configured compact.

[0074] As the alarm indicator is turned on when the water level in the tank 2 exceeds the threshold value, the user can be informed that collection of water in the tank to an allowable limit is the cause for the halting of the suction unit.

[0075] As the enable/disable determining unit that determines whether the operation of the suction unit is enabled or disabled based on a detection signal from the water level detecting unit is provided, it is possible to adequately determine whether the suction unit should be operated or not according to the detection result from the water level detecting unit.

[0076] The present invention is not limited to the foregoing embodiment, and can be modified and adapted in various forms.

For example, the values specified in the foregoing description of the embodiment are illustrative, and are changeable as needed. For example, it is discriminated that water is collected in the tank 2 to a threshold value or above when the low-level state of the water-level detection signal continues for one second or longer. The sustaining time can be set arbitrarily according to the size or the like of the tank 2. The assumed value, threshold value and so forth of the current flowing between the electrodes 27a and 27b are set adequately according to the size of the tank 2, the applied voltage and the like. [0077] Likewise, in the electric operation mode, the time to stop the motor 9 after an external electric tool connected is stopped is not limited to five seconds, and is optional.

The hardware configuration and the operation can be modified as needed as long

as functions similar to those of the present invention can be achieved. [0078]

Various embodiments and changes may be made thereunto without departing from the broad spirit and scope of the invention. The above-described embodiment is (embodiments are) intended to illustrate the present invention, not to limit the scope of the present invention. The scope of the present invention is shown by the attached claims rather than the embodiment (embodiments). Various modifications made within the meaning of an equivalent of the claims of the invention and within the claims are to be regarded to be in the scope of the present invention. [0079] This application is based on Japanese Patent Application No. 2008-009693 filed on January 18, 2008, the entire contents of which are incorporated herein by reference.