JP2008180163A5 - - Google Patents

Description

dishwasher

The present invention relates to dishwashers that are used like industrial and general household or business using a pump equipment for transferring liquid, such as water.

  Conventionally, this type of dishwasher using a pump device detects a rotational speed detected by a rotation sensor by temporarily rising when bubbles are sucked into the pump (see, for example, Patent Document 1). .

  FIG. 12 shows a cross-sectional view of a conventional dishwasher described in Patent Document 1. As shown in FIG. As shown in FIG. 12, the pump 2 using the DC brushless motor 1 has a rotation sensor 4 using a Hall IC for detecting the position of the rotor 3, and the rotation speed can be adjusted from a separately provided control device. The value of the rotation speed of the impeller 5 directly connected to the rotor 3 can be detected from the output of the rotation sensor 4. The washing water sent out from the impeller 5 is jetted into the chamber from the nozzle 6, but when it is lower than the reference water level H, bubble biting occurs.

FIG. 13 shows a pump rotation speed graph when the conventional dishwasher described in Patent Document 1 is chewed with foam. From the time t1 when the generation of bubbles starts to increase, the torque of the load is reduced, and the rotation speed is increased. From S0 without foaming, to reduce the speed at the time t2 when S1 is reached, the speed is reduced. By operating at S2 at a reduced rotational speed, the operation that prevents the biting of the bubbles is continued for 5 minutes, and then returned to the steady rotational speed S0 at t3.
JP-A-2005-511

  However, the conventional configuration has a problem that the device becomes expensive because the rotation sensor 4 using, for example, a Hall IC is required.

  In the prior art, the rotation sensor 4 detects the position of the rotor 3 having a permanent magnet when the DC brushless motor 1 is operated, and therefore exists when the DC brushless motor 1 is configured. However, the cost is high, and there is a configuration in which the DC brushless motor 1 is operated without the rotation sensor 4 using a technique called sensorless vector control, for example.

  However, even if such a configuration is used, an expensive control device generally called an inverter circuit or the like is required, and thus there is an unavoidably high cost.

  On the other hand, it is extremely effective to use a kind of induction motor (induction motor) such as a capacitor motor (capacitor run motor), which is much more effective than a DC brushless motor. Cost can be reduced.

  However, in that case, providing the rotation sensor 4 again for detecting the bubble biting leads to an increase in cost, and the rotation sensor 4 is provided only for the bubble biting detection. When wiring to a circuit board using a microcomputer or the like is provided, there is a problem that even if a low-priced induction motor is used, the cost advantage is small.

The present invention is intended to solve the above problems, in terms of using the induction motor of the low cost, the rotation sensor is not required, Awakami to realize a dishwashing machine using a low cost pump equipment that can be properly detected For the purpose.

In order to solve the above-mentioned problems, a dishwasher according to the present invention has an induction motor that has a plurality of windings including a phase advance capacitor and a winding in which the phase advance capacitor is connected in series, and is supplied with power from an AC power source. A current detection circuit that detects a current flowing through at least one winding, a voltage detection circuit that outputs a signal synchronized with a voltage waveform of the AC power supply, and a bubble biting determination unit, In response to the signal from the current detection circuit, the phase of which changes with respect to the voltage detection circuit, the bubble biting is determined.

As a result, it is possible to realize a dishwasher that does not require an inverter circuit, uses a low-cost induction motor, has a rotation sensor, and is capable of determining bubble biting with a relatively simple configuration. Become.

The present invention can realize a dishwasher using an induction motor and having a low-cost configuration without a rotation sensor and capable of determining bubble chewing.

  A first invention has a plurality of windings including a phase advance capacitor and a winding in which the phase advance capacitor is connected in series, and flows through an induction motor supplied with power from an AC power source and at least one winding A current detection circuit that detects a current; a voltage detection circuit that outputs a signal synchronized with a voltage waveform of the AC power supply; and a bubble biting determination unit, the bubble biting determination unit being in phase with respect to the voltage detection circuit By receiving a signal from the current detection circuit that changes, the configuration is such that the bubble biting is judged, so that it is relatively easy to use the bubble biting while using an inexpensive induction motor and having no rotation sensor. The determination can be made.

  In the second invention, in particular, the voltage detection circuit of the first invention is configured to output a digital signal having an edge near the zero volt point of the AC power supply, so that the voltage detection circuit can be configured with a relatively simple configuration. It can be realized.

  In the third aspect of the invention, in particular, the current detection circuit of the first aspect of the invention is configured to detect the current of the winding to which the phase advance capacitor is not connected, so that it is possible to accurately determine the bubble biting. It will be a thing.

  In the fourth aspect of the invention, in particular, the current detection circuit of the first aspect of the invention is configured to detect the current supplied from the AC power source to the induction motor, and thereby various types of current values supplied to the induction motor are used. In conjunction with the control, it is possible to determine the bubble biting.

In particular, the fifth invention is a mixed region of a plurality of power supply frequencies by providing power supply frequency detection means for detecting the frequency of the AC power supply in addition to the configuration of any one of the first to fourth inventions. Even under AC power supply conditions such as Japan, it is possible to make a correct bubble biting determination adapted to each frequency .

Following, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a circuit diagram of a pump device according to a first embodiment of the present invention. In FIG. 1, an AC power supply 10 having the possibility of two types of frequencies of 100 V 50 Hz or 60 Hz, an induction motor 11 having one terminal connected to the AC power supply, a phase advance capacitor 12, a triac 13, a voltage detection circuit 15, and a current detection circuit 17. A bubble biting judging means 18, constituted by a microcomputer, a 5V DC power supply 20, and resistors 22, 23, 24 and a transistor 25 for turning on and off the triac 13 according to the output Q of the bubble biting judging means 18 are provided. It has become a thing.

  The induction motor 11 includes two windings 30 and 31 and a rotor 32. The winding 30 operates as a main winding, and the winding 31 is connected to the phase advance capacitor 12 in series. In addition, the AC power supply 10 operates as an auxiliary winding to which a current having a phase advanced from that of the winding 30 is supplied.

  The voltage detection circuit 15 includes diodes 35 and 36, resistors 40, 41, 42, 43, and 44, a photocoupler 50 configured as a composite part of a light emitting diode and a phototransistor, a transistor 51, and a capacitor 52, and has a polarity of VAC. Is a high signal in the positive period, low in the negative period, and a digital signal having an edge is output at a timing near the zero volt point where the instantaneous voltage of the AC power supply 10 becomes almost zero.

  The voltage detection circuit 15 used in the present embodiment is assumed to be high / low with respect to the period in which the polarity of the AC power supply 10 is positive / negative, and the edge is near the zero volt point. However, for example, a high signal may be output for a short time near the timing when the absolute value becomes zero, and various circuit configurations may be considered, but any configuration may be used. The voltage detection circuit that generates a signal having an edge near the zero volt point has a relatively simple configuration, and even when the voltage of the AC power supply 10 changes, the relationship between the AC power supply 10 and the edge is affected. In particular, when detecting the phase of the current, there is an advantage that it is possible to operate stably.

  The current detection circuit 17 includes a current transformer 60 having a primary coil connected in series with the winding 30, resistors 61, 62, 63 and 64, protective diodes 66 and 67, and a capacitor 68. Is detected, and an analog voltage V1 corresponding to the instantaneous value of the current is output, which is called a main winding on the side where a phase advance capacitor 12 is not connected in a so-called capacitor motor. A voltage having a waveform corresponding to the current waveform of the winding 30 is output.

  FIG. 2 is a waveform diagram showing the operation of each part of the pump device in the present embodiment when the AC power supply 10 is 60 Hz and foaming is occurring. The voltage VAC waveform, (A) shows the waveform of the output voltage Vz of the voltage detection circuit 15, and (C) shows the waveform of the output voltage Va of the current detection circuit 17.

  At time t0, the voltage of the AC power supply 10 becomes zero, but as shown in (A), at this moment, the voltage detection circuit 15 causes the output voltage Vz to rise from low to high. . After that, every 8.33 ms, the AC power supply 10 is half cycle and repeats high and low.

  Further, (c) is the sampling of the voltage value Va at the timing of t0, t1, t2, t3..., And in the bubble biting judgment means 18 constituted by the microcomputer as v0, v1, v2, v3. It will be taken in.

In the present embodiment, a DC power supply 20 of 5V is used, and the resistors 62 and 63 are both 4.7 kilohms. Therefore, the voltage waveform of Va shown in (c) is 2 at the current zero point. .5V corresponds to the waveform in which the similar waveform of the current waveform flowing in the winding 30 is superimposed on this, and the positive and negative have almost the same amplitude, so the zero point of the current is converted to Va = 2.5V Therefore, analog / digital conversion (A / D conversion) becomes possible by effectively using the voltage range of 0 to 5V, and when converting to an 8-bit digital value, 128 correspond to the positive current value from 129 to 255, and the negative current value from 0 to 127.

  The current waveform flowing through the winding 30 is operated with a delay phase of about 40 degrees with respect to the voltage in the state where there is no bubble biting, but bubble biting occurs and the load torque of the induction motor 11 is reduced. In this case, the amplitude decreases, and at the same time, the power factor of the current supplied to the winding 30, that is, the phase with respect to the voltage waveform of the AC power supply 10 shows a significant change, which is nearly 90 degrees (π / 2). The current phase is delayed until.

  In addition, the Q value (resonance strength) of the resonance operation of the winding 31 and the phase advance capacitor 12 is increased, and the third order to the excitation current due to the magnetic saturation of the iron core in the induction motor 11. Due to the influence of the generation of harmonic components and the like, the distortion of the current and voltage waveform of each part tends to increase.

  However, the degree of occurrence of such a change and the fact that the phase of the current is delayed as compared with the case where there is no bubble biting varies depending on the design of the induction motor 11 and the design of the phase advance capacitor 12. In some cases, the phase change may be reversed.

  FIG. 3 shows a flowchart of a microcomputer program used for the bubble biting determination means 17 of the pump device of the present embodiment.

  In FIG. 3, the process starts from the start 69, passes through the frequency determination routine 70, reaches the Vz rising edge 71, waits for the rising edge of the Vz signal, and moves to the following process.

  In the input 72, the respective sampling data v0 to v11 are sequentially input, and in the fundamental wave calculation 73, approximate values of values corresponding to the sine component and cosine component in terms of Fourier series expansion are signed into the variables S1 and C1. A 16-bit variable is used, and the sum of squares thereof is calculated in A1, which corresponds to an approximate value of a value corresponding to the square of the absolute value of the fundamental wave component.

  In addition, as described above, the current value of zero corresponds to a value of 128, but in the calculation of S1 and C1, in principle, it is canceled by one cycle of integration (sigma calculation). Therefore, even if the digital value corresponding to zero current deviates from 128 due to, for example, resistance value variations of the resistors 62 and 63, the calculation results such as S1, C1, and A1 are not affected. Therefore, even if resistors 62 and 63 having low cost and uneven resistance values are used, the results can be hardly affected.

  As for the fundamental wave calculation 73, since A1 is a value proportional to the square of the effective value of the fundamental wave current, square root calculation may be performed, but in order to reduce the load on the microcomputer, In the form, it is assumed that the numerical value in the state corresponding to the square is used.

  In the A1 determination 74, when the value of the fundamental wave component is equal to or less than a predetermined value, it is excluded from the target condition for the bubble biting determination, thereby generating an unnecessary signal when the induction motor is stopped. It is something that is preventing.

  The fundamental wave calculation 73 performed in the present embodiment is a simple calculation method for calculating an approximate value. In order to further increase the accuracy, a method of shortening the sampling phase interval is used. If it is used, it is possible to suppress a change in the calculated value due to the phase of each order component and a change in the calculated value due to the presence or absence of higher harmonic components.

  In the present embodiment, all 12 data for one cycle of the AC power supply 10 are once input and then S1 and C1 are calculated. However, addition or subtraction may be performed each time sampling is performed. Well, in that case, a slightly higher processing speed of the microcomputer is required, but it is possible to shorten the time until results are obtained, and to reduce the area for storing data The benefits of being able to do so will occur.

  In order to suppress the influence of calculation due to higher harmonics higher than the third order, for example, a method of adding a hard filter circuit in RC and inserting it into the output of the current detection circuit 17 is also effective. There is.

  Further, in order to shorten the sampling phase interval, it may be necessary to increase the processing speed of the microcomputer, but in one cycle (16.67 ms at 60 Hz), all sampling is not completed. If a method of sampling the intermediate timing of the sampling phase of the first cycle in the cycle is used, the microcomputer can be used even with a low processing speed.

  In the tangent calculation 76, a value corresponding to the tangent of the phase angle of the fundamental current with respect to the voltage waveform is obtained from S1 and C1 already calculated, and is set as a variable T1. In other words, when the delay phase is large, it is determined in the “bubble engagement” determination 78 that bubble engagement has occurred, and in this embodiment, Y = −2.1. Thus, appropriate bubble biting determination is made.

  Therefore, in the pump device of the present embodiment, the bubble biting determination means 18 receives a signal including a harmonic component that increases when the bubble bites, from the current detection circuit 17, and determines the bubble biting. In addition, the bubble biting determination means 18 is configured to determine the bubble biting when the predetermined phase range of the current detection circuit 17 with respect to the voltage detection circuit 15 is exceeded.

  In any case, it is not the absolute value (amplitude) of the current but the target of the phase, so that it is less susceptible to variations in characteristics of the current transformer 60 and the resistor 61 of the components of the current detection circuit 17. Thus, there is an effect that it is realized as a pump device capable of performing the bubble biting determination with high reliability.

  FIG. 4 is a flowchart showing the details of the frequency determination routine 70 in some detail. In FIG. 4, from the start 85 of this routine, a Vz rise wait 86 is entered, and at the rise of the Vz signal, the process moves to 18.3 ms wait 87, and after 18.3 ms, Vz = High? If it enters 88 and is high, it will be determined that it is 60 hertz, and if it is low, it will be determined that it is 50 hertz.

  The above-described portion is the configuration of the power supply frequency determination unit 89, and the frequency is determined by reconfirming the state of the Vz signal when 18.3 ms has elapsed from the rising timing of the Vz signal. However, the power frequency determining means 89 is not particularly required to have such a configuration, and various other configurations can be used, and the determination result of the power frequency is affected by noise or the like. For the purpose of elimination, a configuration in which a final determination is performed after performing a plurality of determinations is often used and is very effective in preventing malfunction.

  In the case of 60 Hz, substitution of Y ← −2.1 is performed at 90, and substitution of Ts ← 1.39 ms is performed at 91.

  On the other hand, in the case of 50 hertz, substitution of Y ← −3.1 is made at 93, and substitution of Ts ← 1.67 ms is made at 94.

  Here, Ts is a sampling time interval, and a value that is one-twelfth of the period of the AC power supply 10 is set as Ts. With regard to Y, when bubble biting occurs The value of Y is set according to each frequency as a threshold value that can sufficiently detect the change in phase that occurs.

  In the present embodiment, since the same value is set for X regardless of whether it is 50 Hz or 60 Hz, the flowchart is configured with the X setting 95 combined into one. ing. However, especially when the magnitude of the current is significantly different between 50 Hz and 60 Hz, the values of X may be different from each other, and can be realized by moving before the merge of the flowcharts. At return 96, the frequency determination routine 70 is completed and the process returns to the main routine.

  In this way, the pump device of the present embodiment has the power frequency detecting means 89 for detecting the frequency of the AC power supply 10, and corresponds to two AC power supply frequencies of 50 Hz and 60 Hz, respectively. By setting a value, the threshold value for bubble biting determination is changed, so even in conditions where 50 Hz and 60 Hz regions are mixed as in Japan, at any frequency It is possible to realize a pump device that can perform correct bubble biting determination.

  FIG. 5 shows the output voltage waveform of the current detection circuit 17 in 60 Hz of the pump device of the present embodiment, in which the absence of bubble engagement is indicated by a broken line, and the presence of bubble engagement is indicated by a solid line. (A) shows the output voltage waveform of the voltage detection circuit 15.

  FIG. 6 shows the output voltage waveform of the current detection circuit 17 in 50 Hz of the pump device of the present embodiment, in which the absence of bubble biting is indicated by a broken line, and the presence of bubble biting is indicated by a solid line, (A) shows the output voltage waveform of the voltage detection circuit 15.

  As can be seen in FIG. 5, there are some differences in the current value and current waveform due to the difference in the power supply frequency conditions of 50 Hz and 60 Hz. Since the phase is more delayed when there is a bubble bite, the T1 value corresponding to the tangent of the phase is obtained, and the configuration of this embodiment in which the threshold is appropriately set for each power supply frequency is used. As a result, it is possible to determine the presence or absence of foam biting with sufficient reliability.

(Embodiment 2)
FIG. 7 is a circuit diagram of a pump device according to the second embodiment of the present invention. In FIG. 7, the current detection circuit 17 is connected, and the current to be detected is the supply portion from the AC power source to the induction motor 11. However, the configuration of the other portions is the first embodiment. There is no change, and it uses exactly the same components.

  Therefore, in the present embodiment, the amount of electricity detected by the current detection circuit 17 is a current supplied from the AC power supply 10 to the induction motor 11.

FIG. 8 shows the waveform of the output voltage of the current detection circuit 17 in the present embodiment, which corresponds to the current waveform obtained by summing the supply currents of the induction motor 11. In FIG. 8, (a) is an output waveform of the current detection circuit 17, the state without bubble biting is indicated by a broken line, and the state with bubble biting is indicated by a solid line. Indicates the logic waveform of the output signal of the voltage detection circuit 15. The frequency of the AC power supply 10 is 60 Hz.

  When there is no bubble biting, the current phase is in a high power factor state almost in phase with the voltage. However, when bubble biting occurs, the current phase tends to advance, and at the same time third harmonics, etc. With the addition of harmonic components, the waveform is somewhat distorted.

  In the present embodiment, when there is a bubble bite, the phase of the output of the current detection circuit 17 advances with respect to the output signal of the voltage detection circuit 15, which is the reverse of the first embodiment. Thus, it is possible to determine the bubble biting when the advance phase is increased, that is, when a predetermined positive Y value is exceeded.

  Although it is omitted for the case of the 50 Hz AC power supply 10, since the fundamental wave component of the current tends to advance in the case where there is bubble biting, it is possible to determine bubble biting in the same manner. As the threshold value, there is a tendency for the threshold value to be somewhat smaller (closer to 0 degree) than 60 Hz. Therefore, the threshold value Y by the frequency detection means described in the first embodiment is set as necessary. By using switching or the like, it is possible to perform appropriate bubble biting determination at both frequencies of 50 Hz and 60 Hz.

  In the present embodiment, the magnitude of the current input to the current detection circuit 17 is larger than that in the first embodiment and the second embodiment. Although there is a tendency to require a somewhat larger specification, since it becomes a total current supplied to the induction motor, detection of the state of the induction motor 11 other than the presence or absence of bubble chewing, for example, grasping the state of heat generation, Or it expands as a range which can be used for another control.

(Embodiment 3)
FIG. 9 is a cross-sectional view of a dishwasher according to the third embodiment of the present invention. In FIG. 9, the induction motor 11, the phase advance capacitor 12, the triac 13, the current detection circuit 17, and the bubble biting determination means 18 are the same as those described in the first embodiment, and the pump device 110 is configured. The bubble biting determination is performed based on the phase of the current of the winding 30 with respect to the output of the voltage detection circuit 15.

  As shown in FIG. 1 and the like, the triac 13 is turned on when the Q signal output from the bubble biting determination means 18 using a microcomputer is high, and is turned off when the signal is low. ing.

  The water supply pipe 112 and the water supply valve 113 connected to the water supply constitute the water supply means 114, and the water supply valve 113 can be controlled to be opened / closed by the microcomputer used for the bubble biting determination means 18. It has become.

  The operation of the dishwasher includes a washing process in which water (washing water) containing detergent in the dishes is circulated by the pump device 110, and a rinsing process in which fresh water is circulated. At the stage of completion, there is a process of draining the in-machine water or the washing water from the pump device 110 to the outside of the machine.

FIG. 10 shows an operation waveform diagram of the washing process. (A) is a signal sent to the water supply valve 113 of the water supply means 114, and if it is high, water is supplied. (A) is an output signal of the bubble biting detection means 18. If it is high, it is in a state where it is determined as bubble biting. (C) is an on / off signal Q to the triac 13, and if it is high, the induction motor 11 is driven.

  In the period of the washing process in which dishes are being washed, the dishwasher of the present embodiment temporarily supplies the water supply means 114 at the time t2 when the water supply means 114 is in a water supply state at t1 and the minimum amount of water is introduced into the machine for the time being. Becomes a state where water supply is stopped, and at the same time, Q rises and the pump device 110 is operated. At t3, the pump device 110 determines that the foam is engaged, and at t4, the water supply valve 113 is opened, and the water supply means 114 performs the water supply operation until t5 after 5 seconds from t4.

  In the present embodiment, since the Q signal continues to be high, the induction motor 11 continues to be driven, and the high signal continues until the bubble bite disappears. By such an operation, the water level in the machine rises and the occurrence of bubble biting is suppressed. Thereafter, when the bubble biting determination means 18 detects that there is a bubble bite, the water supply operation is performed each time.

  Therefore, in the present embodiment, when there is no bubble biting, the operation is continued at the same water level, so that it is possible to operate with a sufficient amount of water necessary for the operation of the pump device 110, and wasteful water Consumption can be reduced as much as possible.

  FIG. 11 shows an operation waveform diagram at the time of drainage, and (a), (b), and (c) show operation waveform diagrams of the same part as FIG. At the time of drainage, the drainage operation is started by setting Q to high at time t6, but Q is set to low at time t7 when there is a determination of bubble biting while the pump device 110 is operating. Then, the induction motor 11 is temporarily stopped and the pump device 110 stops operating.

  This is an operation for avoiding the occurrence of bubble biting once the function of the drainage is extremely impaired even if the operation of the pump device is continued as it is.

  As a result, the air that has been engaged in the foam returns to the water surface, and the pump device 110 naturally returns to the state without the foam engagement. At t8 after 5 seconds, Q is set to high, the TRIAC 13 is turned on again, and the draining operation is continued again. By performing such an operation, the amount of water remaining in the machine after draining (residual water amount) ) Can be suppressed as much as possible.

  Therefore, it becomes possible to improve the performance of rinsing by reducing the amount of residual cleaning water containing dirt and detergent, shorten the time by reducing the number of times of rinsing, and when all the steps are completed Since the amount of remaining water can be minimized, adverse effects on the next operation due to rot can be minimized.

As described above, the dishwasher according to the present invention has the induction motor, and the bubble biting determination means receives the signal from the current detection circuit whose phase changes with respect to the voltage detection circuit when the bubble biting occurs. By using the low-cost induction motor, the rotation sensor is unnecessary and the low-cost pump device that can detect the bubble biting appropriately, and the use of wasted water using this are suppressed, A dishwasher that reduces the amount of residual water during drainage can be realized.

Circuit diagram of pump device in Embodiment 1 of the present invention (A) Voltage waveform diagram of AC power supply of the pump device (A) Output voltage waveform diagram of the voltage detection circuit (C) Output voltage waveform diagram of the current detection circuit Main flowchart of microcomputer used for bubble biting determination means of the pump device Flowchart of microcomputer frequency determination routine of the pump device (A) Output voltage waveform diagram of current detection circuit at 60 Hz of the pump device (A) Output voltage waveform diagram of the voltage detection circuit (A) Output voltage waveform diagram of current detection circuit at 50 Hz of the pump device (A) Output voltage waveform diagram of the voltage detection circuit Circuit diagram of pump device in embodiment 2 of the present invention (A) Output voltage waveform diagram of the current detection circuit of the pump device (A) Output voltage waveform diagram of the voltage detection circuit Sectional drawing of the dishwasher in Embodiment 3 of this invention (A) Operation waveform diagram of water supply means in the washing process of the dishwasher (A) Operation waveform diagram of the bubble biting detection means (C) Operation waveform diagram of the triac (A) Operation waveform diagram of water supply means during drainage of the dishwasher (a) Operation waveform diagram of the bubble chewing detection means (c) Operation waveform diagram of the triac Cross-sectional view of a conventional dishwasher Waveform diagram of the dishwasher

DESCRIPTION OF SYMBOLS 10 AC power source 11 Induction motor 12 Phase advance capacitor 15 Voltage detection circuit 17 Current detection circuit 18 Bubble biting determination means 30, 31 Winding 89 Power supply frequency detection means

Claims (5)

An induction motor having a plurality of windings including a phase-advancing capacitor and a winding in which the phase-advancing capacitors are connected in series, and an electric current supplied from an AC power source, and current detection for detecting a current flowing through at least one winding a voltage detection circuit for outputting a circuit, a signal synchronized with the voltage waveform of the AC power source, and a Awakami determining means, said bubble chewing determining means, said current phase changes with respect to the voltage detecting circuit A dishwasher that receives a signal from the detection circuit and determines whether or not it is chewing. 2. The dishwasher according to claim 1, wherein the voltage detection circuit outputs a digital signal having an edge near the zero volt point of the AC power supply. The dishwasher according to claim 1, wherein the current detection circuit detects a current of a winding to which a phase advance capacitor is not connected. The dishwasher according to claim 1, wherein the current detection circuit detects a current supplied from the AC power source to the induction motor. The dishwasher according to any one of claims 1 to 4, further comprising a power frequency detection means for detecting the frequency of the AC power.