Abstract:
The invention provides an apparatus ( 8 ) for cleaning cloth which includes a body ( 10 ) with an aperture, a closure, which is engageable with the aperture, a tub ( 26 ) with an outer shell and a cylindrical Inner cavity which corresponds with the aperture, a drum ( 28 ), which is positioned inside the cylindrical inner cavity ( 54 ) and which includes a wall, with an inner surface, an outer surface and a plurality of perforations ( 62 ) in the wait, a base ( 64 ) and an opposing mouth ( 66 ) which registers with the aperture, a drive means ( 30 ) which is connected to or engaged with the drum and which allows rotational movement of the drum about an axis, a generator ( 32 ) and an electrical power supply ( 78 ), inside the body, wherein the power supply is adapted to provide pulsating electrical power to the generator and wherein the generator is actuable to produce pulses of microwave energy at least into part of the drum.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to a method of cleaning cloth using pulsed microwave energy. 
         [0002]    Machines which make use of microwave energy to clean and/or dry cloth are known in the art. Most of these machines focus on using microwaves to heat the water used during the cleaning process, thereby using less energy than machines that make use of, for example, heating elements. Machines which have a drying function focus on heating the water within the wet or damp cloth, speeding up the drying process. 
         [0003]    Developments in this field of application, have been to positioning a microwave-generating device (the magnetron) within washing machines, as well as methods of directing microwaves to the desired objects, i.e., the water to be heated or the fabric to be dried. U.S. Pat. Nos. 4,356,640, 5,463,821 and 4,334,136 are examples in this regard. 
         [0004]    An important piece of prior art in relation to the present invention is US Patent Application US2002/0062667, entitled “Method and apparatus for washing items having cloth with microwaves”. The specification teaches an apparatus that relies on continuous microwave irradiation onto wet cloth in order to agitate water and soap/detergent molecules within the cloth. The agitation comes about as a result of rotational motion of the molecules due to said microwave irradiation, the primary effect of which is the enhanced cleaning effect of water and detergent. A secondary effect of such irradiation is an increase in temperature of the water itself. 
         [0005]    A drawback of the apparatus is discovered upon practical use thereof. The microwave energy that can be used without adversely affecting the cloth was experimentally found to be relatively low. Consequently, the microwave irradiation would have to be applied for relatively long periods of time in order to achieve enhanced cleaning results. Even then, the degree of cleaning, whilst being better than that achieved through ordinary cleaning means, may not be much greater. The use of detergent would then be additionally needed in order to achieve the enhanced clean. The prior art therefore prescribes the use of detergent to achieve this. 
         [0006]    The invention at least partially addresses the aforementioned limitations of the prior art. 
       SUMMARY OF INVENTION 
       [0007]    The present invention provides an improved method of cleaning cloth utilizing microwave radiation and the pulsing thereof. 
         [0008]    The invention provides an apparatus for cleaning cloth which includes a body with an aperture, a closure, which is engageable with the aperture, a tub with an outer shell and a cylindrical inner cavity which corresponds with the aperture, a drum, which is positioned inside the cylindrical inner cavity and which includes a wall, with an inner surface, an outer surface and a plurality of perforations in the wall, a base and an opposing mouth which registers with the aperture, a drive means which is connected to or engaged with the drum and which allows rotational movement of the drum about an axis, a generator and an electrical power supply, inside the body, wherein the power supply is adapted to provide pulsating electrical power to the generator and wherein the generator is actuable to produce pulses of microwave energy at least into part of the drum. 
         [0009]    The closure may be a door which is fixed to, or removably engaged with, the body. 
         [0010]    The body may include a plurality of vents which provide a passage for air into and out of the body. 
         [0011]    The body may include an inlet and an outlet which allow water to enter and leave the body. 
         [0012]    The drive means may include at least one pulley, which is engaged with the base of the drum, which is connected to an electric motor by means of a belt. Alternatively, the motor may drive the drum directly. 
         [0013]    The drum may have a volume in the range of 10 to 100 litres. 
         [0014]    The generator may be a magnetron. 
         [0015]    The power supply of the magnetron may be a switched mode power supply. 
         [0016]    The apparatus may include at least one of the following control elements located in or on the body; an air heating element, an air bypass flap, an air blower, a microwave choke, a microwave inlet, a water heater, and an exhaust air vent. 
         [0017]    The apparatus may include a sensor to detect at least one of the following: microwave field strength, temperature within the drum, sump water level, water conductivity, drain water level, rinsing water temperature, exhaust gas quality, exhaust gas humidity, exhaust air temperature and inlet air temperature. 
         [0018]    The apparatus may include a programmable microcontroller or microprocessor circuit, electronically interposed between the sensor and the at least one control element, to receive input from the sensor and, in response to control the operation of the control element. 
         [0019]    By controlling the operation of the at least one control element, in response to input from the at least one sensor, the programmable microcontroller or microprocessor may be capable of controlling any one or more of the following: water flow, water quality, water level, microwave power, duty cycle, air velocity, air temperature and drum rotation (hereinafter collectively referred to as “washing parameters”). 
         [0020]    The apparatus may include a user interface which is capable of communicating the washing parameters listed above, to a user. 
         [0021]    The user interface may allow a washing load setting to be input by the user. The washing load setting may relate to one of the following: mass of load of cloth to be cleaned, type of the cloth to be cleaned, and scheduling of cleaning. 
         [0022]    The user interface may be capable of communicating the washing load settings to the programmable microcontroller or microprocessor circuit. 
         [0023]    The invention also provides a method of cleaning cloth with the apparatus described in any one of the preceding claims, the method including the steps of:
       a) placing the cloth into a drum;   b) moistening the cloth in the drum with a liquid; and   c) irradiating the cloth in the drum with the pulses of microwave energy generated by the generator.       
 
         [0027]    The generator may generate pulses of microwave energy at a power density in the range 5 kW and 5000 kW per cubic meter of the volume of the drum. Preferably, the generator generates pulses of microwave energy at a power density of 100 kW per cubic meter of the volume of the drum. 
         [0028]    The power of each pulse of microwave energy may be regulated using the power supply to be in a range of 1 kW to 30 kW. Preferably, the power of each pulse of microwave energy is regulated using the power supply to be in a range of 3 kW to 5 kW. 
         [0029]    The pulses may be regulated using the power supply to be at duty cycles ranging between 5% and 33%. 
         [0030]    The cloth may be moistened by spraying a stream of liquid into the drum. 
         [0031]    The method may include an additional step of frequently or continuously draining the liquid out of the drum such that at least part of the cloth is not submerged during irradiation. 
         [0032]    The method may include the additional step of introducing a hot air stream into the drum to dry the cloth. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    The invention is further described by way of example with reference to the accompanying drawings in which: 
           [0034]      FIG. 1  is a perspective view of a cleaning apparatus according to the invention; 
           [0035]      FIG. 2  is a front view of the cleaning apparatus of  FIG. 1 ; 
           [0036]      FIG. 3  is a perspective view of the cleaning apparatus of  FIG. 1  in a disassembled form; 
           [0037]      FIG. 4  is a plan view of the cleaning apparatus; 
           [0038]      FIG. 5  is a typical power supply required to pulse a 1 kW magnetron; 
           [0039]      FIG. 6  shows the process control system. Inputs are on the left of the process controller and outputs are on the right; 
           [0040]      FIG. 7  is a schematic of a cleaning apparatus illustrating process control elements that are included: 
           [0041]      FIG. 8  is a prepared cloth to be cleaned experimentally using the invention, with various stains having been put on the cloth: 
           [0042]      FIG. 9  compares a prepared grease stain with the cleaning results of continuous microwave energy and pulsing microwave energy after 10 minutes of cleaning using each method; 
           [0043]      FIG. 10  compares a prepared Engine oil stain with the cleaning results of continuous microwave energy and pulsing microwave energy after 10 minutes of cleaning using each method; 
           [0044]      FIG. 11  compares a prepared Pepsi Cola stain with the cleaning results of continuous microwave energy and pulsing microwave energy after 10 minutes of cleaning using each method; 
           [0045]      FIG. 12  compares a prepared Wood-oil stain with the cleaning results of continuous microwave energy and pulsing microwave energy after 10 minutes of cleaning using each method; 
           [0046]      FIG. 13  compares the cleaning results of continuous microwave energy and pulsing microwave energy on a prepared Margarine stain after 10 minutes of cleaning using each method; 
           [0047]      FIG. 14  compares a prepared Kool-aid stain with the cleaning results of continuous microwave energy and pulsing microwave energy after 10 minutes of cleaning using each method; 
           [0048]      FIG. 15  compares a prepared Ketchup stain with the cleaning results of continuous microwave energy and pulsing microwave energy after 10 minutes of cleaning using each method; and 
           [0049]      FIG. 16  compares the cleaning results of continuous microwave energy and pulsing microwave energy on a prepared Engine oil stain after 20 minutes of cleaning using each method. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
       [0050]      FIG. 1  shows a cleaning apparatus  8  to be used according to the invention which includes a body  10  which encloses a volume  12 . The body includes a top  14 , a base  16 , a front panel  18 , a rear panel  20  and two opposing side panels  22  and  24 . 
         [0051]    The apparatus further includes a tub  26 , a drum  28 , a drive means  30  and a generator  32  (see  FIG. 3 ). 
         [0052]    The front panel  18  has an aperture  34 . 
         [0053]    The aperture  34  is closed during operation of the cleaning apparatus by means of a closure  36 , e.g. a door. The closure  36  is engaged with the body  10  by means of a hinge (not shown), but may also be removably engaged with the body  10 . 
         [0054]    The invention is not limited in this respect. 
         [0055]    The body  10  includes a plurality of vents respectively  38  and  40 , an inlet  42  and an outlet  44 . The inlet  42  is in connection with a valve  46  e.g. a solenoid valve, which is engaged with the tub  26  and which regulates the passage of water into the tub  26 . The outlet  44 , which is also in connection with the tub  26 , provides a passage for water out of the body  10 . At least one of the plurality of vents is positioned on the side panel  22 . A removable filter  50  covers the vent  38 , which is on the side panel  22 , and ensures that clean air is fed into the body  10 . 
         [0056]    The tub  26  is positioned inside the body  10  and includes an outer shell  52  and a cylindrical inner cavity  54 . The openings of the cylindrical inner cavity  54  are in register with the aperture  34 . The tub  26  is in connection with the inlet  42  and the outlet  44 . 
         [0057]    The drum  28  is located inside the tub  26  and includes an inner surface  58  and an outer surface  60 , which closely lines the cylindrical inner cavity  54  of the tub  26 , a base  64  and a mouth  66 . The inner surface  58  and the outer surface  60  include a plurality of perforations  62  which allow water, which is in the tub during a wash cycle, to enter the drum  28 . The base  64  is connected to the drive means  30  which allows for rotational movement of the drum about an axis during each wash cycle. The drive means  30  includes a pulley  70  which is linked to an electric motor  72  by means of a belt  74  e.g. a V-belt. The electric motor  72  is secured to the rear panel  20  of the body and causes the drum  28  to rotate for a predetermined duration and speed. This is best illustrated in  FIG. 4 . 
         [0058]    The generator  32 , which is located inside the body  10 , includes a magnetron  76  which produces pulses of electromagnetic waves at a microwave frequency e.g. 2.45 GHz, which are directed into at least part of the drum  28 . 
         [0059]      FIG. 5  shows a block diagram of a typical switched-mode power supply  78  used to pulse the magnetron  76 . The power supply  78  converts normal single-phase household mains electricity (230 Volts in South Africa) from alternating current (ac) form to direct current (dc) form, using a rectifier circuit  80 . A switching circuit  82  then functions as an inverter which outputs high-frequency ac voltage. The frequency and duty cycle of this high-frequency ac voltage are controlled by a programmable microcontroller  88 , which ultimately determines the output power of the power supply  78 . The high-frequency ac voltage is ramped up using a step-up transformer  84 , and then rectified by a second rectifier  86  to give an output dc voltage. This power supply  78  is used because of the following benefits: compact size; light weight due to exclusion of an iron transformer in its construction; variable output voltage and power due to existence of a programmable microcontroller  88  in its circuitry; and capabilities of supplying a pulsed output voltage. 
         [0060]    The invention extends to a method that makes use of pulsed microwaves to clean cloth using the cleaning apparatus  8  described in detail above. Use of the apparatus  8  includes a wash cycle, during which microwave energy is used to clean cloth by removing stains, and drying cycles, during which microwave energy input is used to dry the cloth after a wash cycle. 
         [0061]    The cloth to be washed is placed into the drum  28  as the wash load. During the wash cycle the microwave energy which is directed at high intensity into the drum  28  is thought to directly interact with a stain lodged in the cloth by causing it to heat up in preference to the surrounding cloth. Thus, the high intensity microwave energy allows the temperature of the stain to rise substantially above that of the surrounding textile within short intervals. 
         [0062]    The microwave energy is applied in an intermittent (or pulsed) manner accelerating the cleaning process whilst keeping the cloth at a moderate temperature, thus preventing thermal damage to the cloth. The pulsed microwave energy is applied with sufficient power and in such a manner as to cause power densities ranging between 10 kW and 1000 kW per cubic meter of cavity volume within the drum. The microwave power density and duty cycle are selected to prevent eventual overheating of the wash load from the cumulative energy transfer. 
         [0063]    The method of the invention results in a reduced quantity of detergent being required during a wash cycle. In some instances no detergent is required to wash articles. 
         [0064]    Water is necessary to facilitate cleaning. However, the volume of the water in the drum  28  is minimised. This is because a large volume of water would absorb the microwave energy and reduce the differential heating effect. Large amounts of water may also cover the stain and attenuate the microwave field. Moistening of the cloth thereby occurs by continually spraying water via a water spray means  68  in the drum  28  (see  FIG. 7 ) onto the wash load to carry off any grime released from the cloth and drain it from the drum  28  during the wash cycle. In this manner, the microwave energy available for application to the cloth is maximized. 
         [0065]    The drum  28  has volume of between 10 to 100 litres. With the magnetron  76  having a power rating of 1 kW, the magnetron  76  can be pulsed at 3 kW for 33% of the time or at 5 kW for 20% of the time. The mentioned figures and volumes are not limiting in any way, and are merely exemplary, provided the use of the apparatus  8  results in the required power densities in the drum, i.e., between 10 kw and 1000 kW per cubic meter of cavity volume. This range is set by the need to limit the total energy input into the wash load, to prevent excessive temperatures. 
         [0066]    At the end of a wash cycle the water, within the tub  26 , is drained and leaves the body  10  through the outlet  44 . Once the water is drained from the tub  26  the washed articles are dried by rotation of the drum  28  and by activation of the generator  32 , usually at a reduced power output. The rotation of the drum  28  about an axis allows the energy which is created by the generator  32  to be distributed which ensures that all the cloth articles within the drum are evenly dried. In addition, air flow used to carry off the waste heat generated during operation by the microwave source can be heated further to a drying temperature of between 30° C. and 65° C. and vented through the cavity to effect the drying process. 
         [0067]    The cycles are monitored and/or controlled via a process control system  89  according to one or more of the following process parameters: water quality (conductivity), flow and level; microwave power and duty cycle; gas/air velocity, humidity and temperature; drum rotation. The process control system include control elements, sensors and a programmable microcontroller  88 , the latter which runs a generic control algorithm. The system  89  ensures optimal washing and drying performance of the apparatus  8  and also provides for monitoring of the quality of water to ensure that when saturation with dirt and grime is approached or reached, replacement of such water occurs. 
         [0068]    A schematic layout of the apparatus  8 , illustrating the components making up the process control system  89 , is shown in  FIG. 7 . The system includes a plurality of sensors, including: a microwave field strength meter  96 , a door-mounted infrared pyrometer  98 , a sump water level sensor  100 , a water conductivity sensor (conductivity meter)  102 , a drain water level sensor (float switch)  104 , a rinsing water temperature sensor (thermocouple)  108 , an exhaust gas analyser  112 , a humidity sensor (hygrometer)  114 , an exhaust air temperature sensor (thermocouple)  116  and an inlet air temperature sensor (thermocouple)  118 . The invention is not limited with respect to the type, number and location of the sensors within the apparatus  8 . 
         [0069]    A User Interface Panel  124  is present to provide a communications interface on which a user inputs washing load parameters of his choice, including size of the washing load, nature of the cloth to be washed (e.g. delicates) and scheduling of the wash. 
         [0070]    The input washing load parameters, together with input feedback from the sensors, are communicated into the programmable microcontroller  88 , which processes the input them according to the generic control algorithm.  FIG. 6  is illustrative of this. Microcontroller  88  output then controls the functioning of the control elements of the apparatus  8 , these elements include: an air heating element  90 , an air blower  94  that blows air across the magnetron  76 , an air bypass flap  92  that vents out air during the wash cycle, a microwave choke  120  that prevents microwave energy escaping from the tub  26 , a microwave inlet  122 , an optional water heater  106  for heating the rinsing water, and an exhaust air vent  110 . Again, the invention is not limited to the type, number and location of the elements within the apparatus  8 . 
         [0071]    The magnetron  76  also forms part of the process control elements, as its output power can be controlled by the programmable microcontroller  88 , thereby affecting the environmental conditions found within the apparatus  8 . 
         [0072]    The table below summarises the process parameters measured the element used and the functions of the element: 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Parameter 
                 Element used 
                 Function 
               
               
                   
               
             
             
               
                 Inlet air temperature 
                 Thermocouple 
                 Used to monitor and regulate 
               
               
                   
                   
                 the temperature of air blown 
               
               
                   
                   
                 into the drum during drying 
               
               
                 Exhaust air 
                 Thermocouple 
                 Used to monitor the 
               
               
                 temperature 
                   
                 temperature of exhausted air 
               
               
                   
                   
                 during drying, to determine the 
               
               
                   
                   
                 humidity of the wash load 
               
               
                 Drain water 
                 Thermocouple 
                 Monitors temperature of water 
               
               
                 temperature 
                   
                 drained from the drum. 
               
               
                   
                   
                 Indicates the average 
               
               
                   
                   
                 temperature of the cloth 
               
               
                 Rinse water 
                 Thermocouple 
                 Monitors and controls the 
               
               
                 temperature 
                   
                 temperature of the heated 
               
               
                   
                   
                 water sprayed onto the wash 
               
               
                   
                   
                 load 
               
               
                 Exhaust air humidity 
                 Hygrometer 
                 Monitors humidity of the wash 
               
               
                   
                   
                 load during drying 
               
               
                 Gas presence 
                 Gas analyser 
                 Detects combustion products. 
               
               
                   
                   
                 Used as a safety device. Can 
               
               
                   
                   
                 also be used to detect volatile 
               
               
                   
                   
                 organic compounds, which 
               
               
                   
                   
                 indicate the type of stains 
               
               
                   
                   
                 present 
               
               
                 Microwave field 
                 Microwave 
                 Monitors microwave field 
               
               
                 strength 
                 field strength 
                 strength. Can be used to 
               
               
                   
                 meter 
                 derive wash load size and 
               
               
                   
                   
                 characteristics, to tailor the 
               
               
                   
                   
                 wash cycle. Also used as a 
               
               
                   
                   
                 protective device prevent 
               
               
                   
                   
                 arcing 
               
               
                 Sump water level 
                 Float switch 
                 Detects water level to indicate 
               
               
                   
                   
                 start and end of cycles 
               
               
                 Water conductivity 
                 Conductivity 
                 Measures dissolved products 
               
               
                   
                 meter 
                 in water. Can be used to 
               
               
                   
                   
                 initiate an additional rinse 
               
               
                   
                   
                 cycle. Allows less water to be 
               
               
                   
                   
                 used per cycle 
               
               
                   
               
             
          
         
       
     
         [0073]    The apparatus and method that has been described above provides an advanced or traditional washing machine concept of cleaning via mechanical agitation of cloth in detergent-bearing water. Combining the effectiveness of intermittent high-energy microwaves during the wash cycle, with microwave-assisted drying, allows an efficient small washer/dryer to be realised. 
         [0074]    To illustrate the efficacy of the invention, experiments were undertaken comparing the cleaning performance of continuous-wave microwave power of the type disclosed in important piece of prior art US2002/0062667, with pulsed microwaves according to the present invention. 
         [0075]    Two identical cloths. Test-cloth  1  and Test-cloth  2 , were prepared by staining them identically with clean grease, old engine oil, tomato ketchup, Kool-aid (crème soda flavour), Pepsi cola and wood stain (Teak oil), as illustrated in  FIG. 8 . Two microwave cleaning tests were done. Test-cloth  1  underwent a prior art test utilising a magnetron which generated continuous microwave energy to clean a prepared cloth. Test-cloth  2  underwent a pulsed microwave test utilising a magnetron which generated pulsed microwave energy to clean the other prepared cloth. The same type of apparatus as described in the preferred embodiment of this invention was used, the drum having a volume of 10 litres. 
         [0076]    For the prior art test a constant microwave power of 20 kW per cubic meter of drum cavity volume (typical of a commercial magnetron attached to a domestic washing machine) was applied and the water temperature regulated at 40 degrees Celsius. For the pulsed microwave test a pulsed magnetron generating 80 kW per cubic meter of drum cavity volume was used, the pulse duty cycle being set to 25% in order to yield the same average power as the constant microwave power. Water temperature was also regulated at 40 degrees Celsius. 
         [0077]    After 10 minutes of washing, the cloths were removed and the residual stains photographed. 
         [0078]      FIG. 9 to 16  show analogies between the initial prepared stains (A) of  FIG. 8 , the cleaning results of the prior art test on Test-cloth  1  (B) for each stain, and the cleaning results of the pulsed microwave test on Test-cloth  2  (C) for each