[0001] This invention relates to a method of cleaning doth 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, healing 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 he heated or the fabric to he dried. US Patents No. 4,356,640, 5,403,821 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 US2002/0062687, entitled "Method and apparatus for washing items having doth 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 effeci of water and detergent. A secondary effect of such irradiatson 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 cyiindrical 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 sctuabie 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 asr 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, sir 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 oneof 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

[0024] The generator may generate pulses of microwave energy at a power density in the range 5kW and 5000kW per cubic meter of the volume of the drum. Preferably , the generator generates pulses of microwave energy at a power density of 100kW per cubic meter of the volume of the drum,

[0025] The power of each pulse of microwave energy may be regulated using the power supply to be in a range of 1kW to 30kW. Preferably, the power of each pulse of microwave energy is regulated using the power supply to fee In a range of 3kW to 5kW.

[0026] The pulses may be regulated using the power supply to be at duty cycles ranging between 5% and 33%.

[0027] The cloth may be moistened by spraying a stream of liquid Into the drum.

[0028] 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. [0029] The method may include the additional step of introducing a hot air stream into the drum to dry the doth.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The invention is further described by way of example with reference to the accompanying drawings in which:

Figure 1 is a perspective view of a cleaning apparatus according to the invention; Figure 2 is a front view of the cleaning apparatus of Figure 1 ;

Figure 3 is a perspective view of the cleaning apparatus of Figure 1 in a disassembled form;

Figure 4 is a plan view of the cleaning apparatus;

Figure S is a typical power supply required to pulse a 1kW magnetron;

Figure 6 shows the process control system. Inputs are on the left of the process controller and outputs are on the right;

Figure 7 is a schematic of a cleaning apparatus- illustrating process control elements that are included;

Figure 8 is a prepared cloth to be cleaned experimentally using the invention, with various stains having been put on the cloth;

Figure 3 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;

Figure 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; Figure 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;

Figure 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;

Figure 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;

Figure 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;

Figure 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

figure 18 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

[0031] Figure 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. [0032] The apparatus further includes a tub 26, a drum 28, a drive means 30 and a generator 32 (see Figure 3),

[0033] The front panel 18 has an aperture 34.

[0034] 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 1G.

[0035] The invention Is not limited in this respect,

[0036] 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 28. 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.

[0037] 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 tab 26 is in connection with the inlet 42 and the outlet 44.

[0038] 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 8:2 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 2G of the body and causes the drum 28 to rotate for a predetermined duration and speed. This is best illustrated in Figure 4.

[0039] 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.

[0040] Figure 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. [0041] The invention extends to a method that makes use of pulsed microwaves to dean 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 doth by removing stains, and drying cycles, during which microwave energy input is used to dry the cloth after a wash cycle,

[0042] 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 s 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.

[0043] 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 therrnai 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 10kW and 1000kW 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.

[0044] 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,

[0045] 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 Figure 7) onto the wash load io 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.

[0046] 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 3kW for 33% of the time or at 5kW 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 10kw and 1000kW 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.

[0047] 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 28 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. [0048] 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 wafer occurs,

[0049] A schematic layout of the apparatus 8, illustrating the components making up the process control system 89, Is shown in Figure 7. The system includes a plurality of sensors, including: a microwave field strength meter 98, 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 1 12, a humidity sensor ( hygrometer) 1 14, 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.

[0050] 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. deilcates) and scheduling of the wash. [0051] 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. Figure 8 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 S4 thai 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 wafer 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,

[0052] 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.

[0053] The table below summarises the process parameters measured the element used and the functions of the element:

Table 1

[0054] 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.

[0055] 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.

[0056] 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 (creme soda flavour), Pepsi cola and wood stain (Teak oil), as illustrated in Figure 8. Two microwave cleaning tests were done. Test-cloth 1 underwent a prior art test utilising a magnetron which generated continuous microwave energy to dean 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.

[0057] For the prior art test a constant microwave power of 20kW 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 80kW per cubic meter of drum cavity volume was used, the pulse duty cycle bemg 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.

[0058] After 10 minutes of washing, the cloths were removed and the residual stains photographed.

[0059] Figure 9 to 16 show analogies between the initial prepared stains (A) of Figure 8, the cleaning results of the prior art test on Test-cloth 1 (B) for each stairs, and the cleaning results of the pulsed microwave test on Test-cloth 2 (C) for each