阅读说明：本技术 一种全工况空气制水机蒸发器凝露取水控制方法 (Condensation water taking control method for evaporator of all-condition air water making machine ) 是由 王伟 张连军 魏超 徐垚 毛韦明 于 2020-05-25 设计创作，主要内容包括：本发明公开了一种全工况空气制水机蒸发器凝露取水控制方法,是基于蒸气压缩制冷原理上的一种特殊控制,利用控制器采集环境干球温度T<Sub>1</Sub>、环境露点温度T<Sub>1露</Sub>和蒸发器翅片温度T<Sub>2</Sub>,并与控制器预设的环境最低干球温度T<Sub>1min</Sub>、环境最高干球温度T<Sub>1max</Sub>、环境最低露点温度T<Sub>1露min</Sub>、环境最高露点温度T<Sub>1露max</Sub>、蒸发器翅片温度第一下偏值△T<Sub>1</Sub>、蒸发器翅片温度第二下偏值△T<Sub>2</Sub>进行比较,再通过控制蒸发风机实现对蒸发器取水控制。本发明通过实时检测环境温湿度,得到不同的蒸发器翅片温度控制目标,保持蒸发器在规定温湿度范围内始终处于结露状态。(The invention discloses a condensation water taking control method for an evaporator of an all-condition air water making machine, which is a special control based on a vapor compression refrigeration principle and is used for collecting the ambient dry bulb temperature T by using a controller 1 Ambient dew point temperature T 1 distillate And evaporator fin temperature T 2 And the lowest ambient dry bulb temperature T preset by the controller 1min The highest dry bulb temperature T of the environment 1max Environment minimum dew point temperature T 1 dew min Environment maximum dew point temperature T 1 Lumax First lower deviation △ T of evaporator fin temperature 1 A second lower deviation △ T of evaporator fin temperature 2 And comparing, and controlling the evaporator to take water by controlling the evaporation fan. The invention obtains different evaporator fin temperature control by detecting the environmental temperature and humidity in real timeThe object is to keep the evaporator in a dew condensation state at all times within a predetermined temperature and humidity range.)

1. A full-working-condition air water generator evaporator condensation water taking control method is characterized by comprising the following steps: setting temperature sensors in the air inlet direction of the evaporator to measure the environmental dew point temperature T respectively_{1 distillate}Ambient dry bulb temperature T₁The surface of the evaporator fin is provided with a temperature sensor for measuring the temperature T of the evaporator fin₂And a controller is arranged, the controller is respectively connected with the compressor and an evaporation fan configured by the evaporator in a control way, and each temperature sensor is respectively connected with the controller in a signal transmission way, the method comprises the following steps:

(1) presetting the lowest dry bulb temperature T of the environment in the controller_1minThe highest dry bulb temperature T of the environment_1maxEnvironment minimum dew point temperature T_{1 dew min}Environment maximum dew point temperature T_{1 Lumax}First lower deviation △ T of evaporator fin temperature₁A second lower deviation △ T of evaporator fin temperature₂Wherein △ T₁﹤△T₂；

(2) The controller passes throughRespectively collecting environmental dew point temperature T by temperature sensors_{1 distillate}Ambient dry bulb temperature T₁Evaporator fin temperature T₂；

(3) The temperature T of the ambient dry bulb in the controller₁Respectively with the lowest dry bulb temperature T of the environment_1minThe highest dry bulb temperature T of the environment_1maxComparing and simultaneously comparing the ambient dew point temperature T_{1 distillate}And the lowest dew point temperature T of the environment_{1 dew min}Comparing, if the condition T is satisfied_1min≤T₁≤T_1maxAnd T_{1 distillate}≥T_{1 dew min}The controller starts the compressor and the evaporation fan to reduce the temperature of the evaporator fins, so that the surface condensation of the evaporator fins realizes normal water taking;

(4) and in the water taking process in the step (3), the controller controls the ambient dew point temperature T_{1 distillate}And the maximum dew point temperature T of the environment_{1 Lumax}Comparing, and adjusting the temperature T of the evaporator fins based on the comparison result₂The temperature is maintained in a certain range, and the specific process is as follows:

if T_{1 distillate}﹤T_{1 Lumax}The controller adjusts the evaporation fan to make the temperature T of the evaporator fins₂Is maintained in the range of T_{1 distillate}－△T₂≤T₂≤T_{1 distillate}－△T₁；

If T_{1 distillate}≥T_{1 Lumax}The controller adjusts the evaporation fan to make the temperature T of the evaporator fins₂Is maintained in the range of T_{1 Lumax}－△T₂≤T₂≤T_{1 Lumax}－△T₁。

2. The method for controlling water intake of condensation of the evaporator of the full-working-condition air water generator according to claim 1, characterized by comprising the following steps: judging T in controller₂Not more than 0 ℃ and T₂﹤T_{1 Lumax}－△T₂When the surface of the evaporator fin is frosted and the thickness of the frost layer meets the requirement, the evaporator enters a defrosting and water taking mode, the evaporation fan stops working when defrosting and water taking are carried out, meanwhile, one of the modes of reverse defrosting of a compressor, hot gas bypass defrosting or electric heating defrosting is adopted, after defrosting and water taking are finished,the compressor, the evaporation fan and the like are in the state before recovery, namely, the intermittent water taking state is entered.

3. The method for controlling water intake of condensation of the evaporator of the full-working-condition air water generator according to claim 1, characterized by comprising the following steps: in the step (1), the lowest dry bulb temperature T of the environment_1minThe highest dry bulb temperature T of the environment_1maxEnvironment minimum dew point temperature T_{1 dew min}And ambient maximum dew point temperature T_{1 Lumax}Is determined based on design input, where T_{1 dew min}At the lowest dry bulb temperature T in the working temperature range_1minCorresponding dew point temperature limit and maximum dry bulb temperature T_1maxThe lower value of the corresponding dew point temperature limit value is selected; maximum dew point temperature T of environment_{1 Lumax}Not only according to the highest dew point temperature which can be met by the environment, but also considering the working capacity of the compressor, when the highest evaporation temperature which can be borne by the compressor corresponds to the highest temperature T of the evaporator fins_2max≤T_{1 Lumax}Time, maximum dew point temperature T of the environment_{1 Lumax}According to T_2maxAnd (4) taking values.

4. The method for controlling the intake of water from the evaporator of the all-condition air water generator according to claim 1, wherein in the step (1), the temperature of the evaporator fins has a first lower deviation value of △ T₁A second lower deviation △ T of evaporator fin temperature₂Set up according to the condensation effect and the fluctuation range, respectively, and △ T₁Taking △ T at 1-3 DEG C₂Ratio △ T₁1 to 3 ℃ in height.

5. The method for controlling water intake of condensation of the evaporator of the full-working-condition air water generator according to claim 1, characterized by comprising the following steps: the evaporation fan is a fan capable of carrying out stepless speed regulation, and the controller in the step (4) carries out stepless regulation on the evaporation fan to ensure that the temperature T of the evaporator fins is₂Maintained at a temperature range.

6. The method for controlling water intake of condensation of the evaporator of the full-working-condition air water generator according to claim 2, characterized in that: the throttling element is an electronic expansion valve or a thermal expansion valve which can be controlled electrically so as to meet the requirement of superheat degree adjustment of the evaporator and ensure that the compressor does not hit liquid.

Technical Field

The invention relates to the field of control methods of air water generators, in particular to a condensation water taking control method of an evaporator of an all-working-condition air water generator.

Background

With the increasing living standard and health consciousness of people, an air water generator (also called air water taking) becomes a high-end consumer product at present and is emerging in the market continuously. At present, the mainstream air water generator adopts an evaporation compression type refrigeration principle, namely, a compressor, an evaporator, a condenser, a throttling element and the like are connected through pipelines to form a refrigerant circulation loop, the evaporator is provided with an evaporation fan, the condenser is provided with a condensation fan, air flows in from the air inlet side of the evaporator under the action of the evaporation fan and flows out from the air outlet side of the evaporator after passing through the evaporator, low-temperature and low-pressure liquid refrigerant in the compressor is subjected to gasification phase change in an evaporator pipe, so that the air on the outer surface of the evaporator is cooled and condensed water is formed, and a water source of the air water generator is formed by collecting the condensed water. In the prior art, since an evaporator, a condenser, a compressor, etc. are solidified according to the design of a product system, the adaptability thereof is not excellent enough to face the change of complicated and severe environmental conditions.

For example, the ambient dry bulb temperature range of a common civil air water making machine is 18-43 ℃, and the ambient wet bulb temperature range is 35-95%. Meanwhile, the air water generator is different from an air conditioner in that the air conditioner has an indoor working condition and an outdoor working condition for test evaluation, but the air water generator is tested under the same environmental temperature and humidity condition, for example, some manufacturers determine that the dry bulb temperature is 27 ℃ and the relative humidity is 60% as a rated test working condition. Under the relatively stable working condition, the product design can be better carried out so as to obtain the ideal evaporation temperature and meet the condensation water outlet of the evaporator. However, the surface of the evaporator sometimes does not condense or some places do not condense any more with the change of the environmental temperature and humidity, so that the water outlet effect is poor. When the temperature range of the environment dry bulb is expanded to 5-55 ℃, the temperature range of the environment wet bulb is expanded to 10-95%, and particularly when the humidity is low, the phenomenon that the surface of an evaporator is not condensed is more and more serious, the water yield within the required range cannot be reached, and even high-temperature protection and the like are caused.

The surface temperature of the evaporator fins is a physical phenomenon that condensate water is generated as long as the surface temperature is lower than the dew point temperature of the surrounding air. Of course, if the evaporation temperature is designed to be very low (such as-10 ℃), condensation can be met under all working conditions. However, for vapor compression refrigeration, the design causes low system energy efficiency, and cannot meet the future requirement for energy saving. In the face of different environmental humiture, under the condition that the evaporator can not change the volume or the heat exchange area, a dynamic evaporator fin temperature control method is needed to enable the evaporator to effectively condense moisture.

Disclosure of Invention

The invention aims to provide a condensation water taking control method for an evaporator of a full-working-condition air water generator, which aims to solve the problem that the surface of the evaporator in the air water generator in the prior art is easy to generate non-condensation.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a condensation water taking control method for an evaporator of an all-condition air water generator is characterized in that the evaporator is a finned heat exchanger with a refrigerating function and comprises the following steps: setting temperature sensors in the air inlet direction of the evaporator to measure the environmental dew point temperature T respectively_{1 distillate}Ambient dry bulb temperature T₁The surface of the evaporator fin is provided with a temperature sensor for measuring the temperature T of the evaporator fin₂And a controller is arranged, the controller is respectively connected with the compressor and an evaporation fan configured by the evaporator in a control way, and each temperature sensor is respectively connected with the controller in a signal transmission way, the method comprises the following steps:

(1) presetting the lowest dry bulb temperature T of the environment in the controller_1minThe highest dry bulb temperature T of the environment_1maxEnvironment minimum dew point temperature T_{1 dew min}Environment maximum dew point temperature T_{1 Lumax}First lower deviation △ T of evaporator fin temperature₁A second lower deviation △ T of evaporator fin temperature₂Wherein △ T₁﹤△T₂；

(2) The controller respectively collects the environmental dew point temperature T through each temperature sensor_{1 distillate}Ambient dry bulb temperature T₁Evaporator fin temperature T₂；

(3) The temperature T of the ambient dry bulb in the controller₁Respectively with the lowest dry bulb temperature T of the environment_1minThe highest dry bulb temperature T of the environment_1maxComparing and simultaneously comparing the ambient dew point temperature T_{1 distillate}And the lowest dew point temperature T of the environment_{1 dew min}Comparing, if the condition T is satisfied_1min≤T₁≤T_1maxAnd T_{1 distillate}≥T_{1 dew min}The controller starts the compressor and the evaporation fan to reduce the temperature of the evaporator fins, so that the surface condensation of the evaporator fins realizes normal water taking;

(4) and in the water taking process in the step (3), the controller controls the ambient dew point temperature T_{1 distillate}And the maximum dew point temperature T of the environment_{1 Lumax}Comparing, and adjusting the temperature T of the evaporator fins based on the comparison result₂The temperature is maintained in a certain range, and the specific process is as follows:

if T_{1 distillate}﹤T_{1 Lumax}The controller adjusts the evaporation fan to make the temperature T of the evaporator fins₂Is maintained in the range of T_{1 distillate}－△T₂≤T₂≤T_{1 distillate}－△T₁；

If T_{1 distillate}≥T_{1 Lumax}The controller adjusts the evaporation fan to make the temperature T of the evaporator fins₂Is maintained in the range of T_{1 Lumax}－△T₂≤T₂≤T_{1 Lumax}－△T₁。

The condensation water taking control method for the evaporator of the all-working-condition air water generator is characterized by comprising the following steps of: t is₂Not more than 0 ℃ and T₂﹤T_{1 Lumax}－△T₂When the surface of the evaporator fin is frosted and the thickness of the frost layer meets the requirement, the evaporator enters a defrosting and water taking mode, the evaporation fan stops working when defrosting and water taking are carried out, meanwhile, one of modes of reverse defrosting of a compressor, hot gas bypass defrosting or electric heating defrosting is adopted, after defrosting and water taking are completed, the compressor, the evaporation fan and the like are in a state before recovery, namely, an intermittent water taking state is entered.

Full operating mode air to water machine evaporimeter condensation accuse of fetching waterThe manufacturing method is characterized in that: in the step (1), the lowest dry bulb temperature T of the environment_1minThe highest dry bulb temperature T of the environment_1maxEnvironment minimum dew point temperature T_{1 dew min}And ambient maximum dew point temperature T_{1 Lumax}Is determined based on design input, where T_{1 dew min}At the lowest dry bulb temperature T in the working temperature range_1minCorresponding dew point temperature limit and maximum dry bulb temperature T_1maxThe lower value of the corresponding dew point temperature limit value is selected; maximum dew point temperature T of environment_{1 Lumax}Not only according to the highest dew point temperature which can be met by the environment, but also considering the working capacity of the compressor, when the highest evaporation temperature which can be borne by the compressor corresponds to the highest temperature T of the evaporator fins_2max≤T_{1 Lumax}Time, maximum dew point temperature T of the environment_{1 Lumax}According to T_2maxAnd (4) taking values.

The method for controlling condensation water taking of the evaporator of the all-working-condition air water making machine is characterized in that in the step (1), the temperature of the evaporator fins is a first lower deviation value △ T₁A second lower deviation △ T of evaporator fin temperature₂Set up according to the condensation effect and the fluctuation range, respectively, and △ T₁Taking △ T at 1-3 DEG C₂Ratio △ T₁1 to 3 ℃ in height.

The condensation water taking control method for the evaporator of the all-working-condition air water generator is characterized by comprising the following steps of: the evaporation fan is a fan capable of carrying out stepless speed regulation, such as an EC fan, a variable frequency fan or a pressure and speed regulation fan. The controller in the step (4) performs stepless regulation on the evaporation fan to enable the temperature T of the evaporator fins₂Maintained at a temperature range.

The condensation water taking control method for the evaporator of the all-working-condition air water generator is characterized by comprising the following steps of: the throttling element is an electronic expansion valve or a thermal expansion valve which can be controlled electrically so as to meet the requirement of superheat degree adjustment of the evaporator and ensure that the compressor does not hit liquid.

Compared with the prior art, the invention has the advantages that:

1. according to the invention, different evaporator fin temperature control targets are obtained by detecting the environmental temperature and humidity in real time, the evaporator is kept in a condensation state all the time within a specified temperature and humidity range, and the condensation and water precipitation effects are good.

2. The invention can divide the enthalpy wet state of air into 2 areas, the non-water taking area and the water taking area are only influenced by the lowest dew point temperature of the product, the working range is widened, and the distinction is clear.

3. The invention can be modified and upgraded on the basis of the original water making machine and has stronger popularization.

4. The invention has mature technology, clear flow and easy realization.

Drawings

Fig. 1 is a control schematic of the controller of the present invention.

Fig. 2 is a block flow diagram of the present invention.

Fig. 3 is a diagram of the enthalpy and humidity of the air when the present invention is in operation.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

A condensation water taking control method for an evaporator of an all-condition air water making machine is disclosed, as shown in figure 1, temperature sensors 1.2 and 1.1 are arranged in the air inlet direction of the evaporator and respectively correspond to and measure the ambient dew point temperature T_{1 distillate}Ambient dry bulb temperature T₁The surface of the evaporator 4 fin is provided with a temperature sensor 1.3 for measuring the temperature T of the evaporator fin₂And a controller 1 is arranged, the controller 1 is respectively connected with the compressor and an evaporation fan 2 configured by an evaporator 4 in a control way, and the temperature sensors 1.1, 1.2 and 1.3 are respectively connected with the controller in a signal transmission way.

As shown in fig. 2, the method of the present invention comprises the steps of:

(1) presetting the lowest dry bulb temperature T of the environment in the controller_1minThe highest dry bulb temperature T of the environment_1maxEnvironment minimum dew point temperature T_{1 dew min}Environment maximum dew point temperature T_{1 Lumax}First lower deviation △ T of evaporator fin temperature₁A second lower deviation △ T of evaporator fin temperature₂Wherein △ T₁﹤△T₂；

In the present invention, the environment is the lowest level of drynessBall temperature T_1minThe highest dry bulb temperature T of the environment_1maxEnvironment minimum dew point temperature T_{1 dew min}And ambient maximum dew point temperature T_{1 Lumax}Is determined based on design input, where T_{1 dew min}At the lowest dry bulb temperature T in the working temperature range_1minCorresponding dew point temperature limit and maximum dry bulb temperature T_1maxThe lower value of the corresponding dew point temperature limit value is selected; maximum dew point temperature T of environment_{1 Lumax}Not only according to the highest dew point temperature which can be met by the environment, but also considering the working capacity of the compressor, when the highest evaporation temperature which can be borne by the compressor corresponds to the highest temperature T of the evaporator fins_2max≤T_{1 Lumax}Time, maximum dew point temperature T of the environment_{1 Lumax}According to T_2maxAnd (4) taking values. E.g. T_2max＝25℃，T_{1 Lumax}When the temperature is 30 ℃, then T_{1 Lumax}＝25℃。

In the present invention, the evaporator fin temperature first lower deviation value is △ T₁A second lower deviation △ T of evaporator fin temperature₂Set up according to the condensation effect and the fluctuation range, respectively, and △ T₁Taking △ T at 1-3 DEG C₂Ratio △ T₁1 to 3 ℃ in height.

(2) The controller respectively collects the environmental dew point temperature T through each temperature sensor_{1 distillate}Ambient dry bulb temperature T₁Evaporator fin temperature T₂；

(3) The temperature T of the ambient dry bulb in the controller₁Respectively with the lowest dry bulb temperature T of the environment_1minThe highest dry bulb temperature T of the environment_1maxComparing and simultaneously comparing the ambient dew point temperature T_{1 distillate}And the lowest dew point temperature T of the environment_{1 dew min}Comparing, if the condition T is satisfied_1min≤T₁≤T_1maxAnd T_{1 distillate}≥T_{1 dew min}The controller starts the compressor and the evaporation fan to reduce the temperature of the evaporator fins, so that the surface condensation of the evaporator fins realizes normal water taking;

(4) and in the water taking process in the step (3), the controller controls the ambient dew point temperature T_{1 distillate}And the maximum dew point temperature T of the environment_{1 Lumax}Make a comparisonAnd based on the comparison result, adjusting the evaporation fan to make the temperature T of the evaporator fins₂The temperature is maintained in a certain range, and the specific process is as follows:

if T_{1 distillate}﹤T_{1 Lumax}The controller adjusts the evaporation fan to make the temperature T of the evaporator fins₂Is maintained in the range of T_{1 distillate}－△T₂≤T₂≤T_{1 distillate}－△T₁；

If T_{1 distillate}≥T_{1 Lumax}The controller adjusts the evaporation fan to make the temperature T of the evaporator fins₂Is maintained in the range of T_{1 Lumax}－△T₂≤T₂≤T_{1 Lumax}－△T₁。

In the invention, the evaporation fan 2 is a fan capable of stepless speed regulation, and the controller 1 steplessly regulates the evaporation fan 2 to ensure that the temperature T of the fins of the evaporator 4 is regulated steplessly₂Maintained at a temperature range.

As shown in fig. 1, the refrigeration cycle circuit further includes a throttling element 3, and the throttling element 3 is an electronic expansion valve or a thermal expansion valve capable of being electrically controlled, so as to meet the superheat degree regulation of the evaporator and ensure that the compressor does not liquid impact. Determination of T in controller 1₂Not more than 0 ℃ and T₂﹤T_{1 Lumax}－△T₂When the surface of the evaporator fin is frosted and the thickness of the frost layer meets the requirement, the evaporator enters a defrosting and water taking mode, the evaporation fan stops working when defrosting and water taking are carried out, meanwhile, one of modes of reverse defrosting of a compressor, hot gas bypass defrosting or electric heating defrosting is adopted, after defrosting and water taking are completed, the compressor, the evaporation fan and the like are in a state before recovery, namely, an intermittent water taking state is entered.

Specific examples are as follows:

setting an ambient minimum dry bulb temperature T in a controller_1min5 deg.C, maximum ambient dry bulb temperature T_1max55 deg.C, ambient minimum dew point temperature T_{1 dew min}-7 ℃ maximum dew point temperature T of the environment_{1 Lumax}＝25℃，△T₁＝2℃，△T₂＝3℃。

When the controller collects the temperature T of the environmental dry bulb₁At 5 deg.C, ambient dew point temperature T_{1 distillate}＝4℃(relative humidity 86%), at this time T_{1 distillate}﹤T_{1 Lumax}The controller performs stepless regulation on the evaporation fan to ensure that the temperature T of the evaporator fins₂Is maintained in the range of T_{1 distillate}－△T₂≤T₂≤T_{1 distillate}－△T₁I.e. T is not less than 1 DEG C₂≤2℃。

When the controller collects the temperature T of the environmental dry bulb₁At 5 deg.C, ambient dew point temperature T_{1 distillate}0 ℃ (relative humidity 33%), at which time T_{1 distillate}﹤T_{1 Lumax}The controller performs stepless regulation on the evaporation fan to ensure that the temperature T of the evaporator fins₂Is maintained in the range of T_{1 distillate}－△T₂≤T₂≤T_{1 distillate}－△T₁T is not less than-3 ℃₂Less than or equal to-2 ℃; when frost begins to be generated, the temperature T of the evaporator fins₂The regulation is limited to be lower than-3 ℃, the evaporator fin surface frosts more and more, and the frost layer thickness meets the requirement, the defrosting and water taking mode is entered, the evaporation fan stops working when defrosting and water taking are carried out, meanwhile, one of the modes of reverse defrosting of the compressor, hot gas bypass defrosting or electric heating defrosting is adopted, after defrosting and water taking are completed, the compressor, the evaporation fan and the like recover to the previous state, and the intermittent water taking state is entered.

When the controller collects the temperature T of the environmental dry bulb₁55 deg.C, ambient dew point temperature T_{1 distillate}At 32 ℃ (30% rh), T is then_{1 distillate}≥T_{1 Lumax}And the highest evaporating temperature that the compressor can bear corresponds to the highest temperature T of the evaporator fins_2maxWhen the temperature is 25 ℃, then T_{1 Lumax}At 25 ℃. The controller carries out stepless regulation on the evaporation fan to ensure that the temperature T of the evaporator fins₂Is maintained in the range of T_{1 Lumax}－△T₂≤T₂≤T_{1 Lumax}－△T₁T is more than or equal to 22 ℃₂≤23℃。

As can be seen from the case, the invention has different evaporator fin temperature control under different ambient temperature and humidity.

Fig. 3 is a schematic diagram showing the location of the present invention on the psychrometric chart. In FIG. 3, the water is divided into a non-water intake area and a water intake area to produce waterThe minimum dew point temperature for the machine design is the boundary. Wherein the lowest dew point temperature T_{1 dew min}At the lowest dry bulb temperature T in the working temperature range_1minCorresponding dew point temperature limit and maximum dry bulb temperature T_1maxThe lower of the corresponding dew point temperature limits. If the minimum working temperature is 5 ℃ and the relative humidity limit value is 38.2% (dew point temperature-7 ℃), the maximum working temperature is 55 ℃ and the relative humidity limit value is 10% (dew point temperature 13.81 ℃), then T_{1 dew min}-7 ℃ as borderline value. At this time, the relative humidity can theoretically be expanded to 2.1% at an ambient temperature of 55 ℃. As can be seen from the figure, the water taking area is wider than the environmental area (18-43 ℃) of a common air water making machine, and the water taking area has no blind area.

The above-described embodiments are only preferred embodiments of the present invention, but the present invention is not limited to the above-described embodiments, and any obvious modifications thereof without departing from the principle of the present invention will be apparent to those skilled in the art within the spirit of the present invention and the scope of the appended claims.