Abstract:
When large numbers of children play in a playground, part of the power of their play could be usefully harnessed resulting in large energy storage. This stored energy can then be converted for basic, low-power, applications in the school such as lighting, communication, or operating fans. Energy can be produced through the use of pneumatic (i.e., compressed air) systems such as cylinders, motors, valves, and regulators for the conversion of human power of children&#39;s play in school playgrounds and other public places. The energy of the compressed air can then be converted to electricity for purposes such as lighting and communication. This provides a low-cost, low-resource means of generation of electricity, especially for use in developing countries.

Description:
TECHNICAL FIELD 
   The present invention is based on the use of pneumatic (i.e., compressed air) systems such as cylinders, motors, valves, and regulators for the conversion of human power of children&#39;s play in school playgrounds and other public places. The energy of the compressed air can then be converted to electricity for purposes such as lighting and communication. This provides a low-cost, low-resource means of generation of electricity, especially for use in developing countries. 
   BACKGROUND OF THE INVENTION 
   The current state-of-art inventions using human power are mainly based on harnessing human power at the individual level. Therefore, they are limited to producing low power output and are discontinuous. For example, rotating the crank of a clockwork radio for a few minutes produces enough power for the radio for about half hour or for several seconds of lighting. 
   By contrast, the present invention is based on harnessing the collective energy of a number of children, so the power output is large and sufficient for continuous operation of several lights, fans, and communication equipment for a long time. 
   Secondly, the power is produced as part of play and therefore separate, deliberate effort is not required to produce power. 
   Thirdly, the proposed approach involves low cost: a clockwork radio producing a few watts of power generally costs $50 or more. For the cost of a few hundred dollars, the hardware for the play-based power harvesting system could produce several hundreds of watts of electricity. 
   Finally, the new invention is eminently suited to developing countries where the main constraints are cost, ruggedness, and low-resource and skill requirements (cf. piezoelectric or storage capacitors). The pneumatic technology involved is fairly simple, well known, and requires little or easy maintenance. 
   SUMMARY OF THE INVENTION 
   The present invention is based on the harnessing of human power during children&#39;s play in playgrounds and public places, on devices such as the seesaw, merry-go-round and swings. While individual human calorific consumption of 2500 kilocalories per day is equivalent to the energy stored in about 1050 AA batteries, harnessing this power individually results in expensive, mainly electrical, systems with low-power outputs, e.g., clockwork radio, hand-cranked lantern, etc. 
   Human power was one of the earliest sources of energy known to mankind, and was widely used in the 19 th  and early 20 th  centuries for purposes such as irrigation, operating machinery, and as source of electricity for watching/listening to radio and television. Availability of low-cost energy made it superfluous, but in recent years human power conversion is making a comeback due to economic, environmental, and technological factors. 
   Trevor Baylis&#39;s (re)invention of the clock work radio contributed immensely to this trend. Various new inventions are based on the use of human power conversion for flash lights, cell phone battery charges, wrist watches, power-harvesting shoes for soldiers, laptop and wearable computers, children&#39;s toys, and so on. 
   Compressed air energy storage and actuation have advantages of environment-friendliness and low-cost, and are being employed widely in applications ranging from children&#39;s toys to underground energy storage for peak-power demand. While compressed air systems have low energy efficiency, high-efficiency compressor systems have been developed for gasoline-pneumatic hybrid cars. 
   There are several approaches to harnessing human power: electric, pneumatic, hydraulic, flywheel, piezoelectric, etc. One of the most challenging technologies using human power is the human powered aircraft Bionic Bat developed by Paul MacCready and others. 
   Several commercial products based on the human power conversion exist. Human power conversion has been used in pneumatic orthosis systems to reduce the need for large air reservoirs. It has also been proposed as a power source for emergency rescue situations such as earthquakes. 
   The closest technology to the present invention is a play pump developed by a British group in South Africa, and presented on BBC World TV program “Earth Matters” in 1999. In this system, a reciprocating hydraulic cylinder is used to harness the power of a children&#39;s merry-go-around to activate a hydraulic pump for irrigation purposes in a nearby field. The cost of the system was about £5000. The system can be considered a multi-person version of the conventional manual pump for pumping water. 
   A “Last Page: Think It&#39;s New? Think Again” article in the September 1998 issue of Popular Mechanics refers to how exercise bikes producing electricity have made a comeback after almost 100 years. It mentions that “For instance, a participant at a recent conference on education in developing nations suggested using stationary bicycles to power classroom PCs. It&#39;s not so farfetched—fast pedaling can generate about 100 watts, and teachers worldwide have long sought to harness the vast, untapped power of a room full of 10-year olds”! 
   Using exercise bikes may be considered monotonous by children, compared to playing outdoors in the playground. Therefore, the invention outlined here is a more natural and child-friendly way of producing power for basic needs. 
   When large numbers of children play in a playground, part of the power of their play could be usefully harnessed resulting in large energy storage. This stored energy can then be converted for basic, low-power, applications in the school such as lighting, communication, operating fans, and so on. 
   Compressed air devices are used for the conversion and storage of human power in the present invention, though electric generators can also be used for this purpose. The main reason for this is the hazards of electric shock and fire in the case of malfunction or accidents leaving open wires. Use of compressed air is explosion- and fire-proof and open tubing results simply in air leakage. The lower efficiency of the resulting system (due to pressure drop in pipelines and heat in pressurizing) is compensated by the simplicity, safety, and low-cost of operation of the pneumatic system. 
   The compressed air will be stored in storage tank(s) close to the point of use, and will be used to power a pneumatic actuator such as cylinder or air motor, which will in turn move an electric generator to produce electricity. The electricity will be stored in batteries, and used to power dc-operated lights and appliances or to power ac-operated appliances through the use of inverters and power control circuitry. 
   The energy storage capacity of compressed air is limited compared to alternatives such as batteries. Therefore, low-cost microcontroller-based systems can be used to control and convert the compressed air stored in a limited volume. In many cases, though, storage space is not a constraint around playgrounds or schools, so simpler solutions using mechanical devices such as pressure regulators can be used. 
   These and other objects of the present invention will become apparent upon reading the following detailed description in combination with the accompanying drawings, which depict systems and components that can be used alone or in combination with each other in accordance with the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a preferred embodiment of the present invention wherein the energy conversion is compressed air energy storage based on a seesaw. 
       FIG. 2  illustrates a continuation of the system in  FIG. 1  showing the transmission of compressed air to power generator and showing the power generation from compressed air. 
       FIG. 3  illustrates a preferred embodiment of the present invention wherein the energy conversion is compressed air energy storage based on a seesaw using a slider-crank mechanism. 
       FIG. 4  illustrates a preferred embodiment of the present invention wherein the energy conversion is compressed air energy storage based on a swing using a pneumatic rotary actuator. 
       FIG. 5  illustrates a preferred embodiment of the present invention wherein the energy conversion is compressed air energy storage based on a merry-go-round using an air motor. 
       FIG. 6  illustrates a preferred embodiment of the present invention wherein the energy conversion is compressed air energy storage based on a merry-go-round using a crank-slider mechanism. 
       FIG. 7  illustrates a preferred embodiment of the present invention wherein the energy conversion is based on a seesaw using an electromagnetic generator. 
       FIG. 8  illustrates a preferred embodiment of the present invention wherein the energy conversion is based on a swing using an electromagnetic generator. 
       FIG. 9  illustrates a preferred embodiment of the present invention wherein the energy conversion is based on a merry-go-round using an electromagnetic generator. 
       FIG. 10  illustrates a preferred embodiment of the present invention wherein the energy conversion is based on a stationery bicycle using an electromagnetic generator. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2  illustrate the basic principle of the new invention. For simplicity, we limit our discussion to power conversion based on a seesaw. The cases of a swing and a merry-go-around can be considered similarly. 
   In  FIG. 1 , the seesaw  10  is often supplied with hard cylindrical helical springs  12 ,  14  to smoothen the actions of the seesaw mechanism. In the present mechanism, instead of the springs we employ two pneumatic cylinders  16 ,  18  on the two sides of the seesaw. To prevent any accidents and injuries to players&#39; limbs from the moving pistons, we provide a bellows-type flexible sheath between the bottom of seesaw and the top of the cylinder as shown  20 ,  22 . The outer bodies of the cylinders would get heated due to the compression of air inside. This would require shielding of the outer bodies too (not shown here). 
   To simplify the system and make it portable, the bottom end of the cylinders can also be fixed to the central support of the seesaw, rather than being fixed to the ground. 
     FIG. 2  shows the process of compression of air and its transmission to the power generator stage. For improved compression rate, we consider the case of double acting cylinder. The atmospheric air enters the cylinder input ports  24 ,  26  alternately through check (or plate) valves  36 ,  38 . The reciprocating vertical motion of the piston  34  of the cylinder  32  under the motion of the seesaw results in compressed air being outputted through check valves  40 ,  42  via output ports  28 ,  30  to the pipeline through a union tee joint  44 . Reference numeral  46  indicates that the pipeline could be very long. The compressed air from the pipeline is stored in an air tank  48 . Essential parts of the air tank, such as pressure gage, pressure release valve, regulator, etc are not shown here for simplicity. 
   When the compressed air inside the air tank reaches a set pressure level, the on-off valve  50  is opened. The air is passed through a filter-regulator-lubricator unit  52 . If the pressure of the stored air is low due to pressure drop along long pipeline, then an air booster  54  can be used to reduce the volume and increase the pressure of the air to the power generator unit. 
     FIG. 2  also illustrates the generation of power from the compressed air. The compressed air from the pipeline  56  is used to actuate an air motor  58 . The electric generator  62  is coupled to the air motor  58  through a gear train  60 . The resulting motion of the electric generator produces an electric current through the cables  64 , which is used to charge the battery  66 . 
   In general, air motors are very expensive compared to air cylinders and moreover require extensive gearing. Therefore, to reduce cost we can simply use compressed air from the pipeline  56  to actuate a cylinder which in turn can be used with a slider-crank mechanism to move the electric motor. 
   The operation of this mechanism is shown in FIG.  3 . 
   Here, compressed air from air tank  48  is fed through pipeline  56  to an intake/exhaust valve  68  driven by crank shaft  74 . For simplicity, the components shown in FIG.  2 . viz., on-off valve and filter-regulator-lubricator unit are not shown here. 
   The compressed air drives a piston  72  housed in a cylinder  70  and attached to the crank shaft  74 . A flywheel  76  is attached to the output shaft  78  of the crank shaft. A gear train  60  is connected at the end of the output shaft, and an electric generator-battery-wires combination as shown in  FIG. 2  is used to generate electricity. 
   In the case of harnessing human power of children playing on a swing, a pneumatic rotary actuator can be used as the compression mechanism. 
     FIG. 4  illustrates this case. Here, a rigid arm  86  is connected through a swing pivot  88  to the top cross bar of the swing  80 . The swing seat  82  is connected to the rigid arm  86  through the flexible chain  84 . The use of the rigid arm allows the capture of a large portion of the torque of the swing&#39;s movement. The top end of the rigid arm  86  is fitted with a sector clear  90 , which is connected to a rack gear  98  connected between the pistons  96  housed inside a cylinder  94 . Two actuators are used, one at each end of the swing. 
   The rotational movements of the swing during children&#39;s play result in compression of air in the two closed chambers of the cylinder. The compressed air is released to the storage and power conversion section through output ports  100  under the control of check valves  40  and  42 . The compressed air storage and power conversion sections are similar to those shown in  FIG. 2  for the use of an air motor. Here again, rotary actuators are expensive and therefore a pinion-and-rack gearing mechanism can be used to actuate a double acting cylinder for compression of air. Swings are usually provided with flexible chains, therefore the extraction of the swing force for air compression will only be partial. 
   The mechanism shown in  FIG. 4  may be used for this purpose. Commercial rotary actuators are also composed mainly of cylinders with rack-and-pinion gearing 
   Air motors could be used in the case of merry-go-rounds for compression. 
     FIG. 5  illustrates this case. In the top view, the merry-go-round is shown transparent for clarity. A large diameter drive pulley  104  is connected to the bottom of the rotating disk  112  of the merry-go-round  102 . A V-belt  108  moves along the drive pulley  104  due to the rotation of the merry-go-round. The V-belt passes over a motor pulley  106  whose shaft is connected to the air motor  110 . A tensioner pulley with spring  114  is used to maintain the tongue on the air motor. Here too, due to cost considerations it will be preferable to use crank-slider mechanism (as used in positive displacement reciprocating piston-type compressors) with an air cylinder. 
     FIG. 6  illustrates this case. Here, two double-acting cylinders  118  are mounted on a support platform  120  below the rotating disk  112  of the merry-go-round  102 . A crank  124  is attached to the bottom of the center post  116 . Two cylinders are used with their pistons  126  connected to the crank  124  through connecting rod  128  to the centerpost  122 . 
     FIG. 7  illustrates the use of electromagnetic generators to harness the power of children&#39;s play on the seesaw  10 . A cable  130  runs through pulleys  132  attached to the bottom of the seesaw at the ends. The cable is wound once around the simple pulleys to ensure friction. Further, a spring  136  is used with the cable to maintain tension in the cable. Gear motors  134  are coupled to the shaft of the pulleys and the cable ends are anchored to the ground at  138 . 
   The use of electromagnetic generator to convert the power from the swing is illustrated in FIG.  8 . As in the pneumatic conversion case (shown in FIG.  4 ), the sector gear  90  is used, coupled to the rigid arm  86 . A ear motor  142  is coupled to the shaft of the upper sector gear  140 . 
     FIG. 9  illustrates the use of electromagnetic generator in connection with a merry-go-round. The mechanism is identical to the case of pneumatic conversion with air motor (shown in FIG.  5 ), except that a gear motor  144  acting as a generator replaces the air motor. 
   The up and down motion of the seesaw, and the to and fro motion of the swing results in alternately positive and negative voltage to be generated at the terminals of the gear motors, which act as generators. Therefore, an ac-to-dc rectifier will be used to generate a dc voltage for charging the battery (not shown for simplicity). 
   To reduce maintenance and improve the performance, it is necessary to filter the air entering the compressing cylinders. This is particularly so because air in the playground atmosphere is dust-filled. However, coarse air filters may be sufficient in most cases unlike in precision industrial operation. In practice, trade-offs between cost of air filters and cost of maintenance of low-cost cylinders may also be considered. 
   Finally, it may be mentioned that human power conversion is easily achieved from children&#39;s play under conditions where the children are static relative to the moving mechanism such as seesaw. Where the children are in a dynamic state relative to a static mechanism (e.g., slide) it will be difficult, though not impossible, to employ human power conversion techniques due to considerations of safety and simplicity. 
   The main alternative to the present pneumatic approach for human power conversion based on children&#39;s play would be to use electric (i.e., electromagnetic) generators. This method has the advantage of higher energy efficiency. However, as mentioned before it is constrained by the hazards of electric shock and leak hazards in children&#39;s playgrounds or meeting places. In fact, pneumatic motors are preferred over electric motors in applications such as opening and closing of aquarium tank doors for this same reason. 
   Minor variations of the pneumatic approach could also be implemented in practice: e.g., use mini gas turbines run by compressed air to move electric generators. However, for the kind of low-pressure energy storage system considered here, the reciprocating cylinder-type system is more economical and simpler to use. 
   Other approaches to producing renewable electricity for schools would be to install solar panels or wind turbines. However, the costs of these techniques would be far higher than those for the proposed invention. 
   In recent years, energy use/scarcity has become a serious problem due to depletion of non-renewable energy sources, increasing population, environmental pollution, and Global Warming. While in developed countries, the energy problem is one of short-term scarcity or optimum use, an estimated 40% of the world&#39;s population—or, 2 billion people in the less developed countries—do not have even have access to electricity. Moreover, this number is expected to double by the year 2050. 
   While the costs of solar, wind, geothermal, etc energy generation are coming down gradually, they are still beyond the reach of people in many developing countries, where majority of the population earns per capita incomes of less than a dollar a day. They do not have access to capital, technology, and resources such as oil, coal, or nuclear material. Even where there is an electricity grid, long-duration power outs are very common, particularly in summer when the rivers run dry. 
   Therefore, the invention outlined here could be used in playgrounds to provide very low-cost electric power for basic needs such as lighting, fans, and communication. The technology of compressed air involved is fairly simple, and well within the skills of technicians in developing countries. The material requirements are also fairly minimal: cylinders (variant of bicycle pumps could be used), valves, rubber or PVC pipelines, low-cost pressure gages and regulators, etc. The systems can easily be maintained and upgraded or repaired. 
   The use of the new technology also offers two significant side-benefits to children in developing countries: first, the promise of low-cost guaranteed electric power would encourage the introduction of reasonably well-equipped, safe and ergonomically designed play equipment in their schools and meeting places. Secondly, use of air filters as part of the compressed air systems could help reduce some of the air pollution in their school/background environments. The hybrid pneumatic-gasoline car invented by Guy Negre is similarly being adopted in high-pollution cities in Mexico and other developing countries because it acts as a negative emission vehicle, using atmospheric air for compression through on-board air filters. 
   The proposed systems can also be used for play by children at homes, contributing an alternative source of power. 
   Future modifications of the new invention also will have potential applications in a hi-tech setting, e.g. as a power source for wearable computing, emergency power source during earthquakes, and power assist for the elderly and handicapped. 
   Theoretical and experimental studies can be conducted to optimize the design of the proposed system, e.g., sizing of components, location of play equipment, etc. 
   The present invention has fairly limited application in developed countries where cheap and abundant electric power is readily available. The main potential for this invention lies in developing countries, where electricity supply is non-existent, erratic, or expensive. 
   The technology behind the new invention could be deployed on a wide scale in developing countries, with the manufacturing of the systems by local companies. Labor and materials will be a major part of the expenses involved, and local conditions would have a significant influence on the installation and running of the final systems in schools and playgrounds. 
   Although the invention has been described with particular reference to certain preferred embodiments thereof, variations and modifications can be effected within the spirit and scope of the following claims.