Patent Application: US-201213420886-A

Abstract:
self - regulating pressure source . the pressure source includes a chamber enclosing a chemical monopropellant . a moveable boss is attached to a deformable membrane sealing an air chamber , the moveable boss and air chamber being disposed within the chamber . a catalyst is disposed around the membrane so as to be covered by the boss in a retracted position so that the monopropellant is broken down by the catalyst to produce a gas . the gas pressure will increase within the chamber causing air in the air chamber to compress thereby to pull the boss into the retracted position to cover the catalyst thereby to regulate the pressure within the chamber . the self - regulating pressure source is particularly suited to power fluidic elastomeric actuators .

Description:
our invention is to utilize a chemical approach to achieve portable and silent pressure generation . this is the equivalent of a battery for fluidic systems as it offloads pressure generation to a controlled gas generating chemical process . specifically , we disclose on - demand pressure generation by the mechanical self - regulation of the decomposition of hydrogen peroxide ( h 2 o 2 ) into oxygen ( o 2 ) gas in a closed container . other monopropellants may also be used . suitable monopropellants include hydrazine ( n 2 o 4 ), hydroxyl ammonium nitrate ( han ) ( nh 3 oh )( no 3 ), triethanol ammonium nitrate ( tean ) [ hn ( c 2 h 4 oh ) 3 ]( no 3 ), and hydrozinium nitroformate ( hnf ) ( n 2 h 5 )[ c ( no 2 ) 3 ] with suitable catalysts . an aqueous h 2 o 2 solution is the fuel in a preferred embodiment . it provides high power and is easily replaced with a fresh solution when depleted . pure h 2 o 2 has a theoretical energy density of 2 . 7 kj / g , one of the highest in common monopropellant fuels . while this optimal value cannot be fully utilized at room temperature operation , it indicates the potential of h 2 o 2 as a practical power source . a feature of our portable pneumatic battery design is its rotation - invariant usage , which enables the battery to operate in any orientation . a pneumatic battery or pump mechanism that enables self - regulation in pressure generation from an aqueous h 2 o 2 solution is depicted in fig1 with a sketch and corresponding prototype . with reference to fig1 a , b and c , a pneumatic battery 10 has a cylindrical body 12 , which makes it rotationally invariant . on one side resides an elastomeric deflector 14 that embeds a cylindrical air chamber 16 at atmospheric pressure sealed off from the main chamber 10 by a thin circular membrane 18 . the deflection of the membrane 18 is dependent upon the pressure in the pneumatic battery 10 . self - regulation is achieved by this deflection , creating a mechanical feedback loop as will become clear below . as catalyst , thin sheets 20 of silver ( ag ) are placed on the deflector 14 , around the membrane 18 . the membrane 18 is offset from another disk - shaped elastomeric layer with a boss 22 by a defined distance . with increasing pressure , the membrane 18 deflects inside and pulls the soft layer with boss 22 towards the catalyst 20 pack . at a cut - off pressure value , the opposite layer completely conforms to the catalyst surface and stops the reaction thereby to self - regulate the pressure . an outlet 24 is placed on the other side of the pneumatic battery to use the generated gas pressure for actuation . the gas is filtered by a polytetrafluoroethylene ( ptfe ) membrane 26 with sub - micron pores . the hydrophobic nature of this filter keeps the solution inside while allowing the gas to be removed . the rotational invariance of the mechanism makes it a good candidate for devices that do not necessarily have a defined constant direction of gravity , since it is operational in any orientation . the prototype shown in fig1 c is made from a cylindrical hollow acrylic container , laser machined acrylic lids and custom silicone rubber seals . the deflector is attached to the left lid . the ptfe filter and a pipe fitting are placed on the right lid . the critical pressure of the pneumatic battery p c is tuned based on the following theoretical study . static plate deflection theory predicts that the deflection w of a clamped circular membrane with radius r m under a pressure difference δp = p c − p in is : w ⁡ ( r ) = δ ⁢ ⁢ pr m 4 64 ⁢ ⁢ k ⁢ ( 1 - ( r r m ) 2 ) 2 ( 1 ) where k is the flexural rigidity and v is the poisson &# 39 ; s ratio of the plate . if the air chamber 16 is connected to the atmosphere , its internal pressure p in remains constant and this equation is enough to engineer the necessary amount of offset or membrane thickness for a given target cut - off pressure . for safety , to reduce the possibility of h 2 o 2 leakage , this work uses a closed air chamber . consequently , the membrane 18 deflection decreases the volume of the air chamber 16 and increases its internal pressure due to the ideal gas law . with sufficiently thick walls , the volume v of the air chamber 16 with initial height h is solely due to the membrane 18 deflection . the pressure dependant chamber volume is written by integrating eq . 1 over the membrane area as : v = π ⁢ ⁢ r m 2 ( h - δ ⁢ ⁢ pr m 4 192 ⁢ ⁢ k ) ( 2 ) from the ideal gas law , air chamber 16 internal pressure must satisfy : r m 4 192 ⁢ ⁢ k ⁢ p i ⁢ ⁢ n 2 + ( h - p c ⁢ r m 4 192 ⁢ ⁢ k ) ⁢ p i ⁢ ⁢ n - hp o = 0 ( 3 ) where p o is the initial pressure of the air chamber 16 , typically equal to atmospheric pressure . the positive root of eq . 3 is the final pressure in the air chamber 16 . given the radius of the offset boss r o , the displacement of the opposite layer towards the catalyst pack 20 is calculated as w ( r o ) from eq . 1 . we use this theory to tune the design parameters in order to achieve a certain critical pressure suitable for the fea actuation needs . experimental pressure self - regulation data are displayed in fig2 . for this demonstration , we designed a deflector such that a silicone rubber membrane with 3 mm thickness deflects for about 2 . 7 mm under a critical pressure of 7 . 5 psi . we used a boss 22 height of 2 . 5 mm to ensure proper conformation and sealing of the catalyst . experimental details are described in below . the experiment used an approximately 10 % h 2 o 2 solution in water . the dashed line in fig2 is the target cut - off pressure . the pneumatic battery was vented at 16 minutes . the capability of the h 2 o 2 pneumatic battery 10 to supply pressure to an fea is analyzed in fig3 . in this experiment , the pressure in the pneumatic battery is measured while fluidic channels in an elastomer are pressurized and vented continuously with an approximately 2 sec period using the generated gas . this figure depicts that the pressure generation in the pneumatic battery 10 is canceled by the gas usage of the actuator at around 3 . 5 psi . the integration of the chemical pressure generator to functional devices made of fluidic elastomer actuators is exemplified by a hexagonal rolling mechanism 30 in fig4 . the rolling motion is also selected to underline the utility of the inherent rotational invariance in this chemical pneumatic battery design . as shown in fig4 , the roller 30 is made of six bending feas attached on one end to the body as cantilevers . they act as flaps that bend out and apply torque to push the body forward . the hydrogen peroxide pneumatic battery 10 rests in the center and constitutes the body and the payload of the roller in addition to providing on - board pressure . the internal volume of the pneumatic battery is approximately 1 . 7 fl . oz . a 1 fl . oz fresh 50 % h 2 o 2 aqueous solution is used for these experiments . pressurized gas taken from the outlet fitting at the center of the pneumatic battery feeds an external solenoid valve array ( not shown ). each fea is actuated in order by this valve array to induce rolling . it takes around 7 sec for a single rolling step . the body travels approximately 4 . 75 in after three rolling steps displayed in fig4 . the elastomer samples used for the experiments were 1 . 5 in long , 1 . 5 in wide , and 0 . 25 in thick stripes of smooth - on ™ ecoflex ™ supersoft 0030 silicone rubber . they embedded 13 fluidic channels that were 0 . 04 in long , 1 . 3 in wide , and 0 . 12 in thick . the channels were connected together in a meandering arrangement . the feas were fabricated by molding in two layers . molds were created using a stratasys ™ prodigy plus ™ fused deposition modeling system . the first layer was a 0 . 2 in thick elastomer with open channels on one side . the second layer was a 0 . 05 in thick solid elastomer , same length and width as the first piece . the two pieces were attached together in the thickness direction using an uncured thin layer of the same material as glue such that the open channels were sealed off . for a bending actuator , the second layer also embedded a fabric mesh as an inextensible thin sheet to constrain the axial deformation of this layer . the curing time for each step was about 24 h . the bending displacement measurements were made by image processing in matlab , using a logitech ™ webcam pro 9000 camera attached to a custom setup , clamping the feas on one end and tracking the tip of the actuator using color segmentation . the vertical position of the actuator tip was tracked for this measurement . feas were placed vertically , such that the bending axis coincided with the direction of gravity . pressure measurements were made in matlab , using a honeywell ™ asdx030 gage pressure sensor and a national instruments ™ ni usb - 6008 data acquisition system . 50 % wt . h 2 o 2 solutions were acquired from sigma - aldrich ™ and diluted with deionized water as needed . silver sheets were 0 . 008 in thick and 92 . 5 % pure . pneumatic battery body was an acrylic cylinder 2 in . diameter , ⅛ in . thickness . the deflector was molded in two parts from ecoflex ™ 0030 silicone rubber and glued following the same procedure as for the feas . the air chamber inside the deflector was sealed at ambient conditions . the filters were whatman ™ 7582 - 004 wtp range ptfe membranes with 47 mm diameter and 0 . 2 μm pore size . another embodiment of the invention is shown in fig5 . the embodiment in fig5 is very similar to the embodiment of fig1 . however , as shown in fig5 the air chamber 16 is open to the atmosphere , unlike the closed chamber in the embodiment of fig1 . the air chamber 16 is open on the left side to atmospheric pressure to simplify the design for self - regulation as compared to the embodiment in fig1 . further , the catalyst 20 in the embodiment of fig5 is a three - dimensional hollow cylinder dial increases the catalyst surface area as compared to the earlier embodiment . it is preferred that the catalyst 20 be a platinum plated plastic since silver oxidizes and can become poisoned by some of the inhibitors in die hydrogen peroxide solution . as with the embodiment of fig1 , the embodiment in fig5 operates as follows . as hydrogen peroxide breaks down , pressure within the chamber will increase urging the boss 22 to the left in fig5 . at a selected pressure , the boss 22 will have moved sufficiently so that the catalyst 20 is now no longer in contact with the hydrogen peroxide so the reaction stops . as with the embodiment of fig1 , the embodiment of fig5 thereby regulates pressure to a desired level . the embodiment of fig5 was designed to operate at a critical pressure of 68 . 9 kpa . experiments were carried out and results are shown in fig6 . a honeywell pressure transducer was used to monitor the pressure inside the chamber 50 during operation . fig6 shows that the pressure quickly rises and converges to a constant value around a predicted cutoff pressure indicated by the dashed line . the curves in fig6 demonstrate the repeatability as die cylinder is depressurized three times and similar pressure buildup curves are achieved . those of skill in the art will appreciate that the membrane 18 thickness can be determined using equation 1 set out earlier in this application . yet another embodiment of the invention is shown in fig7 and 8 . this embodiment is made of rigid material and can safely accommodate a pressure of 100 psi . as shown in fig7 and 8 , a piston 60 is slidingly disposed within a cylinder 62 . a catalyst 20 is disposed on the piston 60 . the piston 60 is restrained by a spring 64 as can be seen in the figures . as pressure builds up within the chamber 62 the piston 60 will move toward the left until the catalyst 20 is no longer in contact with monopropellant in the chamber 62 . the reaction will then stop , resulting in pressure self - regulation . the regulated pressure level may be adjusted by turning a knob 66 which compresses the spring 64 to alter the pressure set point . a filter is contemplated in this embodiment , much as the filter 26 in the embodiments of fig1 and fig5 . the filter will keep the monopropellant solution from leaking out of the chamber 62 . a suitable diameter for the chamber 62 is approximately one inch and it may be approximately five inches long . suitable materials are aluminum or steel . in the present invention , pressure generation was offloaded to a chemical process , namely the catalyzed decomposition of hydrogen peroxide . with a unique mechanical self - regulation mechanism , this chemical reaction is controlled to keep the pressure constant at a predefined value . this chemomechanical generator powered feas with no electrical energy consumption as a proof - of - concept demonstration . silent and portable operation of the mechanism disclosed herein provides an important step towards the common application of soft fluidic actuators in functional devices . the cheap and fast fabrication of feas in addition to their inherent safety makes them useful in human interactions . potential applications include artificial muscles [ 15 ], assistive or rehabilitative devices , haptic or tactile displays and interfaces . such applications will benefit from a distributed arrangement of these actuators in arbitrary 3d shapes . silver oxidizes when exposed to air , which leads to catalyst degradation . switching to an alternative catalyst such as platinum may be one solution . also , it has been suggested that a high ph may help this reaction and tin becomes an effective catalyst in a basic solution [ 4 ]. a thorough investigation of the pressure build - up rate in the pneumatic battery for different catalysts and ph values is necessary for optimized operation . we haven &# 39 ; t considered the temperature in the pneumatic battery . especially for high h 2 o 2 concentrations , the temperature increase becomes large and may affect the cut - off pressure value . an open air chamber circumvents this problem , with a potential loss of safety from peroxide leakage . the present invention is an example of green / clean technology in that the pressure source does not discharge any harmful emissions or byproducts . because of the high theoretical density of hydrogen peroxide , the energy density of the pressure source disclosed herein is comparable to the energy density of lithium batteries . as a portable pressure ( energy ) source , the invention has primary application for pressure operated machinery , soft pueumatic / hydraulic robots and devices , injection systems and medical devices . the invention can also be used for oxygen generation , which will eliminate the need for high pressure tanks but can still offer high oxygen density in some applications . the invention can thus be used by astronauts , scuba divers , and search and rescue personnel . the structures of the present invention also generate heat because of the exothermic reaction of the monopropellant . an application can be for personal portable heaters such as hand warmers or for use in small heat engines and for electricity generation . the devices of the invention can be modified slightly to generate other gasses , including , but not limited to , nitrogen , co 2 or hydrogen . hydrogen especially can further be used for flotation in lighter - 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