A process for forming a synthetic based nonwoven web bonded with a crosslinkable polymer wherein an aqueous polymeric emulsion containing a crosslinkable polymer is applied to the synthetic based nonwoven web, the water removed, and the crosslinkable polymer crosslinked. The crosslinkable polymer incorporates acetoacetate functionality and carboxylic acid functionality; wherein crosslinking is achieved by the reaction of the acetoacetate with an effective amount of a polyaldehyde and the reaction of the carboxylic acid with an effective amount of a polyaziridine compound.

Crosslinking systems for effecting cure of emulsion polymers are used to provide nonwoven articles with a desired property such as water or solvent resistance.
Most crosslinking systems for emulsion polymers which are employed today require temperatures in excess of 100xc2x0 C. to ensure the development of a decently cured system. While high temperature cures may be acceptable for many applications, such temperatures may be unacceptable in other applications because of an unsuitability of certain types of substrates, operational difficulties, and lastly, they may represent economic hardship due to the high cost of energy.
One type of crosslinking system employed for polymeric binders includes a crosslinking mechanism based upon the use of pendent acetoacetate functionality such as that derived by the polymerization of acetoacetoxyethyl methacrylate (AAEM) into the polymer and a polyfunctional reactant therewith. The acetoacetate containing polymer then can be reacted with a multi-primary amine functional moiety, for example, to effect crosslinking. This combination has a very short pot-life and often requires the addition of a blocking agent which tend to severely retard cure.
Another type of crosslinking functionality for polymeric binders is based upon the reaction of carboxyl functionality and a polyaziridine.
Still another type of crosslinking system is based on dual functionality in the polymeric binder. For example, U.S. Pat. No. 6,117,492 (Goldstein et al., 2000) discloses emulsion polymers utilizing a dual crosslinking package which contains an acetoacetate moiety that reacts with a polyaldehyde, and a carboxylic acid moiety that reacts with a polyaziridine.
The invention is directed to the use of aqueous polymeric binders having dual crosslinkable functionalities to produce high performance nonwoven webs by bonding synthetic fiber based webs or webs comprising a blend of synthetic fibers and cellulosic fibers with the aqueous polymeric binders. The high performance synthetic fiber based webs exhibit unexpected properties. For example, when used as a topsheet, the high performance webs allow water to transport through the web to an absorbent web below and the topsheet remains dry to the touch.
The aqueous polymeric binders used to form the high performance webs of this invention have two functionalities copolymerized into the polymeric backbonexe2x80x94a acetoacetate moiety and a carboxylic acid moiety. Dual crosslinkability is effected by adding a polyfunctional compound capable of reacting with the acetoacetate moiety and adding another polyfunctional compound capable of reacting with the carboxylic acid functionality. A polyfunctional compound capable of reacting with the acetoacetate moiety is a polyaldehyde, preferably a dialdehyde such as glyoxal or glutaraldehyde. A polyfunctional compound capable of reacting with the carboxyl functionality is a polyaziridine functional compound.
The process of forming the high performance nonwoven webs comprises:
applying an aqueous polymeric emulsion containing a polymer having dual crosslinkable functionality to a synthetic based nonwoven web, wherein the dual crosslinkable polymer incorporates acetoacetate functionality and carboxylic acid functionality;
removing water; and
crosslinking the crosslinkable polymer with an effective amount of a polyaldehyde and an effective amount of a polyaziridine compound.
There are significant advantages to using a dual crosslinkable polymeric emulsions described herein as a binder for synthetic fiber based nonwoven webs:
an ability to effect a low temperature cure sufficient to approach target performance requirements as currently achieved by thermally activated systems; and
an ability to form synthetic based nonwoven fabrics with unexpected excellent topsheet acquisition properties; i.e., properties that render the fabrics dry to touch when exposed to liquids.
The aqueous emulsion polymers are produced by emulsion polymerization methods and are described in detail in U.S. Pat. No. 6,117,492 which is hereby incorporated by reference.
Two types of techniques generally have been utilized in preparing polymeric components having activated acetoacetate functionality. One technique involves the addition polymerization of an ethylenically unsaturated monomer having at least one acetoacetate group via solution, emulsion or suspension polymerization. Examples of preferred ethylenically unsaturated monomers capable of providing acetoacetate functionality include acetoacetoxyethyl acrylate (AAEA), allyl acetoacetate, vinyl acetoacetate, acetoacetoxyethyl methacrylate (AAEM) and N-acetoacetylacrylamide. A second technique for preparing the polymeric component having acetoacetate functionality involves the solution or emulsion polymerization of monomers capable of forming polymers having pendant functional groups convertible to acetoacetate units. The use of hydroxyl functional monomers, e.g., hydroxy acrylates, is one way of forming these polymers. Pendent hydroxyl groups then can be converted to acetoacetate units by reaction with an alkyl acetoacetate, e.g., tert-butyl acetoacetate or by reaction with diketene.
Carboxylic acid functionality can be incorporated into the polymer in a variety of ways well known in polymerization technology. A conventional mechanism is in the polymerization of a carboxyl functional monomer with other monomers in polymer formation. Representative carboxyl functional monomers include acrylic and methacrylic acid, crotonic acid, carboxyl ethyl acrylate, maleic anhydride, itaconic acid, and so forth.
The acetoacetate and carboxyl functional monomers can be polymerized with a variety of ethylenically unsaturated monomers having reactive functionality to form the base polymers. Examples of these monomers include C1-13 alkyl esters of acrylic and methacrylic acid, preferably C1-8 alkyl esters of (meth)acrylic acid, which include methyl methacrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, isodecyl acrylate and the like; vinyl esters such as vinyl acetate and vinyl propionate; vinyl chloride, acrylonitrile; hydrocarbons such as ethylene, butadiene, styrene, etc.; mono and diesters of maleic acid or fumaric acid, the mono and diesters being formed by the reaction of maleic acid or fumaric acid with a C1-13 alkanol, preferably a C1-3 alkanol such as, n-octyl alcohol, i-octyl alcohol, butyl alcohol, isobutyl alcohol, methyl alcohol, amyl alcohol (dibutyl maleate is preferred); C1-8 alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, isopropyl vinyl ether, n-propyl vinyl ether, tert-butyl vinyl ether and n-butyl and isobutyl vinyl ether and alpha, beta-ethylenically unsaturated C3-6 carboxylic acids and vinyl esters can also be employed. Also vinyl esters of C8-13 neo-acids which are comprised of a single vinyl ester or mixture of tri- and tetramers which have been converted to the corresponding single or mixture of C8-13neo-acids may be polymerized.
In producing the relatively ambient temperature dual crosslinkable polymer, the polymer should incorporate from about 1 to 10% preferably 2 to 5% by weight of the acetoacetate functionality as measured relative to the molecular weight of acetoacetoxyethyl methacrylate and based upon the total weight of the polymer. (For monomers other than acetoacetoxyethyl methacrylate, acetoacetate functionality should be relative to the molecular weight of acetoacetoxyethyl methacrylate.) Increasing the level of acetoacetoxyethyl methacrylate or molar equivalent in the polymer beyond about 10% and generally even above about 8% by weight of the polymer may lead to an unstable emulsion or require additional stabilizing surfactant. The latter reduces water resistance. In addition thereto, the system may require an increased level of external crosslinker to effect crosslinking. That increased level too may result in an unstable formulation. Given that the preferred monomer employed in forming the acetoacetate containing polymer is acetoacetoxyethyl methacrylate, the preferred percentage level for polymerized units of acetoacetoxyethyl methacrylate (AAEM) by weight is from 4-8% by weight of the polymer.
Representative Compositions are set forth in the following table:
The sum of the monomer percent must equal 100%.
The polymers should have a Tg of from about xe2x88x925 to +10xc2x0 C. and a Mw of from 200,000 to 225,000 and an Mn of from 7,500 to 10,000.
In forming polymers having dual crosslink functionality, the operative level for the carboxylic acid functionality in the polymer typically is from 1-8 weight percent carboxyl functionality based upon the total weight of the polymer (for monomers other than acrylic acid carboxylic acid functionality is measured relative to the molecular weight of acrylic acid.) Preferably, the carboxylic acid containing comonomer is incorporated into the polymer in a preferred percentage range from 2-5% by weight.
Polymerization can be initiated by thermal initiators or by a redox system. A thermal initiator is preferred at temperatures at or above about 70xc2x0 C. and redox systems are preferred when the polymerization temperature is below about 70xc2x0 C. is used. The viscoelastic properties are influenced by small changes in temperature and by initiator composition and concentration. The amount of thermal initiator used in the process is 0.1 to 3 wt %, preferably from 0.5 to 1.5 wt %, based on total monomers. Thermal initiators are well known in the emulsion polymer art and include, for example, ammonium persulfate, sodium persulfate, and the like. The amount of oxidizing and reducing agent in the redox system is about 0.1 to 3 wt %. Any suitable redox system known in the art can be used; for example, the reducing agent can be a bisulfite, a sulfoxylate, ascorbic acid, erythorbic acid, and the like. The oxidizing agent can include, persulfates, azo compounds, and the like.
The reaction time will also vary depending upon other variables such as the temperature, the catalyst, and the desired extent of the polymerization. It is generally desirable to continue the reaction until less than 0.5% of the vinyl ester remains unreacted. Under these circumstances, a reaction time of about 6 hours has been found to be generally sufficient for complete polymerization, but reaction times ranging from 2 to 10 hours have been used, and other reaction times can be employed, if desired.
The stabilizing system employed for emulsion polymerization typically consists of 0.5-5 wt %, of a surfactant or a blend of surfactants based on the weight of total monomers charged to the system. The surfactants contemplated for the invention include any of the known and conventional surfactants and emulsifying agents, principally the nonionic and anionic materials, heretofore employed in the emulsion copolymerization of vinyl acetate polyalkoxylated surfactants being especially preferred. Among the nonionic surfactants found to provide good results are the ethoxylated secondary alcohols such as the Igepal surfactants supplied by Rhodia and Tergitols supplied by Union Carbide. The Igepal surfactants are members of a series of alkylphenoxy-poly(ethyleneoxy)ethanols having alkyl groups containing from about 7-18 carbon atoms, and having from about 4 to 100 ethyleneoxy units, such as the octylphenoxy poly(ethyleneoxy)ethanols, nonylphenoxy poly(ethyleneoxy)ethanols, and dodecylphenoxy poly(ethyleneoxy)ethanols. Examples of nonionic surfactants include polyoxyalkylene derivatives of hexitol (including sorbitans, sorbides, manitans, and mannides) anhydride, partial long-chain fatty acid esters, such as polyoxyalkylene derivatives of sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate and sorbitan trioleate. Examples of anionic surfactants include sulfosuccinates, e.g., sodium dioctyl sulfosuccinate.
The use of protective colloids such as polyvinyl alcohol and hydroxyethyl cellulose as a component of the stabilizing system can also be used. The presence of conventional levels of polyvinyl alcohol, e.g., 1 to 3% based upon monomers in the polymerization may be used. Polyvinyl alcohol formed by the hydrolysis of polyvinyl acetate having a hydrolysis value of from 85 to 99 mole % is preferred.
Crosslinking of the polymer having acetoacetate and carboxyl functionality is achieved by reaction with at least two multifunctional reactantsxe2x80x94one capable of reacting with the acetoacetate functionality and another with the carboxyl functionality. One of the multifunctional components is a polyaldehyde and preferably a dialdehyde, the other multifunctional component is a polyaziridine. The operative level of each is controlled such that generally at least an effective amount or a stoichiometric amount is added to react with the acetoacetate and carboxyl functionality of the polymer and effect dual crosslinking. To drive the reaction to completion in a short time as required on the production line, an excess of one of the reactants is employed. In crosslinking, through the acetoacetate group each aldehyde group of a dialdehyde can react with the active methylene group of the acetoacetoxy or, alternatively, one of the groups can react with the active methylene group and the other with functionality on the substrate. Examples of aldehydes suited for crosslinking include glutaraldehyde and glyoxal. If glyoxal is used, it typically is added at a level of from about 25 to 125 weight percent of the polymer or from about 50 to 250 wt % when the acetoacetate monomer is considered.
There are numerous polyfunctional aziridinyl compositions that can be used for effecting crosslinking of the polymers containing pendent carboxyl functionality. Representative of polyfunctional aziridines are noted in U.S. Pat. No. 4,278,578 and U.S. Pat. No. 4,605,698 and are incorporated by reference. Typically these polyfunctional aziridine crosslinking agents are aziridine compounds having from 3 to 5 nitrogen atoms per molecule and N-(aminoalkyl)aziridines such as N-aminoethyl-N-aziridilethylamine, N, N-bis-2-aminopropyl-N-aziridilethylamine, N-3,6,9-triazanonylaziridine and the trifunctional aziridine crosslinker sold under the trademark Neocryl CX100. Other examples include bis and tris aziridines of di and tri acrylates of alkoxylated polyols, such as the trisaziridine of the triacrylate of the adduct of glycerine and 3.8 moles of propylene oxide; the tris aziridine of the triacrylate of the adduct of trimethylolpropone and 3 moles ethylene oxide and the tris aziridine of the triacrylate of the adduct of pentaerythritol and 4.7 moles of propylene oxide.
The operative level for the aziridine functional external crosslinker is quite large, e.g., from 25-250% and higher based upon the weight percent carboxyl functionality. Higher levels of aziridine go unused and add to the cost. The aziridine moieties are capable of reacting with a carboxylic acid group and if at least two aziridine moieties react with carboxylic acid groups on two different polymer chains, the polymer chains are crosslinked.
The dual crosslink feature of the polymer is important to achieve significant cure within an appropriate ambient cure temperature range from 20 to 40xc2x0 C. In effecting cure, the conditions are controlled to flash the water from the emulsion and then effect cure. Water may be flashed at a temperature from 60 to 80xc2x0 C. under ambient and reduced pressure and the product removed from the heat source and cure being effected without further addition of heat. The polymer typically cures within seconds.
Although significant cures can be achieved with AAEM as the lone crosslinking functionality in the polymer, the performance is not at levels required for many applications. The same is true when acid functional polymers are crosslinked with polyfunctional aziridines. On the other hand, in systems which have both the acetoacetate and the acid functionality, those treated with both glyoxal and aziridine outperform those with only one functionality, regardless of the level of external crosslinker employed.
The method of forming the high performance nonwoven webs of this invention comprises:
applying an aqueous polymeric emulsion containing a polymer having dual crosslinkable functionality to a synthetic based nonwoven web, wherein the dual crosslinkable polymer incorporates acetoacetate functionality and carboxylic acid functionality;
removing water; and
crosslinking the crosslinkable polymer with an effective amount of a polyaldehyde and an effective amount of a polyaziridine compound.
The synthetic based nonwoven webs comprise a structure of fibers or filaments interlayed in a random fashion. A variety of processes have been used to prepare nonwoven webs and can be used in the preparation of the nonwoven webs described herein. For example, air laying can be used to form an airlaid web.
Appropriate synthetic based nonwoven webs are comprised of polyesters, such as polyethylene terephthalate, polyolefins, such as polyethylene or polypropylene, polyamides, such as nylon, and fiberglass. The synthetic based nonwoven web can also be a blend of synthetic fibers or a blend of synthetic fibers with cellulosic fibers, such as pulp.
Methods well known in the art are used to apply a dual crosslinkable emulsion polymer to the synthetic based nonwoven web.
It has been found that use of a synthetic based nonwoven web, compared to a cellulosic web, unexpectedly results in a synthetic based nonwoven with excellent properties that can make it useful for topsheet applications. For example, synthetic based nonwovens of this invention show little or no wetting at the surface when exposed to liquids, such as water, and facilitate transport of liquids through the surface of the fabric when an absorbent material is below them. It is anticipated that these unexpected properties will make the synthetic based nonwovens of this invention useful in products that require a topsheet that remains dry when exposed to liquids, such as in diapers and absorbent pads.
The invention will be further clarified by consideration of the following example, which is intended to be purely exemplary of the invention.

High performance synthetic nonwovens using polymers having dual crosslinkable functionality


The invention relates to an apparatus for floor cleaning, with several wheels 4, 5, 6 being attached to a frame R in such a way that a curve movement about a momentary center MP, MP1, MP2 can be performed and all momentary centers MP, MP1, MP2 form a momentary center axis MA extending substantially transversally to the frame R, and with a cleaning device 24a, 24b being received in the frame R, which cleaning device forms a cleaning surface area RF which is delimited by a circumferential edge. In order to reduce uncleaned residual surfaces when moving along contours it is provided in accordance with the invention that the momentary center axis MA forms at least one point of intersection S1, S2 in a section of the circumferential edge disposed in the zone of the longitudinal side of the frame R.

The invention relates to an apparatus for floor cleaning according to the preamble of claim 1.
Such apparatuses can be arranged in particular as scrubbing vacuum machines. One or several cleaning brushes act upon the floor surface to be cleaned. Cleansing liquid is sprayed onto the floor surface in the zone of the cleaning brushes and thereafter removed again from the floor surface with the extracted dirt under the influence of a suction apparatus and transferred to a dirty-water collecting vessel.
An apparatus for floor cleaning of this kind is known from DE 197 52 450 A1 for example. Swivelably front and rear wheels are provided on a frame. A circular brush is attached between the front and rear axle which are formed by the wheels. The known apparatus has the disadvantage that when moving around contours, e.g. shelves in supermarkets and the like, a relatively large surface area of the floor is not covered by the cleaning brush. It is necessary to subsequently clean the remaining uncleaned areas again.
In order to remedy the aforementioned disadvantage a floor cleaning device is proposed in DE 42 30 196 in which an additional brush device is provided which can be swiveled out laterally. The provision of such an additional brush device increases the weight of the apparatus, has a negative effect on its versatility and causes costs.
A floor cleaning device is known from DE 196 44 570 A1 in which merely one axle with two wheels is provided. A part of the weight of said floor cleaning device acts on a circular brush disposed in front of the axle. The apparatus is difficult to handle.
A floor cleaning device is known from U.S. Pat. No. 1,472,208 in which two rigid front casters and a swivelable rear caster are attached to a frame. A cleaning device is received on the frame between the front and rear casters. During curve movements, an axis of the momentary center of the curve movement, i.e. the so-called momentary center axis, which extends through the rigid front casters is far outside of a cleaning surface as defined by the cleaning device. When moving around edges there is always a transversal movement of the cleaning device. Uncleaned residual surfaces remain.
A further floor cleaning device is known from DE 41 03 087. A momentary center axis extending through the rigid front wheels intersects the cleaning surface. It does not intersect the cleaning surface in the zone of a circumferential edge of the cleaning surface which is located in the zone of the longitudinal side of the frame. Transversal movements of the cleaning device also occur in this floor cleaning device during curve movements. Uncleaned residual surfaces also remain in this case as well.
It is the object of the invention to eliminate the disadvantages according to the state of the art. An apparatus for floor cleaning is to be provided in particular which is easy to handle. Furthermore, the surface areas remaining when moving past contours are to be as small as possible.
This object is achieved by the features of claim 1. Appropriate embodiments are obtained from the features of claim 2 to 17.
It is provided within the terms of the invention that the momentary center axis forms at least one point of intersection with a section of the circumferential edge which is disposed in the zone of the longitudinal side of the frame.
The momentary center is understood as being a pole, i.e. a static point, about which a leg of a trajectory can be performed with the apparatus. In apparatuses for example with a rigid rear axle and swivelable or steerable front wheels, all momentary centers are disposed on the rear axle or an imaginary lateral extension thereof. A momentary center axis is defined by all momentary centers of an apparatus.
A cleaning surface of the apparatus is defined by the rotating cleaning means, e.g. the circular brushes. The cleaning surface is delimited by a circumferential edge. A section of the circumferential edge can be limited by the longitudinal side of the frame. A section of the circumferential edge is located in the zone of the longitudinal side of the frame when the momentary center axis intersects a lateral 45xc2x0 sector of the circumferential edge.
With the apparatus in accordance with the invention the swinging out of the front or the rear while moving past contours is avoided. The portion of uncleaned residual surface areas and the passage width can thus be kept to a minimum. The apparatus is easy to handle.
According to a preferable feature of the embodiment the momentary center axis extends in the vicinity of the vertical projection of the center of gravity of the apparatus. At least one non-steerable wheel can be attached on the momentary center axis close to the vertical projection of the center of gravity. Moreover, at least two, but preferably four swivelable and steerable wheels can be attached to the frame. Such an apparatus is particularly easy to handle and tilt-resistant.
According to a further embodiment two driven wheels are arranged on the momentary center axis. In this case the driven wheels can be driven with a different speed and/or in different directions of rotation. This variant is also characterized by versatility and ease of handling capability, particularly where riding apparatus are concerned.
It is provided according to a further embodying feature that at least one steerable wheel is attached to the frame. It is understood that also several steerable wheels could be provided. If steerable front and rear wheels are provided which are not disposed on the momentary center axis, the steering of the front and rear wheels must be performed in such a way that their axes always intersect on the momentary center axis when turning the wheels during steering.
The cleaning device is appropriately provided with at least one, preferably two or three, circular brushes, or at least one cleaning roller.
It is regarded as being particularly advantageous that a supply unit which is arranged as an exchangeable module comprises a tank, a dirt receiving device and a power supply unit. The module can be removed from the frame with ease by using a suitable docking station. Operating material can be added in the docking station, the power supply unit can be recharged and the dirt-water receiving device can be emptied. In order to ensure uninterrupted continuation of the work, the module can be exchanged for one with fresh operating material. An apparatus of this kind in combination with one or several features as set out in this paragraph can form per se a separate invention.
Preferably, the at least one non-steerable wheel is attached vertically movable relative to the swivelable wheels on the frame. For this purpose the at least one non-steerable wheel can be received in a lifting apparatus. It can concern, for example, a resiliently held rocker, a spring or a parallelogram-like lifting apparatus. It has further proven to be advantageous that a device is provided for setting the distribution of the load among the at least one non-steerable wheel and the swivelable and steerable wheels. The aforementioned features contribute further to the easy handling capability of the apparatus and the adjustment to the different permissible surface loads of the floor.
It is appropriate that a motor for driving the at least one driven wheel is attached to the frame. When the module is removed it is not necessary to additionally remove the motor from the frame.
It is further appropriate when at least one stop wheel is provided on a lateral brush cover. The apparatus can thus be guided without any frictional losses along a wall for example or precisely about a contour such as a corner or an edge. The stop wheel can be arranged with an axial offset xcex94y in front of the momentary center axis, with the following applying:
xcex94y=a Dbrush diameter
with a being capable of assuming values from 0.15 to 0.35 and Dbrush diameter being the diameter of the brush. It has proven to be particularly advantageous to use a value of 0.25 for a. If several stop wheels are provided one after the other on the lateral brush cover, it is necessary, with respect to the axial offset xcex94y, to consider the distance of a central axis defined by the central points of the stop wheels towards the monopole axis. The central axis extends parallel to the monopole axis and intersects a connecting line between the central points in the middle which are farthest away from one another.
According to a further embodiment, a housing contour in the zone of the cleaning device is disposed at least over sections on the circumference of a circle imagined about a central momentary center. This facilitates in particular the driving around edges, and the driving over edges.
It has proven to be particularly advantageous that the at least one point of intersection is disposed on an outermost lateral section of the circumferential edge preferably projecting beyond the longitudinal side of the frame. In this case there is no transversal movement of the cleaning device during a curve movement. The cleaning surface area can be guided with high precision along the contours. Corners can be cleaned substantially, so that the portion of uncleaned residual areas is minimal.


A conventional circuit for blocking a semiconductor switching device (7) on overcurrent, the semiconductor switching device (7) having at least one continuously driven semiconductor switch (9), comprises a diver circuit (11), which has a driver stage (12) for each semiconductor switch (9), a control pulse generator (10) for producing control pulses (P1 to P6), which are fed in operation to a control input of the semiconductor switching device (7) via the driver circuit (11), and a monitoring device (34), which measures the current (I) flowing through the semiconductor switching device (7) and, when an overcurrent occurs, generates a fault signal (E), which initiates blocking of the semiconductor switching device (7). When the semiconductor switching device is being blocked, a high overvoltage can occur therein, possibly leading to destruction of the semiconductor switching device. In order to reduce, with little outlay, the overvoltage in the semiconductor switching device during blocking thereof, provision is made such that the operating voltage (U) of the driver circuit (11) is arranged to be switched over briefly by the fault signal to a lower, interim value corresponding to a lower current (I) through the semiconductor switching device (7) and then, within the maximum permissible duration for loading the semiconductor switching device (7) with an overcurrent, to be switched off completely.

The invention relates to a circuit for blocking a semiconductor switching device on overcurrent, the semiconductor switching device having at least one continuously driven semiconductor switch, which circuit comprises a driver circuit having a driver stage for each semiconductor switch, a control pulse generator for producing control pulses, which are fed in operation to a control input of the semiconductor switching device via the driver circuit, and a monitoring device, which measures the current flowing through the semiconductor switching device and which, when an overcurrent occurs, generates a fault signal, which initiates blocking of the semiconductor switching device.
The semiconductor switching device is generally an inverter having several power switching transistors in the form of semiconductor switches.
In a known circuit of that type (EP 0 521 260 B1), free-wheeling diodes are connected anti-parallel to each semiconductor switch in order to avoid, at the semiconductor switches, overvoltages that are caused by inductive resistors, such as choke coils, inductive loads or lead inductances, in the circuitry of the semiconductor switches when a semiconductor switch is switched off (blocked) in normal operation. When an overcurrent, for example a short-circuit current, flows through the semiconductor switches, it is, however, possible for even higher overvoltages to occur. The known circuit should reduce those overvoltages by blocking one of the series-connected semiconductor switches simultaneously carrying an overcurrent, without increasing the amount of circuitry involved by using capacitors. Notwithstanding, free-wheeling diodes are still required. Even when those are provided, when a semiconductor switch carrying a very high overcurrent, such as a short-circuit current, is being blocked, in the circuit of which semiconductor switch there is a high inductive reactance, a very high overvoltage can still occur at the blocked semiconductor switch.
The invention is based on the problem of providing a circuit of the kind mentioned at the beginning that allows, with little outlay, a further reduction in an overvoltage at the semiconductor switching device when that is being blocked because of an overcurrent.
According to the invention, that is achieved by means of the fact that the operating voltage of the driver circuit is arranged to be switched over briefly by the fault signal to a lower, interim value corresponding to a lower current through the semiconductor switching device and then, within the maximum permissible duration for loading the semiconductor switching device with an overcurrent, to be switched off completely.
In this solution, therefore, the overcurrent is reduced to zero in stages. For each switching-off stage, the amount by which the current flowing through the semiconductor switching device decreases is, therefore, also smaller. Consequently, the rate of change (di/dt) of the current is correspondingly lower for each switching-off stage, as is, therefore, the voltage induced in the inductive reactance in the circuit of the semiconductor switching device by the change in the current (Ldi/dt). Because the induced voltage is added to the operating voltage of the semiconductor switching device when the semiconductor switching device is being blocked, the total overvoltage at the semiconductor switching device when the blocking occurs is also lower. The semiconductor switching device is, therefore, not unduly loaded and does not require additional circuitry to reduce overvoltage when blocking occurs.
Provision is preferably made such that, for several semiconductor switches jointly supplied from one operating voltage source, the current flowing through the semiconductor switches is measured in a supply line common to all th e semiconductor switches by the monitoring device, a single measuring device in the monitoring device being sufficient for all the semiconductor switches.
Provision can then be made such that, for several semiconductor switches, the driver stages thereof are all supplied from a common operating voltage source, which is galvanically isolated from the driver stages and which, as a function of the fault signal, is arranged to be switched over to the interim value and switched off. In that arrangement, there is no need, when an overcurrent occurs in a semiconductor switch, to determine which semiconductor switch is affected. There is, accordingly, less outlay on resources in the monitoring device.
An advantageous practical form of the circuit can consist in that the operating voltage source of the driver circuit is a direct-current voltage source, which is connected, via a chopper controlled by a pulsed switching signal and a transformer having a secondary winding for each driver stage and via a rectifying circuit connected to the secondary winding, to a (respective) driver stage and the switching signal that controls the chopper is frequency- or pulse-length-modulated as a function of the fault signal. In that arrangement, the reduction in the operating voltage of the driver circuit when an overcurrent occurs is achieved by conversion of the operating voltage into a pulsed voltage and subsequent frequency- or pulse-length-modulation of the pulsed voltage.
The control pulses of the control pulse generator can be fed to a control input of the driver circuit in a customary manner.
Provision is preferably made such that the control pulses and the operating voltage for each driver stage are transmitted by means of a high-frequency carrier signal of an oscillator that is common to all the driver stages, via the same galvanic isolation stage. In that arrangement, galvanic isolation between the switching device, which is optionally operated with high voltage, and the low-voltage-operated switching circuits controlling the driver stage(s) thereof is possible with little outlay on isolation stages.
A simple practical form can consist in combining the control pulses of the control pulse generator (when using frequency- or pulse-length-modulation of a driver circuit direct-current operating voltage converted into a pulsed intermediate circuit voltage by means of the chopper) with the switching signal controlling the chopper by means of an AND gate, in order to transmit the control pulses and the operating voltage to the driver stages with galvanic isolation.
A further alternative arrangement of the operating voltage source of the driver circuit can consist in that it has an output for a high, normal value and an output for the low, interim value, one of which outputs can be selected for the supply of the operating voltage as a function of the fault signal.
In that arrangement, the outputs can be connected by an OR gate.
Provision can then be made such that one output is connected, via a diode, to one end of the switching path of a controllable switch, the other output is connected, via a diode, to the other end of the switching path and to the driver circuit, and the switch is arranged to be switched as a function of the fault signal.

Circuit for blocking a semiconductor switching device on overcurrent


A compact apparatus can form multi X-ray beams with good controllability. Electron beams (e) emitted from electron emission elements (15) of a multi electron beam generating unit (12) receive the lens effect of a lens electrode (19). The resultant electron beams are accelerated to the final potential level by portions of a transmission-type target portion (13) of an anode electrode (20). The multi X-ray beams (x) generated by the transmission-type target portion (13) pass through an X-ray shielding plate (23) and X-ray extraction portions (24) in a vacuum chamber and are extracted from the X-ray extraction windows (27) of a wall portion (25) into the atmosphere.

Conventionally, an X-ray tube uses a thermal electron source as an electron source, and obtains a high-energy electron beam by accelerating the thermal electrons emitted from a filament heated to a high temperature via a Wehnelt electrode, extraction electrode, acceleration electrode, and lens electrode. After shaping the electron beam into a desired shape, the X-ray tube generates X-rays by irradiating an X-ray target portion made of a metal with the beam.
Recently, a cold cathode electron source has been developed as an electron source replacing this thermal electron source, and has been widely studied as an application of a flat panel display (FPD). As a typical cold cathode, a Spindt type electron source is known, which extracts electrons by applying a high electric field to the tip of a needle with a size of several 10 nm. There are also available an electron emitter using a carbon nanotube (CNT) as a material and a surface conduction type electron source which emits electrons by forming a nanometer-order microstructure on the surface of a glass substrate.
Patent references 1 and 2 propose, as an application of these electron sources, a technique of extracting X-rays by forming a single electron beam using a Spindt type electron source or a carbon nanotube type electron source. Patent reference 3 and non-patent reference 1 disclose a technique of generating X-rays by irradiating an X-ray target portion with electron beams from a multi electron source using a plurality of these cold cathode electron sources.
Patent reference 1: Japanese Patent Laid-Open No. 9-180894
Patent reference 2: Japanese Patent Laid-Open No. 2004-329784
Patent reference 3: Japanese Patent Laid-Open No. 8-264139
Non-patent reference 1: Applied Physics Letters 86, 184104 (2005), J. Zhang, "Stationary Scanning X-Ray Source Based on Carbon Nanotube Field Emitters".

Multi X-ray generator and multi X-ray imaging apparatus


The present invention relates to a method and a device for producing plastic molded skins having different subregions. For this purpose, before melting the first plastic material, a region of the molding tool surface (2) is covered with a separate energy self-sufficient mask (3). After the unmasked region of the molded tool surface (2) has been coated, the mask (3) is removed, and in a second manufacturing step the exposed subregions of the molding tool surface (2) is coated with a different plastic material, the two subregions of the plastic skin bonding with each other.

The present invention refers to a method for the production of plastic molded skins having different subregions, as well as a device for the production of such plastic molded skins. The afore-stated plastic molded skins are provided especially for use in interior paneling and instrument dashboards of motor vehicles and include subregions having varying properties, in particular, having different colors.
Methods for the production of multicolored plastic molded skins are known since some time now.
Thus, for example EP 0 972 625 A1 describes a device for rotation sintering of plastic molded skins for the production of instrument dashboards or interior paneling of motor vehicles and are comprised essentially of a heatable mold tool as well as two differently equipped container fitting with the mold tool and containing plastic powder, wherein the containers are utilized sequentially in two different work steps each in combination with the mold tool. The first plastic powder container includes a bowl-shaped projection which extends into the interior of the mold tool covering a portion of the surface of the mold tool. This powder container is utilized with a first plastic powder in a first work step, wherein the first powder is melted at the exposed surface of the warmed mold tool, while the area underneath the bowl-shaped cover of the mold tool remains free of powder.
In the second work step a second powder box is utilized, which contains a differently colored powder and does not include a suitable projection for a cover, such that during the repeated rotation sintering, the second powder melts at the area of the surface of the mold tool previously maintained exposed and there, forms a molded skin in a different color, which combines with the molded skin of the first molded skin to form a multicolored molded skin.
The problem with the device is the high operative expenditure, in particular also for the sealing of the cover (mask), where, especially in complicated molds, there is the danger of leakage and where blurring of the color borders can take place.
In DE 10 2005 020 492 A1 and in DE 10 2005 020 493 A1 a device or a method for the production of multicolored plastic molded skins are described, in particular for motor vehicle parts, such as for example instrument dash boards or door paneling, wherein the plastic molded skins are built by the sintering method through means of sequential multiple continuous melting of plastic powders of different colors at the surface of a heated mold tool. The areas to be provided with plastic powders of different colors at a surface of the mold tool are separated from each other by projections or webs. The covering or mask which in this case is also integrated into the powder container is, at its edges, provided with a gasket that is supported by the webs. In addition, an above atmospheric pressure is produced in the covered surface areas bordered by the webs. In this manner, the problem of the exact color separation is solved, however, in this case also, there is a relatively high expenditure in apparatus required, in particular, in order to integrate the mask as well as the required energy supply for the locking and sealing of the mask at the mold tool surface, as well as the production of the above atmospheric pressure in the masked area integrated in a corresponding powder box.
As an additional problem there is the fact that such masked powder containers, or those provided with covers or similar mold tool counter parts are provided with a series of additional cables and tubes in order to realize the functional capability of the mask. These cable and tubes packets render the manufacturing process undesirably complex and thereby causing considerable spatial restrictions.
Thus, the problem remained to realize a masking technique for the production of plastic molded skins with subregions of different properties, in particular, areas having different coloring, that do not exhibit the drawbacks of the prior art.
The problem is solved by a method for the production of subregions having different properties, in particular, molded plastic skins having different colors, by depositing sequentially different plastic materials onto a surface of a heated mold tool, wherein    a) prior to depositing the first plastic material at least one area of the surface is covered,    b) which at least seals at least a masked area between mask edge and mold tool surface,    c) in a first forming step a first molded skin is formed at the exposed surface of the mold tool,    d) the forming process is subsequently interrupted and the at least one mask is being removed and    e) at the exposed area of surface of mold tool, with a second different plastic material a second molded skin is being formed in a second forming step, wherein the plastic molded skins are bonded to a single molded skin having subregions with different properties, wherein the at least one mask is arranged as a separate energy self-sufficient mask at the surface of the mold tool. The problem is further solved by a device for the production of areas having different properties, in particular, different colors that includes    a) a heatable mold tool for forming of plastic molded skins by depositing plastic material onto a surface of a heated mold tool and    b) at least one mask for covering an area of the surface of a mold tool before the deposit of the first, plastic, wherein the mold tool at its surface has means for receiving at least one mask and the at least one mask is configured as a separate energy self-sufficient mask with corresponding means for building up a bond with the mold tool surface. Further advantageous embodiments of the method as well as the device are reflected in the respective dependent claims.
The essential idea of the invention is such that a separate mask is provided for a subregion of the mold tool surface which is energy self sufficient and can be by itself directly connected to the mold tool or the mold tool surface that is no longer combined with the mold tool counter part. For that, the surface of the mold tool or the mask must at first be provided with means for fixing and centering the mask at the surface of the mold tool. At the same time, the mask itself has to be provided with means which supply energy for the action of locking and unlocking the mask at the mold tool surface, as well as the sealing of the mask edge at the mold tool surface. Under such conditions, one or more subregions of the mold tool surface can be then covered with at least one separate mask and be left free of powders.
In an advantageous embodiment of the present invention, the mask is centrally locked via a locking bolt by means of a locking bushing disposed at the surface of the mold tool. The exact location of the mask is fixed through additional centering pins. For that, an additional centering pin is, for example, disposed at the mold tool surface which engages into a corresponding centering bushing in the mask. In an advantageous embodiment of the present invention, several (at least two) centering pins or centering domes are provided for realizing a fitted arrangement of the mask at the surface of the mold tool.
The afore-described means for fixing and centering the mask at the mold tool surface, or their corresponding counterparts can be mutually disposed either at the mold tool surface or in the mask itself. That is, reversed arrangements are also possible, where the centering pin is integrated into the mask, while the locking bolt is arranged at the mold tool surface, or both bolt and pin can be arranged at one side and the corresponding bushings then at each opposite side.
An advantageous embodiment of the present invention provides that the mold tool is a galvanically produced mold tool, which exhibits a galvanically integrated locking bushing made from steel. The locking of the mask at the surface of the mold tool is advantageously carried out via a locking bolt with spring-loaded pressure balls disposed therein and for realizing the locking action in a simple manner analog the coupling of a trailer. The unlocking of the mask in this case, is carried out by releasing the pretensioned pressure balls by means of a pressure container or pressure cylinder in the interior of the mask.
The first step of the method according to the invention is to fix the mask at the surface of the mold tool. After the mask has been locked and centered at the surface of the mold tool, the masked area at the lower edge of the mask is being sealed against the surface of the mold tool, wherein as an advantageous embodiment of the present invention, a sealing edge is provided at the mask with seals of durable elastic and temperature resistant plastic. An advantageous embodiment of the invention provides that these seals are inflated by means of a pressure container or pressure cylinder disposed in the interior of the mask. After sealing the masked area, a first molded skin can be formed in the uncovered areas of the mold tool surface.
The formation of the molded skin is carried out preferably via rotation sintering or spray sintering.
When carrying out rotation sintering, the mold tool, preferably a so-called "galvano" is closed with plastic powder container as a lower mold counter part and the plastic molded skin is discharged at the heated mold tool surface during rotation of the closed mold.
So that no powder reaches the masked area, the masked area is being sealed. Fort his purpose, seals are provided in the marginal area of the mask that are made from a relatively hard, and heat-resistant material having tensile strength, such as for example, polyurethane or silicon caoutchouc. In order to realize complete sealing of the mask, ductile or inflatable seals are utilized. In an advantageous embodiment, it is contemplated that the inflation of the seals is initiated by means of a timer element integrated into the interior of the mask and in operative contact with a pressure container, and wherein the seal is being inflated only shortly prior to the actual slush-process which is the melting of the plastic. This has the enormous advantage that the seals come in contact only very late with the hot surface of the mold tool and the contact time between seal and mold tool surface is kept as short as possible, which markedly extends the lifetime of the seals.
Advantageous variants which offer themselves for this method for the inflatable seals are two different seal types, both from permanent elastic and thermally stable plastic, such as for example polyurethane or silicon caoutchouc. With the first seal type, a groove is formed in the lower edge of the mask, in which a hinge-type constructed rubber seal is clamped. When inflating the seal the hinges unfold and the rubber seal moves out from the groove and adjoins tightly at the surface of the mold tool.
The second seal type is a seal ring disposed at the mask edge and the sealing results from the inflation and the corresponding expansion of the seal ring.
After a first molded skin with defined properties has been formed via the first work step, the mold tool is opened again and at least one masked subregion is exposed after removal of the mask. In a second work step, in which the plastic powder is changed, a different plastic powder is then deposited on this subregion. Since the "galvano" is evenly heated in all areas for discharging the second plastic layer, at the same time, a connective bonding takes place between the two plastic molded skins into a single plastic molded skin having different properties. This presupposes that the plastic materials involved are at least related polymers with similar melting points that can be melted together. The plastic molded skin so obtained, subsequently can be further handled in the usual manner into an interior paneling or instrument dashboard for a motor vehicle.
Originally, the mask technique was used in particular, for the production of multicolored plastic molded skins. For this purpose, the same basic plastic is usually utilized for both color areas where the powder mixtures differ only by the different dye stuff components. The method according to the present invention is however not limited to the production of different color subregions, but can also be utilized in order to obtain molded skins with subregions of different haptik or having other, different physical properties. These variations can be obtained in that each of the powders contain different additives or that different co-polymerisates are utilized in powder form, which might tie in with the base polymer such that they have a comparable melting point, but differ in each of the copolymers. Of course, chemically very different thermoplastic plastic material can also be utilized, if they exhibit a similar melting point and can bond with each other or are melting with each other.
The method of the present invention is not limited to plastic skins having two different subregions, several independent masks at the mold tool surface with several different subregions can also be arranged, whereby either in successive work steps or all in one work step being removed at the same time, and further plastic layers discharged onto the exposed areas of the mold tool surface that then bond to a single plastic molded skin with several different subregions. In this manner, it is possible to produce molded skins having different subregions in several work steps utilizing different plastic powders.
The special advantage of the present invention is based on each mask being arranged as an energy self-sufficient mask directly at the surface of the mold tool and thus without the need for further cables, tubes or lines in the outer area of the mold. In particular, with the slush-method (rotation sintering), additional cable or hoses in the outer area of the mold means a noticeable complication of the method and a spatial restriction, where the arrangement of the cables and tubes outside of the mold have to be synchronized to the motions of the mold and at the same time when the mold is open, free access to the interior of the mold is always needed, which in view of the multiple supply lines is not easily realized.
Through the introduction of an energy self-sufficient mask configured as a volume dimensioned body and interiorly is provided with pressure cylinders or pressure containers by which the locking and the sealing of the masks can be controlled, these problems disappear, such that the entire production of the molded skins can be controlled fully automatically via a robot and, for example, the mask, with the aid of a robot disposed at the surface of the mold tool, can be centered and locked and subsequently forming the molded skin for the first subregion at the exposed areas of the surface of the mold tool; after this work step the mold tool is again opened and the mask can be removed per robot and cleaned outside of the area of the mold tool, and wherein at the same time, the pressure container integrated into he mask can again be refilled.
The sealing and locking of the mask is controlled by control units within the mask, and the control steps integrated into the entire production process and also adjusted thereto, such that, for example, locking of the mask is carried out during deposit onto the mold tool surface by means of the robot, while the sealing is initiated only shortly before the slush-process. The unlocking takes place again in the coordination with the robot.
A further advantage of the method according to the invention is that the mask as a single piece can be cleaned in a more easy and uncomplicated manner than a mask or cover which is integrated into the powder container or into another counter part of the mold tool.
As already seen from the foregoing description, the masking technique according to the present invention is especially and advantageously suited for rotation sintering but can be utilized also for the spray sintering or any other technique of molding processes where thermoplastic plastic material is processed and the surface areas of the mold tool are to be masked in order to at first prevent formation of a material layer at these sites but where deposits in these areas are then also made in a subsequent step.
Especially suitable plastic materials for the afore-described method according to the invention are polyvinyl chloride (PVC), or thermoplastic polyurethane (TPU) or also co-polymerisates on the basis of PVC or polyurethane.
In the following paragraphs the method according to the present invention will be more readily explained by the following Figures. It is shown in:

Method and device for producing plastic molded skins having different subregions


An improved vehicle seat assembly for mounting on the frame of a vehicle driver""s seat including a polymer support plate attached to the frame, a polyurethane foam base on the support, an inflatable air cell cushion on the base and an elastic cover. The inflatable air cell cushion includes individual inflation zones each comprised of individual interconnected inflation cells. The zones are normally isolated from each other. A center zone having a preset inflation pressure is positioned under the ischial area of the driver. Front, back and side bolster zones provide front-to-back and side-to-side support. The individual air cells of the center zone are interconnected by a serpentine airflow path of reduced area to enhance the vibration and shock absorption characteristics of the zone.

Not Applicable.
The invention relates generally to an improved vehicle truck seat assembly that provides support and shock dampening to the ischial area of the driver as well as front-to-back and lateral stabilization. The seat assembly employs an inflatable air cell cushion with a central inflation zone comprised of individual inflation cells interconnected by an airflow path that provide optimum shock absorption qualities. Bolster zones comprised of individual air cells surround the central inflation zone. The inflation cells have a cell geometry that allows for improved molding of a support cushion comprised of individual fluted or finned cells.
Truck drivers seated for long periods of time in the cab of a truck can suffer discomfort caused by pressure, road shock and vibration. It has been shown that persons who are required to stay seated for long periods of time, for example, long haul truck drivers, experience muscle fatigue, loss of flexibility and back pain, particularly due to truck vibrations transmitted to the driver. Any driver discomfort, soreness or numbness in the buttocks and legs, can be attributed to a loss of blood flow in the tissue from unrelieved pressure on the skin. Besides creating physiological problems, this discomfort may require the driver to make frequent stops or shorter trips, decreasing efficiency.
Inflatable cellular cushions provide the most uniform distribution of weight and thus provide the greatest protection from seating pressure. These cushions have an array of closely spaced air cells that project upwardly from a common base. Within the base the air cells communicate with each other, and thus, all exist at the same internal pressure. Hence, each air cell exerts essentially the same restoring force against the buttocks, irrespective of the extent to which it is deflected. U.S. Pat. No. 4,541,136 shows a cellular cushion for use on wheelchairs.
U.S. Pat. No. 3,870,450 illustrates another cushion design and discloses a conventional method and apparatus for molding and assembling the cushions. U.S. Pat. No. 3,870,450 and U.S. Pat. No. 4,005,236 disclose fluted cells. The cells are spaced apart to prevent material that is in the soft or uncured condition from the dipping process from bridging adjacent cells during forming. U.S. Pat. No. 4,541,136 provides a multicell cushion in which the individual cells have a finned configuration when deflated. This cell configuration allows the cells to contact each other along their sides when inflated to provide a continuous supporting surface.
Generally fluted or finned cells have a higher profile than vacuum molding will allow. That is, to vacuum mold, you would pull the material into the mold to fill out the form stretching it and causing it to thin out and become weak. The thin areas cool off too quickly and can break. This can be avoided with dip molding. Due to the cost, dip-molding methods generally are used to make cushions having individual cells of identical configurations and support characteristics.
Heretofore, molded inflatable air cell cushion technology has been directed to medical uses, such as wheelchair cushions or mattress overlays for compromised patients, and has not been optimally employed in seating for vehicles, such as trucks. Although such cellular cushions work well for preventing pressure sores, they have not necessarily addressed the problems associated with able-bodied vehicle drivers, such as vibration and shock to the ischial area and front-to-back and side-to-side stabilization.
It would be advantageous, therefore, to provide vehicular seating that addresses the problems of pressure, vibration, road shock and stabilization utilizing inflatable air cell technology. It also would be advantageous to develop a vehicular seating assembly incorporating an improved inflatable cellular cushions which can be installed in the vehicle and controlled by the driver that improves seating comfort for these drivers.
It also would be advantageous to vacuum mold plastics to form finned cushion cells. Labor costs are less for vacuum molding. Vacuum molding would allow a manufacturer to make cushions having varied finned cell configurations and arrangements. Thus, cushions could be custom made to fit the anatomy of individual truck drivers.
One aspect of the invention is a seat assembly for a vehicle having enhanced vibration and shock absorption characteristics.
Another aspect of the invention is a seat assembly for a vehicle having enhanced front-to-back and side-to-side stabilization characteristics.
Another aspect of the invention is an improved cushion for use in a vehicle that provides improved seating comfort for the user, particularly drivers who sit for extended periods of time, such as over-the-road truck drivers.
Another aspect of this invention is an improved cushion cell geometry that allows for vacuum molding a finned cushion from urethane or other plastic.
According to the invention, briefly stated, an improved truck seat assembly incorporating an improved inflatable air cell cushion is provided. The inflatable air cushion includes a plurality of inflation zones comprised of individual cells. For example, one such cushion includes five zones. One zone of cells is located approximately at the middle of the cushion to be positioned under the ischial area of the driver. There are four zones comprised around the perimeter of the cushion to function as bolsters. The cushion can be mounted on a relatively solid base or a foam base that can be attached to a seat support plate. A flexible plastic seat support plate allows the truck seat pan to dampen truck vibrations and shock loads. mounted on the frame of the original truck seat. The support, the base and the air cell cushion provide desired road vibration absorption characteristics. In another embodiment, a support fabric supports the base and the air cell cushion. The tension on the fabric can be adjusted to obtain optimal support and vibration dampening characteristics.
The peripheral zones are connected by valve and air lines through an air regulator to the truck""s air supply system to control air pressure in the peripheral zones. The driver can adjust the pressure in the peripheral zones for seating comfort and lateral support or the cushion can be completely automatic and fit to the driver. The air regulator is pre-set to provide optimal pressure to the ischial zone.
In another embodiment of the invention sensors, such as a bottom out sensor or xe2x80x9csmart fabricxe2x80x9d is used to cover the cushion. The xe2x80x9csmart fabricxe2x80x9d is used to determine pressures in various and, through a feedback loop to the air supply, adjust the air pressure.
Also provided is an improved cushion with individual inflation cells having an improved cell geometry that provides optimal support characteristics with manufacturing advantages. The novel cell has an optimum ratio of area of the cell to area of the base (footprint) is 3:1 which allows for vacuum molding. For example, in one embodiment the cushion cell has a 2.5-inch by 2.5-inch (6.25 square inch) base or footprint and a surface area of 18.75 square inches or less. Vacuum molding is less expensive than dip molding and, therefore, making it commercially and economically feasible to provide multiple variations of cushion configurations.