Molded Seat

Abstract

A seat incorporating insert(s) intermediate its upper and lower surfaces. A seat insert for the support of the users buttocks conforms to the user's body, has rebound properties, and areas adapted to underlie the perineum and/or ischiums of a user softer than the rest of the seat insert. Alternatively, a perineal insert and/or ischium inserts may be used without the seat insert described. Finally, a heatable insert can be used in conjunction with or in the absence of said seat inserts to provide heat for the comfort of a seat user. In all cases, the aforesaid inserts are preferably completely encapsulated and enclosed by the foam materials making up the seat, which can be accomplished by molding the seat around the insert(s), creating a seat with various internal density zones, adjustable heat, and enhanced abilities to conform to the user's body, while limiting pressure on perineum and/or ischiums.

Claims

1. A seat, comprising: an insert embedded in a resilient outer layer, which resilient outer layer forms a unitary one-piece layer surrounding said insert; and wherein said insert comprises at least one of: a seat insert comprising a semi-rigid mat having at least one of rebound characteristics, and compression set characteristics, a seat insert including at least one of: a perineal opening, and an ischium opening, a heatable insert, which heatable insert can be electrically activated to provide heat to said seat, a heatable insert, which heatable insert includes at least one of a perineal opening, and an ischium opening, a heatable insert, which heatable insert with an adhesive surface by which it can be adhesively connected to said seat insert, a heatable insert, which heatable insert formed using a material that repels a reacting liquid used to form the resilient outer layer, a perineal insert comprising a material softer than the resilient outer layer, and an ischium insert comprising a material softer than the resilient outer layer.

2. The seat of claim 1, wherein at least one of said seat insert is comprised of closed cell foam, said heatable insert underlies said seat insert, said perineal insert is comprised of a gel-like material. said perineal insert is comprised of sealed gel packets, said perineal insert is comprised of sealed air packets, said perineal insert is comprised of sealed air packets with adjustable pressure, said perineal insert is comprised of super light density foam, said ischium insert is comprised of a gel-like material, said ischium insert is comprised of sealed gel packets, said ischium insert is comprised of sealed air packets, said ischium insert is comprised of sealed air packets with adjustable pressure, and said ischium insert is comprised of super light density foam.

3. The seat of claim 1, wherein at least one of: any said insert is completely encapsulated by said resilient outer layer, any said seat insert is comprised of vinyl nitrile closed cell foam, and said resilient outer layer is comprised of polyurethane foam.

4. The seat of claim 1, wherein said seat has an upper surface and a lower surface, and any said insert is at least one of: substantially parallel to said upper surface, and intermediate said upper and lower surfaces.

5. The seat of claim 1, wherein an opening includes flex tabs.

6. The seat of claim 1, wherein at least one said opening includes a sub-insert of at least one of: a material softer than the resilient outer layer, a super-light density foam, a gel-like material, a sealed gel packet, a sealed air packet, and a sealed air packet with adjustable pressure.

7. A seat, comprising: an insert embedded in a resilient outer layer, which resilient outer layer forms a unitary one-piece layer surrounding said insert; wherein said insert comprises at least one of: a seat insert comprising a semi-rigid mat having at least one of rebound characteristics, and compression set characteristics, a seat insert including at least one of a perineal opening, and an ischium opening, a heatable insert, which heatable insert can be electrically activated to provide heat to said seat, a heatable insert, which heatable insert includes at least one of: a perineal opening, and an ischium opening, a heatable insert, which heatable insert with an adhesive surface by which it can be adhesively connected to said seat insert, a heatable insert, which heatable insert formed using a material that repels a reacting liquid used to form the resilient outer layer, a perineal insert comprising a material softer than the resilient outer layer, and an ischium insert comprising a material softer than the resilient outer layer; wherein said seat has an upper surface and a lower surface, and any said insert is at least one of; substantially parallel to said upper surface, and intermediate said upper and lower surfaces; and wherein any said insert is completely encapsulated by said resilient outer layer.

8. The seat of claim 7, wherein at least one of: said seat insert is comprised of closed cell foam, said heatable insert underlies said seat insert, said perineal insert is comprised of a gel-like material, said perineal insert is comprised of sealed gel packets, said perineal insert is comprised of sealed air packets, said perineal insert is comprised of sealed air packets with adjustable pressure, said perineal insert is comprised of super light density foam, said ischium insert is comprised of a gel-like material, said ischium insert is comprised of sealed gel packets, said ischium insert is comprised of sealed air packets, said ischium insert is comprised of sealed air packets with adjustable pressure, and said ischium insert is comprised of super light density foam. and said resilient outer layer is comprised of reaction injection moldable foam.

9. The seat of claim 7, wherein any said seat insert is comprised of vinyl nitrite closed cell foam, and any said resilient outer layer is comprised of polyurethane foam.

10. The seat of claim 7. wherein an opening includes flex tabs.

11. The seat of claim 7, wherein at least one said opening includes a sub-insert of at least one of: a material softer than the resilient outer layer, a super-light density foam, a gel-like material, a sealed gel packet, a sealed air packet, and a sealed air packet with adjustable pressure.

12. A method for molding a seat, comprising: providing a seat mold defining the shape of a seat having upper and lower surfaces; positioning at least one insert in said mold so as to be intermediate said upper and lower surfaces when said mold is closed; injecting a reacting expanding liquid into said mold in a single injection such that said liquid will expand to till said mold, forming a resilient outer layer surrounding said at least one insert, which resilient outer layer forms a unitary one-piece layer surrounding said insert; and wherein said at least one insert at least one of: has a different density than the resilient outer layer, is softer or harder than the resilient outer layer, has greater or lesser stiffness than the resilient outer layer, has greater ability to conform to the user's body than the resilient outer layer, is more springy than the resilient outer layer, and is a heatable insert.

13. The method of claim 12, wherein said at least one insert comprises at least one of a seat insert comprising a semi-rigid mat having at least one of rebound characteristics, and compression set characteristics, a seat insert including at least one of: a perineal opening, and an ischium opening, a heatable insert, which heatable insert can be electrically activated to provide heat to said seat, a heatable insert, which heatable insert includes at least one of: a perineal opening, and an ischium opening, a heatable insert, which heatable insert with an adhesive surface by which it can be adhesively connected to said seat insert, a heatable insert, which heatable insert is formed using a material that repels the reacting liquid used to form the resilient outer layer, a perineal insert comprising a material softer than the resilient outer layer. and an ischium insert comprising a material softer than the resilient outer layer,

14. The method of claim 13. wherein at least one of: said seat insert is comprised of closed cell foam, said heatable insert underlies said seat insert, said perineal insert is comprised of a gel-like material, said perineal insert is comprised of sealed gel packets, said perineal insert is comprised of sealed air packets, said perineal insert is comprised of sealed air packets with adjustable pressure, said perineal insert is comprised of super light density foam, said ischium insert is comprised of a gel-like material, said ischium insert is comprised of sealed gel packets. said ischium insert is comprised of sealed air packets, said ischium insert is comprised of sealed air packets with adjustable pressure, said ischium se is comprised of super light density foam, said resilient outer layer is comprised of reaction injection moldable foam, and an elastic band is stretched around said pegs over said insert.

15. The method of claim 13, wherein any said insert is completely encapsulated by said resilient outer layer, any said seat insert is comprised of vinyl nitrite closed cell foam, and said resilient outer layer is comprised of polyurethane foam.

16. The method of claim 13, wherein said seat has an upper surface and a lower surface, and any said insert is at least one of: substantially parallel to said upper surface, and intermediate said upper and lower surfaces.

17. The method of claim 13, wherein an opening includes flex tabs.

18. The method of claim 13, wherein at least one said opening includes a sub-insert of at least one of: a material softer than the resilient outer layer, a super-light density foam, a gel-like material. a sealed gel packet, a sealed air packet, and a sealed air packet with adjustable pressure.

19. The method of claim 13 wherein openings in said seat insert aid said reacting expanding liquid in expanding through and around said seat insert so as to fill said mold.

20. The method of claim 19, wherein at least one of said perineal opening and said ischium openings aids said reacting expanding liquid in expanding through and around said insert so as to fill said mold.

21. The method of claim 13, wherein pegs extending from one of said surfaces support said at least one insert in said mold so as to be intermediate said upper and lower surfaces when said mold is closed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 provides a schematic perspective view of a mold and dispenser for forming an exemplary polyurethane seat in accordance with the teachings of prior art.

[0015] FIG. 2 provides a schematic perspective view of a preferred embodiment of a seat insert in accordance with the teachings of my invention.

[0016] FIG. 3 provides a schematic perspective view of the preferred embodiment of a seat insert illustrated in FIG. 2, wherein the perineal gap therein is filled with an insert which may be comprise, e.g., gel-like materials, gel packets, air packets (which may be made adjustable in terms of pressure), and soft foams or other similar filler(s),

[0017] FIG. 4 provides a schematic perspective view of the mold and dispenser of FIG. 1 as adapted for placement and support of a seat insert therein by inclusion of appropriately spaced and configured support pegs in accordance with the teachings of my invention.

[0018] FIG. 5 provides a schematic perspective view of the mold and dispenser including appropriately spaced and configured support pegs as illustrated in FIG. 4 with the seat insert appropriately mounted thereon in accordance with the teachings of my invention.

[0019] FIG. 6 provides another schematic perspective view of the mold and dispenser including appropriately spaced and configured support pegs as illustrated in FIG. 4 with the seat insert appropriately mounted thereon in accordance with the teachings of my invention.

[0020] FIG. 7 provides a schematic perspective view of the mold and dispenser including appropriately spaced and configured support pegs as illustrated in FIG. 4 with another preferred seat insert embodiment appropriately mounted thereon in accordance with the teachings of my invention.

[0021] FIG. 8 provides a schematic cross-sectional perspective view of an exemplary motorcycle seat with integral seat insert of the types previously illustrated included therein. all formed in accordance with the teachings of my invention.

[0022] FIG. 9 provides a schematic perspective view of the mold and dispenser including appropriately spaced and configured support pegs for and with a perineal insert appropriately mounted thereon in accordance with the teachings of my invention.

[0023] FIG. 10 provides a schematic cross-sectional perspective view of an exemplary motorcycle seat with integral perineal insert formed in accordance with the teachings of my invention.

[0024] FIG. 11 provides a schematic perspective view of an exemplary heating element pad/insert in accordance with the teachings of my invention.

[0025] FIG. 12 provides a schematic perspective view of the mold and dispenser including appropriately spaced and configured support pegs with seat insert and heating element pad/insert appropriately mounted thereon in accordance with the teachings of my invention.

[0026] FIG. 13 provides a schematic perspective view of the mold and dispenser including appropriately spaced and configured support pegs with seat insert and heating element pad/insert appropriately mounted thereon in accordance with the teachings of my invention, wherein said inserts have appropriately spaced and configured perineum and ischium openings.

[0027] FIG. 14 provides a schematic perspective view of another version of the initial preferred embodiment of a seat insert in accordance with the teachings of my invention, but having both perineal and ischium openings which are filled with gel-like materials, gel packets, air packets (which may be made adjustable in terms of pressure). and soft foams or other similar filler(s).

[0028] FIG. 15 provides a schematic cross-sectional perspective view of an exemplary motorcycle seat with inserts as illustrated in FIG. 14, all formed in accordance with the teachings of my invention.

[0029] FIG. 16 provides a schematic perspective view of a mold and dispenser including appropriately spaced and configured support pegs for and with a perineal insert and ischium inserts, all appropriately mounted thereon in accordance with the teachings of my invention.

[0030] FIG. 17 provides a schematic cross-sectional perspective view of an exemplary motorcycle seat with inserts as illustrated in FIG. 16, all formed in accordance with the teachings of my invention.

DESCRIPTION

[0031] The process, construction and apparatus used in the instant invention can best be understood by careful and ordered review of the above-referenced drawing figures, beginning with FIG. 1, which illustrates a mold 1 having an upper mold part 1A and a lower mold part 1B, defining a hollow mold space 1C (in the desired shape of a motorcycle seat in this case) when closed together. (The motorcycle seat shown in the drawing figures provides an example of how the teachings of the invention can be applied in this context, but should not be seen as limiting the scope of the inventive concept to this particular type of seating). As illustrated, and in accordance with the prior discussion of the reaction injection molding process, a dispensing unit 2 is used to combine and dispense the reacting liquid 30 into the mold 1 used in forming the finished piece, a polyurethane motorcycle seat (not illustrated), in accordance with the teachings of prior art. Once an appropriate amount of liquid 30 is dispensed into mold space 1C, the mold is closed, and the reacting liquid 30 expands to fully till the mold space 1C, taking the desired form/shape of a motorcycle seat as defined by the shape of mold space 1C.

[0032] With the background previously provided, especially in regard to FIG. 1, the teachings and novelty of FIGS. 2 and 3 can be better appreciated. These drawing figures illustrate an initial preferred embodiment of a seat insert 10 in accordance with the teachings of my invention. As will be noted, both versions illustrated feature foam dispersion and distribution openings/vents 11 scattered across their surfaces, mounting peg openings 12, and a perineal opening 13, with the version of the first embodiment illustrated in FIG. 3 varying from that in FIG. 2 by virtue of the inclusion of a sub-insert/perineal insert 14 in perineal opening 13 which may be comprised of gel-like materials, gel packets air packets, and soft foams or other similar filler(s), such as super-light density foam. (Where an air packet forms an insert or pad such as perineal insert 14, its pressure may be adjusted by means known in the art by the inclusion of a tube (not shown) leading from the packet to an activatable pump (not shown) or release valve (not shown) which can be used to adjust the pressure/firmness of the insert). Another embodiment is illustrated in FIG. 7, where perineal opening 13 forms a gap completely separating the two halves of seat insert 10. However, possible embodiments are not restricted to those including seat inserts 10. An embodiments using only a perineal insert 14 is illustrated in FIGS. 9 and 10, while a still further variation, using only perineal inserts 14 and ischium inserts 15 is illustrated in FIGS. 16 and 17.

[0033] In the embodiments having larger inserts 10, it is sometimes advantageous to include openings 11 so that reacting liquid 30 can freely move through and around the seat inserts 10 so that there are no unfilled gaps left in the molded seat 20. These holes/openings 11 may be of varying size, frequency of distribution or not included at all, depending on the flow characteristics and/or requirements of each particular mold/insert/seat. Thus, they are not shown in all illustrations, particularly those where open perineal openings 13 and/or ischium openings 19 provide alternate means of distribution which have been found sufficient by themselves for the aforesaid purpose without the inclusion of openings 11. However, the primary purpose of perineal openings 13 and/or ischium openings 19 is to create, include and incorporate a softer area or cushion below the perineum and/or ischiums of the person seated on seat 20.

[0034] Perineum/perineal openings 13 are provided as the perineum is more sensitive than surrounding areas for many people. By leaving the perineal opening 13 unfilled (as illustrated in FIG. 2), this area will be filled with the somewhat softer polyurethane foam making up the remainder of seat 20. Alternately, as illustrated in FIGS. 3, 9 and 10, a sub-insert/perineal insert 14which may be comprised of gel-like materials gel packets, air packets (which may be made adjustable in terms of pressure), and soft foams or other similar filler(s), such as super-light density foamprovides an even softer substrate for this same purpose. Thus, in the version of seat insert 10 illustrated in FIG. 2 (and FIG. 7) openings 11 will generally be found to be unnecessary, but in the version of insert 10 illustrated in FIG. 3, they will serve a valuable purpose in allowing the complete and even spreading of reacting liquid 30 so that no gaps remain.

[0035] As will be appreciated from the drawing figures (and in accordance with their anatomical purpose of underlying the perineal regions of a user), perineal opening 13 and perineal inserts 14 are preferably elongate, which shape defines a long axis that will be aligned with the bilateral axis of the user when seated on seat 20, and serve to separate seat 20 and/or mat/insert 10 into two halves, each of which would support, anatomically, respective buttocks/thighs of the user.

[0036] Insert 10 is preferably formed from closed cell foam with characteristics important to the purposes of my invention, though other materials having similar characteristics or other chosen characteristics can be used for this purpose. One such characteristic is Compression Set, a property that describes the fact that a permanent foam setting or deformation is achieved when a load is place on the seat insert 10 over a period of time. In the instant application this is advantageous because it allows the insert to form itself to the contours of the user's body over a period of time, adapting itself to the particular shape and configuration of the user for added user comfort. Vinyl nitrile foam has been found ideal for these purposes. Another important property of any such insert 10 is rebound (or spring-like performance), which is a property of vinyl nitrite foam by virtue of its closed cell construction. The inclusion and incorporation of insert 10 in molded seat 20 results in a final molded foam composite (seat 20) that is enhanced with these added properties derived from insert 10. However, as previously mentioned. other materials may be useful for this purpose, particularly other closed cell foam materials.

[0037] Review of FIGS. 4 through 6 provide insight into the manner in which, and apparatus used, to adapt the mold 1 of FIG. 1 for placement and support of a seat insert 10 therein in a position intermediate upper mold half 1A and lower mold half 1B. In this position it will be completely enveloped and surrounded by polyurethane foam as part of the reaction injection molding process previously described and thereby completely encapsulated in, enveloped by, and embedded in, the seat 20 formed thereby. (See, e.g., FIG. 8). This is accomplished by the inclusion of appropriately spaced and configured support pegs 3 in mold space 1C, preferably via mounting/attachment of said pegs 3 to lower mold part 1B as illustrated in FIG. 4.

[0038] As will be noted, pegs 3 can be advantageously formed with a base portion 3A (adapted for insertion in a registering opening provided in mold base portion 3A), support portion 3B (which holds the insert 10 in place within the mold 1 in spaced relationship to the upper mold portion 1A and lower mold portion 1B when the mold 1 is closed), a ledge portion 3C (with a substantially conical shape providing direct support of the insert 10 from below while allowing the seat 20 to be withdrawndue to its sloped portionfrom the mold 1 when it is formed), a barrel section 3D (dimensioned in terms of diameter and length to fit the width of mounting peg openings 12 and the thickness of insert 10), and a substantially conical head 3E (adapted to push through the somewhat flexible material of insert 10 while holding the insert 10 in place from above). Thus, insert 10 can be pressed onto the pegs 2 in mold 1 (as illustrated in FIGS. 5 and 6) so as to be positioned adjacent barrel section 3D so as to be held firmly in place between ledge portion 3C and head 3E through the molding process, and both insert 10 and seat 20 can be freed from pegs 3 and pulled out of mold 1 easily de-molded), when the molding process is complete.

[0039] However, as a practical matter, it has also been found that the addition of a flexible elastic band 31 (typically in the form of a fairly large circular rubber band) can assist and facilitate the molding process and that the pegs 3 of the invention are ideally shaped and structured for this purpose. The need for such facilitation arises from the fact that the reacting liquid 30 can churn and grow inside the mold in such a manner that it generates enough force to occasionally dislodge element(s) placed on pegs 3 (e.g., heatable insert 16 and/or seat insert 10) and cause it/them to float off of pegs 3 despite the pegs enlarged head 3E. This can be remedied by stretching an elastic band 31 around pegs 3 intermediate inserts 10, 16 and peg heads 3E as illustrated in FIG. 5. The elastic band 31, being flexible, does not have any adverse effect as an artifact left over in the finished seat 20. In addition, it is advisable to add small bumps ( in high) to the surface of the mold in select areas under inserts 10, 16 to keep them from sagging between the pegs 3. (Two to four of these are sufficient). Particularly with this modification, the seats 20 are consistently formed with inserts 10, 16 suspended exactly inch beneath the foam seating surface. When removed, as illustrated in FIG. 8, the seat 20 of the invention will feature a completely embedded and encapsulated insert 10 having the features previously described. Similarly, FIGS. 9 and 10 illustrate the aforesaid teachings and techniques as applied to a perineal insert 14, when used without a seat insert 10.

[0040] FIGS. 11 through 13 provide further insights into the possibilities of my invention. In this case, illustrating the potential for including a heatable seat insert 16 as well as the previously mentioned ischium openings 19 in seat insert 10 and heatable insert 16. The heatable insert 16 can be made from materials suitable for embedding a heating element/wire 17, and can advantageously be electrically activated by leads 18 connected via a switch to a source of electrical power in accordance with techniques known in the electrical and mechanical arts. The heatable insert 16 is best placed under the seat insert 10 (as illustrated in FIGS. 12 and 13), which assists in buffering, spreading and diffusing the heat produced by the heatable insert 16.

[0041] A problem to be dealt with in this context is that the heatable insert 16 may become too rigid when traditional heating pad technology is used. Such heating pads utilize cloth carrier sheets to form the body of the heating pad sandwiching the resistive wire (which in this case would be analogous to, respectively, heatable insert 16 and wires 17). However, the reacting/pressurized liquid 30 forms foam that saturates/plugs such cloth heating pad carrier sheets, creating a very rigid end product that sticks to the material of seat 20, which is counterproductive to comfortable seating. Consequently, in the invention it has been found beneficial to form the heatable insert 16 from a substance that cannot be saturated in this manner. Thus, a preferred embodiment of the invention uses heatable inserts 16 formed using a material that repels reacting liquid 30 such as conformable PTFE, vinyl, or silicone carrier sheets with the right strength, conformability (flex), and temperature rating. By not bonding/sticking to the reacting foam while it is forming, the heatable insert 16 creates its own individual cell and is allowed to float independently inside this cell in the foam comprising seat 20, thus allowing movement (flexibility) within the final foam part. Another way to avoid the problems set forth above is to replace the carrier sheets discussed above in reference to heatable insert 16 with a conformable adhesive film and weaving/placing wires 17 onto the adhesive surface 32 of said film, which is oriented so as to face the foam insert 10 and then sticking the heatable insert 16 formed in this manner to the foam insert 10 before molding it in (s illustrated in FIG. 12). This has been found to provide superior comfort and ease of assembly, when heat is added to the overall assembly.

[0042] The ischium openings 19 illustrated for both seat insert 10 and heatable insert 16 in FIG. 13 are provided because the ischium bones are primary weight supporting skeletal features for the human body when seated, and adjustment of density and seat response under these bones can greatly increase the comfort of a seat to a user. Thus, the ischium openings 19 can be left open as illustrated in regard to seat insert 10 in FIG. 13, or can accommodate an appropriately sized ischium insert 15 having qualities generally in accordance with those previously discussed with regard to perineal inserts 14 in the perineal opening 13. (See, e.g. FIGS. 14 and 15).

[0043] Alternatively, particularly with regard to the heatable insert 16, the size of the seat ischium openings 19 can be left open, but minimized as illustrated in FIG. 13, to allow for less interruption in the density of heating element/wires 17, and also allow for the same heatable insert 16 to be used in other applications with full heat wire coverage when no ischium opening 19 is desired. This can be done by closing off most of the ischium opening 19 with tabs 19A that can flex and give under the weight of a user (alternatively, it could be said that the opening 19 is comprised of X shaped slots that create such tabs 19A).

PARTS AND FEATURES ILLUSTRATED IN DRAWING FIGURES

[0044] 1 Mold [0045] 1A upper mold part [0046] 1B lower mold part

[0047] 2 Dispenser

[0048] 3 Pegs [0049] 3A base portion [0050] 3B support portion [0051] 3C ledge portion [0052] 3D barrel section [0053] 3E conical head

[0054] 10 Seat Insert

[0055] 11 Insert openings

[0056] 12 Mounting peg openings

[0057] 13 Perineal opening

[0058] 14 Perineal insert

[0059] 15 Ischium insert

[0060] 16 Heatable insert

[0061] 17 Embedded heating elements/wires

[0062] 18 Lead wires for heating element

[0063] 19 Ischium opening [0064] 19A Ischium opening tabs

[0065] 20 Seat [0066] 20A upper surface of seat (molded by lower mold part 1B) [0067] 20B lower surface of seat (molded by upper mold part 1A)

[0068] 21 Openings left in seat 20 by part 3B

[0069] 30 Reacting liquid

[0070] 31 Elastic Band

[0071] 32 Adhesive Surface

[0072] In view of the foregoing, it should be clear that numerous chances and variations can be made without exceeding the scope of the inventive concept outlined. Thus, though the preferred embodiment is illustrated in the context of a motorcycle seat, the teachings of the invention are not necessarily restricted to such seats. Indeed, potential applications range from seats for all kinds of riders (horseback/motorcycle/ATV) to more mundane chairs and seats used in other applications. Further, though the preferred materials comprising the seat are specified, other materials with similar support and/or molding characteristics may certainly be substituted. In addition, though single layer mats/inserts are shown, the inventive concept does not preclude multiple mat/insert layers or further subdivision of the mat/insert in terms of its constituent materials than those shown. Accordingly, it is to be understood that the embodiment(s) of the invention herein described is/are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiment(s) is not intended to limit the scope of the claims, which will themselves recite those features regarded as essential to the invention