Cleaning apparatus

[0001] 1. Field of the Invention

[0002] The present invention relates to a cleaning apparatus that may be used in an image forming apparatus such as a copying machine or a printer or in a process cartridge that is detachably mountable in the image forming apparatus, and to a cleaning apparatus for cleaning an image bearing member such as a photosensitive member and a dielectric.

[0003] In this case, the image forming apparatus means an apparatus for forming an image on a recording medium by using, for example, an electrophotographic image forming process and includes, for example, an electrophotographic copying machine, an electrophotographic printer (for example, a laser beam printer and an LED printer), a facsimile machine and a word-processor and the like.

[0004] Also, the process cartridge is made into a cartridge by integrating at least one of charging means, developing mean, and cleaning means with an electrophotographic photosensitive member which is the image bearing member, and is detachably mountable in an image forming apparatus main body.

[0005] 2. Description of Related Art

[0006] Conventionally, in the image forming apparatus using the electrophotographic image forming process, a process cartridge system has been adopted in which an electrophotographic photosensitive member and a processing means for acting on the photosensitive member are integrally made into a cartridge to be detachably mountable in an image forming apparatus main body. According to this process cartridge system, the user may perform the maintenance of the apparatus by himself or herself without depending on a service person so that the operationability may be considerably enhanced. Accordingly, the process cartridge system has been used extensively in the electrophotographic image forming apparatus.

[0007] By the way, in recent years, there has been a strong demand for a longer service life of the process cartridge and the image forming apparatus main body in conformity with a change of the commercial needs. Although it is necessary to increase an amount of toner contained in the cartridge, a size of a waste toner container must be also enlarged in proportion to the increase of the toner. For example, if the amount of toner is doubled, the size of the container must be doubled and the size of the waste toner container also must be doubled. Accordingly, the cleaning container has conventionally been formed by connecting two frames of a cleaning frame and a cleaning lid, thereby increasing the volume of the cleaning container.

[0008] FIG. 12 is a cross-sectional view of a conventional process cartridge and FIG. 13 is an exploded perspective view illustrating the process cartridge. In the process cartridge E shown in FIG. 12, a cleaning frame 113 of a cleaning means 110 supports a photosensitive drum 107 that is an electrophotographic photosensitive member and causes a cleaning blade 110a to abut against the photosensitive drum 107 to remove toner remaining on the photosensitive drum 107. A cleaning lid 114 that is a second cleaning frame is connected with a cleaning container 113a that is a first cleaning frame by ultrasonic welding or friction welding such as vibration welding to form the cleaning frame 113.

[0009] In the cleaning frame 113, a support member 110c supporting the cleaning blade 110a that is the cleaning member is fixed by screws to a mounting surface 113b provided on a cleaning container 113a to form a waste toner reservoir 110b. In the seal structure of the cleaning blade 110a and the cleaning container 113a, an elastic seal member 115 is arranged in a full length in the longitudinal direction on a seal seat surface 113c to which a mounting surface 113b arranged on both ends is connected in the longitudinal direction and a support member 110c is fixed thereon by screws to the mounting surface 113b, thereby eliminating the gap between the support member 110c and the cleaning container 113a to prevent the leakage of the toner from the waste toner reservoir 110b. At this time, the seal seat surface 113c is located lower than the mounting surface 113b by a thickness corresponding to the condition after the compression of the seal. Also, a welding portion 113d of the cleaning container 113a is connected with the seal seat surface 113c.

[0010] Also, FIG. 14 is a view of the cleaning frame 113a as viewed in a mounting direction of the cleaning lid 114. As shown in FIG. 14, an internal wall distance 113L2 of the waste toner reservoir 110b of the mounting surface 113b is longer than a distance 113L1 between the mounting surfaces 113b at both ends to thereby increase the volume of the waste toner reservoir 110b.

[0011] However, when the cleaning frame is constituted by friction-welding the cleaning container and the cleaning lid, the deformation of each member is generated upon welding. This is due to the rigidity of the container, the flatness of the welding surface, the welding condition of the welder (welding strength, welding time) or the like. It is impossible to completely suppress the deformation in view of discrepancies in two-piece resin products.

[0012] Then, in the above-described structure, there is a much deformation also in the cleaning frame and the cleaning lid upon welding. According to this deformation, the positional relationship with the photosensitive drum mounting portion of the cleaning blade positioning portion.

[0013] For this reason, after attaching the cleaning blade to the cleaning container, the positional measurement of the cleaning blade is performed in every step. Also, for the one displaced considerably from a regular position, the reattachment of the cleaning blade is performed.

[0014] An object of the present invention is to provide a cleaning apparatus for preventing the deformation of a cleaning frame.

[0015] Another object of the present invention is to provide a cleaning apparatus for enhancing a mechanical strength of the cleaning frame.

[0016] Still another object of the present invention is to provide a cleaning apparatus for enhancing a positional precision of the cleaning member.

[0017] Still another object of the present invention is to provide a cleaning apparatus for reducing the number of assembling steps for the cleaning apparatus.

[0018] Still another object of the present invention is to provide a cleaning apparatus for enhancing a toner containing amount of the cleaning apparatus.

[0019] Still other objects and features of the present invention will become apparent by reading the following detailed description with reference to the accompanying drawings.

[0020] FIG. 1 is an overview of a structure of an image forming apparatus according to an embodiment of the present invention.

[0021] FIG. 2 is a cross-sectional view illustrating a structure of a process cartridge.

[0022] FIG. 3 is a perspective view of the process cartridge.

[0023] FIG. 4 is a perspective view illustrating a second cleaning frame.

[0024] FIG. 5 is a perspective view illustrating a first cleaning frame.

[0025] FIG. 6 is an exploded perspective view showing the structure of the cleaning frame.

[0026] FIG. 7 is a view illustrating a structure of a process cartridge according to a second embodiment.

[0027] FIG. 8 is an exploded perspective view illustrating a structure of a cleaning frame according to the second embodiment.

[0028] FIG. 9 is a view illustrating a structure of the process cartridge according to the second embodiment.

[0029] FIG. 10 is a cross-sectional view illustrating of how toner enters a cleaning container.

[0030] FIG. 11 is a cross-sectional view illustrating how the toner accumulates in the cleaning container.

[0031] FIG. 12 is a cross-sectional view of a process cartridge according to a conventional example.

[0032] FIG. 13 is an exploded perspective view illustrating a structure of the conventional process cartridge.

[0033] FIG. 14 is a view illustrating a structure of the conventional process cartridge.

[0034] FIG. 15 is a cross-sectional view illustrating how toner enters a cleaning container that is different in structure from the second embodiment.

[0035] FIG. 16 is a cross-sectional view illustrating how the toner accumulates in the cleaning container that is different in structure from the second embodiment.

[0036] A process cartridge and an image forming apparatus according to a first embodiment to which a cleaning apparatus according to the present invention may be applied will now be described with reference to the accompanying drawings. FIG. 1 is an overall structural view of an image forming apparatus according to the embodiment, FIG. 2 is a cross-sectional view illustrating a structure of the process cartridge, FIG. 3 is a perspective view of the process cartridge, FIG. 4 is a perspective view illustrating a second cleaning frame, FIG. 5 is a perspective view illustrating a first frame and FIG. 6 is an exploded perspective view illustrating a structure of a cleaning frame.

[0037] In this embodiment, the image forming apparatus and the process cartridge B will now be described. The process cartridge B is used in the image forming apparatus. Incidentally, the lateral direction of the process cartridge B in the following description means a direction in which the process cartridge B is mounted to or detached from the image forming apparatus main body (hereinafter referred to as an apparatus main body A and corresponds with the transport direction of the recording medium. Also, the longitudinal direction of the process cartridge B means a direction that crosses (substantially in perpendicular to) a direction in which the process cartridge B is mounted to or detached from the apparatus main body A, and the longitudinal direction is parallel to the surface of the recording medium and crosses (substantially in perpendicular to) the transport direction of the recording medium. Also, the right and left hands relating to the process cartridge B mean the right and left hands of the recording medium as viewed from above in the transport direction of the recording medium. Also, the upper surface of the process cartridge B in the following description means a surface located upwardly under the condition that the process cartridge B is mounted in the apparatus main body A and the lower surface means a surface located downwardly in the same condition.

[0038] A laser beam printer will be first exemplified and explained as an electrophotographic image forming apparatus according to the embodiment with reference to FIG. 1. In the apparatus main body A of the laser beam printer, an image is formed on a recording medium 2 (for example, recording paper, OHP sheet, cloth or the like) by an electrophotographic image forming process. A toner image is then formed on a drum-shaped electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum 7) as an image bearing member. More specifically, the photosensitive drum 7 is charged by a charging roller 8, and subsequently, a laser beam L is projected in response to image information from optical means 1 to the photosensitive drum 7 to form thereon a latent image in conformity with the image information. Then, the latent image is developed by developing means 9 to form a toner image.

[0039] On the other hand, in synchronism with the formation of the toner image, the recording medium 2 set in a feed cassette 3a is inverted and transported by a pickup roller 3b, a transport guide 3c and a pair of registration rollers 3e. Subsequently, the toner image formed on the photosensitive drum 7 owned by the process cartridge B is transferred to the recording medium 2 by applying a voltage to the transfer roller 4 used as transfer means.

[0040] Thereafter, the recording medium 2 that is subjected to the transfer of the toner image is transported to fixing means 5 by a transport guide 3f. The fixing means 5 has a drive roller 5c and a fixing roller 5b incorporating a heater 5a. The toner image is transferred by the application of a heat and a pressure to the passing recording medium 2. Then, the recording medium 2 is transported by a pair of delivery rollers 3i to be delivered to a delivery tray 6.

[0041] The process cartridge B will now be described with reference to FIG. 2.

[0042] In the process cartridge B, the photosensitive drum 7 having a photoconductive layer 7e is rotated so that the surface of the photosensitive drum 7 is uniformly charged by the voltage application to the charging roller 8 that is the charging means. Subsequently, the laser beam in response to the image information from the optical means 1 is irradiated to the photosensitive drum 7 through an exposure opening portion 1e to form the latent image. Then, the latent image is developed by the developing means 9 by using the toner. More specifically, the charging roller 8 is provided in contact with the photosensitive drum 7 to thereby charge the photosensitive drum 7. Incidentally, the charging drum 8 is driven and rotated by the photosensitive drum 7. Also, the developing means 9 feeds the toner to the developing region of the photosensitive drum 7 and develops the latent image formed on the photosensitive drum 7.

[0043] The developing means 9 feeds the toner within a toner container 11a to the developing roller 9c by the rotation of a toner feed member 9b. Then, the developing roller 9c incorporating a stationary magnet is rotated, and at the same time a toner layer provided with a frictional electric charge is formed on a surface of the developing roller 9c by the developing blade 9d. The toner is fed to the developing region of the photosensitive drum 7. Then, the toner is moved to the photosensitive drum 7 in response to the latent image to thereby form the toner image to be visible.

[0044] A developing blade 9d is used to regulate the amount of toner on the circumferential surface of the developing roller 9c and to give the frictional electric charge to the toner. Also, a toner agitating member 9e for circulating the toner within a developing chamber 9f is rotatably mounted in the vicinity of the developing roller 9c.

[0045] Subsequently, a voltage having an opposite polarity to that of the toner image is applied to the transfer roller 4, and the toner image formed on the photosensitive drum 7 is transferred to the recording medium 2. Thereafter, the residual toner on the photosensitive drum 7 is removed by cleaning means 10. The cleaning means 10 scrapes off the toner remaining on the photosensitive drum 7 by an elastic cleaning blade that is a cleaning member provided in contact with the photosensitive drum 7 and to collect the toner in a waste toner reservoir 10b that is a waste toner collection portion.

[0046] A housing structure of the process cartridge B in accordance with the embodiment will now be described. The process cartridge B has a housing formed by combining a toner frame 11 having a toner container 11a for containing the toner (toner containing portion) and a developing frame 12 for holding the developing means 9 such as the developing roller 9c, and further combining therewith a cleaning frame 13, to which the photosensitive drum 7, the cleaning means 10 such as a cleaning blade 10a and the charging roller 8 are attached, with the cleaning frame 13 being rotatable with respect to the combination of the toner frame 11 and the developing frame 12. Incidentally, the detail of the structure of the cleaning frame 13 will be described later. Then, the process cartridge B is mounted detachably to the cartridge mounting means provided in the apparatus main body A.

[0047] The exposure opening portion 1e for irradiating the laser beam to the photosensitive drum 7 in response to the image information and a transfer opening portion 13n for causing the photosensitive drum 7 to be opposed to the recording medium 2 are provided in the process cartridge B. More specifically, the exposure opening portion 1e is provided on the cleaning frame 13 and the transfer opening portion 13n is defined between the developing frame 12 and the cleaning frame 13.

[0048] As shown in FIG. 2, the toner feed member 9b is rotatably attached to the toner frame 11. Also, the developing roller 9c and the developing blade 9d are attached to the developing frame 12 and furthermore an agitating member 9e is attached to the developing frame 12 to rotate in the vicinity of the developing roller 9c for circulating the toner within the developing chamber 9f. Also, an antenna rod 9h for detecting the amount of the toner is attached to the developing frame 12 opposite to the developing roller 9c and substantially in parallel with the developing roller 9c in the longitudinal direction. Then, the toner frame 11 and the developing frame 12 are welded (by ultrasonic welding in this embodiment) to form an integral developing unit D (see FIGS. 3 and 4).

[0049] Incidentally, a drum shutter member 18 for covering the photosensitive member 7 when the process cartridge B is removed away from the image forming apparatus main body A and for avoiding the exposure to the light for a long period of time and the contact with foreign matters is attached to the developing unit D. Also, a cleaning unit C (see FIGS. 3 and 5) as a first cleaning frame is constituted by attaching the photosensitive drum 7, the charging roller 8 and the cleaning means 10, respectively to the cleaning frame 13.

[0050] Then, the process cartridge B is constituted by connecting the developing unit D and the cleaning unit C by connecting members 22 that are round pins so that the developing unit D and the cleaning unit C are rotatable with respect to one another. Namely, as shown in FIG. 4, round pivot holes 20 in parallel with the developing roller 9c are provided in the distal ends of the arm portions 19 formed on both sides in the longitudinal direction (in the axial direction of the developing roller 9c) of the developing frame 12. On the other hand, as shown in FIG. 5, recess portions 21 are provided for introducing the arm portions 19 at two positions at both sides in the longitudinal direction of the cleaning frame 13. The arm portions 19 are inserted into the recess portions 21, the connecting members 22 are press-fitted into attaching holes 13e of the cleaning frame 13 and the connecting members 22 are fitted into the pivot holes 20 at the ends of the arm portions 19 to be press-fitted into the holes 13e further on the inside so that the developing unit D and the cleaning unit C may be connected to be rotatable about the connecting members 22. At this time, compression coil springs 22a mounted and inserted into dowels (not shown) implanted in the proximal ends of the arm portions 19 are brought into contact with the upper surfaces of the recess portions 21 of the cleaning frame 13 and the developing frame 12 is biased downwardly by the compression coil springs 22a to thereby depress the developing roller 9c to the photosensitive drum 7 surely.

[0051] The first embodiment of a process cartridge and an image forming apparatus will next be described. FIG. 2 is a cross-sectional view of the process cartridge in accordance with the embodiment. FIG. 6 is exploded perspective view illustrating the structure of the cleaning frame.

[0052] In the cleaning frame 13 of this embodiment, after the support member 10c for supporting the cleaning blade 10a that is the cleaning member is fixed by screws to the attaching portion 13b, the two frames of the cleaning container (first cleaning frame) 13a and the cleaning lid (second cleaning member) 14 are connected together by vibration welding to be made into a single frame and the waste toner reservoir 10b that is the toner receiving portion is formed. At this time, an elastic seal member 15 is provided between the cleaning lid 14 and the support member 10c. When the cleaning container 13a and the cleaning lid 14 are connected together, the elastic seal member 15 is compressed between the upper surface 10d of the support member and the cleaning lid 14. The container 13a is provided with a first opening portion opposed to the photosensitive member 7 and a second opening portion on the top side of the container 13a. The cleaning blade 10a covers a part of the first opening portion and the lid member 14 covers the second opening portion.

[0053] Also, the elastic seal member 15 attached to the support member 10c is arranged at both end portions in the longitudinal direction, i.e., so as to enter onto surfaces different from the surface opposed to the cleaning lid 14 and covers a support member side surface 10e. Then, at each position 15e for covering the support member side surface 10e, the elastic seal member 15 is compressed with an inner wall 13c of the cleaning container 13a to thereby prevent the toner from leaking out of the waste toner reservoir 10b.

[0054] At this time, the elastic seal member 15 made of sponge material is attached to the support member 10c by an adhesive double-coated tape. However, it is possible to inject foamed elastomer, rubber or the like into the position of the elastic seal member 15.

[0055] Also, a beam 13f is provided as a connecting member for connecting both side surfaces in the longitudinal direction of the cleaning container 13a on the side (deep side) of the waste toner reservoir 10b of the cleaning blade 10a of the cleaning container 13a and in the vicinity of the welded portion of the cleaning lid 14. The beam 13f is provided in the lower portion below the uppermost portion of the waste toner reservoir 10b as the toner receiving portion, i.e., below the upper surface portion of the lid member 14 in the posture that the cleaning apparatus perform cleaning of the toner by the cleaning blade 10a. Thus, the beam 13f is provided whereby the rigidity of the peripheral portion of the welding portion with the cleaning lid 14 of the cleaning container 13a is enhanced. As a result, when the cleaning container 13a and the cleaning lid 14 are welded and connected, the cleaning lid 14 follows the shape of the cleaning container 13a that has high rigidity. Accordingly, the deformation upon the welding of the cleaning container 13a may be suppressed as much as possible. Accordingly, since the deformation due to the welding of the cleaning blade attaching portion 13b is also suppressed, it is possible to keep the positional relationship between the cleaning blade 10a and the photosensitive drum 7 with high accuracy.

[0056] Then, as described above, in the structure, the support member 10c of the cleaning blade 10a is fixed by screws to the mounting portion 13b in the cleaning container 13a prior to welding and connecting the cleaning container 13a and the cleaning lid 14. For this reason, the rigidity of the cleaning container 13a is further enhanced and it is possible to keep the positional relationship between the cleaning blade 10a and the photosensitive drum 7 with high accuracy.

[0057] Thus, in the process cartridge B with the structure according to the embodiment, since the positional relationship between the cleaning blade 10a and the photosensitive drum 7 may be kept with high accuracy, the step for measuring and confirming the positional relationship between the cleaning blade 10a and the photosensitive drum 7 may be dispensed with or may be performed only in a sampling manner (not for all inspection) to reduce the number of the steps. Also, since, of course, there is no remarkable positional displacement in the positional relationship between the cleaning blade 10a and the photosensitive drum 7, the correction work therefor is not necessary.

[0058] A second embodiment of a process cartridge and an image forming apparatus to which the cleaning apparatus according to the present invention may be applied will now be described. FIG. 7 is a cross-sectional view of a structure of the process cartridge in accordance with the embodiment. FIGS. 8 and 9 are exploded perspective views illustrating a structure of the cleaning frame. The same reference numerals are used to indicate the same components as the parts and members of the first embodiment and explanation therefor that duplicates the explanation of the first embodiment will be omitted.

[0059] In the cleaning frame 13 in accordance with this embodiment, after the support member 10c of the cleaning blade 10a is fixed by screws to the attaching portion 13b, the two frames of the cleaning container 13a and the cleaning lid 14 are connected into one frame to form the waste toner reservoir 10b. In this case, a rib 14c opposed to the supporting member 10c is provided closer to the photosensitive drum 7 than the support member 10c. When the cleaning container 13a and the cleaning lid 14 are connected together, the elastic seal member 15 is compressed by the support member 10c and the rib 14c.

[0060] Also, the elastic seal member 15 attached to the support member 10c is arranged at both end portions in the longitudinal direction, i.e., so as to enter onto surfaces different from the surface opposed to the rib 14c and covers the support member side surface 10e and the support member upper surface 10d. Then, the elastic seal member 15 is compressed in the positions 15e covering the side surfaces 10e of the support member 10c by the inner wall 13c of the cleaning container 13a and in a position 15d covering the upper surface 10d of the support member 10c by the cleaning lid 14 to thereby prevent the toner from leaking out of the waste toner reservoir 10b.

[0061] At this time, the elastic seal member 15 made of sponge material is attached to the support member 10c by the adhesive double-coated tape. However, it is possible to inject foamed elastomer, rubber or the like into the position of the elastic seal member 15.

[0062] Also, the beam 13f is provided as the connecting member for connecting both side surfaces in the longitudinal direction of the cleaning container 13a on the side (deep side) of the waste toner reservoir 10b of the cleaning blade 10a of the cleaning container 13a and in the vicinity of the welded portion of the cleaning lid 14.

[0063] In this case, as shown in FIG. 10, the beam 13f is located above the extension plane of the support member lower surface 10f of the cleaning blade 10a in a posture that the cleaning apparatus cleans off the toner by the cleaning blade 10a. Also, the beam 13f is provided below the uppermost surface of the waste toner reservoir 10b that is the toner receiving portion, i.e., below the upper surface portion of the lid member 14 in the posture that the cleaning apparatus cleans off the toner by the cleaning blade 10a. Incidentally, the support member upper surface 10d is an upper surface of a bent portion where the support member 10c is bent on the deeper side of the container 13a and the support member lower surface 10f is a lower surface of the bent portion where the support member 10c is bent on the deeper side of the container 13a.

[0064] As a result, as described in conjunction with the above-described first embodiment, when the cleaning container 13a and the cleaning lid 14 are welded and connected, the cleaning lid 14 follows the shape of the cleaning container 13a that has high rigidity. Accordingly, the deformation upon the welding of the cleaning container 13a may be suppressed as much as possible. Accordingly, since the deformation due to the welding of the cleaning blade attaching portion 13b is also suppressed, it is possible to keep the positional relationship between the cleaning blade 10a and the photosensitive drum 7 with high accuracy.

[0065] Also, as shown in FIG. 10, the toner scraped off by the cleaning blade 10a enters the waste toner reservoir 10b substantially in the tangential direction (in the direction indicated by the arrow O) at the cross point of the photosensitive drum 7 with the cleaning blade 10a. The toner splashed substantially in the tangential direction of the photosensitive drum 7 accumulates on the surface that the toner contacts first, i.e., on the lower side from the extension plane of the support member lower surface 10f accumulates in the deeper side (in the left hand in the drawing) of the waste toner reservoir. Accordingly, as shown in FIG. 11, the toner is resided within the waste toner reservoir 10b in the order of E, F and G.

[0066] Inversely, it is possible to locate the beam 13f below the extension plane of the support member lower surface 10f of the cleaning blade 10a unlike the second embodiment. In this case, the toner scraped by the cleaning blade 10a enters the waste toner reservoir 10b in a direction indicated by the arrow P shown in FIG. 15. As shown in FIG. 15, the toner splashed substantially in the tangential direction of the photosensitive drum 7 accumulates on the lower side of the extension plane of the lower surface of the beam 13f and on the deeper side (in the left hand in the drawing) of the waste toner reservoir. Accordingly, the toner accumulates within the waste toner reservoir 10b in the order of I, J and K as indicated in FIG. 16. As a result, since the volume of the waste toner reservoir 10b could not effectively be used, the cleaning container is enlarged.

[0067] As described above, it is preferable that the beam 13f is located above the extension plane of the support member lower surface 10f of the cleaning blade 10a to thereby effectively fill the waste toner into the waste toner reservoir 10b, which leads to the miniaturization of the cleaning container.

[0068] As described above, in the cleaning apparatus, the beam for connecting both side surfaces in the longitudinal direction of the cleaning container in the vicinity of the welding portion with the cleaning lid is provided in the cleaning container for holding the cleaning blade, whereby the rigidity of the periphery of the welding portion of the cleaning container is enhanced. When the cleaning container and the cleaning lid are welded and connected together, the cleaning lid follows the shape of the cleaning container having high rigidity. Accordingly, the deformation upon the welding operation of the cleaning container may be reduced as much as possible. Accordingly, since the deformation due to the welding operation of the cleaning blade mounting portion may also be suppressed, it is possible to keep the positional relation between the cleaning blade and the photosensitive drum with high accuracy. For this reason, the step for measuring and confirming the relationship between the cleaning blade and the photosensitive drum may be dispensed with or the sampling inspection (not for all the steps) to thereby reduce the number of the steps. Also, there is no remarkable positional displacement of the cleaning blade and the photosensitive drum and there are no needs to correct this.

[0069] Also, the beam is located above the support member lower surface of the cleaning blade so that the toner may be filled in the waste toner reservoir at a high efficiency to thereby make it possible to make the cleaning apparatus small in size.

[0070] The present invention is not limited to the above-described embodiments and various modifications and changes are possible within the scope of the spirit of the present invention.