PLATE HEATER FOR A MANIFOLD OF AN INJECTION MOLDING APPARATUS

FIELD OF THE INVENTION

The present invention relates generally to an injection molding apparatus and, in particular to a plate heater for a manifold.

BACKGROUND OF THE INVENTION

As is well known in the art, a typical multi-cavity hot runner injection molding system includes a heated manifold for conveying a pressurized melt stream from an inlet to a plurality of outlets. A heated nozzle communicates with each outlet to deliver the melt to a respective mold cavity through a mold gate. Manifolds have various configurations depending on the number and arrangement of the mold cavities. Different heating arrangements are known for heating manifolds. A common arrangement is an electrical heating element that is received in a groove in a manifold outer surface, as described in U.S. Patent No. 4,688,622 to Gellert, which issued August 25, 1987. Other arrangements include cartridge heaters that are cast into the manifold as described in U.S. Patent No. 4,439,915 to Gellert, which issued April 3, 1984, and plate heaters with cast- in heaters that are secured along the surface of the manifold, as described in U.S. Patent No. 5,007,821 to Schmidt, which issued April 16, 1991. Manufacture and assembly of each of these heating arrangements requires machining of the manifold, the heater or both, which can be both costly and time consuming.

For certain large molded parts that require melt delivered from large heated manifolds, the melt stream is heated by either multiple smaller heater plates attached to the manifold or heater elements pressed within grooves machined into the manifold surface. Each of these solutions has its benefits and limitations.

Heater plates provide more consistent heat distribution than a heater element in contact with the manifold surface. Further, heater plates may include more than one heater element allowing for redundancy. However, heater plates are typically made by investment casting methods, which does not accommodate the manufacture of larger plates due to warpage and bending that occurs as the plates get longer. Therefore, multiple shorter plates, i.e., plates typically less than 170 mm, are utilized for larger manifold applications, which require more control zones to operate. Further, heater elements of current heater plates are cast within the heater plate and cannot be replaced once they fail, so that the entire heater plate must be replaced upon failure of the heater elements therein.

Alternatively, heater elements that are pressed-in machined grooves on the surface of a manifold may be removed for replacement, although machining such grooves is time consuming and expensive. In addition, redundancy is provided for by machining a corresponding groove in an opposing surface of the manifold and pressing a secondary heater element into the second groove, adding to the time and cost associated with this production method. Accordingly, what is needed is a manifold heater arrangement that provides the improved heat distribution and redundancy of a heater plate and provides for replacement of failed heater elements and fewer control zones. In addition, a heater plate that may be efficiently constructed, particularly at longer sizes, is desired.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention there is provided an injection molding apparatus including a heated manifold with a melt channel for transferring molten material from an injection molding machine to one or more hot runner nozzles which in turn inject the molten material to one of more cooled mold cavities to form a plastic part. One

or more heaters are connected to the manifold in a configuration to provide heat to maintain the temperature of the molten material throughout the entire length of the melt channels in the manifold. The plate heater includes a heater plate body and at least two heating elements. A surface of the heater plate body has at least two channels therein and each heating element is received within a respective channel. At least one end cap is provided for commonly fixing terminal ends of at least two of the heating elements relative to the heater plate body.

Another embodiment of the present invention includes a method of manufacturing a plate heater for a hot runner manifold. The method includes providing an extruded bar like blank having at least two straight longitudinal grooves therein; planing a flat contact face of the blank; machining the grooves to fine forming straight longitudinal channels in the blank to gain a heater plate body; inserting longitudinal heating elements into the longitudinal channels in the heater plate body.

Further advantageous embodiments are defined in the dependent claims.

BRIEF DESCRIPTION OF THE FIGURES Embodiments of the present invention will now be described more fully with reference to the accompanying drawings in which like reference numerals indicate similar structure. The drawings are not to scale.

Figure 1 is a side sectional view of an injection molding apparatus according to an embodiment of the present invention. Figure 2 is an isometric view of a portion of the injection molding apparatus of Figure 1.

Figure 3 is a top view of a plate heater of the injection molding apparatus of Figure 2.

Figure 4 is an isometric view of the heater of Figure 3.

Figure 5 is a cross-section along line 5-5 of the heater plate of Figure 3 with the heating elements removed.

Figure 5A is a profile of an extruder die used to produce the cross- section of the heater plate body shown in Figure 5. Figure 6 is an isometric view of an injection molding apparatus according to another embodiment of the present invention.

Figure 7 is an isometric view of a plate heater according to another embodiment of the present invention.

Figure 8 is an isometric view of a plate heater according to another embodiment of the present invention.

Figure 9 is an isometric view of a portion of the plate heater shown in Figure 8.

Figure 10 is a cross-section along line 10-10 of the heater plate body of Figure 9 with the heating elements removed. Figure 1OA is a profile of an extruder die used to produce the cross- section of the heater plate body shown in Figure 10.

Figure 11 is a top view of a plate heater according to another embodiment of the present invention.

Figure 12 is a cross-section along line 12-12 of the plate heater shown in Figure 11.

Figure 13 is a perspective view of a plate heater according to another embodiment of the present invention.

Figure 13A is an isometric view of a portion of the plate heater shown in Figure 13. Figure 13B is a cross-section along line 13-13 of a heater plate body in accordance with another embodiment of FIG. 13.

Figure 14 is a perspective view of a plate heater according to another embodiment of the present invention.

Figure 15 is a perspective view of the plate heater shown in Figure 14 with one end cap taken away.

Figure 16 is an enlarged view of the left end of the plate heater shown in Figure 15.

Figure 17 is an enlarged view of the left end of the plate heater shown in Figure 15 with the cap clamp removed.

Figure 18 is a view similar as in Figure 17 with the lower half of the end cap attached.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to Figure 1, an injection molding apparatus 10 is generally shown. Injection molding apparatus 10 includes a manifold 12 having a manifold melt channel 14. Manifold melt channel 14 extends from an inlet 16 to manifold outlets 18. Inlet 16 of manifold melt channel 14 receives a melt stream of moldable material from a machine nozzle (not shown) through a sprue bushing 20 and delivers the melt to hot runner nozzles 22, which are in fluid communication with respective manifold outlets 18. Although a pair of hot runner nozzles 22 is shown in Figure 1, it will be appreciated that a typical injection molding apparatus may include only one or a plurality of hot runner nozzles for receiving melt from respective manifold outlets.

Each hot runner nozzle 22 is received in an opening 32 in a mold plate 34. A collar 28 surrounds the nozzle 22. The collar 28 abuts a step 36, which is provided in opening 32 to maintain a nozzle head 26 of the hot runner nozzle 22 in abutment with an outlet surface 40 of manifold 12. A nozzle tip 30 is received in a downstream end of hot runner nozzle 22 and may be threaded thereto. A nozzle melt channel 24 extends through hot runner nozzle 22 and nozzle tip 30. Nozzle melt channel 24 is in communication with manifold outlet 18 to receive melt from manifold channel 14. Hot runner nozzle 22 is heated by a heater 54 and further includes a thermocouple 56.

A mold cavity 50 is provided between mold plate 34 and a mold core 52. Mold cavity 50 receives melt from nozzle melt channel 24 through a mold gate 48. Cooling channels 58 extend through mold plate 34 to cool mold cavity 50. Manifold 12 is maintained in position relative to mold plate 34 by a locating ring 46. Spacers 44 are provided between an inlet surface 38 of manifold 12 and a back plate 42. Referring also to Figure 2, manifold 12 is heated by heaters 60, which are coupled to the outlet surface 40 and side surfaces 62 of the manifold 12. As shown in Figures 3 - 5, each plate heater 60 includes a heater plate body 64 having flange portions 76 and base portions 78 that define a pair of channels 66 therebetween,. Each channel 66 extends within a respective side surface 69 of heater plate 64. Although heater plate body 64 is shown having a pair of channels 66, the heater plate body 64 may be adapted to alternatively include one channel 66 or a plurality of channels 66.

The heater plate body 64 is formed by an extrusion process, as described below, from a material that is more thermally conductive than the manifold 12, which is typically made from tool steel such as H13, P20 or SS420, for example. Suitable thermally conductive materials for heater plate body 64 include aluminum, aluminum alloys, copper and copper alloys, such as brass and bronze. Alternatively, another suitable material may be used.

Channels 66 of heater plate body 64 are shaped and sized to receive and secure heating elements (not shown) therein. As illustrated in

Figure 5, a cross-section of channel 66 may be described as key-shaped or bulb-shaped having a narrowed neck portion 71 and an enlarged cavity portion 67. In one embodiment, neck portion 71 is narrower than a heating element to be seated in cavity portion 67, wherein cavity portion 67 is sized to securely receive the heating element. Flange portions 76, which form the upper surface of channels 66, and base portions 78, which form the lower surface of channels 66, include heating element retaining

holes 74 for receiving fasteners (not shown) that force a mating surface 80 of flange portion 76 toward a surface 82 of base portion 78 to impart a clamping force on the heating element. The clamping force increases the amount of contact, and therefore heat transfer, between the heating element and the heater plate body 64.

The plate heater 60 further includes relief holes 68, which are located at regular intervals along the length of the heater plate body 64. The relief holes 68 are provided to receive mechanical items, including fasteners (not shown), for coupling the plate heater 60 to the manifold 12. A thermocouple aperture 70 extends through heater plate body 64 and receives a thermocouple (not shown). Connectors 72, which allow the heating elements to communicate with a power source (not shown), are coupled to the free ends of each of the heating elements. The heating elements may be powered independently, in parallel or in series. By powering the heating elements independently or in parallel, a fail-safe, redundant arrangement is provided in which one plate heater will continue to provide heat even if the other heating element fails. In an embodiment where independent control of each heating element is provided, an additional control zone and thermocouple are utilized. However in accordance with the present invention, regardless of how the plate heater is operated, the heating element(s) may be accessed for replacement simply by removing the fasteners from retaining holes 74 and exposing/removing the heating element from channel 66.

In operation, melt is injected from the machine nozzle into manifold channel 14 of manifold 12 through sprue bushing 20. Nozzle melt channels 24 of nozzles 22 receive melt from manifold outlets 18 and deliver the melt to mold cavities 50 through mold gates 48. Plate heaters

60 provide heat to the manifold 12 so that the melt flowing through the manifold channel 14 is maintained at a desired temperature. Once the mold cavities 50 have been filled with melt, the melt is cooled and the molded parts are ejected from injection molding apparatus 10.

Production of the heater plate body 64 will now be described. A billet of a selected material in a raw form is pushed through a die incorporating the profile shown in Figure 5A, to produce a heater plate having the cross-section shown in Figure 5. The die profile includes a linear portion 65', which corresponds to a contact surface 65 on the heater plate body 64, and at least one extended portion 66', which corresponds to channel 66 of the heater plate 64. The heater plate body 64 is manufactured using an extrusion process, which includes cold- working the initial extruded form. The cold-working of the extruded plate makes it harder and stiffer than its cast counterpart, allowing for improved performance with less warpage and bending. As such, a longer extruded heater plate body that is flatter and straighter than a plate produced by a casting process, for example, is achieved.

In one embodiment, a single extruded heater plate body may be later cut to produce a plurality of custom length heater plate bodies 64. Accordingly, following extrusion, heater plate body 64 is cut to a desired length, which is determined by the surface 40, 62 of the manifold 12 to which the plate heater 60 is to be coupled. Also following extrusion, contact surface 65 of the heater plate body 64 may be machined by a machining process such as milling or grinding, for example, in order to smooth out any imperfections resulting from the extrusion process. Machining of the contact surface 65 maximizes the amount of contact between the contact surface 65 and the surfaces 40, 62 of the manifold 12 and therefore optimizes heat transfer therebetween. Relief holes 68 and thermocouple holes 70 are also machined into the heater plate body 64. Following machining, the heating elements are positioned in the channels 66 and the fasteners are installed to clamp the heating elements in position. Once assembled, the plate heater 60 is coupled to the manifold 12 and the heating elements are linked to the power source. The heating elements are removable from the channel 66 by unscrewing the fasteners to release the clamping pressure on the heating elements. The manner in which the heating elements are secured allows

them to be replaced by an operator in the event that one or both of the heating elements needs to be repaired or replaced. As such, the entire plate heater 60 does not need to be scrapped and replaced when one or more heating elements fail, which provides a cost savings. The plate heater 60 further provides some flexibility in that channels 66 accommodate heating elements having different diameters. In applications where heating elements having smaller diameters are installed, it may be desirable to fill any gaps between the heating element and the channel 66 with a thermally conductive paste. The thermally conductive paste does not affect the removal of the heating elements 90 from the channels 66 and breaks away when the heating elements are removed.

Referring to Figure 6, an injection molding apparatus 10a includes a manifold 12a having a plate heater 60a, which is similar to plate heater 60 of Figures 1-5. The plate heater 60a is coupled to a front surface 84 of the manifold 12a. As shown, the plate heater 60a is the only primary source of heat for the manifold 12a. In another embodiment, the plate heater 60a may be provided in combination with additional plate heaters on the outlet and side surfaces 40a and 62a of the manifold 12a, as shown in Figure 1. The plate heater 60a may alternatively be provided in combination with a heater located on inlet surface 38a, adjacent to sprue bushing 20a. The plate heater 60a may also be paired with another manifold heating method known in the art, such as an embedded heating element, a cartridge heater or a film heater, for example. Operation of plate heater 60a is similar to operation of plate heater 60 of the previous embodiment and therefore will not be described further here.

Figure 7 shows another embodiment of a plate heater 60b for heating a manifold. Plate heater 60b is similar to the heaters 60, 60a of the previous embodiments; however, plate heater 60b includes a central aperture 86, which extends through plate heater 64b. The central aperture 86 is provided in order to allow a melt transporting, manifold supporting or manifold locating component to pass therethrough. The

type of component is determined by the location of the plate heater 60b on the manifold. For example, if the plate heater 60b is located on an inlet surface of the manifold, a sprue bushing may extend through the central aperture 86, whereas if the plate heater 60b is located on an outlet surface of the manifold, a nozzle may extend through the central aperture 86. Incorporating the central aperture 86 into the plate heater 60b increases the number of different locations at which the plate heater 60b may be coupled to the manifold.

Referring to Figures 8-10, another embodiment of a plate heater 60c for a manifold is shown. Plate heater 60c includes a heater plate body 64c having channels 66c provided in an upper surface 88 thereof. Heating elements 90 are fully received within channels 66c. Similar to channels 66 of the embodiment of Figure 5, channels 66c are key-shaped to include a narrowed portion 71c and an enlarged portion 67c, as shown in Figure 10. Accordingly, heating elements 90 sit below heater plate upper surface 88 in contact with substantially the entire surface of enlarged portion 67c to provide for optimal heat transfer therebetween. As shown, a longitudinal length of each heating element 90 is generally arranged in a U-shape and includes an elbow 92 at one end and terminal ends 94 at an opposite end. The terminal ends 94 of each heating element 90 communicate with a power source (not shown) through a connector (not shown). Suitable materials for heater plate body 64c are the same as have been previously described with respect to plate heater 64 of Figures 1-5. In addition, the number and arrangement of the heating elements 90 and channels 66c depends on the amount of heat required for a particular application and is not limited to the embodiment shown in Figures 8-10.

End caps 96 are provided at ends 98 and 100 of the heater 60c.

Each end cap 96 is coupled to the heater plate body 64c by fasteners (not shown), which extend through apertures 102. The end caps 96 are provided to distribute the heat from the exposed elbow 92 and terminal end 94 portions of the heating elements 90. The plate heater 60c further

includes relief holes 68c, which are drilled at regular intervals along the length of the extruded heater plate body 64c. The relief holes 68c are provided to receive mechanical items including fasteners (not shown) for coupling the heater 60c to the manifold. As shown, the plate heater 60c includes multiple thermocouple apertures 70c for receiving thermocouples (not shown). Each thermocouple is dedicated to one control zone of the plate heater 60c. Each control zone typically controls a maximum heater input of 15 amps. The number of control zones, and therefore thermocouples, is determined by the desired heat output for plate heater 60c. Heating elements 90 may be powered independently, in parallel or in series. Powering the heating elements 90 independently or in parallel provides a fail-safe, redundant arrangement for the plate heater 60c. In one embodiment, a parallel arrangement requires fewer control zones and therefore is less costly than independent control of each heating element 90.

Operation of the plate heater 60c is similar to operation of plate heaters 60, 60a, 60b of the previously described embodiments, and therefore will not be described further here.

The plate heater 60c is produced in a similar manner as has been previously described with respect to heater 60 of Figures 1-5; however, the profile for the die of plate heater 60c differs and is shown in Figure

1OA. The profile includes a linear portion 65c', which corresponds to contact surface 65c of the heater plate body 64c and extended portion

66c', which corresponds to channel 66c of the heater plate body 64c. Following extrusion, ends 98, 100 of the heater plate body 64c are machined by a machining operation such as milling or grinding, for example, to accommodate the terminal ends 94 of the heating elements

90. The heating elements 90 are then positioned in the channels 66c and may be deformed to provide three-sided contact with its respective channel 66c, by a technique such as rolling a tool under pressure over the heating elements 90. In accordance with one embodiment of the present invention, the rolling or swaging operation flattens the top side of heating

element 90 and maximizes the amount of contact between the remaining three-sides of heating element 90 and its respective channel 66c, in order to optimize the heat transfer therebetween. Other techniques for deforming the heating elements 90 may alternatively be used. The heating elements 90 are replaceable by an operator. This provides a cost savings, as the entire plate heater 60 does not need to be scrapped and replaced when one or more heating elements fail. In various embodiments of the present invention, deformation of the heating elements 90 in the channels 66c makes it possible for heating elements 90 having different diameters to be installed without significantly reducing the amount of contact between the heating element 90 and the channel 66c. In embodiments where heating elements having smaller diameters are installed, it may be desirable to fill any gaps between the heating element 90 and the channel 66c with a thermally conductive paste. The thermally conductive paste does not affect the removal of the heating elements 90 from the channels 66c and breaks away when the heating elements 90 are removed for repair or replacement.

It will be appreciated by a person skilled in the art that by deforming the heating elements 90 into the channels 66c, no additional clamping plate is required so that the heating elements 90 are unenclosed.

Referring to Figures 11 and 12, another embodiment of a plate heater 6Od for a manifold 12d is shown. In this embodiment, a heater plate body 64d includes a pair of channels 66d for receiving heating elements 90d. The channels 66d are provided in a contact surface 65d of the heater plate body 64d so that upon assembly, the heater elements 9Od contact an upper surface 38d of the manifold 12d. This arrangement allows for direct contact between the heating elements 9Od and the manifold 12d, therefore providing efficient heat transfer therebetween. A thermally conductive paste may be included to fill any gaps and increase the amount of contact between the heating element 9Od and the both the channel 66d and the manifold 12d. Apertures 104 are provided for

receiving fasteners (not shown) to fix the plate heater 6Od to the manifold 12d and clamp the heating elements 9Od to the upper surface 38d.

Although plate heater 6Od is shown coupled to the upper surface 38d of the manifold, it will be appreciated that similar to the previous heater embodiments, the plate heater 6Od may be coupled to any surface of the manifold 12d. Further, one channel 66d or a plurality of channels 66d may be provided depending on the amount of heat required for a particular application.

The heater plate body 64d may be formed by an extrusion process or a combination of extrusion and machining. The heater plate body 64d is made of a suitable material such as those materials previously described with respect to plate heater 60 of Figures 1-5.

Another embodiment of the present invention is shown in Figures 13 and 13A. Plate heater 6Oe includes an extruded heater plate body 64e having four channels 66e for receiving four heating elements 9Oe in an upper surface 88e thereof. Although four channels and heating elements are shown, a fewer or greater number may be employed without departing from the scope of the present invention. Channels 66e and heating elements 9Oe extend the length of heater plate 64e in parallel with each other. In contrast to the embodiment shown in cross-section in Figure 10, channels 66e have a straight-walled, u-shaped cross-section sized slightly larger than heating element 9Oe with a channel depth that fully receives heating elements 9Oe therein. Accordingly, an uppermost point of heating elements 9Oe sits at or below heater plate body upper surface 88e in contact with the walls of channel 66e to provide for optimal heat transfer therebetween. Heating element 9Oe may be swaged, or otherwise pressed, into channel 66e to make three-sided contact with heater plate body 64e. In one embodiment, a top surface of heating element 9Oe may be flattened during the swaging process. Heating elements 9Oe are thus held in-place within channels 66e without an additional cover or clamping arrangement so that they are easily replaced if one should fail.

In another embodiment shown in FIG. 13B which is combinable with the embodiment of FIG. 13), channels 66e may have a groove portion 71e and an undercut portion 67e that is a slightly enlarged area below groove 71e, similar to narrowed portion 71c and enlarged portion 67c shown in Figure 10. Heating elements 9Oe, each of which has an outer diameter that is slightly larger than groove portion 71e but roughly equivalent to undercut portion 67e, are then pressed through groove portions 71e to sit within undercut portions 67e of channel 66e. In an embodiment, undercut portion 67e is sized to fully receive and to maintain contact with heating element 9Oe for maximum heat transfer therebetween. One method of making the embodiment of FIG. 13B, includes forming an undersized version of channel 66e during the extrusion process that forms heater plate body 64e, and then machining groove portion 71e and undercut portion 67e to a suitable geometry to accommodate heating element 9Oe as previously described.

Each heating element 9Oe includes terminal ends 94e (one of which is shown in Figure 13A), and is connected in parallel to or wired independent of at least one other heating element 9Oe. Thus, multiple heating elements 9Oe wired in parallel or independently provide redundancy in operation for heater plate 64e. Terminal ends 94e are positioned between an upper and lower portion of a respective end cap 110, which are attached at each end of heater plate 64e by clamps 112. As in previous embodiments, one or more heater 6Oe may be attached to a top, side and/or bottom surface of the manifold depending on the application and heating needs. The end cap 110 comprises four inlets, each aligned with one of the channels 66e respectively and receiving a terminal end 94e of a heating element 9Oe. The upper and lower portion of the end cap 110 each including a half of four inlet channels 95e for receiving a straight portion of the terminal ends 94e. The inlet channels 95e intersecting a through channel 96e for receiving bent end portions of the terminal ends 94e. The through channel 96e having two outlets 97e from which the connecting ends 98e of the terminal ends 94e project. The upper and the lower portion of the end 110 each including a half of

the through channel 96e. The end cap 110 is made out of an electrically insulative material that can withstand molding temperatures, preferably a ceramic material.

The end cap 110 is shaped like an extension of the heater plate body 64e and the height h _c and the width w _c of the end cap 110 are equal or smaller than the height h _b and the width w _b of the heater plate body 64e. Due to the fact that not only a straight portion, but also a bent portion of the terminal ends 94e are positioned in the end cap 110 forces applied to the connecting ends 98e do not influence the connection of the heating element 9Oe in the channels 66e. As with the embodiment shown in FIG. 9 such an end cap 110 could also position not only terminal ends 94e, but also the combination of terminal ends 94e and a conventional bend (like elbow 92 in FIG. 9) or only such conventional bends. The two halves of the end cap 110 are identical and having respective connecting means to be fitted together.

With regard to the materials of the heater plate body 64e, the arrangements of heating elements and their electrical connection etc. it is referred to the above embodiments. These features and techniques are also applicable here. Another embodiment of the present invention is shown in FIG. 14 -

18. This embodiment is similar to the embodiment disclosed in FIG. 13 - 13B. Thus, only the differences are explained in the following. With regard to the remaining features and aspects it is therefore referred to the above. This embodiment also includes end caps 110 on both ends of the plate heater 6Of. The height h _c of the end cap 110 is smaller than the height h _b of the heater plate body 64f. Each end cap 110 is connected to the end of the heater plate body 64f by using a U-shaped clamp 112f. Whereas the side face of the end cap 110 including the inlets is pressed against the end face of the heater plate body 64f the three other side faces of the end cap 110 are held in the framelike structure of the U- shaped clamp 112f. The clamp 112f does not only have an overall U-

shape, but also a U-shape cross-section. So that the end cap 110 can be inserted in this framelike structure provided by clamp 112f. The legs of the U-shaped clamp 112f are bolted to the heater plate body 64f. The clamp 112f does have side windows 99f being in alignment with the outlets 97f of the end cap 110 so that the connecting ends 98f projecting out of the windows 99f respectively. The clamp 112f is preferably made from a steel material.

End caps 110 as described with some of the above embodiments can be used with all of the heater designs disclosed. The many features and advantages of the invention are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the invention that fall within the true spirit and scope of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.