Jig and method for positioning spot welding electrode

A positioning jig for a spot-welding electrode includes an attaching portion for temporarily attaching to a workpiece. A positioning portion of the jig is disposed in parallel to a central axis of the attaching portion and spaced from the central axis. The positioning portion has an imaginary central axis coinciding with the central axis of the attaching portion. With the attaching portion attached to that part of a workpiece surface which is to be spot welded, the electrode is set on the central axis of the attaching portion. An inclination of the electrode is corrected to make the electrode stand parallel to the positioning portion such that, even when the workpiece surface is curved, the electrode can be positioned perpendicularly to the workpiece surface part to be spot welded.

FIELD OF THE INVENTION

The present invention relates to positioning of an electrode of a spot welder.

BACKGROUND OF THE INVENTION

It is important to set suitable values of electric currents, select suitable positions of electrodes and, especially, position the electrodes perpendicularly to portions of workpieces to be subjected to spot welding, so as to provide high quality of spot-welded portions of the workpieces. Positioning jigs have been used in positioning electrodes for spot welding, as disclosed in, for example, JP-A-2004-82168. The disclosed positioning jig for use in positioning an electrode will be discussed with reference toFIG. 13andFIG. 14hereof.

FIG. 13illustrates the conventional positioning jig designated at100for positioning an electrode105for spot welding. The jig100includes an attaching portion103for magnetically attaching to a surface102of a flat workpiece101, and a bar-shaped positioning portion104extending upwardly from the attaching portion103and disposed perpendicularly to the surface102of the workpiece101.

The positioning portion104has a lower part spaced an interval Y1from the electrode105. The positioning portion104has an upper part spaced an interval Y2from the electrode105. When the interval Y1is found to be equal to the interval Y2through comparison of the interval Y1with the interval Y2, the electrode105is disposed in parallel to the positioning portion104and therefore the electrode105is found to be appropriately positioned. When the interval Y1is different from the interval Y2, the electrode105is inclined relative to the positioning portion104. Therefore, the inclination of the electrode105is corrected to make the interval Y1equal to the interval Y2.

When the workpiece101is curved, as shown inFIG. 14, however, the electrode105is not disposed in parallel to the positioning portion104. In this case, if a posture of the electrode105is adjusted to make the interval Y1equal to the interval Y2, the electrode105is not disposed perpendicularly to a portion of the workpiece101to be subjected to spot welding. With the electrode105disposed not perpendicularly to the portion of the workpiece101, spot welding can not be satisfactorily performed on the portion of the workpiece. For the positioning jig100, therefore, it is impossible to appropriately evaluate a posture of the electrode on the basis of the intervals Y1, Y2when the workpiece is curved as shown inFIG. 14.

To address the above problem, there is a demand for a technique capable of positioning an electrode perpendicularly to a portion of a workpiece to be subjected to spot welding, regardless of whether the workpiece is flat or curved.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a jig for positioning an electrode by correcting an inclination of the electrode relative to surfaces of workpieces to be spot-welded together, the jig comprising: an attaching portion for temporarily attaching to the workpiece; a positioning portion disposed in parallel to a central axis of the attaching portion and offset from the central axis; and an interconnecting portion interconnecting the attaching portion and the positioning portion.

With the jig thus arranged, the electrode can be positioned perpendicularly to a portion (a welding target portion) of the workpiece to be subjected to the spot welding. Because the inclination of the electrode is corrected with reference to the positioning portion disposed in parallel to the central axis of the attaching portion, the electrode can be positioned perpendicularly to the portion of the workpiece subjected to spot welding, even when the workpiece is not flat but curved. Thus, it becomes possible to readily, accurately check whether the electrode is appropriately positioned, regardless of a configuration of the workpiece.

Preferably, the positioning portion is connected through the interconnecting portion to the attaching portion in such a manner as to revolve on the attaching portion. Generally, the inclination of the electrode relative to two directions, typically, a right-and-left direction and a front-and-rear direction should be checked in positioning the electrode. In the preferred embodiment, the positioning portion is arranged to revolve on the attaching portion. After the inclination of the electrode in one direction is corrected, the positioning portion can revolve on the attaching portion through 90 degrees for correction of the inclination of the electrode in the other direction. Thus, the positioning of the electrode can be efficiently performed.

Desirably, the positioning portion includes a rotary shaft offset from the central axis of the attaching portion, and an elliptic or circular cylinder secured to the rotary shaft in eccentric relation to the rotary shaft. With this arrangement, the circular or elliptic cylinder can be rotated by rotation of the rotary shaft to thereby contact or come close to the electrode. Therefore, the inclination of the electrode can be more readily corrected with the result that the positioning of the electrode can be performed with improved efficiency.

In a preferred form, the positioning portion is disposed on the interconnecting portion in such a manner as to slide in a direction perpendicular to the central axis of the attaching portion between a central axis position on the central axis and an offset position offset from the central axis position, the positioning portion being selectively positioned at the central axis position and the offset position. Since the positioning portion is sidable on the interconnecting portion between the central axis position and the offset position, the positioning jig can change a form of measurement of the inclination of the electrode in correspondence to type of a workpiece. Moreover, because the positioning portion is slidable, the positioning portion can contact or come close to the electrode for readily checking the inclination of the electrode with reference to the positioning portion.

According to a second aspect of the present invention, there is provided a method for positioning an electrode by correcting an inclination of the electrode relative to surfaces of workpieces to be spot-welded together, the method comprising the steps of; providing a jig having an attaching portion for temporarily attaching to the workpiece, a positioning portion disposed in parallel to a central axis of the attaching portion and offset from the central axis, and an interconnecting portion interconnecting the attaching portion and the positioning portion; temporarily attaching the attaching portion to that part of a workpiece surface which is subjected to spot welding; setting the electrode on the interconnecting portion to bring a central axis of the electrode into coincidence with the central axis of the attaching portion; correcting the inclination of the electrode with reference to the positioning portion to direct the electrode perpendicularly to the surface of the portion of the workpiece; removing the jig from the workpiece; and advancing the electrode into contact with that part of the workpiece surface to be spot-welded.

Preferably, the positioning portion includes a rotary shaft offset from the central axis of the attaching portion, and an elliptic or circular cylinder attached to the rotary shaft in eccentric relation to the rotary shaft, and wherein the inclination of the electrode is corrected with reference to the elliptic or circular cylinder.

Desirably, the positioning portion is disposed on the interconnecting portion in such a manner as to slide in a direction perpendicular to the central axis of the attaching portion between a central axis position on the central axis of the attaching portion and an offset position offset from the central axis position, and wherein the step of setting the electrode on the interconnecting portion comprises sliding the positioning portion along the interconnecting portion to select one of the central axis position and the offset position in correspondence to a configuration of the workpiece surface.

Thus, the positioning portion can slide to be selectively located on the two positions, and hence form of measurement of the inclination of the electrode can be changed to correspond to a flat or curved surface of the workpiece. Therefore, the electrode can be quickly accurately positioned regardless of a configuration of the workpiece.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is merely exemplary in nature and is in no way intended to limit the application or its uses.

Referring toFIG. 1throughFIG. 3, there is shown a jig10A for positioning an electrode of a spot welder, according to a first embodiment of the present invention. The jig10A will be hereinafter referred to as “positioning jig10A”.

The positioning jig10A includes an attaching portion14with a permanent magnet11and is capable of magnetically attaching to a surface13of a workpiece12, an interconnecting portion15extending horizontally from an upper surface of the attaching portion14, and a bar-shaped positioning portion16extending upwardly from the interconnecting portion15and directed perpendicularly to the interconnecting portion15.

The attaching portion14attaches to the workpiece12by the action of the permanent magnet11incorporated in the attaching portion14.

The attaching portion14has its central axis19generally coinciding with a central axis18of an electrode17. The positioning portion16is disposed at a position offset from the central axis18of the electrode17. That is, the positioning portion16is disposed on the interconnecting portion15in parallel to the central axis19of the attaching portion14and is offset from the electrode17. The positioning portion16thus has an imaginary central axis identical to the central axis of the attaching portion. The interconnecting portion15is horizontally disposed at right angles to the attaching portion14. The positioning portion16is disposed perpendicularly to the interconnecting portion15. Accordingly, when the electrode17is disposed in parallel to the positioning portion16, the central axis18of the electrode17generally coincides with the central axis19of the attaching portion14.

The attaching portion14, the interconnecting portion15and the positioning portion16are arranged in the above-mentioned relation. The positioning portion16is secured to the attaching portion14through the interconnecting portion15.

Although, in fact, two, three or four workpieces12to be spot-welded together lie one over the other, a single workpiece12will be illustrated inFIGS. 1,3,4,5,10,11,12A and12B for convenience of illustration.

Description will be made as to how the positioning jig10A is used. First, with the electrode17spaced away from the workpiece12, the attaching portion14attaches to that part (welding portion) of the workpiece surface13which is to be spot-welded to another workpiece12(not shown). The positioning jig10A is thus set on the surface13of the workpiece12. Then, the electrode17is brought closely to the interconnecting portion15.

A lower interval W1between a lower portion of the positioning portion16and the electrode17is measured and then an upper interval W2between an upper portion of the positioning portion16and the electrode17is measured for checking whether the electrode17is inclined. The lower and upper intervals W1, W2can be manually measured using a scale or other appropriate tools such as, preferably, a thickness gage.

When the electrode17is inclined, the lower interval W1and the upper interval W2are measured. The inclination of the electrode17is then adjusted along an axis X—X in such a manner as to make the lower interval W1equal to the upper interval W2, as shown inFIG. 2A. When the lower interval W1is made equal to the upper interval W2, the inclination of the central axis18of the electrode17with respect to the axis X—X is corrected.

Next, the attaching portion14is removed from the workpiece12and the positioning jig10A is turned through 90 degrees as shown inFIG. 2A. The thus turned positioning jig10A is shown inFIG. 2B.

After turning of the positioning jig10A, the attaching portion14attaches again to the welding portion of the workpiece12. Subsequently, the electrode17is brought closely to the interconnecting portion15.

A lower interval V1between the lower portion of the positioning portion16and the electrode17is measured and then an upper interval V2between the upper portion of the positioning portion16and the electrode17is measured for checking whether the electrode17is inclined.

When the electrode17is inclined, the lower interval V1between the lower portion of the positioning portion16and the electrode17is measured and the upper interval V2between the upper portion of the positioning portion16and the electrode17is measured. Then, the inclination of the electrode17is adjusted along the axis Y—Y in such a manner as to make the lower interval V1equal to the upper interval V2. When the lower interval V1is made equal to the upper interval V2, the inclination of the central axis18of the electrode17with respect to the axis Y—Y is corrected.

Since the inclinations of the electrode17with respect to the both axes X—X and Y—Y are corrected, the electrode17can be rendered parallel to the positioning portion16. Thus, the central axis18of the electrode17coincides with the central axis19of the attaching portion14. When the workpiece17is a flat sheet, the electrode17is fixed perpendicularly to the surface13of the workpiece17.

Thereafter, the positioning jig10A is removed from the workpiece12, and the electrode17is applied to the surface13of the welding portion of the workpiece12for spot welding.

Discussion will be made in relation toFIG. 3as to how the positioning jig10A is used for a workpiece12having a curved surface.

As shown inFIG. 3, the attaching portion14of the positioning jig10A is attached to a curved surface13of a welding portion P to thereby set the positioning jig10A on the curved surface13of the workpiece12. The interconnecting portion15is disposed in parallel to a tangential line Z passing through the welding portion P. The positioning portion16is disposed perpendicularly to the tangential line Z. A tip end portion of the electrode17is then brought into abutment on the interconnecting portion15.

Next, as explained in relation toFIG. 2A, the lower interval W1between the lower portion of the positioning portion16and the electrode17is measured and then the upper interval W2between the upper portion of the positioning portion16and the electrode17is measured for checking whether the electrode17is inclined relative to the positioning portion16.

When the electrode17is inclined relative to the positioning portion16, the intervals W1, W2are measured and then the inclination of the electrode17is adjusted along the X—X axis in such a manner as to make the intervals W1, W2equal to each other for correcting the inclination of the electrode17with respect to the axis X—X.

Next, as explained in relation toFIG. 2B, the attaching portion14is removed from the workpiece12and the positioning jig10A is turned through 90 degrees. Thereafter, the attaching portion14is again attached to the welding portion P of the workpiece12. Then, the tip end portion of the electrode17is brought into abutment on the interconnecting portion15.

The lower interval V1between the lower portion of the positioning portion16and the electrode17is measured and then the upper interval V2between the upper portion of the positioning portion16and the electrode17is measured for checking whether the electrode17is inclined relative to the positioning portion16.

When the electrode17is inclined relative to the positioning portion16, the intervals V1, V2are measured and the inclination of the electrode17is adjusted along the axis Y—Y in such a manner as to make the intervals V1, V2equal to each other. When the lower interval V1and the upper interval V2become equal to each other, the inclination of the central axis18of the electrode17with respect to the axis Y—Y is corrected.

Therefore, the central axis18of the electrode17coincides with the central axis19of the attaching portion14and hence, even when the workpiece12is curved, the central axis18is directed perpendicularly to the tangential line passing through the welding portion P. With this arrangement, the electrode17is disposed in position relative to the attaching portion14. Accordingly, the position of the electrode17can be easily, accurately checked regardless of the configuration of the workpiece12.

FIG. 4illustrates a jig10B (hereinafter referred to as “positioning jig10B”) for positioning an electrode of a spot welder according to a second embodiment of the present invention.

The positioning jig10B in the second embodiment of the present invention is the same as the positioning jig10A in the first embodiment of the present invention except that an interconnecting portion15of the positioning jig10B can turn relative to an attaching portion14.

The interconnecting portion15of the positioning jig10B is rotatably attached by a screw21to the attaching portion14with a lubricative spacer22interposed therebetween. By virtue of a spring washer31and a plain washer32interposed between the screw21and the interconnecting portion15, rotational force applied to the interconnecting portion15can be adjusted by adjustment of a degree to which the screw21is fastened to the interconnecting portion15.

It is to be noted that the spacer22may be eliminated if contact area between the attaching portion14and the interconnecting portion15is rendered lubricative.

By virtue of the interconnecting portion15arranged to turn relative to the attaching portion14, the intervals W1, W2, V1, V2between a positioning portion16and an electrode17can be efficiently measured because the interconnecting portion15directed in a direction of the axis X—X can be readily turned to be directed in a direction of the axis Y—Y without removal of the attaching portion14from the workpiece12as discussed in relation toFIG. 2AandFIG. 2B. Therefore, it is unlikely that the attaching portion14is displaced from the welding portion P due to the removal from the workpiece12.

The positioning jig10B in the second embodiment can be used for a curved workpiece as well as a flat workpiece12, as can the positioning jig10A in the first embodiment.

FIG. 5throughFIG. 7show a jig10C (hereinafter referred to as “positioning jig10C”) for positioning an electrode of a spot welder according to a third embodiment of the present invention.

The positioning jig10C in the third embodiment includes an attaching portion14incorporating therein a single-piece magnet11, and an interconnecting portion15. The positioning jig10C further includes a positioning portion16extending upwardly from the interconnecting portion15and disposed perpendicularly to the interconnecting portion15. The attaching portion14has a central axis19coinciding with a central axis18of an electrode17.

The positioning portion16includes a rotary shaft24offset from the central axis18of the electrode17, and an elliptic cylinder25mounted on the rotary shaft24. The rotary shaft24is eccentric to the elliptic cylinder25, that is, the rotary shaft24is offset from a central axis of the elliptic cylinder25. The rotary shaft24has a lower end to which a primary dial26is attached for rotating the rotary shaft24. The rotary shaft24has an upper end to which a secondary dial27is attached for rotating the rotary shaft24in the same manner as the primary dial26. Either of the primary dial26and the secondary dial27is used in measuring an inclination of the electrode17. Although the rotary shaft24may be equipped with at least one of the dials26,27, the primary dial26is preferably used if only one dial is selected. The reason why the primary dial26is preferred to the secondary dial27is that since the primary dial26is disposed in the vicinity of the interconnecting portion15supporting the rotary shaft24, the primary dial26rotates the rotary shaft24without applying a bending force to the rotary shaft24, that is, without deforming the rotary shaft24.

The elliptic cylinder25is secured to the rotary shaft24by means of plural screws28. Between a lower end of the elliptic cylinder25and a boss portion15aintegral with the interconnecting portion15, there is interposed a lubricative spacer22.

Discussion will be made in relation toFIG. 6andFIG. 7as to how the positioning jig10C is used.

First, the primary dial26is rotated clockwise to rotate the rotary shaft24for turning the elliptic cylinder25clockwise, as shown inFIG. 6, so that the interconnecting portion15provides a place for the electrode17to be positioned. The elliptic cylinder25is in a position shown by a dash line ofFIG. 7.

Second, the electrode17is placed on the interconnecting portion15(FIG. 6), after which the primary dial26(FIG. 6) is rotated back (counterclockwise) to bring the elliptic cylinder25into contact with the electrode17, as shown by a solid line ofFIG. 7. When no gap is formed between the electrode17and the elliptic cylinder25, the electrode17is disposed in parallel to the elliptic cylinder25. When a gap is formed between the electrode17and the elliptic cylinder25, the inclination of the electrode17is corrected to provide no gap between the electrode17and the elliptic cylinder25. By the use of the positioning jig10C, the inclination of the electrode17can be adjusted in a short time because whether the electrode17is inclined can be visually checked. In the previously discussed first embodiment, the intervals W1, W2between the electrode17and the positioning portion16should be measured using a measuring tool, for example, a thickness gage for adjusting the inclination of the electrode. In contrast, in the third embodiment, such a measuring tool as required in the first embodiment need not be used and hence the inclination of the electrode17can be checked and corrected in a shorter time.

FIG. 8shows an alternative to the positioning jig shown inFIG. 5throughFIG. 7. The positioning jig shown inFIG. 8includes a circular cylinder29having a circular cross-section in place of the elliptic cylinder25forming the positioning portion16. The rotary shaft24is eccentric to the circular cylinder, that is, is offset from a central axis of the circular cylinder29. The positioning jig having the circular cylinder29shown inFIG. 8is used in the same manner as the positioning jig10C explained with reference toFIG. 5throughFIG. 7. Whether the electrode17is inclined or not can be visually checked for the same reason as applied to the positioning jig10C in the third embodiment. The circular cylinder29is advantageous in that the cylinder29is cheaper than the elliptic cylinder25because the circular cylinder29is easier to manufacture than the elliptic cylinder25. This leads to reduced cost for the positioning jig shown inFIG. 8.

FIG. 9shows a jig10D (hereinafter referred to as “positioning jig10D”) for positioning an electrode of a spot welder according to a fourth embodiment of the present invention.

While, in the positioning jig10C ofFIG. 5according to the third embodiment, the attaching portion14and the interconnecting portion15are integral with each other, in the positioning jig10D according to the fourth embodiment, an attaching portion14and an interconnecting portion15are separated from each other, more specifically, the interconnecting portion15is rotatably attached to the attaching portion14. It will be noted that the interconnecting portion15is rotatably attached to the attaching portion14in the same manner as the interconnecting portion15of the positioning jig10B ofFIG. 4in the second embodiment, and hence descriptions of components used for the attachment of the interconnecting portion15to the attaching portion14will be omitted. The positioning jig10D in the fourth embodiment has a structure obtained by combining a feature of the positioning jig10B ofFIG. 4in the second embodiment with a feature of the positioning jig10C ofFIG. 5in the third embodiment.

The turning of the interconnecting portion15relative to the attaching portion14assists adjustment of inclinations of an electrode with respect to the axes X—X and Y—Y Moreover, whether the electrode is inclined can be readily checked by the elliptic cylinder25being turned into contact with the electrode.

FIG. 10andFIG. 11show a jig10E (hereinafter referred to as “positioning jig10E”) for positioning an electrode of a spot welder according to a fifth embodiment of the present invention.

In the positioning jig10E according to the fifth embodiment, a central axis19of an attaching portion14generally coincides with a central axis18of an electrode17. A positioning portion16is offset from the central axis18of the electrode17. The positioning portion16is attached via an interconnecting portion15to the attaching portion14. Reference numeral32denotes a plain washer.

The interconnecting portion15includes a guide plate41having a slit-shaped guide groove41afor guiding a slide movement of the positioning portion16, a slide screw42fitted with the guide groove41afor sliding together with the positioning portion16, and a U-shaped cross-sectional interconnecting body43accommodating therein a head42aof the slide screw42and retaining the guide plate41.

The interconnecting body43of the interconnecting portion15is secured to the attaching portion14by welding. The guide plate41is secured to the interconnecting body43by welding. Namely, the interconnecting portion15is secured to the attaching portion14by welding.

The positioning portion16is connected by the slide screw42to the interconnecting portion15. More specifically, as shown inFIG. 11, the head42aof the slide screw42is located in a space defined by the interconnecting body43of U-shaped cross-section. The slide screw42has a threaded portion42bscrewed through the slit-shaped guide groove41aformed in the guide plate41and through a spacer22into a lower part16aof the positioning portion16, such that the positioning portion16is rotatably attached to the interconnecting portion15.

The positioning portion16is attached to the interconnecting portion15in such a manner as to slide in a direction perpendicular to the central axis19of the attaching portion14. In other words, the positioning portion16can be selectively set at a central axis position located on the central axis19of the attaching portion14and an offset position offset from the electrode17. Thus, the position at which the positioning portion16is set can be changed over between the central axis position and the offset position, such that the electrode17can be positioned relative to a flat or curved workpiece12as will be discussed in relation toFIG. 12AandFIG. 12B. This means that the positioning jig10E provide a suitable form of measurement of the inclination of the electrode not only when a workpiece is a flat but also when a workpiece is curved.

The positioning jig10E in the fifth embodiment has a changeable measurement form. The measurement form can be changed merely by the slide movement of the positioning portion16. Moreover, the inclination of the electrode17can be efficiently, easily measured because the positioning portion16can slide close to or into contact with the electrode17.

By virtue of the lubricative spacer22interposed between the lower part16aof the positioning portion16and the guide plate41, the positioning portion16can rotate relative to the guide plate41, that is, relative to the interconnecting portion15. The positioning portion16of the positioning jig10E according to the fifth embodiment may take the form of the elliptic cylinder25of the positioning jig10C according to the third embodiment. In this case, the positioning portion16in the form of the elliptic cylinder25can rotate and slide towards the electrode17to thereby contact the electrode17. Thus, the inclination of the electrode17can be easily visually checked, as in the case of the positioning jig10C in the third embodiment.

Alternatively, the positioning portion16may slide without rotating relative to the interconnecting portion15. In this case, the slide screw42becomes incapable of rotating, for example, provided that the head42aof the slide screw42has a square shape configured to abut on a surface of an inner wall of the interconnecting body43. By thus rendering the slide screw42incapable of rotating, rotation of the positioning portion16is prevented.

It will be understood that the guide plate41may be secured to the interconnecting body43by, for example, screws or adhesives rather than by the welding discussed in the fifth embodiment. Similarly, securing of the interconnecting portion15to the attaching portion14may be effected using, for example, screws or adhesives rather than the welding.

Now, discussion will be made with reference toFIG. 12AandFIG. 12Bas to how the positioning jig10E according to the fifth embodiment is used.

FIG. 12Ashows that the positioning portion16of the positioning jig10E is positioned when the jig10E is used for a flat or curved workpiece12as in the case of the first and second embodiments. More specifically, the positioning portion16is set at a position offset from the central axis19of the attaching portion14. The attaching portion14is attached a welding portion surface13of a workpiece12. A tip end portion of the electrode17is placed on the interconnecting portion15such that the central axis18of the electrode17coincides with the central axis19of the attaching portion14. An inclination of the electrode17is then measured with reference to the positioning portion16, as in the case of the first and second embodiments. Provided that the positioning portion16is in the form of an elliptic cylinder described in the third embodiment, the positioning portion16is rotated into contact with the electrode17for checking an inclination of the electrode17.

FIG. 12Bshows that the positioning portion16is positioned when the positioning jig10E is used for a flat workpiece12only.

First, the attaching portion14is magnetically attached a welding portion surface13of the flat workpiece12. The positioning portion16is then slid such that a central axis16aof the positioning portion16coincides with the central axis19of the attaching portion14. The positioning jig10E is used in the same manner as the conventional positioning jig100shown inFIG. 13.

As discussed in relation toFIG. 12AandFIG. 12B, the positioning jig10E is advantageous in that because the positioning jig16can slide between the two positions, two different forms of measurement of an inclination of the electrode can be provided. That is, the positioning jig10E easily addresses various types of workpieces for measurement and adjustment of the inclination of the electrode, such that the electrode can be quickly appropriately positioned for spot welding.

Obviously, various minor changes and modifications of the present invention are possible in the light of the above teaching. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.