| 1. | A connector fur use in a card reader for reading an information from a memory card, the connector comprising: a frame for accommodating the card therein, the frame having an opening through which the card is inserted into the frame and removed from the frame; a plurality of connector terminals mounted on the frame, being insulated from one another and contacted to card terminals, respectively, each of the connector terminals extending out of the frame; a switch for detecting a complete insertion of the memory card, the switch mounted in an inner rear portion of the frame, maintaining an insulation state; and a landing yoke supporting one portion of each of the connector terminals and pivotably mounted with the frame to minimize a sliding contact area of the memory card with the connector terminals during an insertion or removal of the memory card. |
| 2. | The connector of claim 1, wherein said switch includes a movable member elastically deformed when its lead comes into a contact with the memory card and the fixed member elastically contacted to the movable member before the movable member is deformed by the memory card. |
| 3. | The connector of claim 1, wherein said landing yoke is pivotable within a predetermined angular range about a hinge and serves to connect one portion of each of the connector terminals to the card terminals by raising the portion, when the memory card is inserted into the frame by a predetermined distance. |
| 4. | A connector for use in a card reader for reading an information from a memory card, the connector comprising: a frame for accommodating the card therein, the frame having an opening through which the card is inserted into the frame and removed from the frame ; a plurality of connector terminals mounted on the frame, being insulated from one another and contacted to card terminals, respectively, each of the connector terminals extending out of the frame; a switch for detecting a complete insertion of the memory card, the switch mounted in an inner rear portion of the frame, maintaining an insulation state; and a lever supporting one portion of each of the connector terminals and detachably mounted on the frame to allow an upper portion of each of the connector terminals to be evenly contacted to the memory card. |
| 5. | The connector of claim 4, wherein said frame is divided into an upper member and a lower member for receiving the memory card, and has a plurality of hooks for firmly securing the upper member to the lower member, each of the hooks having an upper and a lower slant surfaces adjacent to each other, the lower slant surface facilitating the insertion of the hook and the upper slant surface preventing the inserted hook from being easily deviated from the proper position. |
| 6. | The connector of claim 5, wherein a pair of posts and a pair of receiving holes are formed with the frame to allow the upper and the lower members to be firmly combined into each other, and each of the posts extending above each of the receiving holes is melted and then processed to have a diameter larger than that of the receiving hole. |
| 7. | The connector of claim 4, further comprising a push plate for pushing the memory card in one direction in order to minimize an unwanted movement of the memory card inserted into the frame. |
| 8. | The connector of claim 4, wherein each of the connector terminals is provided with an external end, a curved portion, a bent portion, an inclined portion and an inner end which are integrally formed with one another, the curved portion having a convex configuration for a contact with the memory card, the inner end bent at an end of the curved portion to extend inwardly, the inclined portion outwardly extending from the curved portion with a slant angle of about 7.5° with a horizontal line, the external end outwardly extending from the inclined portion through the bent portion whose radius is about Imm, and an extending direction of the external end being changed at the bent portion. |
| 9. | The connector of claim 8, wherein said external end is provided with a bead evenly protruding along its vertical length to reinforce the external end. |
| 10. | The connector of claim 4, wherein said lever includes a frontal and a rear beads for limiting an upward deformation of the inclined portion of the connector terminals and a center bead for limiting an upward deformation of the inner end. |
| 11. | The connector of claim 11, wherein said frontal and the rear beads and the center bead have heights substantially identical to one another and smaller than that of the curved portion of the connector terminals. |
| 12. | The connector of claim 4, wherein said switch includes a movable member elastically deformed when its lead comes into a contact with the memory card and the fixed member elastically contacted to the movable member before the movable member is deformed by the memory card. |
Description of the Prior Art In recent years, many different kinds of cards have become more popular and have been widely used. A credit card, bank card, identification card and many other cards are used under the demand of the complicated and rapidly changed society. More recently, an memory card or a smart card having integrated circuit (IC) memory chip has been developed with increased capability of storing data, which can hold much more information than a magnetic strip type card. Use of the memory cards are rapidly increasing in the banking industry and for the purpose of storing personal data, such as electronic identification card, driver's license, social security card, financial card and others.
Accordingly, a memory card reader which can read the data stored on the memory card is also developed. To access the information stored in the memory card, the card reader should be equipped with a connector making an electrical connection with the contact elements of the semiconductor
device, e. g. the IC chip. The present invention is related to a novel means of ensuring good connection with the memory card contact elements.
Typically, terminals of the memory card reader and the contacting elements are touching each other to provide electrical connection between the terminals and the contacting elements. To provide good connection between the terminals of the memory card reader and the contacting elements of the memory card, a slot of the memory card reader for inserting a card has been narrowly designed to hold the memory card tightly in a proper position.
Moreover, the memory card must be pressured against the terminals of memory card reader to reduce change of the resistance at the terminals.
However, contacting surface between the memory card and the card reader should be minimized for smooth insertion and removal of the memory card.
Less contacting surface can provide an operative reliability and durability for the card and for the memory card reader. In addition, malfunctioning by static electricity caused by the sliding contact can be reduced.
A number of attempts have been made in the prior art to accomplish an effective memory card reader. One attempt to solve the problems of prior art has been demonstrated by a US patent, US4,900,272 which pressurize the memory card against the terminals of memory card reader in an attempt to ensure consistent contact with the contact elements of memory card.
However, the prior art has some disadvantages which are generally recognized in the industry. Even though the memory card is pressured, the contacting force is no more than the bending force generated by the terminals.
Moreover, terminals can easily be bent from a sudden insertion of card or any other strong force, resulting a short circuit for the card reader. When a terminal is bent and touching the adjacent terminal, the card reader no longer functions properly. Furthermore, because of the pressure against the
terminals, strong force has to be applied to insert or remove the memory card.
Consequently, the previous prior art has low durability and short lifetime.
Those who skilled in the art have tried to increase the durability and the efficiency which essentially increase the lifetime of the device. However, this has not been accomplished yet.
Disclosure of the Invention In view of foregoing, it is a primary object of the present invention to provide a connector for use in a card reader, which is capable of increased operative reliability and endurance, and at the same time, ensuring an exact electrical contact between the memory card and the card reader.
It is also an object of the present invention to provide a connector for use in a card reader, which is capable of smoothly inserting and removing movement of the memory card.
Consistent with the foregoing objects, and in accordance with the invention as embodied broadly described herein, a connector for use in a card reader is disclosed in one embodiment of the present invention, comprising: a frame for accommodating the card therein, the frame having an opening through which the card is inserted into the frame and removed from the frame; a plurality of connector terminals mounted on the frame, being insulated from one another and each of the connector terminal being extended from the frame to be contacted with each of the card contact element ; a card sensor switch for detecting a complete insertion of the memory card is mounted in an inner rear portion of the frame, maintaining an insulation state; and a landing yoke supporting one portion of each of the connector terminals is pivotly mounted in the frame to minimize a sliding contact area of the memory card with the connector terminals during insertion or removal of the
memory card.
The foregoing and other objects and features of the present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS Understanding that these drawings depict only typical embodiments of the invention and are, therefore, not to be considered limiting of its scope, the invention will be described with additional specificity and detail through use of the accompanying drawings in which: Fig. 1 is a perspective view of the present invention, showing the connector being assembled in a preferred embodiment; Figs. 2 is a sectional view of a preferred embodiment of the present invention, showing an memory card being inserted but a card sensor switch not being activated yet; Figs. 3 is another sectional view of a preferred embodiment of the present invention, showing an memory card being fully inserted and a card sensor switch being activated; Figs. 4 and 5 offer schematic sectional views of a landing yoke in an initial state of the memory card insertion and a completion state of the memory card insertion, respectively ; Fig. 6 is a perspective view of a preferred embodiment of the present invention, also showing another preferred embodiment of the card sensor switch of the present invention; Fig. 7 is a side view of a connector terminal in accordance with the preferred embodiment of the present invention; Fig. 8 is a sectional view of the preferred embodiment of the present
invention, depicting structure of a lever and terminals; Fig. 9 is a perspective view of a card sensor switch in accordance with the preferred embodiment of the present invention; and Fig. 10 is an enlarged view of a hook of the connector in accordance with the preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION It will be readily understood that the components and steps of the present invention, as generally described and illustrated in the Figures herein and accompanying text, could be arranged and designed in a wide variety of different configurations while still utilizing the inventive concept. Thus, the following more detailed description of the preferred embodiments of the system and method of the present invention, as represented in Figures 1 through 10 and accompanying text, is not intended to limit the scope of the invention, as claimed, but it is merely representative of the presently preferred embodiments of the invention. The presently preferred embodiments of the invention will be best understood by reference to the drawings, wherein like parts or steps are designated by like numerals throughout.
Referring to Fig. 1, the connector for use in a card reader reads information stored in a memory chip of the memory card (C) by making electrical contacts between the terminals (13 and 14) of the card reader and contacting elements (C') of the memory card.
The memory card (C) can be inserted into a frame (10) and removed from the frame (10) through an opening (lOa). The frame (10) constitutes the inventive connector. The frame (10) is preferably divided into at least two portions in such a manner that each of the portions is made of plastic by an injection molding and then is assembled into a united member. However,
other generally known manufacturing method can also be used to achieve the objects of the present invention. The opening (lOa) and other elements of the frame (10) define the inner space for the memory card (C) to properly hold the memory card in a desired position and to be properly inserted into the card reader and removed from the card reader without much of friction.
Still referring to Fig. 1, a plurality of a connector terminals (13 and 14) making electrical connection with the card contacting element (C') are mounted on the frame (10) by one end, and the other end of connector terminals are extend toward the other set of terminals (13 and 14). Each terminal is electrically insulated from each other by the frame (10) and other elements of the present invention. The connector terminals (13 and 14) are made of alloy containing copper and preferably have a connection resistance of 100 mQ or less. Curved portions (15) are smoothly curved at end portion of the connector terminals (13 and 14) to be contactable with the card contacting elements (C') of the memory card (C), with predetermined heights.
The connector terminals (13) are extended to the curved portion of the terminals (13). Similarly, the connector terminals (14) are also extended to the curved portion as shown in Fig. 1.
Now referring to Fig. 2 and Fig. 3, a preferred embodiment of a card sensor switch (20) is activated when the memory card (C) is fully inserted.
Fig. 2 depicts the status of the card sensor switch (20) still being inactivated when the memory card (C) is inserted in the card reader but not yet fully inserted.
In a preferred embodiment of the present invention, the card sensor switch (20) for detecting a complete insertion of the memory card (C) is preferably mounted in an inner rear portion of the frame (10), maintaining an insulation state from other elements of the invention. The card sensor
switch (20) comprises a movable member (21) and a fixed member (22).
Both ends of the movable member (21) and the fixed member (22) are preferably fixed in the frame (10), and connection points for both members are extended to the outside of the frame (10) for mounting on a printed circuit board.
The movable member (21) is elastically deformed to be disconnected from the fixed member (22), when its lead (21 a) comes into a contact with the memory card (C). The lead (21a) extends near an inner space of the frame (10), having a J-shaped configuration for avoiding a damage of the memory card (C). The fixed member (22) has a U-shaped portion at its free end on which a mid portion of the movable member (21) is elastically contacted. The card sensor switch (20) preferably have an elastic force which is enough to maintain a predetermined level of strength to assure engagement and disengagement of the movable member (21) from the fixed member (22) to generate a clear on or off signal for a card sensing circuit.
When the memory card (C) is inserted into the frame (10) and is reached near the rear wall of the frame (10), the lead (21 a) of the movable member (21) is depressed by the memory card (C) rearwardly. As the movable member (21) moves further toward the rear wall of the frame (10), the fixed member (22) is also slightly moved in the same direction. However, an extension (22a) of the fixed member (22) is preferably bent downwardly to be engaged in a hole (18). The hole (18) limits the moving distance of the fixed member (22). Therefore, the movable member (21) can be disengaged from the fixed member (22) as the memory card (C) pushes the moveable member (21) furthermore back. When an electrical state of the card sensor switch (20) is changed and informs of the completion of the insertion of the memory card (C) through an electrical circuit, a controller (not shown) of the
card reader preferably starts a predetermined algorithm to read the information from the memory card (C). When the memory card (C) is removed from the frame (10), the movable member (21) is elastically restored from its stressed position to a rest position. When the memory card (C) is dis-engaged from the movable member (21), the fixed member (22) card sensor switch (20) is also elastically restored, and the movable member (21) and the fixed member (22) become in contact again, allowing the controller of the card reader to be on a stand-by state.
Now returning to Fig. 1 and referring to Fig. 3 and Fig. 4, a landing yoke (30) supporting one set of the connector terminals (13 and 14) is pivotably mounted with the frame (10) to minimize a sliding contact area of the memory card (C) with the frame (10) during an insertion or removal of the memory card (C). The landing yoke (30) has a plurality of slots for the set of the connector terminals (13 and 14) spaced apart from one another and is made of plastic by preferably using an injection molding. Therefore, each contacting terminal of the set of the connector terminals (13 and 14) is electrically insulated from the adjacent terminals by the landing yoke (30).
Figs. 4 and 5 show preferable schematic sectional views of the landing yoke in an initial state of the memory card (C) insertion and a completion state of the memory card insertion, respectively.
The landing yoke (30) is preferably engaged within a predetermined angular range about a hinge (31). As the memory card (C) being fully inserted, a slanted abutment (30a) is preferably pushed downward and the other end of the landing yoke (30) is raised upwardly. Accordingly, the contact points of the connector terminals (13 and 14) are also preferably raised to make good contacts with the contacting elements (C') of the memory card (C). The slanted abutment (30a) of a rear portion of the
landing yoke (30) extends beyond a rear wall (12) of the frame (10). The rear wall (12) is preferably designed to allow upward and downward movement of the landing yoke (30). In this preferred embodiment, the rear wall (12) is preferably split on both sides to allow the upward and downward movement of the landing yoke (30) therebetween. The end portions of the connector terminals (13 and 14) forwardly extending from the curved portion (15) are prefereably designed to be engaged on the landing yoke (30), so that the connector terminals (13 and 14) cannot be easily deviated from the landing yoke (30).
When the memory card (C) is inserted in the card reader and reached almost the rear wall of the frame (10) as shown in Fig. 4, the card contact elements (C') are not yet in contact with the connector terminals (13 and 14).
As the memory card (C) is pushed more toward the rear wall (12), the memory card (C) in contact with the slanted abutment (30a) of the landing yoke (30). Then, the slanted abutment (30a) is pushed downward, rotating the landing yoke (30) counter clockwise around the hinge (31).
Consequently, the curved portion (15) of the connector terminals (13 and 14) are preferably raised and elastically forced to make good connection with the contacting elements (C') of the memory card (C). When the raised curved portion (15) is contacted to the card contact elements (C'), the connecting operation is completed and the controller of the card reader can access the data stored in the memory card (C) through the card contact elements (C').
When the memory card (C) is removed from the frame (10), the slanted abutment (30a) of the landing yoke (30) is raised to its original position, and the other end of the landing yoke (30) is lowered. Consequently, the curved portion (15 ? is elastically restored and the connector terminals (13 and 14) are also elastically restored. As explained above, the card contacting
elements (C') are preferably not in contact with any other elements of the frame (10) except the contact terminals (13 and 14), avoiding any unnecessary friction, resistance, scratch, or rubbing. Therefore, the card contact elements (C') are preferably protected from wear and tear, and can last longer by the present invention than any other card reader known to those skilled in the art.
In accordance with the present invention, the operation of the card sensor switch (20) and the operation of connecting the terminals (13 and 14) to the contacting elements (C') may occur almost at the same time during the memory card insertion. However, either operation may be electrically detected by the respect to the algorithm of the card reader system.
Now referring to Fig. 6, the drawing depicts the second preferable embodiment of the present invention which includes another preferred embodiment other than the disclosed preferred embodiment above.
A configuration of a frame (40) is similar to the frame (10) shown in Figs.
1 through 5. Functionally, the frame (40) also accommodate the memory card (C) which is insertable thereinto or removable therefrom through the opening (40a).
A pair of posts (47) is preferably formed an upper member of the frame (4) and a pair of receiving holes (43) as the counterpart member of the posts (47) are formed to firmly combine the upper member and the lower member of the frame (40). Each of the post (47) is preferably extended beyond the lower member of the frame (40) in length through the receiving hole (43) when the upper member and the lower member of the frame (40) are assembled together. When the upper member and the lower member are assembled into the frame (40), portions of the posts (47) extending beyond the receiving holes (43) are preferably melted down to have a diameter larger
than the diameter of the receiving hole (43), allowing the upper member and the lower member of the frame (40) tightly assembled together. This configuration can prevent a middle portion of the frame (40) from being separated from each other, increasing a reliability of the connection between the memory card (C) and the frame (40).
In order to minimize an unwanted movement of the memory card (C) in the frame (40) and also to make sure positioning of the memory card (C) is consistent, a pair of push plates (44) for nudging the memory card (C) in one direction are preferably formed in the frame (40) as shown in Fig. 6. Each of the push plates (44) is preferably facing each other with an angle the end of push plates (44) are curved to reduce a friction with the memory card (C).
The push plate (44) is integrally molded with the frame (40) by preferably using an injection molding. It is also possible to have the push plates on both sides of the frame (40). However, the preferred embodiment of the present invention shows one push plates (44) to achieve the objects of the present invention. An optimal clearance or a gap between the memory card (C) and the frame (40) may be necessary although the push plate (44) exerts a nudging force on the memory card (C).
Fig. 7 depicts a connector terminal (50) in accordance with the second embodiment of the present invention.
As shown in Figs. 6 and 7, a plurality of a connector terminals (50) to provide electrical connection with the card contact elements (C') are preferably mounted on the frame (40) as described in the first preferred embodiment of the present invention. The connector terminals (50) are also extended out of the frame (40) as shown in the Fig. 6, and are also electrically insulated by the frame (40). The connector terminals (50) have forwardly extending portions and rearwardly extending portions which are
similar to those of the connector terminals (13 and 14) shown in Figs. 1.
Similarly, installation of the connector terminals (50) on the frame (40) and the electrical connection between the connector terminals (50) and the card terminals (C') of the memory card (C) are identical to those of the connector terminals (13 and 14) as described in the section associated with Fig. 1.
As shown in Fig. 7, each of the connector terminals (50) is provided with an external end (51), a bent portion (53), an inclined portion (54), a curved portion (52) and an inner end (55) which are integrally formed with one another. The external end (51) is preferably extended from the inclined portion (54) through the bent portion (53). The inclined portion (54) is slightly bent with a predetermined slant angle 0 with the horizontal line as shown in Fig. 7. The curved portion (52) preferably has a convex configuration for a contact with the contact elements (C') of the memory card (C). The inner end (55) is bent at the end of the curved portion (52).
The connector terminal (50) can be preferably made by a press working.
However, other methods of making the connector terminal (50) known to those skilled in the art are also feasible. It has been found that when the slant angle A is approximately 7.5°, the elastic force exerted on the memory card (C) by the curved portion (52) can be maximized. However, the angle can be changed depending on other factors, such as, the total length of the connector terminal (50), materials used, the shape of the curved portion (52), and others. It has been also found that when a radius of the bent portion (53) is about 1 mm, occurrence of the crack is minimized and intensity of the bent portion (53) is maximized. This also can be varied depending on other factors, such as the angle of the slanted portion (54), material used, the total length or size of the connector terminal (50) and others.
Firmly engaged with the external end (51) of the connector terminal (50)
is a bead (5 la) evenly protruding along the external end (51) to reinforce the external end (51). The bead (51 a) can reinforce the external end (51), and also prevents solder from flowing down along the external end (51).
It is preferable that the external end (51) be plated with tin-lead (SnPb) in a thickness of 4 u, m, the bent portion (53) be plated with nickel (Ni) in a thickness of 4 pm, and the curved portion (52) be plated with gold (Au) in a thickness of 1.2 urn. However, other thickness for each element can be possible depending on the application of the present invention.
Fig. 8 represents a sectional view of a lever in accordance with the second embodiment of the present invention.
As shown in Figs. 6 through 8, in the preferred embodiment of the present invention, the lever (60) supporting one portion of the connector <BR> <BR> <BR> <BR> <BR> terminals (50) is detachably mounted on the frame (40). The lever (60) can guide the curved portion (52) to help an even contact thereof to the memory card (C). As like the landing yoke (30) as shown in Fig. 1, the lever (60) electrically insulates the connector terminals (50) each other. However, the lever (60) is detachably fixed on the frame (40), unlike the landing yoke (30) which can be rotated when the memory card (C) is inserted into the frame (10).
The lever (60) includes a frontal and a rear beads (61) for limiting an upward deformation of the inclined portion (54) of the connector terminals (50) and a center bead (62) for limiting an upward deformation of the inner end (55). When the lever (60) is installed on the frame (40) preferably by a press-fit manner, the inclined portions (54) are pressed by the frontal and the rear beads (51) and the inner ends (55) are pressed by the center bead (62), with the curved portion (52) protruding upwardly.
The beads (61 and 62) have heights substantially identical to each other
and smaller than that of the curved portion (52) of the connector terminals (50). In this configuration, the lever (60) preferably comes into a contact with the memory card (C) only at the frontal and the rear beads (61) and the center bead (62) rather than an entire surface of the lever (60). Therefore, the friction between the memory card (C) and the lever (60) is significantly reduced and also reduce a possibility of malfunctioning due to the static electricity.
In operation, when the memory card (C) is inserted into the frame (40) and is arrived at the connector terminals (50) through the frontal bead (61), the connector terminals (50) is slightly pushed down. As the memory card (C) is further pushed in the frame (10), the curved portions (52) come into a contact with the memory card (C). Reading the data from the memory card (C) is similar to the first embodiment of the present invention as shown in Figs. 4 and 5. When the memory card (C) is removed from the frame (40), each of the connector terminals (50) starts to be elastically restored until it is limited by the frontal and the rear beads (61) and the center bead (62). As a result, the heights of the curved portions (52) can be kept substantially identical to one another.
Fig. 9 depicts another preferred embodiment of a card sensor switch (70) of the present invention.
As shown in Figs. 6 through 9, the card sensor switch (70) for detecting a complete insertion of the memory card (C) is preferably mounted in an inner rear portion of the frame (40), maintaining an insulation state from other components. As like the card sensor switch (20) described in Figs. 2 and 3, the card sensor switch (70) is provided with a movable member (71) and a fixed member (72).
The movable member (71) is elastically deformed, when its contact
extension (73) comes into a contact with the memory card (C). It is preferable that the movable member (71) and the contact extension (73) be made in a bending manner as shown in the Fig. 9. An end (71a) of the movable member (71) and an end (72a) of the fixed member (72) are bent to have a U-shaped configuration. Likewise, the end (73a) of the contact extension (73) is bent to have an L-shaped configuration which can preferably be pushed by the memory card (C) when fully being inserted.
As like he fixed member (22) shown in Figs. 2 and 3, the end (72a) of the fixed member (72) is preferably bent downwardly which is engaged within a groove (48) formed on the frame (40). The movement of the fixed member (72) is limited in a predetermined range. Therefore, when the memory card (C) is inserted into the frame (40), the movable member (71) and the fixed member (72) start to be concurrently and elastically deformed and then the fixed member (72) is stopped at a predetermined position, whereas the movable member (71) continues to be deformed. Accordingly, the movable member (71) is disconnected from the fixed member (72).
On the other hand, as shown in Figs. 6 through 8. a number of base feet (49) are formed on a lower surface of the frame (40) to keep the frame (40) spaced apart from a circuit board in a predetermined distance, avoiding any irregular surface of the printed circuit board and also preventing transformation of the frame (40). It is preferable that the height of the base feet (49) is about 0.3 mm. The base feet (49) are preferably positioned in such a manner that they are equally spaced.
Referring to Fig. 10, a hook (46) of the upper member of the frame (10) is shown in accordance with the second embodiment of the present invention.
As shown in Figs. 6 through 10, the frame (40) having the upper member and the lower member has a plurality of hooks (46) for firmly securing the
upper member to the lower member. Each of the hooks (46) has two slant surfaces (46a) and (46b) adjacent to each other. The lower slant surface (46a) can guide the insertion of the hook (46). The upper slant surface (46b) can sustain the inserted hook (46) in a proper position, holding the assembled frame of the upper member and the lower member tightly together.
Industrial Applicability The inventive connector for use in a card reader for reading data from a memory card constructed in this manner can increase an operative reliability and endurance by ensuring an exact electrical contact between the memory card and the card reader.
Although the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.
The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.