Patent Publication Number: US-2022217853-A1

Title: Universal Control Module for a Reversing Contactor

Description:
BACKGROUND INFORMATION 
     The subject matter disclosed herein relates to a control module for a reversing contactor. More specifically, an adaptable control module for contactors of varying sizes is configured to receive a single communication connection which provides control signals for both forward and reverse contactors. 
     As is known to those skilled in the art, electric motors are widely used in industrial control systems to drive a desired motion, such as a fan, pump, gearbox, linear actuator, or the like. In some applications, precise control of speed and/or position of the motor is desired. A motor drive may receive a motion profile and control the motor accordingly. In many applications, however, control of the motor may require simply that the motor be enabled or disabled to operate at rated speed according to the frequency of the line voltage to which it is connected. It may also be desirable to control the motor to run either forward or reverse. In such applications, a contactor, for single direction operation, or a pair of contactors, for dual direction operation may be provided. Control signals are provided to energize each of the contactors, closing the contacts and providing line voltage to the motor. 
     Historically, it was known to provide a pair of relays which, in turn, could be controlled by an industrial controller, such as a programmable logic controller (PLC), to control operation of a reversing motor contactor. A first relay is configured to selectively close responsive to control signals from the PLC and to provide voltage to the solenoid on the forward contactor, and a second relay is configured to selectively close responsive to control signals from the PLC and to provide voltage to the solenoid on the reverse contactor. When voltage is provided to either solenoid, the respective contactor closes, supplying line voltage to the motor. 
     As is also known to one skilled in the art, when the line voltage is a three-phase, alternating current (AC) voltage, connecting the line voltage to the motor with a first phase relationship, such as Va, Vb, and Vc, causes the motor to rotate in one direction. Connecting the line voltage to the motor in a second phase relationship, such as Va, Vc, and Vb, where two of the phases are reversed, causes the motor to rotate in the other direction. The input terminals of a forward contactor, therefore, may be wired in the first phase relationship, and the input terminals of a reverse contactor may be wired in the second phase relationship. The motor is wired to the output terminals of each contactor in a consistent relationship. Alternately, the line voltage could be wired to the input terminals of each contactor in a consistent relationship and two output terminals from the different contactors may be connected to the motor in a reverse relationship. Energizing the solenoid and closing the contacts within the respective contactors will supply the line voltage to the motor with a differing phase relationship to achieve a desired direction of rotation of the motor. 
     Because two of the phases are reversed between a forward and a reverse contactor, it would be undesirable to have both contactors closed at the same time. Closing both contactors would result in a short circuit between the two reversed phases of the line voltage. In order to avoid both contactors closing in tandem, the relays and contactors are electrically connected in a manner to prevent such an operating condition. Auxiliary contacts on each contactor open and close in tandem with the primary contacts used to supply line voltage to the motor. The auxiliary contacts are wired in series with the control signal to the control relays for each contactor requiring the reverse contactor to be open prior to closing the forward contactor and requiring the forward contactor to be open prior to closing the reverse contactor. 
     However, the additional wiring required to ensure that both contactors are not open at the same time is not without certain disadvantages. The additional relays create expense and require space in a control cabinet. The additional wiring from the auxiliary contacts to interlock the two contactors creates still further expense and is prone to wiring errors. 
     Thus, it would be desirable to provide to provide a control module for a reversing contactor that prevents both contactors from being closed in tandem without requiring the additional electrical wiring between control relays. 
     BRIEF DESCRIPTION 
     According to one embodiment of the invention, a control module for a first contactor and a second contactor defining, at least in part, a reversing contactor includes a housing, first, second, and third connectors, and an interlock circuit. The housing is configured to be mounted to the first contactor and to the second contactor. The first connector is accessible via an opening in the housing, and the first connector is configured to receive a complementary control connector. The second connector is mounted within the housing and is configured to connect to the first contactor. The third connector is mounted within the housing and is configured to connect to the second contactor. The interlock circuit is mounted within the housing and is operatively connected between the first connector and each of the second and third connectors. The complementary control connector is configured to deliver a first command signal and a second command signal to the control module. The first command signal is conducted from the first connector to the second connector via the interlock circuit to control operation of the first contactor, and the second command signal is conducted from the first connector to the third connector via the interlock circuit to control operation of the second contactor. The interlock circuit prevents the first contactor and the second contactor from closing in tandem. 
     According to another embodiment of the invention, a method for controlling a first contactor and a second contactor defining, at least in part, a reversing contactor is disclosed. A control module is mounted to the first contactor and to the second contactor, where the control module includes a housing, a first connector extending from the housing and configured to engage the first contactor, and a second connector extending from the housing and configured to engage the second contactor. A first command signal and a second command signal are received at a third connector in the control module. The first command signal controls operation of the first contactor, and the second command signal controls operation of the second contactor. The first command signal and the second command signal from the third connector are transmitted to an interlock circuit mounted within the housing. The interlock circuit verifies that the second contactor is open prior to transmitting the first command signal to the first contactor via the first connector and verifies that the first contactor is open prior to transmitting the second command signal to the second contactor via the second connector. 
     According to another embodiment of the invention, a control module for a first contactor and a second contactor defining, at least in part, a reversing contactor, includes a housing, a first, second, and third connector, and a first and second circuit board. The housing is configured to be mounted to the first contactor and to the second contactor. The first connector is configured to receive a complementary control connector via a first opening in the housing. The first circuit board is mounted within the housing, and the second connector is mounted to the first circuit board. The second connector extends through a second opening in the housing and is configured to connect to the first contactor. The second circuit board is mounted within the housing, and the third connector is mounted to the second circuit board. The third connector extends through a third opening in the housing and is configured to connect to the second contactor. The complementary control connector is configured to deliver a first command signal and a second command signal to the control module. The first command signal is conducted from the first connector to the second connector to control operation of the first contactor, and the second command signal is conducted from the first connector to the third connector to control operation of the second contactor. The housing has an adjustable width and is configured to mount to first and second contactors of varying widths. 
     These and other advantages and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various exemplary embodiments of the subject matter disclosed herein are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which: 
         FIG. 1  is an isometric view of a reversing contactor and a control module according to one embodiment of the invention; 
         FIG. 2  is a schematic representation of a reversing contactor and a control module according to one embodiment of the invention; 
         FIG. 3  is a front elevation view of the control module of  FIG. 1 ; 
         FIG. 4  is bottom plan view of the control module of  FIG. 1 ; 
         FIG. 5  is a rear elevation view of the control module of  FIG. 1 ; 
         FIG. 6  is top plan view of the control module of  FIG. 1 ; 
         FIG. 7  is a front elevation view of the control module of  FIG. 1  with the housing extended; 
         FIG. 8  is bottom plan view of the control module of  FIG. 1  with the housing extended; 
         FIG. 9  is a rear elevation view of the control module of  FIG. 1  with the housing extended; 
         FIG. 10  is top plan view of the control module of  FIG. 1  with the housing extended; 
         FIG. 11  is partial perspective view illustrating the circuit boards and panels of the control module of  FIG. 1 ; and 
         FIG. 12  is a schematic representation of an industrial controller connected to multiple contactors and multiple control modules. 
     
    
    
     In describing the various embodiments of the invention which are illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the word “connected,” “attached,” or terms similar thereto are often used. They are not limited to direct connection but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art. 
     DETAILED DESCRIPTION 
     The various features and advantageous details of the subject matter disclosed herein are explained more fully with reference to the non-limiting embodiments described in detail in the following description. 
     The subject matter disclosed herein describes a control module for a reversing contactor that prevents both contactors from being closed in tandem without requiring the additional electrical wiring between control relays. The control module includes a housing configured to mount to the forward contactor and to the reverse contactor of a reversing contactor. The control module is configured to receive a control connector, where the control connector delivers a first command signal for the forward contactor and a second command signal for the reverse contactor. According to one embodiment of the invention, the control module includes a first connector, accessible through an opening in the front of the housing, which is configured to receive the control connector. Second and third connectors extend from the rear of the housing and are configured to engage the forward and reverse contactors. It is contemplated that the second and third connectors may extend through openings in the rear of the housing or be mounted to the rear of the housing with electrical connections established to the connectors within the housing. 
     The control module is configured to eliminate external wiring which was previously required to interlock the forward and reverse contactors, preventing them from being activated in tandem. An interlock control circuit is included within the housing of the control module. The interlock control circuit is configured to receive the first and second command signals from the first connector. According to one embodiment of the invention, the first and second command signals may be discrete signals corresponding to a forward command or to a reverse command. According to another embodiment of the invention, the control module may be configured to connect to an industrial network via the first connector and may include a network interface to extract the forward and reverse commands from data packets transmitted via the industrial network. The interlock control circuit may also receive feedback signals from the forward and reverse contactors via the second and third connectors, where the feedback signals indicate whether the contactor is open or closed. The interlock circuit is configured to use the forward and reverse commands as well as the feedback signals to prevent both the forward and reverse contactors from being closed in tandem. The interlock circuit transmits the forward and reverse commands to the forward and reverse contactors to close the respective contactor. 
     The control module is also configured to mount to contactors having different physical sizes. The forward and reverse contactors may be configured to control motors having different current ratings. As a result, the forward and reverse contactors may similarly be configured for different current ratings. As the current rating of a device increases, the wire/conductor size as well as the physical size of other components typically increases as well. As a result, the physical size of the contactor increases to accommodate the increased current rating. The forward and reverse contactors are typically arranged in a side-by-side configuration for a reversing contactor. The control module is configured to mount to the forward and reverse contactors by engaging the second and third connectors with complementary connectors on each of the forward and reverse contactors. Because the size of the forward and reverse contactors changes, the control module is configured to have a variable width. The housing may be configured as a telescoping housing, where one portion of the housing is fixed and a second portion of the housing slides with respect to the fixed portion of the housing to adjust the width of the control module. The second connector may be mounted in the fixed portion of the housing and the third connecter may be mounted in the second portion of the housing, such that the spacing between the two connectors which engage the contactors may be varied according to the physical size of the contactors. 
     Turning initially to  FIG. 1 , a reversing contactor  10  and a control module  50  according to one embodiment of the invention are illustrated. The reversing contactor  10  is made up of a pair of individual contactors. A first contactor  20  controls one direction of rotation of a motor, and a second contactor  30  controls an opposite direction of rotation of a motor. For convenience, the first contactor  20  will be discussed herein as the forward contactor and the second contactor  30  will be discussed herein as the reverse contactor. The directions are not intended to be limiting and it is understood that the first contactor  20  may be configured to control reverse rotation of the motor and the second contactor  30  may be configured to control forward rotation of the motor. 
     With reference also to  FIG. 2 , each contactor  20 ,  30  is configured to selectively supply line voltage  15  to a motor when commanded. As shown in  FIG. 2 , the forward contactor  20  receives a three-phase line voltage  15  at input terminals  22  of the forward contactor. For the forward contactor  20 , the three-phase line voltage is connected in a positive sequence with phase A connected to a first input terminal, L 1 ; phase B connected to a second input terminal, L 2 ; and phase C connected to a third input terminal, L 3 . The reverse contactor  30  also receives the three-phase line voltage  15  at input terminals  32  of the reverse contactor. For the reverse contactor  30 , the three-phase line voltage is connected in a negative sequence with phase A connected to a first input terminal, L 1 ; phase C connected to a second input terminal, L 2 ; and phase B connected to a third input terminal, L 3 . The output terminals of each contactor  20 ,  30  may be connected to a motor (not shown). According to the illustrated embodiment, the output terminals  24  (U, V, and W) of the forward contactor  20  are connected to the output terminals  34  (U, V, and W) of the reverse contactor  30 . The output terminals are then connected to a motor. Internal to each contactor  20 ,  30  the input terminals  22  or  32  are selectively connected to the output terminals  24  or  34  to supply the line voltage  15  to the motor. When the line voltage  15  is supplied in the positive sequence through the forward contactor  20 , the motor is controlled to rotate in the forward direction, and when the line voltage  15  is supplied in the negative sequence through the reverse contactor  30 , the motor is controlled to rotate in the reverse direction. As will be discussed in more detail below, the control module  50  is configured to enable only one of the two contactors  20 ,  30  at a time. 
     With reference also to  FIGS. 3-6 , the control module  50  includes a housing  52  having a front surface  51  and a rear surface  53  opposite the front surface. A pair of opposing side surfaces  55 ,  57  extend between the front surface  51  and the rear surface  53 . The housing  52  also includes a top surface  59  and a bottom surface  61  opposite the top surface. Relational terms such as front, rear, top, bottom, left, right, side, upper, lower, and the like are not intended to be limiting. The relational terms are utilized herein with respect to the illustrated embodiments for ease of description. It is understood that the control module  50  and the contactors  20 ,  30  may be mounted in different orientations, resulting in different relational terms describing like features. 
     The housing  52  is a telescoping housing to vary the width of the housing and further includes a first portion  54  and a second portion  56 . According to the illustrated embodiment, the first portion  54  is considered to be a fixed portion and the second portion  56  is movable with respect to the first portion. As shown in  FIGS. 3-6 , the second portion  56  is slid into a first position where the second portion  56  is located generally within the front of the housing. When the second portion  56  is in the first position, the housing  52  has a first width, W 1 . As shown in  FIGS. 7-10 , the second portion  56  is slidably moved into a second position where the second portion  56  protrudes from one side  57  of the housing  52 . When the second portion  56  is in the second position, the housing has a second width, W 2 . The two sets of figures illustrate the second portion  56  either fully retracted ( FIGS. 3-6 ) or fully extended ( FIGS. 7-10 ). It is contemplated that the second portion  56  may be positioned at any position between the fully retracted or fully extended positions. Because the width of the contactors  20 ,  30  vary based on the style and/or rating of the contactor, the width of the control module  50  is adjustable to fit on different contactors. 
     The variable width of the control module  50  allows the mechanical and electrical connections to be made between the control module  50  and the contactors  20 ,  30  on contactors of varying widths. Each control module  50  includes a first movable connector  66  and a second movable connector  68 . The movable connectors  66 ,  68  are identified as such because they may be configured to detect motion of a plunger on the contactor to which they are mounted. As discussed in more detail below, the moveable connector may include an electrical, mechanical, optical, or other detection method for detecting the state of the contactor  20 ,  30 . The first movable connector  66  is configured to be inserted into a complementary receptacle on the forward contactor  20 , and the second movable connector  68  is configured to be inserted into a complementary receptacle on the reverse contactor  30 . Each movable connector  66 ,  68  establishes the electrical connections between the control module  50  and the forward and reverse contactors  20 ,  30 . The movable connectors  66 ,  68  may also serve, in part, to establish a mechanical connection between the control module  50  and the forward and reverse contactors  20 ,  30 . 
     Additional stationary connectors are provided to establish the mechanical connection between the control module  50  and the contactors  20 ,  30 . The stationary connectors are identified as such because they are not detecting motion. The stationary connectors provide a mechanical connection between the control module  50  and the contactors  20 ,  30  and may also include, for example, a spring clip to establish an electrical connection between the control module  50  and each of the forward and revers contactors  20 ,  30 . A first pair of stationary connectors  72  are provided on a first panel  70  on the rear of the control module  50 , and a second pair of stationary connectors  82  are provided on a second panel  80  on the rear of the control module  50 . Each of the stationary connectors  72 ,  82  are formed as a tab protruding from the rear surface  53  of the housing  52 . A complementary slot on each contactor  20 ,  30  is configured to receive the tab. Each connector  72 ,  82  may have, for example, a hook on the end of the tab, where the connectors  72 ,  82  on the control module  50  are inserted into slots on the contactors  20 ,  30  and pressed downward to engage the hooks on the housing of the contactor. Optionally, the connector  72 ,  82  may have a tab that is deflected from its original position as the connector is inserted through an opening on the contactor  20 ,  30 . The connecter may be made of a resilient material such that the tab returns to its original position after being inserted through the opening on the contactor  20 ,  30  positively retaining the control module  50  to the contactor. It is contemplated that still other configurations of stationary connector  72 ,  82  and complementary receptacle on the contactor  20 ,  30  may be utilized without deviating from the scope of the invention. The first pair of stationary connectors  72  are configured to plug into the forward contactor  20 , and the second pair of stationary connectors  82  are configured to plug into the reverse contactor  30 . At least one of the first panel  70  and the second panel  80  are slidably adjusted with respect to the housing  52  to vary the width of the control module  50 . The slidable panel, or panels, are spaced apart at a distance such that the first panel  70  may engage the forward contactor  20  and the second panel  80  may engage the reverse contactor  30 . At least one of the movable connectors  66 ,  68  and one of the stationary connectors  72 ,  82  are mounted to the slidable panel, allowing a spacing between the pair of movable connectors  66 ,  68  and between the pair of stationary connectors  72 ,  78  to be adjusted and then the control module  50  is press-fit onto the contactors such that the movable connectors  66 ,  68  and the stationary connectors  72 ,  82  on the control module engage the complementary connectors on the contactors to retain the control module  50  to the contactors. 
     In operation, the control module  50  receives the command signals for controlling operation of the reversing contactor  10  and manages activation of the first and second contactors  20 ,  30  to ensure that the contactors are not energized in tandem. With reference again to  FIGS. 1 and 2 , a connector  90  is accessible via an opening  63  in the front surface  51  of the housing  52 . According to one embodiment of the invention, the connector  90  may be configured to receive discrete signals on individual pins  91  in the connector. As illustrated in  FIG. 2 , a ribbon cable  105  may be provided to conduct command signals to the control module  50  and to transmit feedback signals from the control module  50 . A first conductor  110  in the ribbon cable  105  may supply control power to the control module  50 . The control power may be, for example, twenty-four volts (24 VDC), forty-eight volts (48 VDC) or any other suitable control voltage according to the application requirements. A second conductor  112  in the ribbon cable  105  may be used to conduct the state of the forward contactor  20 , and a third conductor  114  in the ribbon cable  105  may be used to conduct the state of the reverse contactor  30 . A fourth conductor  116  may provide a common connection for both status signals conducted in the second and third conductors. A fifth conductor  118  in the ribbon cable  105  may provide a first command signal to the control module  50 , where the first command signal controls operation of the forward contactor  20 . A sixth conductor  120  in the ribbon cable  105  may provide a second command signal to the control module  50 , where the second command signal controls operation of the reverse contactor  30 . A seventh conductor  122  in the ribbon cable  105  may provide a common reference for both command signals conducted in the fifth and sixth conductors. 
     According to another embodiment of the invention, the connector  90  may be configured to connect to an industrial network. The control module  50  may include a network interface operative to receive data packets from and transmit data packets via the industrial network. The status signals for each contactor  20 ,  30  may be inserted into a data packet and transmitted from the control module  50  and the command signals may be received in a data packet and extracted by the network interface for use in the control module  50 . 
     Turning next to  FIG. 12 , an exemplary environment is illustrated in which a pair of reversing contactors  10  are included. An industrial controller  200 , such as a PLC, includes a power supply module  205 , a processing module  210 , a network module  215 , an input module  220 , and an output module  225 . It is contemplated that the industrial controller  200  may take many different configurations and include various additional modules and/or various combinations of the illustrated modules. A network cable  230  connects the network module  215  to a gateway  11 . The gateway  11  may be located within the same control cabinet or at a remote location in a separate control cabinet from the industrial controller  200 . The gateway receives data packets from then network module  215  according to the protocol for the industrial network and extracts data to be transmitted via discrete signals on a ribbon cable  105  to the reversing contactors  10 . A first reversing contactor  10 A controls operation of a first motor  250 A, and a second reversing contactor  10 B controls operation of a second motor  250 B. The processing module  210  is configured to execute a control program to generate forward and reverse command signals for each motor  250 A,  250 B and transmit the command signals via the network module  215  and the network cable  230 . Each control module  50 A,  50 B receives the status of the contactors  20 ,  30  and transmits the status to the gateway  11 , where the gateway inserts the status into a data packet transmitted back to the processing module  210  via the network module  215 . 
     With reference again to  FIG. 2 , the first and second command signals are received at the connector  90  of the control module  50  and are then transmitted to a control circuit  152 . The control circuit  152  may include the network interface if the control module  50  is configured to receive the command signals from an industrial network. The control circuit  152  also includes an interlock circuit which is used to prevent the control module  50  from closing both the forward contactor  20  and the reverse contactor  30  in tandem. With reference also to  FIG. 11 , the first panel  70  includes a first printed circuit (PC) board  150 , and the second panel  80  includes a second PC board  170 . The first PC board  150  includes a first set of terminals  154 , and the second PC board  170  includes a second set of terminals  174 . Each set of terminals  154 ,  174  may include pins extending from the respective PC board and require a cable  180  be soldered to the pins. Optionally, the terminals  154 ,  174  may be part of a first half of a connector and the cable  180  may have the second half of the connector mounted to each end, where the cable  180  is then attached via the connector. The cable  180  conducts signals between the two circuit boards as required and has a loop, allowing for two PC boards to remain connected as the first panel  70  and second panel  80  are slidably adjusted within the housing  52  of the control module  50 . 
     The interlock circuit within the control circuit  152  receives feedback signals corresponding to the present operating state of both the forward contactor  20  and the reverse contactor  30 . According to one embodiment of the invention, the forward contactor  20  and the reverse contactor  30  each include an auxiliary contact configured to provide an output signal corresponding to whether the contact is open or closed. The output signal may be conducted from the forward contactor  20  to the control module  50  via the first movable connector  66  and from the reverse contactor  30  to the control module via the second movable connector  68 . These feedback signals are then transmitted from the respective connectors with the contactors to the interlock circuit. 
     According to another embodiment of the invention, the control module  50  includes alternate methods of detecting the state of the forward and reverse contactors  20 ,  30 . Each contactor includes a plunger which is typically viewable from the front of the contactor. When the contactor is off, or de-energized, the plunger is pushed outward, toward the surface of the contactor to which the control module  50  mounts. When the contactor is on, or energized, the plunger is drawn into the contactor, away from the surface of the contactor to which the control module  50  mounts. It is contemplated that the either the rear surface  53  of the control module  50  or each movable connector  66 ,  68  may include an additional apparatus to detect the state of the contactors  20 ,  30  to which the control module  50  is mounted. For example, a microswitch may be positioned on the rear of the control module or within the movable connector and extending from the control module a sufficient distance, such that the microswitch is closed by the plunger when the contactor is de-energized and the microswitch is open as a result of the plunger being drawn into the contactor when the contactor is energized. Optionally, the control module  50  may, in turn, include a second plunger configured to engage the first plunger, where the second plunger travels in and out with the plunger in the contactor  20 ,  30 . The control module  50  may include any suitable detection means internal to the control module  50  to detect the change in position of the second plunger. According to still another option, the control module  50  may include an optical sensor, where the optical sensor emits a signal toward the end of the plunger. The optical sensor may use, for instance, a time-of-flight calculation to detect how long light emitted from the sensor takes to return to the sensor to determine the present state of the plunger in the contactor. Any of the detection apparatus may generate a suitable feedback signal to the interlock circuit to indicate the present operating state of each contactor  20 ,  30 . 
     The interlock circuit may include integrated circuits (ICs) mounted to either the first circuit board  150  or the second circuit board  170 . The ICs may include digital logic which utilizes the feedback signals from the contactors  20 ,  30  or from the detection circuits and the command signals corresponding to desired operation of the contactors  20 ,  30  to prevent both contactors from being closed in tandem. For instance, when the control module  50  receives the first command signal to close the forward contactor  20 , the digital logic may require that the feedback signal from the reverse contactor  30  indicate that the reverse contactor is open before transmitting the first command signal to the first movable connector  66  and, in turn, to the forward contactor  20 . Similarly, when the control module  50  receives the second command signal to close the reverse contactor  30 , the digital logic may require that the feedback signal from the forward contactor  20  indicate that the forward contactor is open before transmitting the second command signal to the second movable connector  68  and, in turn, to the reverse contactor  30 . Thus, the interlock circuit included in the control circuit  152  of the control module  50  replaces the external wiring and external relays previously required for a reversing contactor. Further, a single connector  90  is plugged into the control module  50  to provide for control of both the forward contactor  20  and the reverse contactor  30 , thereby simplifying wiring which will reduce assembly time and reduce the potential for wiring error. 
     It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. 
     In the preceding specification, various embodiments have been described with reference to the accompanying drawings. It will, however, be evident that various modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the broader scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.