Abstract:
An interface circuit having releasable electrical connectors and as little as a single relay providing a standardized connection between panel controls intended for three-wire, two-wire or combination three-wire/two-wire control and a motor drive or motor controller. In this way, greatly simplified manufacturing of control cabinets may be provided with variations in control strategy being implemented simply by the provision of different panel controls having prewired harnesses and connectors.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to systems incorporating “motor power units” including motor soft starters and motor drives as are used to control industrial motors, and in particular to an interface circuit that simplifies the assembly of systems incorporating motor power units. 
         [0002]    The sophisticated control of large electrical motors used in industry and manufacturing may be provided through the use of an electronic “motor drive” or “motor controller” (herein collectively termed “motor power units”) having solid-state power processing circuitry controlled by microprocessor circuitry receiving control signals to start and stop the motor while providing overload and for motor drives, short circuit protection functions. An example advanced feature implemented by motor power units is a “soft start” where power is applied gradually to the motor after a start command is received to reduce surge currents and mechanical shock to attached equipment. Overload and short circuit protection functions, when provided, may not only disconnect the motor but also may provide current limiting and power management functions. 
         [0003]    In practice, motor power units are normally incorporated into a metal control cabinet used to hold and interconnect the motor power unit and other circuit elements such as circuit breakers and disconnect switches. The control cabinet may have an enclosing front panel serving as mounting point for panel controls (such as switches and indicator lights) providing an interface with the motor power unit and associated circuitry. 
         [0004]    The panel controls may include one or more electrical switches used to provide signals to the motor power unit to start and stop the motor being controlled. Such panel controls may be implemented in a number of different forms. In a “two-wire” system, a multiposition switch connects to the motor controller to “start” the motor in a first position and “stop” the motor in a second position. In a “three-wire” system, two independent momentary-contact pushbuttons may be used. A “start” pushbutton starts the motor when it is pressed. The motor remains running when the start pushbutton is released until a “stop” pushbutton is pressed. 
         [0005]    Variations on the two-wire system includes a three-state “hand/off/auto” system which allows the incorporation of remote control to the motor (auto) as well as a manual run state (hand) and stop state (off). Another variation may combine two-wire and three-wire control. 
         [0006]    Motor power units typically include separate “start” and “stop” input terminals to receive commands from the panel controls. The different control systems (two-wire, three-wire, etc.) may be implemented by using different panel controls and changing the wiring pattern between the panel controls and the motor power unit. Different control configurations can require many different wiring patterns increasing the complexity of manufacture and the possibility of error in the assembly of control cabinets. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention is an electrical circuit that provides a standardized interface circuit between the panel controls and the motor power unit. The standardized interface circuit allows a wide variety of different control configurations to be implemented simply by attaching prewired panel controls for each of the various control strategies to a single common interface connector of the standard interface. In this way the standardized interface circuit permits pre-assembly of the control cabinet, motor power unit, and motor power unit harness for a wide variety of configurations while allowing variation in configuration to be provided simply by selection of prewired panel controls that may simply connect to the standardized interface circuit, for example, with pre-marked electrical connectors. 
         [0008]    Specifically, in one embodiment, the invention provides an interface system connecting panel controls to a motor power unit, the interface system having a relay and a connector providing a first, second, third, and fourth interconnection point. The first interconnection point provides power; the second interconnection point connects to a relay coil of a relay; the third interconnection point communicates with the second interconnection point through a first normally-open relay contact of the relay; and the fourth interconnection point communicates with the second interconnection point through a two-terminal socket adapted to receive remotely controlled contact. A second normally-open relay contact of the relay communicates with a start input of the motor power unit so that prewired panel control switches for each of two-wire and three-wire controls of the motor power unit may alternately be connected through the releasable connector to the motor power unit without alteration of the interface circuit to provide two-wire and three-wire control of the motor power unit. 
         [0009]    It is thus a feature of at least one embodiment of the invention to eliminate the complexity of custom wiring of a motor power unit two controls through the use of an interface that allows the selection of the controls to also select the desired control strategy. 
         [0010]    The interface system may further include a panel control electrical switch prewired to a harness terminating in a first plug and wherein the connector of the interface system is a corresponding second plug adapted to receive a first plug. 
         [0011]    It is thus a feature of at least one embodiment of the invention to allow the selection of the control strategy to be implemented with a simple attachment of electrical connectors without complexity or possible error that can occur from point-to-point wiring. 
         [0012]    The panel control electrical switch maybe prewired to provide two-wire control of the motor power unit. 
         [0013]    It is thus a feature of at least one embodiment of the invention to provide an option of common two-wire control. 
         [0014]    For two-wire control, the panel control electrical switch may be a three-way switch having a pole connected to the first interconnection point, one throw connected to the second interconnection point, one throw connected to the fourth interconnection point and a remaining throw unconnected. 
         [0015]    It is thus a feature of at least one embodiment of the invention to provide a standard connection that can accommodate a three-way switch (for hand/off/auto two-wire control) with one uncommitted interconnection point. 
         [0016]    Alternatively, the panel control electrical switch maybe prewired to provide three-wire control of the motor power unit. 
         [0017]    It is thus a feature of at least one embodiment of the invention to alternately permit common three-wire control using the standard interface. 
         [0018]    For three-wire control, the panel control electrical switches may provide a series-connected normally-closed and normally-open pushbutton communicating between the first interconnection point and the second interconnection point with the connection between the pushbuttons communicating with the third interconnection point. 
         [0019]    It is thus a feature of at least one embodiment of the invention to permit three-wire control in a standard connector by changing a single uncommitted interconnection point. 
         [0020]    The panel control may further provides a three-way switch having a pole and one throw connected in series between the first interconnection point and the series-connected normally-closed and normally-open pushbuttons, a second throw connected to the fourth interconnection point, and the third throw unconnected. 
         [0021]    It is thus a feature of at least one embodiment of the invention to permit combined two-wire and three-wire control by using each of the interconnection points of the standard interface. 
         [0022]    The second plug may include an indicium matching with the indicium associated with the corresponding first plug. For example, the indicium corresponding to the first plug may be a colored sleeve surrounding the harness and the indicium of the second plug is a corresponding color. 
         [0023]    It is thus a feature of at least one embodiment of the invention to permit configuration of the control system for two-wire or three-wire control simply by selecting panel controls and assembling them according to pre-established color codes. 
         [0024]    The interface system may further include a socket for receiving a lamp connected to contacts of the motor power unit. 
         [0025]    It is thus a feature of at least one embodiment of the invention to extend the concept of the present invention to the arbitrary provision of indicator lights and the like. 
         [0026]    The second normally-open relay contact may communicate directly with the start input of the motor power unit or may control a second relay coil having a normally-open relay contact communicating power to the start input of the motor power unit. 
         [0027]    It is thus a feature of at least one embodiment of the invention to permit the interface to be used with motor power units that are susceptible to race conditions between the start and stop buttons as well as those that are un-sensitive to race conditions. 
         [0028]    The interface system may further include a third normally-open contact of the relay communicating between the fourth interconnection point and the second interconnection point. 
         [0029]    It is thus a feature of at least one embodiment of the invention to provide an additional relay contact for the handling of logic when a race condition may be exhibited by the motor power unit. 
         [0030]    These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0031]      FIG. 1  is a front view of a control cabinet suitable for use with the present invention; 
           [0032]      FIG. 2  is a view similar to  FIG. 1  showing the control cabinet open showing a motor power unit and the interface of the present invention, and showing example prewired panel controls; 
           [0033]      FIG. 3  is a block diagram of the interface of  FIG. 1  together with three prewired panel control configurations for implementing two- and three-wire and combination two- and three-wire control strategies by attachment of the panel control configurations to a standardized connector assembly; 
           [0034]      FIG. 4  is a fragmentary detailed schematic of the interface of  FIG. 1 ; 
           [0035]      FIG. 5  is a figure similar to that of  FIG. 4  showing an alternative configuration for use when the motor power unit is sensitive to timing (race) conditions; 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0036]    Turning initially to  FIG. 1 , an industrial enclosure  10  has a metal or plastic housing  11  having removable cover  13  openable to provide access to the inside of the housing  11  and to devices mounted within the housing  11 . Optionally, the housing  11  may include, for example, a hinged door or removable panel to provide access to the inside of the housing  11 . Still other configurations of the housing may be utilized without deviating from the scope of the invention. 
         [0037]    The housing  11  includes a number of externally accessible panel controls  20  mounted to the front surface cover  13 . According to the illustrated embodiment, the externally accessible panel controls  20  include an indicator lamp  22 , a start/stop switch having a momentary contact pushbutton  24   a,  which is pressed to start a device, and a second momentary contact pushbutton  24   b,  which is pressed to stop the device, and an emergency stop pushbutton  30 . Alternatively or in addition, the panel controls  20  may include a three positioned hand/off/auto switch as will be discussed below. The externally accessible panel controls  20  provide an interface to an operator. Devices such as switches, pushbuttons, dials, and the like may be mounted to the housing  11  to receive input from the operator, and devices such as lamps, displays, speakers, and the like may be mounted to the housing  11  to provide audio or visual indications to the operator. It is contemplated that numerous combinations and configurations of devices may be provided on various surfaces of the housing  11  according to an application&#39;s requirements without deviating from the scope of the invention. 
         [0038]    Turning next to  FIG. 2 , the industrial enclosure  10  is illustrated with the cover  13  removed from to reveal the back panel  12 . The back side of each of the externally accessible panel controls  20  is visible and extends through the front surface of the cover  13  such that electrical connections to each of the externally accessible panel controls  20  are made within the industrial enclosure  10 . The interior of the industrial enclosure  10  also has multiple internally mounted electronic devices  14  contained therein. According to the illustrated embodiment, one of the internally mounted electronic devices  14  is a transformer  72 . The transformer  72  is configured to receive a voltage at a first level at input terminals and provide a voltage at a second level at the output terminals. For example, a 230 or 460 VAC voltage may be supplied to the industrial enclosure  10  and connected to the input terminals of the transformer  72 , and a 110 VAC voltage may be provided at the output terminals of the transformer to operate the a motor power unit  38  such as a motor drive or motor soft starters and/or the indicator lamp  22 . Example motor power units  38  suitable for use with the present invention include motor controllers available from Rockwell Automation under the trade designator SMC™ and motor drives under the trade designator of PowerFlex®. Other components may also be incorporated into the control cabinet  10  including for example overload relays, disconnect switches, circuit breakers and the like. 
         [0039]    An integral protective block  15 , including fuses, is mounted to the illustrated transformer  72 . Optionally, the protective block  15  may be provided and mounted separately from the transformer  72  and/or include a circuit breaker or a combination of fuses and circuit breakers. Another of the internally mounted electronic devices  14  is a motor power unit  38  which may be energized or de-energized by the connecting the  110  VAC voltage from the output of the transformer  72  to the appropriate terminals of the motor power unit  38 . The indicator light  22  may illuminate when power is present at the secondary of the transformer  72  as will be discussed below. 
         [0040]    According to the illustrated control cabinet  10 , when the start button  24   a  is pressed a signal is provided to the motor power unit  38  causing a control motor to operate. In two-wire control, power is maintained, keeping the controlled device operational, until either the stop button  24   b  or the emergency stop button  17  is pressed. The stop button  24   b  may initiate, for example, a controlled shut down, of the controlled device, and the emergency stop button  17  may immediately remove power from the controlled device and further set a brake, insert a pin, or, by any other suitable method, cause, the controlled device to come to an immediate stop. 
         [0041]    Electrical conductors, of various harnesses  26  are provided within the control cabinet  10  to connect the panel controls  20  and interface circuit  40  mounted on the back panel  12 . According to the illustrated embodiment, each of the externally accessible panel controls  20  has a first end of a harness  26  prewired to the panel control  20  of sufficient length to span between the cover  13  in the open position and the interface circuit  40 . A second end of each of the harnesses  26  is connected to the interface circuit  40 . 
         [0042]    Each of the harnesses  26  for one of the externally accessible panel controls  20  is bundled into a single group. According to the illustrated embodiment, a color-coded sleeve  34 , for example, a braided sheath, is provided that slides over each of the conductors of the harnesses for one of the panel controls  20  as held by a cable tie. The color-coded sleeve  34  extends along a majority of the length of the harness  26  leaving enough length the remaining ends of the harnesses  26  extending through the color-coded sleeve  34  to be connected to a plug connector  36 . Optionally, the color-coded sleeve may be a wire loom, wire wrap, or other suitable outer jacket or material to hold the conductors of the harness  26  together in a group. 
         [0043]    The interface circuit  40  may be assembled on a DIN rail  41  holding a set of DIN rail mounted terminal blocks  19  and at least one DIN mounted relay  25  that may be interconnected by point-to-point wiring  21  and or enter terminal block jumpers performed in a factory environment to implement interface circuit  40  as will now be described. Terminal block suitable for this purpose are available from Rockwell Automation under the Trade Designator 1492 “Spring Clamp Connection Terminal Blocks” and related family devices. 
         [0044]    The terminal blocks  19  may provide for sockets to receive the plugs  36  so that the panel controls  20  may be attached to the interface circuit  40  with a simple plug connection after matching colors on the color-coded sleeves with corresponding colored indicia  23  placed on the terminal blocks. A system of simplifying the matching of connectors  43  and  36  using color-coded harnesses  32  is described in U.S. Pat. No. 9,225,099 assigned to the assignee of the present invention and hereby incorporated by reference in its entirety. 
         [0045]    Referring also to  FIG. 3 , the interface circuit  40  may communicate with the motor power unit  38  by means of a harness  42  providing connections to a start input terminal  44  and a stop input terminal  46 , as well as various other optional contacts and inputs  48  as will be discussed. This harness  42  may be standardized for the particular motor power unit  33  and interface circuit  40  to operate without modification for a wide variety of different control strategies as will be discussed below. 
         [0046]    The start input terminal  44  and stop input terminal  46  will generally observe the following logic: 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                 Start button 
                 Stop button 
                 Action 
               
               
                   
               
             
             
               
                 0 
                 0 
                 Stop 
               
               
                 0 
                 1 
                 Stop 
               
               
                 1 
                 0 
                 Run 
               
               
                 1 
                 1 
                 Stop 
               
               
                   
               
             
          
         
       
     
         [0047]    Where the stop input terminal  46  has a negative logic where a low voltage is an assertion (1) and a high voltage is a release (0). 
         [0048]    The interface circuit  40  provides a standardized connector assembly  50  providing interconnection points  52   a - 52   d  which may receive panel controls  20  pre-configured for a variety of different control strategies. The standardized connector assembly  50  may be implemented, for example, by one or more electrical connectors attachable to the connectors  36  discussed above. 
         [0049]    In one example the panel controls  20  may be prewired to provide a three-wire panel control configuration  54 . For example, the three-wire panel control configuration  54  may provide a first through fourth interconnection terminal  56   a - 56   d  attaching respectively to the first through fourth interconnection points  52   a - 56   d.  The panel controls  20  may include a first, normally-closed, momentary-contact pushbutton  24   a  and a second normally-open momentary-contact pushbutton  24   b  connected in series between terminals  56   a  and  56   b.  The junction between the momentary-contact pushbuttons  24   a  and  24   b  may connect to terminal  56   c  and terminal  56   d  maybe left unconnected. 
         [0050]    As noted above, each of the control configurations will generally include one or more panel controls  20  prewired to a connector  36  with a harness  32  sharing a common color-coded sleeve  34 . The panel controls  20  are independently mountable on the cover  13  which provides an integrating structure. 
         [0051]    In an alternative two-wire panel control configuration  58  (adopting the same terminal numbering convention as above) a single pole three-way switch  60  may have its throw connected to terminal  56   a  and a first pole connected to terminal  56   b  (the “hand” position). A middle throw may be unconnected (the “off” position) and the remaining throw may be connected to terminal  56   d  (the “auto” position). 
         [0052]    In yet a further alternative, a combination two-wire/three-wire panel control configuration  62  (also adopting the same terminal numbering convention as above) may combine the elements of the three-wire panel control configuration  54  and two-wire panel control configuration  58  by connecting three-position switch  60  such that its throw is connected to terminal  56   a  and a first throw connects to the series connection of momentary-contact pushbuttons  24   a  and  24   b  in turn leading to terminal  56   b.  As before the junction between momentary-contact pushbuttons  24   a  and  24   b  that connect with terminal  56   c  and the remaining or third pole of switch  60  connects with terminal  56   d.    
         [0053]    Referring now to  FIG. 4 , the interface circuit  40  may receive line power  70 , for example, through a port  16  shown in  FIG. 1 . This line power  70  connects to the primary of a transformer  72  which in turn provides power to power rails  74  and  76 , the latter through an emergency stop disconnect switch  78 . A power on indicator lamp  79  may be connected across these power rails  76  and  74  provided by a panel control (e.g., similar to lamp  22 ) providing an indicator light when power is applied to the control cabinet  10 . The same transformer  72  may also provide power to the motor power unit  38  or an alternative power source may be used. 
         [0054]    Power rail  76  is provided to interconnection point  52   a  of the standardized connector assembly  50 . Interconnection point  52   b  connects to a relay coil  80  (designated SR) whose remaining terminal connects to power rail  74 . Interconnection point  52   c  may connect to interconnection points  52   b  through a contact  82 , the latter being a normally-open contact of relay SR. Interconnection points  52   d  may connect through a two-pin socket  84  with interconnection points  52   b.  This two-pin socket  84  may receive contacts  85  controlled by a remote control signal. Interconnection points  52   d  may also connect through jumper  95  with the stop input terminal  46  of the motor power unit  38 . A second normally-open contact  86  of relay SR may connect from power rail  76  to the start input terminal  44  of the motor power unit  38 . 
         [0055]    Various sockets  90  may be provide, for example, to receive lamps  22  having one socket pin connected to power rail  76  and the remaining pin connected to a contact of the motor power unit  38  so that signals may be relayed from the motor power unit  38  to the panel controls. Similarly one or more sockets  92  may be provided, for example, receiving panel controls  20  and having one pin connected the power rail  76  and the remaining pin connected to an input of the motor power unit  38  so that commands may be sent to the motor power unit  38  in optional configurations. 
         [0056]    Referring now to  FIGS. 3 and 4 , it will be appreciated that when the three-wire panel control configuration  54  is connected via the standardized connector assembly  50 , a pressing of the start momentary-contact pushbutton  24   b  will cause power to be applied to the relay SR in turn closing contact  82 . Closing of contact  82  insures that when momentary-contact pushbutton  24   b  is released, power is continued to be applied to relay SR thus providing a latching operation. Relay SR also controls contact  86  which provides power to the start input terminal  44  of the motor controller allowing the attached motor to be started. 
         [0057]    Power applied to the stop input terminal  46  is obtained via jumper  95  enabling the controller to receive commands from a communication module (not shown) via a communication network or human interface module. Otherwise, and more generally, a signal is not required, in this configuration, to the stop input  46  of the motor power unit  38  which may start and stop based solely on the presence or absence of a signal at the start input  44 . It will be appreciated that the remote control contact  85  in socket  84  may be used to lock out a starting of the motor but when closed allows starting of the motor. 
         [0058]    After the motor has started, if momentary-contact pushbutton  24   a  (acting as a stop button) is pressed, power is removed from the relay SR unlatching the contacts  82  and  86  causing the motor to stop in response to the motor power unit  38  receiving no signal at the start input terminal  44 . 
         [0059]    Referring still to  FIGS. 3 and 4 , consider instead the connection of the two-wire panel control configuration  58  as installed into the standardized connector assembly  50  using the same connection points. In this case when the switch  60  is in the “hand” position as connecting to terminal  56   b,  power will flow to relay SR closing contact  86  to apply power to the start input terminal  44  of the motor power unit  38 . This action will cause the motor to start. 
         [0060]    In this control configuration, there is no latching and when the switch  60  is moved to the “off” position, power is removed from the start input terminal  44  and the motor stops. When the switch  60  is moved to the “auto” position, power is applied to the relay SR and thus contact  86  is closed only if remote contact  85  in socket  84  is closed allowing automatic control of the motor. When the switch  60  is moved to the “auto” position and jumper  95  is present, power is applied to the stop input terminal  46  enabling the controller to receive commands from a communication module via communication network or human interface module 
         [0061]    By similar operation, the control configurations  54  and  58  may be combined into control configuration  62  to provide combined functionality. The operation of this control configuration  62  will be evident from the description provided above. 
         [0062]    Referring now to  FIG. 5 , in some cases, motor power unit  38  may be sensitive to race conditions between signals presented at the stop input terminal  46  and start input terminal  44 . This sensitivity requires that power must be applied to the stop input terminal  46  before power is applied to the start input terminal  44  in order for the start input to have effect. Near simultaneous application of power to start input terminal  44  and the stop input terminal  46 , if the stop input  46  is not clearly asserted first, will cause the start input to be ignored, undesirably leaving the motor in the stop state. 
         [0063]    For motor power units  38  sensitive to race conditions, the interface circuit  40  may be modified by the introduction of an additional relay (designated R 1 ) whose coil  94  receives power upon closure of relay contact  96  being a normally-open contact of relay SR. An additional relay contact  99  of relay SR may connect between interconnection points  52   b  and stop terminal  46 . Now when power is applied to relay coil  80  (either latched through interconnection points  52   c  or unlatched through interconnection points  52   b ) contact  99  closes providing power to the stop input terminal  46 . Relay R 1  closes activating coil  94  which then closes relay contact  100  after the normal relay delay of a mechanical relay applying power to the start input terminal  44 . Jumper  95  is installed to apply power to the stop input  46  for configurations where the controller  38  receives commands from a communication module via a communication network or human interface module. 
         [0064]    Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. When elements are indicated to be electrically connected, that connection may be direct or through an intervening conductive element. 
         [0065]    When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
         [0066]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties.