Abstract:
A method for utilizing a three-wire programming box with a motor control circuit is provided. The method includes providing a three-wire to two-wire interface. The method further includes connecting the three-wire to two-wire interface between the three-wire programming box and the motor control circuit such that the three-wire programming box communicates bi-directionally with the motor control circuit utilizing less than three connections between the three-wire to two-wire interface and the motor control circuit.

Description:
BACKGROUND OF INVENTION 
     This invention relates generally to dynamoelectric machines and, more particularly, to motor control circuits for an electronically commutated brushless direct current motor. 
     Dynamoelectric machines are utilized in many manufacturing applications. Dynamoelectric machine failures can cause lost production time, injury to personnel, and loss of capital equipment, all of which can reduce profitability. Therefore, a dynamoelectric machine manufacturer typically tests a motor before the motor leaves a production facility. An electronically commutated motor (ECM) typically includes a motor housing, a stator mounted to the housing, and a rotor shaft rotatably mounted within a bore of the stator. A rotor core is mounted on the rotor shaft and includes a plurality of permanent magnets. The stator includes a stator core including a plurality of electrically excitable windings. The stator windings generate a plurality of magnetic fields that oppose magnetic fields from the permanent magnets on the rotor. For the rotor to turn, the windings on the stator reverse polarity through commutation. A brushless commutator placed on one end of the rotor provides a signal to the stator windings to reverse polarity. In certain known ECMs, an integrated circuit times the switching of the electric currents to the stator. Frequently, a programmable chip is used with the brushless DC motor to provide multispeed capabilities. Typically, the programmable chip utilizes pulse width modulation (PWM) to control the speed of the motor. 
     Typically, the PWM input is applied through a two-wire interface in a control housing. The two-wire interface is unidirectional and does not provide feedback useful for testing purposes. Therefore, conventional motors also include a three wire bi-directional interface that a motor manufacturer uses for factory testing the motor. The three-wire interface is also in the control housing and from a customer perspective adds unnecessary lead wires to the control housing. 
     SUMMARY OF INVENTION 
     In one embodiment, a method for utilizing a three-wire programming box with a motor control circuit is provided. The method includes providing a three-wire to two-wire interface. The method further includes connecting the three-wire to two-wire interface between the three-wire programming box and the motor control circuit such that the three-wire programming box communicates bi-directionally with the motor control circuit utilizing less than three connections between the three-wire to two-wire interface and the motor control circuit. 
     In another embodiment, an interface circuit for interfacing with a motor control circuit including a first input circuit is provided. The interface circuit includes a three-wire to two-wire interface including a second input circuit electrically equivalent to the first input circuit of the motor control circuit. 
     In a further embodiment, a motor control and testing circuit includes a first input circuit, a second input circuit coupled to the first input circuit, and a microcontroller connected to the second input circuit. The circuit further includes a first output circuit coupled to the microcontroller, and a second output circuit coupled to the first output circuit. The second output circuit is connected to the first input circuit and is configured to send outputs from the microcontroller to the first input circuit. 
     In another embodiment, a motor control and testing circuit includes a first input circuit, a second input circuit coupled to the first input circuit, and a microcontroller connected to the second input circuit. The circuit further includes a first output circuit coupled to the microcontroller, and a second output circuit coupled to the first output circuit. The second output circuit is connected to the first input circuit and is configured to send outputs from the microcontroller to the first input circuit. The circuit further includes a third input circuit electrically equivalent to the first input circuit, and a comparator. The third input circuit and the first input circuit are connected to the comparator forming an impedance bridge. 
     In a further embodiment, an electrically commutated motor includes a housing, and a stator including a plurality of windings and a bore therethrough. The stator is mounted in the housing. The motor further includes a rotor shaft extending at least partially through the bore, and a rotor core mounted on the rotor shaft. The rotor core includes a plurality of magnets. The motor also includes a commutator connected to the windings, and a motor control and testing circuit connected to the commutator. The motor control and testing circuit includes a first input circuit, a second input circuit coupled to the first input circuit, and a microcontroller connected to the second input circuit. The motor control and testing circuit further includes a first output circuit coupled to the microcontroller, and a second output circuit coupled to the first output circuit. The second output circuit is connected to the first input circuit and is configured to send outputs from the microcontroller to the first input circuit. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic of a known motor control circuit. 
     FIG. 2 is a schematic of a motor control circuit according to one embodiment of the invention. 
     FIG. 3 is a schematic of the three-wire to two-wire interface shown in FIG.  2 . 
     FIG. 4 is a schematic of the impedance bridge shown in FIG.  3 . 
     FIG. 5 is a cross sectional view of a motor including the motor control circuit shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a schematic of a known motor control circuit  10  including a three-wire interface  12  and a two-wire interface  14 . Motor control circuit  10  is included within a motor housing (not shown) and both three-wire interface  12  and two-wire  14  are accessible from outside the housing. Three-wire interface  12  is bi-directional and is utilized by a motor manufacturer for factory testing purposes. Three-wire interface  12  is not used in typical motor applications and from a user&#39;s perspective is unnecessary. Rather, the typical motor application uses two-wire interface  14  to control a speed of a motor (not shown) controlled by motor control circuit  10 . Circuit  10  includes a first optocoupler  16  optically coupling a diode bridge rectifier  18  with a DC input circuit  20  providing an input to a microcontroller  22 . Microcontroller  22  outputs to a first output circuit  24  optically coupled to a second output circuit  26  by a second optocoupler  28 . Additionally, three-wire interface  12  is connected to two-wire interface  14  at a first node  30  and a second node  32 . Nodes  30  and  32  allow a factory programmer to program a programming box  34  at three-wire interface. 
     In use, an alternating current (AC) voltage signal is applied to diode bridge rectifier  18  that rectifies the signal before the signal is transmitted through optocoupler  16  and becoming a DC signal for DC input circuit  20 . DC input circuit  20  inputs the DC signal to microcontroller  22 , which controls the motor according to the DC signal as is known in the art. 
     During manufacture of a motor including control circuit  10 , the motor is tested through the use of three-wire interface  12  and a mechanical three-pin plug (not shown). Three-wire interface  12  is electrically connected to two-wire interface  14  as shown in FIG. 1, and three-wire interface  12  is also connected to second output circuit  26 . Therefore three-wire interface  12  is bi-directional in that a user receives feedback from the motor via second output circuit  26  while controlling the motor utilizing the connection to two-wire interface  14 . 
     FIG. 2 is a schematic of a motor control circuit  40  according to one embodiment of the invention. Motor control circuit  40  includes a two-wire interface  42  connected to a first input circuit  44  which is optically coupled to a second input circuit  46  by a first optocoupler  48 . In one embodiment, first input circuit  44  is a diode bridge rectifier input circuit and hereinafter thus referred. Second input circuit  46  provides inputs to a microcontroller  50 . Microcontroller  50  is connected to a first output circuit  52  which is optically coupled to a second output circuit  54  by a second optocoupler  56 . As used herein, the term microcontroller is not limited to just those integrated circuits referred to in the art as microcontrollers, but broadly refers to microcontrollers, processors, computers, microcomputers, application specific integrated circuits, and other programmable circuits. 
     Diode bridge rectifier input circuit  44  includes an unrectified input  58  and a rectified output  60 . Second output circuit  54  is connected to rectified portion  60  of diode bridge rectifier input circuit  44  by a resistor  62  and a Zener diode  64 . A three-wire programming box  66  is connected to circuit  40  via a three-wire to two-wire interface  68 . Motor control circuit  40  is mounted inside a motor (not shown in FIG. 2) and while two-wire interface  42  is accessible from exterior the motor, connections for programming box  66  are not accessible from exterior the motor as were connections for programming box  12  (shown in FIG.  1 ). Accordingly, a motor with circuit  40  has less lead wires extending from it than a motor with circuit  10  (shown in FIG.  1 ). Interface  68  is connected to second output circuit  54  and to two-wire interface  42 . Interface  68  is connected to motor control circuit  40  at a first connection  70  and a second connection  72 . 
     During operation of motor control circuit  40 , a voltage signal is applied to diode bridge rectifier input circuit  44  via two-wire interface  42 . Diode bridge rectifier input circuit  44  rectifies the AC signal before the signal is transmitted through optocoupler  48  forming a DC signal for second input circuit  46 . Second input circuit  46  inputs the DC signal to microcontroller  50 , which controls a motor (not shown in FIG. 2) according to the DC signal as is known in the art. 
     During manufacture of the motor controlled by control circuit  40 , the motor is not tested through the use of a mechanical three-pin plug because the connection to programming box  66  is not accessible from outside the motor. Rather, the motor is tested using two-wire interface  42  which is bi-directional due to resistor  62  and diode  64  connecting second output  54  to diode bridge rectifier input circuit  44  and due to interface  68  as explained below. 
     FIG. 3 is a schematic of three-wire to two-wire interface  68  (also shown in FIG.  2 ). Interface  68  includes a comparator  80  configured in an impedance bridge  82  including a first arm  84  including a first resistor  86 , and a second arm  88  including a second resistor  90 . First resistor  86  and second resistor  90  are substantially the same resistance. Impedance bridge  82  further includes a third arm  92  including a circuit  94  which is electrically equivalent to diode bridge rectifier input circuit  44  (shown in FIG.  2 ). Impedance bridge  82  also includes a fourth arm  96  that is connected to diode bridge rectifier input circuit  44  (shown in FIG. 2) via connections  70  and  72 . Comparator  80  includes an output  98  that is connected to programming box  66 . 
     In use, programming box  66  varies a voltage across a first pin  100  and a second pin  102  which are connected to both diode bridge rectifier input circuit  44  and to circuit  94 . An output of comparator  80  reflects an output of microcontroller  50  regardless of the status of diode bridge rectifier input circuit  44  because bridge  82  acts to change a reference level of comparator  80  to effectively filter out input circuit  44  utilizing circuit  94  which is electrically equivalent to input circuit  44 . In other words, comparator  80  compares the status of circuit  94  with the status of circuit  44  and the difference represents the contribution to the status of circuit  44  from microcontroller  50  fed into circuit  44  via resistor  62  and Zener diode  64  (shown in FIG.  2 ). 
     FIG. 4 is a schematic of impedance bridge  82  (also shown in FIG. 3) including first arm  84  including first resistor  86 , and second arm  88  including second resistor  90 . As explained above, impedance bridge  82  also includes third arm  92  including circuit  94 , and fourth arm  96  including circuit  44 . Comparator  80  compares circuit  94  with circuit  44 , and outputs the contribution to circuit  44  from microcontroller  50 . 
     FIG. 5 is a cross sectional view of a motor  110  including motor control circuit  40  (shown in FIG.  2 ). Motor  110  includes a housing  112  and two endshields  114  mounted to housing  112 . Endshields  114  include a plurality of bearings  116 . Motor  110  further includes a stator  118  having a bore  120  therethrough. Stator  118  is mounted to housing  112  via a back iron  122 , and includes a plurality of stator windings  124 . A rotor shaft  126  is mounted within bearings  116  and extends through bore  120 . A rotor core  128  is mounted on rotor shaft  122  and includes a plurality of permanent magnets  130 . A brushless commutator  132  is placed on an end  134  of stator and is connected to motor control circuit  40 . Brush commutator  132  reverses polarity of stator windings  124  when directed by microcontroller  50  and, thus controls the speed of motor  110 . 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.