Abstract:
A method for correctly connecting the wiring for the hall effect sensors and the motor phase terminals of a three-phase brushless DC motor to the corresponding connections on an amplifier, the method using known waveforms that describe the electrical operational characteristics of the motor and amplifier. The method comprising connecting the hall effect sensors in any order, determining two motor phase terminals that correspond to a back-electro-magnetic-force peak in the middle of a waveform for a first hall effect sensor and a third motor phase terminal that does not, determining an amplifier pin that does not carry current during the middle of a wave form for a first hall sensor input on the amplifier. The correct connection is thus determined to be between the third motor phase terminal and the identified amplifier pin. The remaining connections are determined in the same manner by repeating this process, but in relation to the other hall effect sensor waveforms.

Description:
BACKGROUND OF THE INVENTION 
     Motion control engineers have long struggled with determining the correct wiring for phase and hall sensor relationships between three phase brushless DC motors and amplifiers. The problem becomes significant for development efforts on complex machines that require a plurality of different motors, amplifiers and manufacturers to adequately satisfy motion requirements. To aggravate the problem further, there is no standard nomenclature between hall and phase connections between motor and amplifier vendors. For three hall sensor wires, there are six possible connections between the motor and amplifier. Similarly, for three phase wires, there are six possible connections between the motor and amplifier. The net result is that there are 36 possible unique wiring combinations of which only six are correct. However, once any combination has been chosen for the hall wires, the problem becomes determining which one of the six possible motor combinations is correct (it is equally valid to connect the motor first and then determine which one of the six hall combinations is correct). 
     For correct motor phasing, current must be applied to each motor phase by the amplifier at the same moment in time that the back-electro-motive-force or BEMF, measured as voltage, for that motor phase is at a peak. A mechanical analogy is firing a spark plug when the piston is at the top of its stroke. 
     Conventional phasing methods use a trial-and-error approach in which the halls are attached to the amplifier, and then the correct motor wiring is determined by finding the combination that seems to run the best. Of the six possible combinations for a single set of hall connections, three of these will result in rotation that is the opposite of the hall signal rotation pattern and will not work at all. Of the remaining three, one will not turn the motor at all (current will flow through the windings but it will produce no torque), one will run the motor at reduced torque and one will be the correct connection. Trial-and-error methods have been demonstrated to be subject to error because it is sometimes difficult to determine which combination is best without the use of a dynomometer. In many cases, two out of the six possible phase wiring combinations will appear to run the motor satisfactorily, but only one is correct. 
     Phasing problems are particularly apparent in machines, such as high speed inserting machines for mass producing mailings, which use many brushless DC servo motors. In such machines, technicians may incorrectly phase one or more motor applications. Such incorrectly phased applications can commutate improperly for several months, resulting in elevated motor temperature and occasional software initiated motor stoppages due to excessive position error. Such stoppages can be incorrectly attributed to intermittent motor encoder failures because the motor&#39;s encoder value might intermittently fail to change when the motor is commanded to perform an aggressive acceleration. However, the encoder is not to blame when the rotor has become stalled at an angular position where a commutation switch point occurred. Incorrect commutation can result in reduced generated torque at a particular rotor position and the reduced torque might not overcome the sum of the motor cogging torque and friction load torque, resulting in rotor stall. 
     SUMMARY OF THE INVENTION 
     Using the present invention, proper phase wiring between the motor and amplifier can be determined without using trial-and-error techniques. The present invention requires that the user know the BEMF waveforms and hall sensor output relationships for the motor, and the phase current output waveforms and hall sensor input relationships for the amplifier. These relationships are typically depicted as a function of the rotor positions in electrical degrees. Proper phase wiring between the motor and the amplifier can be achieved by reconciling desired rotor positions that are commonly described by the known characteristics of both the motor and amplifier. 
     In accordance with the present invention, proper phase wiring is achieved using the following steps. First, hook the three hall sensor signal wires from the motor to the amplifier in any order. Next, referring to the known characteristics of the motor, for a first selected hall sensor find out which two motor phases (and their corresponding connections) produce a BEMF peak at the same rotor position (in electrical degrees) as the middle of a peak of the waveform for the first hall sensor signal. The polarity is not important at all, as a negative peak is just as good as a positive. 
     Then, referring to the known characteristics of the amplifier, for a first hall sensor input connected to the first hall sensor in the motor, determine which two amplifier phase connection pins are intended to provide current during the middle of a peak in the waveform for the first hall sensor input signal. Again, the polarity does not matter. 
     Based on these observations, it is determined that the two identified motor phase connections should be connected to the two identified amplifier pins, but it is not known which is which. However, regardless of the polarity, it is known that the third motor phase connection needs to be connected to the third amplifier pin because they form the unused phase connection for the portion of the motor&#39;s electrical cycle under consideration. Accordingly, the third motor phase connection should be connected to the third amplifier pin. 
     Next, this process is repeated for a second selected hall sensor. Again, for another portion of the motor&#39;s electrical cycle at the middle of a peak in the waveform for the second hall sensor&#39;s signal, two sets of motor and amplifier connections will be identified as providing current. The unused phase connection for that portion of the motor&#39;s electrical cycle will also be identified. Accordingly, the unused motor phase connection should be connected to the unused amplifier pin. 
     By process of elimination, the final unconnected motor phase connection must connect to the final amplifier phase connection pin. However, if desired the above process can be repeated with respect to the third and final hall sensor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified depiction of a typical three-phase brushless DC motor and amplifier for which the present invention is applicable; 
     FIG. 2 depicts exemplary amplifier operational characteristics; 
     FIG. 3 depicts exemplary three-phase brushless DC motor operational characteristics; and 
     FIG. 4 is a table including exemplary tabulations of data from FIGS. 2 and 3 for determining proper phase connections pursuant to the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a simplified depiction of a three-phase brushless DC motor  10  and a corresponding amplifier  20  for providing power to the motor stator  14  three phase windings. Sequenced electric current supplied from amplifier  20  to the motor stator  14  windings, provides electromotive force to turn the magnetized rotor  11 . Motor  10  also includes hall sensors  12  for detecting the position of the rotor  11  as it turns. The hall sensors  12  in FIG. 1 are individually designated H 1 , H 2 , and H 3  respectively. 
     The hall sensors  12  are connected to the halls sensor inputs  21  of amplifier  20  by hall sensor wires  31 . The hall sensor inputs  21  are designated H 1 ′, H 2 ′, and H 3 ′ respectively. From rotor position signals received at hall sensor inputs  21 , amplifier  20  determines the appropriate timing for providing current to the three motor phases in order to achieve the desired torque and rotation for rotor  11 . Electric current is supplied in sequence to the phases of motor  10  from amplifier  20 , via amplifier phase connection pins  22  which connect to motor phase terminals  13  via phase power supply wires  32 . In FIG. 1, the amplifier phase connection pins  21  are designated A, B, and C, and motor phase terminals  13  are designated M 1 , M 2 , and M 3 . 
     In accordance with the present invention, correct phase wiring between motor  10  and amplifier  20  is preferably determined with reference to vendor provided information, typically be depicted as shown in FIGS. 2 and 3. Referring to FIG. 2, phase current output signal and hall sensor input signal relationships are taken from an amplifier manufacturer&#39;s application notes. The relationship between the sensor inputs (at H 1 ′, H 2 ′ and H 3 ′) and the phase current outputs (at A, B and C) are valid for all 60 degree hall, 6-step commutating amplifiers. FIG. 2 depicts the expected operational motor phase current with respect to the hall sensor inputs in terms of the position of the motor rotor  11  position in electrical degrees. In practice, amplifier vendor labels all vary and are not necessarily in logical order. 
     FIG. 3 provides the characteristics of for the three-phase brushless DC motor  10 . In FIG. 3, BEMF waveforms and hall sensor outputs are shown for the motor in terms the position of the motor rotor in electrical degrees. In FIG. 2, the BEMF voltage is depicted as would be measure between pairs of the motor terminals M 1 , M 2 , and M 3 . FIG. 2, also show the hall sensor output wave forms for the motor hall sensors H 1 , H 2 , and H 3 . 
     The steps for implementing the present invention to achieve proper phase wiring are now explained using amplifier and motor characteristics depicted in FIGS. 2 and 3. Information gathered from FIGS. 2 and 3 may be tabulated as shown in FIG. 4 in order to facilitate the method. 
     First, connect the hall sensors (H 1 , H 2 , and H 3 ) of the motor  10  to the halls sensor input terminals (H 1 ′, H 2 ′, and H 3 ′) of the amplifier  20 . The wires  31  for the halls sensor connections between the motor  10  and the amplifier  20  can be in any order. The designations of the hall sensors  12  and the respective hall sensor inputs  21  may be arbitrary, however for the purpose of this explanation, the designations are as follows: hall sensor H 1  connects to hall sensor input H 1 ′; hall sensor H 2  connects to hall sensor input H 2 ′, and hall sensor H 3  connects to hall sensor input H 3 ′. These hall sensors  12  and the respective amplifier sensor inputs  21  are listed in columns  41  and  42  of the table in FIG.  4 . 
     Next, referring to FIG. 3, for a first selected hall sensor H 1  find out which two motor phases (and their corresponding connection terminals  13 ) produce a BEMF peak at the same rotor  11  position (in electrical degrees) as the middle portion  51  of a peak of the waveform for the first hall sensor signal. The polarity is not important at all, as a negative peak is just as good as a positive. Looking at the waveform for hall sensor H 1  in FIG. 3, it is seen that the middle portion  51  of the square wave occurs at a rotor  11  position of 300-360 electrical degrees. For the same rotor  11  position in electrical degrees it can be seen that a peak  52  occurs in the BEMF waveform between terminals M 3 -M 1  when the rotor is at the position of 300-360 electrical degrees. Once again in looking at BEMF peaks, it does not matter whether the peak is positive or negative. Accordingly, for the row corresponding to hall sensor H 1 , the M 3 -M 1  terminals are listed in column  43  of FIG.  4 . 
     The reason looking at the middle of a peak of the waveforms for a hall sensor  12  is that in the middle of a high hall sensor signal during motor operation, the other two hall sensor signals are both low. This makes it much easier to find specific positions on the graphs, such as those in FIGS. 2 and 3. Also, if it is desired to determine which phases are active with an oscilloscope, the middle of any hall sensor waveform will always look the same regardless of the direction of rotation chosen (a rising hall sensor signal in one direction looks like a falling hall sensor signal if the motor is spun the other way). Using this technique, there is never a need to look at two hall sensor signals on the oscilloscope at the same time. If you look at the middle of the hall sensor signal, one at a time is always enough. 
     Alternatively, it is possible to use a portion of the hall sensor signal other than the middle, but choosing another location can add unnecessary complexity to the procedure. If another location is chosen, the direction of the rotor  11  rotation and the hall sensor signal polarity (+or −) need to be tracked in order to maintain a unique location common to both the amplifier and motor waveforms as shown in FIGS. 2 and 3. 
     For the next step, referring to FIG. 2 (the characteristics of the amplifier  20 ), for selected hall sensor input H 1 ′, determine which two amplifier phase connection pins (A, B or C) are intended to provide current during the middle portion  61  of a peak in the waveform for the H 1 ′ hall sensor input signal. Again, the polarity does not matter. From FIG. 2 it can be seen that amplifier connection pins A and C are providing current during the 60-120 electrical degree rotor position which corresponds to the middle portion of the square waveform for H 1 ′. Accordingly, for the row corresponding to hall sensor H 1  and hall sensor input H 1 ′, amplifier connection pins A and C are listed in column  44  of FIG. 4, as providing current for the portion  61  of the hall waveform currently being examined. 
     Based on the observations made so far, it is determined that motor terminals M 3  and M 1  and amplifier phase connection pins A and C should be connected in some order in order to operate properly during the portion of the cycle being considered, but, it is not known which active motor terminal connects to which amplifier phase connector pin. However, regardless of the polarity, the unused motor phase terminal M 2  (as listed in column  45  of FIG. 4) needs to be connected to the unused amplifier pin B (listed in column  46  of FIG.  4 ), because they form the unused phase connection for the portion (shown at  51  and  61  in FIGS. 3 and 2 respectively) of the motor&#39;s electrical cycle under consideration. Accordingly, motor phase terminal M 2  should be connected to amplifier pin B, as listed in column  47  of FIG.  4 . 
     At this stage in the process one of the proper phase connections between the motor  10  and the amplifier  20  has been identified. Next, this process described above for hall sensor H 1  is repeated for a second selected hall sensor H 2 . Referring to FIG. 3, it is seen that a BEMF voltage peak  54  for motor terminals M 2 -M 3  corresponds to the middle portion  53  of the square waveform for hall sensor H 2 . Accordingly, those two motor terminals are entered into the table in FIG. 4 in column  43 , for the row corresponding to hall sensor H 2 . 
     From FIG. 2 it is seen that for the middle portion  62  of the square wave corresponding to hall sensor input H 2 ′, electrical current is flowing in amplifier phase pins B and A. Accordingly, those two amplifier phase pins are identified in the appropriate row of column  44  of FIG.  4 . Using the same process discussed above, it is readily determined that motor terminal M 1  and amplifier phase connection pin C are not used during the portion (shown at  53  and  62 ) of the motor&#39;s electrical cycle being examined, as entered at columns  45  and  46  of FIG.  4 . Thus a second proper phase connection is determined between motor terminal M 1  and amplifier phase connection pin C, as entered in column  47  of FIG.  4 . 
     With two of the three proper connections determined, by default the remaining phase connections for the motor  10  and amplifier  20  must be the correct connections for one another. Accordingly, motor terminal M 3  should be connected to amplifier phase connection pin A, as listed in column  47  of FIG.  4 . Alternatively, the process described above may be repeated for the waveforms corresponding to hall sensor H 3 , and the same result should be achieved. Thus, the three proper connections for the exemplary data provided in FIGS. 2 and 3 is shown in column  47  of FIG.  4 . Note, however, that these connections are only valid when the amplifier hall sensor inputs H 1 ′, H 2 ′ and H 3 ′ are connected to motor hall sensors H 1 , H 2  and H 3 , respectively, as described in the example above. The three hall sensors  12  could have actually been connected five other different ways, but by using this methodology for any combination, the correct results will be achieved. 
     An advantage of the process described above is that instead of a direct substitution method, the describe method permits the polarity of the BEMF peaks and the direction of current flow in the windings to be irrelevant for the procedure. 
     FIGS. 2 and 3 illustrate actual amplifier  20  and motor  10  waveforms as supplied by their respective vendors. If the motor vendor does not provide this information, the BEMF and hall sensor relationships can be determined by mechanically back-driving the motor  10  and capturing the waveforms for each of the three phases and hall sensors  11  on an oscilloscope. Back-driving the motor  10  can also provide the added benefit of confirming that the motor phase stator windings  14  are properly phased with the hall sensors  11 , i.e. the zero crossings for the BEMF waveforms should line up with the rising and falling hall sensor outputs. In practice, during the motor selection process for the high speed-inserting machine mentioned previously, information provided by motor vendors has been found to contain errors in describing BEMF waveforms and their respective hall sensors  11  outputs. Such errors can result in significantly reduced rated output torque from the rated torque that the vendors advertised in their data sheets. 
     Although the present invention has been described with emphasis on a particular embodiment, it should be understood that the figures and data provided are for illustration of the exemplary embodiment of the invention and should not be taken as limitations or thought to be the only means of carrying out the invention. Further, it is contemplated that changes and modifications may be made to the steps of the invention without departing from the scope and spirit of the invention as disclosed.