Abstract:
A brake-controllable brushless motor has a rotor and a stator having polyphase coils; a polar position detector whereby electric power is supplied to the coil selected by its phase in response to the polar positions of the rotor detected by the polar position detector; a driver division for controlling the electric supply to the coils; a motor pulse identifier for recognizing motor pulse signals fed from the polar position detector; and a delayed pulse generator for producing phase-delayed pulse signals in response to the pulse signals fed from the motor pulse identifier, thereby ensuring that when the brushless motor is braked, the phase delay of the delayed pulse signals is progressively and continuously enlarged, and that the coils receive a controlled electric supply from the driver division in response to the delayed pulse signals.

Description:
TECHNICAL FIELD 
     The present invention relates to a brake-controllable brushless motor, and more particularly, to a brake-controllable brushless motor adapted for use in a device having a rotary member such as a rotary cutter in the grass mower and in the roller conveyor. 
     BACKGROUND ART 
     Brushless motors are widely used instead of brushed motors; for example, JP Laid-open Application No. 2007-20588 teaches that they are used in grass-mowers having a power-driven rotary cutter. 
     Another example is shown by JP Patent No. 3673923 which discloses a power-driven roller-conveyor and a power-driven winder for winding up a long object, such as paper, film or cloth. The roller conveyor must transport the cartons constantly kept upright to the delivery port, and the winder must roll up a long object constantly in a stretched manner. 
     However, the problem tends to arise from the inertia involved in the stoppage of the motor. The inertia is likely to loosen the fasteners in the rotary cutter, thereby releasing the rotary cutter from the body of the grass mower. This is very dangerous for the operator and people nearby. The same trouble occurs in the roller conveyor in that the cartons placed on the rollers fall down on the floor, thereby damaging the contents of the cartons. In the case of the winder the tensioned object detrimentally becomes loose. 
     Therefore, in those apparatus using rotary members such as rotary cutters and rollers it is required to stop the motors gradually so as to minimize the inertia. 
     The present invention is directed to solve the problems discussed above, and is to provide a brake-controllable brushless motor adapted for use in the apparatus having a power-driven rotary member. 
     SUMMARY OF THE INVENTION 
     A first version of a brake-controllable brushless motor has a rotor and a stator having polyphase coils; a polar position detector whereby electric power is supplied to the coil selected by its phase in response to the polar position of the rotor detected by the polar position detector; a driver division for controlling the electric supply to the coils; a motor pulse identifier  30  for recognizing motor pulse signals fed from the polar position detector; and a delayed pulse generator for producing phase-delayed pulse signals in response to the pulse signals fed from the motor pulse identifier  30 , thereby ensuring that when the brushless motor is braked, the phasic delay of the delayed pulse signals is progressively and continuously enlarged, and the coils receive controlled electric supply from the driver division in response to the delayed pulse signals. 
     A second version of a brake-controllable brushless motor additionally includes a clock signal generator for producing a predetermined number of clock signals, whereby the delayed pulse generator produces delayed pulse signals whose phases are delayed for the motor pulses recognized by the motor pulse identifier  30 , thereby ensuring that after the braking operation starts, the number of clock signals diminishes at every predetermined period of time 
     A third version of a brake-controllable brushless motor additionally includes a chargeable battery for storing the electric power induced when the brushless motor is stopped 
     A fourth version of a brake-controllable brushless motor, the rotor is mechanically connected to a rotating shaft adapted for connection to a rotary member, thereby ensuring that the rotation of the rotary member is gradually stopped in response to the braking control signal. 
     A fifth version of a brake-controllable brushless motor, the rotary member is a rotary cutter of a grass mower. 
     A sixth version of a brake-controllable brushless motor, the rotary member is a roller of the roller conveyor used for carrying cartons from one place to another. 
     A seventh version of a brake-controllable brushless motor, the brushless motor is built in a selected number of rollers as motorized rollers. 
     An eighth version of a brake-controllable brushless motor, the rotary member is a pair of rollers for supporting a sheet which is reciprocally moved from one roller to the other, thereby preventing inertia from occurring when the rollers are stopped 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram diagrammatically illustrating the structure of a motor-driven grass mower embodying the present invention; 
         FIG. 2  is a schematic cross-section illustrating the internal structure of the motor; 
         FIG. 3A  is a timing diagram showing a pattern of pulse signals recognized in the motor pulse recognizing division; 
         FIG. 3B  is a timing diagram showing a pattern of delay pulses generated in the delay pulse division; 
         FIG. 3C  is a timing diagram showing the advance of time-lag; 
         FIG. 3D  is a timing diagram showing a pattern of clock signals; 
         FIG. 4A  is a timing diagram showing a pattern of pulses generated in the regular operation of the motor; 
         FIGS. 4B and 4C  are timing diagrams showing delay signals generated in the delay pulse division at t 1  and t 2 , respectively; 
         FIGS. 5A to 5D  are schematic views showing various aspects of the movements of the brushless motor in the regular operation; 
         FIG. 6  is a flow chart showing the process of operation of the brushless motor of  FIG. 1 ; 
         FIG. 7  is a perspective view showing the grass mower shown in  FIG. 1 ; 
         FIG. 8  is a cross-sectional view a motorized roller for a roller conveyor, the roller including the brake-controller of the present invention; 
         FIG. 9A  is a motorized roller conveyor including the brake-controller of the present invention; and 
         FIGS. 9B and 9C  each are a display unit including a brake-controller of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a brushless motor system  1  (“motor system  1 ”) and a brushless motor brake-controller  10  (“controller  10 ”) embodying the present invention will be described: 
     The motor system  1  includes a driver division  2 , a power source  3 , a switch  5  and the controller  10 . The driver division  2  includes a brushless motor  7  (“motor  7 ”) and a rotary member  6 . 
     The motor  7  has a rotor  15 , a stator  16  having polyphase coils, and Hall elements  17 , wherein the rotor  15  is a bipolar (N-S) magnet and is rotatively connected to a rotating shaft  18  by means of one or more fasteners such as bolts and nuts. The stator  16  is provided with polyphone (n phases) coil  20 , hereinafter called “coil  20 U,  20 V and  20 W”, respectively. 
     The Hall elements  17  are used to generate pulse signals by monitoring the poles of the rotor  15 , thereby identifying the poles of the rotor  15  varying from time to time. In this embodiment three Hall elements  17   a ,  17   b  and  17   c  are located at 120° angular displacements. These three Hall elements  17   a  to  17   c  constitute a polar position detector  19 . 
     Referring to  FIG. 4A  the Hall elements  17   a ,  17   b  and  17   c  independently generate pulse signals Pa, Pb and Pc, respectively. As a result, the coil  20   s  are energized one by one in response to the pulse signals Pa, Pb and Pc, thereby causing the motor  7  to rotate the rotor  15  and the rotating shaft  18  in a desired direction. When the coils  20   a  are de-energized, the rotor  15  and the rotating shaft  18   a  are stopped. 
     The rotary member  6  is connected to the rotating shaft  18  so as to ensure their unitary rotation and the rotating shaft  18  are integrally connected to the rotary member  6  by means of the fastener  21 , such as screws, bolts and nuts. Typical examples of the rotary member  6  are a rotary cutter used in a grass mower and rollers used in a roller conveyor. These examples will be described in detail below: 
     In  FIG. 1  the reference numeral  3  designates a power source  25 , such as a battery, electrically connected to the motor  7  located in the driver division  2 . This electrical connection ensures that the electric power involving in putting a brake on the motor  7  is stored in the battery  25 . 
     The switch  5  is used to start and stop the motor system  1 . When the switch  5  is on, a start-signal is fed to a driver division  33 , thereby causing the rotary member  6  to rotate through the rotating shaft  18 . When the switch is off, the rotary member  6  stops through the rotating shaft  18 . 
     In addition to the driver division  33 , the controller  10  includes a motor pulse identifier  30 , a clock signal generator (“signal generator”)  31 , a delay pulse generator  32 , a delayed-time timer  35 , and a short brake timer  36 . The controller  10  is electrically connected to the motor  7  and the switch  5 . 
     The motor pulse identifier  30  receives motor pulse signals Pa, Pb or Pc fed by the Hall elements  17   a ,  17   b  or  17   c , and the pulse signal P received is transferred to the delay pulse generator  32  and the driver division  33 . 
     The signal generator  31  can generate a predetermined number of clock signals, and these signals are fed to the delay pulse generator  32 . The signal generator  31 , as shown in  FIG. 3D , adjusts the intervals at which the clock signals are fed, which means that the number of clock signals is adjusted. 
     The delay pulse generator  32  operates when the motor  7  starts, and generates a pulse signal (“delayed pulse signal L”) whose phase is delayed against a motor pulse signal P received from the motor pulse identifier  30 . More particularly, when the delay pulse generator  32 , as shown in  FIG. 3A , identifies the pulse signals fed from the motor  7 , the point of time when the pulse signal P is produced, as shown in  FIG. 3B , is used as a basis the delay pulse signal L is produced with its phase being delayed in correspondence to one pulse fed from the signal generator  31 . More particularly, as shown in  FIGS. 4B and 4C , the delay pulse generator  32  produces delayed pulse signals La, Lb, and Lc with their phases being delayed in correspondence to one clock signal fed from the signal generator  31 . 
     The driver division  33  receives motor pulse signals P fed from the motor pulse identifier  30 , delay pulse signals L fed from the delay pulse generator  32 , and on/off signals fed from the switch  5 , and the power supply controlled in response to these pulse signals is received by the motor  7 . More particularly, while the motor  7  is put into operation by turning on the switch  5 , the driving signals are fed to the driver division  33 . At this stage, the driver division  33  controls the electric power supplied to the coil  20  in response to the motor pulse signal P fed from the motor pulse identifier  30 . 
     In regular operation if the poles (N and S) of the rotor  15  are found located at the places shown in  FIG. 5A  by the Hall elements  17   a  to  17   c , the driver division  33  regulates the flow of electric current from the coil  20 U to the coil  20 W, thereby causing the rotor  15  to rotate in the direction indicated by the arrow in  FIG. 5A  (in the anti-clockwise direction). Subsequently, the driver division  33  switches the flow of electricity, as shown in  FIG. 5C , so that the flow of electricity is changed from the coil  20 V to the coil  20 W. In this way, the driving coil  20 W is excited to the N-pole and the driving coil  20 V is excited to the S-pole. The rotor  15  is rotated anti-clockwise as shown by the arrows in  FIG. 5C  and  FIG. 5D . 
     If the motor  7  is to be stopped, where the switch  5  is turned on to send a braking signal to the driver division  33 , the signal generator  31  continues to feed clock signals to the delay pulse generator  32  for a given period of time from the point of time when the braking signal is fed. At the same time, the delay pulse generator  32  feeds a delay pulse signal L to the driver division  33  which, in response to the signals L, puts a brake on the rotor  15 . In this way the rotor  15  is gradually and then completely stopped. 
     More specifically, while a braking signal is fed to the clock signal generator  31  by the switch  5  (the “on” state), the clock signal generator  31  feeds clock signals from the point of time when the generation of the braking signal starts. The clock signal generator  31  changes the number of clocks so as to prolong the time period corresponding to one clock (“clock period”) at every predetermined unit-time interval. This means that after the braking signal becomes “on”, the time periods T 1 , T 2  . . . Tn (n=1, 2, 3, 4 . . . ) are successively set, wherein the clock periods of the clock signals fed within the time period Tn are set as tn (n=1, 2, 3, 4 . . . ). Then, the following relation will be established:
 
 tn&gt;t ( n− 1)
 
     In this way the clock signals are fed to the delay pulse generator  32  which produces the delay pulse signal L in response to the motor pulse signal P and the clock, and the delay pulse signal L is fed to the driver division  33 . 
     After the braking signal becomes on, the delay signal L is fed to the driver division  33  which then energizes the coils  20 U,  20 V and  20 W. As a result, the rotor  15  stops for a period of time corresponding to the delayed phase. In addition, while the braking signal is on, the clock period tn is prolonged at every unit time, thereby enlarging the delay of the phase accordingly. In this way, the rotor  15  is subjected to an increasing braking force while the unit time T passes. 
     While the rotor  15  stops, the driving coils  20  of the motor  7  induce electric power, which is delivered to the power source  3  where the electricity is stored in the battery  25 . 
     The above-described braking state continues from when the braking signal becomes “on” up to when the predetermined period of time passes. In the illustrated embodiment when the braking signal becomes “on”, the counting of the signals starts from the point of time, and the braking operation stops when the delayed-time timer  35  is up. 
     When the generation of the braking signals is finished, the driver division  33  is braked for a short time after the lapse of a predetermined period, thereby stopping the rotor  15  completely. Now, referring to  FIG. 6 , the sequence will be described: 
     At Step  1  the switch  5  of the controller  10  is turned on, and when it is recognized that the driver division  33  is energized, the sequence advances to Step  2  where the motor  7  is put into regular rotation. 
     Then, the sequence advances to Step  3  where the braking signal is recognized about whether it is “on” or not. If the braking signal is found to be “off” (indicated “No”), the motor  7  continues its regular operation. If it is found to be “on”, the sequence advances to Step  4  where the delayed-time timer  35  and the short-brake timer  36  start their counting operations. The sequence advances to Step  5 . 
     At Step  5  the controller  10  starts its braking operation in response to the delayed pulse signal L fed to the driver division  33  from the delay pulse generator  32 . 
     When the braking operation starts, the coils  20 U,  20 V and coil W are energized at the delayed phases corresponding to one clock (time tn) fed from the signal generator  31 . At this stage, the braking force gradually increases upon the rotor  15  at the intervals of time (tn), thereby causing the rotor  15  to slow down gradually. 
     At this stage, the sequence advances to Step  6  where the delayed-time timer  35  recognizes that the braking time is up, but if it is not yet up, the sequence advances to Step  9  where it recognizes that the driving signal is on. If the “on” state is ascertained, the sequence is returned to Step  2  where the regular operation resumes. At Step  9  if the driving signal is recognized to be “off”, the sequence returns to Step  6 , thereby continuing the braking operation. 
     If Step  6  recognizes that the delayed-time timer  35  is up, the sequence advances to Step  7 , where it is checked whether the short braking timer  36  is up or not. If it is not yet up, the sequence advances to Step  10 , where the braking signal is checked for being “on” or not. If it is “on”, the sequence returns to Step  2  where the regular operation resumes. On the other hand, if it is “off”, the sequence returns to Step  7  where the sequence waits for the short brake timer  36  being up. When it is found to be up, the sequence advances to Step  8  where the motor  7  is braked for a short time, and then is completely stopped. In this way, the flow of sequence shown in  FIG. 6  is finished. 
     The function of the controller  10  is to regulate the electric supply to the driving coil  20  in response to the delayed pulse L. After a brake is put on the motor  7 , the phase of the delayed pulse L is progressively delayed each unit time T. This means that the braking on the rotor  15  is progressively increased, thereby bringing the rotor  15  into a gradual standstill. 
     The controller  10  includes the clock signal generator  31  which produces a clock signal and can produce the delayed pulse L based upon the clock signal. The clock signal produced in the clock signal generator  31  is prolonged pulse by pulse each unit time T, thereby ensuring that the delayed phase of the delayed pulse signals L fed by the generator  32  is progressively enlarged. In this way the rotor  15  gradually slow down. 
     As an alternative embodiment, the clock signal generator  31  can be modified so as to continue to produce a predetermined number of clock signals irrespective of the lapsing of time, and produce delayed pulse signal L whose phase is delayed by the number X of clocks against the motor pulse signal P, wherein the number X is increased with time, thereby amplifying the phasic delay of the pulse signal L. 
     In another alternative embodiment the number X of the clock signal generator  31  is diminished each unit time T, and at the same time, the number X is increased with time, thereby amplifying the phasic delay of the delayed pulse signal L. 
     In the motor system  1  of the present invention the rotary member  6  is fastened to the rotating shaft  18  by means of known fasteners  2 , such as screws, bolts and nuts, but the fasteners  2  are protected from unexpected loosening due to the inertia involved in the stoppage of the motor  7 . 
     The controller  10  of the present invention ensures that the loaded battery  25  stores the electric power induced when the motor is stopped, thereby saving electricity. 
     According to a further modification it is possible to continue to amplify the phase delay described above. 
     Instead of the Hall elements  17   a  to  17   c , photo-transistors can be employed. 
     Instead of the battery  25  a known capacitor can be used. 
     In the embodiments described above the rotor  15  is completely stopped by putting a short brake thereon when the delay timer  35  is up after the braking signal becomes “on”. The present invention is not restricted to it, but the rotating speeds of the rotor  15 , the rotating shaft  18  and the rotary member  6  can be recognized by using a known rotary encoder, and when the slowing rotating speed reaches a predetermined low speed, the short brake is operated. 
     EXAMPLE 1 
       FIG. 7  shows a grass mower  50  which includes the brushless motor system  1  and the brushless controller  10 . The grass mower  59  is driven by the motor  7 . The grass mower additionally includes a front operating lever  51  and a rear operating lever  52 . The front operating lever  51  is provided with a driving division  53  which consists essentially of a rotary cutter  57 . The rear operating lever  52  is provided with a power source  54  and a controller division  56 . The reference numeral  55  designates a motor division. 
     The front operating lever  51  is hollow enough to accommodate a power transmission shaft (not shown) for connection to the driver division  53 . The power transmission shaft is connected to the rotary cutter  57  through a train of bevel gears. 
     The motor division  55  includes the motor  7  whose rotor  15  is connected to the power transmission shaft (not shown) in the lever  51 , thereby enabling the rotary cutter  57  to rotate. 
     The rear lever  52  is provided with an operating handle  58  having a knob  58   a  and a switch  58   b  for controlling the speed of the rotary cutter  57 . The rear lever  52  is provided with a controller division  56  at the rear end, wherein the controller division  56  houses the controller  10  described above, and also another switch  5 . The controller  10  and the switch  5  are electrically connected to the motor  7 . 
     The reference numeral  54  designates a power source  54  including the battery  25 , which is electrically connected to the motor  7 . 
     The controller  10  ensures that when the rotary cutter  57  is stopped by turning on the switch  5 , the rotation of the rotary cutter  57  is gradually stopped with least inertia, thereby preventing the fasteners from becoming loose. 
     EXAMPLE 2 
     Another example will be described by referring to  FIG. 8 , which shows a motorized-roller conveyor RS, which includes the controller  10  at one end of a spindle  75 . 
     More particularly, the motorized roller  70  includes a roller  71  as the main body, spindles  73  and  75  carried in the roller  71 , and plugs  72 . The roller  71  is a tubular body of metal, and closed by the plugs  72 . The spindles  73  and  75  are rotatively carried on bearings  76  and  77 . 
       FIG. 8  and  FIG. 9A  show the controller  10  applied to the motorized roller conveyor  70  so as to ensure that the rotation of the roller conveyor  70  is gradually stopped with least inertia. Under the least inertia the cartons placed on the rollers are protected from falling off the conveyor even if the rollers are suddenly stopped. 
     EXAMPLE 3 
       FIG. 9B  shows a display unit  100  for winding up a long object  101  such as a screen, which will be more particularly described: 
     In addition to the screen  101 , the display unit  100  includes a pair of motorized reels  70 , wherein one of the reels  70  is fastened to one end of the screen  101 , and the other reel  70  is fastened to the other end thereof. The screen  101  is subjected to a certain amount of tension so as to constantly hold it in a stretched manner. 
     The screen  101  bears an advertising phrase or the like which is displayed in slow reciprocal movement between the reels  70 . 
     In displaying the screen  101 , the loosened screen  101  looks ugly for the viewers. By providing the motors  70  with the controller  10  described above, the motors  70  can stop without inertia, thereby protecting the screen  101  from slackening which otherwise would occur at every time when the motor  70  stops. 
     The application of the controller  10  is not limited to the examples described above, but it can be applied in a wider range of fields where the use of a power-driven rotary member is involved.